10 research outputs found
ED<sub>50</sub> values for various GABA<sub>A</sub> receptor positive allosteric modulators as derived from in-vivo binding of [<sup>3</sup>H]flumazenil to mouse forebrain.
<p>Data represent 2 independent experiments with nβ=β3 for all drugs in each experiment; range shown in parenthesis.</p
Effect of acutely administered vehicle or diazepam (5 mg/kg, IP) on (A) the stress-induced hyperthermia response, (B) basal body temperature and (C) distance travelled in the open field measured 60 minutes post-administration, in mice treated chronically with bretazenil (5 mg/kg/day) or vehicle (Experiment 3).
<p>***: p<0.001 (**: p<0.01) compared to acute vehicle administration. #: p<0.05 compared to the chronic vehicle group acutely receiving diazepam. BRET: bretazenil; DZP: diazepam; VEH: vehicle.</p
Effect of acute vehicle or diazepam (5 mg/kg, IP) administration on the stress-induced hyperthermia (SIH) response measured 60 minutes post-administration in mice treated chronically with various different GABA<sub>A</sub> receptor positive allosteric modulators (see Methods and
<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0043054#pone-0043054-t002" target="_blank"><b>Table 2</b></a><b>).</b> *: p<0.05 acute diazepam effect compared to day 1. VEH: vehicle; DZP: diazepam; ZOL: zolpidem; TPA: TPA023.</p
GABA<sub>A</sub> Receptor Ξ± Subunits Differentially Contribute to Diazepam Tolerance after Chronic Treatment
<div><h3>Background</h3><p>Within the GABA<sub>A</sub>-receptor field, two important questions are what molecular mechanisms underlie benzodiazepine tolerance, and whether tolerance can be ascribed to certain GABA<sub>A</sub>-receptor subtypes.</p> <h3>Methods</h3><p>We investigated tolerance to acute anxiolytic, hypothermic and sedative effects of diazepam in mice exposed for 28-days to non-selective/selective GABA<sub>A</sub>-receptor positive allosteric modulators: diazepam (non-selective), bretazenil (partial non-selective), zolpidem (Ξ±<sub>1</sub> selective) and TPA023 (Ξ±<sub>2/3</sub> selective). In-vivo binding studies with [<sup>3</sup>H]flumazenil confirmed compounds occupied CNS GABA<sub>A</sub> receptors.</p> <h3>Results</h3><p>Chronic diazepam treatment resulted in tolerance to diazepam's acute anxiolytic, hypothermic and sedative effects. In mice treated chronically with bretazenil, tolerance to diazepam's anxiolytic and hypothermic, but not sedative, effects was seen. Chronic zolpidem treatment resulted in tolerance to diazepam's hypothermic effect, but partial anxiolytic tolerance and no sedative tolerance. Chronic TPA023 treatment did not result in tolerance to diazepam's hypothermic, anxiolytic or sedative effects.</p> <h3>Conclusions</h3><p>Our data indicate that: (i) GABA<sub>A</sub>-Ξ±<sub>2</sub>/Ξ±<sub>3</sub> subtype selective drugs might not induce tolerance; (ii) in rodents quantitative and temporal variations in tolerance development occur dependent on the endpoint assessed, consistent with clinical experience with benzodiazepines (e.g., differential tolerance to antiepileptic and anxiolytic actions); (iii) tolerance to diazepam's sedative actions needs concomitant activation of GABA<sub>A</sub>-Ξ±<sub>1</sub>/GABA<sub>A</sub>-Ξ±<sub>5</sub> receptors. Regarding mechanism, in-situ hybridization studies indicated no gross changes in expression levels of GABA<sub>A</sub> Ξ±<sub>1</sub>, Ξ±<sub>2</sub> or Ξ±<sub>5</sub> subunit mRNA in hippocampus or cortex. Since selective chronic activation of either GABA<sub>A</sub> Ξ±<sub>2</sub>, or Ξ±<sub>3</sub> receptors does not engender tolerance development, subtype-selective GABA<sub>A</sub> drugs might constitute a promising class of novel drugs.</p> </div
Effect of acute vehicle or diazepam (5 mg/kg, IP) administration on basal body temperature measured 60 minutes post-administration in mice treated chronically with various different GABA<sub>A</sub> receptor positive allosteric modulators (see Methods and
<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0043054#pone-0043054-t002" target="_blank"><b>Table 2</b></a><b>).</b> *: p<0.05 compared to the acute diazepam on day 1. VEH: vehicle; DZP: diazepam; ZOL: zolpidem; TPA: TPA023.</p
Chronological sequence of experimental studies/assessments in animals treated chronically with various GABA<sub>A</sub> receptor positive allosteric modulators (see Methods and <b>Tables 2</b> & <b>3</b>).
<p>SIH: stress-induced hyperthermia test; OF: open field test. In experiment 2, only one OF was carried out.</p
Experimental protocol of repeat weekly testing with acute administration of vehicle or diazepam (5 mg/kg, IP) in mice chronically administered vehicle, diazepam, zolpidem or TPA023 (15 mg/kg/day) for 4-weeks via subcutaneously implanted osmotic minipumps (<b>Experiment 1</b>).
<p>Experimental protocol of repeat weekly testing with acute administration of vehicle or diazepam (5 mg/kg, IP) in mice chronically administered vehicle, diazepam, zolpidem or TPA023 (15 mg/kg/day) for 4-weeks via subcutaneously implanted osmotic minipumps (<b>Experiment 1</b>).</p
Differences in expression of GABA<sub>A</sub> receptor Ξ±<sub>1</sub> (A), Ξ±<sub>2</sub> (B) and Ξ±<sub>5</sub> (C)mRNA in the hippocampus and cortex (retrosplenial and primary motor cortex) in mice chronically treated with various GABA<sub>A</sub> receptor (see Methods and <b>Table 2</b>).
<p>*: p<0.05.</p
Effect of acute diazepam (5 mg/kg IP) or vehicle administration on total distance travelled (A) and percentage of time moving (B) in the open field, in mice treated chronically with various different GABA<sub>A</sub> receptor (see Methods and
<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0043054#pone-0043054-t002" target="_blank"><b>Table 2</b></a><b>) for approximately 4 weeks (Experiment 2, see text).</b> **: p<0.01 compared to vehicle. VEH: vehicle; DZP: diazepam; ZOL: zolpidem; TPA: TPA023.</p
Experimental protocol of repeated weekly testing with acute administration of vehicle or diazepam (5 mg/kg, IP) in mice chronically administered vehicle or bretazenil (5 mg/kg/day) for 4-weeks via subcutaneously implanted osmotic minipumps (<b>Experiment 2</b>).
<p>Experimental protocol of repeated weekly testing with acute administration of vehicle or diazepam (5 mg/kg, IP) in mice chronically administered vehicle or bretazenil (5 mg/kg/day) for 4-weeks via subcutaneously implanted osmotic minipumps (<b>Experiment 2</b>).</p