Aspirin or amiloride for cerebral perfusion defects in cocaine dependence

Social threat exposure in juvenile mice promotes cocaine-seeking by altering blood clotting and brain vasculature

Childhood maltreatment is associated with increased severity of substance use disorder and frequent relapse to drug use following abstinence. However, the molecular and neurobiological substrates that are engaged during early traumatic events and mediate the greater risk of relapse are poorly understood and knowledge of risk factors is to date extremely limited. In this study, we modeled childhood maltreatment by exposing juvenile mice to a threatening social experience (social stressed, S‐S). We showed that S‐S experience influenced the propensity to reinstate cocaine‐seeking after periods of withdrawal in adulthood. By exploring global gene expression in blood leukocytes we found that this behavioral phenotype was associated with greater blood coagulation. In parallel, impairments in brain microvasculature were observed in S‐S mice. Furthermore, treatment with an anticoagulant agent during withdrawal abolished the susceptibility to reinstate cocaine‐seeking in S‐S mice. These findings provide novel insights into a possible molecular mechanism by which childhood maltreatment heightens the risk for relapse in cocaine‐dependent individuals.

Stress-induced changes in mood and cortisol release predict mood effects of amphetamine

BACKGROUND

Stress is thought to contribute to both initiation and relapse to drug abuse. However, the mechanisms by which stress influences drug use are unclear. Interestingly, responses to acute administration of stimulant drugs resemble certain neuronal and hormonal responses to acute stress, and there is accumulating evidence that individual variation in the positive reinforcing or euphorigenic effects of a drug is related to individual differences in responsivity to acute stress.

METHODS

In this study we evaluated relationships between physiological and subjective responses to a stressful task and to an oral dose of d-amphetamine in healthy adult volunteers (N=34). Individuals participated in four experimental sessions; two behavioral sessions involving a stressful task (i.e., public speech) or a non-stressful control task, and two drug sessions involving oral administration of d-amphetamine (20mg) or a placebo. The dependent measures included salivary cortisol, heart rate, mean arterial pressure, and subjective ratings of mood.

RESULTS

As expected, both stress and d-amphetamine increased cortisol, heart rate and blood pressure. Stress increased negative mood, whereas d-amphetamine induced prototypic stimulant effects and increased ratings of drug liking. Analyses revealed that increased negative mood states after stress were correlated with positive mood after amphetamine. In addition, increased cortisol after stress was correlated with positive mood responses to amphetamine. Finally, there were modest positive correlations between cortisol and heart rate increases after stress and mean arterial pressure after amphetamine.

CONCLUSIONS

These results support and extend previous observations that responses to acute stress are correlated with certain subjective, hormonal and cardiovascular effects of a stimulant drug.

Perfusion magnetic resonance imaging in psychiatry

INTRODUCTION

Cerebral perfusion imaging using magnetic resonance imaging (MRI) is widely used in the research and clinical fields to assess the profound changes in blood flow related to ischemic events such as acute stroke, chronic steno-occlusive disease, vasospasm, and abnormal vessel formations from congenital conditions or tumoral neovascularity. With continuing improvements in the precision of MRI-based perfusion techniques, it is increasingly feasible to use this tool in the study of the subtle brain perfusion changes occurring in psychiatric illnesses. This article aims to review the existing literature on applications of perfusion MRI in psychiatric disorder and substance abuse research. The article also provides a brief introductory overview of dynamic susceptibility contrast MRI and arterial spin labeling techniques. An outlook of necessary steps to bring perfusion MRI into the realm of clinical psychiatry as a diagnostic tool is brought forth. Opportunities for research in unexplored disorders and with higher field strengths are briefly examined.

METHODS

PubMed, ISI Web of Knowledge & Scopus were used to search the literature and cross reference several neuropsychiatric disorders with a search term construct, including "magnetic resonance imaging," "dynamic susceptibility contrast," "arterial spin labeling," perfusion or "cerebral blood flow" or "cerebral blood volume" or "mean transit time." The list of disorders used in the search included schizophrenia, depression and bipolar disorder, dementia and Alzheimer's disease, Parkinson's disease, posttraumatic stress disorder, autism, Asperger disease, attention deficit, Tourette syndrome, obsessive-compulsive disorder, Huntington's disease, bulimia nervosa, anorexia nervosa, and substance abuse. For each disorder for which perfusion MRI studies were found, a brief overview of the disorder symptoms, treatment, prevalence, and existing models is provided, and previous findings from nuclear medicine-based perfusion imaging are overviewed. Findings of perfusion MRI studies are then summarized, and overlap of findings are discussed. Overarching conclusions are made, or an outlook for future work in the area is offered, where appropriate.

