Effects of L-type calcium channel antagonists on the serotonin-depleting actions of MDMA in rats

Studies on the mechanisms underlying amiloride enhancement of 3,4-methylenedioxymethamphetamine-induced serotonin depletion in rats

Amiloride and several of its congeners known to block the Na(+)/Ca(2+) and/or Na(+)/H(+) antiporters potentiate methamphetamine-induced neurotoxicity without altering methamphetamine-induced hyperthermia. We now examine whether amiloride also exacerbates 3,4-methylenedioxymethamphetamine (MDMA)-induced long-term serotonin (5-HT) loss in rats. Amiloride (2.5 mg/kg, every 2 h x 3, i.p.) given at ambient temperature 30 min before MDMA (5 mg/kg, every 2 h x 3, i.p.), markedly exacerbated long-term 5-HT loss. However, in contrast to methamphetamine, amiloride also potentiated MDMA-induced hyperthermia. Fluoxetine (10 mg/kg i.p.) completely protected against 5-HT depletion caused by the MDMA/amiloride combination without significantly altering the hyperthermic response. By contrast, the calcium channel antagonists flunarizine or diltiazem did not afford any protection. Findings with MDMA and amiloride were extended to the highly selective Na(+)/H(+) exchange inhibitor dimethylamiloride, suggesting that the potentiating effects of amiloride are probably mediated by the blockade of Na(+)/H(+) exchange. When the MDMA/amiloride combination was administered at 15 degrees C hyperthermia did not develop and brain 5-HT concentrations remained unchanged 7 days later. Intrastriatal perfusion of MDMA (100 microM for 8 h) in combination with systemic amiloride caused a small depletion of striatal 5-HT content in animals made hyperthermic but not in the striatum of normothermic rats. These data suggest that enhancement of MDMA-induced 5-HT loss caused by amiloride or dimethylamiloride depends on their ability to enhance MDMA-induced hyperthermia. We hypothesise that blockade of Na(+)/H(+) exchange could synergize with hyperthermia to render 5-HT terminals more vulnerable to the toxic effects of MDMA.

Effect of bromazepam on stress-induced gastric ulcer in rats and its relation to brain neurotransmitters

The possible antiulcer potential of bromazepam was investigated in relation to its effect on the levels of central neurotransmitters in rats. Peptic ulcer was induced by cold-restraint stress, by immobilizing the animals in open wire restraint cages placed for 2 h at 4 degrees C. Bromazepam (1 and 2 mg x kg(-1), i.p.) was given as prophylactic regimens, either as a single (2 h before ulcer induction) or repeated (twice daily for 15 days) administration. Results revealed that single (1 mg x kg(-1)) and repeated (1 and 2 mg x kg(-1)) dose regimens of bromazepam succeeded in preventing gastric ulceration, without significant effects on the protein-bound hexose content of gastric mucus. Increases in gamma-aminobutyric acid (GABA) concentrations in almost all tested brain regions were observed in bromazepam-treated groups, as compared to the control stressed group. Cortical dopamine (D) concentrations were reduced following single (2 mg x kg(-1)) as well as repeated administration of bromazepam. Similarly, norepinephrine (NE) concentrations were decreased in the cerebral cortex and thalamus/hypothalamus by repeated doses of bromazepam. Cortical 5-hydroxytryptamine (5-HT) was elevated by single (1 mg x kg(-1)) and repeated (1 mg x kg(-1)) doses of the drug. It could be concluded that bromazepam affords a good gastroprotective potential against cold-restraint stress-induced gastric ulceration and the possible mechanisms might involve an increase in the inhibitory GABA and a suppression of the stimulatory NE and D in central regions, especially the cerebral cortex and/or thalamus/hypothalamus.

AMPA/Zn(2+)-induced neurotoxicity in rat primary cortical cultures: involvement of L-type calcium channels

Zn2+ is believed to be an endogenous modulator of glutamatergic excitation. It has been shown to attenuate NMDA receptor-mediated excitation and to increase AMPA-induced excitatory transmission. The dual activity of Zn2+ on ionotropic excitatory neurotransmission suggests that Zn2+ plays a role in the modulation of excitatory neurodegenerative events. Stimulation of rat primary cortical cultures with the combination of 50 microM AMPA and 300 microM Zn2+ for 30 min induced approximately 50% cell death compared with only approximately 20% cell death induced by AMPA alone. The degree of neurotoxicity 48 h after the incubation was reproducible and was attenuated by CNQX, EDTA, EGTA, diltiazem and DHP-type Ca2+ channel blockers but not by MK-801. These findings suggest that an initial depolarization induced by AMPA and a subsequent influx of Ca2+ and Zn2+ ions through voltage-operated L-type Ca2+ channels are crucial events which finally lead to neuronal death. Racemic nimodipine and its (+)- and (-)-enantiomers had remarkable in vitro neuroprotective efficacies, the IC50 values being 4 nM for the racemate, 11 nM for the (+)- and 1 nM for the (-)-enantiomer. This suggests a possible therapeutic role for Ca2+ channel blockers in neurodegenerative diseases which are characterized by a disturbance of cellular Ca2+ homeostasis.