LOCALIZATION OF SOMATOSTATIN RECEPTORS IN SUBCORTICAL VISUAL CENTERS OF THE RAT DURING DEVELOPMENT - EFFECT OF NEONATAL ENUCLEATION ON THE EXPRESSION OF SOMATOSTATIN RECEPTORS

Previous studies have shown that both somatostatin and somatostatin receptors are expressed in the visual system of the rat early during ontogenesis, suggesting that somatostatin plays a role in the development of visual functions. In the present study, we have examined the localization of somatostatin receptors in the lateral geniculate nucleus and the superior colliculus of the developing rat by autoradiography, and we have investigated the effect of neonatal enucleation on the density of receptors in young and adult animals. In the dorsal part of the lateral geniculate nucleus, somatostatin receptors were transiently expressed during the first two postnatal weeks, while in the ventral part, receptors were detected during the whole developmental period. In the superior colliculus, a high density of somatostatin receptors was measured before eye opening; thereafter the concentration of receptors decreased markedly in the whole structure to reach the adult level. Uni- or bilateral enucleation one day after birth only induced minor modifications of the expression of somatostatin receptors in the lateral geniculate nucleus and colliculus. Conversely, bilateral enucleation caused a significant reduction of the density of receptors in the inter-geniculate leaflet and the medial zone of the ventral lateral geniculate nucleus. Taken together, these results indicate that, in the relay nuclei, somatostatin receptors are not borne by retinal afferents. The presence of high densities of receptors in the lateral geniculate nucleus and superior colliculus during development suggests that somatostatin exerts trophic activities in these structures. In adult rat, somatostatin is probably involved in the modulation of visual information in the superior colliculus, but not in the dorsal lateral geniculate nucleus.