Binding of cholecystokinin, bombesin and muscarine to neurons and astrocytes in explant cultures of rat central nervous system: autoradiographic and immunohistochemical studies.

The cellular localization of binding sites for the gastrointestinal peptides [3H]cholecystokinin and [125I]bombesin as well as the cholecystokininB-antagonist [3H]L-365,260 was investigated in explant cultures of rat cortex, cerebellum, brainstem and spinal cord using autoradiographic techniques. Many neurons in cortical, brainstem and spinal cord cultures revealed intense labelling of the radioligands whereas cerebellar neurons showed only little binding. In addition to neurons, binding sites for these peptides were also observed on astrocytes. Labelling of glial cells in cerebellar cultures was usually weaker than in the other CNS areas studied, suggesting a certain specialization of astrocytes in various brain regions. By means of combined immunohistochemical and autoradiographic techniques it was demonstrated that many neurons and astrocytes which expressed binding sites for [3H]cholecystokinin, [3H]L-365,260 and [125I]bombesin were also immunostained by the monoclonal muscarinic receptor antibody M 35 providing evidence for a co-localization of peptidergic and cholinergic receptors on the membrane of these cells. Our autoradiographic findings suggesting the presence of receptors for cholecystokinin and bombesin on astrocytes are supported by electrophysiological studies demonstrating that both peptides induce a hyperpolarization of glial cells.