Antisense inhibition of striatal GABAA receptor proteins decreases GABA-stimulated chloride uptake and increases cocaine sensitivity in rats

A quantitative trait variant in Gabra2 underlies increased methamphetamine stimulant sensitivity

Psychostimulant (methamphetamine, cocaine) use disorders have a genetic component that remains mostly unknown. We conducted genome-wide quantitative trait locus (QTL) analysis of methamphetamine stimulant sensitivity. To facilitate gene identification, we employed a Reduced Complexity Cross between closely related C57BL/6 mouse substrains and examined maximum speed and distance traveled over 30 min following methamphetamine (2 mg/kg, i.p.). For maximum methamphetamine-induced speed following the second and third administration, we identified a single genome-wide significant QTL on chromosome 11 that peaked near the Cyfip2 locus (LOD = 3.5, 4.2; peak = 21 cM [36 Mb]). For methamphetamine-induced distance traveled following the first and second administration, we identified a genome-wide significant QTL on chromosome 5 that peaked near a functional intronic indel in Gabra2 coding for the alpha-2 subunit of the GABA-A receptor (LOD = 3.6-5.2; peak = 34-35 cM [66-67 Mb]). Striatal cis-expression QTL mapping corroborated Gabra2 as a functional candidate gene underlying methamphetamine-induced distance traveled. CRISPR/Cas9-mediated correction of the mutant intronic deletion on the C57BL/6J background to the wild-type C57BL/6NJ allele was sufficient to reduce methamphetamine-induced locomotor activity toward the wild-type C57BL/6NJ-like level, thus validating the quantitative trait variant (QTV). These studies show the power and efficiency of Reduced Complexity Crosses in identifying causal variants underlying complex traits. Functionally restoring Gabra2 expression decreased methamphetamine stimulant sensitivity and supports preclinical and human genetic studies implicating the GABA-A receptor in psychostimulant addiction-relevant traits. Importantly, our findings have major implications for studying psychostimulants in the C57BL/6J strain-the gold standard strain in biomedical research.

Silencing the α2 subunit of γ-aminobutyric acid type A receptors in rat dorsal root ganglia reveals its major role in antinociception posttraumatic nerve injury

BACKGROUND

Neuropathic pain (NPP) is likely the result of repetitive high-frequency bursts of peripheral afferent activity leading to long-lasting changes in synaptic plasticity in the spinal dorsal horn. Drugs that promote γ-aminobutyric acid (GABA) activity in the dorsal horn provide partial relief of neuropathic symptoms. The authors examined how in vivo silencing of the GABA receptor type A (GABAA) α2 gene in dorsal root ganglia (DRG) controls NPP.

METHODS

After crush injury to the right sciatic nerve of female rats, the α2 GABAA antisense and mismatch oligodeoxynucleotides or NO-711 (a GABA uptake inhibitor) were applied to the L5 DRG. In vivo behavioral assessment of nociception was conducted before the injury and ensuing 10 days (n = 4 to 10). In vitro quantification of α2 GABAA protein and electrophysiological studies of GABAA currents were performed on acutely dissociated L5 DRG neurons at relevant time points (n = 6 to 14).

RESULTS

NPP postcrush injury of a sciatic nerve in adult female rats coincides with significant down-regulation of the α2 subunit expression in the ipsilateral DRG (approximately 30%). Selective down-regulation of α2 expression in DRGs significantly worsens mechanical (2.55 ± 0.75 to 5.16 ± 1.16) and thermal (7.97 ± 0.96 to 5.51 ± 0.75) hypersensitivity in crush-injured animals and causes development of significant mechanical (2.33 ± 0.40 to 5.00 ± 0.33) and thermal (10.80 ± 0.29 to 7.34 ± 0.81) hypersensitivity in sham animals (data shown as mean ± SD). Conversely, up-regulation of endogenous GABA via blockade of its uptake in DRG alleviates NPP.

CONCLUSION

The GABAA receptor in the DRG plays an important role in pathophysiology of NPP caused by sciatic nerve injury and represents promising target for novel pain therapies.

