Acute changes in cranial blood flow after cocaine hydrochloride

Cocaine Constrictor Mechanisms of the Cerebral Vasculature

Cocaine constriction of the cerebral vasculature is thought to contribute to the ischemia associated with cocaine use. However, the mechanisms whereby cocaine elicits relevant vasoconstriction remain elusive. Indeed, proposed intra- and intercellular mechanisms based on over 3 decades of ex vivo vascular studies are, for the most part, of questionable relevancy due to the generally low contractile efficacy of cocaine combined with the use of nonresistance-type vessels. Furthermore, the significance attached to mechanisms derived from in vivo animal studies may be limited by the inability to demonstrate cocaine-induced decreased cerebral blood flow, as observed in (awake) humans. Despite these apparent limitations, we surmise that the vasoconstriction relevant to cocaine-induced ischemia is elicited by inhibition of dilator and activation of constrictor pathways because of cocaine action on the neurovascular unit (neuron, astrocyte, and vessel) and on vessels outside the unit. Furthermore, previous cocaine exposure, that is, conditions present in human subjects, downregulates and sensitizes these dilator and constrictor pathways, respectively, thereby enhancing constriction to acute cocaine. Identification of specific intra- and intercellular mechanisms requires investigations in the isolated microvasculature and the neurovascular unit from species chronically exposed to cocaine and in which cocaine decreases cerebral blood flow.

Neurologic Complications of Psychomotor Stimulant Abuse

Psychomotor stimulants are drugs that act on the central nervous system (CNS) to increase alertness, elevate mood, and produce a sense of well-being. These drugs also decrease appetite and the need for sleep. Stimulants can enhance stamina and improve performance in tasks that have been impaired by fatigue or boredom. Approved therapeutic applications of stimulants include attention deficit hyperactivity disorder (ADHD), narcolepsy, and obesity. These agents also possess potent reinforcing properties that can result in excessive self-administration and abuse. Chronic use is associated with adverse effects including psychosis, seizures, and cerebrovascular accidents, though these complications usually occur in individuals with preexisting risk factors. This chapter reviews the adverse neurologic consequences of chronic psychomotor stimulant use and abuse, with a focus on two prototypical stimulants methamphetamine and cocaine.

Cocaine use and risk of stroke: a systematic review

BACKGROUND

Both cocaine use and strokes impact public health. Cocaine is a putative cause of strokes, but no systematic review of the scientific evidence has been published.

METHODS

All relevant bibliographic-databases were searched until January 2014 for articles on the epidemiological association between cocaine use and strokes. Search strings were supervised by expert librarians. Three researchers independently reviewed studies for inclusion and data extraction following STROBE recommendations. Quality appraisal included study validity and bias. Both ischemic and hemorrhagic strokes were considered.

RESULTS

Of 996 articles, 9 were selected: 7 case-control studies (CCS) and 2 cross-sectional (CSS) studies. One CCS (aOR=6.1; 95% CI: 3.3-11.8) and one CSS (aOR=2.33; 95% CI: 1.74-3.11) showed an association between cocaine and hemorrhagic strokes. The latter study also found a positive relationship with ischemic stroke (aOR=2.03; 95% CI: 1.48-2.79). Another CCS found the exposure to be associated with stroke without distinguishing between types (aOR=13.9; 95% CI: 2.8-69.4). One forensic CCS found that deaths with cocaine-positive toxicology presented a 14.3-fold (95% CI: 5.6-37) and 4.6-fold (95% CI: 2.5-8.5) increased risk of atherosclerosis compared to opioid-related deaths and hanging-deaths respectively. One CCS did not provide an aOR but found a statistically significant association between cocaine and hemorrhagic stroke. Three CCS and one CSS did not find any relationship between cocaine and strokes. Inadequate control for confounding was not uncommon.

CONCLUSIONS

Epidemiological evidence suggests that cocaine use increases the risk of stroke. Larger, more rigorous observational studies, including cohort approaches, are needed to better quantify this risk, and should consider stroke type, hypertension variation, frequency/length of cocaine use, amphetamines co-use, and other factors.

Neuroimaging and drug taking in primates

RATIONALE

Neuroimaging techniques have led to significant advances in our understanding of the neurobiology of drug taking and the treatment of drug addiction in humans. Neuroimaging approaches provide a powerful translational approach that can link findings from humans and laboratory animals.

