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

Abstract

The time courses of changes in rat brain neuroactive steroid concentrations and γ-aminobutyric acid type A (GABA_A) receptor function elicited by acute stress were investigated in animals exposed to CO₂ for 1 min, a treatment known to induce stress in rats and panic attacks in humans. Inhalation of CO₂ 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 CO₂ inhalation and had returned to basal values by 30 and 60 min, respectively. In contrast, pregnenolone and 3_α-hydroxy-5_α-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 CO₂ 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_A receptor function, assessed either biochemically by t-[³⁵S]butylbicyclophosphorothionate ([³⁵S]TBPS) binding to cerebral cortical membranes or behaviorally by the punished responding score in Vogel’s test, showed that the effects of CO₂ inhalation on both parameters were maximal (+51 and –40%, respectively) after 10 min; the behavioral reaction returned to normal after 60 min, whereas [³⁵S]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_A receptors, occurred at a time (30 min) when both conflict behavior and [³⁵S]TBPS binding begun to decrease, and (b) both allopregnanolone concentrations and [³⁵S]TBPS binding had returned to control values 120 min after CO₂ inhalation. The data are thus consistent with a physiological role of neuroactive steroids in restoring GABAergic tone after stress.

Neurosteroids in the context of stress: Implications for depressive disorders

“…In keeping with the early observations of Selye (1941Selye ( , 1956) that steroid hormone metabolites could exert central effects within minutes of administration, Purdy and colleagues (Purdy et al, 1991;Barbaccia et al, 1996Barbaccia et al, , 1997 were among the first to demonstrate in rat models that acute stress results in significant increases in both plasma and CNS concentrations of the 3α-hydroxy ring A-reduced steroid metabolites, 3α,5α-THP (allopregnanolone) and 3α,5α-THDOC (allotetrahydroDOC), in physiologic ranges known to enhance GABA receptoractivated Cl-currents (Purdy et al, 1991;Reddy, 2006).…”

“…PMDD women also report more traumatic life stress, including sexual and physical abuse histories (Paddison et al, 1990;Golding & Taylor, 1996Girdler et al, 2003Girdler et al, , 2007. Since allopregnanolone is stress responsive, at least in animal models (Purdy et al, 1991;Barbaccia et al, 1996Barbaccia et al, , 1997, greater allostatic load in PMDD resulting from more severe life stress could contribute to the elevated allopregnanolone concentrations that we have seen in PMDD women (Girdler et al, 2001) and result in the documented alterations in GABA A receptor function in PMDD (Sundstrom et al, 1997a(Sundstrom et al, , 1997b(Sundstrom et al, , 1998, including alterations in the agonism properties of the GABA A receptor as animal models (Smith et al, 2006) and human studies of PMDD suggest (Le Melledo et al, 2000). This could then explain the seemingly paradoxical association between increasing allopregnanolone concentrations in the luteal phase and increased dysphoric mood states in PMDD.…”

σ1 Receptor Ligands and Related Neuroactive Steroids Interfere with the Cocaine-Induced State of Memory

“…Depending on physiological conditions and neuroendocrine responses, neurosteroids may contribute to the constraint of memory according to StD concept or not. For instance, in stressful situations, steroid biosyntheses led to very high levels in reduced metabolites of progesterone as compared to precursor steroids (Paul and Purdy, 1992;Barbaccia et al, 1996;Urani et al, 2001), and thus to state-dependent memory processes, whereas, in normophysiological conditions, state-independent processes may prevail. In addition, basal levels in neuroactive steroids and life-long variations in biosyntheses levels vary considerably among individuals.…”

Clozapine, but not Haloperidol, Increases Brain Concentrations of Neuroactive Steroids in the Rat

“…For long-term treatment, clozapine (10 mg/kg) or haloperidol (0.1 mg/kg) was administered once a day for 19 days; the animals were challenged with a single injection of the same dose of the respective drug or vehicle 48 h after the last injection of the long-term treatment protocol. Rats were killed by focused microwave irradiation (70 W/cm 2 for 4 s) to the head, a procedure that minimizes post-mortem tissue metabolism of neurosteroids (Barbaccia et al 1996a) for measurement of brain steroid concentrations, or by decapitation, for parallel measurements of brain and plasma steroid concentrations. The brain was rapidly removed after killing either by decapitation or irradiation, and the cortex and striatum were dissected and frozen at Ϫ 80 Њ C until steroid extraction and mesurement.…”

“…Brain and plasma steroid concentrations were measured as previously described (Barbaccia et al 1996a). In brief, cortical or striatal tissue were homogenized in 5 or 3 ml of phosphate-buffered saline (pH 7.0), respectively, after which the homogenate was extracted three times with an equal volume of ethyl acetate, the extract was dried, and the residue was reconstituted with 2 ml of n -hexane and fractionated by high-performance liquid chromatography (HPLC) on a Lichrosphere-diol column (250 by 4 mm; pore size, 5 m) (Phenomenex).…”