Aversion But Not Aggression: Emotional Traits of KM Rats in Sociability Tests
Nadezhda D Broshevitskaya 
, Anastasia A Rebik , Lidia M Birioukova , Maria I. Zaichenko , Inna S Midzyanovskaya *
-
Institute of Higher Nervous Activity and Neurophysiology of the Russian Academy of Sciences, Moscow, Russian Federation
* Correspondence: Inna S Midzyanovskaya
Academic Editor: Vivek Kumar
Special Issue: Neurobiology of Mood Disorders
Received: September 28, 2025 | Accepted: February 09, 2026 | Published: February 25, 2026
OBM Neurobiology 2026, Volume 10, Issue 1, doi:10.21926/obm.neurobiol.2601326
Recommended citation: Broshevitskaya ND, Rebik AA, Birioukova LM, Zaichenko MI, Midzyanovskaya IS. Aversion But Not Aggression: Emotional Traits of KM Rats in Sociability Tests. OBM Neurobiology 2026; 10(1): 326; doi:10.21926/obm.neurobiol.2601326.
© 2026 by the authors. This is an open access article distributed under the conditions of the Creative Commons by Attribution License, which permits unrestricted use, distribution, and reproduction in any medium or format, provided the original work is correctly cited.
Abstract
The inbred Krushinsky-Molodkina (KM) rat strain, characterized by latent genetic epilepsy, reduced social motivation, and a high propensity for freezing, is a promising model for translational research of social deficits in autism spectrum disorder (ASD). In clinical practice, social deficits often lead to social withdrawal and can be accompanied by aggression. It was unknown if KM rats exhibit such aggression during inescapable social encounters. We assessed intraspecific aggression in KM and control rats using the resident-intruder test, and autonomic nervous system responses were evaluated via heart rate variability analysis in a small separate cohort using a modified social-challenge paradigm that prevented direct physical contact. In the resident-intruder test, KM rats displayed significantly less aggression toward unfamiliar intruders than controls, exhibiting fewer attacks, fights, and competitive wins. Electrocardiographic analysis during the social preference test further revealed that the social challenge triggered parasympathetic, rather than sympathetic, nervous system activation in KM rats. Together, these findings indicate that social load in KM rats evokes a stress response, marked by a hypolocomotion and an atypical autonomic reaction. Conversely, control rats, which displayed a typical fight response to unfamiliar intruders, exhibited marked sympathetic activation during the sociability test. These findings suggest the KM strain may help model specific aspects of ASD-relevant social behavior alongside autonomic dysregulation.
Graphical abstract
Keywords
Social deficits; aggression; aversion; latent epilepsy; heart rate variability (HRV); autism spectrum disorder (ASD); comorbidity
1. Introduction
Autism spectrum disorder (ASD) is a heterogeneous neurodevelopmental condition characterized by social communication deficits and restricted, repetitive behaviors [1]. Its clinical variability is likely amplified by frequent comorbidities such as attention deficit hyperactivity disorder [1,2] and epilepsy [3,4]. Although no drugs target core ASD symptoms, available pharmacotherapies manage co-occurring conditions to support behavioral and educational progress [5,6,7]. Behavioral interventions like Applied Behavior Analysis (ABA) are beneficial [8,9], yet optimal pharmacological strategies and timing remain unclear.
Advancing treatment may require decomposing autism into biologically defined subtypes [1,10,11] to support personalized medicine. However, categorizing ASD by underlying pathology is challenging given its genetic complexity and convergence of diverse molecular pathways onto common neurobiological mechanisms [12,13,14,15,16]. A promising subtyping approach focuses on individual differences in the autonomic stress response [17]. For individuals with ASD, social demands constitute a significant stressor [18,19], and involuntary physiological reactions may shape maladaptive behaviors, including aggression, a common yet non-core comorbidity likely influenced by cultural and environmental factors [20,21,22,23,24,25]. Animal models can help dissect the physiological basis of social aversion by linking an observable behavior to internal autonomic states.
Emotional stress regulation depends in part on the balance between the sympathetic and parasympathetic branches of the autonomic nervous system (ANS). Heart rate variability (HRV) analysis provides a noninvasive method for evaluating this balance, offering insight into physiological stress mechanisms [26] and, thus, potential pathways for improving social functioning in ASD. Rodent studies confirm that social challenges are potent stressors, inducing depressive-like behaviors and cardiovascular dysregulation [27,28,29,30,31]. Paradigms such as social defeat trigger acute neuroendocrine and autonomic activation, leading in susceptible individuals to persistent dysfunction: elevated sympathetic tone, reduced baroreflex sensitivity, and lowered HRV [32,33,34], without structural cardiac damage [35,36].
The KM rat strain, genetically predisposed to audiogenic seizures [37,38,39,40], consistently avoids conspecifics in preference tests [41,42,43,44], accompanied by the production of aversive ultrasonic vocalizations [44]. Furthermore, KM rats display reduced behavioral contagion when observing a freely behaving demonstrator rat in a long-term experimental paradigm [45], a trait that mirrors the social learning difficulties observed in individuals with ASD. Importantly, these contact-motivation deficits are evident in both seizure-naïve and seizure-experienced animals [42] and are therefore not secondary to seizure activity. KM rats are hypolocomotive and frequently exhibit freezing behavior in novel or social contexts [41,43].
