IMMUNOCYTOCHEMICAL EVIDENCE FOR AN AXONAL LOCALIZATION OF GABA IN THEOPTIC NERVES OF RABBITS, RATS, AND CATS

We have examined, by light-microscopic immunocytochemistry, the distri bution of GABA in the optic nerves of adult rabbits, rats, and cats. W ithin the optic nerves, immunoreactivity for GABA was restricted to a small subset of axons; some axons were strongly labelled, others weakl y labelled, whilst most axons were unlabelled. Glia and other non-neur onal elements were always unlabelled. Our ability to detect GABA in op tic nerve axons of adult mammals contrasts with previous reports that indicate a lack of GABA immunoreactivity in such axons. We suggest tha t this discrepancy may be due to the sensitivity of our immunocytochem ical techniques which enable us to detect low concentrations of GABA.