Exaggerated MK-801-induced motor hyperactivity in rats with the neonatal lesion of the ventral hippocampus

Neonatal lesions of the ventral hippocampus in rats produce changes in spontaneous and pharmacologically induced dopamine-dependent behaviors that emerge in early adulthood. Neural mechanisms underlying these changes may have implications for understanding the neurobiology of schizophrenia, putatively a neurodevelopmental disorder. In this study, we evaluated the effects of MK-801 (dizocilpine), on automated measures of distance traveled and stereotypies in adult rats with neonatal (postnatal day 7) lesions, and tested the effects of haloperidol, clozapine and an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic (AMPA) antagonist LY293558 on the MK-801-induced behaviors. The lesioned rats showed significantly greater increases in motor activity after 0.05 and 0.1 mg/kg of MK-801 than did controls. Both haloperidol (0.1 and 0.4 mg/kg) and clozapine (4 and 10 mg/kg) reduced hyperlocomotion elicited by 0.2 mg/kg MK-801 in the ventral hippocampus (VH)-lesioned and sham rats. Haloperidol was more potent than clozapine in decreasing MK-801-induced stereotypy, especially in the lesioned rats. Moreover, an AMPA antagonist normalized exaggerated MK-801-induced hyperolocomotion in the lesioned rats at doses that had no effect in controls. These results demonstrate that the lesioned rats are more sensitive to MK-801 during adulthood than control rats, and that antidopaminergic drugs as well as AMPA antagonists antagonize the MK-801-induced behaviors. The neonatal lesion rat model may be useful to further our understanding of the interactions between dopamine and glutamate and their role in the pathophysiology of schizophrenia. (C) 2000 Lippincott Williams & Wilkins.