The present study examines the differential effects of three
excitotoxins,
kainic acid (KA),
N-methyl-D-aspartate (
NMDA), and alpha-amino-2,3-dihydro-5-methyl-3-oxo-4-isoxazolepropanoic
acid (
AMPA) on neurons within the
ganglion cell layer (GCL) of the chick retina. Two-day-old chicks were given a single, 5 microliters,
intravitreal injection of KA,
NMDA, or
AMPA at a range of doses. Following treatment with 40 nmol KA, there was a 21% loss of neurons in the GCL. At 200 nmol KA, the loss increased to 46%. Exposure to KA eliminated mainly small neurons of
soma area 5-15 microns2, and medium-sized
ganglion cells of
soma area 15-25 microns2. Large
ganglion cells (greater than 25 microns2) remained unaffected. The vast majority of small cells were probably displaced amacrine cells. Exposure to 400 nmol
NMDA resulted in a 14% loss of neurons, predominantly involving the large
ganglion cells. At a dose of 3000 nmol
NMDA, no further loss of cells was evident. Exposure to 200 nmol
AMPA resulted in a 30% loss of large and some medium-sized
ganglion cells. In a further series of experiments, exposure to
excitotoxin was followed by a
retinal scratch, which eliminated retinal ganglion cells within the axotomized region. The results indicate that only a small proportion of displaced amacrine cells are destroyed by
NMDA and
AMPA, whereas virtually all displaced amacrine cells are sensitive to KA. The findings of this study indicate the existence of subclasses of
ganglion cells with specificity towards different types of
excitatory amino acids (EAA).