Synaptic association between enkephalin-containing axon terminals and proopiomelanocortin-containing neurons in the arcuate nucleus of rat hypothalamus.

By employing an electron microscopic dual immunolabeling technique, a synaptic association between neurons containing immunoreactive adrenocorticotropin (ACTH) and axonal terminals containing immunoreactive methionine-enkephalin octapeptide (Enk-8) was found in the arcuate nucleus of the rat hypothalamus. The axonal terminals contained many small clear vesicles and some large cored vesicles. At the synaptic portions, membrane specialization was asymmetric.