Benzodiazepines (BZs) enhance inhibitory gamma-aminobutyric acid type A receptors (GABARs) in the central nervous system and are clinically used to treat insomnia, anxiety, and seizure disorders. Misuse of CNS depressant drugs, such as the BZs, is of growing concern. There has been increased non-medical use of CNS depressants among adolescents since 2001 and BZ misuse and abuse resulted in over 150,000 emergency room visits in 2004. Of particular concern is the fact that chronic BZ use can lead to physical dependence manifested by a withdrawal syndrome, which limits the clinical usefulness of BZs. Our lab models BZ dependence using a well-established protocol of chronic treatment of rats with the BZ, fluraze- pam (FZP). We have linked withdrawal anxiety to enhanced excitatory receptor function in the rat hippocam- pal CA1 region. We also discovered that voltage-gated calcium channel (VGCC) current density doubles during chronic FZP treatment and remains elevated following withdrawal. Interestingly, selectively blocking calcium influx through L-type VGCCs with nimodipine prevented the excitatory receptor changes and associated withdrawal anxiety, suggesting that L-VGCCs play a critical role in BZ withdrawal phenomena. The overall objective of this project is to determine the mechanisms of L-VGCC modulation during FZP treatment and withdrawal, as this could suggest a previously unknown mechanism of developing BZ physiological dependence.
The specific aims of this project are to: 1) Determine if GABAR-mediated depolarization, known to be induced by chronic BZ treatment, activates L- VGCCs during FZP withdrawal using electrophysiologic and fluorescent calcium-imaging techniques. 2) Investigate changes in L-VGCC subunit expression and phosphorylation after chronic FZP treatment, using immunoblot, immunofluorescent, and electron microscopic techniques. 3) Investigate the often unrecognized ability of BZs to directly modulate L-VGCC function. Direct inhibition of recombinant L-VGCCs by BZs will be measured using whole-cell patch clamp techniques. Chronic misuse of prescription benzodiazepines (BZs) can result in physical dependence and remains a major concern in today's society. The results of this project could reveal a novel mechanism of neuroadaptive changes mediating the BZ withdrawal phenomenon, which current evidence suggests may be similar to other frequently abused CNS depressants, such as ethanol. Elucidation of this mechanism could reveal new therapeutic targets for BZ withdrawal, and possibly withdrawal from other drugs of abuse.
|Earl, Damien E; Tietz, Elizabeth I (2011) Inhibition of recombinant L-type voltage-gated calcium channels by positive allosteric modulators of GABAA receptors. J Pharmacol Exp Ther 337:301-11|