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Extracellular Somatostatin Measured by Microdialysis in the Hippocampus of Freely Moving Rats: Evidence for Neuronal Release
Author(s) -
Vezzani A.,
Ruiz R.,
Monno A.,
Rizzi M.,
Lindefors N.,
Samanin R.,
Brodin E.
Publication year - 1993
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1993.tb03200.x
Subject(s) - veratridine , microdialysis , chemistry , somatostatin , tetrodotoxin , endocrinology , medicine , depolarization , radioimmunoassay , ouabain , perfusion , extracellular , sodium , biology , sodium channel , biochemistry , organic chemistry
Intracerebral microdialysis combined with a sensitive and specific radioimmunoassay was used to monitor the neuronal release of somatostatin (somatostatin‐like immunoreactivity, SLI) in the dorsal hippocampus of freely moving rats. The sensitivity of the radioimmunoassay was optimized to detect <1 fmol/ml. The basal concentration of SLI in 20‐min dialysate fractions (5 μl/min) collected 24 h after probe implantation was stable over at least 200 min. The spontaneous efflux dropped by 54 ± 6.4% ( p < 0.05) when Ca 2+ was omitted and 1 m M EGTA added to the Krebs‐Ringer solution and by 65.5 ± 3.2% ( p < 0.05) in the presence of 1 μ M tetrodotoxin. Depolarizing concentrations of the Na + channel opener veratridine (6.25, 25, 100 μ M ) induced 11 ± 2 ( p < 0.05), 17 ± 2 ( p < 0.05), and 21 ± 5 ( p < 0.01) fold increase in SLI concentration, respectively, during the first 20 min of perfusion. The effect of 100 μ M veratridine was blocked by coperfusion with 5 μ M tetrodotoxin ( p < 0.01) and reduced by 79% ( p < 0.01) in the virtual absence of Ca 2+ . Neuronal depolarization by 20 min of perfusion with Krebs‐Ringer solution containing 25 and 50 m M KCl and proportionally lowered Na + increased the dialysate SLI 4.4 ± 1 ( p < 0.05) and 17 ± 3 ( p < 0.01) fold baseline, respectively. Ten micromolar ouabain, a blocker of Na + ,K + ‐ATPase, increased the dialysate SLI 15‐fold baseline, on average ( p < 0.05), during 80 min of perfusion. The results demonstrate the suitability of brain microdialysis for monitoring the neuronal release of SLI and for studying its role in synaptic transmission.