EFFECT OF RETINAL IMPULSE BLOCKAGE ON CYTOCHROME OXIDASE-POOR INTERPUFFS IN THE MACAQUE STRIATE CORTEX - QUANTITATIVE EM ANALYSIS OF NEURONS

One of the hallmarks of the primate striate cortex is the presence of cytochrome oxidase-rich puffs in its supragranular layers. Neurons in puffs have been classified as type A, B, and C in ascending order of c ytochrome oxidase content, with type C cells being the most vulnerable to retinal impulse blockade. The present study aimed at analysing cyt ochrome oxidase-poor interpuffs with reference to their metabolic cell types and the effect of intraretinal tetrodotoxin treatment. The same three metabolic types were found in interpuffs, except that type B an d C neurons were smaller and less cytochrome oxidase-reactive in inter puffs than in puffs. Type A neurons had small perikarya, low levels of cytochrome oxidase, and received exclusively symmetric axosomatic syn apses. The largest neurons were pyramidal, type B cells with moderate cytochrome oxidase activity and were also contacted exclusively by sym metric axosomatic synapses. Type C cells were medium-sized with a rich supply of large, darkly reactive mitochondria and possessed all the c haracteristics of GABAergic neurons. They were the only cell type that received both symmetric and asymmetric axosomatic synapses. Two weeks of monocular tetrodotoxin blockade in adult monkeys caused all three major cell types in deprived interpuffs to suffer a significant downwa rd shift in the size and cytochrome oxidase reactivity of their mitoch ondria, but the effects were more severe in type B and C neurons. In n ondeprived interpuffs, all three cell types gained both in size and ab solute number of mitochondria, and type A cells also had an elevated l evel of cytochrome oxidase, indicating that they might be functioning at a competitive advantage over cells in deprived columns. However, ty pe B and C neurons showed a net loss of darkly reactive mitochondria, indicating that these cells became less active. Thus, mature interpuff neurons remained vulnerable to retinal impulse blockade and the metab olic capacity of these cells remains tightly regulated by neuronal act ivity.