Neurotransmitter Regulation of CRF Secretion in Vitro
A decade prior to elucidation of the sequence of corticotropin-releasing factor (CRF), investigators were already studying the neurotransmitter regulation of CRF release in vitro using bioassays for adrenocorticotropin (ACTH) and adrenal glucocorticoids as a measure of "CRF" activity. Utilizing immunocytochemical methods, Liposits et al. have demonstrated tyrosine hydroxylase immunoreactive nerve terminals, a specific marker for catecholaminergic neurons, innervating CRF-containing perikarya in the paraventricular nucleus (PVN). In some studies animals were hypophysectomized or adrenalectomized prior to experimentation to increase CRF secretion as much as three to four times the rate in control animals. Both in vivo and in vitro data support a stimulatory role for serotonin on hypothalamic CRF secretion. The chapter focuses on CRF release from the median eminence. Releasable pools of CRF are found in other areas of the brain as well. Because of the tortuous pathway taken by the CRF neuron from the PVN to the median eminence, the explant block cannot feasibly be made much smaller.