Chronic Treatment with Mood-Stabilizers Attenuates Abnormal Hyperlocomotion of GluA1-Subunit Deficient Mice

Peer reviewe

GABA(B) receptor positive allosteric modulators with different efficacies affect neuroadaptation to and self-administration of alcohol and cocaine

Drugs of abuse induce widespread synaptic adaptations in the mesolimbic dopamine (DA) neurons. Such drug-induced neuroadaptations may constitute an initial cellular mechanism eventually leading to compulsive drug-seeking behavior. To evaluate the impact of GABA(B) receptors on addiction-related persistent neuroplasticity, we tested the ability of orthosteric agonist baclofen and two positive allosteric modulators (PAMs) of GABA(B) receptors to suppress neuroadaptations in the ventral tegmental area (VTA) and reward-related behaviors induced by ethanol and cocaine. A novel compound (S)-1-(5-fluoro-2,3-dihydro-1H-inden-2-yl)-4-methyl-6,7,8,9-tetrahydro-[1,2,4]triazolo[4,3-a]quinazolin-5(4H)-one (ORM-27669) was found to be a GABA(B) PAM of low efficacy as agonist, whereas the reference compound (R,S)-5,7-di-tert-butyl-3-hydroxy-3-trifluoromethyl-3H-benzofuran-2-one (rac-BHFF) had a different allosteric profile being a more potent PAM in the calcium-based assay and an agonist, coupled with potent PAM activity, in the [S-35] GTP gamma S binding assay in rat and human recombinant receptors. Using autoradiography, the high-efficacy rac-BHFF and the low-efficacy ORM-27669 potentiated the effects of baclofen on [S-35] GTP gamma S binding with identical brain regional distribution. Treatment of mice with baclofen, rac-BHFF, or ORM-27669 failed to induce glutamate receptor neuroplasticity in the VTA DA neurons. Pretreatment with rac-BHFF at non-sedative doses effectively reversed both ethanol- and cocaine-induced plasticity and attenuated cocaine i.v. self-administration and ethanol drinking. Pretreatment with ORM-27669 only reversed ethanol-induced neuroplasticity and attenuated ethanol drinking but had no effects on cocaine-induced neuroplasticity or self-administration. These findings encourage further investigation of GABA(B) receptor PAMs with different efficacies in addiction models to develop novel treatment strategies for drug addiction.Peer reviewe

Importance of GluA1 Subunit-Containing AMPA Glutamate Receptors for Morphine State-Dependency

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Conditioned Aversion and Neuroplasticity Induced by a Superagonist of Extrasynaptic GABAA Receptors: Correlation With Activation of the Oval BNST Neurons and CRF Mechanisms

tTHIP (gaboxadol), a superagonist of the delta subunit-containing extrasynaptic GABA(A) receptors, produces persistent neuroplasticity in dopamine (DA) neurons of the ventral tegmental area (VTA), similarly to rewarding drugs of abuse. However, unlike them THIP lacks abuse potential and induces conditioned place aversion in mice. The mechanism underlying the aversive effects of THIP remains elusive. Here, we show that mild aversive effects of THIP were detected 2 h after administration likely reflecting an anxiety-like state with increased corticosterone release and with central recruitment of corticotropin-releasing factor corticotropin-releasing factor receptor 1 (CRF1) receptors. A detailed immunohistochemical c-Fos expression mapping for THIP-activated brain areas revealed a correlation between the activation of CRF-expressing neurons in the oval nucleus of the bed nuclei of stria terminalis and THIP-induced aversive effects. In addition, the neuroplasticity of mesolimbic DA system (24 h after administration) and conditioned place aversion by THIP after four daily acute sessions were dependent on extrasynaptic GABAA receptors (abolished in delta-GABA(A) receptor knockout mice) and activation of the CRF1 receptors (abolished in wildtype mice by a CRF1 receptor antagonist). A selective THIP-induced activation of CRF-expressing neurons in the oval part of the bed nucleus of stria terminalis may constitute a novel mechanism for inducing plasticity in a population of VTA DA neurons and aversive behavioral states.Peer reviewe

Increased Motor-Impairing Effects of the Neuroactive Steroid Pregnanolone in Mice with Targeted Inactivation of the GABA(A) Receptor gamma 2 Subunit in the Cerebellum

