Abstract
In slices of guinea pig brain, intracellular recordings were obtained from neurones of the ventromedial nucleus of the hypothalamus (VMH). [ d-Ala 2, NMePhe 4, Gly-ol 5]enkephalin (DAGO), an agonist selective for γ-opioid receptors, caused an inhibition of spontaneous firing activity and a membrane hyperpolarization. This effect was reversible, concentration-dependent and could be blocked by naloxone. DAGO directly inhibited VMH neurones since its effect persisted when the slice was perifused with a solution that blocks synaptic transmission. The hyperpolarization induced by DAGO was associated with a marked decrease in membrane input resistance and it was reversed in polarity at membrane potentials 30–40 mV more negative than the resting potential. A chloride current did not contribute to the hyperpolarization brought about by DAGO. We conclude that DAGO inhibits VMH neurones, probably by opening membrane potassium channels.
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