Effects of Milnacipran in Animal Models of Anxiety and Memory

Absence of sibutramine effect on spontaneous anxiety in rats

INTRODUSTION: Sibutramine has been described as a drug recommended for treatment of obesity, since it has the ability to inhibit the reuptake of serotonin and noradrenaline in the central nervous system, thereby increasing energy expenditure.

OBJECTIVE

Investigate the anxiogenic and anxiolytic effects of acute and chronic treatment with sibutramine in rats submitted to the task of the elevated plus-maze.

METHODS

Diazepam was used as a positive control for the anxiolytic effect, and the task of the elevated plus-maze showed sensitivity to detect the effect. In the chronic treatment, sibutramine was ingested for a period of two months.

RESULTS

The acute and chronic treatments at the studied dose, which is described to produce a maximum effect of anti-obesity in rats, did not interfere with anxiety.

CONCLUSIONS

The acute and chronic administration of sibutramine is not related to anxiolytic or anxiogenic effects.

The noradrenergic symptom cluster: clinical expression and neuropharmacology

Signs and symptoms of depression can be linked to one or more monoaminergic systems, specifically the norepinephrine (NE), the dopamine (DA), and the serotonin (5-HT) systems. In particular, the modulation of energy, vigilance, and arousal can be directly linked to the NE system. There is, however, a great deal of overlap in the modulation of the symptoms of depression between these monoaminergic systems. There are considerable reciprocal interactions between the NE, DA, and the 5-HT systems. When using a selective serotonin reuptake inhibitor (SSRI), for example, 5-HT transmission is enhanced, but at the same time there is a dampening of the activity of NE and DA neurons through inhibitory 5-HT(2A) and 5-HT(2C) receptors, respectively. This could explain the residual symptoms of fatigue, lack of energy, and anhedonia, often seen after patients present an overall positive response to a SSRI. Using a dual 5-HT and NE reuptake inhibitor (SNRI), such as milnacipran, would result in an additional increase in NE activity. Futhermore, inhibiting NE reuptake increases DA availability in the frontal cortex since DA is mainly cleared by the NE transporters in several brain regions. A risk inherent in increased NE activity is that of provoking anxiety. This is avoided however by the attenuation of the phasic reactivity of the firing of NE neurons through prolonged administration of SSRI and SNRI.

Milnacipran: a selective serotonin and norepinephrine dual reuptake inhibitor for the management of fibromyalgia

Milnacipran, a serotonin and norepinephrfrine reuptake inhibitor with preferential inhibition of norepinephrine reuptake over serotonin, is approved in the United States for the management of fibromyalgia. Owing to its effects on norepinephrine and serotonin, as well as its lack of activity at other receptor systems, it was hypothesized that milnacipran would provide improvements in pain and other fibromyalgia symptoms without some of the unpleasant side effects associated with other medications historically used for treating fibromyalgia. The clinical safety and efficacy of milnacipran 100 and 200 mg/day in individuals with fibromyalgia has been investigated in four large, randomized, double-blind, placebo-controlled studies and three long-term extension studies. The clinical studies used composite responder analyses to identify the proportion of individual patients reporting simultaneous and clinically significant improvements in pain, global status, and physical function, in addition to assessing improvement in various symptom domains such as fatigue and dyscognition. In the clinical studies, patients receiving milnacipran reported significant improvements in pain and other symptoms for up to 15 months of treatment. Most adverse events were mild to moderate in severity and were related to the intrinsic pharmacologic properties of the drug. Long-term exposure to milnacipran did not result in any new safety concerns. As with other serotonin and norepinephrine reuptake inhibitors, increases in heart rate and blood pressure have been observed in some patients with milnacipran treatment.

Milnacipran: beyond a role of antidepressant

Milnacipran is a serotonin and norepinephrine reuptake inhibitor (SNRI) with negligible effects on any presynaptic or postsynaptic receptors. Milnacipran has unique pharmacokinetic and pharmacodynamic characteristics that distinguish it from the other marketed serotonin and norepinephrine reuptake inhibitors, venlafaxine, desvenlafaxine, and duloxetine such as equipotent serotonin and norepinephrine reuptake inhibition and a linear dose-concentration trend at therapeutic doses. The half-life of milnacipran is approximately 8 hours. In addition, milnacipran does not inhibit the cytochrome P 450 system, indicating minimal propensity for drug-drug interactions. The antidepressant efficacy of milnacipran has been clearly established in a number of randomized, double-blind, placebo-controlled clinical trials, and it has been widely used for treating major depressive disorder. Moreover, evidence suggests that milnacipran is effective and tolerable in the treatment of fibromyalgia and may have usefulness for fatigue and anxiety symptoms. The current paper reviews researches conducted to date that is relevant to the efficacy, tolerability, and mechanism of action of milnacipran in the treatment of depression, fibromyalgia, and other psychiatric syndromes. Future directions of research are also identified.

