Regional 5-hydroxytryptamine following selective midbrain raphe lesions in the rat

Abstract

Lesions were produced in either the dorsal or median raphe nucleus and regional 5-hydroxytryptamine (5-HT), 5-hydroxyindole acetic acid (5-HIAA), and norepinephrine (NE) determined 26–30 days post-operatively. Only lesions in the dorsal raphe nucleus produced a fall (54%) in striatal 5-HT, while only lesions in the median raphe nucleus reduced (62%) hippocampal 5-HT. Reductions in the 5-HT and 5-HIAA contents of the remaining portion of the telencephalon and of the diencephalon following dorsal raphe lesions were twice as great as after median raphe lesions. The lowered 5-HT concentration (50%) of the telecephalon (excluding hippocampus and striatum) after dorsal raphe lesions, furthermore, was twice as large as that of the diecephalon (24%). Only dorsal raphe lesions produced a fall in brain stem 5-HT content. Neither lesion affected spinal (cervical-thoracic) 5-HT, nor NE in any of the brain areas assayed. It would appear that the dorsal and median raphe nuclei project 5-HT fibers into the forebrain but not to the spinal cord. The marger number of 5-HT fibers seems to originate in the dorsal raphe nucleus, which also seems to send a greater number of its 5-HT fibers to telecephalic than diencephalic structures. And, lastly, hippocampal and striatal 5-HT inputs apparently originate chiefly in the median and dorsal raphe nuclei, respectively.