VISUALIZATION OF NEUROPEPTIDE-BINDING SITES ON INDIVIDUAL TELENCEPHALIC NEURONS OF THE RAT

The identification of high-affinity binding sites for neuropeptides on individual target cells is a prerequisite when studying the sites of action and the manner in which peptides act as neuromediators. In situ and in vitro, this can be achieved using newly synthesized, biologica lly active conjugates of somatostatin or cholecystokinin (sulphated oc tapeptide) with colloidal gold. Labelled neurons show a peptide-specif ic, non-overlapping distribution in rat telencephalic structures; i.e, whereas the somatostatin-gold conjugate labels binding sites on neuro ns and glial cells, cholecystokinin-binding sites are restricted to ne urons. Binding of either gold-labelled ligand can be competitively sup pressed by excess amounts of the native peptide or its analogues. Neur onal somatostatin-binding sites are visualized on neurons in lamina II I and, in particular, in lamina V/VI of the primary somatosensory cort ex and in the magnocellular nucleus of the telencephalic cholinergic s ystem. Cholecystokinin-binding sites are localized in the main olfacto ry bulb, on neurons in the cortical ''hindlimb'' and ''forelimb'' regi on, in the hippocampus, and in the cingulate and visual cortex.