Temporal dynamics of brain tissue nitric oxide during functional forepaw stimulation in rats

We report the first dynamic measurements of tissue nitric oxide (NO) during functional activation of rat somatosensory cortex by electrical forepaw stimulation. Cortical tissue NO was measured electrochemically with rapid-responding recessed microelectrodes (tips <10 microm). Simultaneous blood flow measurements were made by laser-Doppler flowmetry (LDF). NO immediately increased, reaching a peak 125.5 +/- 32.8 (SE) nM above baseline (P < 0.05) within 400 ms after stimulus onset, preceding any LDF changes, and then returned close to prestimulus levels after 2 s (123 signal-averaged trials, 12 rats). Blood flow began rising after a 1-s delay, reaching a peak just before electrical stimulation was ended at t = 4 s. A consistent poststimulus NO undershoot was observed as LDF returned to baseline. These findings complement our previous study (B. M. Ances et al., 2001, Neurosci. Lett. 306, 106-110) in which a transient decrease in rat somatosensory cortex tissue oxygen partial pressure was found to precede blood flow increases during functional activation.