Progesterone withdrawal I: pro-convulsant effects.

Pro-convulsant withdrawal properties have been reported for a variety of GABA-modulatory drugs, such as the benzodiazepines (BDZs, [S.E. File, The history of BDZ dependence: a review of animal studies, Neurosci. Biobehav. Rev. 14 (1990) 135-146; P.R. Finley, P. E. Nolan, Precipitation of BDZ withdrawal following sudden discontinuation of midazolam, DICP 23 (1989) 151-152]), barbiturates and ethanol [N. Kokka, D.E. Sapp, U. Witte, R.W. Olsen, Sex differences in sensitivity to pentylenetetrazol but not in GABAA receptor binding, Pharm. Biochem. Behav. 43 (1992) 441-447]. In this report, we test the hypothesis that pro-convulsant effects are produced by withdrawal from the GABA-modulatory neurosteroid 3alpha-OH-5alpha-pregnan-20-one (3alpha,5alpha-THP) after sustained exposure to elevated circulating levels of its parent compound progesterone (P). Seizure activity was precipitated by picrotoxin or with the BDZ inverse agonist n-methyl-beta-carboline-3-carboxamide (beta-CC), and a seizure rating determined 24 h after abrupt discontinuation of P following a multiple withdrawal/chronic administration paradigm. In some cases, a pseudopregnant rat model was employed to produce increased ovarian production of P prior to withdrawal (ovariectomy). Rats undergoing P withdrawal exhibited greater seizure-like activity than vehicle-treated controls, and received seizure scores in the same range as rats undergoing BDZ withdrawal. Administration of a 5alpha-reductase blocker, MK-906, along with P, prevented this pro-convulsant effect of P withdrawal, suggesting that the GABA-modulatory 3alpha,5alpha-THP is the active compound responsible for this withdrawal effect. Combined administration of P and diazepam produced synergistic effects upon withdrawal and produced a seizure score higher than observed after withdrawal from either agent alone. These results suggest that P exhibits withdrawal properties via the neuroactive steroid 3alpha, 5alpha-THP, that include exacerbation of seizure activity. These results may have clinical relevance, as increased incidence and severity of seizures has been reported in susceptible women during times of declining circulating levels of P across the menstrual cycle [T. Backstrom, B. Zetterlund, S. Blom, M. Romano, Effects of intravenous progesterone infusions on the epileptic discharge frequency in women with partial epilepsy, Acta Neurol. Scand. 69 (1984) 240-248; A.G. Herzog, Progesterone therapy in women with complex partial and secondary generalized seizures, Neurology 45 (1995) 1660-1662].

Progesterone withdrawal. II: insensitivity to the sedative effects of a benzodiazepine.

Previous results from this lab have demonstrated that the GABA-modulatory steroid 3alpha-OH-5alpha-pregnan-20-one (3alpha, 5alpha-THP) exhibits withdrawal properties, increasing anxiety [M.A. Gallo, S.S. Smith, Progesterone withdrawal decreases latency to and increases duration of electrified prod burial: a possible rat model of PMS anxiety, Pharmacol. Biochem. 46 (1993) 897-904.] and seizure susceptibility [S.S. Smith, Q.H. Gong, F.-C. Hsu, R.S. Markowitz, J. M.H. ffrench-Mullen, X. Li, GABAA receptor alpha4 subunit suppression prevents withdrawal properties of an endogenous steroid, Nature 392 (1998) 926-930.] upon abrupt discontinuation after chronic administration of its parent compound, progesterone (P), in a manner similar to other GABA-modulatory drugs. Further, we have demonstrated that withdrawal from P produces insensitivity to the potentiating effects of the benzodiazepine (BDZ) lorazepam (LZM) on GABA-gated Cl- current [A.-M.N. Costa, K.T. Spence, S.S. Smith, J.M. H. ffrench-Mullen, Withdrawal from the endogenous steroid progesterone results in GABAA currents insensitive to BDZ modulation in rats CA1 hippocampus, J. Neurophysiology 74 (1995) 464-469; S.S. Smith, Q.H. Gong, F.-C. Hsu, R.S. Markowitz, J.M.H. ffrench-Mullen, X. Li, GABAA receptor alpha4 subunit suppression prevents withdrawal properties of an endogenous steroid, Nature 392 (1998) 926-930.], assessed using whole cell patch clamp procedures on pyramidal neurons acutely dissociated from CA1 hippocampus. The purpose of the present study was to examine the withdrawal effects of P on the sedative potency of LZM, tested behaviorally as the ability to maintain position on a variable speed treadmill following LZM administration (0.75 mg/kg). Both continuous (continuous release P capsule, single withdrawal) as well as discontinuous (multiple P injection, multiple withdrawal) paradigms were tested. Longer continuous release paradigms were more effective in abolishing the sedative effects of LZM, without producing a change in baseline response. The LZM insensitivity observed following the multiple withdrawal paradigm was prevented by prior intraventricular administration of antisense oligonucleotide against the alpha4 subunit of the GABAA receptor. These results support the hypothesis that withdrawal from P decreases the behavioral response to LZM as a direct result of increases in the alpha4 subunit of the GABAA receptor. Withdrawal from P occurs endogenously during pre-menstrual and post-partum periods, when decreased response to BDZ has been reported.

Withdrawal from 3alpha-OH-5alpha-pregnan-20-One using a pseudopregnancy model alters the kinetics of hippocampal GABAA-gated current and increases the GABAA receptor alpha4 subunit in association with increased anxiety.

In the present study, we have characterized properties of steroid withdrawal using a pseudopregnant rat model. This paradigm results in increased production of endogenous progesterone from ovarian sources and as such is a useful physiological model. "Withdrawal" from progesterone induced by ovariectomy on day 12 of pseudopregnancy resulted in increased anxiety, as determined by a decrease in open arm entries on the elevated plus maze compared to control rats and pseudopregnant animals not undergoing withdrawal. Similar findings were obtained 24 hr after administration of a 5alpha-reductase blocker to a pseudopregnant animal, suggesting that it is the GABAA-modulatory 3alpha-OH-5alpha-pregnan-20-one (3alpha, 5alpha-THP) that produces anxiogenic withdrawal symptoms. Twenty-four hours after steroid withdrawal, the time constant for decay of GABAA-gated current was also reduced sixfold, assessed using whole- cell patch-clamp procedures on pyramidal neurons acutely dissociated from CA1 hippocampus. Thus, 3alpha,5alpha-THP withdrawal results in a marked decrease in total GABAA current, a possible mechanism for its anxiogenic, proconvulsant sequelae. In addition, 3alpha,5alpha-THP withdrawal resulted in insensitivity to the normally potentiating effect of the benzodiazepine lorazepam (LZM) on GABAA-gated Cl- current. This withdrawal profile is similar to that reported for other GABAA-modulatory drugs such as the benzodiazepines (BDZs), barbiturates, and ethanol. These changes were also associated with significant two and threefold increases in both the mRNA and protein for the alpha4 subunit of the GABAA receptor, respectively, in hippocampus. The pseudopregnancy paradigm may be a useful model for periods of endogenous 3alpha,5alpha-THP withdrawal such as premenstrual syndrome and postpartum or postmenopausal dysphoria, when increased emotional lability and BDZ insensitivity have been reported.