ACTIVITY CORRELATES OF CYTOCHROME OXIDASE-DEFINED COMPARTMENTS IN GRANULAR AND SUPRAGRANULAR LAYERS OF PRIMARY VISUAL-CORTEX OF THE MACAQUEMONKEY

To determine if changes in metabolic capacity revealed by cytochrome o xidase (GO) histochemistry are related to sustained changes in energy- utilizing neuronal activity, we assayed CO levels and recorded multiun it firing rates along nearly tangential penetrations of VI in seven ad ult macaque monkeys before and after single, monocular injections of T TX. Within as little as 14 h, TTX blockade began to reduce CO staining in zones of layer 4C that received dominant input from the injected e ye. Since simple monocular occlusion has only minor effects on cortica l CO levels (Trusk et al., 1990), the changes in activity that were sp ecifically associated with CO depletion were isolated by comparing spi ke rates during monocular TTX blockade and during monocular occlusion. Five second samples of multiunit spike rate were obtained after 2-min adaptation to each of four adapting fields: black, gray, white, and t extured. Results were similar for these four conditions. In layer 4C, ocular dominance zones with input from the TTX eye had ongoing spike r ates that were 48% of the rates in zones with input from a normal but occluded eye. In six animals, it was possible to record activity at a single site before, during, and after the onset of TTX blockade. Backg round activity at these interpuff sites decreased as much as 3-fold in less than 1 h but stabilized within 3-4 h to an average of 53% of pre -TTX rates. These data support the interpretation that energy utilizat ion linked to sustained spike rates partially regulates CO levels unde r normal conditions, at least in layer 4. Furthermore, changes in neur onal activity induced by retinal TTX preceded the detectable reduction in CO activity in V1 suggesting that the adjustment of CO levels was in response to the altered activity.