DIFFERENTIAL GLUTAMATERGIC INNERVATION IN CYTOCHROME OXIDASE-RICH ANDOXIDASE-POOR REGIONS OF THE MACAQUE STRIATE CORTEX - QUANTITATIVE EM ANALYSIS OF NEURONS AND NEUROPIL

One of the hallmarks of the primate striate cortex is the presence of cytochrome oxidase (CO)-rich puffs and CO-poor interpuffs in its supra granular layers. However, the neurochemical basis for their difference s in metabolic activity and physiological properties is not well under stood. The goals of the present study were to determine whether CO lev els in postsynaptic neuronal compartments were correlated with the pro portion of excitatory glutamate-immunoreactive (Glu-IR) synapses they received and if Glu-IR terminals and synapses in puffs differed from t hose in interpuffs. By combining CO histochemistry and postembedding G lu immunocytochemistry on the same ultrathin sections, the simultaneou s distribution of the two markers in individual neuronal profiles was quantitatively analyzed. As a comparison, adjacent sections were ident ically processed for the double labeling of CO and GABA, an inhibitory neurotransmitter. In both puffs and interpuffs, most axon terminals f orming asymmetric synapses (84%)-but not symmetric ones, which were GA BA-IR-were intensely immunoreactive for Glu. GABA-IR neurons received mainly Glu-IR synapses on their cell bodies, and they had three times as many mitochondria darkly reactive for CO than Glu-rich neurons, whi ch received only GABA-IR axosomatic synapses. In puffs, GABA-IR neuron s received a significantly higher ratio of Glu-IR to GABA-IR axosomati c synapses and contained about twice as many darkly CO-reactive mitoch ondria than those in interpuffs. There were significantly more Glu-IR synapses and a higher ratio of Glu- to GABA-IR synapses in the neuropi l of puffs than of interpuffs. Moreover, Glu-IR axon terminals in puff s contained approximately three times more darkly CO-reactive mitochon dria than those in interpuffs, suggesting that the former may be synap tically more active. Thus, the present results are consistent with our hypothesis that the levels of oxidative metabolism in postsynaptic ne urons and neuropil are positively correlated with the proportion of ex citatory synapses they receive. Our findings also suggest that excitat ory synaptic activity may be more prominent in puffs than in interpuff s, and that the neurochemical and synaptic differences may constitute one of the bases for physiological and functional diversities between the two regions. (C) 1996 Wiley-Liss, Inc.