Decreased neuroendocrine responses to meta-chlorophenylpiperazine (m-CPP) but normal responses to ipsapirone in marathon runners

Exercise reduces the anxiogenic effects of meta-chlorophenylpiperazine: The role of 5-HT2C receptors in the bed nucleus of the stria terminalis

Introduction

Two weeks of voluntary exercise in group-housed mice produces a reduction in anxiety-like behaviors across a number of different measures, including a reduction in the anxiety levels typically produced by the anxiogenic serotonergic drug m-chlorophenylpiperazine (mCPP), an agonist at 5-HT2C/2b receptors. We have previously demonstrated that 2-weeks of voluntary exercise blunted the anxiogenic effects of systemic mCPP, and we have also shown that mCPP infused into the bed nucleus of the stria terminalis (BNST) is anxiogenic. Here we follow up on these reports.

Methods

In Experiment 1 we infused several doses of mCPP into the BNST with or without the 5-HT2C antagonist SB242084. In Experiment 2, we administered mCPP into amygdala subregions and the dorsal hippocampus to investigate site specificity. In Experiment 4 we lesioned the BNST and subsequently infused mCPP systemically, and in Experiment 4 we used RNAscope^® to assess BNST 5-HT2C transcripts following wheel running.

Results

BNST mCPP infusion increased acoustic startle responding, which was by 5-HT2C antagonism, while neither mCPP infused into the amygdala nor hippocampus was anxiogenic. Lesions of the BNST prevented the anxiogenic effect of systemically administered mCPP. Lastly, exercise reduced 5-HT2C transcripts in the BNST.

Discussion

These results suggest that the BNST is a critical site of action for the effects of exercise on mCPP. Together these data suggest that exercise may reduce 5-HT2C receptor function in the BNST, which may, in part, explain some of the anxiolytic effects associated with wheel running.

Exercise in the treatment of clinical anxiety in general practice - a systematic review and meta-analysis

BACKGROUND

Anxiety disorders are common, yet treatment options in general practice are often limited to medication or CBT. There is a lack of evidence for the effectiveness of exercise in the treatment of anxiety in patients who present to general practice and also about the intensity of exercise required to lead to improvement. The aim of this systematic review was to assess the use of exercise versus waiting list control groups in the treatment of anxiety and also to assess the benefit of high intensity exercise vs low intensity exercise. Long term follow up scores were also analysed. We included patients who met diagnostic criteria for anxiety disorders or had clinically raised anxiety levels on a validated rating scale and performed a subgroup analysis of the outcomes between the two groups. The intervention was any aerobic exercise programme carried out for at least two weeks, or exercise carried out at high intensity for at least two weeks. The comparison groups were either a waiting list control group or low intensity exercise.

METHOD

Systematic review of randomised controlled trials. Three databases were searched; CENTRAL, Medline and Embase. Outcome assessment was based on validated anxiety rating scales. The quality of the studies was appraised according to the Cochrane Risk of Bias tool. Effect sizes were calculated using the standardised mean difference.

RESULTS

Fifteen studies were identified with a total of 675 patients. Nine trials had participants with diagnosed anxiety disorders and six trials had participants with raised anxiety on a validated rating scale. Aerobic exercise was effective in the treatment of raised anxiety compared to waiting list control groups (effect size - 0.41, 95% CI = - 0.70 to - 0.12). High intensity exercise programmes showed greater effects than low intensity programmes. There was no significant difference in outcomes between groups of patients with diagnosed anxiety disorders and patients who had raised anxiety on a rating scale. Conclusions were limited by the small number of studies and wide variation in the delivery of exercise interventions.

CONCLUSION

Exercise programmes are a viable treatment option for the treatment of anxiety. High intensity exercise regimens were found to be more effective than low intensity regimens. The results have implications for the use of exercise schemes in General Practice.

