Tolerance develops to the sympathomimetic but not the local anesthetic effects of cocaine

Methylenedioxypyrovalerone (MDPV) mimics cocaine in its physiological and behavioral effects but induces distinct changes in NAc glucose

Methylenedioxypyrovalerone (MDPV) is generally considered to be a more potent cocaine-like psychostimulant, as it shares a similar pharmacological profile with cocaine and induces similar physiological and locomotor responses. Recently, we showed that intravenous cocaine induces rapid rise in nucleus accumbens (NAc) glucose and established its relation to neural activation triggered by the peripheral drug actions. This study was conducted to find out whether MDPV, at a behaviorally equivalent dose, shares a similar pattern of NAc glucose dynamics. Using enzyme-based glucose sensors coupled with amperometery in freely moving rats, we found that MDPV tonically decreases NAc glucose levels, a response that is opposite to what we previously observed with cocaine. By analyzing Skin-Muscle temperature differentials, a valid measure of skin vascular tone, we found that MDPV induces vasoconstriction; a similar effect at the level of cerebral vessels could be responsible for the MDPV-induced decrease in NAc glucose. While cocaine also induced comparable, if not slightly stronger peripheral vasoconstriction, this effect was overpowered by local neural activity-induced vasodilation, resulting in rapid surge in NAc glucose. These results imply that cocaine-users may be more susceptible to addiction than MDPV-users due to the presence of an interoceptive signal (i.e., sensory cue), which may result in earlier and more direct reward detection. Additionally, while health complications arising from acute cocaine use are typically cardiovascular related, MDPV may be more dangerous to the brain due to uncompensated cerebral vasoconstriction.

Central and peripheral contributions to dynamic changes in nucleus accumbens glucose induced by intravenous cocaine

The pattern of neural, physiological and behavioral effects induced by cocaine is consistent with metabolic neural activation, yet direct attempts to evaluate central metabolic effects of this drug have produced controversial results. Here, we used enzyme-based glucose sensors coupled with high-speed amperometry in freely moving rats to examine how intravenous cocaine at a behaviorally active dose affects extracellular glucose levels in the nucleus accumbens (NAc), a critical structure within the motivation-reinforcement circuit. In drug-naive rats, cocaine induced a bimodal increase in glucose, with the first, ultra-fast phasic rise appearing during the injection (latency 6–8 s; ~50 μM or ~5% of baseline) followed by a larger, more prolonged tonic elevation (~100 μM or 10% of baseline, peak ~15 min). While the rapid, phasic component of the glucose response remained stable following subsequent cocaine injections, the tonic component progressively decreased. Cocaine-methiodide, cocaine's peripherally acting analog, induced an equally rapid and strong initial glucose rise, indicating cocaine's action on peripheral neural substrates as its cause. However, this analog did not induce increases in either locomotion or tonic glucose, suggesting direct central mediation of these cocaine effects. Under systemic pharmacological blockade of dopamine transmission, both phasic and tonic components of the cocaine-induced glucose response were only slightly reduced, suggesting a significant role of non-dopamine mechanisms in cocaine-induced accumbal glucose influx. Hence, intravenous cocaine induces rapid, strong inflow of glucose into NAc extracellular space by involving both peripheral and central, non-dopamine drug actions, thus preventing a possible deficit resulting from enhanced glucose use by brain cells.

Electrophysiologic and Hemodynamic Effects of Sodium Bicarbonate in a Canine Model of Severe Cocaine Intoxication

OBJECTIVE

Cocaine toxicity causes myocardial depression, malignant dysrhythmias, and sudden death, partially due to cocaine-related myocardial sodium channel blockade. Because of cocaine's ability to block cardiac sodium channels, sodium bicarbonate (NaHCO3) has been proposed as an antidote. The hypothesis of this study was that NaHCO3 would correct cocaine-induced conduction abnormalities and resultant hemodynamic compromise in an animal model simulating severe cocaine intoxication.

METHODS

DESIGN

Prospective, controlled, experimental study in which 15 anesthetized dogs were given three successive boluses of cocaine (7 mg/kg) and then randomized to receive NaHCO3, 2 mEq/kg (n = 8) or placebo (n =7).

MEASUREMENTS

Arterial, left ventricular, and pulmonary artery pressures; cardiac output (CO); electrocardiogram (ECG); blood gases; and serum concentrations of cocaine were measured at baseline, at fixed time intervals after each bolus of cocaine, and then after administration of NaHCO3 or placebo. Statistical significance was determined by analysis of variance (ANOVA) for repeated measures.

