Selective reduction of γ-aminobutyric acid type A receptor δ subunit mRNA levels by MK-801 in rat dentate gyrus

Evaluation the effects of dextromethorphan and midazolam on morphine induced tolerance and dependence in mice

The main aim of this study was to evaluate the effects of dextromethorphan and midazolam and their combination on morphine tolerance and dependence in mice. In the present study, different groups of mice were rendered randomly and received morphine (50 mg kg(-1), s.c.), morphine (50 mg kg(-1), s.c.) + Dextromethorphan (25, 50 and 75 mg kg(-1), i.p.), morphine (50 mg kg(-1), s.c.) + midazolam (0.5, 1 and 2 mg kg(-1), i.p.), morphine (50 mg kg(-1), s.c.) + [Dextromethorphan (25 mg kg(-1), i.p. ) + midazolam (0.5 mg kg(-1), i.p.)] once a day for four days. Tolerance was assessed by administration of morphine (9 mg kg(-1), i.p.) on fifth day. Withdrawal symptoms (markers for dependence) was assessed by administration of naloxone (4 mg kg(-1), i.p.) 2 h after co-administration of morphine with either Dextromethorphan or midazolam or their combination. Results showed that pretreatment with Dextromethorphan or midazolam decreased the degree of tolerance and withdrawal symptoms significantly. Additionally co-administration ofDextromethorphan and midazolam couldn't decreased the tolerance and dependence significantly. From these results it may concluded that Dextromethorphan and midazolam alone or in combination could prevent the development of morphine induced tolerance and dependence. These effects can be related to the N-Methyl-D-Aspartate (NMDA) receptor antagonist behavior of Dextromethorphan and GABA-receptor agonist property of midazolam.

Lifelong ethanol consumption and brain regional GABAA receptor subunit mRNA expression in alcohol-preferring rats

Brain regional gamma-aminobutyric acid type A (GABAA) receptor subunit mRNA expression was studied in ethanol-preferring AA (Alko, Alcohol) rats after moderate ethanol drinking for up to 2 years of age. In situ hybridization with oligonucleotide probes specific for 13 different subunits was used with coronal cryostat sections of the brains. Selective alterations were observed by ethanol exposure and/or aging in signals for several subunits. Most interestingly, the putative highly ethanol-sensitive alpha4 and beta3 subunit mRNAs were significantly decreased in several brain regions. The age-related alterations in alpha4 subunit expression were parallel to those caused by lifelong ethanol drinking, whereas aging had no significant effect on beta3 subunit expression. The results suggest that prolonged ethanol consumption leading to blood concentrations of about 10 mM may downregulate the mRNA expression of selected GABAA receptor subunits and that aging might have partly similar effects.

AMPA/kainate receptor-mediated up-regulation of GABAA receptor δ subunit mRNA expression in cultured rat cerebellar granule cells is dependent on NMDA receptor activation

We have studied the effects of AMPA/kainate receptor agonists on GABA(A) receptor subunit mRNA expression in vitro in cultured rat cerebellar granule cells (CGCs). Kainate (KA) (100 microM) and high K(+) (25 mM) dramatically up-regulated delta subunit mRNA expression to 500-700% of that in control cells grown in low K(+) (5 mM). KA or high K(+) had no effect on the expression of the other major GABA(A) receptor subunits alpha1, alpha6, beta2, beta3 or gamma2. Up-regulation of delta mRNA was also detected with the AMPA receptor-selective agonist CPW-399 and to a lesser extent with the KA receptor-selective agonist ATPA. AMPA/kainate receptor-selective antagonist DNQX completely inhibited KA-, CPW-399- and ATPA-induced delta mRNA up-regulation indicating that the effects were mediated via AMPA and KA receptor activation. NMDA receptor-selective antagonist MK-801 inhibited 76% of the KA- and 57% of the CPW-399-induced delta up-regulation suggesting that KA and CPW-399 treatments may induce glutamate release resulting in NMDA receptor activation, and subsequently to delta mRNA up-regulation. In CGCs, delta subunit is a component of extrasynaptic alpha6betadelta receptors that mediate tonic inhibition. Up-regulation of delta during prolonged glutamate receptor activation or cell membrane depolarization may be a mechanism to increase tonic inhibition to counteract excessive excitation.