The influence of modulation of [alpfa]5 subunit-containing GABAA receptors on the behavioral deficits induced by dizocilpine, scopolamine and amphetamine in rats

Poslednjih godina intenzivirana su istraživanja čiji je cilj razvoj adekvatnih terapijskih opcija za kognitivne deficite koji se javljaju u shizofreniji, ali i drugim poremećajima koje prati kognitivno propadanje. Posebno su važni napori da se poveća translaciona validnost animalnih testova i modela, među kojima veliki značaj imaju testovi vizuelnog učenja i pamćenja (test prepoznavanja novog objekta, Morrisov vodeni lavirint) i socijalne kognicije (procedura socijalnog prepoznavanja). Imajući u vidu ulogu GABA-ergičkog sistema u procesima učenja i pamćenja, modulacija GABAA receptora je predložena kao potencijalno koristan pristup kod poremećaja povezanih sa smanjenjem kognitivnih sposobnosti. Promene utvrđene post mortem na mozgovima pacijenata sa shizofrenijom upućuju na promene u GABA-ergičkom sistemu, ne samo u nivou GAD67 i parvalbumin pozitivnih neurona, već i u nivou α5 subjedinice GABAA receptora. Kao potencijalno nova terapijska opcija u lečenju kognitivnih deficita predložena je modulacija α5 GABAA receptora, shodno njihovoj specifičnoj lokalizaciji i afirmativnim rezultatima dobijenim na životinjama kod kojih postoji potpun ili delimičan gubitak ovih receptora. Studije sprovedene sa više inverznih agonista BDZ mesta vezivanja α5 GABAA receptora pokazale su određeni prokognitivni potencijal ovih liganada u pretkliničkim istraživanjima. I pored određenih iskustava u ispitivanjima na ljudima, u kliničkoj praksi nema nootropnih lekova koji su inverzni agonisti BDZ mesta vezivanja α5 GABAA receptora, delom zbog neadekvatne podnošljivosti. Aktuelna su postala ispitivanja uloge kako negativne, tako i pozitivne modulacije α5 GABAA receptora u poboljšanju kognitivnih deficita. U našem istraživanju korišćeni su inverzni agonist PWZ-029 i pet agonista (MP-III-022, MP-III-004, SH-053-2’F-R-CH3, SH-I-75 i SH-I-047) BDZ mesta vezivanja na α5 GABAA receptoru. Naši rezultati pokazuju da negativni modulator α5 GABAA receptora PWZ-029 u animalnim modelima relevantnim za oštećenja viđena u shizofreniji ispoljava preventivno dejstvo na razvoj pojedinih promena. Korišćeni su dobro validirani pretklinički modeli: hipofunkcija NMDA receptora izazvana primenom MK-801, hiperdopaminergičko stanje izazvano amfetaminom, kao i promene indukovane antagonistom muskarinskih receptora skopolaminom...In recent years, intensive efforts have been made to develop adequate therapies for cognitive deficits associated with schizophrenia and other disorders marked by cognitive deterioration. Of especial importance are activities aimed to further enhance translational value of animal models and tests, most notably those assessing visual learning and memory (novel object recognition test, Morris water maze) and social cognition (social novelty discrimination). Having in mind the involvement of GABAergic system in processes of learning and memory, the modulation of GABAA receptors has been suggested as a potentially useful pharmacologic approach to the treatment of disorders with decreased cognitive abilities. The post mortem changes seen in schizophrenic patients’ brains pointed to differences in GABAergic system, not only in level of GAD67 and parvalbumin positive neurons, but also in the degree of α5 subunit of GABAA receptors. Modulation of α5 GABAA receptors has been proposed as a potentially novel therapeutic option in treating cognitive deficits, which corresponds well with the specific localization of α5 GABAA receptors and affirmative results from animals with partial or full depletion of these receptors. Moreover, studies with inverse agonists of α5 GABAA receptors have revealed their procognitive potential in preclinical settings. Although there exist some data in humans, no nootropic drugs acting as inverse agonists at α5 GABAA receptors have been approved so far, in part due to their inadequate tolerability. The examinations of the role of both, negative and positive modulation of α5 GABAA receptors in amelioration of cognitive deficits are in progress. In the present study, we used one inverse agonist, PWZ-029 and five agonists (MP-III-022, MP-III-004, SH-053-2’F-R-CH3, SH-I-75 and SH-I-047) of the benzodiazepine (BDZ) binding site at α5 GABAA receptors. Our results demonstrated that the negative modulator of α5 GABAA receptors, PWZ-029, exerts protective effects on development of distinct changes in animal models relevant to deficits seen in schizophrenia. The highly validated preclinical models: hypofunction of NMDA receptors induced by MK-801, amphetamine-induced hyperdopaminergic state as well as changes induced by muscarinic receptors antagonist, scopolamine, have been used. In tests that assessed cognitive ability of rats, PWZ-029 achieved a significant beneficial effect on deficits induced by MK-801 and scopolamine..

