Repetitive self-grooming behavior in the BTBR mouse model of autism is blocked by the mGluR5 antagonist MPEP

Abstract

Autism is a neurodevelopmental disorder characterized by abnormal reciprocal social interactions, communication deficits, and repetitive behaviors with restricted interests. BTBR T+tf/J (BTBR) is an inbred mouse strain that shows robust behavioral phenotypes with analogies to all three of the diagnostic symptoms of autism, including well-replicated deficits in reciprocal social interactions and social approach, unusual patterns of ultrasonic vocalization, and high levels of repetitive self-grooming. These phenotypes offer straightforward behavioral assays for translational investigations of pharmacological compounds. Two suggested treatments for autism were evaluated in the BTBR mouse model. Methyl-6-phenylethynyl-pyridine (MPEP), an antagonist of the mGluR5 metabotropic glutamate receptor, blocks aberrant phenotypes in the Fmr1 mouse model of Fragile X, a comorbid neurodevelopmental disorder with autistic features. Risperidone has been approved by the United States Food and Drug Administration for the treatment of irritability, tantrums, and self-injurious behavior in autistic individuals. We evaluated the actions of MPEP and risperidone on two BTBR phenotypes, low sociability and high repetitive self-grooming. Open field activity served as an independent control for non-social exploratory activity and motor functions. C57BL/6J (B6), an inbred strain with high sociability and low self-grooming, served as the strain control. MPEP significantly reduced repetitive self-grooming in BTBR, at doses that had no sedating effects on open field activity. Risperidone reduced repetitive self-grooming in BTBR, but only at doses that induced sedation in both strains. No overall improvements in sociability were detected in BTBR after treatment with either MPEP or risperidone. Our findings suggest that antagonists of mGluR5 receptors may have selective therapeutic efficacy in treating repetitive behaviors in autism.

Figure 1

MPEP reduced self-grooming behavior in BTBR. Cumulative time spent self-grooming was scored over a 10-min session, for the data shown in Figures 1 and 5. (a) B6 mice did not show any significant differences in the amount of time spent self-grooming after treatment with saline vehicle or MPEP at doses of 0.5 mg/kg, 1.0 mg/kg, 10 mg/kg, or 30 mg/kg i. p. (b) BTBR showed significant reductions in their innately high levels of repetitive self-grooming after treatment with MPEP at doses of 1.0 mg/kg, 10 mg/kg, and 30 mg/kg, ^*p<0.05 as compared with saline. N=6–10 per dose for each strain. Data are shown as ± SEM in all figures. Significant differences are as compared with vehicle treatment in all figures. Please see Results section for individual post hoc comparisons and statistics for all figures.

Figure 2

MPEP did not reduce exploratory locomotion. Total distance traversed was assayed in 5-min time bins across a 30-min session in a novel open field arena, for the data shown in Figures 2 and 6. (a) B6 showed no significant reductions in locomotor activity after administration of MPEP at doses of 10 mg/kg. An overall significant increase in activity compared with vehicle was observed for the 30 mg/kg treatment group ^*p<0.05. Significant increases in total distance during the first and fourth 5-min interval were observed compared with the 10 mg/kg dose. (b) BTBR showed no significant reductions in locomotor activity after administration of MPEP at doses of 10 mg/kg and 30 mg/kg. MPEP increased locomotion at the 30 mg/kg dose, significant during the first, second, fifth, and sixth 5-min time bins ^*p<0.05. N=7–9 per dose for each strain.

Figure 3

B6 sociability was unaffected by MPEP administration. Social approach was assayed in an automated photocell-equipped three-chambered arena, along with observer scoring of direct sniffing interactions from videotapes of the social approach session, in Figures 3, 4, 7, and 8. (a) B6 showed normal sociability as expected, defined as more time in the side chamber with the novel mouse than in the side chamber with the novel object, after saline and MPEP treatments, ^*p<0.05. (b) B6 showed significantly more time spent sniffing the novel mouse than the novel object, after saline and MPEP treatments, ^*p<0.05 (c) B6 showed no difference in number of entries into the side chambers after MPEP treatment, indicating no drug effect on general exploratory activity during the social approach task. (d) B6 showed no innate chamber side bias during the 10-min habituation phase before the start of the sociability test. N=8–10 per dose.

Figure 4

BTBR lack of sociability was unaffected by MPEP administration. (a) BTBR failed to show sociability as expected, spending similar amounts of time in the novel mouse chamber as compared with the novel object chamber after saline treatment. Lack of sociability in BTBR was similarly observed in each MPEP treatment group. (b) BTBR generally did not show significantly more time spent sniffing the novel mouse than the novel object after MPEP treatments. However, increased time spent sniffing was detected in the BTBR group treated with the 30 mg/kg dose of MPEP (^*p<0.05), indicating a trend toward improvement in social interactions. (c) No difference in number of entries into the side chambers was detected after MPEP treatments, indicating no drug effects on general exploratory activity during the sociability task. (d) BTBR showed no innate chamber side bias during the 10-min habituation phase before the start of the sociability test. N=9–11 per dose.

Figure 5

Risperidone reduced self-grooming behavior in BTBR. (a) B6 mice did not show any significant differences in the amount of time spent self-grooming after treatment with risperidone at doses 0.125 mg/kg and 0.25 mg/kg. (b) BTBR showed significant reductions in their innately high levels of repetitive self-grooming after treatment with risperidone at doses 0.125 mg/kg and 0.25 mg/kg, as compared with vehicle, ^*p<0.05. N=7–8 mice per dose.

Figure 6

Risperidone reduced exploratory locomotion in an open field. (a) B6 showed significant reductions in locomotor activity after administration of risperidone at doses of 0.125 mg/kg, 0.25 mg/kg, and 0.5 mg/kg. (b) BTBR showed significant reductions in locomotor activity after administration of risperidone at doses of 0.125 mg/kg, 0.25 mg/kg, and 0.5 mg/kg, during the first and second 5-min time bins ^*p<0.05. Risperidone treatment at a dose of 0.5 mg/kg reduced locomotion across 5 of the 6 assessed 5-min time bins ^*p<0.05. N=9–14 per dose for each strain.

Figure 7

B6 sociability was reduced by risperidone administration. (a) B6 showed significant sociability, as expected, after vehicle treatment, ^*p<0.05. Risperidone reduced normal sociability in B6, resulting in approximately equal low amounts of time spent in the two side chambers, concomitant with more time spent in the center chamber. (b) B6 showed significantly more time spent sniffing the novel mouse than the novel object after vehicle and 0.25 mg/kg risperidone treatments, ^*p<0.05, but did not after 0.125 mg/kg and 0.5 mg/kg risperidone treatments. (c) B6 showed a reduction in the number of entries into the side chambers, indicating a sedating effect of risperidone during the sociability task ^#p<0.05. (d) B6 showed no innate chamber side bias during the 10-min habituation phase before the start of the sociability test. N=8–10 per dose ^#p<0.05.

Figure 8

BTBR lack of sociability was unaffected by risperidone administration. (a) BTBR did not show sociability after vehicle or risperidone treatment. (b) BTBR did not show significantly more time spent sniffing the novel mouse than the novel object, after vehicle and risperidone administration. (c) BTBR showed a reduction in the number of entries into the side chambers, indicating a sedating effect of risperidone during the sociability task at doses 0.25 mg/kg and 0.5 mg/kg, ^#p<0.05. (d) BTBR showed the normal lack of innate chamber side bias during the 10-min habituation phase before the start of the sociability test, ^#p<0.05. N=10–11 per dose.