RESULTS

Despite the now fairly broad availability of perfusion MRI, only a limited number of studies were found using this technology. The search produced 13 studies of schizophrenia, 7 studies in major depression, 12 studies in Alzheimer's disease, and 2 studies in Parkinson's disease. Drug abuse and other disorders have mainly been studied with nuclear medicine-based perfusion imaging. The literature concerning the use of perfusion imaging in psychiatry has not been reviewed in the last 5 years or more. The use of MRI for perfusion measurements in psychiatry has not been reviewed in 10 years.

CONCLUSIONS

Although MRI-based perfusion imaging in psychiatry has mainly been used as a research tool, a path is progressively being cleared for its application in clinical diagnostic and treatment monitoring. The precision of perfusion MRI methods now rivals that of nuclear medicine-based perfusion imaging techniques. Because of their noninvasive nature, arterial spin labeling methods have gained popularity in studies of neuropsychiatric disorders such as schizophrenia, depression, Alzheimer's, and Parkinson's diseases. Perfusion imaging measurements have yet to be included within the diagnostic criteria of neuropsychiatric disorders despite having shown to have great discriminant power in specific disorders. As this young methodology continues to improve and research studies demonstrate the correlation of measured perfusion abnormalities to microcirculatory abnormalities and neuropsychiatric symptomatology, the idea of including such a test within diagnostic criteria for certain mental illnesses becomes increasingly plausible.

SPECT neuroimaging in translational research of CNS disorders

High resolution SPECT imaging is an emerging field and there are only limited studies as yet available in this direction. Still there is continuous effort to achieve better spatial and temporal resolution in order to obtain detailed structural and functional information of different brain regions in small experimental animals. Recently, SPECT imaging system has been used to perform in vivo imaging using specific radioligands to further elucidate the role of dopaminergic, serotonergic, and cholinergic neurotransmission in relation to regional cerebral blood flow in various human CNS disorders and in gene-manipulated mouse models of neurodegeneration. Although in vivo and non-invasive translational research can be performed by high-resolution microPET imaging system, its limited spatial resolution restricts detailed anatomical and functional information of different brain regions involved in disease process. Recently developed NanoSPECT/CT imaging system has a better spatial resolution hence can be used to correlate and confirm microPET imaging data and determine the precise structural and functional anatomy of CNS disorders and their remission. Moreover SPECT imaging system reduces the cost and number of animals and provides detailed information of CNS disorders at the cellular, molecular and genetic level. Furthermore, SPECT system is economical, provides less radiation burden, and can be used to study bio-distribution of newly synthesized radioligands with increased target to non-target ratios, quality control, and clinical applications. It is envisaged that high-resolution SPECT imaging system will further improve in vivo non-invasive translational research on CNS disorders of unknown etiopathogenesis and their treatment in future.

Inhibition of nitric oxide synthase enhances cocaine's developmental toxicity: vascular and CNS effects

Ischemia and/or reperfusion injury from free radicals may cause cocaine's toxicity, including its effect upon neurobehavioral development. We previously used salicylate to measure hydroxyl free radicals in chick embryos exposed to cocaine. The combination was more toxic than cocaine alone. We postulated that salicylate enhanced the vasoconstriction and toxicity via inhibition of compensatory processes (eg by inhibition of the synthesis of vasodilatory prostanoids and/or nitric oxide). A nontoxic dose of N(G)-nitro-L-arginine methyl ester (L-NAME) was used to inhibit nitric oxide synthase to test this hypothesis. In one experiment, cocaine was injected every 1.5 h (total dose =67.5 mg/kg egg) on day 15 of development, 1 h after injection of L-NAME (200 mg/kg egg) to determine viability and hatchability, which are measures of toxicity. Another experiment measured diameters of blood vessels after L-NAME injection, followed by NaCl or cocaine infusion (0.23 mg/egg/min; total dose=67.5 mg/kg egg) at 15 and 5 min afterwards. Lastly, brains of embryos pretreated with L-NAME before cocaine injections were analyzed for nitric oxide synthase activity. Cocaine decreased viability and hatchability. L-NAME enhanced cocaine's effect upon both parameters. Blood vessel diameters were decreased by cocaine after 15 min of infusion. L-NAME+cocaine caused a decrease in vessel diameter as soon as 5 min into the infusion and was greater with time, compared with other groups. Enzyme activity in brains was decreased only in the L-NAME+cocaine group. Thus, inhibition of nitric oxide synthesis interferes with the embryos' capacity to mount a compensatory vasodilatory response.