Olfactory Hallucinations without Clinical Motor Activity: A Comparison of Unirhinal with Birhinal Phantosmia

Olfactory hallucinations without subsequent myoclonic activity have not been well characterized or understood. Herein we describe, in a retrospective study, two major forms of olfactory hallucinations labeled phantosmias: one, unirhinal, the other, birhinal. To describe these disorders we performed several procedures to elucidate similarities and differences between these processes. From 1272, patients evaluated for taste and smell dysfunction at The Taste and Smell Clinic, Washington, DC with clinical history, neurological and otolaryngological examinations, evaluations of taste and smell function, EEG and neuroradiological studies 40 exhibited cyclic unirhinal phantosmia (CUP) usually without hyposmia whereas 88 exhibited non-cyclic birhinal phantosmia with associated symptomology (BPAS) with hyposmia. Patients with CUP developed phantosmia spontaneously or after laughing, coughing or shouting initially with spontaneous inhibition and subsequently with Valsalva maneuvers, sleep or nasal water inhalation; they had frequent EEG changes usually ipsilateral sharp waves. Patients with BPAS developed phantosmia secondary to several clinical events usually after hyposmia onset with few EEG changes; their phantosmia could not be initiated or inhibited by any physiological maneuver. CUP is uncommonly encountered and represents a newly defined clinical syndrome. BPAS is commonly encountered, has been observed previously but has not been clearly defined. Mechanisms responsible for phantosmia in each group were related to decreased gamma-aminobutyric acid (GABA) activity in specific brain regions. Treatment which activated brain GABA inhibited phantosmia in both groups.

Repetitive transcranial magnetic stimulation and drug addiction

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive brain stimulation technique that is now being tested for its ability to treat addiction. This review discusses current research approaches and results of studies which measured the therapeutic use of rTMS to treat tobacco, alcohol and illicit drug addiction. The research in this area is limited and therefore all studies evaluating the therapeutic use of rTMS in tobacco, alcohol or illicit drug addiction were retained including case studies through NCBI PubMed ( http://www.ncbi.nlm.nih.gov ) and manual searches. A total of eight studies were identified that examined the ability of rTMS to treat tobacco, alcohol and cocaine addiction. The results of this review indicate that rTMS is effective in reducing the level of cravings for smoking, alcohol, and cocaine when applied at high frequencies to the dorsolateral prefrontal cortex (DLPFC). Furthermore, these studies suggest that repeated sessions of high frequency rTMS over the DLPFC may be most effective in reducing the level of smoking and alcohol consumption. Although work in this area is limited, this review indicates that rTMS is a promising modality for treating drug addiction.

Effects of single and repeated phencyclidine administration on [3H]flunitrazepam binding in rat brain

Repeated administration of phencyclidine (PCP) induces behavioral sensitization to dopaminergic neural transmission. This phenomenon has been implicated in the pathophysiology of schizophrenia. Recently, GABAergic agonists have been shown to reduce behavioral activity induced by enhanced dopaminergic neural transmission, which is mediated by the GABA(A)/benzodiazepine (BZD) receptor complex. Thus, to investigate the role of BZD receptors during induction and expression of behavioral sensitization in PCP-sensitized animals, the effects of both single and repeated PCP administration on BZD receptors in rat brain were examined using in vitro quantitative autoradiography. Repeated PCP administration failed to significantly alter levels of [3H]flunitrazepam (FNZ) binding in any of the regions examined. However, significant increases in levels of [3H]FNZ binding were found in the nucleus accumbens and ventral pallidum 1 h after single administration of PCP. These results suggest that BZD binding sites may not play important roles in the development of PCP-induced sensitization at several sites of GABA(A)/BZD receptor complex, while changes in GABA function in the nucleus accumbens differ from other areas following single administration of N-methyl-D-aspartate (NMDA) antagonist.

Discrete cell gene profiling of ventral tegmental dopamine neurons after acute and chronic cocaine self-administration

Chronic cocaine administration induces a number of biochemical alterations within the mesolimbic dopamine system that may mediate various aspects of the addictive process such as sensitization, craving, withdrawal, and relapse. In the present study, rats were allowed to self-administer cocaine (0.5 mg/infusion) for 1 or 20 days. Tyrosine hydroxylase immunopositive cells were microdissected from the ventral tegmental area (VTA) using laser capture microdissection, and changes in the abundances of 95 mRNAs were assessed using cDNA macroarrays. Five GABA-A receptor subunit mRNAs (alpha4, alpha6, beta2, gamma2, and delta) were down-regulated at both 1 and 20 days of cocaine self-administration. In contrast, the catalytic subunit of protein phosphatase 2A (PP2alpha), GABA-A alpha1, and Galphai2 were significantly increased at both time points. Additionally, calcium/calmodulin-dependent protein kinase IIalpha mRNA levels were increased initially followed by a slight decrease after 20 days, whereas neuronal nitric-oxide synthase mRNA levels were initially decreased but returned to near control levels by day 20. These results indicate that alterations of specific GABA-A receptor subtypes and other signal transduction transcripts seem to be specific neuroadaptations associated with cocaine self-administration. Moreover, as subunit composition determines the functional properties of GABA-A receptors, the observed changes may indicate alterations in the excitability of dopamine transmission underlying long-term biochemical and behavioral effects of cocaine.

