Frank P. Bymaster

Antipsychotic Drugs: Comparison in Animal Models of Efficacy, Neurotransmitter Regulation, and Neuroprotection

Various lines of evidence indicate the presence of progressive pathophysiological processes occurring within the brains of patients with schizophrenia. By modulating chemical neurotransmission, antipsychotic drugs may influence a variety of functions regulating neuronal resilience and viability and have the potential for neuroprotection. This article reviews the current literature describing preclinical and clinical studies that evaluate the efficacy of antipsychotic drugs, their mechanism of action and the potential of first- and second-generation antipsychotic drugs to exert effects on cellular processes that may be neuroprotective in schizophrenia. The evidence to date suggests that although all antipsychotic drugs have the ability to reduce psychotic symptoms via D2 receptor antagonism, some antipsychotics may differ in other pharmacological properties and their capacities to mitigate and possibly reverse cellular processes that may underlie the pathophysiology of schizophrenia.

The Discovery of Fluoxetine Hydrochloride (Prozac)

In the early 1970s, evidence of the role of serotonin (5-hydroxytryptamine or 5-HT) in depression began to emerge and the hypothesis that enhancing 5-HT neurotransmission would be a viable mechanism to mediate antidepressant response was put forward. On the basis of this hypothesis, efforts to develop agents that inhibit the uptake of 5-HT from the synaptic cleft were initiated. These studies led to the discovery and development of the selective serotonin-reuptake inhibitor fluoxetine hydrochloride (Prozac; Eli Lilly), which was approved for the treatment of depression by the US FDA in 1987. Here, we summarize this research and discuss the many challenges that we encountered during the development of fluoxetine hydrochloride, which has now been widely acknowledged as a breakthrough drug for depression.

Effect of the attention deficit/hyperactivity disorder drug atomoxetine on extracellular concentrations of norepinephrine and dopamine in several brain regions of the rat

Atomoxetine is a selective inhibitor of norepinephrine transporters and is currently being used in the pharmacotherapy of attention deficit/hyperactivity disorder (ADHD). We have previously shown that atomoxetine increased extracellular (EX) concentrations of norepinephrine and dopamine in prefrontal cortex, but unlike the psychostimulant methylphenidate, did not alter dopamine(EX) in nucleus accumbens or striatum. Using the in vivo microdialysis technique in rat, we investigated the effects of atomoxetine on norepinephrine(EX) and dopamine(EX) concentrations in several other brain regions and also evaluated the role of inhibitory autoreceptors on atomoxetine-induced increases of norepinephrine(EX) concentrations. Atomoxetine (3mg/kg i.p.) increased norepinephrine(EX) robustly in prefrontal cortex, occipital cortex, lateral hypothalamus, dorsal hippocampus and cerebellum, suggesting that norepinephrine(EX) is increased throughout the brain by atomoxetine. In lateral hypothalamus and occipital cortex where dopamine(EX) was quantifiable, atomoxetine did not increase dopamine(EX) concentrations, in contrast to parallel increases of norepinephrine(EX) and dopamine(EX) in prefrontal cortex, indicating a unique effect in prefrontal cortex. Administration of the alpha(2)-adrenergic antagonist idazoxan 1h after atomoxetine resulted in increases in prefrontal cortical norepinephrine efflux greater than either compound alone, indicating an attenuating effect of the adrenergic autoreceptors on norepinephrine efflux.

Depression and pain.

Depression and pain disorders are often diagnosed in the same patients. Here we summarize the shared pathophysiology between both disorders and the importance of addressing all symptoms in patients with comorbid pain and depression. We describe anatomical structures that are activated and/or altered in response to both depression and pain--examples include the insular cortex, the prefrontal cortex, the anterior cingulate cortex, the amygdala, and the hippocampus. Both disorders activate common neurocircuitries (e.g. the hypothalamic-pituitary-adrenal axis, limbic and paralimbic structures, ascending and descending pain tracks), common neurochemicals (e.g. monoamines, cytokines, and neurotrophic factors), and are associated with common psychological alterations. One explanation for the interaction and potentiation of the disease burden experienced by patients affected by both pain and depression is provided by the concept of allostasis. In this model, patients accumulate allostatic load through internal and external stressors, which makes them more susceptible to disease. To break this cycle, it is important to treat all symptoms of a patient. Therapeutic approaches that address symptoms of both depression and pain include psychotherapy, exercise, and pharmacotherapy.

