The Effect of Propionic Acid on the Habituation to Social and Non-social Odour Cues in Adult Male Rats
Abstract
The enteric bacterial metabolite, propionic acid (PPA), elicits physiological and behavioural changes in rodents reminiscent of autism spectrum disorder (ASD). This includes abnormal sensory processing and social behaviour. ASD may contribute to social deficits through impaired habituation; therefore, the present study examined the effects of intraperitoneal PPA on the habituation to social and non-social odours. Adult male rats were injected daily with PPA or the vehicle control, and for 3 days, habituated to a conspecific odour or vanilla extract for 10 minutes. On day 4, rats were exposed to a novel conspecific odour or almond extract for 10 minutes to observe dishabituation. Behaviours were measured in the open-field and analyzed via an automated system and by the manual scoring of video-recordings. Results from both scoring methods strongly correlated with one another. PPA treatment significantly increased repetitive behaviours and hypoactivity. Drug and odour had no significant effects on odour habituation, although PPA non-social rats displayed reduced habituation for entries into the odour quadrant and sniffing. Group differences were insignificant. No dishabituation to the odour was observed in all groups. However, an insignificant, subtle reduction in dishabituation to the open-field was seen in PPA groups for total distance travelled. PPA may influence odour discrimination in rodents and contribute to sensory habituation deficits in ASD. Differences in body temperature and weight post-injection were measured to monitor a potential sickness response from the bacterial by-product. Results for PPA rats did not differ from controls, suggesting that PPA exerts its effects through other mechanisms.