Glutamate affects the development of the thalamofugal visual projection of the chick.

Examination of the thalamofugal visual projections of the chick following treatment of the hyperstriatal regions with glutamate was undertaken to investigate whether structural change underlies slowed learning known to follow such treatment. On the second day after hatching from eggs exposed to light, chicks were injected bilaterally with 5 microl of 100 mM glutamate or physiological saline. On post-hatching day 8, retrograde fluorescence labelling of the thalamofugal projections with True Blue and FluoroGold led to the labelling of thalamic cells which project to the visual hyperstriatum. The number of contralateral and ipsilateral projections relative to each dye injection site was determined. Glutamate prevented the development of the structural asymmetry which is present in control chicks. The resultant symmetry of the thalamofugal projections in glutamate-treated chicks may cause deficits in visual discrimination.