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γ ‐Amino Butyric Acid Control of Arginine Vasopressin Release from the Ewe Hypothalamus In Vitro : Sensitivity to Oestradiol
Author(s) -
Ghuman SPS,
Prabhakar S,
Smith RF,
Dobson H
Publication year - 2007
Publication title -
reproduction in domestic animals
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.546
H-Index - 66
eISSN - 1439-0531
pISSN - 0936-6768
DOI - 10.1111/j.1439-0531.2006.00816.x
Subject(s) - muscimol , bicuculline , endocrinology , vasopressin , medicine , chemistry , gabaa receptor , hypothalamus , agonist , arginine , median eminence , oxytocin , receptor , preoptic area , amino acid , biology , biochemistry
Contents The present study aims to ascertain the influence of γ ‐amino butyric acid (GABA) A or B receptors on arginine vasopressin (AVP) release in vitro and determine whether E 2 modulates GABA–AVP interaction. Within 10 min of ewe killing, saggital midline hypothalamic slices (from the anterior preoptic area to the mediobasal hypothalamus along with the median eminence, 2‐mm thick, two per ewe) were dissected, placed in oxygenated minimum essential media (MEM)‐ α at 4°C and within 2 h were singly perifused at 37°C with oxygenated MEM‐ α (pH 7.4; flow rate 0.15 ml/min), either with or without E 2 (24 pg/ml). After 4‐h equilibration, 10‐min fractions were collected for 4 h interposed with a 10‐min exposure at 60 min to a specific GABA A or B receptor agonist or antagonist at various doses (0.1–10 m m ). GABA A (muscimol; no E 2 , n = 7 perifusion chambers, with E 2 , n = 11) or GABA B (baclofen; no E 2 , n = 8, with E 2 , n = 15) agonists (10 m m ) did not influence AVP concentrations. However, AVP release increased (p < 0.05) 20–30 min after exposure to 10 m m GABA A or B antagonists (bicuculline, no E 2 , n = 7: from 4.6 ± 0.7 to 33.0 ± 0.4, with E 2 , n = 17: from 11.9 ± 1.4 to 32.8 ± 6.0; CGP52432, with E 2 , n = 14: from 14.0 ± 2.6 to 28.8 ± 3.9 pg/ml). At the end of the collection period, hypothalamic slices responded to KCl (100 m m ) with AVP efflux (p < 0.05). GABA B but not GABA A antagonist‐stimulated AVP release was enhanced in the presence of E 2 . In summary, AVP release is under the inhibitory influence of GABA input with further potentiation by E 2 through GABA B receptors in vitro .