Distribution of thyrotropin-releasing hormone binding sites: autoradiographic study in infant and adult human hippocampal formation.

The rostrocaudal distribution of thyrotropin-releasing hormone (TRH) binding sites was studied in the human hippocampus. Cryostat sections of the right and left hippocampi from 6 infants (2 h to 5 months of age) and 11 adults (24 to 92 years) were subjected to in vitro quantitative autoradiography using [3H]MeTRH as a ligand. A single class of high affinity [3H]MeTRH binding sites with an apparent dissociation constant in the nanomolar range has been shown both in the infant and the adult. The maximal number of these sites was higher in the infant. No significant difference was observed between the general patterns of the right and the left hippocampi when taking postmortem delay and age as parameters. The highest concentrations of [3H]MeTRH binding sites were localized in the uncinate gyrus, the uncal subiculum and in the whole length of the molecular layer of the dentate gyrus. The lowest densities were present in the ventral subiculum. The major difference observed between the infant and the adult appeared in the molecular layer of the dentate gyrus where the densities were two-fold higher in infants (189 +/- 6 versus 88 +/- 2 fmol/mg of tissue). The only marked difference in the distribution was localized in the caudal part of the body where no specific labeling was found in the presubiculum of the infant.