A new class of small inhibitory interneurones in the lamprey spinal cord.

Paired intracellular recordings of interneurones and motoneurones have been performed in the lamprey spinal cord in vitro. One new type of small interneurone (10-15 microns in diameter) which produces monosynaptic inhibitory postsynaptic potentials (IPSPs) in motoneurones is described. The IPSP is strychnine-sensitive and thus presumably glycinergic. This type of interneurone undergoes rhythmical membrane potential oscillations during fictive locomotion and intracellular stimulation can have a profound effect on the burst generation occurring during fictive locomotion.