ganaxolone and gaboxadol

Allopregnanolone (ALLO) is an endogenous neuroactive steroid thought to alter the reinforcement value of alcohol (ethanol) due to its actions as a positive modulator of the GABAA receptor (GABAAR). Extrasynaptic GABAARs may be a particularly sensitive target of ethanol and neuroactive steroids. Previous work showed that systemic injections of an ALLO analog, ganaxolone (GAN), or an extrasynaptic GABAAR agonist (gaboxadol; THIP) decreased ethanol intake in male mice with limited access to ethanol.. The present studies tested whether activation of GABAARs in the nucleus accumbens (NAc) shell by GAN or THIP was sufficient to reduce ethanol intake. C57BL/6J male mice had 2-h access to 10 % ethanol (10E) and water, and 10E intake was measured following site-specific infusions of GAN or THIP.. Decreases in limited-access 10E consumption were observed following site-specific bilateral infusions of either drug into the NAc shell. Significant changes in intake were absent when the drugs were infused in a region dorsal to the target site (GAN) or into the lateral ventricle (THIP). Locomotor data confirmed that the decreases in intake were not due to a sedative effect of the drugs.. These data demonstrate the sufficiency of GABAAR activation by a positive allosteric modulator or an agonist with selectivity for extrasynaptic GABAARs to decrease ethanol consumption in mice. Importantly, more refined GABAAR-active targets that decrease ethanol intake may enhance our understanding and ability to treat alcohol use disorders.

Topics: Alcohol Drinking; Animals; Ethanol; GABA-A Receptor Agonists; Infusions, Intraventricular; Isoxazoles; Male; Mice; Mice, Inbred C57BL; Nucleus Accumbens; Pregnanolone; Receptors, GABA-A; Treatment Outcome

The endogenous neuroactive steroid allopregnanolone (ALLO) has previously been shown to induce reinstatement of ethanol seeking in rodents. ALLO is a positive allosteric modulator at both synaptic and extrasynaptic GABAA receptors. The contribution of each class of GABAA receptors in mediating reinstatement of ethanol seeking is unknown. The first aim of the present study was to determine whether ganaxolone (GAN), a longer-acting synthetic analog of ALLO, also promotes reinstatement of ethanol seeking. The second aim was to examine whether preferentially activating extrasynaptic GABAA receptors with the selective agonist gaboxadol (THIP) was sufficient to reinstate responding for ethanol in mice. Male C57BL/6J mice were trained to lever press for access to a 10% ethanol (v/v) solution (10E), using a sucrose-fading procedure. Following extinction of the lever-pressing behavior, systemic THIP (0, 4 and 6mg/kg) and GAN (0, 10, and 15mg/kg) were tested for their ability to reinstate ethanol-appropriate responding in the absence of 10E access. GAN significantly increased lever pressing on the previously active lever, while THIP did not alter lever-pressing behavior. The results of this study suggest that direct activation of extrasynaptic GABAA receptors at the GABA site is not sufficient to induce ethanol seeking in the reinstatement procedure. Future studies are necessary to elucidate the mechanisms and brain areas by which differences in the pharmacological activity of GAN and THIP at the GABAA receptor contribute to the dissimilarity in their effect on the reinstatement of ethanol seeking. Nonetheless, based on the increased use of these drugs in clinical trials across multiple disease states, the effects of GAN or THIP on alcohol seeking may be an important consideration if these drugs are to be used clinically in a population with a co-occurring alcohol use disorder.

Topics: Animals; Behavior, Animal; Ethanol; Extinction, Psychological; GABA Agonists; Isoxazoles; Male; Mice, Inbred C57BL; Pregnanolone; Receptors, GABA-A

Spinal gamma-aminobutyric acid receptor type A (GABA(A)) receptor modulation with agonists and allosteric modulators evokes analgesia and antinociception. Changes in K(+)-Cl(-) cotransporter isoform 2 (KCC2) expression or function that occur after peripheral nerve injury can result in an impairment in the Cl(-) extrusion capacity of spinal dorsal horn neurons. This, in turn, alters Cl(-)-mediated hyperpolarization via GABA(A) receptor activation, contributing to allodynia or hypersensitivity associated with nerve injury or inflammation. A gap in knowledge exists concerning how this loss of spinal KCC2 activity differentially impacts the analgesic efficacy or potency of GABA(A) agonists and allosteric modulators. We utilized intrathecal drug administration in the tail flick assay to measure the analgesic effects of general GABA(A) agonists muscimol and Z-3-[(aminoiminomethyl)thio]prop-2-enoic acid (ZAPA), the ∂-subunit-preferring agonist 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol (THIP), and allosteric modulators of the benzodiazepine (midazolam) and neurosteroid (ganaxolone) class, alone or in the presence of K(+)-Cl(-) cotransporter isoform (KCC) blockade. Intrathecal muscimol, ZAPA, THIP midazolam, and ganaxolone all evoked significant analgesia in the tail flick test. Coadministration of either agonists or allosteric modulators with [(dihydroindenyl)oxy] alkanoic acid (DIOA) (a drug that blocks KCC2) had no effect on agonist or allosteric modulator potency. On the other hand, the analgesic efficacy of muscimol and ZAPA and the allosteric modulator ganaxolone were markedly reduced whereas THIP and midazolam were unaffected. Finally, in the spared nerve injury model, midazolam significantly reversed tactile hypersensitivity while ganaxolone had no effect. These results indicate that the KCC2-dependent Cl(-) extrusion capacity differentially regulates the analgesic efficacy of agonists and allosteric modulators at the GABA(A) receptor complex.. Our work suggests that drug discovery efforts for the treatment of chronic pain disorders should target benzodiazepine or ∂-subunit-containing sites at the GABA(A) complex.

