Effects of excitatory amino acids on immunocytochemically identified populations of neurons in turtle retina.

Excitatory amino acids play an important role in visual processing in the retinas of many species, but little is known about the identity of the specific postsynaptic cell types and the pharmacology of their receptors. To investigate which specific cell types were affected by excitatory amino acids, we examined the effects of exogenous aspartate, glutamate, kainic acid, N-methyl-D-aspartate, and MK-801 on retinal neurons. Specific populations of neurons were labelled using antibodies directed against glucagon, enkephalin, neurotensin, gamma-aminobutyric acid, glutamic acid decarboxylase, serotonin, glycine, glutamate or aspartate. We analyzed a combination of long-term in vivo injections (seven days following an intraocular injection of kainic acid) and short term in vitro incubations. There were changes in the labelling intensity and sometimes in the relative localization of all of the antigens in the drug treated retinas. Some observations suggested that the drugs were altering neurotransmitter metabolism. Differential responses were seen in specific cell types within the populations of neurons with neurotensin-, glutamate-, aspartate-, glycine, gamma-aminobutyric acid-, and glutamic acid decarboxylase-like immunoreactivity. The immunocytochemical approach used in these studies was able to determine specific retinal cell types which were influenced by particular excitatory amino acids. The broad extent of cell types influenced and the potential metabolic effects suggest that excitatory amino acids and their receptors play a complex role in visual processing.