OBJECTIVE

This review describes the utility of neuroimaging toward understanding the neurobiological basis of drug taking and documents the close concordance that can be achieved among neuroimaging, neurochemical, and behavioral endpoints.

RESULTS

The study of drug interactions with dopamine and serotonin transporters in vivo has identified pharmacological mechanisms of action associated with the abuse liability of stimulants. Neuroimaging has identified the extended limbic system, including the prefrontal cortex and anterior cingulate, as important neuronal circuitry that underlies drug taking. The ability to conduct within-subject longitudinal assessments of brain chemistry and neuronal function has enhanced our efforts to document long-term changes in dopamine D2 receptors, monoamine transporters, and prefrontal metabolism due to chronic drug exposure. Dysregulation of dopamine function and brain metabolic changes in areas involved in reward circuitry have been linked to drug taking behavior, cognitive impairment, and treatment response.

CONCLUSIONS

Experimental designs employing neuroimaging should consider well-documented determinants of drug taking, including pharmacokinetic considerations, subject history, and environmental variables. Methodological issues to consider include limited molecular probes, lack of neurochemical specificity in brain activation studies, and the potential influence of anesthetics in animal studies. Nevertheless, these integrative approaches should have important implications for understanding drug taking behavior and the treatment of drug addiction.

Acute brain metabolic effects of cocaine in rhesus monkeys with a history of cocaine use

Cocaine addiction involves an escalation in drug intake which alters many brain functions. The present study documented cocaine-induced changes in brain metabolic activity as a function of cocaine self-administration history. Experimentally naive rhesus monkeys (N = 6) were given increasing access to cocaine under a fixed-ratio schedule of intravenous (i.v.) drug self-administration. PET imaging with F-18 labeled fluorodeoxyglucose (FDG) was used to measure acute intramuscular (i.m.) cocaine-induced changes in brain metabolism in the cocaine-naïve state, following 60 sessions under limited-access conditions (1 h/day), following 60 sessions under extended-access conditions (4 h/day), and following 4 weeks of drug withdrawal. In the cocaine-naïve state, cocaine-induced increases in brain metabolism were restricted to the prefrontal cortex. As cocaine exposure increased from limited to extended access, metabolic effects expanded throughout the frontal cortex and were induced within the striatum. Conversely, cocaine-induced activation was far less robust following withdrawal. The results highlight a progressive expansion of the metabolic effects of cocaine to include previously unaffected dopamine innervated brain regions as a consequence of cocaine self-administration history. The identification of brain regions progressively influenced by drug exposure may be highly relevant toward efforts to develop treatments for cocaine addiction.

Cortical activation during cocaine use and extinction in rhesus monkeys

RATIONALE

Acute re-exposure to cocaine or drug cues associated with cocaine use can elicit drug craving and relapse. Neuroimaging studies have begun to define neurobiological substrates underlying the acute effects of cocaine or cocaine cues in cocaine-dependent subjects.

OBJECTIVE

The present study was the first to use functional brain imaging to document acute cocaine-induced changes in brain activity during active drug use in nonhuman primates.

MATERIALS AND METHODS

Positron emission tomography imaging with O15-labeled water was used to measure drug-induced changes in cerebral blood flow. The acute effects of cocaine administered noncontingently were characterized in four drug-naïve rhesus monkeys. The same subjects were trained to self-administer cocaine under a fixed ratio schedule during image acquisition. Subsequently, three subjects with an extensive history of cocaine use were trained to self-administer cocaine under a second-order schedule. The same subjects also underwent extinction sessions during which saline was substituted for cocaine under the second-order schedule.

RESULTS

Noncontingent administration of cocaine in drug-naïve subjects induced robust activation of prefrontal cortex localized primarily to the dorsolateral regions. In contrast, the pattern of brain activation induced by self-administered cocaine differed qualitatively and included anterior cingulate cortex. Moreover, drug-associated stimuli during extinction also induced robust activation of prefrontal cortex.

CONCLUSIONS

The effects of cocaine and associated cues extend beyond the limbic system to engage brain areas involved in cognitive processes. The identification of neural circuits underlying the direct pharmacological and conditioned stimulus effects of cocaine may be highly relevant toward efforts to develop treatments for cocaine addiction.