Endogenous neurosteroids and neuroactive steroids have potent and widespread actions on the brain via inhibitory GABA(A) receptors. In recombinant receptors and genetic mouse models their actions depend on the alpha, beta, and delta subunits of the receptor, especially on those that form extrasynaptic GABA(A) receptors responsible for non-synaptic (tonic) inhibition, but they also act on synaptically enriched gamma 2 subunit containing receptors and even on alpha beta binary receptors. Here we tested whether behavioral sensitivity to the neuroactive steroid agonist 5 beta-pregnan-3 alpha-ol-20-one is altered in genetically engineered mouse models that have deficient GABA(A) receptor mediated synaptic inhibition in selected neuronal populations. Mouse lines with the GABA(A) receptor gamma 2 subunit gene selectively deleted either in parvalbumin-containing cells (including cerebellar Purkinje cells), cerebellar granule cells, or just in cerebellar Purkinje cells were trained on the accelerated rotating rod and then tested for motor impairment after cumulative intraperitoneal dosing of 5 beta-pregnan-3 alpha-ol-20-one. Motor impairing effects of 5 beta-pregnan-3 alpha-ol-20-one were strongly increased in all three mouse models in which gamma 2 subunit-dependent synaptic GABA(A) responses in cerebellar neurons were genetically abolished. Furthermore, rescue of postsynaptic GABA(A) receptors in Purkinje cells normalized the effect of the steroid. Anxiolytic/explorative effects of the steroid in elevated plus maze and light:dark exploration tests in mice with Purkinje cell gamma 2 subunit inactivation were similar to those in control mice. The results suggest that, when the deletion of gamma 2 subunit has removed synaptic GABA(A) receptors from the specific cerebellar neuronal populations, the effects of neuroactive steroids solely on extrasynaptic alpha beta or alpha beta delta receptors lead to enhanced changes in the cerebellum-generated behavior.Peer reviewe

Addiction-related interactions of pregabalin with morphine in mice and humans : reinforcing and inhibiting effects

The gabapentinoid pregabalin is a rapid-acting anxiolytic and analgesic, possibly suitable in supervised opioid detoxification. However, clinicians have been cautious in using it because of its unknown addictive risk and rising number of mortalities after pregabalin self-medication in opioid abusers. Here, we studied interactions of pregabalin and morphine on reward functions of the dopamine system in mice and the efficacy of pregabalin on withdrawal in opioid addicts. After the treatment of mice with pregabalin and morphine, we used electrophysiology to study neuroplasticity in midbrain slices, self-administration and conditioned place preference tests to investigate the rewarding potential of pregabalin and naloxone-precipitated morphine withdrawal to evaluate opioid withdrawal symptoms. Further, we ran a pilot single-blind, randomized, controlled trial (34 heroin addicts) to evaluate the efficacy and safety of pregabalin in the treatment of opioid withdrawal syndrome. Pregabalin alone did not induce glutamate receptor neuroplasticity of dopamine neurons in the ventral tegmental area, but pre-treatment with pregabalin suppressed morphine-induced neuroplasticity, hyperlocomotion and morphine self-administration. Pregabalin administration after chronic morphine exposure failed to induce any rewarding effects. Instead, pregabalin suppressed withdrawal symptoms in both morphine-treated mice and opioid addicts and was well tolerated. Intriguingly, pregabalin administration after a low dose of morphine strongly facilitated ventral tegmental area neuroplasticity and led to increased conditioned place preference. Pregabalin appears to have the efficacy to counteract both reinforcing and withdrawal effects of opioids, but it also has a potentiating effect when given to mice with existing opioid levels.Peer reviewe

Does ethanol act preferentially via selected brain GABAA receptor subtypes? the current evidence is ambiguous

In rodent models, γ-aminobutyric acid A (GABAA) receptors with the α6 and δ subunits, expressed in the cerebellar and cochlear nucleus granule cells, have been linked to ethanol sensitivity and voluntary ethanol drinking. Here, we review the findings. When considering both in vivo contributions and data on cloned receptors, the evidence for direct participation of the α6-containing receptors to increased ethanol sensitivity is poor. The α6 subunit-knockout mouse lines do not have any changed sensitivity to ethanol, although these mice do display increased benzodiazepine sensitivity. However, in general the compensations occurring in knockout mice (regardless of which particular gene is knocked out) tend to fog interpretations of drug actions at the systems level. For example, the α6 knockout mice have increased TASK-1 channel expression in their cerebellar granule cells, which could influence sensitivity to ethanol in the opposite direction to that obtained with the α6 knockouts. Indeed, TASK-1 knockout mice are more impaired than wild types in motor skills when given ethanol; this might explain why GABAA receptor α6 knockout mice have unchanged ethanol sensitivities. As an alternative to studying knockout mice, we examined the claimed δ subunit-dependent/γ2 subunit-independent ethanol/[3H]Ro 15-4513 binding sites on GABAA receptors. We looked at [3H]Ro 15-4513 binding in HEK 293 cell membrane homogenates containing rat recombinant α6/4β3δ receptors and in mouse brain sections. Specific high-affinity [3H]Ro 15-4513 binding could not be detected under any conditions to the recombinant receptors or to the cerebellar sections of γ2(F77I) knockin mice, nor was this binding to brain sections of wild-type C57BL/6 inhibited by 1–100 mM ethanol. Since ethanol may act on many receptor and channel protein targets in neuronal membranes, we consider the α6 (and α4) subunit-containing GABAA receptors unlikely to be directly responsible for any major part of ethanol's actions. Therefore, we finish the review by discussing more generally alcohol and GABAA receptors and by suggesting potential future directions for this research.This study and review was supported by the Finnish Foundation for Alcohol Studies, the Academy of Finland and the Sigrid Juselius Foundation.Peer reviewe

