Evidence for autapses in the substantia nigra.

Intracellular recording and intracellular HRP staining were employed to trace the recurrent terminal plexus of cat substantia nigra pars reticulata neurons. Autaptic neurons were labeled. The axon of an autaptic neuron was found to emit a recurrent collateral which distributed 'en passage' and terminal boutons contacting dendrites of the parent cell. Antidromic ventromedial thalamic stimulation elicited a recurrent IPSP in the autaptic neuron.