Progesterone-metabolite prevents protein kinase C-dependent modulation of gamma -aminobutyric acid type A receptors in oxytocin neurons

Abstract

Gonadal steroid feedback to oxytocin neurons during pregnancy is in part mediated via the neurosteroid allopregnanolone (3␣-OH-DHP), acting as allosteric modulator of postsynaptic ␥-aminobutyric acid type A (GABA A) receptors. We describe here a form of nongenomic progesterone signaling by showing that 3␣-OH-DHP not only potentiates GABAA receptor-channel activity but also prevents its modulation by protein kinase C (PKC). Application of oxytocin or stimulation of PKC suppressed the postsynaptic GABA responses of oxytocin neurons in the absence, but not in the presence of 3␣-OH-DHP. This finding was true at the juvenile stage and during late pregnancy, when the GABAA receptor is sensitive to 3␣-OH-DHP. In contrast, after parturition, when the GABAA receptors expressed by oxytocin neurons are less sensitive to 3␣-OH-DHP, this neurosteroid no longer counteracts PKC. The change in GABA A-receptor responsiveness to 3␣-OH-DHP helps to explain the onset of firing activity and thus the induction of oxytocin release at parturition. O xytocin plays a key role in the initiation of parturition and lactation in female rats. Synchronous firing of magnocellular neurons in the supraoptic nucleus (SON) and the paraventricular nucleus triggers oxytocin release. The spiking frequency of these neurons is under control of a GABAergic input (1-3). The postsynaptic ␥-aminobutyric acid type A (GABA A ) receptors that mediate this input are susceptible to allosteric interaction with the neurosteroid allopregnanolone 3␣-OH-DHP during some stages of the female reproductive cycle, in particularly during pregnancy (4, 5). In addition, somatodendritic release of oxytocin within the SON acting on autoreceptors (6) decreases the fast synaptic inhibition of the magnocellular cells, via suppression of postsynaptic GABA A receptor activity in a Ca 2ϩ -dependent manner (7,8). Because 3␣-OH-DHP and oxytocin both affect the activity of the postsynaptic GABA A receptor, we investigated whether allosteric interaction of 3␣-OH-DHP with this receptor may inf luence its modulation by metabotropic pathways. If so, this finding would imply a novel pathway of nongenomic steroid hormone signaling in the central nervous system. Methods Dissection and Recordings. Juvenile male (21-24 days postnatal) or adult female Wistar rats, either after 20 days of pregnancy (P20) or on the first day after parturition (PPD1) were decapitated, and 400-m-thick coronal hypothalamus slices incorporating the middle portion of the SON were prepared as described (4, 5, 7) by using a Leica (Nussloch, Germany) vibratome slicer. Spontaneous GABAergic synaptic currents were recorded at room temperature (20°C) at a holding potential of Ϫ70 mV with an Axopatch 200A amplifier (Axon Instruments, Foster City, CA) in the whole-cell voltage clamp mode (see refs. 4, 5, and 7 for recording criteria). Electrodes had a tip resistance of around 2 M⍀ and uncompensated series resistance Ͻ 12 M⍀ (which usually was compensated for 70%). The external solution contained 125 mM NaCl, 25 mM NaHCO 3 , 3 ...

Relationships of circulating pregnanolone isomers and their polar conjugates to the status of sex, menstrual cycle, and pregnancy

“…Despite the number of mechanism suggested (McLean & Smith 2001, Patel et al 2003, Condon et al 2004, Mesiano 2004, our knowledge regarding the primary impulse for the human parturition remains inadequate. The role of neuroactive reduced progesterone metabolites -and particularly the most abundant of them, PIs -in the timing of human parturition is still unclear, despite studies reporting their major effects in other mammals (Brussaard et al 1997(Brussaard et al , 2000. In rats, decreasing allopregnanolone levels just before labor induce a positive feedback loop in oxytocin production, resulting in a rapid delivery (Brussaard et al 1997(Brussaard et al , 2000.…”

“…these neuroactive steroids either due to the changed expression of the receptor subunits and/or as a result of the changed phosphorylation status of the specific sites on the GABA A -R (Leng & Russell 1999, Brussaard et al 2000, Koksma et al 2003.…”

Role of Neuroactive Steroid Allopregnanolone in Antipsychotic-like Action of Olanzapine in Rodents

“…Our observation that bicuculline pretreatment antagonized the effects of olanzapine on CAR-and apomorphineinduced climbing behaviors suggests that the antipsychoticlike action of olanzapine could be mediated via activation of GABA A receptors. Consequently it may be speculated that the influence of ALLO on dopaminergic neurotransmission might be mediated via GABA A receptors (Motzo et al, 1996;Khisti et al, 2002) perhaps through modulation of intracellular signaling mechanisms like protein kinase C (PKC) (Brunig et al, 1999;Brussard et al, 2000;Liu et al, 2000). That the activation or inhibition of PKC increases or decreases, respectively, dopamine release in striatum has already been demonstrated (Gimbalvo, 1988).…”

“…That the activation or inhibition of PKC increases or decreases, respectively, dopamine release in striatum has already been demonstrated (Gimbalvo, 1988). Interestingly, interaction of ALLO with GABA A receptors prevents the PKC from phosphorylating GABA A receptor itself and prolongs the receptor ion channel open time (Twyman and Macdonald, 1992;Brussard et al, 2000). Further, PKC deficiency results in enhanced GABA A receptor sensitivity to allosteric modulators including ALLO or pregnanolone Hodge et al, 2002).…”

Physiological Relevance of Pregnanolone Isomers and Their Polar Conjugates with Respect to the Gender, Menstrual Cycle and Pregnancy

“…Withdrawal effect in case of abrupt drop of steroid positive modulators rapidly supervenes like the addiction effect while increasing the steroid levels. Changing 5Ǐ/ǐ-PI concentrations induce a decreased affinity of GABA A -r for these steroids due to the changed expression of the receptor subunits and/or as a result of the changed phosphorylation status of the specific sites on the GABA A -r (Brussaard, Wossink, Lodder, & Kits, 2000;Koksma, et al, 2003;Leng & Russell, 1999;). The aforementioned mechanism requires synchronization, the disturbances of which could have significant neuropsychiatric consequences in physiological and pathological situations like pregnancy, parturition, onset of menopause, traumas, endocrine diseases, and stress.…”