Altogether, this may establish the KM strain as a new translational model for social disability within a defined domain of autism spectrum disorder (ASD), notably associated with comorbid (either latent or active) epilepsy, but not with ADHD. While the behavioral phenotype of KM rats resembles that of the prenatal valproic acid model (also marked by social impairments, reduced exploration, and increased seizure susceptibility [46,47], direct comparative studies are currently lacking. A key advantage of the KM model is its absence of pharmacological confounds, as it is a genetically selected strain, which avoids systemic toxicity and side effects.
This study investigated emotional traits in Krushinsky-Molodkina (KM) rats in social contexts. The behavioral profiling employed two paradigms: aggressive behavior was assessed via a resident-intruder test, and autonomic regulation was evaluated during a modified social preference test that measured contact behavior and HRV. In the latter, rats in an open-field arena were presented sequentially with an empty container and one housing an unfamiliar, caged conspecific. The social preference was quantified by comparing the contact approaches. Age- and sex-matched Wistar rats served as the maternal control strain throughout.
2. Materials and Methods
2.1 Animals
A total of 39 adult rats, comprising 20 KM and 19 Wistar males, were used in this study. KM rats were sourced from the exclusive breeder at the Biological Faculty of Moscow State University, while Wistar rats were obtained from the Stolbovaya animal supplier. Upon arrival at 1-2 months of age, all animals were housed under standard conditions in the institutional vivarium, with 4-6 rats per cage and ad libitum access to food and water. All the rats were seizure-naïve. Behavioral experiments started when the rats were 5-6 months old.
Experiment 1, which employed the ‘resident-intruder’ paradigm, was conducted on 29 naive intact male rats (15 KM, 14 Wistar). In a parallel series, Experiment 2 recorded cardiac activity during a modified social preference test in a separate cohort of 10 rats (5 KM, 5 Wistar). These animals were surgically implanted with subcutaneous cardiac electrodes and four epidural electrodes, with a reference electrode placed over the cerebellum. ECoG data are not reported here.
Before testing, the experimental animals were individually housed. Rats in Experiment 1 were isolated for 4 days before the resident-intruder test, whereas those in Experiment 2 underwent a 2-week isolation period for post-surgical recovery. Both groups maintained ad libitum access to food and water during isolation. The intruder rats (for Experiment 1) and social stimulus rats (for Experiment 2) continued to be housed under standard group conditions (4-6 per cage).
Because the KM and Wistar rat strains are visually indistinguishable, it was not feasible to blind the experimenters to group identity during data collection. To mitigate potential observational bias, behavioral scoring was performed on video recordings in which animals were identified by randomly assigned numeric IDs. The corresponding video data can be made available upon reasonable request.
2.2 Test “Resident-Intruder”
Intraspecific aggression in adult male Wistar and KM rats was assessed using the resident-intruder paradigm. To minimize the effects of prior agonistic experience and enhance territorial aggression, the experimental rats (residents) were individually housed in cages (30 × 45 × 20 cm) for 4 days before testing.
The test was conducted in the resident’s home cage. A novel, younger (3.5-4 months), lighter, same-sex Wistar rat was introduced as the intruder. A 10-minute behavioral interaction was video-recorded under dim lighting (20-25 lux). The following parameters of the resident’s aggressive behavior were quantified:
Attacks: The number of bouts initiated by the resident that culminated in the intruder assuming a submissive supine posture or escalating into a fight.
Fights: The number and total duration of mutual physical confrontations.
Offensive Uprights: The frequency of instances where both rats stood facing each other.
Boxing: The number of times the resident adopted an upright, face-to-face posture.
Pursuits: The number and duration of pursuits accompanied by anogenital sniffing that often preceded an aggressive action.
Mounting: The number of times the resident mounted the intruder from behind. In males, this was typically followed by genital grooming. Based on the established methodology [48], this was interpreted as dominant, rather than sexual, behavior.
To prevent the effects of repeated defeat, each intruder rat was used only once. In rare cases, an intruder was used a second time, but only to test a resident who had previously shown no aggression.
2.3 Modified Social Novelty Test
The modified social preference test was conducted in a black wooden open-field arena (60 × 60 × 60 cm). Following a 20-30-minute habituation period for all rats, the test protocol comprised three sequential 10-minute sessions:
- Arena Exploration: The rat was placed in the empty arena for free exploration.
- Social Odor Cue: A mesh container filled with bedding from the home cage of an unfamiliar conspecific (the “stimulus rat”) was introduced into one corner of the arena.
- Social Preference: The bedding container was replaced with an identical mesh container containing the stimulus rat itself.
An electrocardiogram (ECG) was recorded continuously throughout all three stages. All sessions were video-recorded from above the arena and analyzed using a combination of automated tracking and manual ethological scoring.
Automated Tracking: Locomotor activity was analyzed automatically using ToxTrac software (v.2.98, Umeå) with the XLD identification algorithm. This algorithm tracks the animal’s center of mass to quantify total path length, velocity, and the duration of freezing episodes [49].
Manual Ethological Scoring: An expert observer, blinded to the experimental groups, manually scored the videos for specific social and anxiety-related behaviors. These included the number of contacts with the container, the frequency of rearings, and the duration of short and long grooming bouts.
Contact: it was defined as a freely-moving experimental animal directing snout pokes at either (a) the enclosure containing a conspecific or (b) an empty control enclosure (containing only bedding). The total number of distinct contact bouts was quantified.
Urination: it was scored as a behavioral event, followed by the deposition of a urine spot on the test arena floor.
