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Enkephalin suppresses afferent cochlear neurotransmission
C Bürki1, D Felix, K Ehrenberger
1Division of Neurobiology, University of Berne, Switzerland.
Summary
Enkephalin, a neurotransmitter, inhibits inner hair cell activity by blocking excitatory amino acids. This effect is reversed by naloxone, confirming enkephalin
Area of Science:
- Neuroscience
- Auditory Physiology
- Cellular Biology
Background:
- Inner hair cells are crucial for hearing.
- Efferent neurons modulate inner hair cell function.
- The role of endogenous opioids in the auditory system is not fully understood.
Purpose of the Study:
- To investigate the effects of enkephalin on guinea pig inner hair cell activity.
- To determine if enkephalin acts as a neurotransmitter or neuromodulator in the auditory pathway.
- To explore the involvement of opioid receptors in efferent modulation of hair cells.
Main Methods:
- Iontophoretic application of enkephalin and naloxone.
- Recording of induced firing activity in guinea pig inner hair cell afferent dendrites.
- Testing the effects of enkephalin on N-methyl-D-aspartate (NMDA), quisqualate, and kainate induced activity.
Main Results:
- Enkephalin significantly depressed the depolarizing effects of NMDA, quisqualate, and kainate.
- Enkephalin showed a stronger inhibitory effect on non-NMDA receptor-mediated activity.
- The inhibitory effect of enkephalin was blocked by the opiate antagonist naloxone, indicating a specific opioid receptor-mediated action.
Conclusions:
- Enkephalin acts as a neurotransmitter or neuromodulator in the efferent innervation of inner hair cells.
- Opioid signaling plays a role in modulating auditory nerve activity originating from inner hair cells.
- These findings contribute to understanding the complex neurochemical regulation of hearing.