Effects of dalargin on excitation induced by L-glutamate agonists in the frog vestibular organs.

Abstract

We have used an electrophysiological approach to investigate the action of a synthetic analog of leu-enkephalin dalargin (DAL) on chemically induced afferent activity in the frog vestibular organs. Administration of 5.0 microM kainic acid (KA), 5.0 microM (AMPA) and 50 microM NMDA produced an increase in the frequency of the resting discharge. Firing evoked by KA, AMPA or NMDA could be depressed by administration of 1 nM Dal by 55.5 +/- 9.9% (n = 10, p < 0.05), 64.5 +/- 11.2% (n = 13, p < 0.05) and 21.3 +/- 11.1% (n = 14, p = 0.051), respectively. Thus, the frequency decrease under NMDA was statistically non-significant. These results show that non-NMDA, but not NMDA subtypes of receptors are mostly involved in opioid action at the vestibular organs of the frog.