Nonhuman primate neuroimaging and the neurobiology of psychostimulant addiction

Neuroimaging techniques have led to significant advances in our understanding of the neurobiology and treatment of drug addiction in humans. The capability to conduct parallel studies in nonhuman primates and human subjects provides a powerful translational approach to link findings in human and animal research. A significant advantage of nonhuman primate models is the ability to use drug-naïve subjects in longitudinal designs that document the neurobiological changes that are associated with chronic drug use. Moreover, experimental therapeutics can be evaluated in subjects with well-documented histories of drug exposure. The in vivo distribution and pharmacokinetics of drug binding in brain have been related to the time-course of behavioral effects associated with the addictive properties of stimulants. Importantly, the characterization of drug interactions with specific protein targets in brain has identified potential targets for medication development. Neuroimaging has proven especially useful in studying the dynamic changes in neuronal function that may be associated with environmental variables. Last, neuroimaging has been used effectively in nonhuman primates to characterize both transient and long-lasting changes in brain chemistry associated with chronic drug exposure. Although there is some evidence to suggest neurotoxicity in humans with long histories of stimulant use, parallel studies in nonhuman primates have not identified consistent long-term changes in such neurochemical markers. Collectively, the results of these studies of nonhuman primates have enhanced our understanding of the neurobiological basis of stimulant addiction and should have a significant impact on efforts to develop medications to treat stimulant abuse.

Measurement of dopamine transporter occupancy for multiple injections of cocaine using a single injection of [F-18]FECNT

The fraction of transporters occupied following injection of specific inhibitors is an important parameter for defining and comparing the molecular mechanisms of different drugs. This work generalizes the reference tissue method to estimate dopamine transporter occupancy for two levels of cocaine administration using only a single injection of [(18)F]FECNT. The results are validated by comparison with literature values. Five rhesus monkeys were studied. On each animal, a baseline scan was collected following [(18)F]FECNT injection (phase a). At 120 min postinjection, 0.1 mg/kg cocaine was injected and the animal was scanned for 50 additional min (phase b). Then 1.0 mg/kg cocaine was injected and another 50-min scan sequence was collected (phase c). Time-activity curves (encompassing all three phases) were generated for each animal from regions drawn over the putamen and cerebellum. The putamen curve was modeled using the cerebellum as the input function. Percent DAT occupancy following the cocaine injections was determined by comparing k(3)/k(4) = B(max)/k(D) for the three phases. The 0.1 and 1.0 mg/kg cocaine doses occupied 53% +/- 5% and 87% +/- 5% of the transporters, respectively. The measured occupancies are consistent with literature values that maintain self-administration in animals and produce a "high" in human subjects. This work demonstrates that a single injection of [(18)F]FECNT can be used to measure the effects of multiple cocaine challenges. Two advantages of this technique are: reduced variability in dose-response curves because the subject is his/her own control, and the (18)F label allows evaluation of longer-acting drugs.

Cocaine-induced cerebral vasoconstriction differs as a function of sex and menstrual cycle phase

BACKGROUND

Chronic cocaine abusing women experience fewer cerebral perfusion defects and less neuronal injury than men with comparable drug use histories. This study assessed whether a basis for this discrepancy is a sex difference in cocaine's acute cerebrovascular effects.

METHODS

The subjects in this study were 13 healthy and neurologically normal women, reporting occasional cocaine (mean 13, range 1-40 lifetime cocaine exposures). All subjects were administered cocaine (0.4 mg/kg) intravenously, during both the follicular (days 3-8) and luteal (days 18-24) menstrual cycle phases. Dynamic susceptibility contrast magnetic resonance imaging assessments of relative global cerebral blood volume (CBV) changes were conducted on both study days, 10 min after cocaine administration.

RESULTS

Cocaine did not alter CBV in follicular phase women, but reduced luteal phase CBV by 10%, indicative of vasoconstriction (analysis of variance [ANOVA], F = 5.1, p <.05). Postcocaine CBV was lower in men administered the drug via an identical protocol relative to follicular phase women (ANOVA, F = 5.4, p <.04). Postcocaine CBV was also lower in the male referent group relative to luteal phase women, but this difference did not achieve statistical significance. No measurable sex or menstrual cycle phase differences in cocaine's cardiovascular effects were noted.

