MESSENGER-RNAS CODING FOR NEUROTRANSMITTER RECEPTORS IN RABBIT AND RAT VISUAL AREAS

Levels of mRNAs encoding neurotransmitter receptors in the visual cort ex, lateral geniculate nucleus, and superior colliculus of the rabbit and rat, and properties of the receptors expressed, were studied using Xenopus laevis oocytes. mRNA extracted from these areas was injected into the oocytes, which then acquired functional receptors. Electrical recordings of neurotransmitter-induced membrane currents reflect the relative amounts of mRNAs encoding the corresponding receptors. Recept ors to gamma aminobutyric acid (GABA), kainate, glutamate, and seroton in exhibited uniformly high levels of expression, whereas expression o f receptors to glycine and N-methyl-D-aspartate was uniformly low. In contrast, the expression of receptors to acetylcholine and substance P was highly non-uniform. Expression of acetylcholine receptors was hig h in oocytes injected with mRNA from the visual cortex, low for the la teral geniculate nucleus, and very low or absent for the superior coll iculus. Conversely, the currents elicited by substance P were large in oocytes injected with superior colliculus mRNA, but were small or abs ent in oocytes injected with mRNAs from the other regions. Immunohisto chemical analysis, at the light and electron microscopic levels, was u sed to localize choline acetyltransferase, the acetylcholine-synthesiz ing enzyme, and substance P-containing synaptic boutons in the three v isual areas. Their presence closely paralleled the potency of mRNAs co ding for acetylcholine and substance P receptors. The ability of rat m RNA, from each visual area, to induce neurotransmitter receptors was s imilar to that observed in the corresponding rabbit mRNAs. In addition to the marked differential distribution of mRNA encoding neurotransmi tter receptors in the visual system, our findings reveal the probable existence of as yet uncharacterized receptors, whose new molecular for ms may be revealed by further study. Our results also provide the basi c information required for subsequent studies on the effect of monocul ar deprivation on the expression of neurotransmitter receptors in the visual system. (C) 1993 Wiley-Liss, Inc.