Direct inhibitory synaptic connections of pontine omnipause neurons with burst neurons in Forel's field H related to vertical saccades in the cat

Abstract

This study investigated synaptic connections of omnipause neurons (OPNs) in the midline pontine tegmentum with medium-lead burst neurons (BNs) in Forel's field H (FFH), using the spike-triggered averaging technique in chronically prepared alert cats. OPNs were identified behaviorally by tonic firing during the intersaccadic period, whereas medium-lead BNs were identified by spike bursts during upward or downward saccades. A positive shift of field potential in the BN area, associated with suppression of the BNs' bursts, was observed during tonic firing of OPNs and during microstimulation in the OPN area. Averaging of BN area field potentials triggered by spikes of single OPNs on both sides, which were antidromically evoked from the BN area, revealed positive waves with monosynaptic latencies. These results strongly suggest that OPNs on both sides make direct inhibitory synaptic connections with vertical eye movement-related medium-lead BNs in the FFH.