[Cholinergic mechanisms in the retina of rats]

In rats with extra- or intracranial dissection of the visual pathway the activities of acetylcholinesterase (AChE) and choline acetyltransferase (ChAc) were determined in retina, optic nerve and optic tract quantitatively by bio- and histochemical methods after one or five weeks of survival time. One week after intracranial (chiasma-near) dissection of the optic nerve an initial ipsilateral enhancement in the enzyme activity of AChE was found histochemically in retina layers and optic nerve. Five weeks following the dissection significant losses in AChE activity could be determined in the optic nerve, less pronounced in the retina. However, the activity of ChAc in the retina never was changed, neither after short nor after long survival times. Therefore, the high activity of both enzymes connected with cholinergic transmission normally present in different retinal layers must belong to local neurons, probably amacrine cells. To elucidate the question of the existence of a centrifugal cholinergic innervation of the retina one eye was enucleated. One week after operation a significant increase in the activity of AChE and ChAc was found in central parts of the dissected optic nerve and in the opposite optic tract indicating the existence of centrifugal cholinergic fibers in the optic nerve, but no evidence for the origin of these fibres could be obtained. The possible role of a central cholinergic control of the visual information processing already in retinal level is discussed in analogy to similar results obtained in the olfactory bulb.