Freezing was defined as complete immobility, except for movements associated with respiration, lasting at least 1 second. This behavior was automatically detected offline using ToxTrack software [49].
Path length: it was defined as the total distance traveled by the animal’s center point during the trial. It was calculated as the cumulative sum of the linear displacements between consecutive tracking points over the entire session. This behavior was automatically detected offline using ToxTrack software [49].
2.4 ECG Recording
A subcutaneous electrode was implanted for ECG recording. Before surgery, rats were transported to the operating room in individual carriers. The animal was deeply anesthetized using 5% isoflurane in an induction chamber for 5-8 minutes. Surgical anesthesia was maintained throughout the procedure at 2-3% isoflurane delivered via an inhalation mask. Local anesthesia was induced via a subcutaneous injection of Novocaine (0.5 ml) at the planned incision site on the left shoulder.
An ECG electrode was subcutaneously implanted in the left shoulder area. A subcutaneous cable connected the electrode to a connector, which was then affixed to the skull in a standard manner.
ECG signals were acquired using an L-Card ADC system (L-Card, RF) and the PowerGraph software (PowerGraph, RF). Data were recorded at a sampling rate of 1000 Hz. To minimize electrical interference, a hardware filter was applied at 50 Hz. Before analysis, raw recordings were digitally bandpass-filtered to retain frequencies between 2 and 45 Hz.
2.5 Heart Rate Variability
Heart rate variability (HRV) was analyzed from the acquired ECG signals using proprietary Physiobelt software (v.2.9.0; Neurobotics, Russia). We computed a standard set of parameters for short-term (<5 min) HRV assessment, including key time-domain and frequency-domain indices [50,51]:
Time-Domain Indices: HR: Mean heart rate (beats per minute); RRNN: Mean RR interval (ms); SDNN: Standard deviation of all normal NN intervals (ms); RMSSD: Root mean square of successive differences between normal heartbeats (ms); CV: Coefficient of variation (CV = SDNN/RRNN × 100%); Min RR: Minimum RR interval (ms); Max RR: Maximum RR interval (ms).
Frequency-Domain Indices: TP: Total power spectral density (ms2); HF%: High-frequency power in normalized units (% of TP); LF%: Low-frequency power in normalized units (% of TP); VLF%: Very-low-frequency power in normalized units (% of TP); LF/HF ratio: Ratio of low-frequency to high-frequency power; IC: Centralization index (IC = (LF + VLF)/HF).
2.6 Statistical Analysis
Statistical analyses were conducted in Statistica 10 (StatSoft Inc., USA). The Figures present data as median and interquartile range (IQR). Detailed group-level statistics for the experimental group can be found in the Tables S1-S10.
Resident-Intruder test (confirmatory): Between-group (KM vs. Wistar) comparisons used the Mann‑Whitney U test. The Benjamini-Hochberg procedure controlled the FDR at α = 0.05. Effect sizes are given as rank‑biserial correlation (r); |r*| ≈ 0.1, 0.3, 0.5 correspond to small, medium, and large effects [52].
Three-stage social preference test (exploratory): The Wilcoxon matched pair test assessed within-group differences across stages (Arena Exploration, Social Odor Cue, Social Preference); the Mann‑Whitney U test assessed between-group differences at each stage. Given the exploratory, hypothesis-generating nature of this novel paradigm, no multiple comparison correction was applied.
2.7 Ethics Statement
The Institutional Ethics Committee approved the research, statements 0125022021 and 230042021.
3. Results
3.1 Test “Resident-Intruder”
In this test, the experimental rats were confronted with an unfamiliar young intruder introduced into their home cage. During the ensuing inescapable interaction, the resident exhibited a range of defensive behaviors to protect its territory (Figure 1, Table 1).
Figure 1 a: The schematic of the «Resident-Intruder» test. b-f: Social behavior of Wistar (n = 14) and KM (n = 15) rats in «Resident-Intruder» test. Mann-Whitney U test: ***p < 0.001, **p < 0.01, *p < 0.05.
Table 1 Behavioral parameters of resident rats (KM and Wistar) in the resident-intruder test.
We observed that KM rats displayed significantly less aggression towards an intruding conspecific than Wistar controls. Specifically, KM males initiated fewer attacks (U = 31.50, Z = 3.22, p = 0.0007; Figure 1b), were engaged in fewer fights (U = 18.50, Z = 4.14, p = 0.0008, Figure 1c) of shorter duration (U = 28, Z = 3.68, p = 0.0008, Figure 1f), and achieved fewer wins (U = 44, Z = 2.70, p = 0.010, Figure 1d). At the same time, there was no difference between the KM and Wistar groups in the number and duration of sniffings and pursuits (Figure 1e). The observed effects remained significant after correction for multiple comparisons and were strong according to rank-biserial correlation coefficients.
3.2 Modified Social Preference Test
3.2.1 Behavioral Parameters
During the modified social preference test, experimental animals were exposed to three conditions: exploration of an empty arena (Session 1, Figure 2a.1), the arena containing a cage with conspecifics’ odor cues (Session 2, Figure 2a.2), and the same setup with an unfamiliar live rat inside the cage (Session 3, Figure 2a.3). We measured social contacts and locomotor activity (Figure 2b and Figure 2c; Tables S1-S5). Social preference was quantified by comparing the amount of contact activity directed at the empty cage versus the cage housing a conspecific.
