Anatomical distribution and physiological effects of enkephalin in rat inferior olive.
The opioid peptide enkephalin was evaluated as a possible synaptic transmitter in the inferior olivary complex using anatomical and physiological techniques. With standard immunohistochemical procedures, fibres and terminals containing enkephalin-like immunoreactivity were found to be heterogenously distributed in the inferior olive of the rat. Enkephalin-like immunoreactivity was found in the medial and dorsal accessory nuclei, but was sparse in the principal nucleus. Iontophoresis or pressure microapplication of Leu5-enkephalin, or a peptidase-resistant enkephalin analogue, depressed both spontaneous and amino acid-evoked firing of inferior olivary complex cells. The effect appeared to be postsynaptic, since the excitatory effects of iontophoretically-applied DL-homocysteic acid were suppressed. No selective effect on a calcium-mediated component of the action potential was seen. We conclude that enkephalin may act as a neurotransmitter or neuromodulator at afferent synapses in the inferior olive.
D000596:Amino Acids / Q000494:pharmacology; D000818:Animals; D004594:Electrophysiology; D004723:Endorphins / Q000032:analysis* / Q000494:pharmacology*; D004743:Enkephalin, Leucine; D004745:Enkephalins / Q000032:analysis* / Q000276:immunology / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D006710:Homocysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D007124:Immunoenzyme Techniques; D007478:Iontophoresis; D009474:Neurons / Q000502:physiology; D009847:Olivary Nucleus / Q000032:analysis* / Q000502:physiology; D051381:Rats; D014018:Tissue Distribution
D000596:Amino Acids; D004723:Endorphins; D004745:Enkephalins; D006710:Homocysteine; C007956:homocysteic acid; D004743:Enkephalin, Leucine