raclopride and Fever

Methylone (2-methylamino-1-[3,4-methylenedioxy-phenyl]propan-1-one), an amphetamine analog, has emerged as a popular drug of abuse worldwide. Methylone induces hyperthermia, which is thought to contribute toward the lethal consequences of methylone overdose. Methylone has been assumed to induce hyperthermic effects through inhibition of serotonin and/or dopamine transporters (SERT and DAT, respectively). To examine the roles of each of these proteins in methylone-induced toxic effects, we used SERT and DAT knockout (KO) mice and assessed the hyperthermic and lethal effects caused by a single administration of methylone. Methylone produced higher rates of lethal toxicity compared with other amphetamine analogs in wild-type mice. Compared with wild-type mice, lethality was significantly lower in DAT KO mice, but not in SERT KO mice. By contrast, only a slight diminution in the hyperthermic effects of methylone was observed in DAT KO mice, whereas a slight enhancement of these effects was observed in SERT KO mice. Administration of the selective D1 receptor antagonist SCH 23390 and the D2 receptor antagonist raclopride reduced methylone-induced hyperthermia, but these drugs also had hypothermic effects in saline-treated mice, albeit to a smaller extent than the effects observed in methylone-treated mice. In contradistinction to 3,4-methylenedioxymethamphetamine, which induces its toxicity through SERT and DAT, these data indicate that DAT, but not SERT, is strongly associated with the lethal toxicity produced by methylone, which did not seem to be dependent on the hyperthermic effects of methylone. DAT is therefore a strong candidate molecule for interventions aimed at preventing acute neurotoxic and lethal effects of methylone.

Topics: Animals; Benzazepines; Body Temperature; Central Nervous System Stimulants; Dopamine Antagonists; Dopamine Plasma Membrane Transport Proteins; Female; Fever; Male; Methamphetamine; Mice, Knockout; Models, Animal; Raclopride; Receptors, Dopamine D1; Receptors, Dopamine D2; Serotonin Plasma Membrane Transport Proteins

Methamphetamine (METH) induces hyperthermia in warm and hypothermia in cool environments. Our first goal was to further study the role of ambient temperature in METH's effect on core temperature in rats. Previously, these effects were primarily demonstrated in high doses; we extended this investigation to the low-dose range (1 mg/kg METH). Our second goal was to identify the role of the D2 receptor in METH's effects in cool ambient temperatures.. Rats received METH (saline, 1, 5, and 10 mg/kg), raclopride (saline, 0.3, 0.6, and 1.2 mg/kg), or a combination (all doses of raclopride combined with 10 mg/kg METH). Treatments occurred in ambient temperatures of 18, 24, or 30 °C.. Consistent with prior research, 5 and 10 mg/kg METH caused hyperthermia or hypothermia in a dose- and ambient temperature-dependent manner (60 min after METH). In contrast, 1 mg/kg produced similar levels of hyperthermia at all ambient temperatures. These findings suggest that a threshold METH dose exists; below this dose, METH still changes core temperature, but CNS control over temperature regulation is left intact. In our experiments regarding D2 blockade, raclopride decreased METH-induced core temperature at 30 and 24 °C (60 min after METH), consistent with previous findings. We extended these findings by demonstrating that in a cool ambient temperature (18 °C), raclopride pretreatment also lowered the core temperature response to METH. Although the D2 receptor is known to mediate hypothermia, the combination of METH and D2 blockade suggests a complex mediation of the core temperature response, perhaps involving neurotransmitter interactions.

Topics: Animals; Body Temperature; Dopamine Agents; Dopamine Antagonists; Dopamine D2 Receptor Antagonists; Dose-Response Relationship, Drug; Fever; Hypothermia; Male; Methamphetamine; Raclopride; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D2; Temperature

