Binding sites for glutamate and aspartate in the rat cerebral cortex during ontogeny

Sanderson, Catherine (1984). Binding sites for glutamate and aspartate in the rat cerebral cortex during ontogeny. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000fcda

Abstract

The interaction of the putative excitatory neurotransmitters glutamate and aspartate with rat cortical membranes was examined by the utilization of a radiochemical binding assay. The specific binding of 3H-L-Glu at OoC reached a maximum after approx 12 mins. and was measurable over a pH range of 4 - 9 although pH? was optimal. The binding was strongly dependent on the presence of K+ ions and showed -ta biphasic response to the presence of Na+ ions, being inhibited at concentrations below l0mM but stimulated several fold at higher (Na+) reaching a maximum at around 40 mM.

It was possible to distinguish two binding sites for glutamate on cortical membranes prepared from adult rats. One of these was a low density high affinity site, the other was present at higher concentrations and lower affinity and was strongly dependent on the presence of Na $\$ Aspartate also bound to adult cortical membranes with similar characteristics. Discrimination between these glutamate and aspartate binding sites was possible as the binding of these ligands was differentially affected by freeze/thawing and by amino acid analogues investigated in displacement studies. The binding of the excitotoxic glutamate analogue kainic acid shows characteristics incompatible with its proposed role as a glutamate agonist with affinity for the putative post-synaptic glutamate receptor site.

The development of glutamate and aspartate binding sites was also investigated. The binding of both ligands showed very different characteristics in young rats ( 30 days) than in adult rats. It was much, more difficult to distinguish between glutamate and aspartate binding sites in these younger animals.

The binding of glutamate to cortical membranes prepared from normal mice and 'reeler' mutant mice was also investigated in an attempt to localize the binding to a specific cortical area.