Effects of 6-hydroxydopamine lesioning of the medial prefrontal cortex on social interactions in adolescent and adult rats

Abstract

Bilateral depletion of dopamine (DA) in the medial prefrontal cortex (mPFC) following local infusions of 6-hydroxydopamine (6-OHDA) was reported to affect mesolimbic DA neurotransmission and augment spontaneous and amphetamine-induced locomotion. However, the effects of 6-OHDA lesioning of the mPFC of adolescent rats have never been investigated. Given that dopaminergic neurons reach the peak of maturation during adolescence, we hypothesized that 6-OHDA lesioning of the mPFC during adolescence would have greater impact on subsequent behavioral parameters than would such lesioning during adulthood. The aim of this study was to investigate the effects of 6-OHDA lesioning of the mPFC on the open-field activities and novel investigative and socially interactive behaviors of adolescent and adult rats. Using a stereotaxic apparatus, 6-OHDA (8.0 µg) was injected bilaterally into the mPFC of adolescent and adult rats. After a 1-week recovery period, rats were placed in an open-field chamber, and spontaneous locomotion and other behaviors were monitored. Next, a novel toy was place in the center and behavioral responses were observed. One day later, socially interactive behaviors were measured by placing the lesioned rats into a cage with four unfamiliar rats matched for age. The tests of locomotor activity and novel investigative behaviors revealed no significant differences between the lesioned and sham groups of adolescent or adult rats. Grooming and socially interactive behaviors were significantly lower in the adolescent and adult lesioned groups than in each sham group. Interestingly, we observed more extensive impairment in socially interactive behaviors among the adolescent lesioned rats compared to the adult lesioned rats. The present study indicates that DA depletion in the mPFC causes significantly reduced grooming and socially interactive behaviors; this phenomenon may be comparable to the negative symptoms observed in schizophrenia. Further research is warranted to investigate the mechanisms underpinning the detrimental effects of 6-OHDA lesioning of the mPFC on social behaviors.