Novel approaches to the treatment of cocaine addiction

Cocaine addiction continues to be an important public health problem with over 1.7 million users in the US alone. Although there are no approved pharmacotherapies for cocaine addiction, a number of medications have been tested with some promising results. In this review, we summarise some of the emerging targets for cocaine pharmacotherapy including dopaminergic and GABA medications, adrenoceptor antagonists, vasodilators and immunotherapies. The brain dopamine system plays a significant role in mediating the rewarding effects of cocaine. Among dopaminergic agents tested for cocaine pharmacotherapy, disulfiram has decreased cocaine use in a number of studies. Amantadine, another medication with dopaminergic effects, may also be effective in cocaine users with high withdrawal severity. GABA is the main inhibitory neurotransmitter in the brain, and accumulating evidence suggests that the GABA system modulates the dopaminergic system and cocaine effects. Two anticonvulsant medications with GABAergic effects, tiagabine and topiramate, have yielded positive findings in clinical trials. Baclofen, a GABA(B) receptor agonist, is also promising, especially in those with more severe cocaine use. Some of the physiological and behavioural effects of cocaine are mediated by activation of the adrenergic system. In cocaine users, propranolol, a beta-adrenoceptor antagonist, had promising effects in individuals with more severe cocaine withdrawal symptoms. Cerebral vasodilators are another potential target for cocaine pharmacotherapy. Cocaine users have reduced cerebral blood flow and cortical perfusion deficits. Treatment with the vasodilators amiloride or isradipine has reduced perfusion abnormalities found in cocaine users. The functional significance of these improvements needs to be further investigated. All these proposed pharmacotherapies for cocaine addiction act on neural pathways. In contrast, immunotherapies for cocaine addiction are based on the blockade of cocaine effects peripherally, and as a result, prevent or at least slow the entry of cocaine into the brain. A cocaine vaccine is another promising treatment for cocaine addiction. The efficacy of this vaccine for relapse prevention is under investigation. Many initial promising findings need to be replicated in larger, controlled clinical trials.

Vasoconstriction caused by cocaine is enhanced by sodium salicylate: is inducible nitric oxide synthase mRNA related?

We have previously found that sodium salicylate (NaSal), injected into chicken eggs at nontoxic doses used for quantifying hydroxyl free radicals in hearts and brains of embryos, caused or exacerbated hemorrhages and dramatically reduced hatchability when combined with cocaine (Coc). It has also been reported that inducible nitric oxide synthase (iNOS) gene expression is altered in brain in response to vascular damage and inflammation. In this study we measured diameters of membrane-bound blood vessels (BV) before and after pretreatment with saline (NaCl) or NaSal (100 mg/kg egg), followed by infusion of either NaCl or Coc HCl (total of 67.5 mg/kg egg) during 15 min. Brains and hearts of the embryos were then analyzed for iNOS messenger RNA (mRNA) concentrations. Coc caused vasoconstriction that was significant 5 min postinfusion (5 min PI) of the entire dose (ie after 67.5 mg/kg egg). Significant vasoconstriction was evident within 5 min in the group injected with NaSal followed by infusion with Coc (ie after 22.5 mg Coc/kg egg). Expression of iNOS mRNA was significantly increased only in the brains of the group exposed to NaSal plus Coc, and the increase was inversely related to BV diameter. These data are discussed in relation to effects of salicylate upon prostanoid synthesis and/or nitric oxide synthesis via iNOS inhibition and their possible relationship to Coc-associated cerebral vascular and/or cardiovascular events in abusing humans.

Platelet abnormalities associated with cerebral perfusion defects in cocaine dependence

BACKGROUND

This study assessed whether reduced regional cerebral blood flow (rCBF; hypoperfusion) in cocaine-dependent (CD) patients is associated with platelet abnormalities and whether these platelet abnormalities predict improvement in hypoperfusion after 1 month of abstinence.

METHODS

We correlated platelet number and aggregation with rCBF hypoperfusion in 54 CD patients at baseline and after a month of abstinence while taking either 325 mg aspirin or placebo. We measured rCBF by (SPECT) with (Tc-HMPAO). Platelet aggregation to adenosine diphosphate was compared at baseline and after treatment.

RESULTS

At baseline the number of hypoperfused voxels positively correlated with higher platelet aggregation, and five brain regions (bilateral frontal, right insula, right cingulate, left temporal lobes) showed significantly more hypoperfusion in the high than low platelet aggregation group. After abstinence, hypoperfusion significantly improved regardless of treatment assignment, and greater platelet aggregation at baseline predicted greater improvement in hypoperfusion. After abstinence, only the cingulate continued to show more hypoperfusion in the high- than low-aggregation group.

CONCLUSIONS

Because platelet function was related to hypoperfusion primarily in the distribution of the middle cerebral artery, where CD patients most commonly have strokes, more potent antiplatelet agents than aspirin might be effective.