Current status of brain hypophysiotropic factors: morphologic aspects.
Nearly 40 putative neurotransmitters and other chemical messengers, mostly peptides, are present in the median eminence that constitutes the final common pathway for signals from the brain to the pituitary. The majority of them are produced in perikarya located in different nuclei of the hypothalamus; however, some of them arise from the brainstem. The neurons contacting capillaries of the median eminence (hypophysiotropic neurons) are intermixed with neurons containing the same transmitter (hypophysiotropic factor(1)), but projecting to other areas of the brain. Depending on their site of release, the hypophysiotropic factors may function as neurohormones acting an the pituitary or neurotransmitters affecting the activity of other neurons in the central nervous system. Based on retrograde tracing studies in combination with immunocytochemistry, the origin of many nerve terminals in the median eminence has been determined.
Merchenthaler
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Functional Morphology Section, Laboratory of Molecular and Integrative Neuroscience, NIEHS, National Institutes of Health, Research Triangle Park, NC 27709, USA.