Negative modulation of alpha(5) GABA(A) receptors in rats may partially prevent memory impairment induced by MK-801, but not amphetamine- or MK-801-elicited hyperlocomotion

Reportedly, negative modulation of alpha(5) GABA(A) receptors may improve cognition in normal and pharmacologically-impaired animals, and such modulation has been proposed as an avenue for treatment of cognitive symptoms in schizophrenia. This study assessed the actions of PWZ-029, administered at doses (2, 5, and 10 mg/kg) at which it reached micromolar concentrations in brain tissue with estimated free concentrations adequate for selective modulation of alpha(5) GABA(A) receptors, in three cognitive tasks in male Wistar rats acutely treated with the noncompetitive N-methyl-D-aspartate receptor antagonist, MK-801 (0.1 mg/kg), as well in tests of locomotor activity potentiated by MK-801 (0.2 mg/kg) or amphetamine (0.5 mg/kg). In a hormetic-like manner, only 5 mg/kg PWZ-029 reversed MK-801-induced deficits in novel object recognition test (visual recognition memory), whereas in the Morris water maze, the 2 mg/kg dose of PWZ-029 exerted partial beneficial effects on spatial learning impairment. PWZ-029 did not affect recognition memory deficits in social novelty discrimination procedure. Motor hyperactivity induced with MK-801 or amphetamine was not preventable by PWZ-029. Our results show that certain MK-801-induced memory deficits can be ameliorated by negative modulation of alpha(5) GABA(A) receptors, and point to the need for further elucidation of their translational relevance to cognitive deterioration in schizophrenia

PWZ-029, an inverse agonist selective for alpha(5) GABA(A) receptors, improves object recognition, but not water-maze memory in normal and scopolamine-treated rats

Inverse agonism at the benzodiazepine site of alpha(5) subunit-containing GABA(A) receptors is an attractive approach for the development of putative cognition-enhancing compounds, which are still far from clinical application. Several ligands with binding and/or functional selectivity for alpha(5) GABA(A) receptors have been synthesized and tested in a few animal models. PWZ-029 is an alpha(5) GABA(A) selective inverse agonist whose memory enhancing effects were demonstrated in the passive avoidance task in rats and in Pavlovian fear conditioning in mice. In the present study we investigated the effects of PWZ-029 administration in novel object recognition test and Morris water maze, in normal and scopolamine-treated rats. All the three doses of PWZ-029 (2,5 and 10 mg/kg) improved object recognition after the 24-h delay period, as shown by significant differences between the exploration times of the novel and old object, and the respective discrimination indices. PWZ-029 (2 mg/kg) also successfully reversed the 0.3 mg/kg scopolamine-induced deficit in recognition memory after the 1-h delay. In the Morris water maze test, PWZ-029 (5,10 and 15 mg/kg) did not significantly influence swim patterns, either during five acquisition days or during the treatment-free probe trial. PWZ-029 (2, 5 and 10 mg/kg) also proved to be ineffective in the reversal of the 1 mg/kg scopolamine-induced memory impairment in the water maze. The present mixed results encourage use of a variety of tests and experimental conditions in order to increase the predictability of preclinical testing of selective as GABA(A) inverse agonists

Odloženi bihejvioralni efekti SH-I-048A, novog neselektivnog pozitivnog modulatora GABAA receptora, nakon povrede perifernog nerva pacova

