Enkephalin-induced inhibition of hypothalmaic paraventricular neurons

The Met-enkephalin analogues FK 33-824 and FW 34-569 were bath-applied to coronal slices from adult rat hypothalamus. At 5·10 −8 M, these substances caused a 50% reduction of the firing of paraventricular (PVN) neurons, which was antagonized by 10 −6 M naloxone. Morphine at 10 −6 −10 −4 M also inhibited PVN neurons. The results, which indicate that opiates produce a potent and apparently specific reduction in PVN firing, suggest that enkephalins may regulate posterior pituitary secretion by acting at hypothalamic and neurohypophysial levels.