Effects of somatostatin-14 on the in vitro release of [3H]GABA from slices of rat caudatoputamen.
Slices (300 microns) of rat caudatoputamen were incubated in Krebs-Henseleit medium and loaded with [3H]glutamine, part of which was converted to [3H]GABA. This conversion takes place only in GABA-neurons most of which probably contribute to the striatonigral pathway. After a 24 min equilibration period, release of radioactivity was stimulated with veratridine (3.1-4 mumol/l) or K+ (15-25 mmol/l) in the absence or presence of somatostatin-14. From the radioactivity released [3H]GABA was separated by cationic exchange chromatography and measured. Somatostatin-14 affected the release of [3H]GABA in a manner which depended on its concentration as well as on the extent of stimulus-evoked release. Somatostatin-14 (1 nmol/l) enhanced the moderate release (2-4% of tissue content) elicited by veratridine (3.1 mumol/l) or K+ (20 mmol/l), but had no effect on the more pronounced release (5-8% of tissue content) elicited by veratridine (4 mumol/l) or K+ (25 mmol/l). Somatostatin-14 (10 nmol/l) had no effect on the moderate release of [3H]GABA, but diminished the pronounced one. Further experiments provided evidence that the somatostatin-14-induced enhancement was not brought about by a direct action on GABA-neurons but was probably indirect, i.e. mediated by other striatal neurons. In contrast, the diminution of the release of [3H]GABA caused by somatostatin-14 may be due to its direct action on releasing neurons. Two antisera against somatostatin lowered the pronounced release indicating that endogenous somatostatin may also enhance the release of [3H]GABA. In addition, endogenous somatostatin seems also to be able to diminish the release under certain experimental conditions.(ABSTRACT TRUNCATED AT 250 WORDS)
Meyer
D K
DK
Department of Pharmacology, University of Freiburg, F.R.G.
Conzelmann
U
U
Schultheiss
K
K
D000818:Animals; D002421:Caudate Nucleus / Q000378:metabolism*; D002845:Chromatography / Q000379:methods; D003543:Cysteamine / Q000494:pharmacology; D007106:Immune Sera / Q000276:immunology; D066298:In Vitro Techniques; D008297:Male; D011188:Potassium / Q000494:pharmacology; D011699:Putamen / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013004:Somatostatin / Q000494:pharmacology* / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D014316:Tritium; D014701:Veratridine / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D007106:Immune Sera; D014316:Tritium; D013779:Tetrodotoxin; D013004:Somatostatin; D005680:gamma-Aminobutyric Acid; D003543:Cysteamine; D014701:Veratridine; D011188:Potassium