NEUROTRANSMITTER RECEPTORS IN THE PROLIFERATIVE ZONES OF THE DEVELOPING PRIMATE OCCIPITAL LOBE

Film autoradiography was used to investigate the expression of several neurotransmitter receptor subtypes in the transient ventricular and s ubventricular 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 ventricula r and subventricular zones of the monkey occipital lobe produce neuron s destined for the visual cortex. In the second group, fetuses were be tween 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, alpha 1- and alpha 2-adrenergic and high affinity kainate receptors. The ac tivation of these receptors has previously been shown to stimulate cel l proliferation in other cell systems. The possible involvement of the se receptors in regulation of neuronal production is also supported by their absence in the deep laminae of the embryonic cerebral wall afte r E107, after cortical neurogenesis has been completed. The only excep tion is a high density of alpha 2-adrenergic receptors maintained near the ventricular surface long after all cortical neurons have been gen erated. We also found that during neurogenesis, proliferative zones in E66-E90 fetuses displayed virtually no 5-HT2-serotonergic, D2-dopamin ergic, beta-adrenergic, M1-muscarinic cholinergic, gamma aminobutyric acid (GABA)(A), N-methyl-D-aspartate (NMDA), or alpha-amino-3-hydroxy- 5-menthy-4-isoxazole proprionate (AMPA) sites; most of these receptor subtypes have been reported to mediate the suppression of cell prolife ration. The present findings suggest that dividing and/or newly genera ted cortical neurons are capable of receiving specific signals from mu ltiple neurotransmitters present in their environment. (C) 1995 Wiley- Liss, Inc.