Regulated Expression and Function of the Somatodendritic Catecholamine Neurotransmitter Transporters

Pain, analgesia and genetics

OBJECTIVES

In the clinical setting, there is marked intersubject variability in the intensity of pain reported by patients with apparently similar pain states, as well as widely differing analgesic dosing requirements between individuals to produce satisfactory pain relief with tolerable side-effects. Genetic and environmental factors as well as their interaction are implicated, and these are discussed in this review.

KEY FINDINGS

Pioneering work undertaken in mice more than a decade ago, showed a strong genetic contribution to levels of nociception/hypersensitivity as well as levels of antinociception produced by commonly available analgesic agents. To date more than 300 candidate 'pain' genes have been identified as potentially contributing to heritable differences in pain sensitivity and analgesic responsiveness in animals and humans, with this information available in a publicly accessible database http://www.jbldesign.com/jmogil/enter.html. Since then, many genetic association studies have been conducted in humans to investigate the possibility that single nucleotide polymorphisms (SNPs) in an individual gene may explain drug inefficacy or excessive toxicity experienced by a small subset of the whole population who have the rare allele for a particular SNP.

SUMMARY

Despite the fact that SNPs in more than 20 genes that affect pain sensitivity or contribute to interindividual variability in responses to analgesic medications have been identified in the human genome, much of the data is conflicting. Apart from deficiencies in the design and conduct of human genetic association studies, recent research from other fields has implicated epigenetic mechanisms that facilitate dynamic gene-environment communication, as a possible explanation.

Performance enhancing, non-prescription use of Ritalin: a comparison with amphetamines and cocaine

Ritalin, known under chemical name methylphenidate (MPH), is a psychostimulant prescribed to treat attention-deficit/hyperactivity disorder (ADHD) and other conditions. Psychotropic effects and pharmacological pathways evoked by MPH are similar, but not identical to those produced by amphetamines and cocaine. Although not completely understood in detail, MPH psychostimulation is mediated by the increase of central dopamine (DA) and possibly norepinephrine (NE) and serotonin (ST) due to decrease of their re-uptake via binding to and inhibition of DA, NE, and ST transporters. Despite similarity in psychopharmacological effects, the rewarding/ reinforcing ability of MPH appears to be significantly lower than amphetamines and especially cocaine. MPH and similar medications have been widely used on College campuses and by students preparing for exams. Nicknamed 'steroids for SATs,' MPH and related medications are purchased without prescription and their use may even be encouraged by parents and tutors. However, while widely and safely used and administered for over forty years, Ritalin generated significant controversy including MPH abuse and addiction, and adverse reactions. It is now clear that treatment of ADD/ADHD with psychostimulants prevents drug abuse and addictions. Use by those without any medical or psychiatric diagnosis is increasing. In this mini-review, we discuss psychopharmacological and behavioral aspects, and outline neurochemical mechanisms that may provoke Ritalin abuse, addiction and adverse effects compared to amphetamines and cocaine.

Approaches to the development of medications for the treatment of methamphetamine dependence

BACKGROUND

Methamphetamine abuse has become an increasing problem in both the United States and globally with concomitant increases in adverse medical, social and environmental sequelae. Behavioral therapies have been used with some success to treat methamphetamine abusers and dependent individuals, but are not universally efficacious. Methamphetamine has a rich pharmacology that theoretically provides many opportunities for potential pharmacotherapeutic intervention. Nevertheless, there are no approved medications with an indication for treating methamphetamine abusers or addicts at this time.

AIM

To describe briefly how methamphetamine functions and affects function in brain and report how basic researchers and clinicians are attempting to exploit and exploiting this knowledge to discover and develop effective pharmacotherapies.

RESULTS

Scientifically based approaches to medications development by evaluating medications that limit brain exposure to methamphetamine; modulate methamphetamine effects at vesicular monoamine transporter-2 (VMAT-2); or affect dopaminergic, serotonergic, GABAergic, and/or glutamatergic brain pathways that participate in methamphetamine's reinforcing effects are presented.

CONCLUSION

The evidence supports the rationale that pharmacotherapies to decrease methamphetamine use, or reduce craving during abstinence may be developed from altering the pharmacokinetics and pharmacodynamics of methamphetamine or its effects on appetitive systems in the brain.