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, biologically active conjugates of somatostatin or cholecystokinin (sulphated octapeptide) with colloidal gold. Labelled neurons show a peptide-specific, non-overlapping distribution in rat telencephalic structures; i.e, whereas the somatostatin-gold conjugate labels binding sites on neurons and glial cells, cholecystokinin-binding sites are restricted to neurons. Binding of either gold-labelled ligand can be competitively suppressed by excess amounts of the native peptide or its analogues. Neuronal somatostatin-binding sites are visualized on neurons in lamina III and, in particular, in lamina V/VI of the primary somatosensory cortex and in the magnocellular nucleus of the telencephalic cholinergic system. Cholecystokinin-binding sites are localized in the main olfactory bulb, on neurons in the cortical "hindlimb" and "forelimb" region, in the hippocampus, and in the cingulate and visual cortex.