Neuroactive steroids inhibit spinal reflex potentiation by selectively enhancing specific spinal GABAA receptor subtypes

Abstract

Recently, we demonstrated a spinal GABA(A) receptor (GABA(A)R)-dependent inhibition on the induction of repetitive stimulation-induced spinal reflex potentiation. However, it remains unclear whether steroid hormones modulate such an inhibition. Here, we show that progesterone is capable of producing GABA(A)Rs-dependent inhibition of the induction of spinal reflex potentiation by actions through neurosteroid metabolites. Progesterone (5mg/kg, twice daily for 4 days) up-regulates the expression of GABA(A)R alpha2, alpha3, alpha4 and delta subunits, and is associated with attenuated repetitive stimulation-induced spinal reflex activity in ovariectomized rats. These changes were blocked by finasteride (50mg/kg, twice daily), an antagonist of neurosteroid synthesis from progesterone, but not by the progesterone receptor antagonist, RU486 (100mg/kg, twice daily). The induction of spinal reflex potentiation was attenuated after a short (30 min) intrathecal treatment with the neurosteroids, allopregnanolone (ALLOP, 10 microM, 10 microL) and 3 alpha,5 alpha-tetrahydrodeoxycorticosterone (THDOC, 10 microM, 10 microL). Acute intrathecal administration of the GABA(A)R antagonist, bicuculline (10 microM, 10 microL) reversed the inhibition produced by progesterone, THDOC and allopregnanolone. These results imply that progesterone-mediated effects on GABA(A)R expression and neural inhibition are regulated by neurosteroids synthesis rather than progesterone receptor activation.

A study of subunit selectivity, mechanism and site of action of the delta selective compound 2 (DS2) at human recombinant and rodent native GABAA receptors

“…Based on the preclinical data on gaboxadol demonstrating a hypnotic profile in rats (Thakkar et al, 2008) and that the effects of the drug on EEG were blunted in d 0/0 mice (Winsky-Sommerer et al, 2007), it was pursued as a novel treatment for insomnia, reaching phase III clinical development (Wafford and Ebert, 2006;Roth et al, 2010). Given the literature indicating a role for d-GABAA receptors in female stress disorders (Maguire and Mody, 2007;Smith et al, 2007), epilepsy (Mihalek et al, 1999), pain (Peng et al, 2009;Bonin et al, 2011), post-traumatic stress disorder (Wiltgen et al, 2005;Pibiri et al, 2008), schizophrenia (Marx et al, 2006), autism (Olmos-Serrano et al, 2011), major depression (Holm et al, 2010) and potentially alcoholism (Enoch, 2008;Rewal et al, 2009), the need for d-selective tools is clear. Furthermore, it should not be overlooked that a major swathe of the literature, only partly cited above, alluding to the potential therapeutic relevance of d-GABAA receptors has been based on studies with neurosteroids, which are not completely selective for these extrasynaptic receptors (Belelli et al, 2009).…”

Endogenous ephrinB2 mediates colon-urethra cross-organ sensitization via Src kinase-dependent tyrosine phosphorylation of NR2B

“…Pharmacological investigations indicated spinal NR2B subunit phosphorylation is crucial in the induction of cross-organ sensitization (19,20,23). Although the physiological/pathophysiological relevance is still without final proof, cross-organ sensitization was linked to the development of viscero-visceral referred pain in the pelvic area, for it is characterized by pathological enhancement of urethra activity caused by activation of nociceptive afferent fiber arising from visceral organs (24). Therefore, we hypothesize that the interactions between ephrinB2 and EphBRs as well as the downstream intracellular cascade are involved in cross-organ sensitization.…”

Advances in the pharmacology of lGICs auxiliary subunits

“…Recent evidence suggests that δ-GABA A R play a critical role in central pain sensitization [58,59]. Behavioral characterization of gabrd knockout mice (gabrd−/−) which lack δ subunit, showed that injection of formalin in the hind paw induces a biphasic response, and have reduced formalin phase II response.…”