Functional and morphological studies of peptide-containing neuroendocrine cells in goldfish hypothalamus

We report the development of a double‐label method which combines intracellular recording, dye‐marking, and immunocytochemistry for the study of functional and morphological aspects of peptide‐containing neurons in the magnocellular preoptic nucleus of the goldfish hypothalamus. Using multiple techniques, we distinguish three types of peptide‐containing neurons: enkephalin (27%), isotocin (49%), and vasotocin (24%). Drawings of serial sections containing the dye‐injected cells were the basis for subsequent reconstruction. These peptidecontaining cells measure 14‐56 μm in somata diameter, are unipolar, bipolar, or multipolar in somata shape and lie 6–244 μm from the ependymal lining of the preoptic recess of the third ventricle. Their electrophysiological properties match those of other mammalian and fish magnocellular neuroendocrine cells. This report confirms the one neuron, one hormone (peptide) hypothesis, supports synaptic over electrotonic coupling between peptidergic and adjacent hypothalamic neurons, and suggests that chemical and functional classification of single electrophysiologically and neuroanatomically studied central neurons is feasible technologically.