Dopamine receptors mediate cocaine-induced temperature responses in spontaneously hypertensive and Wistar-Kyoto rats

Risperidone and 5-HT2A Receptor Antagonists Attenuate and Reverse Cocaine-Induced Hyperthermia in Rats

BACKGROUND

Cocaine (benzoylmethylecgonine) is one of the most widely used illegal psychostimulant drugs worldwide, and mortality from acute intoxication is increasing. Suppressing hyperthermia is effective in reducing cocaine-related mortality, but a definitive therapy has not yet been found. In this study, we assessed the ability of risperidone to attenuate acute cocaine-induced hyperthermia and delineated the mechanism of its action.

METHODS

Rats were injected i.p. with saline, risperidone, ketanserin, ritanserin, haloperidol, or SCH 23 390 before and after injection of cocaine (30 mg/kg) or with WAY-00 635, SB 206 553, or sulpiride before cocaine injection; thereafter, the rectal temperature was measured every 30 minutes for up to 4 hours. In vivo microdialysis was used to reveal the effect of risperidone on cocaine-induced elevation of dopamine (DA), serotonin (5-HT), and noradrenaline concentrations in the anterior hypothalamus. For post-administration experiments, saline or risperidone (0.5 mg/kg) were injected into rats, and cocaine (30 mg/kg) was injected 15 minutes later. For every 30 minutes thereafter, DA, 5-HT, and noradrenaline levels were measured for up to 240 minutes after cocaine administration.

RESULTS

Risperidone, 5-HT2A receptor antagonists, and D1 receptor antagonistic drugs prevented and reversed cocaine-induced hyperthermia. In contrast, receptor antagonists for 5-HT1A, 5-HT2B/2C, and D2 did not alter cocaine-induced hyperthermia. Risperidone treatment further attenuated cocaine-induced elevation of DA.

CONCLUSIONS

Our results indicate that risperidone attenuates cocaine-induced hyperthermia primarily by blocking the activities of the 5-HT2A and D1 receptors and may be potentially useful for treating cocaine-induced acute hyperthermia in humans.

Methanandamide attenuates cocaine-induced hyperthermia in rats by a cannabinoid CB1-dopamine D2 receptor mechanism

Evidence implicates anandamide in dopamine-related cocaine function. In the present study, we investigated the effect of methanandamide (5 mg/kg, i.p.), a stable anandamide analog, on the hyperthermia and hyperactivity induced by a fixed dose of cocaine (15 mg/kg,i.p.). Cocaine administered to rats produced hyperthermia and hyperactivity whereas methanandamide was ineffective. For combined administration, methanandamide attenuated the hyperthermia, but not hyperactivity, induced by cocaine. The effect of methanandamide was abolished by pretreatment with a cannabinoid CB1 receptor antagonist, SR141716A (5 mg/kg, i.p.), or dopamine D2 receptor antagonist, S(−)-raclopride(5 mg/kg, i.p.) but not by capsazepine (40 mg/kg, i.p.), a transient receptor potential vanilloid 1 cation channel antagonist. Methanandamide also attenuated the hyperthermia caused by a dopamine D1 receptor agonist, SKF 38393 (10 mg/kg, s.c.), indicating that it reduces hyperthermia produced by dopamine D1 receptor activation. URB597 (0.25 mg/kg, i.p.), an inhibitor of anandamide metabolism, did not alter cocaine-induced hyperthermia. Our results demonstrate that methanandamide activates cannabinoid CB1 receptors to attenuate cocaine-induced hyperthermia, and that dopamine D2 receptor activation plays a permissive role in the thermoregulatory effects of methanandamide.

Increased hepatotoxicity and cardiac fibrosis in cocaine-treated butyrylcholinesterase knockout mice

