Immunocytochemistry for arginine in the rat central nervous system. P.Petrusz, V. Kharazia, G. Grossman, R.J Weinberg, T.E. Salt Dept. of Cell Biology and Anatomy, University of North Carolina, Chapel Hill, NC 27599, U.S.A. and Institute of Ophthalmology, University of London U.K.

Modulation of activity in the thalamus involves several mechanisms. Recent data have shown that stimulation of afferents to the ventrobasal thalamic complex triggers release of L-arginine (Do et al., 1994), suggesting a modulatory role for nitric oxide in thalamic mechanisms of somatosensation. We performed immunocytochemistry to study the regional and cellular distribution of arginine. Antibodies were prepared in rabbits against arginine, conjugated to keyhole limpet hemocyanin according to Aoki et al. (1991). These antibodies were shown by ELISA to be highly sensitive and specific for arginine. Anesthetized Sprague-Dawley rats were perfused with aldehydes; brains were removed and postfixed in the same fixatives for 2-8 hours. Sections of paraffin-embedded material on slides, or free-floating Vibratome-cut material, were processed for immunocytochemistry. Staining in the thalamus was predominantly in endothelium and in cells recognizable for their appearance and distribution as neuroglia. Nuclei of many neurons were immunopositive and staining was in the cytoplasm of neurons in some extrathalamic structures, e.g raphe and septum. Post-embedding electron microscopic immunocytochemistry confirms that staining is predominantly in endothelial cells and glia. The results support previous information about the location of arginine in the central nervous system (Aoki et al., 1991). Arginine in the thalamus may be stored in glia whence it is supplied to terminals as substrate for the activity of nitric oxide synthase.