CONCLUSIONS

These findings suggest both menstrual cycle phase and sex differences in cocaine's acute cerebrovascular effects, which may contribute to sex differences in the severity of brain dysfunction found in chronic cocaine abusers. These findings imply that gonadal steroids or the factors they modulate merit study as possible therapeutic agents for reducing cocaine-induced cerebrovascular disorders.

Proton magnetic resonance spectroscopy of human basal ganglia: response to cocaine administration

BACKGROUND

Proton magnetic resonance spectroscopy was used to determine the effects of intravenous cocaine or placebo administration on human basal ganglia water and metabolite resonances.

METHODS

Long echo time, proton magnetic resonance spectra of water and intracellular metabolites were continuously acquired from an 8-cm(3) voxel centered on the left caudate and putamen nuclei before, during, and after the intravenous administration of cocaine or a placebo in a double-blind manner.

RESULTS

Cocaine, at both 0.2 and 0.4 mg/kg, did not alter the peak area for water. Cocaine at 0.2 mg/kg induced small and reversible increases in choline-containing compounds and N-acetylaspartate peak areas. Cocaine at 0.4 mg/kg induced larger and more sustained increases in choline-containing compounds and N-acetylaspartate peak areas. No changes in either water or metabolite resonances were noted following placebo administration.

CONCLUSIONS

These increases in choline-containing compounds and N-acetylaspartate peak areas may reflect increases in metabolite T2 relaxation times secondary to osmotic stress and/or increased phospholipid signaling within the basal ganglia following cocaine administration. This is the first report of acute, drug-induced changes in the intensity of human brain proton magnetic resonance spectroscopy resonance areas.

The regulation of cerebral blood flow during intravenous cocaine administration in cocaine abusers

Cocaine abuse is associated with heightened risk of life-threatening neurological complications such as strokes, seizures, and transient ischemic attacks. We used transcranial Doppler (TCD) sonography, a continuous measure of cerebral blood flow velocity, to better understand the changes in cerebral hemodynamics produced by cocaine administration, which may lead to an increased risk for stroke in cocaine abusers. Heart rate and blood pressure were also measured. Blood flow velocity of seven cocaine abusers was studied during placebo, 10-, 25-, and 50-mg intravenous (i.v.) injections of cocaine. A significant increase in mean and systolic velocity which lasted for about two minutes was observed with all doses of cocaine, with no change in the placebo condition. This increase in systolic velocity indicates that cocaine produces an immediate and brief period of vasoconstriction in large arteries of the brain. The present results elucidate the time course of cocaine's acute cerebrovascular effects and provide a better understanding of etiology of cocaine-related stroke and transient ischemic attacks.

Cocaine decreases cortical cerebral blood flow but does not obscure regional activation in functional magnetic resonance imaging in human subjects

The authors used functional magnetic resonance imaging (fMRI) to determine whether acute intravenous (i.v.) cocaine use would change global cerebral blood flow (CBF) or visual stimulation-induced functional activation. They used flow-sensitive alternating inversion recovery (FAIR) scan sequences to measure CBF and blood oxygen level-dependent (BOLD) sensitive T2* scan sequences during visual stimulation to measure neuronal activation before and after cocaine and saline infusions. Cocaine (0.6 mg/kg i.v. over 30 seconds) increased heart rate and mean blood pressure and decreased end tidal carbon dioxide (CO2). All measures returned to baseline by 2 hours, the interinfusion interval, and were unchanged by saline. Flow-sensitive alternating inversion recovery imaging demonstrated that cortical gray matter CBF was unchanged after saline infusion (-2.4 +/- 6.5%) but decreased (-14.1 +/- 8.5%) after cocaine infusion (n = 8, P < 0.01). No decreases were detected in white matter, nor were changes found comparing BOLD signal intensity in cortical gray matter immediately before cocaine infusion with that measured 10 minutes after infusion. Visual stimulation resulted in comparable BOLD signal increases in visual cortex in all conditions (before and after cocaine and saline infusion). Despite a small (14%) but significant decrease in global cortical gray matter CBF after acute cocaine infusion, specific regional increases in BOLD imaging, mediated by neurons, can be measured reliably.