Ultrastructural evidence of enkephalinergic input to glucoreceptor neurons in ventromedial hypothalamic nucleus

A combination of intracellular injection of horseradish peroxidase into the ventromedial hypothalamic nucleus glucoreceptor neurons and immunohistochemical staining for enkephalin allowed ultrastructural visualization of interrelations between these electrophysiologically identified neurons and enkephalin-like immunoreactive (ENK-IR) terminals. The results show that glucoreceptor neurons receive direct inputs from ENK-IR neurons. This is the first evidence that glucoreceptor neurons, identified electrophysiologically, can be affected monosynaptically by endogenous enkephalin, probably released from ENK-IR terminals.