Changes in markers of brain serotonin activity in response to chronic exercise in senior men

Aging is associated with noticeable impairments in brain serotonin transmission, which might contribute to increased vulnerability to developing depression in later life. Animal and human studies have shown that aerobic exercise can stimulate brain serotonin activity and trigger parallel elevations in tryptophan (TRP, the serotonin precursor) availability in blood plasma. However, the influence of chronic exercise on serotonergic activity in older adults is not yet known. Sixteen men aged 64 ± 3 years exercised for 1 h (67%–70% peak oxygen consumption) at baseline and following 16 weeks of aerobic training. The main outcome measures were cardiorespiratory fitness, body composition, branched-chain amino acids (BCAA), TRP, prolactin, lactate, and free fatty acids (FFA). Changes in plasma free-TRP/BCAA and prolactin served as surrogates for TRP availability and serotonin activity, respectively. Chronic exercise decreased body mass (P < 0.05) whilst it increased ventilatory threshold 2 (P < 0.01). Although training did not affect plasma TRP availability to the brain at rest, both pre- and post-training exercise challenges markedly increased TRP availability (P < 0.001). The free-TRP/BCAA values reached a ceiling during exercise that was lower following training (P < 0.05), whereas similar patterns were found for prolactin, lactate, and FFA. These data show that aerobic exercise elicits consistent transient elevations in plasma TRP availability to the brain in older men; the elevations were independent from physical training, although less pronounced following training. The data support the contention that repeated elevations in brain serotonin activity might be involved in the antidepressant effect of exercise training in older adults.

Exercise and sleep in aging: emphasis on serotonin

Reductions in central serotonin activity with aging might be involved in sleep-related disorders in later life. Although the beneficial effects of aerobic exercise on sleep are not new, sleep represents a complex recurring state of unconsciousness involving many lines of transmitters which remains only partly clear despite intense ongoing research. It is known that serotonin released into diencephalon and cerebrum might play a key inhibitory role to help promote sleep, likely through an active inhibition of supraspinal neural networks. Several lines of evidence support the stimulatory effects of exercise on higher serotonergic pathways. Hence, exercise has proved to elicit acute elevations in forebrain serotonin concentrations, an effect that waned upon cessation of exercise. While adequate exercise training might lead to adaptations in higher serotonergic networks (desensitization of forebrain receptors), excessive training has been linked to serious brain serotonergic maladaptations accompanied by insomnia. Dietary supplementation of tryptophan (the only serotonin precursor) is known to stimulate serotonergic activity and promote sleep, whereas acute tryptophan depletion causes deleterious effects on sleep. Regarding sleep-wake regulation, exercise has proved to accelerate resynchronization of the biological clock to new light-dark cycles following imposition of phase shifts in laboratory animals. Noteworthy, the effect of increased serotonergic transmission on wake state appears to be biphasic, i.e. promote wake and thereafter drowsiness. Therefore, it might be possible that acute aerobic exercise would act on sleep by increasing activity of ascending brain serotonergic projections, though additional work is warranted to better understand the implication of serotonin in the exercise-sleep axis.

Exercise-associated changes in the corticosterone response to acute restraint stress: evidence for increased adrenal sensitivity and reduced corticosterone response duration

Exercise promotes stress resistance and is associated with reduced anxiety and reduced depression in both humans and in animal models. Despite the fact that dysfunction within the hypothalamic pituitary adrenal (HPA) axis is strongly linked to both anxiety and depressive disorders, the evidence is mixed as to how exercise alters the function of the HPA axis. Here we demonstrate that 4 weeks of voluntary wheel running was anxiolytic in C57BL/6J mice and resulted in a shorter time to peak corticosterone (CORT) and a more rapid decay of CORT following restraint stress. Wheel running was also associated with increased adrenal size and elevated CORT following systemic administration of adrenocorticotropic hormone. Finally, the HPA-axis response to peripheral or intracerebroventricular administration of dexamethasone did not suggest that wheel running increases HPA-axis negative feedback through GR-mediated mechanisms. Together these findings suggest that exercise may promote stress resilience in part by insuring a more rapid and shortened HPA response to a stressor thus affecting overall exposure to the potentially negative effects of more sustained HPA-axis activation.

