Ultrastructural immunocytochemical localization of enkephalin in the goldfish preoptic nucleus

This study describes the ultrastructural localization of the opioid peptide enkephalin (ENK) in the preoptic nucleus of the goldfish. Using immunocytochemical techniques, ENK could be seen in neurosecretory granules and throughout the cytoplasm of magnocellular neurons with an agranular distribution. ENK was also associated with small clear vesicles and large dense-core vesicles within certain axon terminals in the preoptic nucleus. In this report, we discuss the cellular and synaptic relationships of ENK neurons in the preoptic nucleus of the teleost.