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      Time-Dependent Changes in Rat Brain Neuroactive Steroid Concentrations and GABA A Receptor Function after Acute Stress

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          The time courses of changes in rat brain neuroactive steroid concentrations and γ-aminobutyric acid type A (GABA<sub>A</sub>) receptor function elicited by acute stress were investigated in animals exposed to CO<sub>2</sub> for 1 min, a treatment known to induce stress in rats and panic attacks in humans. Inhalation of CO<sub>2</sub> induced increases in cerebral cortical steroid concentrations, the time dependence of which varied with the steroid examined. Thus, progesterone and deoxycorticosterone showed maximal increases (10- and 4-fold, respectively) 10 min after CO<sub>2</sub> inhalation and had returned to basal values by 30 and 60 min, respectively. In contrast, pregnenolone and 3<sub>α</sub>-hydroxy-5<sub>α</sub>-pregnan-20-one (allopregnanolone) concentrations showed maximal increases (+174 and +200%, respectively) at 30 min, were still higher than control at 60 min and returned to control values 120 min after stress. Inhalation of CO<sub>2</sub> also resulted in increases in plasma steroid concentrations, most of which peaked at 30 min and had returned to control values by 60 min. A parallel analysis of the stress-induced changes in GABA<sub>A</sub> receptor function, assessed either biochemically by t-[<sup>35</sup>S]butylbicyclophosphorothionate ([<sup>35</sup>S]TBPS) binding to cerebral cortical membranes or behaviorally by the punished responding score in Vogel’s test, showed that the effects of CO<sub>2</sub> inhalation on both parameters were maximal (+51 and –40%, respectively) after 10 min; the behavioral reaction returned to normal after 60 min, whereas [<sup>35</sup>S]TBPS binding had returned to control values 120 min after stress. The results show that: (a) the maximal increase in the brain concentrations of allopregnanolone, a potent and efficacious positive modulator of GABA<sub>A</sub> receptors, occurred at a time (30 min) when both conflict behavior and [<sup>35</sup>S]TBPS binding begun to decrease, and (b) both allopregnanolone concentrations and [<sup>35</sup>S]TBPS binding had returned to control values 120 min after CO<sub>2</sub> inhalation. The data are thus consistent with a physiological role of neuroactive steroids in restoring GABAergic tone after stress.

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          Author and article information

          S. Karger AG
          09 April 2008
          : 63
          : 2
          : 166-172
          aDepartment of Experimental Medicine, University of Rome ‘Tor Vergata’, Rome, Italy; bDepartment of Experimental Biology, Chair of Pharmacology, University of Cagliari, Italy; cDepartment of Psychiatry, University of California, San Diego, Calif., USA
          126953 Neuroendocrinology 1996;63:166–172
          © 1996 S. Karger AG, Basel

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          Page count
          Pages: 7
          Gonadotropin-Releasing Hormone and Gonadal Steroid Feedback


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