REGIONAL LOCALIZATION OF AGMATINE IN THE RAT-BRAIN - AN IMMUNOCYTOCHEMICAL STUDY

The distribution of agmatine (decarboxylated arginine) was mapped in t he central nervous system (CNS) in the rat. Agmatine-like immunoreacti vity was identified by light microscopy. exclusively in the cytoplasm of neuronal perikarya. Immunoreactive neurons were present in the cere bral cortex, predominantly within laminae VI and V and, to a lesser ex tent. III and mainly in retrosplenial, cingulate, primary somatosensor y and auditory cortices, and the subiculum. In the lower brainstem, im munoreactivity was selectively localized to visceral relay nuclei: the nucleus tractus solitarii and pontine parabrachial complex, and periv entricular areas including the laterodorsal nucleus, locus coeruleus a nd dorsal raphe. In the midbrain, immunolabeled cells were concentrate d in the ventral tegmental area and periaqueductal gray. In the forebr ain, subcortical neurons were labeled predominantly in the preoptic ar ea, amygdala, septum, bed nucleus of the stria terminalis, midline tha lamus, and the hypothalamus. Ultrastructural analysis of layer V of th e somatosensory cortex demonstrated agmatine-immunoreactivity in neuro ns, primarily in large dense-core vesicles located in the cytoplasm. A gmatine immunoreactivity was also affiliated with endoplasmic reticulu m and the plasmalemma. Cortical neurons and the subiculum were labeled in animals not administered the axonal transport inhibitor, colchicin e; thus, may normally contain higher concentrations of the amine than other brain regions. The central distribution of agmatine is consisten t with the hypothesis that the amine may be a novel neurotransmitter o f neurons involved in behavioral and visceral control. (C) 1998 Elsevi er Science B.V.