THE CENTRAL EFFECTS OF XYLOPININE IN MICE

Leakage of the blood-brain barrier followed by vasogenic edema as the ultimate cause of death induced by acute methamphetamine overdose

Methamphetamine (METH) is a potent CNS stimulant that is widely used as a recreational drug. Due to its ability to increase bodily heat production and diminish heat loss due to peripheral vasoconstriction, METH is able to increase brain and body temperature. The hyperthermic effects of METH are potentiated when the drug is used under conditions of psycho-physiological activation and in warm ambient temperatures. In this short review, we present and discuss our data on the effects of METH on brain temperature and a number of neural parameters that characterize permeability of the blood-brain barrier (albumin immunoreactivity), glial activity (GFAP immunoreactivity), brain tissue water content, and structural abnormalities of brain cells. We demonstrate that the extent of these neural alterations strongly depends on METH-induced brain temperature elevation and they all dramatically increase following exposure to METH in warm (29°C) vs. standard (23°C) ambient temperatures. Based on these data we consider possible pathophysiological mechanisms underlying acute METH toxicity, suggesting the critical role of drug-induced brain hyperthermia, temperature-dependent leakage of the blood-brain barrier (BBB), and the development of vasogenic edema that could finally result in decompensation of vital functions and death.

The hidden side of drug action: brain temperature changes induced by neuroactive drugs

RATIONALE

Most neuroactive drugs affect brain metabolism as well as systemic and cerebral blood flow, thus altering brain temperature. Although this aspect of drug action usually remains in the shadows, drug-induced alterations in brain temperature reflect their metabolic neural effects and affect neural activity and neural functions.

OBJECTIVES

Here, I review brain temperature changes induced by neuroactive drugs, which are used therapeutically (general anesthetics), as a research tool (dopamine agonists and antagonists), and self-administered to induce desired psychic effects (cocaine, methamphetamine, ecstasy). I consider the mechanisms underlying these temperature fluctuations and their influence on neural, physiological, and behavioral effects of these drugs.

RESULTS

By interacting with neural mechanisms regulating metabolic activity and heat exchange between the brain and the rest of the body, neuroactive drugs either increase or decrease brain temperatures both within (35-39 °C) and exceeding the range of physiological fluctuations. These temperature effects differ drastically depending upon the environmental conditions and activity state during drug administration. This state-dependence is especially important for drugs of abuse that are usually taken by humans during psycho-physiological activation and in environments that prevent proper heat dissipation from the brain. Under these conditions, amphetamine-like stimulants induce pathological brain hyperthermia (>40 °C) associated with leakage of the blood-brain barrier and structural abnormalities of brain cells.

CONCLUSIONS

The knowledge on brain temperature fluctuations induced by neuroactive drugs provides new information to understand how they influence metabolic neural activity, why their effects depend upon the behavioral context of administration, and the mechanisms underlying adverse drug effects including neurotoxicity.

Environmental conditions modulate neurotoxic effects of psychomotor stimulant drugs of abuse

Psychomotor stimulants such as methamphetamine (METH), amphetamine, and 3,4-metylenedioxymethamphetamine (MDMA or ecstasy) are potent addictive drugs. While it is known that their abuse could result in adverse health complications, including neurotoxicity, both the environmental conditions and activity states associated with their intake could strongly enhance drug toxicity, often resulting in life-threatening health complications. In this review, we analyze results of animal experiments that suggest that even moderate increases in environmental temperatures and physiological activation, the conditions typical of human raves parties, dramatically potentiate brain hyperthermic effects of METH and MDMA. We demonstrate that METH also induces breakdown of the blood-brain barrier, acute glial activation, brain edema, and structural abnormalities of various subtypes of brain cells; these effects are also strongly enhanced when the drug is used at moderately warm environmental conditions. We consider the mechanisms underlying environmental modulation of acute drug neurotoxicity and focus on the role of brain temperature, a critical homeostatic parameter that could be affected by metabolism-enhancing drugs and environmental conditions and affect neural activity and functions.

Acute methamphetamine intoxication: brain hyperthermia, blood-brain barrier, brain edema, and morphological cell abnormalities

Methamphetamine (METH) is a powerful and often abused stimulant with potent addictive and neurotoxic properties. While it is generally assumed that multiple chemical substances released in the brain following METH-induced metabolic activation (or oxidative stress) are primary factors underlying damage of neural cells, in this work we present data suggesting a role of brain hyperthermia and associated leakage of the blood-brain barrier (BBB) in acute METH-induced toxicity. First, we show that METH induces a dose-dependent brain and body hyperthermia, which is strongly potentiated by associated physiological activation and in warm environments that prevent proper heat dissipation to the external environment. Second, we demonstrate that acute METH intoxication induces robust, widespread but structure-specific leakage of the BBB, acute glial activation, and increased water content (edema), which are related to drug-induced brain hyperthermia. Third, we document widespread morphological abnormalities of brain cells, including neurons, glia, epithelial, and endothelial cells developing rapidly during acute METH intoxication. These structural abnormalities are tightly related to the extent of brain hyperthermia, leakage of the BBB, and brain edema. While it is unclear whether these rapidly developed morphological abnormalities are reversible, this study demonstrates that METH induces multiple functional and structural perturbations in the brain, determining its acute toxicity and possibly contributing to neurotoxicity.

Disposition of catecholamine-derived alkaloids in mammalian systems

Tetrahydropapaveroline, the tetrahydroisoquinoline alkaloid derived from dopamine, is converted in vivo by rats and by rat liver and brain preparations to tetrahydroprotoberberine alkaloids. The latter alkaloids have also been identified for the first time in the urine of parkinsonian patients receiving L-dopa therapy. These findings suggest that man, like plants, may have the ability to elaborate several classes of alkaloids with potentially important pharmacological consequences. Thus, this newly demonstrated ability of mammalian systems to evoke the biosynthesis of benzyl-tetrahydroisoquinoline-derived alkaloids - a capability previously considered unique to plants - elects the tetrahydroprotoberberine alkaloids as representative of the first class of a possible constellation of complex mammalian alkaloids elaborated from the neuroamines.