Figure 2 a: The schematic of the modified social novelty test with three sequential 10-minute sessions: a.1: arena exploration; a.2: a cage with a social odor cue; a.3: social preference. b-e: The locomotor and social behavior of Wistar (blue bars) and KM (yellow bars) rats in the modified social novelty test. The data are shown as median and interquartile range (IQR). Statistical significance of the Wilcoxon matched-pairs test, #p < 0.05.
In Sessions 1 and 2, the KM rats showed no differences from the control group in locomotor activity (Table S1 and Table S2). Both groups explored the empty cage to a similar extent. During Session 3, the KM group exhibited significant locomotor suppression (Figure 2b; Table S3 and Table S5) and the lowered contact behavior (Figure 2c; Table S5).
3.2.2 Heart Rate and Heart Rate Variability
Cardiac activity was recorded throughout the modified social preference test (Figure 3). No differences in heart rate or heart rate variability (HRV) were observed between groups during Session 1 (Arena Exploration, Table S6).
Figure 3 Heart rate variability in Wistar and KM rats. Wistar rats are represented by blue bars; KM rats by yellow bars. Values are presented as median and interquartile range (IQR). Significant between-group differences (p < 0.05, Mann-Whitney U-test) are denoted by asterisks (*). Significant within-group differences (p < 0.05, Wilcoxon matched-pairs test) are denoted by pound signs (#).
In Session 2, however, KM rats exhibited longer R-R intervals (denoted here as RRNN, indicating a slower heart rate) compared to Wistar controls. KM rats showed a higher maximal RR interval in their ECGs, as well as a tendency toward increased minimum and mean RR intervals (Table S7). Concurrently, the high-frequency (HF) component of the HRV power spectral density significantly increased in KM rats relative to their levels in Session 1 (Figure 3b; Table S7). Conversely, the very low-frequency (VLF) portion decreased significantly (Figure 3c; Table S7). This shift was paralleled by an increase in the centralization index (Figure 3d; Table S7). The observed changes are suggestive of a greater parasympathetic activity. The effects were not seen in control rats.
Session 3, which allowed for contact with a caged unfamiliar conspecific, elicited distinct cardiac responses in the two experimental groups (Table S9 and Table S10). In control rats, this session was characterized by a shortening of R-R intervals (Figure 3a, green bars; Table S9), corresponding to an increased heart rate (Table S9). Compared to Session 1, these rats also showed a significant increase in the high-frequency (HF%) component of HRV (Figure 3b, green bars). In contrast, KM rats exhibited no significant change in inter-beat intervals (Table S10). However, their HRV parameters altered dramatically: the portions of both the HF (Figure 3b, yellow bars; Table S10) and low-frequency (LF) bands (Figure 3e, yellow bars; Table S10) increased significantly. This occurred at the expense of a reduced very low-frequency (VLF) component (Figure 3c; Table S10). Furthermore, the centralization index remained significantly elevated (Figure 3d; Table S10), suggesting a shift in sympathetic modulation.
4. Discussion
Emotions are fundamental to social functioning, and their dysregulation (common in autism spectrum disorder) often leads to anxiety, depression, and social withdrawal [53]. Sensory hypersensitivity is thought to contribute to social aversion, with spatial avoidance serving as a coping strategy to manage overwhelming sensory input [54]. Although aggressive behaviors pose significant challenges for caregivers and educators of autistic individuals, such manifestations are likely not intrinsic biological features of social deficits, but may instead arise from interactions between biological and environmental factors.
Our findings in KM rats align with this framework. Notably, our prior observation that KM rats dominate Wistar rats in a tube test [42] was attributed to behavioral rigidity: the KM rats exhibited a persistent, forward-driven strategy (holding position or advancing), in contrast to the Wistar rats’ more varied tactics involving lateral pushes and retreats [42]. In the present study, KM rats exhibited fewer aggressive behaviors (i.e., fights and attacks; Figures 1b, 1c) when defending their home cage against an intruder rat than Wistar controls. Consequently, data from competitive and defensive contexts provide convergent evidence for a core behavioral phenotype in KM rats: reduced proactive social engagement manifesting as diminished direct aggression in male-to-male encounters.
Surprisingly, in the second experiment, the KM cohort failed to display their expectedly elevated freezing response, a behavior consistently documented in this strain [40,41,43]. We attribute this to a putative side effect of mandatory post-surgical isolation in small individual cages, which may have altered their locomotor behavior. However, their hypolocomotive phenotype became evident under social load. During the third session of the modified social preference test (Figure 2), KM rats displayed diminished locomotor and contact activity, consistent with previous reports [42,43]. Notably, this reduced activity was accompanied by an absence of cardiovascular markers indicative of ‘fight-or-flight’ readiness (Figure 3). Specifically, while control Wistar rats displayed mild but significant tachycardia during social encounters (Figure 3), which is consistent with a readiness to interact, KM rats showed no sympathetic surge in response to social stimuli (Figure 3). Instead, they exhibited a mild bradycardic response and a parasympathetic-dominant shift to an empty cage with odor cues (Figure 3a, 3b; Table S5). This initial parasympathetic response was subsequently modulated by a significant rise in the index of centralization upon live social exposure (Figure 3d). Notably, KM rats displayed a significant decrease in VLF power across consecutive phases of the social preference test (Figure 3c). Although the physiological interpretation of VLF remains debated, it is recognized as one of the strongest predictors of all-cause and cardiac mortality [50]. This reduction may indicate dysregulation in long-term regulatory processes, such as neuroendocrine or thermoregulatory control.