Reducing GABA receptors

A number of important drugs act on GABA(A) receptors, pentameric GABA-gated chloride channels assembled from among 19 known subunits. In trying to discover the roles in the brain of the subunits and their combinations, with the goal of developing more selective drugs, one tool has been to reduce expression of the subunits and examine the functional consequences. After briefly examining the properties of GABA(A) receptors, this review surveys the means available for receptor subunit reduction, and some of the observations to which their application has led. The methods discussed include radiation-induced deletion, gene knockout, knock-in mutations, antisense, ribozymes, RNA interference, dominant negative constructs, and transcriptional regulation, e.g., via decoy oligonucleotides.

Gamma-vinyl GABA, an irreversible inhibitor of GABA transaminase, alters the acquisition and expression of cocaine-induced sensitization in male rats

We examined the effect of (+/-)-gamma-vinyl GABA (GVG, Vigabatrin), an irreversible inhibitor of the enzyme GABA transaminase, on the acquisition and expression of cocaine-induced sensitization in albino male Sprague-Dawley rats. Animals received a single injection of 1 ml/kg i.p. of 0.9% saline or 15 mg/kg i.p. of (-)-cocaine and locomotor activity was assessed using automated locomotor cages and stereotyped behaviors were scored using a 4-point rating scale (Day 1). Subsequently, animals were given 15 mg/kg i.p. of cocaine every 48 h in their home cage for 1 week (Days 3, 5, and 7) and then given no treatment for 1 week. A challenge injection of 15 mg/kg i.p. of cocaine, but not vehicle, produced a significant increase in locomotor activity and stereotyped behaviors on Day 15 compared to animals that received cocaine on Day 1. Administration of 75 mg/kg i.p. of GVG 2.5 h before the cocaine injections did not significantly alter the acquisition of cocaine-induced locomotor sensitization. However, 150 mg/kg i.p. of GVG significantly attenuated the acquisition of cocaine-induced locomotor sensitization. Administration of 150 mg/kg i.p. of GVG 2.5 h before the cocaine challenge injection on Day 15 significantly attenuated the expression of cocaine-induced locomotor sensitization. Acquisition and expression of cocaine-induced sensitization of stereotypy was also significantly attenuated by 150 mg/kg i.p. of GVG. Since sensitization may be one of the factors involved in relapse to drug use, the present results, in combination with previous findings that GVG blocks the rewarding and incentive motivating effects of cocaine, suggest that GVG might prove useful in the treatment of cocaine addiction.

Site-specific administration of antisense oligonucleotides using biodegradable polymer microspheres provides sustained delivery and improved subcellular biodistribution in the neostriatum of the rat brain

Antisense oligonucleotides (ODNs) are being increasingly used in the central nervous system as biological tools, as drug-target validation agents and as potential therapeutic agents. Although the local delivery of naked ODNs to the brain can result in the desired biological effects, the duration of efficacy is relatively short lived due to the combined effects of rapid ODN degradation and elimination half-lives in vivo. In this study, we have examined the use of biodegradable polymer microspheres as a site-specific delivery system for targeting ODNs to the neostriatum of the rat brain. Model phosphorothioate backbone-modified ODNs were entrapped within poly(D,L-lactide-co-glycolide) (PLAGA) microspheres using a double emulsion-deposition method and the formulations characterised in terms of particle size, surface morphology, percent encapsulation efficiency, ODN loading and in vitro release profiles. For in vivo evaluation, PLAGA microspheres containing fluorescently-labelled ODNs were stereo-taxically administered to the neostriatum of the rat brain and biodistribution of ODNs monitored after 48 h. Administration of free fluorescently-labelled ODNs to the neostriatum resulted in a punctate cellular distribution of ODNs after 24 h with little or no ODN remaining in the neostriatum after 48 h. In comparison, fluorescently-labelled ODNs delivered using polymer microspheres were intensely visible in cells after 48 h post-administration and the fluorescence appeared to be diffuse covering both cytosolic and nuclear regions. Dual-label immunohistochemical analyses suggested that ODNs were mainly distributed to neuronal cells. These data indicate that site-specific administration of ODNs using biodegradable polymer microspheres will not only provide sustained delivery of nucleic acids but can also improve the cellular distribution of ODNs to brain cells. Sustained or controlled-release biodegradable polymer formulations, therefore, represent an attractive strategy for improved local delivery of ODNs to the CNS.

