Alterations in Brain-Derived Neurotrophic Factor in the Mouse Hippocampus Following Acute but Not Repeated Benzodiazepine Treatment

Benzodiazepines (BZs) are safe drugs for treating anxiety, sleep, and seizure disorders, but their use also results in unwanted effects including memory impairment, abuse, and dependence. The present study aimed to reveal the molecular mechanisms that may contribute to the effects of BZs in the hippocampus (HIP), an area involved in drug-related plasticity, by investigating the regulation of immediate early genes following BZ administration. Previous studies have demonstrated that both brain derived neurotrophic factor (BDNF) and c-Fos contribute to memory- and abuse-related processes that occur within the HIP, and their expression is altered in response to BZ exposure. In the current study, mice received acute or repeated administration of BZs and HIP tissue was analyzed for alterations in BDNF and c-Fos expression. Although no significant changes in BDNF or c-Fos were observed in response to twice-daily intraperitoneal (i.p.) injections of diazepam (10 mg/kg + 5 mg/kg) or zolpidem (ZP; 2.5 mg/kg + 2.5 mg/kg), acute i.p. administration of both triazolam (0.03 mg/kg) and ZP (1.0 mg/kg) decreased BDNF protein levels within the HIP relative to vehicle, without any effect on c-Fos. ZP specifically reduced exon IV-containing BDNF transcripts with a concomitant increase in the association of methyl-CpG binding protein 2 (MeCP2) with BDNF promoter IV, suggesting that MeCP2 activity at this promoter may represent a ZP-specific mechanism for reducing BDNF expression. ZP also increased the association of phosphorylated cAMP response element binding protein (pCREB) with BDNF promoter I. Future work should examine the interaction between ZP and DNA as the cause for altered gene expression in the HIP, given that BZs can enter the nucleus and intercalate into DNA directly

Neuroadaptations and behavioral profiles associated with cocaine self-administration in Rhesus monkeys (Macaca mulatta)

Cocaine abuse and addiction are widespread problems with profound medical and socioeconomic consequences. At present, the neurobiological adaptations associated with short- and long-term cocaine abuse are not well understood, which contributes to the lack of availability of broadly effective treatments for this type of addiction. Recently, some studies have implicated GABAA receptor subtypes in the neuroadaptations underlying addiction. To explore the contributions of GABAA receptors to the neurobiological basis of cocaine abuse, we utilized a non-human primate model of cocaine self-administration and examined changes in species typical behaviors, and corresponding alterations in three GABAA receptor subtypes within five reward-related areas of the brain. Sixteen rhesus monkeys either self-administered cocaine intravenously (1-hr/day, 0.03 mg/kg/injection of cocaine) or received passive infusions of saline yoked to the cocaine injections (yoked control). Monkeys either self-administered cocaine for ~10 days (short-term group) or ~100 days (long-term group). Twenty-four hours after the last session, animals were sacrificed and brains were removed. We examined alterations in &agr;1, &agr;2, and &agr;3 subunit-containing GABAA receptors (&agr;1, &agr;2, and &agr;3GABAA receptors) using immunohistochemistry (IHC), in situ hybridization (ISH), and real-time PCR experiments (RTPCR) within reward-related areas of the brain including the nucleus accumbens, ventral tegmental area, caudate, putamen, and anterior cingulate cortex. Long-term cocaine taking animals self-administered cocaine in a cyclical pattern, and increased number of cocaine injections taken within the initial portion of daily self-administration sessions. We observed behavioral alterations in behaviors including locomotor, stereotypic, scratching and affiliative behaviors. IHC results demonstrated alterations in &agr;1GABAA receptors within all regions of interest after long-term self-administration. After short-term cocaine self-administration decreases in &agr;3GABAA receptors were observed in all regions examined. When examining transcript levels using ISH and RTPCR, we found relatively few changes in comparison to protein alterations. The notable change was a decrease of all three receptor mRNAs within the anterior cingulate cortex after short-term cocaine exposure. The present model of drug may expand our understanding of addiction-related behaviors and the role of GABA in addiction. Furthermore, our findings suggest GABAA receptors may serve as viable targets for pharmacotherapeutic approaches to treat addiction

Increased MeCP2 association with BDNF promoter IV in the HIP following acute BZ treatment.

<p>(A) There is no change in total MeCP2 protein levels in the HIP following BZ treatment as measured by western blots (n= 3); (B) There is a significant increase in MeCP2 association with BDNF promoter IV in the HIP following ZP treatment as measured by ChIP (n= 3-4). * <i>p</i>< 0.05; IDV: integrated density values.</p

No change in histone acetylation in the HIP following acute BZ treatment.

<p>(A) There is no change in total AcH3 protein levels in the HIP following BZ treatment as measured by western blots (n= 3); (B) There is no change in AcH3 association with BDNF promoters in the HIP following ZP treatment as measured by ChIP (n= 4). IDV: integrated density values.</p

Reinforcing effects of compounds lacking intrinsic efficacy at α1 subunit-containing GABAA receptor subtypes in midazolam- but not cocaine-experienced rhesus monkeys

Benzodiazepines are prescribed widely but their utility is limited by unwanted side effects, including abuse potential. The mechanisms underlying the abuse-related effects of benzodiazepines are not well understood, although α1 subunit-containing GABAA receptors have been proposed to have a critical role. Here, we examine the reinforcing effects of several compounds that vary with respect to intrinsic efficacy at α2, α3, and α5 subunit-containing GABAA receptors but lack efficacy at α1 subunit-containing GABAA receptors ('α1-sparing compounds'): MRK-623 (functional selectivity for α2/α3 subunit-containing receptors), TPA023B (functional selectivity for α2/α3/α5 subunit-containing receptors), and TP003 (functional selectivity for α3 subunit-containing receptors). The reinforcing effects of the α1-sparing compounds were compared with those of the non-selective benzodiazepine receptor partial agonist MRK-696, and non-selective benzodiazepine receptor full agonists, midazolam and lorazepam, in rhesus monkeys trained to self-administer midazolam or cocaine, under a progressive-ratio schedule of intravenous (i.v.) drug injection. The α1-sparing compounds were self-administered significantly above vehicle levels in monkeys maintained under a midazolam baseline, but not under a cocaine baseline over the dose ranges tested. Importantly, TP003 had significant reinforcing effects, albeit at lower levels of self-administration than non-selective benzodiazepine receptor agonists. Together, these results suggest that α1 subunit-containing GABAA receptors may have a role in the reinforcing effects of benzodiazepine-type compounds in monkeys with a history of stimulant self-administration, whereas α3 subunit-containing GABAA receptors may be important mediators of the reinforcing effects of benzodiazepine-type compounds in animals with a history of sedative-anxiolytic/benzodiazepine self-administration