Our findings provide further biological evidence supporting a dissociation between social withdrawal and heightened aggression in the context of autism-like phenotypes. Notably, this contrasts with other etiological models, such as early-life proinflammatory stress induced by lipopolysaccharide (LPS). In the LPS model, which elicits offspring behavioral traits reminiscent of autism, adult rats exposed to LPS during development exhibit increased aggression in the resident-intruder paradigm [55].
Our results suggest that functional stratification of ASD phenotypes may be achieved through profiling of the autonomic nervous system. Although sympathetic dominance is often reported in ASD and may be further exacerbated by comorbid epilepsy [56,57], it is not a universal feature. In KM rats—which exhibit latent audiogenic epilepsy—we observed a context-specific shift toward parasympathetic activation under social challenge (Figure 3). Interestingly, in epileptic patients, vagotonia (parasympathetic dominance) has been linked to left-hemispheric seizure foci [58,59]. However, the epileptic activity in KM rats is characterized as, or interpreted as, bilateral [60,61].
It is important to note that behavioral quietness in social contexts may reflect a stress-induced autonomic dysregulation rather than calm engagement. These observations highlight the necessity of evaluating autonomic function across both resting and socially challenging conditions, particularly given the absence of baseline differences between the rat cohorts in our study. Assessments confined to resting states risk failing to detect pathological vagotonia—a condition in which interventions such as vagus nerve stimulation could prove counterproductive. Conversely, the approach may hold therapeutic potential for individuals exhibiting sympathetic-dominant autonomic profiles [62,63].
Within the Polyvagal Theory framework [64,65], KM rats may exhibit elevated dorsal vagal tone and reduced ventral vagal activity, which promote social disconnection and freeze responses. A comprehensive, multi-method assessment across conditions is therefore essential for accurate characterization of autonomic dysfunction in ASD models and patients.
5. Conclusion and Future Directions
Social withdrawal is not obligatorily linked with increased aggression, as evidenced by the behavioral profile of KM rats. In these animals, reduced aggression toward an unfamiliar intruder (in the resident-intruder test) is paralleled by a parasympathetic surge – indexed by elevated heart rate variability markers – during forced social exposure in the social preference test. Cardiac/autonomic measures may provide a useful physiological readout to complement behavioral phenotyping in future mechanistic studies.
Several important directions emerge for future research. To assess generalizability, replicating this paradigm in female KM rats is a critical next step, given that sex differences are a major factor in neurodevelopmental disorders. To evaluate specificity and mechanism, pharmacological interventions should be employed; for instance, testing whether anxiolytic/antidepressant treatment normalizes social approach. Finally, chronic studies could determine if early pharmacological intervention prevents the development of these social deficits. Such multi-pronged approaches will solidify the model’s validity and translational relevance.
6. Limitations
Several methodological limitations of this study warrant consideration. First, the exclusive use of male rats (due to the unavailability of female KM rats from the breeder) limits the generalizability of the findings to females. Second, behavioral and physiological measures were collected in separate experimental sessions: aggression was assessed in a resident-intruder paradigm, whereas HRV was recorded during a modified social preference test that prevented direct physical contact. This procedural separation may have attenuated autonomic responses in the less confrontational social-preference setting compared with a direct aggressive encounter. Third, animals in the HRV experiment underwent a period of post‑surgical social isolation for recovery, which could have elevated basal stress or altered locomotor and social motivation, thereby introducing potential confounds. Finally, the modest sample size in the second experiment restricts the statistical power to exploratory inference; therefore, these findings should be interpreted as preliminary and require validation in larger, confirmatory studies.
Author Contributions
Dr. N.B. conducted the experiments and collected the data, L.B. was responsible for the surgeries and cardiological analysis, A.R. collected the data, performed statistical analysis and designed the figures; Dr. M.Z. and Dr. I.M. were responsible for the project administration, data curation, writing and editing.
Competing Interests
The authors have declared that no competing interests exist.
AI-Assisted Technologies Statement
Artificial intelligence (AI) tools were used solely for basic grammar correction and language refinement in the preparation of this manuscript. Specifically, Open AI Tool DeepSeek was employed to improve the readability and linguistic clarity of the English text. All scientific content, data interpretation, and conclusions were developed independently by the author. The authors have thoroughly reviewed and edited the AI-assisted text parts, to ensure its accuracy and accept full responsibility for the content of the manuscript.
Additional Materials
The following additional materials are uploaded at the page of this paper.
- Table S1: Between-group comparison of behavioral parameters from the first session (empty arena) of the modified Social Preference Test.
- Table S2: Between-group comparison of behavioral parameters from the second session (arena + bedded container) of the modified Social Preference Test.
- Table S3: Between-group comparison of behavioral parameters from the third session (arena + caged unfamiliar rat) of the modified Social Preference Test.
- Table S4: Comparison of behavioral parameters within the control (Wistar) group across different sessions of the modified social preference test.
- Table S5: Comparison of behavioral parameters within the experimental (KM) group across different sessions of the modified social preference test.
- Table S6: Between-group comparison of HRV metrics from the first session (empty arena) of the modified Social Preference Test.
- Table S7: Between-group comparison of HRV metrics from the second session (arena + bedded cage) of the modified Social Preference Test.
- Table S8: Between-group comparison of HRV metrics from the third session (arena + caged rat) of the modified Social Preference Test.