Elevated motor threshold in drug-free, cocaine-dependent patients assessed with transcranial magnetic stimulation

BACKGROUND

Transcranial magnetic stimulation (TMS) provides a noninvasive method of examining cortical inhibitory and excitatory processes and cortical excitability in awake subjects. There is evidence from clinical and electroencephalographic (EEG) data that cortical excitability may be abnormal in some psychiatric populations. Chronic cocaine abuse influences a number of neurotransmitters that are involved in the excitatory/inhibitory balance of the cerebral cortex. This pilot study was conducted to ascertain the possible utility of TMS in examining cortical excitability in a population of chronic cocaine abusers.

METHODS

The right and left motor thresholds of ten cocaine-dependent subjects, according to DSM-IV, and ten normal control subjects were examined using single pulse TMS.

RESULTS

The resting motor thresholds resulting from stimulation of the right or the left motor cortical regions were significantly elevated in cocaine-dependent subjects compared with matched control subjects.

CONCLUSIONS

These pilot data suggest that chronic cocaine use significantly alters cortical excitability in the direction of increased inhibition or decreased excitability. We hypothesize that this observation reflects adaptation to those effects of cocaine intoxication that promote cortical excitability and seizures.

Chronic cocaine differentially affects diazepam's anxiolytic and anticonvulsant actions. Relationship to GABA(A) receptor subunit expression

Benzodiazepines are used to treat the anxiety associated with cocaine withdrawal, as well as cocaine-induced seizures. Since cocaine exposure was shown to affect BZ binding density, abuse liability, subjective hypnotic actions and seizure susceptibility, we assessed whether chronic cocaine alters diazepam's anxiolytic and anticonvulsant actions. Changes in GABA(A) receptor subunit protein expression were also assessed as they may relate to BZ activity at the receptor. Male Sprague-Dawley rats were injected with cocaine-HCl (15 mg/kg, i.p.) or saline once daily for 14 days. One day after the last injection, DZP (1 mg/kg i.p.) significantly increased time spent on and entries into open arms of an elevated plus maze in both saline- and cocaine-treated groups, yet the effect was greater in cocaine-treated rats. Eight days after cessation of treatment DZP did not have a significant anxiolytic effect in either group. To assess the effect of cocaine on DZP's anticonvulsant actions, PTZ was infused at a constant rate via the lateral tail vein and clonus onset was recorded in the presence and absence of DZP (5 mg/kg, i.p). DZP significantly elevated seizure threshold in both groups of rats. Chronic cocaine also had no effect on the beta-CCM seizure threshold. Quantitative immunohistochemistry of GABA(A) receptor subunit protein demonstrated significant regulation of alpha2 (-10%) and beta3 (+9%) subunits in the hippocampal dentate gyrus and CA1 regions, respectively. Small changes in GABAR subunit expression in specific brain areas may relate to DZP's enhanced anxiolytic effectiveness whereas it's anticonvulsant actions likely remain intact following cocaine administration.

Time-course effects of a single administration of cocaine on receptor binding and subunit mRNAs of GABA(A) receptors

We investigated the time-course effects of a single administration of cocaine (20 mg/kg) on GABA(A) receptor binding labeled by t-[(35)S]butylbicyclophophorothionate (TBPS) and on several types of GABA(A) receptor subunit mRNAs in the rat brain by in vitro quantitative receptor autoradiography and in situ hybridization. The levels of alpha 1, beta 2, and beta 3 subunit mRNAs in several brain regions such as the cortex, cerebellum, and striatum were significantly decreased within 1 h, while beta 3 subunit mRNA was increased in the dentate gyrus. All of these changes were transient, occurring within 1 h after the injection of cocaine. In the cortex and cerebellum, the reduction in alpha1 subunit mRNA was followed by a significant decrease in [(35)S]TBPS receptor binding, which occurred 4 h after cocaine injection. These findings suggest that acute cocaine administration discretely regulates GABA(A) receptor subunit mRNA levels in several brain regions through a change in transcription or turnover rates of subunit mRNAs, which may be closely related to cocaine-induced behavioral abnormalities.

