VASOACTIVE INTESTINAL POLYPEPTIDE PEPTIDE HISTIDINE ISOLEUCINE MESSENGER-RNA IN THE RAT RETINA - ADULT DISTRIBUTION AND DEVELOPMENTAL EXPRESSION/

In the adult nervous system, vasoactive intestinal polypeptide acts as a neurotransmitter or neuromodulator, and during development, it may also act as a neurotrophic factor. In the adult mammalian retina, this peptide is contained in a population of wide-field amacrine cells. Us ing in situ hybridization histochemistry, we examined the distribution and developmental expression of vasoactive intestinal polypeptide/pep tide histidine isoleucine messenger RNA in the rat retina. Retinas col lected from birth to adulthood were hybridized with an RNA probe as wh ole mounts, and then cut either perpendicular or parallel to the vitre al surface. Adult retinas were used in double labeling experiments for the visualization of both the hybridization signal and vasoactive int estinal polypeptide immunoreactivity in the same tissue section. In ad ult retinas, vasoactive intestinal polypeptide/peptide histidine isole ucine messenger RNA is localized to amacrine cells positioned in the p roximal inner nuclear layer, and rarely to displaced amacrine cells in the inner plexiform layer and ganglion cell layer. The neurons expres sing this messenger RNA are sparsely distributed, with a non-random di stribution and densities of about 190 cells/mm(2). An estimate of thei r total number gives about 12,350 cells/retina. The double labeling ex periments showed that the hybridization signal is specifically confine d to neurons displaying vasoactive intestinal polypeptide immunoreacti vity. Vasoactive intestinal polypeptide/peptide histidine isoleucine m essenger RNA is first detected at postnatal day 5 in cells located in the proximal part of the neuroblastic layer. A greater number of these neurons is present in the inner nuclear layer at postnatal day 10, an d a few labeled neurons are also detected in the inner plexiform layer and in the ganglion cell layer. At this time, vasoactive intestinal p olypeptide/peptide histidine isoleucine messenger RNA-containing amacr ines in the inner nuclear layer are non-randomly distributed on the re tinal surface, as in adult retinas. At postnatal day 15 (eye opening), there is a peak in both the density and the estimated number of label ed neurons, and their pattern of distribution in the retinal layers is similar to that in the adult. The present study shows that in the adu lt rat retina vasoactive intestinal polypeptide and peptide histidine isoleucine are synthesized in a sparsely distributed amacrine cell pop ulation, extending previous immunohistochemical findings. The appearan ce of vasoactive intestinal polypeptide/peptide histidine isoleucine m essenger RNA during the first postnatal week is consistent with the re ported appearance of other transmitter-identified amacrine cell popula tions. The peak in density and number of vasoactive intestinal polypep tide/peptide histidine isoleucine messenger RNA-containing cells at ey e opening suggests that these peptides are of importance in this parti cular phase of maturation. Since neurotrophic actions have been descri bed in the nervous system for vasoactive intestinal polypeptide but no t for peptide histidine isoleucine, we suggest that the increased expr ession of their precursor messenger RNA at eye opening indicates a rol e played by vasoactive intestinal polypeptide in retinal maturation.