- Table S9: Comparison of behavioral parameters within the control (Wistar) group across different sessions of the modified social preference test.
- Table S10: Comparison of behavioral parameters within the experimental (KM) group across different sessions of the modified social preference test.
References
- Grzadzinski R, Huerta M, Lord C. DSM-5 and autism spectrum disorders (ASDs): An opportunity for identifying ASD subtypes. Mol Autism. 2013; 4: 12. [CrossRef] [Google scholar]
- Hours C, Recasens C, Baleyte JM. ASD and ADHD comorbidity: What are we talking about? Front Psychiatry. 2022; 13: 837424. [CrossRef] [Google scholar]
- Antshel KM, Russo N. Autism spectrum disorders and ADHD: Overlapping phenomenology, diagnostic issues, and treatment considerations. Curr Psychiatry Rep. 2019; 21: 34. [CrossRef] [Google scholar]
- Mendez MA, Canitano R, Oakley B, San José-Cáceres A, Tinelli M, Knapp M, et al. Autism with co-occurring epilepsy care pathway in Europe. Eur Psychiatry. 2023; 66: e61. [CrossRef] [Google scholar]
- Antshel KM, Zhang-James Y, Wagner KE, Ledesma A, Faraone SV. An update on the comorbidity of ADHD and ASD: A focus on clinical management. Expert Rev Neurother. 2016; 16: 279-293. [CrossRef] [Google scholar]
- Frye RE, Rossignol DA. Identification and treatment of pathophysiological comorbidities of autism spectrum disorder to achieve optimal outcomes. Clin Med Insights Pediatr. 2016; 10. doi: 10.4137/CMPed.S38337. [CrossRef] [Google scholar]
- Politte LC, Howe Y, Nowinski L, Palumbo M, McDougle CJ. Evidence-based treatments for autism spectrum disorder. Curr Treat Options Psychiatry. 2015; 2: 38-56. [CrossRef] [Google scholar]
- Roane HS, Fisher WW, Carr JE. Applied behavior analysis as treatment for autism spectrum disorder. J Pediatr. 2016; 175: 27-32. [CrossRef] [Google scholar]
- Eckes T, Buhlmann U, Holling HD, Möllmann A. Comprehensive ABA-based interventions in the treatment of children with autism spectrum disorder-A meta-analysis. BMC Psychiatry. 2023; 23: 133. [CrossRef] [Google scholar]
- Harris JC. The necessity to identify subtypes of autism spectrum disorder. JAMA Psychiatry. 2019; 76: 1116-1117. [CrossRef] [Google scholar]
- Uljarević M, Phillips JM, Schuck RK, Schapp S, Solomon EM, Salzman E, et al. Exploring social subtypes in autism spectrum disorder: A preliminary study. Autism Res. 2020; 13: 1335-1342. [CrossRef] [Google scholar]
- Arpi MN, Simpson TI. SFARI genes and where to find them; modelling autism spectrum disorder specific gene expression dysregulation with RNA-seq data. Sci Rep. 2022; 12: 10158. [CrossRef] [Google scholar]
- Chorbadjiev L, Cokol M, Weinstein Z, Shi K, Fleisch C, Dimitrov N, et al. Analyzing the large and complex SFARI autism cohort data using the Genotypes and Phenotypes in Families (GPF) platform. Genome Res. 2025; 35: 2352-2362. [CrossRef] [Google scholar]
- Torres EB. Precision autism: Genomic stratification of disorders making up the broad spectrum may demystify its “Epidemic Rates”. J Pers Med. 2021; 11: 1119. [CrossRef] [Google scholar]
- Abrahams BS, Arking DE, Campbell DB, Mefford HC, Morrow EM, Weiss LA, et al. SFARI Gene 2.0: A community-driven knowledgebase for the autism spectrum disorders (ASDs). Mol Autism. 2013; 4: 36. [CrossRef] [Google scholar]
- Wiśniowiecka-Kowalnik B, Nowakowska BA. Genetics and epigenetics of autism spectrum disorder-current evidence in the field. J Appl Genet. 2019; 60: 37-47. [CrossRef] [Google scholar]
- Song R, Liu J, Kong X. Autonomic dysfunction and autism: Subtypes and clinical perspectives. N A J Med Sci. 2016; 9: 172-180. [Google scholar]
- van der Linden K, Simons C, Viechtbauer W, Ottenheijm E, van Amelsvoort T, Marcelis M. A momentary assessment study on emotional and biological stress in adult males and females with autism spectrum disorder. Sci Rep. 2021; 11: 14160. [CrossRef] [Google scholar]
- Bishop-Fitzpatrick L, Minshew NJ, Mazefsky CA, Eack SM. Perception of life as stressful, not biological response to stress, is associated with greater social disability in adults with autism spectrum disorder. J Autism Dev Disord. 2017; 47: 1-16. [CrossRef] [Google scholar]
- Fitzpatrick SE, Srivorakiat L, Wink LK, Pedapati EV, Erickson CA. Aggression in autism spectrum disorder: Presentation and treatment options. Neuropsychiatr Dis Treat. 2016; 12: 1525-1238. [CrossRef] [Google scholar]
- Kanne SM, Mazurek MO. Aggression in children and adolescents with ASD: Prevalence and risk factors. J Autism Dev Disord. 2011; 41: 926-937. [CrossRef] [Google scholar]