GABA-transaminase antisense oligodeoxynucleotide modulates cocaine- and pentylenetetrazol-induced seizures in mice

The mechanism of action of many anticonvulsive agents is to increase the function of the GABAergic system. Inhibition of GABA-Transaminase (GABA-T), the degradative enzyme for GABA, increases GABA levels in the brain. In this study, antisense oligodeoxynucleotides (ASO) targeted at the start codon region of GABA-Transaminase mRNA were used to modify seizure activity. Mice were treated, by intracerebroventricular injection, with antisense oligos or appropriate controls. At various times after treatment, the animals were challenged with cocaine (70 mg/kg, i.p.) and observed for seizure activity. At 15 hours after treatment, 1.152 and 1.44 nmol antisense oligo blocked cocaine-induced seizures. There was no effect of antisense oligo 8 or 36 hours after treatment. In addition, treatment with 7.2 nmol antisense oligo prevented pentylenetetrazol-induced seizures. These data demonstrate the modulation of seizure threshold using antisense oligodeoxynucleotides to GABA-T.

Increased acute cocaine sensitivity and decreased cocaine sensitization in GABA(A) receptor beta3 subunit knockout mice

The role of the GABA(A) receptor beta3 subunit in determining acute cocaine sensitivity and behavioral sensitization to repeated cocaine was measured in mice missing both (-/-), one (+/-), or neither (+/+) allele of the beta3 gene. Locomotor stimulation induced by one cocaine injection (20 mg/kg, i.p.) was found to be greater in -/- mice compared with +/+ mice, whereas cocaine-induced behaviors were intermediate in +/- mice. Amphetamine did not cause greater locomotor responses in -/- mice, suggesting that the increased sensitivity of -/- mice to cocaine does not generalize to other psychomotor stimulants. GABA-stimulated chloride uptake was 51% lower in striatum of -/- mice compared with +/+ mice, but only 27% lower in cortex. After 14 daily cocaine injections, the behavioral response to cocaine was increased in +/+ and +/- mice, but was not increased further in -/- mice. Additionally, repeated cocaine exposure decreased striatal GABA(A) receptor function in +/+ and +/- mice. In -/- mice, GABA(A) receptor function was not decreased any further by repeated cocaine injections. Thus, alterations in the beta3 subunit may be responsible for determining the behavioral responses induced by acute and repeated cocaine treatment, as well as mediating the neurochemical adaptation that occurs during sensitization to repeated cocaine.

An update on GABAA receptors

Recent advances in molecular biology and complementary information derived from neuropharmacology, biochemistry and behavior have dramatically increased our understanding of various aspects of GABAA receptors. These studies have revealed that the GABAA receptor is derived from various subunits such as alpha1-alpha6, beta1-beta3, gamma1-gamma3, delta, epsilon, pi, and rho1-3. Furthermore, two additional subunits (beta4, gamma4) of GABAA receptors in chick brain, and five isoforms of the rho-subunit in the retina of white perch (Roccus americana) have been identified. Various techniques such as mutation, gene knockout and inhibition of GABAA receptor subunits by antisense oligodeoxynucleotides have been used to establish the physiological/pharmacological significance of the GABAA receptor subunits and their native receptor assemblies in vivo. Radioligand binding to the immunoprecipitated receptors, co-localization studies using immunoaffinity chromatography and immunocytochemistry techniques have been utilized to establish the composition and pharmacology of native GABAA receptor assemblies. Partial agonists of GABAA receptors are being developed as anxiolytics which have fewer and less severe side effects as compared to conventional benzodiazepines because of their lower efficacy and better selectivity for the GABAA receptor subtypes. The subunit requirement of various drugs such as anxiolytics, anticonvulsants, general anesthetics, barbiturates, ethanol and neurosteroids, which are known to elicit at least some of their pharmacological effects via the GABAA receptors, have been investigated during the last few years so as to understand their exact mechanism of action. Furthermore, the molecular determinants of clinically important drug-targets have been investigated. These aspects of GABAA receptors have been discussed in detail in this review article.