Role of brain allopregnanolone in the plasticity of γ-aminobutyric acid type A receptor in rat brain during pregnancy and after delivery

Abstract

The relation between changes in brain and plasma concentrations of neurosteroids and the function and structure of ␥-aminobutyric acid type A (GABA A ) receptors in the brain during pregnancy and after delivery was investigated in rats. In contrast with plasma, where all steroids increased in parallel, the kinetics of changes in the cerebrocortical concentrations of progesterone, allopregnanolone (AP), and allotetrahydrodeoxycorticosterone (THDOC) diverged during pregnancy. Progesterone was already maximally increased between days 10 and 15, whereas AP and allotetrahydrodeoxycorticosterone peaked around day 19. The stimulatory effect of muscimol on 36 Cl ؊ uptake by cerebrocortical membrane vesicles was decreased on days 15 and 19 of pregnancy and increased 2 days after delivery. Moreover, the expression in cerebral cortex and hippocampus of the mRNA encoding for ␥2L GABA A receptor subunit decreased during pregnancy and had returned to control values 2 days after delivery. Also ␣1,␣2, ␣3, ␣4, ␤1, ␤2, ␤3, and ␥2S mRNAs were measured and failed to change during pregnancy. Subchronic administration of finasteride, a 5␣-reductase inhibitor, to pregnant rats reduced the concentrations of AP more in brain than in plasma as well as prevented the decreases in both the stimulatory effect of muscimol on 36 Cl ؊ uptake and the decrease of ␥2L mRNA observed during pregnancy. These results indicate that the plasticity of GABA A receptors during pregnancy and after delivery is functionally related to f luctuations in endogenous brain concentrations of AP whose rate of synthesis͞metabolism appears to differ in the brain, compared with plasma, in pregnant rats.An important feature of ␥-aminobutyric acid type A (GABA A ) receptors in rat brain is their plasticity in response to exposure to brief or long-lasting physiological stimuli or to long-term pharmacological treatments. The kinetic characteristics of the various binding sites located on the GABA A receptor, as well as the density and function of these receptors in different areas of the rat brain, are affected by acute stressful stimuli (handling, foot shock, swimming), postnatal development, aging, kindling, and long-term administration of anxiolytic, hypnotic, or anticonvulsant drugs (1-6). Although recent studies have suggested that some of these changes may be mediated at the level of expression of receptor subunit genes (7-10), the chemical or molecular events that underlie such rapid, shortterm, or persistent changes in the density and affinity of binding sites associated with GABA A receptors, as well as in the function of the receptor complex, remain to be characterized.Neurosteroids accumulate in the mammalian brain in a manner that is, at least in part, independent of the peripheral tissues (adrenal glands and gonads) that synthesize these compounds (11). Systemic administration of progesterone or its metabolites 3␣-hydroxy-5␣-pregnan-20-one (allopregnanolone, AP) and 3␣,21-dihydroxy-5␣-pregnan-20-one (allotetrahydrodeoxycorticosterone, THDOC) induces an...

A quantitiative LC-MS/MS method for the measurement of arachidonic acid, prostanoids, endocannabinoids, N-acylethanolamines and steroids in human plasma

“…Different studies have reported levels of THDOC and THP in human and rodent plasma using gas chromatography chemical ionization mass spectrometry (GC-MS) or radioimmunassays [50][51][52][53][54][55]. Using our LC-MS/MS, we were unable to detect these analytes.…”

Steroid modulation of GABAA receptor-mediated transmission in the hypothalamus: Effects on reproductive function

“…With respect to the hypothalamus, allopregnanolone levels were also shown to vary across the estrous cycle, but, in contrast to cortex, the lowest levels were reported on the evening of proestrus (~40 pg/mg protein) and the highest levels during the morning of diestrus I (~95 pg/mg protein) (Genazzani et al, 1995). The differences in concentrations of progestin-and testosterone-derived neurosteroids as a function of hormonal state contrasts with that for THDOC which shows only a small increase from ~1.5 ng/g during estrus to ~ 3ng/g in late pregnancy (Concas et al, 1998).…”

“…Using this methodology, allopregnanolone concentrations in cortical homogenates were estimated to be ~1-2 ng/g in juvenile, ~1 ng/g in diestrous, 4-6 ng/g in estrous, and 4-8 ng/g in proestrous females, with levels reaching ~10-30 ng/g during pregnancy (Paul and Purdy, 1992;Corpéchot et al, 1993;Concas et al, 1998;Kellogg and Frye, 1999). These assessments have been used to estimate that allopregnanolone levels are diestrus females (Paul and Purdy, 1992), but can reach ~100 nM during the late stages of pregnancy (see for example; Brussaard et al, 1997;Lambert et al, 2003).…”

Neuroactive Steroid 3α-Hydroxy-5α-Pregnan-20-One Modulates Electrophysiological and Behavioral Actions of Ethanol

“…It was administered subcutaneously in a 2 ml/kg suspension of finasteride in 20% (w/ v) 2-hydroxypropyl-␤-cyclodextrin (HCD) (Research Biochemicals, Natick, M A) at either a 25 or 50 mg / kg dose. Doses of finasteride were determined by review of finasteride use in previous behavioral and biochemical experiments in rodents (Lephart et al, 1996;Concas et al, 1998;Kokate et al, 1999). Finasteride (50 mg / kg, s.c.) alters open field behavior in pregnant females rats and decreased enzyme activity by 60 -80% (Lephart et al, 1996).…”

“…3␣,5␣-THP is an endogenous pregnane steroid and potent agonist modulator of the inhibitory neurotransmitter GABA A receptor subtype. 3␣,5␣-THP is increased in brain in many stress paradigms (Purdy et al, 1991;Barbaccia et al, 1996;Barbaccia et al, 1997), as well as during naturally occurring hormonal fluctuations such as the estrus cycle (Ichikawa et al, 1974;Paul and Purdy, 1992;Finn and Gee, 1993) and pregnancy (Concas et al, 1998). A wealth of evidence demonstrates that the anxiolytic, sedative/ hypnotic, and anticonvulsant effects attributed to 3␣,5␣-THP are mediated by enhancement of chloride ion conductance through GABA A receptors in brain (Morrow, 1995).…”