The hypophysiotropic galanin system of the rat brain.

The external zone of the rat median eminence contains a large amount of galanin-immunoreactive terminals indicating that galanin might function as a hypophysiotropic hormone. The possible sources of these galanin-containing nerve terminals were studied in the male and female rat by means of retrograde labeling in combination with fluorescence immunocytochemistry. Fluoro-Gold was used as retrograde tracer, and it was injected peripherally. Fluoro-Gold does not penetrate the blood-brain barrier, but it is taken up by nerve terminals which project to areas supplied by capillaries that lack the blood-brain barrier. The simultaneous detection of Fluoro-Gold taken up by nerve terminals in the median eminence and the endogenous galanin in thin paraffin sections has revealed that approximately 60% of the hypophysiotropic galanin cells are located in the arcuate nucleus. The remaining portion is located in the parvocellular subdivision of the paraventricular nucleus. Only scattered hypophysiotropic galanin cells are present in the medial preoptic area.