Brain autoradiographic study in the golden hamster after intracarotid injection of [14C]melatonin.

The distribution of [14C]melatonin [( 14C]MT) after systemic injection was studied in the plasma and brain of golden hamsters. Thin-layer chromatographic analysis indicated that the radioactivity of the biological samples taken at two different times following the injection of label was exclusively associated with [14C]MT. Representative autoradiograms revealed a heterogeneous localization of [14C]MT in the grey matter. Two min after injection, the highest regional values were found in the hippocampus, caudate-putamen, medial thalamus and choroid plexuses. Lower radioactive concentrations were observed in the cingulate and frontoparietal cortex, anterior thalamus, inferior colliculus, dorsolateral geniculate nucleus, lateral and medial hypothalamus and amygdala. Fifteen min after injection, a significant level of radioactivity remained in the hippocampus, caudate-putamen, ventral thalamus and hypothalamus area. The heterogeneous distribution and the partial retention of [14C]MT in the brain are compatible with the existence of specific brain binding sites for this hormone.