Stress-protective neural circuits: not all roads lead through the prefrontal cortex

Exposure to an uncontrollable stressor elicits a constellation of physiological and behavioral sequel in laboratory rats that often reflect aspects of anxiety and other emotional disruptions. We review evidence suggesting that plasticity within the serotonergic dorsal raphe nucleus (DRN) is critical to the expression of uncontrollable stressor-induced anxiety. Specifically, after uncontrollable stressor exposure subsequent anxiogenic stimuli evoke greater 5-HT release in DRN terminal regions including the amygdala and striatum; and pharmacological blockade of postsynaptic 5-HT(2C) receptors in these regions prevents expression of stressor-induced anxiety. Importantly, the controllability of stress, the presence of safety signals, and a history of exercise mitigate the expression of stressor-induced anxiety. These stress-protective factors appear to involve distinct neural substrates; with stressor controllability requiring the medial prefrontal cortex, safety signals the insular cortex and exercise affecting the 5-HT system directly. Knowledge of the distinct yet converging mechanisms underlying these stress-protective factors could provide insight into novel strategies for the treatment and prevention of stress-related psychiatric disorders.

Exercise affects symptom severity but not biological measures in depression and somatization - results on IL-6, neopterin, tryptophan, kynurenine and 5-HIAA

Exercise leads to symptom reduction in affective disorders and functional somatic syndromes. Biological hypotheses of underlying mechanisms include serotonergic and immunological pathways. We aimed to investigate biological features in persons with major depression and somatoform syndromes, and to analyze effects of short-term graded exercise on these parameters. Baseline values for depressive and somatoform symptoms, tryptophan, kynurenine, 5-hydroxyindoleacetic acid, neopterin and interleukin-6 were compared with those after one week of increased and one week of reduced physical activity. Thirty-eight persons with major depression, 27 persons with a minimum of 6-8 somatoform symptoms, and 48 healthy controls participated in the study. Depressive and somatoform symptoms were reduced after the active week, and an interaction pointed towards group-specific reduction of psychopathology. Participants with major depression had lower levels of kynurenine compared to controls, with intermediate concentrations in somatoform patients. There were no systematic associations of symptom improvement with biological changes. A possible limitation of the design is that a control condition with low physical activity, but no placebo condition was included. People with multiple somatoform symptoms and major depression benefit from a short and low-graded exercise intervention. These effects do not seem to be mediated by changes in serotonergic and inflammatory parameters.

5-HT2C receptors in the basolateral amygdala and dorsal striatum are a novel target for the anxiolytic and antidepressant effects of exercise

Physical activity reduces the incidence and severity of psychiatric disorders such as anxiety and depression. Similarly, voluntary wheel running produces anxiolytic- and antidepressant-like effects in rodent models. The specific neurobiological mechanisms underlying the beneficial properties of exercise, however, remain unclear. One relevant pharmacological target in the treatment of psychiatric disorders is the 5-HT(2C) receptor (5-HT(2C)R). Consistent with data demonstrating the anxiogenic consequences of 5-HT(2C)R activation in humans and rodents, we have previously reported that site-specific administration of the selective 5-HT(2C)R agonist CP-809101 in the lateral/basolateral amygdala (BLA) increases shock-elicited fear while administration of CP-809101 in the dorsal striatum (DS) interferes with shuttle box escape learning. These findings suggest that activation of 5-HT(2C)R in discrete brain regions contributes to specific anxiety- and depression-like behaviors and may indicate potential brain sites involved in the anxiolytic and antidepressant effects of exercise. The current studies tested the hypothesis that voluntary wheel running reduces the behavioral consequences of 5-HT(2C)R activation in the BLA and DS, specifically enhanced shock-elicited fear and interference with shuttle box escape learning. After 6 weeks of voluntary wheel running or sedentary conditions, the selective 5-HT(2C)R agonist CP-809101 was microinjected into either the BLA or the DS of adult Fischer 344 rats, and shock-elicited fear and shuttle box escape learning was assessed. Additionally, in-situ hybridization was used to determine if 6 weeks of voluntary exercise changed levels of 5-HT(2C)R mRNA. We found that voluntary wheel running reduced the behavioral effects of CP-809101 and reduced levels of 5-HT(2C)R mRNA in both the BLA and the DS. The current data indicate that expression of 5-HT(2C)R mRNA in discrete brain sites is sensitive to physical activity status of the organism, and implicates the 5-HT(2C)R as a target for the beneficial effects of physical activity on mental health.

