Annual Meeting of the Society for Neuroscience edition:35 location:Washington DC, U.S.A. date:November 12-16, 2005
Our knowledge of the morphological and biochemical heterogeneity within the glutamatergic neuronal population in mammalian neocortex is far less extensive compared to the GABAergic neuronal population. We here monitored the distribution and morphology of the glutamatergic neurons in cat visual cortex through immunocytochemistry for Phosphate-activated glutaminase (PAG), the major enzyme involved in the synthesis of the excitatory neurotransmitter glutamate in neurons of the mammalian cerebral cortex. A detailed qualitative analysis indicated that the vast majority of PAG immunoreactivity was observed in pyramidal cells, but PAG immunoreactivity was also detected in a paucity of non-pyramidal neurons. Next, we categorized the PAG-positive neurons by means of double-stainings for PAG with three calcium-binding proteins (calbindin, calretinin, parvalbumin) to determine to what extent GABAergic non-pyramidal cells can express PAG, and for PAG with neurofilament protein (NFP), a marker for a subset of pyramidal neurons, throughout all six cortical layers of area 17. Quantitative analysis of the total PAG population revealed that PAG co-existed in about 2,4% of the CB-, 6,7% of the PV- and 7,6% of the CR-positive cells, and that co-localization of PAG with NFP occurred in only 5,4%. Comparison of the laminar proportion of the double-labelled PAG population revealed that PAG/PV immunoreactive cells were found throughout all cortical layers with a majority of double-labelled cells in layer IV (23,8%). PAG/CB and PAG/CR were mainly found in supragranular layers. Interestingly, layer I PAG immunoreactivity mainly occurred in CR-positive cells (31%), but also in CB-positive labelled cells (8,2%). All NFP-positive cells were double-labelled with PAG (100%). We here present a first detailed neurochemical map of the glutamatergic cell population based on its synthesizing enzyme PAG allowing the categorization of cortical neurons with excitatory function within the visual system.