Neuroendocrine CRF motoneurons: intrahypothalamic axon terminals shown with a new retrograde-Lucifer-immuno method

Neuroendocrine CRF motoneurons constitute the major final common pathway for central influences on anterior pituitary adrenocorticotropic hormone release. Activity of these cells, therefore, provides the major regulation of adrenal glucocorticoid release following a variety of physical and emotional stressors. Corticotropin-releasing factor (CRF) is expressed in many different neuronal cell types but it functions in two main roles: (1) as a hypothalamic hormone and (2) as a neurotransmitter involved in extrahypothalamic circuits. Because neuroendocrine CRF cells may also express at least 6 different neuropeptides, some without known direct hypophyseal actions, these neurons may also give rise to axon terminals within the brain. To test this, a method for intracellular filling of retrogradely labeled, immunohistochemically identified neurons was developed. The results demonstrate that the axon of some neuroendocrine CRF cells in the rat paraventricular nucleus give rise to terminal boutons just outside the nucleus, and may thus synapse with other hypothalamic neurons, as well as releasing neuropeptides into the hypophyseal portal system.