The complex clinical picture of mono-neuropathy following injury of peripheral nerve is often accompanied by changes in the patients' affective states. It has been shown that positive allosteric modulators of GABAA receptors can decrease nociceptive transmission in animal pain models. However, recent findings suggest a possibility that at least some of the antinociceptive effects of benzodiazepines, related to neuropathic painful stimuli, may to a significant degree be a consequence of their anxiolytic action. In this study we evaluated the possible delayed effects of SH-I-048A, a newly- synthesized high-efficacy nonselective positive modulator of GABAA receptors, on anxiety-like behavior and locomotor activity in Wistar rats with a previously induced peripheral nerve injury. Assessment of behavioral parameters, using spontaneous locomotor activity and elevated plus maze tests, was performed 48h after completion of single-day three i.p. injections treatment consisting of zero, one, two or three doses of SH-I-048A (10 mg/kg). In general, rats' behavior observed 72 h after a moderate peripheral nerve injury did not indicate the persistence of sequelae of mono-neuropathic pain. The rats treated with three doses of SH-I-048A displayed an enhanced immobility time in the locomotor activity test, without concomitant decrease of the total distance traveled. On the other hand, in the group treated with two doses of SH-I-048A, a decrease in the emotional reactivity in the elevated plus maze test was observed. Subtle changes in the regimen of dosing of SH-I-048A affect locomotor activity and anxiety-related behavior in animals with peripheral nerve injury.Kompleksna klinička slika neuropatije nakon povrede perifernog nerva često je praćena i promenama afektivnog stanja pacijenata. U animalnim modelima bola pokazano je da pozitivni alosterni modulatori GABAA receptora mogu da smanje nociceptivnu transmisiju. Međutim, skorašnji nalazi ukazuju i na mogućnost da je prividni antinociceptivni efekat benzodiazepina nakon delovanja akutnog bolnog stimulusa u značajnoj meri posledica anksiolitičnog efekta. U ovoj studiji ispitani su mogući odloženi efekti novosintetisanog, neselektivnog liganda GABAA receptora (SH-I-048A) na lokomotornu aktivnost i ponašanje u vezi sa anksioznošću kod pacova soja Wistar prethodno podvrgnutih povredi perifernog nerva. Procena bihejvioralnih parametara sprovedena je testovima spontane lokomotorne aktivnosti i uzdignutog plus lavirinta 48 sati nakon što su životinje u periodu od 24 sata primile rastvarač, jednu, dve ili tri doze SH-I-048A (10 mg/kg). Generalno, ponašanje pacova praćeno 72 sata nakon umerene povrede perifernog nerva nije ukazivalo na prisustvo perzistentnih posledica neuropatskog bola. Pacovi prethodno tretirani sa tri doze SH-I-048A ispoljili su povećano vreme imobilnosti u testu lokomotorne aktivnosti, bez značajnog smanjenja ukupnog pređenog puta. S druge strane, u grupi koja je tretirana sa dve doze SH-I-048A zapažena je smanjena emocionalna reaktivnost u uzdignutom plus lavirintu. Kod životinja sa povredom perifernog nerva, suptilne razlike u režimu doziranja pozitivnog modulatora GABAA, mogu značajno da utiču na ponašanje vezano za lomotornu aktivnost i nivo anksioznosti

The role of alpha(1) and alpha(5) subunit-containing GABA(A) receptors in motor impairment induced by benzodiazepines in rats

Benzodiazepines negatively affect motor coordination and balance and produce myorelaxation. The aim of the present study was to examine the extent to which populations of gamma-aminobutyric acid A (GABA(A)) receptors containing alpha(1) and alpha(5) subunits contribute to these motor-impairing effects in rats. We used the nonselective agonist diazepam and the alpha(1)-selective agonist zolpidem, as well as nonselective, alpha(1)-subunit and alpha(5)-subunit-selective antagonists flumazenil, beta CCt, and XLi093, respectively. Ataxia and muscle relaxation were assessed by rotarod and grip strength tests performed 20 min after intraperitoneal treatment. Diazepam (2 mg/kg) induced significant ataxia and muscle relaxation, which were completely prevented by pretreatment with flumazenil (10mg/kg) and beta CCt (20 mg/kg). XLi093 antagonized the myorelaxant, but not the ataxic actions of diazepam. All three doses of zolpidem (1, 2, and 5 mg/kg) produced ataxia, but only the highest dose (5 mg/kg) significantly decreased the grip strength. These effects of zolpidem were reversed by beta CCt at doses of 5 and 10 mg/kg, respectively. The present study demonstrates that alpha(1) GABA(A) receptors mediate ataxia and indirectly contribute to myorelaxation in rats, whereas alpha(5) GABA(A) receptors contribute significantly, although not dominantly, to muscle relaxation but not ataxia. Behavioural Pharmacology 23:191-19

beta CCT, an antagonist selective for alpha(1)GABA(A) receptors, reverses diazepam withdrawal-induced anxiety in rats

