Melatonin binding sites in the brain of sheep exposed to light or pinealectomized.

The binding sites of [125I]melatonin were identified in the sheep brain using a specific and sensitive autoradiographical method. Rams were either untreated (controls) or exposed to light before slaughter or pinealectomized (px). In all animals labelling was intense in the pars tuberalis (PT) and absent in the suprachiasmatic nucleus (SCN). In light-treated and in px rams, but not in controls, we demonstrated melatonin binding sites in the intermediate and ventrolateral septum and in the stratum lacunosum of the hippocampus. Labelling was less marked in nervous tissues than in PT cells and did not seem to be different between treatments. These results indicate the presence of light-dependent melatonin binding sites in the septum and hippocampus of sheep, but rise the question of the involvement of melatonin in the SCN activity in this species.