- Matson JL, Adams HL. Characteristics of aggression among persons with autism spectrum disorders. Res Autism Spectr Disord. 2014; 8: 1578-1584. [CrossRef] [Google scholar]
- Im DS. Treatment of aggression in adults with autism spectrum disorder: A review. Harv Rev Psychiatry. 2021; 29: 35-80. [CrossRef] [Google scholar]
- Brown CE, Borduin CM, Dopp AR, Mazurek MO. The social ecology of aggression in youths with autism spectrum disorder. Autism Res. 2019; 12: 1636-1647. [CrossRef] [Google scholar]
- Perepa P. Cultural basis of social ‘deficits’ in autism spectrum disorders. Eur J Spec Needs Educ. 2014; 29: 313-326. [CrossRef] [Google scholar]
- Peabody JE, Ryznar R, Ziesmann MT, Gillman L, Ryznar RJ, Gillman LM. A systematic review of heart rate variability as a measure of stress in medical professionals. Cureus. 2023; 15: e34345. [CrossRef] [Google scholar]
- Sachser N, Dürschlag M, Hirzel D. Social relationships and the management of stress. Psychoneuroendocrinology. 1998; 23: 891-904. [CrossRef] [Google scholar]
- Bartolomucci A, Palanza P, Sacerdote P, Panerai AE, Sgoifo A, Dantzer R, et al. Social factors and individual vulnerability to chronic stress exposure. Neurosci Biobehav Rev. 2005; 29: 67-81. [CrossRef] [Google scholar]
- Deussing JM. Animal models of depression. Drug Discov Today. 2006; 3: 375-383. [CrossRef] [Google scholar]
- Sgoifo A, Carnevali L, Grippo AJ. The socially stressed heart. Insights from studies in rodents. Neurosci Biobehav Rev. 2014; 39: 51-60. [CrossRef] [Google scholar]
- Crestani CC. Emotional stress and cardiovascular complications in animal models: A review of the influence of stress type. Front Physiol. 2016; 7: 251. [CrossRef] [Google scholar]
- Koolhaas JM, De Boer SF, De Rutter AJ, Meerlo P, Sgoifo A. Social stress in rats and mice. Acta Physiol Scand Suppl. 1997; 640: 69-72. [Google scholar]
- Carnevali L, Mastorci F, Graiani G, Razzoli M, Trombini M, Pico-Alfonso MA, et al. Social defeat and isolation induce clear signs of a depression-like state, but modest cardiac alterations in wild-type rats. Physiol Behav. 2012; 106: 142-150. [CrossRef] [Google scholar]
- Morais-Silva G, Gomes-de-Souza L, Costa-Ferreira W, Pavan JC, Crestani CC, Marin MT. Cardiovascular reactivity to a novel stressor: Differences on susceptible and resilient rats to social defeat stress. Front Physiol. 2022; 12: 781447. [CrossRef] [Google scholar]
- Molkentin JD, Dorn II GW. Cytoplasmic signaling pathways that regulate cardiac hypertrophy. Annu Rev Physiol. 2001; 63: 391-426. [CrossRef] [Google scholar]
- Lumbers ER, Boyce AC, Joulianos G, Kumarasamy V, Barner E, Segar JL, et al. Effects of cortisol on cardiac myocytes and on expression of cardiac genes in fetal sheep. Am J Physiol Regul Integr Comp Physiol. 2005; 288: R567-R574. [CrossRef] [Google scholar]
- Poletaeva II, Surina NM, Kostina ZA, Perepelkina OV, Fedotova IB. The Krushinsky-Molodkina rat strain: The study of audiogenic epilepsy for 65 years. Epilepsy Behav. 2017; 71: 130-141. [CrossRef] [Google scholar]
- Poletaeva II, Fedotova IB, Sourina NM, Kostina ZA. Audiogenic seizures-biological phenomenon and experimental model of human epilepsies. In: Clinical and genetic aspects of epilepsy. Hamburg, Germany: BoD; 2011. pp. 115-148. [Google scholar]
- Garbuz DG, Davletshin AA, Litvinova SA, Fedotova IB, Surina NM, Poletaeva II. Rodent models of audiogenic epilepsy: Genetic aspects, advantages, current problems and perspectives. Biomedicines. 2022; 10: 2934. [CrossRef] [Google scholar]
- Fedotova IB, Surina NM, Nikolaev GM, Revishchin AV, Poletaeva II. Rodent brain pathology, audiogenic epilepsy. Biomedicines. 2021; 9: 1641. [CrossRef] [Google scholar]
- Rebik AA, Riga VD, Smirnov KS, Sysoeva OV, Midzyanovskaya IS. Social behavioral deficits in Krushinsky-Molodkina rats, an animal model of audiogenic epilepsy. J Pers Med. 2022; 12: 2062. [CrossRef] [Google scholar]
- Rebik A, Broshevitskaya N, Kuzhuget S, Aleksandrov P, Abbasova K, Zaichenko M, et al. Audiogenic seizures and social deficits: No aggravation found in Krushinsky-Molodkina rats. Biomedicines. 2023; 11: 2566. [CrossRef] [Google scholar]
- Nikolaisvili M, Nanobashvili Z, Mitagvaria N, Chkadua G, Bilanishvili I, Nozadze E, et al. Effects of inhalation of low doses of radon in the Krushinsky-Molodkina rat strain and study of various behavioral characteristics. Exp Clin Med Georgia. 2023. doi: 10.52340/jecm.2023.03.20. [CrossRef] [Google scholar]
