NITRIC-OXIDE MODULATES DOPAMINE RELEASE DURING GLOBAL TEMPORARY CEREBRAL-ISCHEMIA

Dopamine (DA) is released in large quantities from the striatum during cerebral ischemia. Along with excitatory neurotransmitters, DA plays a role in cellular neuronal ischemic injury. In this study we examined the role of nitric oxide (NO) in the ischemia-induced release of DA. A microdialysis probe was stereotactically placed into the corpus striatum of 16 Sprague-Dawley rats for DA, 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) level determinations. After probe stabilization, the animals received either N-G-nitro-L-arginine-methyl. ester (L-NAME), a NO synthase inhibitor, or vehicle through the microdialysis probe. Temporary global forebrain ischemia was induced using bilateral carotid artery ligature tightening and controlled hemorrhagic hypotension for 15 min. L-NAME administration caused a reduction in ischemic estimated extraneuronal DA concentration by 60% (P < 0.005) compared with control. There was an increase in both DOPAC and HVA concentrations during the recovery period compared to baseline values in the control group (P < 0.05). L-NAME also caused a reduction in HVA concentration compared to vehicle administration during the latter part of recovery (P < 0.05). These data support the concept that ischemic dopamine release may be mediated by NO. This NO-modulated DA release may contribute to the previously reported deleterious neurotoxic effects of NO during ischemia.