THALAMOCORTICAL AFFERENTS IN RAT TRANSIENTLY EXPRESS HIGH-AFFINITY SEROTONIN UPTAKE SITES

Autoradiographic techniques using [H-3]citalopram were employed in 8-d ay-old (P-8) and adult rats to delineate the distribution of high-affi nity serotonin (5-HT) uptake sites in the cerebral cortex. In the post natal rats, [H-3]citalopram binding sites were densely distributed in the lower portion of layer III, lamina IV, and upper layer V in the pr imary visual, somatosensory, and auditory cortices. In the primary som atosensory cortex, these binding sites were arrayed in a manner exactl y matching the representation of the body surface as demonstrated by o ther methods such as staining for cytochrome oxidase (GO) or acetylcho linesterase (AChE). In adult rats, there was no differential distribut ion of [H-3]citalopram binding sites in the cerebral cortex. Neonatal administration of the 5-HT neurotoxin, 5,7-dihydroxytryptamine (5,7-DH T), resulted in a nearly complete destruction of the 5-HT innervation of the cortex on P-8, but the patterned distribution of [H-3]citalopra m binding sites remained visible. In contrast, thalamic lesions carrie d out on P-4 caused a complete loss of the patterned distribution of [ H-3]citalopram binding sites in rats killed on either P-5 or P-8. Thes e results are consistent with the conclusion that thalamocortical affe rents in postnatal rats transiently express high-affinity uptake sites for 5-HT and thus may accumulate this amine.