Neuromodulatory effects of angiotensin II in the visual layers of the rat superior colliculus.

Recent autoradiographic studies have revealed the presence of both AT1 and AT2 angiotensin II (AngII) receptor subtypes in the superficial layers of the rat superior colliculus (SC). We have investigated the effects of activating these receptors on visually evoked potentials (VEP) in the SC of adult rats. A recording injecting microelectrode filled with AngII was lowered into the superficial layers of the SC. AngII was injected at concentrations varying from 10(-4) to 10(-10) M. Injection of the peptide yielded a reduction in the amplitude of the VEP. This reduction usually occurred within 2-3 min following AngII injection with a 50% recovery of most of the signal 20-30 min thereafter. AngII did not modify the signal when injected in collicular layers ventral to the stratum opticum. Furthermore, concomitant injection of AngII with the specific AT, receptor antagonist Losartan failed to reduce the evoked response suggesting that the effects of AngII in the SC are likely mediated by AT1 receptors.