Topics: Analgesia; Analgesics; Animals; Benzodiazepines; Chlorides; GABA-A Receptor Agonists; Isoxazoles; K Cl- Cotransporters; Male; Mice; Mice, Inbred ICR; Muscimol; Neuralgia; Peripheral Nerve Injuries; Pregnanolone; Receptors, GABA-A; Sciatic Nerve; Symporters

Recent evidence suggests that GABA(A) receptor ligands may regulate ethanol intake via effects at both synaptic and extrasynaptic receptors. For example, the endogenous neurosteroid, allopregnanolone (ALLO) has a similar pharmacological profile as ethanol, and it alters ethanol intake in rodent models. Additionally, recent evidence suggests that δ-subunit-containing extrasynaptic GABA(A) receptors may confer high sensitivity to both ethanol and neurosteroids. The purpose of the present study was to determine the effects of ganaxolone (GAN; an ALLO analog) and gaboxadol (THIP; a GABA(A) receptor agonist with selectivity for the extrasynaptic δ-subunit) on ethanol intake, drinking patterns, and bout characteristics in operant and limited-access self-administration procedures. In separate studies, the effects of GAN (0-10 mg/kg) and THIP (2-16 mg/kg) were tested in C57BL/6J male mice provided with 2-h access to a two-bottle choice of water or 10% ethanol or trained to respond for 30 min of access to 10% ethanol. GAN had no overall significant effect on operant ethanol self-administration, but tended to decrease the latency to consume the first bout. In the limited-access procedure, GAN dose-dependently decreased ethanol intake. THIP dose-dependently decreased ethanol intake in both paradigms, altering both the consummatory and appetitive processes of operant self-administration as well as shifting the drinking patterns in both procedures. These results add to literature suggesting time-dependent effects of neurosteroids to promote the onset, and to subsequently decrease, ethanol drinking behavior, and they support a role for extrasynaptic GABA(A) receptor activation in ethanol reinforcement.

Topics: Alcohol Deterrents; Alcohol Drinking; Animals; Conditioning, Operant; Dose-Response Relationship, Drug; Drugs, Investigational; Ethanol; GABA-A Receptor Agonists; Isoxazoles; Male; Mice; Mice, Inbred C57BL; Molecular Targeted Therapy; Nootropic Agents; Pregnanolone; Protein Subunits; Receptors, GABA-A; Reinforcement, Psychology; Self Administration; Time Factors

Neurosteroids and other γ-aminobutyric acid(A) (GABA(A) ) receptor-modulating compounds have been shown to affect ethanol intake, although their mechanism remains unclear. This study examined how patterns of 24-hour ethanol drinking in mice were altered with the synthetic GABAergic neurosteroid ganaxolone (GAN), with an inhibitor of neurosteroid synthesis (finasteride [FIN]), or a GABA(A) receptor agonist with some selectivity at extrasynaptic receptors (gaboxadol HCL [THIP]).. Male C57BL/6J mice had continuous access to a 10% v/v ethanol solution (10E) or water. Using lickometer chambers, drinking patterns were analyzed among mice treated in succession to GAN (0, 5, and 10 mg/kg), FIN (0 or 100 mg/kg), and THIP (0, 2, 4, 8, and 16 mg/kg).. GAN shifted drinking in a similar but extended manner to previous reports using low doses of the neurosteroid allopregnanolone (ALLO); drinking was increased in hour 1, decreased in hours 2 and 3, and increased in hours 4 and 5 postinjection. THIP (8 mg/kg) and FIN both decreased 10E drinking during the first 5 hours postinjection by 30 and 53%, respectively, while having no effect on or increasing water drinking, respectively. All 3 drugs altered the initiation of drinking sessions in a dose-dependent fashion. FIN increased and GAN decreased time to first lick and first bout. THIP (8 mg/kg) decreased time to first lick but increased time to first bout and attenuated first bout size.. The present findings support a role for the modulation of ethanol intake by neurosteroids and GABA(A) receptor-acting compounds and provide hints as to how drinking patterns are shifted. The ability of THIP to alter 10E drinking suggests that extrasynaptic GABA(A) receptors may be involved in the modulation of ethanol intake. Further, the consistent results with THIP to that seen previously with high doses of ALLO suggest that future studies should further examine the relationship between neurosteroids and extrasynaptic GABA(A) receptors, which could provide a better understanding of the mechanism by which neurosteroids influence ethanol intake.

Topics: Alcohol Drinking; Animals; Behavior, Animal; Dose-Response Relationship, Drug; Drinking Behavior; Finasteride; GABA-A Receptor Agonists; Isoxazoles; Male; Mice; Mice, Inbred C57BL; Models, Animal; Pregnanolone; Receptors, GABA-A