RESULTS

Seven dogs experienced significant arrhythmias, including VT, pulseless electrical activity, and third-degree atrioventricular block; 2 of these dogs expired prior to receiving NaHCO3 and were excluded. Immediately after administering NaHCO3, QRS duration decreased by 30% (p < 0.001), returning to baseline more quickly than in the control group. This effect was associated with a brief 30% decrease in MAP (p = NS). After NaHCO3, CO increased 78% and remained increased for 5 min (p < 0.007). One dog converted from complete heart block to sinus rhythm shortly after NaHCO3 administration.

CONCLUSIONS

NaHCO3 improved ECG changes secondary to cocaine toxicity and improved myocardial function.

Cardiovascular responses elicited during binge administration of cocaine

Cocaine use is often characterized by a repeated pattern of frequent administrations (binge) followed by periods of abstinence. The repeated binge administration of methamphetamine and 3,4-methylenedioxymethamphetamine (MDMA) alters cardiovascular function and the arterial pressure and heart rate responses elicited by these drugs. Whether repeated binges of cocaine similarly affect cardiovascular function and cardiovascular responsiveness is unknown. Radiotelemetry was used to record the cardiovascular responses elicited during three successive cocaine binges (5 mg/kg, t.i.d., for 4 days) in conscious, unrestrained rats. Each binge was separated by a 10-day cocaine-free period. The effects of cocaine administration on vascular reactivity and vasovagal, Bezold-Jarisch reflex function were also evaluated. The intravenous administration of cocaine increased both mean arterial pressure (MAP) and heart rate. The arterial pressure and heart rate responses elicited by cocaine, both within and between the binges, were remarkably similar. The arterial pressure and heart rate responses elicited by the intravenous administration of sodium nitroprusside, acetylcholine and phenylephrine before each binge and 10 days after the last binge were not altered after the binge administration of cocaine. Likewise, Bezold-Jarisch reflex function elicited by intravenous serotonin was unchanged after the binge administration of cocaine. These results indicate that the administration of cocaine using this repeated binge model does not alter the arterial pressure and heart rate responses elicited by the drug, nor does it alter the cardiovascular responses elicited by a variety of vasoactive substances.

Cocaethylene's effects on coronary artery blood flow and cardiac function in a canine model

OBJECTIVES

Cocaethylene is a toxic metabolite of cocaine formed in the presence of ethanol. Though cocaine causes coronary vasoconstriction, cocaethylene's effects on coronaryflow are unknown. The aim of our study was to describe cocaethylene 's effects on coronary flow and cardiac function.

METHODS

Sixteen alpha-chloralose anesthetized dogs were monitored with Swan-Ganz, arterial and venous catheters, and an electrocardiogram. Dopplerflow probes were placed on the circumflex and left anterior descending coronary arteries. Dogs were allotted 15 mg/kg (n = 10) or 30mg/kg (n = 6) of cocaethylene given as a continuous intravenous infusion. Measurements were made at fixed time intervals during the 60-minute cocaethylene infusion and 2-hour observation period.

RESULTS

The cocaethylene concentrations were maximal at the end of the infusion and cocaethylene was rapidly metabolized to benzoylecognine. One low-dose animal died of ventricular fibrillation. Five high-dose dogs experienced ventricular arrhythmias or pulseless electrical activity (PEA), and three died. In the low-dose group, cocaethylene caused a 38% increase in mean arterial pressure relative to baseline, and increased systemic vascular resistance. In the high-dose group, at maximal cocaethylene concentrations, stroke volume decreased by 42% (p < 0.0002), and circumflex blood flow decreased by 30% (p = 0.03) relative to baseline, when arrhythmias occurred. The PR, QRS, and QTc intervals increased by 48, 209, and 29%, respectively (p < 0.001). As cocaethylene levels declined, circumflex blood flow increased by 77% (p = 0.05) and mean arterial pressure increased 49% (p < 0.01), also relative to baseline.

CONCLUSIONS

Cocaethylene caused hypertension and increased systemic vascular resistance. At high concentrations, it decreased myocardial function, slowed cardiac conduction, and was arrhythmogenic. The cocaethylene's toxicity does not appear to be mediated by effects on coronary blood flow.