Single large doses of methamphetamine (METH) cause endoplasmic reticulum (ER) stress and mitochondrial dysfunctions in rodent striata. The dopamine D(1) receptor appears to be involved in these METH-mediated stresses. The purpose of this study was to investigate if dopamine D(1) and D(2) receptors are involved in ER and mitochondrial stresses caused by single-day METH binges in the rat striatum. Male Sprague-Dawley rats received 4 injections of 10 mg/kg of METH alone or in combination with a putative D(1) or D(2) receptor antagonist, SCH23390 or raclopride, respectively, given 30 min prior to each METH injection. Rats were euthanized at various timepoints afterwards. Striatal tissues were used in quantitative RT-PCR and western blot analyses. We found that binge METH injections caused increased expression of the pro-survival genes, BiP/GRP-78 and P58(IPK), in a SCH23390-sensitive manner. METH also caused up-regulation of ER-stress genes, Atf2, Atf3, Atf4, CHOP/Gadd153 and Gadd34. The expression of heat shock proteins (HSPs) was increased after METH injections. SCH23390 completely blocked induction in all analyzed ER stress-related proteins that included ATF3, ATF4, CHOP/Gadd153, HSPs and caspase-12. The dopamine D(2)-like antagonist, raclopride, exerted small to moderate inhibitory influence on some METH-induced changes in ER stress proteins. Importantly, METH caused decreases in the mitochondrial anti-apoptotic protein, Bcl-2, but increases in the pro-apoptotic proteins, Bax, Bad and cytochrome c, in a SCH23390-sensitive fashion. In contrast, raclopride provided only small inhibition of METH-induced changes in mitochondrial proteins. These findings indicate that METH-induced activation of striatal ER and mitochondrial stress pathways might be more related to activation of SCH23390-sensitive receptors.

Topics: Animals; Benzazepines; Biomarkers; Endoplasmic Reticulum Chaperone BiP; Endoplasmic Reticulum Stress; Fever; Heat-Shock Proteins; HSP40 Heat-Shock Proteins; HSP70 Heat-Shock Proteins; Male; Methamphetamine; Mitochondria; Neostriatum; Raclopride; Rats; Rats, Sprague-Dawley; Receptors, Dopamine D1; Receptors, Dopamine D2; RNA, Messenger; Stress, Physiological; Time Factors; Up-Regulation

Factors influencing the disappearance of radioactivity from mouse brain after injections of tracer doses of the very selective receptor antagonists [3H]raclopride and [3H]robalzotan (NAD-299) which bind with high affinity to dopamine-D2 and 5-hydroxytryptamine1A receptors, respectively, were studied. For both ligands the amount of radioactivity in cerebellum was taken as non-specific binding and subtracted from the amount of radioactivity found in the brain regions studied. The disappearance of the radioactivity in naive mice followed apparent first-order reactions with T1/2=16.8+/-1.4 min for [3H]raclopride in striatum and T1/2=22+/-2 min and 17+/-2 min for [3H]robalzotan in hippocampus and frontal cortex, respectively. Pretreatment of mice with 1 mg/kg s.c. reserpine 20 h before the experiment strongly prolonged the dissociation phase for the two ligands. Injection of the dopamine-D2 receptor antagonist etioclopride 1 h after [3H]raclopride in the reserpinized mice rapidly reduced the radioactivity in striatum to the same level as in cerebellum. Similarly, the 5-HT1A receptor antagonist WAY-100,635 injected 1 h or 4 h after [3H]robalzotan rapidly reduced the radioactivity in hippocampus and frontal cortex to the cerebellum level showing that the intact drugs were still bound to the receptors. In reserpinized mice kept at 30 degrees C 1 h before and during the experiment, which normalised the body temperature, the disappearance of radioactivity was more like that in untreated animals but was still significantly higher than in the control animals. Mice treated with anaesthetic agents, e.g. gamma-butyrolactone (GBL), pentobarbital sodium and chloral hydrate, also strongly prolonged the rate of disappearance of [3H]raclopride and [3H]robalzotan from the receptor-rich brain regions. The pronounced effect of hypothermia on the dissociation of these 3H ligands from their receptors is probably caused by a general decrease in brain nervous activity. However, the decreased rate of dissociation evoked by reserpine, GBL, baclofen and prazosin after normalisation of the body temperature may be due to specific actions of these compounds causing decrease in dopaminergic and serotoninergic nerve activity which results in reduced synaptic concentration of the transmitter amines. In accordance with this view, increased synaptic 5-HT evoked by the 5-HT releasing agent p-chloroamphetamine enhanced the disappearance of [3H]robalzotan from hippocampus and frontal cortex.

Topics: Animals; Benzopyrans; Brain; Dopamine Antagonists; Fever; Male; Mice; Raclopride; Receptors, Dopamine D2; Receptors, Serotonin; Receptors, Serotonin, 5-HT1; Serotonin Antagonists