Complementary medicine, exercise, meditation, diet, and lifestyle modification for anxiety disorders: a review of current evidence

Use of complementary medicines and therapies (CAM) and modification of lifestyle factors such as physical activity, exercise, and diet are being increasingly considered as potential therapeutic options for anxiety disorders. The objective of this metareview was to examine evidence across a broad range of CAM and lifestyle interventions in the treatment of anxiety disorders. In early 2012 we conducted a literature search of PubMed, Scopus, CINAHL, Web of Science, PsycInfo, and the Cochrane Library, for key studies, systematic reviews, and metaanalyses in the area. Our paper found that in respect to treatment of generalized anxiety or specific disorders, CAM evidence revealed current support for the herbal medicine Kava. One isolated study shows benefit for naturopathic medicine, whereas acupuncture, yoga, and Tai chi have tentative supportive evidence, which is hampered by overall poor methodology. The breadth of evidence does not support homeopathy for treating anxiety. Strong support exists for lifestyle modifications including adoption of moderate exercise and mindfulness meditation, whereas dietary improvement, avoidance of caffeine, alcohol, and nicotine offer encouraging preliminary data. In conclusion, certain lifestyle modifications and some CAMs may provide a beneficial role in the treatment of anxiety disorders.

Exploring exercise as an avenue for the treatment of anxiety disorders

Anxiety disorders constitute a significant public health problem. Current gold standard treatments are limited in their effectiveness, prompting the consideration of alternative approaches. In this review, we examine the evidence for exercise as an intervention for anxiety disorders. This evidence comes from population studies, studies of nonclinical anxiety reduction, as well as a limited number of studies of clinically anxious individuals. All of these studies provide converging evidence for consistent beneficial effects of exercise on anxiety, and are consistent with a variety of accounts of the mechanism of anxiety reduction with exercise. Further study of clinical populations is encouraged, as are studies of the mechanism of change of exercise interventions, which have the potential to help refine exercise intervention strategies. Likewise, studies that identify moderators of treatment efficacy will assist clinicians in deciding how and for whom to prescribe exercise.

Exercise and severe depression: preliminary results of an add-on study

BACKGROUND

Physical exercise has been extensively researched as a therapeutic option for treatment of major depression.

METHODS

In a randomized controlled trial, we analyze the effects of aerobic physical exercise as an add-on strategy for treatment of severe depressed inpatients. The exercise has a "Dose" of 16.5 kcal/kg/week, three times a week during all the hospitalization.

RESULTS

Our preliminary results show that there is no significant difference in scores of Hamilton in the second week between groups (Mean[SD]=8.2[5.96] × 11.18[5.03], p=0.192). However, there is a significant reduction in Hamilton scores of patients in exercise group at discharge (Mean[SD]=5.93[4.46] × 9.45[3.56], p=0.041). Regarding Quality of Life (QoL), no significant difference were found between groups in the second week in physical domain (Mean[SD]=56.98[8.96] × 54.54[9.18], p=0.511) and psychological domain (Mean[SD]=50.88[13.88] × 42.04[12.42], p=0.106). However, there is a significant difference in psychological domain (Mean[SD]=55.88[9.92] v 41.66[13.04], p=0.004) and a trend but no statistical significance in the physical (Mean[SD]=58.80[9.14] × 52.12[8.70], p=0.07) at discharge.

LIMITATIONS

Many patients receive different treatment strategies, like ECT (1 patient at exercise group × 3 at control group). Other limitation is the small number of participants included until this moment.

CONCLUSION

Our preliminary results suggest that physical exercise could be a feasible and effective add-on strategy for treatment of severe depressed inpatients, improving their depressive symptoms and QoL.

A randomized, controlled trial of aerobic exercise in combination with paroxetine in the treatment of panic disorder

OBJECTIVES

Regular aerobic exercise (running) has been shown to be superior to a pill placebo in the treatment of panic disorder. Combined drug and exercise treatment has not been investigated in randomized controlled studies to date.

METHODS

This is a randomized, 10-week, controlled, parallel group, pilot study. A total of 75 outpatients with panic disorder with or without agoraphobia (DSM-IV and ICD-10) received either (1) exercise plus paroxetine 40 mg/day (n=21), (2) relaxation plus paroxetine (n=17), (3) exercise plus pill placebo (n=20), or (4) relaxation plus pill placebo (n=17). Changes in the Panic and Agoraphobia Scale (P&A), and the Clinical Global Impression Scale (CGI) underwent repeated measure analysis.

