Enkephalin suppresses afferent cochlear neurotransmission.
The effects of enkephalin and naloxone, applied iontophoretically, were tested on induced firing activity of the afferent dendrites on inner hair cells in the guinea pig. Enkephalin strongly depresses the depolarizing effect of N-methyl-D-aspartate (NMDA), quisqualate and kainate. Enkephalin exerted a stronger inhibitory effect on non-NMDA-induced fibre activity than on NMDA-induced activity. It was possible to block this inhibitory effect by applying the opiate antagonist naloxone, which suggests a specific enkephalin action. Our results appear to demonstrate that enkephalin acts as a neurotransmitter or a neuromodulator in the efferent neurones of inner hair cells which have synaptic contact to the afferents of the inner hair cells.
Bürki
C
C
Division of Neurobiology, University of Berne, Switzerland.
Felix
D
D
Ehrenberger
K
K
D000818:Animals; D003051:Cochlea / Q000294:innervation*; D003712:Dendrites / Q000187:drug effects; D004745:Enkephalins / Q000494:pharmacology*; D006168:Guinea Pigs; D006199:Hair Cells, Auditory, Inner / Q000187:drug effects*; D007608:Kainic Acid / Q000494:pharmacology; D016202:N-Methylaspartate / Q000494:pharmacology; D009270:Naloxone / Q000494:pharmacology*; D009475:Neurons, Afferent / Q000187:drug effects*; D009476:Neurons, Efferent / Q000187:drug effects; D016318:Quisqualic Acid / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects*
D004745:Enkephalins; D009270:Naloxone; D016202:N-Methylaspartate; D016318:Quisqualic Acid; D007608:Kainic Acid