Functional impairment of the rat superior colliculus after kainic acid intraocular injection: a 2-deoxyglucose study

Long Evans rats monocularly injected with the kainic acid (KA), were exposed to "tonic" (diffuse steady light, stationary pattern, total darkness) and "phasic" (flashing, moving pattern) stimulations. By means of the autoradiographic 2-deoxyglucose (2DG) technique we assessed the functional activity of the Superior Colliculus (SC) contralateral to the injected eye as compared to the normal eye SC. In the control SC all "tonic" stimulations determined low 2DG uptake not modified by the intraocular KA injection. On the contrary, "phasic" stimulations elicited a strong 2DG consumption in the normal SC, with a peculiar pattern of distribution depending on the kind of stimulus. Considering the total 2DG uptake as the added intrinsic and afferent metabolism, KA was able to affect only the latter, decreasing two-fold that expected for the afferent input loss. These findings can suggest a possible KA effect on off-line ganglion cells and, on the other side, they confirm the role of the SC in discriminating "phasic" and sudden phenomena from "tonic" and continuous ones.