The Dual Transporter Inhibitor Duloxetine: A Review of its Preclinical Pharmacology, Pharmacokinetic Profile, and Clinical Results in Depression

Major depressive disorder (MDD) poses a significant health problem and is estimated to be the third most costly and disabling disorder in the United States. Pharmacotherapy of depression has been successful, but improvements in response rates, remission rates, side effects, compliance and faster onset of therapeutic action have become prime objectives in drug development. There is considerable support for the hypothesis that dysfunctional serotonergic or noradrenergic neurotransmission may be etiological in depressed patients. Duloxetine is a balanced and potent reuptake inhibitor of serotonin (5-HT) and norepinephrine (NE) being studied as an antidepressant medication. In this review, we highlight the preclinical pharmacology, pharmacokinetic profile, and effects of duloxetine in the pharmacotherapy of depression. Evidence for 5-HT and NE reuptake inhibition by duloxetine comes from in vitro and in vivo transporter binding and functional uptake studies. Taken together with efficacy data from in vivo microdialysis, electrophysiological and behavioral studies, it is evident that duloxetine is balanced as a dual serotonin norepinephrine uptake inhibitor in vivo. The clinical efficacy and safety of duloxetine in the treatment of MDD has been studied in 6 multicenter, randomized, double-blind, placebo-controlled trials. In these studies, duloxetine was found to be effective in the treatment of emotional/psychological and painful physical symptoms associated with depression. More importantly, duloxetine appears to have better response rates and remission from depressive symptoms, perhaps due to its ability to treat a wider range of symptoms.

Fluoxetine, a selective serotonin uptake inhibitor.

Fluoxetine is a selective serotonin uptake inhibitor in man. Platelets harvested from subjects to whom fluoxetine was administered (30 mg daily for 1 wk) had a diminished ability to accumulate 3H‐serotonin. The inhibition of uptake was positively correlated with the plasma concentrations of fluoxetine. Plasma from fluoxetine‐treated subjects also inhibited the uptake of 3H‐serotonin by platelets obtained from nontreated subjects. Fluoxetine was without effect on the noradrenergic nerve endings; pressor effects induced after the administration of norepinephrine or tyramine were similar whether subjects were receiving fluoxetine or placebo. Fluoxetine administration for 30 days produced similar pharmacologic effects as after the 7‐day study and included: (1) no change in sensitivity to the pressor effects of tyramine and norepinephrine and (2) marked inhibition in the uptake of 3H‐serotonin by platelets harvested from subjects on this regimen. In addition, fluoxetine caused a diminution of the concentration of endogenous serotonin in platelets, resulting in serotonin levels of only 20% of control. Fluoxetine was well absorbed and achieved peak plasma concentration at 6 hr after administration. Fluoxetine and the major metabolite, norfluoxetine, appeared to reach a steady state within 12 to 14 days. Fluoxetine, administered in single doses of 1 to 90 mg produced no behavioral or adverse effects. Similarly, after 1 wk of fluoxetine administration, no behavioral or adverse effects were observed.

A review of the abuse potential assessment of atomoxetine: a nonstimulant medication for attention-deficit/hyperactivity disorder

RationaleTreatment of attention-deficit/hyperactivity disorder (ADHD) has for many years relied on psychostimulants, particularly various formulations of amphetamines and methylphenidate. These are central nervous system stimulants and are scheduled because of their abuse potential. Atomoxetine (atomoxetine hydrochloride; Strattera®) was approved in 2002 for treatment of ADHD, and was the first nonstimulant medication approved for this disorder. It was classified as an unscheduled medication indicating a low potential for abuse. However, the abuse potential of atomoxetine has not been reviewed.ObjectivesIn this article, we review the evidence regarding abuse potential of atomoxetine, a selective inhibitor of the presynaptic norepinephrine transporter, which is unscheduled/unrestricted in all countries where it is approved.MethodsResults from receptor binding, in vitro electrophysiology, in vivo microdialysis, preclinical behavioral, and human laboratory studies have been reviewed.ResultsAtomoxetine has no appreciable affinity for, or action at, central receptors through which drugs of abuse typically act, i.e., dopamine transporters, GABAA receptors, and opioid μ receptors. In behavioral experiments in rodents, atomoxetine does not increase locomotor activity, and in drug discrimination studies, its profile is similar to that of drugs without abuse potential. Atomoxetine does not serve as a reinforcer in monkey self-administration studies, and human laboratory studies suggest that atomoxetine does not induce subjective effects indicative of abuse.ConclusionNeurochemical, preclinical, and early clinical studies predicted and supported a lack of abuse potential of atomoxetine, which is consistent with the clinical trial and postmarketing spontaneous event data in the past 10xa0years.