GLUTAMATE IN TERMINALS OF THALAMOCORTICAL FIBERS IN RAT SOMATIC SENSORY CORTEX

Thalamocortical terminals in layer IV of the somatic sensory cortex (SI) were identified by anterograde transport from ventrobasal thalamus. They were large, contained loosely packed round clear vesicles and abundant mitochondria, and made asymmetric contacts mainly with dendritic spines. Post-embedding immunocytochemistry revealed these terminals to be enriched in glutamate. Levels of glutamate in thalamocortical terminals, and in dendritic spines postsynaptic to them, were significantly higher than in nearby dendrites, astroglia, or in GABAergic terminals (identified by double immunostaining). These results support glutamate as neurotransmitter in thalamocortical fibers, and suggest that dendritic spines may take up glutamate released by these terminals.