In mice, cocaine is detoxified to inactive products by butyrylcholinesterase (BChE) and carboxylesterase. In human beings, cocaine detoxification is primarily by BChE. The focus of this investigation was to elucidate the importance of BChE in reducing pathophysiological effects following cocaine exposure. Previous studies examining the effects of cocaine on BChE deficient animals relied on chemical inhibition of BChE with tetraisopropyl pyrophosphoramide (iso-OMPA). The creation of the BChE knockout mouse has provided a model for studying pathological effects of cocaine in mice free of chemical confounders. We hypothesized that mice with low or no BChE activity would have reduced cocaine metabolism, leading to hepatotoxicity and cardiomyopathy. A high-resolution in vivo imaging system recorded cardiac and respiratory function following treatment with a carboxylesterase inhibitor and a high dose of cocaine (100 mg/kg, intraperitoneally). The BChE-/- mice demonstrated depressed respiration through 12 hr after dosing and abnormal respiratory patterns consisting of a pause at full inspiration (apneusis), whereas BChE+/+ mice had recovered normal respiration rates by 30 min. after dosing and exhibited no apneusis. Liver and cardiac histology sections were analysed following a 20 mg/kg intraperitoneally dose of cocaine administered daily for 7 days. BChE-/- mice treated for 7 days with the chronic low dose showed significant hepatotoxicity and cardiac perivascular fibrosis compared to BChE+/+ mice. The observed functional changes following acute high-dose and chronic low-dose cocaine in BChE-/- and +/- mice warrants further investigation into the possibility of increased cocaine toxicity in human beings with BChE deficiency.

Differential Effects of Cocaine-Induced Seizures and Lethality on M1-Like Muscarinic and Dopaminergic D1- and D2-Like Binding Receptors in Mice Brain

This work was designed to study the changes produced by cocaine-induced seizures and lethality on dopaminergic D(1)- and D(2)-like receptors, muscarinic M(1)-like binding sites, as well as acetylcholinesterase activity in mice prefrontal cortex (PFC) and striatum (ST). Binding assays were performed in brain homogenates from the PFC and ST and ligands used were [(3)H]-N-methylscopolamine, [(3)H]-NMS (in the presence of carbachol), [(3)H]-SCH 23390 and [(3)H]-spiroperidol (in presence of mianserin), for muscarinic (M(1)-like), D(1)- and D(2)-like receptors, respectively. Brain acetylcholinesterase (AChE) activity was also determined in these brain areas. Cocaine-induced SE decreased [(3)H]-SCH 23390 binding in both ST and PFC areas. A decrease in [(3)H]-NMS binding and an increase in [(3)H]-spiroperidol binding in PFC was also observed. Cocaine-induced lethality increased [(3)H]-spiroperidol binding in both areas and decreased [(3)H]-NMS binding only in PFC, while no difference was seen in [(3)H]-SCH 23390 binding. Neither SE, nor lethality altered [(3)H]-NMS binding in ST. AChE activity increased after SE in ST while after death the increase occurred in both PFC and ST. In conclusion, cocaine-induced SE and lethality produces differential changes in brain cholinergic and dopaminergic receptors, depending on the brain area studied suggesting an extensive and complex involvement of these with cocaine toxicity in central nervous system.

Cardiovascular disorders associated with cocaine use: myths and truths

Cocaine produces a pattern of cardiovascular responses that are associated with apparent myocardial ischemia, arrhythmias, and other life-threatening complications in some individuals. Despite recent efforts to better understand the causes of cocaine-induced cardiovascular dysfunction, there remain a number of unanswered questions regarding the specific mechanisms by which cocaine elicits hemodynamic responses. This review will describe the actions of cocaine on the cardiovascular system and the evidence for the mechanisms by which cocaine elicits hemodynamic and pathologic responses in humans and animals. The emphasis will be on experimental data that provide the basis for our understanding of the mechanisms of cardiovascular toxicity associated with cocaine. More importantly, this review will identify several controversies regarding the causes of cocaine-induced cardiovascular toxicity that as yet are still debated. The evidence supporting these findings will be described. Finally, this review will outline the obvious deficits in our current concepts regarding the cardiovascular actions of cocaine in hope of encouraging additional studies on this grave problem in our society.

Time course of brain temperature and caudate/putamen microdialysate levels of amphetamine and dopamine in rats after multiple doses of d-amphetamine

Brain temperature monitoring and microdialysis were performed simultaneously in the caudate/putamen (CPu) of conscious, freely moving rats dosed with d-amphetamine (AMPH). The brain temperature was determined via a thermistor inserted through a microdialysis guide cannula located in the left CPu, while the microdialysis probe was positioned in the right CPu. The peak AMPH and dopamine (DA) levels were reached 40 to 60 min after dosing, while peak brain temperature was not achieved until 20 to 40 min thereafter in rats becoming moderately hyperthermic. Those rats becoming severely hyperthermic (temperatures above 41.0 degrees C) had microdialysate concentrations of AMPH and DA almost 2-fold higher than those with moderate hyperthermia after the second dose of 5 mg/kg AMPH. However, these peaks were not reached until 60 to 80 min after dosing. This was probably due, in part, to the longer half-life of AMPH in the severely hyperthermic group. The changes in brain temperature observed after exposure to neurotoxic doses of AMPH closely paralleled core body temperature changes previously reported during AMPH exposure. Temperature plays an important role in many types of neurotoxicity, and monitoring brain temperature during microdialysis studies can be done continuously, and with less chance of damage to the microdialysis equipment than most of the traditional methods used to measure core body temperature.

