VASOACTIVE-INTESTINAL-PEPTIDE PEPTIDE HISTIDINE ISOLEUCINE MESSENGER-RNA IN THE EYE AND SUPRACHIASMATIC NUCLEUS OF NORMAL AND MONOCULARLY ENUCLEATED RATS

The localization of the messenger RNA (mRNA) encoding vasocative intes tinal peptide/peptide histidine isoleucine (VIP/PHI) in the rat eye wa s studied by in situ hybridization histochemistry using a synthetic S- 35-labeled oligodeoxyribonucleotide. Among the layers of the retina, s pecific labeling was found in the soma of some cells in the innermost lamina of the inner nuclear layer. Occasionally, labeled cells were al so present in the ganglion cell layer. No specific labeling was detect ed in any ocular structures other than the retina, including the corne a, iris, ciliary body, choroid, choriocapillaris, optic nerve and scle ra. We also examined VIP/PHI mRNA expression in the suprachiasmatic nu cleus (SCN) of the hypothalamus, which is the pacemaker of circadian r hythms and synchronizes-them with the environmental light-dark cycle. High labeling was found in the ventrolateral part of the nucleus, whic h is the site of most projections from the retina, Monocular enucleati on of rats at birth resulted in an increase of VIP/PHI mRNA expression in SCN ipsilateral to the removed eye after postnatal day 60. The dis crete pattern of hybridization for VIP/PHI mRNA indicates that these t wo peptides are synthetized in rat retina and SCN and suggests that th ey may play a key role in the photic entrainment to the SCN regulating various circadian rhythms.