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.

1 This study was undertaken to investigate the relationship between a reduction in brain GABA A receptor function and the cerebro-cortical content of 3a-hydroxy-5a-pregnan-20 one (allopregnanolone, AP), a potent endogenous positive modulator of g-aminobutyric acid (GABA) action at GABA A receptors, with anticon¯ict and anticonvulsant e ects in rodents. 2 An acute depletion of the cerebral content of GABA or an attenuation of GABA A receptor-mediated transmission by systemic injections of isoniazid (375 mg kg 71 , s.c.) or FG 7142 (15 mg kg 71 , i.p.) induced a transient increase in the cerebro-cortical and plasma concentrations of AP in handlinghabituated (not stressed) rats. 3 Two stress paradigms, handling in naive rats and mild foot shock in handling-habituated rats, that reduce central GABAergic tone mimicked the e ects of isoniazid and FG 7142 on cortical AP content; foot shock in handling-habituated rats, but not handling in naive animals, also increased plasma AP. Isoniazid, FG 7142, and foot shock also each increased the concentrations of the AP precursors, pregnenolone and progesterone, in both brain and plasma of handling-habituated rats, whereas handling in naive rats increased the concentrations of these steroids only in brain. 4 Pretreatment of handling-habituated rats with the anxiolytic b-carboline derivative abecarnil, a positive allosteric modulator of GABA A receptors, which per se failed to a ect the AP concentration in brain or plasma, prevented the increase in brain and plasma AP induced by foot shock or isoniazid. 5 In adrenalectomized and castrated rats foot shock or isoniazid failed to increase AP both in brain cortex and plasma. 6 These observations indicate that inhibition of GABAergic transmission, induced by foot shock or pharmacological manipulations, results in an increase in the concentrations of AP in brain and plasma, possibly via a modulation of hypothalamic-pituitary-adrenal (HPA) axis. 7 Given that AP enhances GABA A receptor function with high e cacy and potency, an increase in brain AP concentration may be important in the ®ne tuning of the GABA-mediated inhibitory transmission in the central nervous system.

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The influence of a methanolic extract of Hypericum perforatum L. and of purified hypericin has been comparatively tested on the growth of a human erythroleukemic cell line (K562). After 1 h exposure to increasing concentrations (as hypericin content) of both agents in the dark, leukemic cells were grown for 24 h and 48 h. The effects on cell growth were determined by viable cell count, flow cytometry analysis and fluorescence microscopy. Our data show that purified hypericin has only a weak inhibitory effect on cell growth and no effect in inducing apoptotic cell death. In contrast, the Hypericum flower extract shows a significant concentration-dependent and long-lasting inhibition of cell growth, and induces apoptotic cell death. This work con fi rms the interesting role of Hypericum perforatum L. in cancer therapy and strongly supports the hypothesis that agents, other than hypericin, present in the total extract can impair tumor cell growth acting separately or in a combined manner.