Premium
Release of Cholecystokinin‐Like Immunoreactivity in the Frontal Cortex of Conscious Rats as Assessed by Transcerebral Microdialysis: Effects of Different Depolarizing Stimuli
Author(s) -
Vallebuona F.,
Paudice P.,
Raiteri M.
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.tb02150.x
Subject(s) - microdialysis , tetrodotoxin , cholecystokinin , chemistry , depolarization , endocrinology , medicine , extracellular , receptor , biochemistry
The release of cholecystokinin‐like immunoreactivity (CCK‐LI) from the frontal cortex of freely moving rats has been studied using a transcerebral microdialysis technique coupled to a radioimmunoassay procedure. Basal levels of CCK‐LI in the dialysate were above detection limits (2.4 ± 0.7 pg/20 min; n = 8). High‐K + media evoked CCK‐LI overflow in a concentration‐dependent manner. The threshold concentration was 50 mM KCI. The peak overflow evoked by 100 mM K + amounted to 42.7 ± 2.8 pg/20 min (n = 6); it was totally Ca 2+ dependent but insensitive to 1 μM tetrodotoxin. Infusion of 4‐aminopyridine (1 mM ; 20 min) evoked an overflow of CCK‐LI (32 ± 2.3 pg/ 20 min; n = 4), wnich was totally Ca 2+ dependent and tetrodotoxin sensitive. Depolarization with 100 μg/ml of veratrine (20 min) provoked a CCK‐LI overflow (62.2 ± 10 pg/20 min; n = 6), which was also blocked by tetrodotoxin or by the absence of Ca 2+ ions. The CCK‐LI material collected under basal conditions or during veratrine infusion consisted essentially of CCK octapeptide sulfate. The veratrine‐induced CCK‐LI overflow did not change significantly when the infusion time was prolonged to 100 min. A second 20‐min stimulus with 100 μg/ml of veratrine applied 200 min after a first 20‐min stimulus evoked a barely significant CCK‐LI overflow. These data suggest that one single 20‐min stimulus with 100 μg/ml of veratrine may be sufficient to deplete the CCK‐LI releasable stores and that >200 min are required to replenish the depleted CCK‐containing vesicles. Taken together the data allow us to conclude that the physiology and the pharmacology of CCK release can be adequately studied in vivo by brain microdialysis.