The abrupt discontinuation of prolonged benzodiazepine treatment elicits a withdrawal syndrome with increased anxiety as a major symptom. The neural mechanisms underlying benzodiazepine physical dependence are still insufficiently understood. Flumazenil, the non-selective antagonist of the benzodiazepine binding site of GABA(A) receptors was capable of preventing and reversing the increased anxiety during benzodiazepine withdrawal in animals and humans in some, but not all studies. On the other hand, a number of data suggest that GABA(A) receptors containing alpha(1) subunits are critically involved in processes developing during prolonged use of benzodiazepines, such are tolerance to sedative effects, liability to physical dependence and addiction. Hence, we investigated in the elevated plus maze the level of anxiety 24 h following 21 days of diazepam treatment and the influence of flumazenil or a preferential alpha(1)-subunit selective antagonist beta CCt on diazepam withdrawal syndrome in rats. Abrupt cessation of protracted once-daily intraperitoneal administration of 2 mg/kg diazepam induced a withdrawal syndrome, measured by increased anxiety-like behavior in the elevated plus maze 24 h after treatment cessation. Acute challenge with either flumazenil (10 mg/kg) or beta CCt (1.25, 5 and 20 mg/kg) alleviated the diazepam withdrawal-induced anxiety. Moreover, both antagonists induced an anxiolytic-like response close, though not identical, to that seen with acute administration of diazepam. These findings imply that the mechanism by which antagonism at GABA(A) receptors may reverse the withdrawal-induced anxiety involves the alpha(1) subunit and prompt further studies aimed at linking the changes in behavior with possible adaptive changes in subunit expression and function of GABA(A) receptors

Ester to amide substitution improves selectivity, efficacy and kinetic behavior of a benzodiazepine positive modulator of GABA(A) receptors containing the alpha 5 subunit

We have synthesized and characterized MP-III-022 ((R)-8-ethynyl 6 (2 fluorophenyl)-N,4-dimethyl4H-benzo[f]imidazo[1,5-alpha][1,4]diazepine-3-carboxamide) in vitro and in vivo as a binding- and efficacy selective positive allosteric modulator of GABA(A) receptors containing the alpha 5 subunit (alpha 5GABA(A)Rs). By approximation of the electrophysiological responses which the estimated free rat brain concentrations can induce, we demonstrated that convenient systemic administration of MP-III-022 in the dose range 110 mg/kg may result in a selective potentiation, over a wide range from mild to moderate to strong, of alpha 5 beta gamma 2 GABA(A) receptors. For eliciting a comparable range of potentiation, the widely studied parent ligand SH-053-2'F-R-CH3 containing an ester moiety needs to be administered over a much wider dose range (10-200 mg/kg), but at the price of activating non-alpha 5 GABA(A)Rs as well as the desired alpha 5GABA(A)Rs at the highest dose. At the dose of 10 mg/kg, which elicits a strong positive modulation of alpha 5GABA(A)Rs, MP-III-022 caused mild, but significant muscle relaxation, while at doses 1-10 mg/kg was devoid of ataxia, sedation or an influence on the anxiety level, characteristic for non-selective benzodiazepines. As an amide compound with improved stability and kinetic properties, MP-III-022 may represent an optimized tool to study the influence of alpha 5GABA(A)Rs on the neuronal pathways related to CNS disorders such as schizophrenia, Alzheimer's disease, Down syndrome or autism

Duration of treatment and activation of alpha(1)-containing GABA(A) receptors variably affect the level of anxiety and seizure susceptibility after diazepam withdrawal in rats

Long-term use of benzodiazepine-type drugs may lead to physical dependence, manifested by withdrawal syndrome after abrupt cessation of treatment. The aim of the present study was to investigate the influence of duration of treatment, as well as the role of alpha(1)-containing GABA(A) receptors, in development of physical dependence to diazepam, assessed through the level of anxiety and susceptibility to pentylenetetrazole (PTZ)-induced seizures, 24 h after withdrawal from protracted treatment in rats. Withdrawal of 2 mg/kg diazepam after 28, but not after 14 or 21 days of administration led to an anxiety-like behavior in the elevated plus maze. Antagonism of the diazepam effects at alpha(1)-containing GABA(A) receptors, achieved by daily administration of the neutral modulator beta CCt (5 mg/kg), did not affect the anxiety level during withdrawal. An increased susceptibility to PTZ-induced seizures was observed during diazepam withdrawal after 21 and 28 days of treatment. Daily co-administration of beta CCt further decreased the PTZ-seizure threshold after 21 days of treatment, whilst it prevented the diazepam withdrawal-elicited decrease of the PTZ threshold after 28 days of treatment. In conclusion, the current study suggests that the role of alpha(1)-containing GABA(A) receptors in mediating the development of physical dependence may vary based on the effect being studied and duration of protracted treatment. Moreover, the present data supports previous findings that the lack of activity at alpha(1)-containing GABA(A) receptors is not sufficient to eliminate physical dependence liability of ligands of the benzodiazepine type

