DELAYED-EFFECTS OF NEONATAL HIPPOCAMPAL DAMAGE ON HALOPERIDOL-INDUCED CATALEPSY AND APOMORPHINE-INDUCED STEREOTYPIC BEHAVIORS IN THE RAT

The developmental effects of neonatal excitotoxic ventral hippocampal (VH) damage on behaviors related to dopaminergic (DA) transmission in the basal ganglia were investigated in the rat. Ibotenic acid (in Lesion) or artificial cerebrospinal fluid (in Sham) was infused into the VH of 7-day-old (PD7) rat pups. Haloperidol-induced (1 mg/kg, i.p.) catalepsy and apomorphine-induced (0.75 mg/kg, s.c.) stereotypic behaviors as well as locomotion were assessed in Sham and Lesion rats prior to (PD35) and after puberty (PD56). On PD35, Lesion and Sham animals did not differ in induced catalepsy or stereotypy. On PD56, however, Lesion animals were less cataleptic following haloperidol injection and manifested supersensitivity to apomorphine as compared to Sham rats. At both, PD35 and PD56, locomotor activity after apomorphine was significantly increased in Lesion animals as compared with controls. These results indicate that the neonatal excitotoxic VH lesion results in a unique time-dependent pattern of behavioral changes related to striatal DA transmission. Moreover, the response to apomorphine differs qualitatively from that previously reported after the analogous lesion induced in adult animals in which stereotypy was reduced. These findings suggest that early hippocampal deefferentation affects the development of other brain regions, such as the medial prefrontal cortex, that are also involved in the regulation of striatal DA function.