Modulation of NA-synthase activity in rat cortex using NA measurement with ultramicro carbon electrode following topical applications of pharmacological agents.
The aim of the study was to document NA, the active product of brain NA-synthase known as NO-synthase in rat cortex. NA measurements in brain extracellular fluid were performed using an ultramicro carbon electrode (0.5-2 microm) with differential pulse voltammetry. The ultramicro carbon electrode was inserted at a fixed depth (125 microm) into the frontal cortex. A constant level of neuronal NA (0.66 mM) was found in rat cortex during a few hours in the basal state. Topical applications of competitive inhibitors of brain NO-synthase (L-NNA, L-NMA, D-arginine, 1 mg ml(-1)) and a NO-donor (SNAP, 1 mg ml(-1)) resulted in a complete disappearance of NA. Simultaneous in vivo measurements of L-NNA, an electroactive inhibitor (-1.2 V vs. Ag/AgCl), and NA (-1.66 V vs. Ag/AgCl) allowed the following of the diffusion of this neuronal specific inhibitor and the simultaneous inhibition of NA synthesis. Topical addition of acetylcholine (10 microM) produced a NA increase, while bradykinin, adenosine, and hydrogen peroxide (10 microM each) resulted in the disappearance of NA. Topical addition of radical oxygen species (ROS) scavengers (oxy-hemoglobin, methylen blue, ascorbic acid and cystein, l mg ml(-1)) had no influence on NA concentrations which remained at a constant level in brain cortex. These preliminary results indicated that NA is continuously produced at a high level by neurons. Acetylcholine and vasodilatators modulated neuronal NA synthesis after topical application, but ROS had no effect.
Meulemans
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A
Laboratoire de Biophysique, Faculté de Médecine Xavier Bichat, 16 rue H. Huchard, 75018 Paris, France. alain.meulemans@voila.fr
D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000096:biosynthesis*; D002244:Carbon; D002540:Cerebral Cortex / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D008839:Microelectrodes; D020030:Nitric Oxide Donors / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000494:pharmacology; D009603:Nitroso Compounds; D051381:Rats; D017207:Rats, Sprague-Dawley
D020030:Nitric Oxide Donors; D009603:Nitroso Compounds; C084185:N-nitrosoarginine; D002244:Carbon; D001120:Arginine; D019001:Nitric Oxide Synthase