CHARACTERIZATION OF THE EXTRACELLULAR SEROTONIN RELEASE IN THE SUBSTANTIA-NIGRA OF THE FREELY MOVING RAT USING MICRODIALYSIS

The characteristics of the serotonin release were investigated in the substantia nigra (SN) of the freely moving rat using microdialysis. We also examined whether the delay between surgery and microdialysis exp eriments might influence these characteristics by implanting rats with a guide cannula 1 or 2 days prior to microdialysis experiments. In th e first group, the tissue was not punctured until the microdialysis pr obe was inserted the evening before the experiment. In the second grou p, the nigral tissue was punctured with an extended obturator which wa s then replaced by a microdialysis probe the evening before the experi ment. After administration of 60 mM K+ a more pronounced increase in s erotonin was observed in the first group (260%) compared to the second group (159%). Calcium-free and tetrodotoxin (TTX, a sodium channel bl ocker) (1 mu M) perfusion reduced extracellular serotonin to respectiv ely 77% and 80% in the first group and 70% and 64% in the second group . These results suggest that vesicular release of nigral serotonin onl y occurs partially in this region and that minimizing the damage cause d by implantation of the probe results only in 10% more vesicular rele ase of serotonin. However, blockade of the serotonin reuptake carrier caused more TTX sensitivity of the serotonin release. Also, stimulatio n of the dorsal raphe by locally perfusing 60 mM K+ decreased serotoni n in the SN, confirming the anatomical and functional link between bot h areas. (C) 1997 Elsevier Science B.V.