Removal of GABA(A) Receptor gamma 2 Subunits from Parvalbumin Neurons Causes Wide-Ranging Behavioral Alterations

Peer reviewe

The Role of α6 Subunit-containing GABAA Receptors in Behavioral Effects of Alcohol and Drug Treatments

α6-Alayksikön sisältävien GABAA-reseptorien merkitystä alkoholi- ja lääkekäsittelyjen aiheuttamiin käyttäytymisvaikutuksiin tutkittiin käyttäen kahta erilaista geneettistä jyrsijämallia. Näille reseptorialatyypeille ei ole selektiivisiä ligandeja joten geneettistä muokkausta käytettiin alayksikön merkityksen selvittämiseksi. a6-Alayksikkö ilmenee ainoastaan pikkuaivojen jyvässoluissa ja sen sisältämät reseptorit ovat epäherkkiä bentsodiatsepiinien sitoutumispaikan agonisteille kuten diatsepaamille, ainakin in vitro. Tämä helpottaa tulosten tulkintaa arvioitaessa tämän reseptorialatyypin roolia käyttäytymisessä. Pistemutaatio rottamallissa (ANT/AT rotat) tekee normaalisti bentsodiatsepiiniagonisti-epäherkistä a6-alayksikön sisältävistä GABAA-reseptoreista herkkiä bentsodiatsepiiniagonisteille. a6-Poistogeenisessä hiirikannassa (a6-/-) a6-alayksikköä koodaava geeni on inaktivoitu, joten a6-alayksikköä ei ilmennetä a6-/- hiirissä. a6-Alayksikön puuttuminen ei vaikuttanut hiirten motorisiin toimintoihin lukuunottamatta diatsepaamin aiheuttaman liikesuorituksen heikkenemisen voimistumista. Lisäksi a6-/- hiirten ahdistuneisuuden taso oli lievästi kohonnut ja niiden latenssi korkean lämpötilan aiheuttamalle kivulle pidentynyt. a6-Alayksikön puuttumisella ei ollut vaikutusta toleranssin kehittymiseen alkoholin ja diatsepaamin liikesuoritusta heikentävälle vaikutukselle. Krooninen altistus kohtuullisille alkoholiannoksille ei vaikuttanut a6-geenin transkription säätelyyn. Poistogeeninen a6-/- hiirikanta ja mutantti rottamalli eroavat luonnostaan toisistaan, mahdollistaen siten erilaisten GABAA-reseptori-alatyyppien merkityksen tutkimisen pikkuaivojen fysiologiassa. a6-Alayksikön sisältävien GABAA-reseptorien farmakologista aktivointia tulisi välttää jotta rajoitetaan liikesuorituksen heikkeneminen. Niiden aktivaatio saattaa tosin lievittää ahdistusta. Villityypin a6-alayksikkö reseptorikompleksissa estää epänormaalin voimakkaan diatsepaamiherkkyyden, mutta a6-alayksikkö ei osallistu toleranssin kehittymiseen kroonisissa alkoholi- ja diatsepaamikäsittelyissä.The role of a6 subunit-containing GABAA receptors in behavioral effects of alcohol and drug treatments was studied by using two different genetic rodent models. The shortage of selective ligands to probe these receptors in vivo forces to use genetic modifications to identify significance of the subunit. Well-known localization of the a6 subunit expression in the cerebellar and cochlear nucleus granule cells and its pharmacological insensitivity to diazepam, a benzodiazepine (BZ) site agonist, assure interpretation of behavioral results. The point mutation in rat model (ANT/AT rat lines) makes the normally BZ agonist-insensitive a6 subunit-containing GABAA receptors BZ agonist-sensitive. In the a6 knockout mouse line the a6 subunit gene is inactivated and, consequently, a6 subunit is not produced in the a6-/- mice. The lack of the a6 subunit did not affect the motor functions in mice but exclusively increased motor-impairing effect of diazepam. The slightly increased anxiety level and slowed latency to thermal pain were additional phenotypic features of the a6-/- mice. The lack of the a6 subunit was not crucial for the development of tolerance to motor-impairing effects of ethanol and diazepam. Chronic administration of moderate ethanol doses did not affect the transcriptional control of the a6 subunit gene. Moreover, the knockout mouse and mutant rat models are inherently distinct and allow studying different aspects of cerebellar GABAA receptor function. Thus, the activation of a6 subunit-containing GABAA receptors should be avoided to limit impairment of motor performance, although this action might contribute to anxiolysis. The presence of the wild-type a6 subunit staves off abnormally strong diazepam sensitivity, although this subunit does not participate in tolerance development to chronic ethanol and diazepam administrations