Glutamate, GABA and precursor amino acids in adult mouse neocortex: Cellular diversity revealed by quantitative immunocytochemistry

Glutamate is an important amino acid in the neocortex for metabolic and neu rotransmitter functions. The objective of this study was to detect variatio ns in cellular glutamate content using quantitative immunocytochemistry. We show that glutamate is present in almost all cortical cells and coexists w ith other amino acids such as aspartate, glutamine or gamma -aminobutyric a cid (GABA). The patterns of aspartate and glutamine content suggests that t here are no purely aspartatergic or glutaminergic neurons. GABAergic neuron s showed variable levels of the precursors such as glutamate, glutamine and aspartate. Comparison of immunoreactive patterns between two cortical area s did not detect any statistically significant differences. The mean cellul ar intensity for GABA and glutamate was constant across different layers. S urprisingly, we found that GABAergic neurons could coexist with either low or high levels of glutamate, suggesting that metabolic levels of glutamate in these neurons could he variable. Alternatively some GABA neurons may uti lize both GABA and glutamate for neurotransmission. We show that when varia tions in amino acid content are separately mapped onto individual cells, co -registration is a useful technique for reporting heterogeneity among corti cal cells.