Enhancement of cocaine-induced hyperthermia fails to elicit neurotoxicity

The neurotoxic potential of cocaine when administered under conditions conducive to the initiation of hyperthermia was investigated. Rats were administered cocaine at ambient temperatures of 22 degrees C or 30 degrees C. To determine the thermal response, body temperatures were measured every 30 min and the total thermal response (TTR), representing the area under the temperature vs. time curve, was calculated. Saline administered at 22 degrees C or 30 degrees C resulted in a normal thermal response (TTR = 9.8+/-0.9 and 11.2+/-0.9, respectively). Cocaine administration resulted in ambient temperature-dependent hyperthermia. Cocaine (4 x 25 mg/kg) administered at 22 degrees C resulted in a TTR of 15.1+/-0.9 whereas cocaine (4 x 15 or 25 mg/kg) administered at 30 degrees C resulted in TTRs of 22.2+/-0.9 and 21.9+/-0.8, respectively. Regardless of the dose or thermal response, cocaine administration did not result in depletion of dopamine (DA) or serotonin (5-HT) in the caudate-putamen. Cocaine administration also failed to induce an increase in the concentration of glial fibrillary acidic protein (GFAP), a marker for neurotoxicity. These results demonstrate that hyperthermia does not promote cocaine-induced neurotoxicity in the rat caudate-putamen.

Drug-induced hyperthermia

Drug-related causes of hyperthermia can often be overlooked in the setting of elevated body temperature. This article reviews the pathophysiology, presentation, and treatment of several drug-induced hyperthermia syndromes: malignant hyperthermia, neuroleptic malignant syndrome, sympathomimetic poisoning, and anticholinergic toxicity. Although the general approach is similar, specific management strategies may be required for each syndrome.

Changes in locomotor activity, core temperature, and heart rate in response to repeated cocaine administration

The effects of daily single injections of 20 mg/kg cocaine on locomotor activity, core temperature, and heart rate were determined by radiotelemetry. There was a progressive increase in locomotor activity over the 30-day treatment period. Cocaine-induced activity was 9-12-fold greater than that of saline-treated animals. Cocaine also caused increases in core temperature and heart rate. Tolerance did not develop to the locomotor, hyperthermic, and tachycardic responses resulting from repeated cocaine administration. Comparison of the time-course of the cocaine-induced responses revealed that, on Day 1 and 3, the peak locomotor activity was observed 15 min after cocaine administration, whereas the hyperthermic response peaked at 95 min on those days. The fact that the peak locomotor activity and the hyperthermic response occurred at different times suggests that different processes acting independently or interacting may be involved in these actions of cocaine.

Differential effects of NMDA receptor and dopamine receptor antagonists on cocaine toxicities

Cocaine produces not only euphoric effects but also a wide range of detrimental effects, including seizures and lethality. The present study examined the involvement of the N-methyl-D-aspartate (NMDA) subtype of the glutamate receptors and the dopamine D1 and D2 receptors in seizure activity and lethality observed following single and repeated injections of cocaine in ddY mice. Repeated injections of 60 mg/kg cocaine resulted in the development of sensitization to the convulsant effects of cocaine during an initial 3 or 4 days, followed by the development of tolerance at day 5 and day 6. Repeated injections of 90 mg/kg cocaine augmented the lethal effect of cocaine progressively over the course of treatment. Treatment with 0.1-0.4 mg/kg of the noncompetitive NMDA receptor antagonist, MK-801, prevented the development of sensitization to cocaine-induced seizures in a dose-dependent manner, and attenuated partially the cocaine-induced lethality. In contrast, treatment with 10-50 mg/kg of the dopmaine D2 receptor antagonist, sulpiride, had no effects on the development of sensitization and tolerance to cocaine-induced seizures. On the other hand, treatment with 0.1-0.5 mg/kg of the dopamine D1 receptor antagonist, SCH 23390, not only prolonged the latency to 90 mg/kg cocaine-induced seizures but also delayed the development of sensitization to the convulsant effects of cocaine. The increased lethality observed following repeated injection of cocaine was unaffected by treatment with SCH 23390, but was severely aggravated by treatment with sulpiride.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperthermia in psychostimulant overdose

