EVIDENCE FOR THE EXISTENCE OF GALANIN RECEPTORS ON CULTURED ASTROCYTES OF RAT CNS - COLOCALIZATION WITH CHOLINERGIC RECEPTORS

The cellular localization of binding sites for [I-125]galanin was stud ied in explant cultures of rat neocortex, cerebellum, locus coeruleus and spinal cord by means of autoradiography. Binding sites for the pep tide were observed on a great number of astrocytes in all CNS regions studied. In addition to astrocytes, many neurones were intensely label led by [I-125]galanin. Binding of [I-125]galanin (10(-8) M) to both as trocytes and neurones was markedly reduced or inhibited by the unlabel led peptide at high concentration (10(-6) M), suggesting 'specific' bi nding of the radioligand. Evidence for the colocalization of galanin a nd cholinergic receptors on astrocytes was provided by combined autora diographic and immunohistochemical studies. Many astrocytes were label led by [I-125]galanin and immunostained with antibodies to either musc arinic or nicotinic receptors. Electrophysiological studies revealed t hat addition of galanin (10(-9) to 10(-7) M) to the bathing fluid caus ed a dose-dependent hyperpolarization of the majority of astrocytes st udied. When galanin (10(-8) M) and the cholinergic agonists muscarine and nicotine (10(-6) M) were tested on the same astrocyte, all three c ompounds induced a hyperpolarization, suggesting a colocalization of f unctional galanin and cholinergic receptors on the glial membrane. (C) 1997 Elsevier Science B.V.