Activation of the superior colliculus has been shown to reproduce the
antiepileptic effect of the inhibition of the substantia nigra reticulata. A circuit involving neurons of the caudal deep layers of the superior colliculus has been suggested to control brain stem convulsive
seizures. The present study was designed to examine whether a similar circuit is also involved in the control of absence
seizures. For this, activation of either the rostral or caudal parts of the deep and intermediate layers of the superior colliculus was applied in a genetic model of absence
seizures in the rat (GAERS). Single-
shock (5 s) electrical stimulation of the rostral and caudal superior colliculus interrupted ongoing spike-and-wave discharges at an intensity (
antiepileptic threshold) significantly lower than the intensity inducing behavioral effects. At this intensity, no interruption of licking behavior was observed in water-deprived rats. Repeated stimulations (5 s on/5 s off) at the
antiepileptic threshold reduced absence
seizures only during the first 10 min. Bilateral microinjection of a
GABA antagonist (
picrotoxin, 33 pmol/side) significantly suppressed spike-and-wave discharges when applied in the caudal aspect of the superior colliculus. This
antiepileptic effect appears dissociated from an anxiogenic effect, as tested in an elevated plus maze test. Finally, bilateral injection of
picrotoxin (33 pmol/side) appeared more effective in the superficial and intermediate layers of the caudal superior colliculus, whereas such
injections had only weak effects on absence
seizures when applied in the deep layers. These results suggest that a specific population of neurons located in the intermediate and superficial layers of the caudal superior colliculus is involved in the inhibitory control of absence
seizures. It may constitute an important relay for the control of absence
seizures by the basal ganglia via the substantia nigra reticulata.