The effect of [Met]enkephalin on the periaqueductal gray neurons of the rat: an in vitro study.
Intracellular and extracellular recording techniques and in vitro preparation were used to examine the effect of [Met]enkephalin on the rat periaqueductal neurons. In the 20 cells that were recorded intracellularly, [Met]enkephalin caused an increase in the resting membrane conductance, hyperpolarization of the cell membrane, an increase in the firing threshold and a decrease in the spontaneous firing rate. This effect of [Met]enkephalin could be blocked by naloxone. The effect of [Met]enkephalin on 99 neurons was also examined using extracellular recording. In 59% of cells, pressure application of [Met]enkephalin caused a dose-dependent inhibition that could be blocked by naloxone; 15% of the cells were excited and the remaining neurons (26%) did not respond. Nineteen per cent of responsive cells were located in the dorsolateral subdivision; 41% in the ventrolateral and 13% in the dorsal regions. In 10 cells, perfusion with physiological saline solution/Mg did not alter the inhibitory effect of [Met]enkephalin. However, perfusion with physiological saline solution/Mg abolished the excitatory response to [Met]enkephalin in four cells. It is concluded that: (1) the major effect of [Met]enkephalin on periaqueductal gray cells is inhibition that occurs through a direct postsynaptic process. This inhibition is probably due to an increase in permeability to potassium; (2) a small population of periaqueductal gray cells are excited by [Met]enkephalin, probably through a presynaptic process.
Behbehani
M M
MM
Department of Physiology and Biophysics, University of Cincinnati College of Medicine, OH 45267.
Jiang
M
M
Chandler
S D
SD
D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D004744:Enkephalin, Methionine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D009270:Naloxone / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects*; D010487:Periaqueductal Gray / Q000166:cytology / Q000187:drug effects*; D051381:Rats; D011919:Rats, Inbred Strains; D012965:Sodium Chloride / Q000494:pharmacology
D009270:Naloxone; D012965:Sodium Chloride; D004744:Enkephalin, Methionine; D008274:Magnesium