Reticulospinal neurones provide monosynaptic glycinergic inhibition of spinal neurones in lamprey

In lamprey, distinct groups of reticulospinal neurones utilize different neurotransmitters such as glutamate or serotonin. The present study demonstrates that a group of reticulospinal neurones inhibit their target neurones by an action on glycine receptors. Simultaneous intracellular recordings from a reticulospinal neurone and spinal target neurone shows that the former may evoke an IPSP in the latter. These IPSPs are elicited at a constant latency and amplitude, and follow high frequency stimulation (100 Hz). Furthermore, the IPSPs are maintained when the excitatory amino acid synaptic transmission is blocked, suggesting that the effects are not elicited via a powerful disynaptic pathway. These data taken together establish the monosynaptic nature of the pathway. IPSPs elicited from single reticulospinal neurones or from electrical stimulation of the reticular formation are suppressed by administration of strychnine, suggesting that glycine is the neurotransmitter of these inhibitory reticulospinal neurones.