MONOSYNAPTIC EXCITATION OF PREGANGLIONIC VASOMOTOR NEURONS BY SUBRETROFACIAL NEURONS OF THE ROSTRAL VENTROLATERAL MEDULLA

Extracellular single unit recordings were made from barosensitive neur ons in the subretrofacial nucleus (SRF) of the rostral ventrolateral m edulla in chloralose-anaesthetised cats. At the same time, single preg anglionic neuron activity was recorded from filaments of the cervical sympathetic trunk (CST); barosensitive units were selected for study. Evidence for monosynaptic connections between the two neuron groups wa s sought by cross-correlation analysis of their ongoing activity. Cros s-correlograms of 16/16 SRF/CST neuron pairs showed a broad peak (100- 200ms wide), reflecting the synchronising action of arterial barorecep tors on both neurons' activity. Two of the 16 cross-correlograms addit ionally showed a robust, statistically significant, narrow peak of a s ingle 2 ms bin width, providing the first physiological demonstration that ventrolateral medullary neurons monosynaptically excite pregangli onic sympathetic neurons. Deductions are made about the strength, conv ergence and divergence of the connection.