DISTRIBUTION AND DENSITY OF MONOAMINE RECEPTORS IN THE PRIMATE VISUAL-CORTEX DEVOID OF RETINAL INPUT FROM EARLY EMBRYONIC STAGES

Developmental mechanisms that regulate the areal and laminar distribut ion of various macromolecules, including neurotransmitter receptors in the cerebral cortex, are not known. In the present study, we examined the development of monoaminergic receptors in the rhesus monkey stria te and peristriate visual cortex in the absence of input from the reti na. Binocular enucleation was performed between embryonic days E60 and E81, prior to the ingrowth of geniculocortical fibers into the cortic al plate and before genesis of the granular and supragranular layers o f the visual cortex. The animals were delivered at term (E165) and sac rificed at 2 or 12 months of age, and their brains frozen and the occi pital robes cut at 20 mu m in the coronal plane. Cortical binding of H -3-clonidine, I-125-pindolol, H-3-5-HT, H-3-ketanserin, H-3-spiperone, H-3-SCH23390, and H-3-prazosin that label various monoamine receptors were autoradiographically visualized and quantified using a computer imaging system. All radioligands displayed specific laminar patterns i n the striate and prestriate areas in both groups of animals. The area l and laminar distribution in the anophthalmic monkeys was similar to that in the controls. Significantly, in all enucleated animals, just a s in the controls, a particularly high density of H-3-clonidine and H- 3-prazosin was observed in the sublayers of layer IV involved in color vision. The present results show that the monoamine receptors in prim ate visual cortex can establish and maintain distinct laminar and area l patterns in the absence of activity or molecular cues originated fro m the retina, and provide new insight into the cortical consequences o f secondary congenital anophthalmia.