Dopaminergic control of feline hippocampal epilepsy: a nigro hippocampal pathway.

Substantia nigra is a mesencephalic structure inserted along several circuits which appear to play a key role in epilepsy. In previous researches we postulated that substantia nigra pars compacta (SNpc) may be the site of a precise control of hippocampal epilepsy while substantia nigra pars reticulata (SNpr) may exert a modulation of both neocortical epilepsy and spreading of hyperactivity toward a motor target. In order to better understand mechanisms subserving nigral action in feline hippocampal epilepsy we electrically stimulated SNpc (dopaminergic), before and after sulpiride (dopamine receptor-antagonist) intravenous injection. Furthermore we compared hippocampal epileptiform activity prior to and after apomorphine (dopamine receptor-agonist) intrahippocampal injection as well as prior to and after SNpc electrolytic destruction. Results showed that SNpc is able to regulate hippocampal epilepsy. This effect is selectively antagonized by sulpiride while apomorphine exerts, synergically with SNpc stimulation, inhibitory effects. On the contrary SNpc lesions induces a significant enhancement of hippocampal epileptiform spikes. Experimental findings suggest that SNpc represents a strategic region for the control of hippocampal excitability and that this regulation appears to be dopaminergic in nature.