CELLULAR-LOCALIZATION OF THE 5-HT1A RECEPTOR IN PRIMATE BRAIN NEURONSAND GLIAL-CELLS

Activation of 5HT(1A) receptors produces many different physiologic re sponses, which may be due to their localization on diverse cells in th e brain. A 5-HT1A receptor antipeptide (aa170-186) antibody was produc ed that showed both high titer for peptide binding and immunocytochemi cal staining. Studies performed in perfusion-fixed brain tissue showed immunoreactive neurons, glial, and ependymal cells in the rat, mouse, cat, and monkey. Results from our studies of Macaca fascicularis brai ns are presented. We observed two main neuronal labeling patterns in t he primate brain: (1) A general, diffuse somatodendritic distribution of 5-HT1A receptor immunoreactivity is seen in the raphe nuclei where the dendritic shaft, its branches and spines, and the entire perikaryo n are immunolabeled. This pattern is also observed in the nucleus locu s coeruleus, in scattered large brainstem reticular neurons, and in de ntate gyrus hilar interneurons. (2) A discrete localization of 5-HT1A receptor immunoreactivity on the initial axon segment (axon hillock) i s noted in pyramidal neurons of layer III and V of cerebral cortex, Co rnu Ammonus (1-4) of the hippocampus, and in most brainstem and cervic al spinal cord motoneurons. In addition to neuronal labeling, 5-HT1A r eceptor immunoreactivity is seen in the cell body and processes of ast rocytes, and other nonneuronal cells. This pattern is particularly evi dent in the white matter of cerebral cortex and spinal cord, the ponti ne nuclei, the brainstem tectum, and the hilus of the dentate gyrus. T he clinical implications of 5-HT1A cellular localization are briefly d iscussed.