Effects of angiotensin II on visual evoked potentials in the superior colliculus of juvenile rats

There are age-related changes in the relative expression of the AT(1)and AT(2)receptors of angiotensin II (Ang II) in brain regions such as the superior colliculus, a midbrain visual structure where both receptor subtypes are found. We investigated the effects of Ang II on gross visual activity in the colliculus of anesthetized rats aged between 15 and 35 post-natal days. Microinjection of Ang II in the superficial layers yielded a strong reduction in the amplitude of visual evoked potentials in a dose-related manner. Injection of the peptide in more ventral collicular layers did not modify the potential confirming the discrete localization of the angiotensinergic receptors in the superficial layers. Preliminary data indicated that the co-injection of Ang II with Losartan or PD 123319 yielded a partial blockade of Ang II suppressive effects, indicating that both AT(1)and AT(2)receptors are likely to be involved in mediating these responses. Overall, this study shows that the inhibitory nature of Ang II action is similar in juvenile and adult animals (Merabet et al. 1994 and Merabet et al. 1997)