Psychostimulant drugs such as amphetamines, amphetamine derivatives, and cocaine produce a variety of potentially lethal effects, and an understanding of these toxic effects is important for emergency physicians. While some effects of psychostimulant poisonings such as cardiovascular compromise and seizures have been discussed extensively, other metabolic derangements such as hyperthermia are less well characterized. In fact, hyperthermia is a common feature of severe-to-lethal poisonings and may be the primary mode of demise in some patients. Animal studies confirm that drug-induced hyperthermia alone can be lethal in some species, although other toxic effects may predominate at different drug doses or rates of administration. In non-lethal poisonings, hyperthermia can produce rhabdomyolysis, leading to further morbidity. Clinical reports and animal studies indicate that hyperthermia is a primary effect of psychostimulant drugs and can occur independently of seizures or increased motor activity. Furthermore, activation of particular dopamine receptors in the central nervous system appears to mediate psychostimulant-induced hyperthermia. The literature suggests cooling and tranquilization of psychostimulant-poisoned patients after cardiovascular stabilization. Paralysis and mechanical ventilation may be required. The involvement of dopamine receptor activation in psychostimulant toxicity suggests that dopamine-blocking neuroleptic drugs may be a useful adjunct to current treatment regimens. However, further studies are required to assess this approach. In summary, hyperthermia is a potentially lethal but treatable manifestation of severe psychostimulant poisoning.

Antagonism of the toxicity of cocaine by MK-801: differential effects in spontaneously hypertensive and Wistar-Kyoto rats

A putative role for endogenous excitatory amino acid systems in the mediation of the cardiovascular and toxic responses to acute administration of cocaine, was examined in spontaneously hypertensive and normal Wistar-Kyoto rats. Conscious, restrained, male hypertensive and normal rats (12 weeks of age) received either the non-competitive excitatory amino acid receptor antagonist, MK-801 (0.01-10 mg/kg, i.v.) or vehicle, 30 min prior to initiation of infusion of cocaine hydrochloride (1.25 mg/kg min, i.v.). Administration of MK-801 produced increases in mean blood pressure and heart rate in both hypertensive and normal rats. Resting rectal temperature was reduced by MK-801 only at the largest dose tested (10 mg/kg). Infusion of cocaine caused convulsions and death at doses of 27.8 +/- 2.3 and 48.2 +/- 5.7 mg/kg, respectively in the normals, and 21.2 +/- 2.5 (P < 0.05) and 31.1 +/- 3.4 (P < 0.05) in the hypertensive rats. Pretreatment with MK-801 abolished the enhanced sensitivity of the hypertensive rats to the toxicity of cocaine. The doses of cocaine required to cause death were significantly increased, in the hypertensive rats at doses > or = 0.05 mg/kg, an effect which was not evident, at any dose, in the normals. The maximally effective dose of MK-801 (0.5 mg/kg) increased the dose of cocaine required to cause lethality by 272% (P < 0.05) in the hypertensive rats; the increase produced by MK-801 in the normals (163%) was not significant. Cocaine-induced convulsions were abolished in both hypertensive and control rats with doses of MK-801 > 0.1 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Cocaine-induced brainstem seizures and behavior

A variety of abnormal sensory/motor behaviors associated with electrical discharges recorded from the bilateral brainstem were induced in adult WKY rats by mechanical (electrode implants) and DC electrical current stimulations and by acute and chronic administration of cocaine. The electrode implant implicated one side or the other of the reticular system of the brainstem but subjects were not incapacitated by the stimulations. Cocaine (40 mg/kg) was injected subcutaneously for an acute experiment and subsequent 20 mg/kg doses twice daily for 3 days in a chronic study. Cocaine generated more abnormal behaviors in the brainstem perturbation group, especially the electrically perturbated subjects. The abnormal behaviors were yawning, retrocollis, hyperactivity, hypersensitivity, "beating drum" behavior, squealing, head bobbing, circling, sniffing, abnormal posturing, and facial twitching. Shifts in the power frequency spectra of the discharge patterns were noted between quiet and pacing behavioral states. Hypersensitivity to various auditory, tactile, and visual stimulation was present and shifts in the brainstem ambient power spectral frequency occurred in response to tactile stimulation. These findings suggest that the brainstem generates and propagates pathological discharges that can be elicited by mechanical and DC electrical perturbation. Cocaine was found to activate the discharge system and thus induce abnormal behaviors that are generated at the discharge site and at distant sites to which the discharge propagates. Cognitive functions may also be involved since dopaminergic and serotonergic cellular elements at the brainstem level are also implicated.