Neurotransmitter receptors in the proliferative zones of the developing primate occipital lobe

Abstract

Film autoradiography was used to investigate the expression of several neurotransmitter receptor subtypes in the transient ventricular and subventricular proliferative zones of the developing occipital lobe in two groups of macaque monkey fetuses. The first group of fetuses were between 60 and 93 days after conception (E60‐E93), when the ventricular and subventricular zones of the monkey occipital lobe produce neurons destined for the visual cortex. In the second group, fetuses were between E107 and E128, after generation of cortical neurons has ceased. In the E60–E93 group of fetuses, ventricular and subventricular zones displayed high densities of 5‐HT1‐serotonergic, D1‐dopaminergic, α1‐and α2‐adrenergic and high affinity kainate receptors. The activation of these receptors has previously been shown to stimulate cell proliferation in other cell systems. The possible involvement of these receptors in regulation of neuronal production is also supported by their absence in the deep laminae of the embryonic cerebral wall after E107, after cortical neurogenesis has been completed. The only exception is a high density of α2‐adrenergic receptors maintained near the ventricular surface long after all cortical neurons have been generated. We also found that during neurogenesis, proliferative zones in E66–E90 fetuses displayed virtually no 5‐HT2‐serotonergic, D2‐dopaminergic, β‐adrenergic, M1‐muscarinic cholinergic, gamma aminobutyric acid (GABA)_A, N‐methyl‐D‐aspartate (NMDA), or β‐amino‐3‐hydroxy‐5‐menthy‐4‐isoxazole proprionate (AMPA) sites; most of these receptor subtypes have been reported to mediate the suppression of cell proliferation. The present findings suggest that dividing and/or newly generated cortical neurons are capable of receiving specific signals from multiple neurotransmitters present in their environment.