- Rebik AA, Broshevitskaya ND, Riga VD, Aleksandrov PL, Zaichenko MI, Midzyanovskaya IS. Ultrasound communications reveal social aversion in rats with contact motivation deficits but not anhedonia. Alpha Psychiatry. 2025; 26: 43990. [CrossRef] [Google scholar]
- Smirnov K, Starkov I, Sysoeva O, Midzyanovskaya I. Novel automated method to assess group dynamics reveals deficits in behavioral contagion in rats with social deficits. Front Behav Neurosci. 2024; 18: 1519486. [CrossRef] [Google scholar]
- Nicolini C, Fahnestock M. The valproic acid-induced rodent model of autism. Exp Neurol. 2018; 299: 217-227. [CrossRef] [Google scholar]
- Chaliha D, Albrecht M, Vaccarezza M, Takechi R, Lam V, Al-Salami H, et al. A systematic review of the valproic-acid-induced rodent model of autism. Dev Neurosci. 2020; 42: 12-48. [CrossRef] [Google scholar]
- Suchomelova L, Thompson KW, Baldwin RA, Niquet J, Wasterlain CG. Interictal aggression in rats with chronic seizures after an early life episode of status epilepticus. Epilepsia Open. 2023; 8: S82-S89. [CrossRef] [Google scholar]
- Rodriguez A, Zhang H, Klaminder J, Brodin T, Andersson PL, Andersson M. ToxTrac: A fast and robust software for tracking organisms. Methods Ecol Evol. 2018; 9: 460-464. [CrossRef] [Google scholar]
- Shaffer F, McCraty R, Zerr CL. A healthy heart is not a metronome: An integrative review of the heart’s anatomy and heart rate variability. Front Psychol. 2014; 5: 1040. [CrossRef] [Google scholar]
- Shaffer F, Ginsberg JP. An overview of heart rate variability metrics and norms. Front Public Health. 2017; 5: 258. [CrossRef] [Google scholar]
- Cohen J. Statistical power analysis for the behavioral sciences. New York, NY: Routledge; 2013. [CrossRef] [Google scholar]
- Posar A, Visconti P. Autism spectrum disorder in 2023: A challenge still open. Turk Arch Pediatr. 2023; 58: 566-571. [Google scholar]
- Baron-Cohen S, Robertson C. Sensory perception in autism. Nat Rev Neurosci. 2017; 18: 671-684. [CrossRef] [Google scholar]
- Pavlova IV, Broshevitskaya ND. Influence of immune system activation in early ontogenesis on aggressiveness and sexual motivation in adult Wistar rats. J Evol Biochem Physiol. 2023; 59: 1851-1861. [CrossRef] [Google scholar]
- Precenzano F, Parisi L, Lanzara V, Vetri L, Operto FF, Pastorino GM, et al. Electroencephalographic abnormalities in autism spectrum disorder: Characteristics and therapeutic implications. Medicina. 2020; 56: 419. [CrossRef] [Google scholar]
- Tye C, Runicles AK, Whitehouse AJ, Alvares GA. Characterizing the interplay between autism spectrum disorder and comorbid medical conditions: An integrative review. Front Psychiatry. 2019; 9: 751. [CrossRef] [Google scholar]
- Sorokina ND, Selitsky GV, Tsagashek AV, Zherdeva AS. Neurophysiological parameters and the tone of the autonomic nervous system in patients with migraine and epilepsy. Epilepsy Paroxysmal Cond. 2018; 10: 26-34. [CrossRef] [Google scholar]
- Zhuravlev DV, Lebedeva AV, Lebedeva MA, Guekht AB. Current concepts about autonomic dysfunction in patients with epilepsy. Zh Nevrol Psikhiatr Im S S Korsakova. 2022; 122: 131-138. [CrossRef] [Google scholar]
- Krivopalov S, Yushkov B, Sarapultsev A. Wireless EEG recording of audiogenic seizure activity in freely moving Krushinsky-Molodkina rats. Biomedicines. 2024; 12: 946. [CrossRef] [Google scholar]
- Litvinova SА, Yakovleva AA, Voronina TА, Gladysheva NS, Radontseva VV, Surina NM, et al. Ontogeny of the epileptic system in rats of the Krushinsky-Molodkina line with genetically determined audiogenic epilepsy. Dokl Ross Akad Nauk Nauki O Žizni. 2025; 521: 180-186. [CrossRef] [Google scholar]
- Kong Y, Zhao K, Zeng D, Lu F, Li X, Wu Y, et al. Effects of vagus nerve stimulation on cognitive function in patients with epilepsy: A systematic review and meta-analysis. Front Neurol. 2024; 15: 1332882. [CrossRef] [Google scholar]
- Sun K, Li Y, Zhai Z, Yin H, Liang S, Zhai F, et al. Effects of transcutaneous auricular vagus nerve stimulation and exploration of brain network mechanisms in children with high-functioning autism spectrum disorder: Study protocol for a randomized controlled trial. Front Psychiatry. 2024; 15: 1337101. [CrossRef] [Google scholar]
- Porges SW. The polyvagal perspective. Biol Psychol. 2007; 74: 116-143. [CrossRef] [Google scholar]
- Porges SW. Polyvagal theory: Current status, clinical applications, and future directions. Clin Neuropsychiatry. 2025; 22: 169-184. [Google scholar]
