THE EFFECTS OF A PHOTOSENSITIVE NITRIC-OXIDE DONOR ON BASAL AND ELECTRICALLY-STIMULATED DOPAMINE EFFLUX FROM THE RAT STRIATUM IN-VITRO

The reported effects of nitric oxide (NO) on dopamine release from the striatum are variable and its precise effect on striatal nerve termin als is unclear. In the present study a novel method of applying NO to brain tissue in situ was employed. Photo-activation of Roussin's Black Salt (RBS), retained in isolated perfused brain tissue, was used to r elease NO at will upon illumination. Basal and electrically-stimulated dopamine efflux from the rat striatum in vitro was measured in real t ime using fast cyclic voltammetry. Illumination of an RBS pre-treated brain slice elicited a light intensity-related increase in basal dopam ine efflux. Concomitantly there was a decrease in the level of electri cally-stimulated dopamine efflux. Illumination in the absence of RBS p re-treatment had no effect on basal or stimulated dopamine efflux. The increase in basal dopamine efflux upon photo-activation of RBS was re duced by the presence of 10 mu M oxyhaemoglobin, but was insensitive t o the removal of extracellular calcium or the addition of 1 mu M sulpi ride. The decrease in electrically-stimulated dopamine efflux followin g illumination was not affected by the presence of either oxyhaemoglob in or sulpiride. It is concluded that NO, produced by photo-activation of RBS, releases dopamine from the rat striatum in vitro by a mechani sm independent of extracellular calcium entry.