Beta-adrenergic receptor distribution in human and rat hippocampal formation: marked species differences

The topography of beta-adrenergic receptors in the rat and human hippocampal formation was assessed by in vitro binding of 125I-pindolol to tissue sections. Marked differences were found in the distribution of beta-adrenergic receptors and in the relative amounts of beta 1 and beta 2 receptor subtypes in the two species. In the human, the highest receptor densities were present in the pyramidal cell layer and in the stratum lacunosum-moleculare. In the rat hippocampus, those regions contained the lowest densities of 125I-pindolol binding sites. The highest densities of beta-adrenergic receptors in the rat hippocampal formation were found in the ventral subiculum and in the entorhinal cortex. In contrast, in the human hippocampus, the subiculum and entorhinal cortex contained relatively low densities of the receptors. Competition studies with beta 1- and beta 2-selective antagonists revealed that beta 2-adrenergic receptors predominate in the human hippocampus and beta 1-adrenergic receptors predominate in the rat hippocampus. The marked species differences observed suggest that the pharmacological responsivity of the hippocampus to adrenergic agents and the role of noradrenaline in regulation of hippocampal function could be very different in rats compared to humans.