Prosocial effects of oxytocin in two mouse models of autism spectrum disorders

Abstract

Clinical evidence suggests that oxytocin treatment improves social deficits and repetitive behavior in autism spectrum disorders (ASDs). However, the neuropeptide has a short plasma half-life and poor ability to penetrate the blood-brain barrier. In order to facilitate the development of more bioavailable oxytocinergic compounds as therapeutics to treat core ASD symptoms, small animal models must be validated for preclinical screens. This study examined the preclinical utility of two inbred mouse strains, BALB/cByJ and C58/J, that exhibit phenotypes relevant to core ASD symptoms. Mice from both strains were intraperitoneally administered oxytocin, using either acute or sub-chronic regimens. Acute oxytocin did not increase sociability in BALB/cByJ; however, sub-chronic oxytocin had significant prosocial effects in both BALB/cByJ and C58/J. Increased sociability was observed 24 h following the final oxytocin dose in BALB/cByJ, while prosocial effects of oxytocin emerged 1-2 weeks post-treatment in C58/J. Furthermore, acute oxytocin decreased motor stereotypy in C58/J and did not induce hypoactivity or anxiolytic-like effects in an open field test. This study demonstrates that oxytocin administration can attenuate social deficits and repetitive behavior in mouse models of ASD, dependent on dose regimen and genotype. These findings provide validation of the BALB/cByJ and C58/J models as useful platforms for screening novel drugs for intervention in ASDs and for elucidating the mechanisms contributing to the prosocial effects of oxytocin.

Fig. 1. Experimental timelines for the acute and sub-chronic oxytocin regimens, and behavioral tests in BALB/cByJ and C58/J mice

The acute regimen was a single-dose of vehicle or oxytocin (1.0 mg/kg) administered 50 minutes before behavioral testing. The sub-chronic regimen consisted of four doses of either vehicle or oxytocin (1.0 mg/kg) across an 8–9 day period, with at least 48 hours between each IP injection. Sociability (Social) or repetitive (Rep.) behavior testing occurred on the indicated days. C58/J Cohorts 3 and 4 are not shown.

Fig. 2. Lack of prosocial effects of oxytocin with acute treatment in male BALB/cByJ mice

Oxytocin (1.0 mg/kg) was administered 50 minutes before evaluating social approach in the three-chambered choice test. Data shown are means (+ SEM) for 6 mice per treatment group.

Fig. 3. Prosocial effects of oxytocin with sub-chronic treatment in male BALB/cByJ mice

The sub-chronic regimen consisted of four doses of either vehicle or oxytocin (1.0 mg/kg) across an 8–9 day period, with at least 48 hours between each IP injection. Subjects were tested for sociability in the three-chambered choice test 24 hours following the final dose. N=12–18 per group. Sniffing data are missing from two mice in Cohort 2 due to experimenter error. * p<0.05, within-group comparison.

Fig. 4. Prosocial effects of sub-chronic oxytocin in C58/J mice

The sub-chronic regimen consisted of four doses of either vehicle or oxytocin (1.0 mg/kg) across an 8–9 day period, with at least 48 hours between each IP injection. Subjects were tested for sociability 24 hours following the final dose (N=16 per sex, per treatment). Half of the mice were further tested 1 week (1wk) after the sub-chronic oxytocin regimen, and the remaining mice were tested 2 weeks (2wk) following treatment. Data were lost for one female subject at the 24-hour time point due to equipment failure. * p<0.05, within-treatment group comparison.

Fig. 5. Effects of sub-chronic oxytocin on time spent sniffing the stranger cage or empty cage

The sub-chronic regimen consisted of four doses of either vehicle or oxytocin (1.0 mg/kg) across an 8–9 day period, with at least 48 hours between each IP injection. Subjects were tested for sociability 24 hours following the final dose (N=16 per sex, per treatment). Half of the mice were further tested 1 week (1wk) after the sub-chronic oxytocin regimen, and the remaining mice were tested 2 weeks (2wk) following treatment. * p<0.05, within-treatment group comparison.

Fig. 6. No effects of sub-chronic oxytocin on number of entries in C58/J mice

The sub-chronic regimen consisted of four doses of either vehicle or oxytocin (1.0 mg/kg) across an 8–9 day period, with at least 48 hours between each IP injection. Subjects were tested for sociability 24 hours following the final dose (N=16 per sex, per treatment). Half of the mice were further tested 1 week (1wk) after the end of the oxytocin regimen, and the remaining mice were tested 2 weeks (2wk) following the final dose. Data were lost for one female subject at the 24-hour time point due to equipment failure.

Fig. 7. Effects of acute and sub-chronic oxytocin on motor stereotypy in C58/J mice

A–C) Oxytocin (1 mg/kg) or vehicle was administered 50 minutes before a 20-minute session. Means (+ SEM) are presented for the first and second 10-minute intervals. Data for five mice with zero levels of stereotypy after vehicle treatment were not included. Remaining number of mice were N=16 (9 males and 7 females). D–F) The sub-chronic regimen consisted of four doses of either vehicle or oxytocin (1.0 mg/kg) across an 8–9 day period, with at least 48 hours between each IP injection. Subjects were first tested for sociability 24 hours or 1 week following the final dose, and then given a 30-minute session for repetitive behavior following each test. Data are presented for the final 10 minutes. * p<0.05.

Fig. 8. Lack of oxytocin effects on activity and anxiety-like behavior in an open field test

Oxytocin (1.0 mg/kg) or vehicle was administered immediately before the start of a 2-hour open field test. Data are means (+ SEM) for 16 C58/J mice (8 males and 8 females), each tested once with vehicle and once with oxytocin, using a crossover design.