[Evidence for glutamatergic neurotransmission in the geniculo-cortical pathway in the rat]

Abstract

Purpose: To investigate the possible participation of glutamate in the neurotransmission of the rat geniculo-cortical pathway.

Methods: In a first set of experiments, we studied the effects of microiontophoresis of kynurenate, a broad spectrum antagonist of glutamate receptors, on the excitation evoked in visual cortex cells by electrical stimulation of the dorsal lateral geniculate nucleus and the optic tract. Cell activity was determined by extracellular unit recordings. In a second set of experiments, we studied the effects of electrical stimulation of the dorsal lateral geniculate nucleus and the optic tract on the release of glutamate and aspartate in the visual cortex in vivo. Push pull perfusions were made in the visual cortex and the amino acids contents of the perfusates were analysed by high performance liquid chromatography.

Results: Microiontophoresis of kynureate in area 17 cells selectively supressed the excitatory response to dorsal geniculate nucleus and optic tract stimulation. On the other hand, stimulation of these structures significantly increased glutamate, but not aspartate, release in area 17.

Conclusions: These results demonstrate that glutamate is the neurotransmitter of the geniculo-cortical pathway in the rat.