Insights into functional pharmacology of alpha(1) GABA(A) receptors: how much does partial activation at the benzodiazepine site matter?

Synthesis of ligands inactive or with low activity at alpha(1) GABA(A) receptors has become the key concept for development of novel, more tolerable benzodiazepine (BZ)-like drugs. WYS8, a remarkably (105 times) alpha(1)-subtype selective partial positive modulator, may serve as a pharmacological tool for refining the role of alpha(1) GABA(A) receptors in mediation of BZs' effects. Here, the effects of WYS8 on GABA-induced currents and on diazepam-induced potentiation of recombinant BZ-sensitive GABA(A) receptors were studied in more detail. In addition, the behavioral profile of WYS8 (0.2, 1, and 10 mg/kg i.p.), on its own and in combination with diazepam, was tested in the spontaneous locomotor activity, elevated plus maze, grip strength, rotarod, and pentylenetetrazole tests. WYS8, applied at an in vivo attainable concentration of 100 nM, reduced the stimulation of GABA currents by 1 mu M diazepam by 57 % at alpha(1)beta(3)gamma(2), but not at alpha(2)beta(3)gamma(2), alpha(3)beta(3)gamma(2), or alpha(5)beta(3)gamma(2) GABA(A) receptors. The administration of WYS8 alone induced negligible behavioral consequences. When combined with diazepam, WYS8 caused a reduction in sedation, muscle relaxation, and anticonvulsant activity, as compared with this BZ alone, whereas ataxia was preserved, and the anxiolytic effect of 2 mg/kg diazepam was unmasked. Hence, a partial instead of full activation at alpha(1) GABA(A) receptors did not necessarily result in the attenuation of the effects assumed to be mediated by activation of these receptors, or in the full preservation of the effects mediated by activation of other GABA(A) receptors. Thus, the role of alpha(1) GABA(A) receptors appears more complex than that proposed by genetic studies

Sex-Dependent Anti-Stress Effect of an alpha 5 Subunit Containing GABA(A) Receptor Positive Allosteric Modulator

Rationale: Current first-line treatments for stress related disorders such as major depressive disorder (MDD) act on monoaminergic systems and take weeks to achieve a therapeutic effect with poor response and low remission rates. Recent research has implicated the GABAergic system in the pathophysiology of depression, including deficits in interneurons targeting the dendritic compartment of cortical pyramidal cells. Objectives: The present study evaluates whether SH-053-2'F-R-CH3 (denoted "alpha 5-PAM"), a positive allosteric modulator selective for (alpha 5-subunit containing GABA(A) receptors found predominantly on cortical pyramidal cell dendrites, has anti stress effects. Methods: Female and male C57BL6/J mice were exposed to unpredictable chronic mild stress (UCMS) and treated with alpha 5-PAM acutely (30 min prior to assessing behavior) or chronically before being assessed behaviorally. Results: Acute and chronic alpha 5-PAM treatments produce a pattern of decreased stress induced behaviors (denoted as "behavioral emotionality") across various tests in female, but not in male mice. Behavioral Z-scores calculated across a panel of tests designed to best model the range and heterogeneity of human symptomatology confirmed that acute and chronic alpha 5-PAM treatments consistently produce significant decreases in behavioral emotionality in several independent cohorts of females. The behavioral responses to alpha 5-PAM could not be completely accounted for by differences in drug brain disposition between female and male mice. In mice exposed to UCMS, expression of the Gabra5 gene was increased in the frontal cortex after acute treatment and in the hippocampus after chronic treatment with alpha 5-PAM in females only, and these expression changes correlated with behavioral emotionality. Conclusion: We showed that acute and chronic positive modulation of alpha 5 subunit containing GABA(A) receptors elicit anti-stress effects in a sex-dependent manner, suggesting novel therapeutic modalities