Local changes in the redox potential in the rabbit cerebral cortex accompanying the acquisition of a conditioned defensive reflex.

The oxidative-reductive (redox) potential (E) of brain tissue depends on the ratio of the speeds of processes occurring in the glycolysis (the evolutionarily ancient energy compartment operating without oxygen) and oxidative metabolism (evolutionarily younger and energetically more efficient) compartments. E in the cortex was recorded using implanted platinum electrodes. A conditioned defensive reflex (CDR) was developed by combination of a light and electrocutaneous stimulation (ECS) of the ear. The results showed that after a series of combinations of the light and the ECS, the light started to elicit a change in E. By 200 combinations, the brain developed both increases and decreases in E during combinations. As the number of combinations increased, increases in E were gradually replaced by decreases. We believe that this dynamic of the balance of the major sources of brain energy supply suggests that formation of the CDR may involve a significant role for subcellular structures receiving energy from oxidative metabolism formed at the relatively young evolutionary level, while the major source of energy for brain function during performance of the acquired CDR is the older evolutionary compartment - glycolysis.