Serotonin norepinephrine reuptake inhibitors (SNRIs) in anxiety disorders: a comprehensive review of their clinical efficacy

Anxiety disorders are common psychiatric conditions that typically require long-term treatment. This review summarizes current knowledge of the pharmacological treatment of anxiety disorders with serotonin norepinephrine reuptake inhibitors (SNRIs) with specific emphasis on the findings of recent randomized clinical trials and relevant neurobiological investigations. It is now well established that gabaergic, noradrenergic and serotonergic systems play a critical role in the pathophysiology of anxiety disorders, abnormalities in these systems being related to structural and functional alterations in specific brain areas such as the amygdala, prefrontal cortex, locus coeruleus and hippocampus, as repeatedly shown by neuroimaging studies. SNRIs selectively inhibit norepinephrine and serotonin reuptake and have shown to be efficacious and generally well tolerated treatments in patients with anxiety disorders, with some potential clinical advantages over selective serotonin reuptake inhibitors (SSRIs), which are considered by many to represent first-line pharmacological treatments in patients with anxiety disorders. Anxiety disorders are characterized by a typically chronic course, high rates of comorbidity and frequent partial response to standard treatments, and the increasing use of SNRIs reflects currently unmet clinical need, in terms of overall response, remission rates and treatment tolerability.

Effect of acute and chronic treatment with milnacipran potentiates the anticonvulsant activity of conventional antiepileptic drugs in the maximal electroshock-induced seizures in mice

RATIONALE

Depression often coexists with epilepsy. Simultaneous therapy of the two diseases may be associated with pharmacodynamic and/or pharmacokinetic interactions between antiepileptic and antidepressant drugs.

OBJECTIVES

The aim of this study was to investigate the influence of acute and chronic treatment with intraperitoneal milnacipran (MLN), a selective serotonin/noradrenaline reuptake inhibitor, on the protective activity of valproate, carbamazepine (CBZ), phenytoin, or phenobarbital (PB) in the maximal electroshock (MES) test in mice.

MATERIALS AND METHODS

Electroconvulsions were produced by an alternating current (50 Hz, 25 mA) delivered via ear-clip electrodes. Motor coordination and long-term memory were evaluated in the chimney test and passive-avoidance task, respectively. Brain concentrations of antiepileptic drugs (AEDs) were assessed by immunofluorescence.

RESULTS

Given acutely, MLN at 10 mg/kg increased the convulsive threshold. Acute MLN applied at the subprotective dose of 5 mg/kg enhanced the anticonvulsant effects of CBZ and PB. Chronic treatment with MLN (5-30 mg/kg once daily for 2 weeks) did not affect either the electroconvulsive threshold or the anticonvulsant action of all studied conventional antiepileptic drugs. Since the antidepressant did not affect brain concentrations of antiepileptics used in the study, the revealed interactions seem to be of pharmacodynamic nature. Moreover, acute and chronic MLN, AEDs, and their combinations did not produce significant motor and long-term memory impairment.

CONCLUSIONS

Acute, but not chronic, treatment with MLN can increase the effectiveness of some AEDs against MES-induced seizures in mice. It seems that MLN may also be considered as a candidate drug for clinical trials in patients with epilepsy and depressive disorders.

Involvement of vasopressin V1b receptor in anti-anxiety action of SSRI and SNRI in mice

Arginine vasopressin (AVP) is critical in the regulation of hypothalamic-pituitary-adrenal axis activity, a major component of the stress response. The vasopressin V1b receptor (V1bR) mediates the stimulatory effect of AVP on adrenocorticotropin release. Previous studies showed that AVP facilitates aggression while serotonin inhibits aggression by blocking the activity of the vasopressin system. To examine whether the interaction of the V1bR and serotonin in the central nervous system controls anxiety-related behavior, we investigated the effects of acute and chronic treatment with a selective serotonin reuptake inhibitor (SSRI) and with a serotonin noradrenalin reuptake inhibitor (SNRI) on V1bR knockout (KO) mice and on V1bR antagonist (SSR149415)-treated mice. The effects were evaluated in experiments using an elevated plus-maze (EPM) test and a hole-board (HB) test, well established tests for evaluating anxiety-like behavior. For both the V1bR KO mice and V1bR antagonist-treated mice, acute treatment with either SSRI or SNRI did not change the time spent on the EPM open arms or the number of head dips in the HB. Chronic treatment of V1bR KO mice with SSRI did not change the amount of time spent on the open arms, the number of head dips, or the number of rearings, while chronic treatment with SNRI significantly increased the time spent on the open arms and the number of head dips. These results suggest that the anti-anxiety action of 5-HT reuptake inhibitors might partly involve V1bR regulating the anxiety behaviors.

The efficacy of milnacipran in panic disorder: an open trial

The aim of this study is to evaluate the efficacy of milnacipran in the acute treatment of patients with panic disorder. Thirty-one patients who met Diagnostic and statistical manual of mental disorders-IV criteria for panic disorder with or without agoraphobia were included in the study. Patients were initially treated with milnacipran 25 mg twice daily and then 50 mg twice daily until the 10th week. The treatment outcome and panic disorder severity were determined by the Panic Disorder Severity Scale, Panic Inventory, Clinical Global Impression and Hamilton Anxiety Scale, all of which were applied during every evaluation interview. Quality of life (WHOQOL-bref) was evaluated at baseline and at the end of the study. Missing data were handled by using the last observation carried forward for all participants who had taken at least one dose of study medication. Intention-to-treat was used in the analyses. Pharmacological treatment resulted in a clinically and statistically significant mean reduction in all severity measures. Remission (Clinical Global Impression < or = 2) was obtained in 58.1% of the sample. Regarding WHOQOL, we found a significant improvement (P<0.05) across treatment in all the domains studied. Although results may be influenced by the open design of this pilot study and by the small sample size, our findings suggest that milnacipran may be effective for the treatment of panic disorder and justify further research.