SELECTIVE CHANGES IN ANGIOTENSIN-II AT(1) AND AT(2) RECEPTOR SUBTYPES IN THE RAT SUPERIOR COLLICULUS FOLLOWING EYE ENUCLEATION

In the brain of young (two weeks old) rats, angiotensin II receptors (AT(2) receptors) are found in brain nuclei which receive and integrate direct visual input from the retina, the suprachiasmatic nuclei (containing only AT(1) receptors), the lateral geniculate nuclei (containing AT(2) receptors) and the superior colliculus (which contains both receptor types with a majority of AT(2)). In adult rats, angiotensin II receptors are present in the suprachiasmatic nuclei and the superior colliculus but not in the lateral geniculate, Using quantitative autoradiography we found that, in adult rats, bilateral eye enucleation caused a significant decrease in AT(2) receptor binding, but not in AT(1) receptor binding, and only in the superior colliculus. Unilateral enucleation of 12-day-old pups led to a decrease in AT(2) receptor binding from the contralateral superior colliculus, as early as day 2 postenucleation. Conversely, there was a significant increase in binding to AT(1) receptors in the ipsilateral superior colliculus after seven days. No changes were seen in the lateral geniculate or suprachiasmatic nuclei. Angiotensin II binding to subcellular fractions of tissue from the superior colliculus region of 19-day-old pups suggested that AT(2) receptor sites were present on the plasma membrane of the postsynaptic cell body. Membrane binding studies also showed a significant decrease in AT(2) receptor binding to the same subcellular fractions when 19-day-old pups, enucleated seven days earlier, were compared to sham-operated animals. Our results suggest that expression of AT(1) and AT(2) receptors in the superior colliculus may be regulated by retinal input.