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      Seizure Activity Is Increased in Endocrine States Characterized by Decline in Endogenous Levels of the Neurosteroid 3α,5α-THP

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          To examine the role of progesterone (P) and its 5α-reduced metabolite, the neurosteroid 5α-pregnan-3α-ol-20-one (3α,5α-THP), in endogenous variations in ictal activity rats were tested for kainic acid-induced seizures in different hormonal milieu. Corresponding plasma and central P and 3α,5α-THP levels were measured. Cycling Long-Evans rats in estrus and proestrus had seizures of significantly shorter duration and more central and plasma 3α,5α-THP and P than animals in metestrus or diestrus. Females with luteal functioning had seizures of significantly shorter duration and increased central and plasma 3α,5α-THP and P compared to animals that recently had luteal functioning discontinued. Pregnant rats had significantly shorter seizures and greater central and plasma 3α,5α-THP and central P than animals tested 1–2 days postparturition. In all test paradigms, seizure activity was increased in animals that had decreased 3α,5α-THP or P; overall, central 3α,5α-THP was more inversely related to ictal activity than central P or plasma P and 3α,5α-THP. To investigate a causal relationship between 3α,5α-THP and seizures, a 5α-reductase inhibitor, finasteride, or vehicle was administered to pregnant rats. Finasteride administration significantly decreased central and plasma 3α,5α-THP, but had no significant effect on plasma or central P of pregnant rats. Finasteride, but not vehicle administration, to pregnant rats significantly increased seizure duration. These findings support the hypothesis that variations in seizure threshold over endogenous hormonal milieu may be related to endogenous 3α,5α-THP. Of all of the endocrine conditions, seizure durations were greatest in diestrus animals; this group did not experience the lowest or the greatest decrease in 3α,5α-THP concentrations; however, of all of the endocrine conditions, cycling rats experienced the most rapid cycles of 3α,5α-THP variation. This suggests that cycles of endogenous variations in 3α,5α-THP may influence seizure threshold.

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          Most cited references 19

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          Gender influences outcome of brain injury: progesterone plays a protective role.

          The contributions of gender and gonadal hormones in the cascade of events following brain injury are largely unexplored. We measured cerebral edema following cerebral contusion in rats under three hormonal conditions to address this issue. Normally cycling females exhibited significantly less edema than males, and pseudopregnant females were virtually spared from post-injury edema. Subsequent studies of ovariectomized females, with or without hormone treatment, indicated that the reduction of cerebral edema was associated primarily with the presence of circulating progesterone. We conclude that progesterone has a protective effect on the brain following traumatic injury.
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            Progesterone facilitates cognitive recovery and reduces secondary neuronal loss caused by cortical contusion injury in male rats.

            The ability of progesterone to reduce the cerebral edema associated with traumatic brain damage first became apparent when we observed that males had significantly more edema than females after cortical contusion. In addition, edema was almost absent in pseudopregnant female rats, a condition in which progesterone levels are high relative to estrogen. Progesterone injections given after injury also reduced edema and were equally effective in both males and females. The present experiment was done to determine if the progesterone-induced reduction in edema could also prevent secondary neuronal degeneration and reduce the behavioral impairments that accompany contusion of the medial frontal cortex. Progesterone-treated rats were less impaired on a Morris water maze spatial navigation task than rats treated with the oil vehicle. Progesterone-treated rats also showed less neuronal degeneration 21 days after injury in the medial dorsal thalamic nucleus, a structure that has reciprocal connections with the contused area.
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              GABA(A) receptor alpha4 subunit suppression prevents withdrawal properties of an endogenous steroid.

              The hormone progesterone is readily converted to 3alpha-OH-5alpha-pregnan-20-one (3alpha,5alpha-THP) in the brains of males and females. In the brain, 3alpha,5alpha-THP acts like a sedative, decreasing anxiety and reducing seizure activity, by enhancing the function of GABA (gamma-aminobutyric acid), the brain's major inhibitory neurotransmitter. Symptoms of premenstrual syndrome (PMS), such as anxiety and seizure susceptibility, are associated with sharp declines in circulating levels of progesterone and, consequently, of levels of 3alpha,5alpha-THP in the brain. Abrupt discontinuation of use of sedatives such as benzodiazepines and ethanol can also produce PMS-like withdrawal symptoms. Here we report a progesterone-withdrawal paradigm, designed to mimic PMS and post-partum syndrome in a rat model. In this model, withdrawal of progesterone leads to increased seizure susceptibility and insensitivity to benzodiazepine sedatives through an effect on gene transcription. Specifically, this effect was due to reduced levels of 3alpha,5alpha-THP which enhance transcription of the gene encoding the alpha4 subunit of the GABA(A) receptor. We also find that increased susceptibility to seizure after progesferone withdrawal is due to a sixfold decrease in the decay time for GABA currents and consequent decreased inhibitory function. Blockade of the alpha4 gene transcript prevents these withdrawal properties. PMS symptoms may therefore be attributable, in part, to alterations in expression of GABA(A) receptor subunits as a result of progesterone withdrawal.

                Author and article information

                S. Karger AG
                October 1998
                14 October 1998
                : 68
                : 4
                : 272-280
                Neuroscience Program, Connecticut College, New London, Conn., USA
                54375 Neuroendocrinology 1998;68:272–280
                © 1998 S. Karger AG, Basel

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                Page count
                Figures: 5, Tables: 1, References: 50, Pages: 9
                Reproductive Neuroendocrinology


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