Reticulospinal inhibition of interneurones

Abstract

The effect of electrical stimulation of the brain stem on interneurons in the dorsal horn and intermediary region was investigated in decerebrate cats after partial transection of the spinal cord. Stimuli that effectively depress reflex transmission without giving a primary afferent depolarization inhibit the discharge evoked from the flexor reflex afferents in interneurons. Brain stem stimulation did not give post-synaptic potentials in the great majority of interneurons but effectively depressed the excitatory post-synaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) evoked from the flexor reflex afferents in these interneurons. IPSPs were, however, evoked in 5 of 7 intracellu-larly recorded interneurons. These 5 interneurons were mono-synaptically activated from primary afferents. Possibly a dorsal reticulospinal system inhibits reflex transmission by giving postsynaptic inhibition in first order interneurons. The results are also discussed in relation to effects on interneurons from other descending pathways.