Benzodiazepine receptors in the human hippocampal formation: a pharmacological and quantitative autoradiographic study.

The pharmacological characteristics and anatomical distribution of benzodiazepine receptors in the human hippocampal formation were studied in seven cases aged 4-68 years. The pharmacology of the receptors was studied by computerized, non-linear least squares regression analysis of [3H]flunitrazepam displacement by flunitrazepam, CL218,872 and ethyl beta-carboline-3-carboxylate binding to membranes and the anatomical localization of these receptors was demonstrated using quantitative autoradiography following in vitro labelling of cryostat sections with [3H]flunitrazepam. The pharmacological studies indicated that the human hippocampal formation contained equal numbers of benzodiazepine receptors with high affinity (Type I) and low affinity (Type II) for CL218,872 and ethyl beta-carboline-3-carboxylate. The autoradiograms demonstrated that the benzodiazepine receptors were distributed in a heterogeneous fashion throughout the major regions of the human hippocampal formation; the highest concentrations of receptors were present in the dentate gyrus (molecular layer) and field CA1 of Ammon's horn (strata pyramidale, oriens, lacunosum), with moderate concentrations in field CA2 of Ammon's horn (stratum pyramidale) and in regions of the subicular complex and entorhinal cortex, and with considerably lower densities in fields CA3 and CA4. Quantitative analyses of the autoradiograms showed that the regions containing the highest densities of receptors (molecular layer of dentate gyrus and the strata oriens, pyramidale and lacunosum of CA1) were enriched with Type 1 receptors whereas other regions of lower receptor densities were enriched with either Type I or Type II receptors.(ABSTRACT TRUNCATED AT 250 WORDS)