RESULTS

Effects sizes were large for all groups (d=1.53-3.87), however not significantly different. Paroxetine-treated patients were significantly more improved than placebo-treated patients. On the CGI, patients in the exercise groups (plus paroxetine or placebo) had a trend toward better improvement compared to relaxation (P=0.06). Response and remission rates were higher in the paroxetine compared to pill placebo groups.

CONCLUSIONS

While paroxetine was superior to placebo, aerobic exercise did not differ from relaxation training in most efficacy measures.

The response of neurons in the bed nucleus of the stria terminalis to serotonin: implications for anxiety

Substantial evidence has suggested that the activity of the bed nucleus of the stria terminalis (BNST) mediates many forms of anxiety-like behavior in human and non-human animals. These data have led many investigators to suggest that abnormal processing within this nucleus may underlie anxiety disorders in humans, and effective anxiety treatments may restore normal BNST functioning. Currently some of the most effective treatments for anxiety disorders are drugs that modulate serotonin (5-HT) systems, and several decades of research have suggested that the activation of 5-HT can modulate anxiety-like behavior. Despite these facts, relatively few studies have examined how activity within the BNST is modulated by 5-HT. Here we review our own investigations using in vitro whole-cell patch-clamp electrophysiological methods on brain sections containing the BNST to determine the response of BNST neurons to exogenous 5-HT application. Our data suggest that the response of BNST neurons to 5-HT is complex, displaying both inhibitory and excitatory components, which are mediated by 5-HT(1A), 5-HT(2A), 5-HT(2C) and 5-HT(7) receptors. Moreover, we have shown that the selective activation of the inhibitory response to 5-HT reduces anxiety-like behavior, and we describe data suggesting that the activation of the excitatory response to 5-HT may be anxiogenic. We propose that in the normal state, the function of 5-HT is to dampen activity within the BNST (and consequent anxiety-like behavior) during exposure to threatening stimuli; however, we suggest that changes in the balance of the function of BNST 5-HT receptor subtypes could alter the response of BNST neurons to favor excitation and produce a pathological state of increased anxiety.

The acute antipanic and anxiolytic activity of aerobic exercise in patients with panic disorder and healthy control subjects

Regular physical activity is anxiolytic in both healthy subjects and patients with panic disorder. In contrast, acute exercise may induce acute panic attacks or increase subjective anxiety in patients with panic disorder more than in other people. The effects of quiet rest or an aerobic treadmill exercise (30 min at an intensity of 70% of the maximal oxygen uptake, VO2max) on cholecystokinin tetrapeptide (CCK-4) induced panic attacks were studied in a crossover design in 12 patients with panic disorder and 12 matched healthy subjects. The effects of CCK-4 (25 microg in patients and 50 microg in control subjects) were measured with the Acute Panic Inventory (API) score, comparing panic attack frequencies, total score, and subscores for anxiety and somatic symptoms. CCK-4-induced panic attacks were less frequent after prior exercise: they occurred in 15 (62.5%) subjects after rest (9 patients and 6 control subjects), but only 5 (20.8%) subjects after exercise (4 patients and 1 control subject). In both conditions, CCK-4 administration induced a significant increase in the total API score and the anxiety and somatic symptoms subsores. However, compared to prior rest, exercise resulted in a significantly reduced CCK-4-induced increase of the total API score and the anxiety subscore. In patients with panic disorder exercise increased the total API score and the somatic symptoms subscale but not the anxiety subscore. Patients with panic disorder showed increased somatic but not anxiety symptoms after an acute bout of exercise. Severity of CCK-4-induced panic and anxiety, on the other hand was reduced by exercise. These findings suggest that in addition to exercise training an acute bout of exercise may be used to reduce anxiety and panic attack frequency and intensity in panic disorder patients.

Anxiety-like behaviors produced by acute fluoxetine administration in male Fischer 344 rats are prevented by prior exercise

RATIONALE

Although selective 5-HT reuptake inhibitors (SSRIs) can reduce anxiety after chronic treatment, acute SSRI administration is associated with an increase in anxiety consistent with an acute increase in 5-HT neurotransmission. Exercise is anxiolytic in humans, and wheel running prevents anxiety-like behavioral consequences of uncontrollable stress in rats, but the effects of exercise on acute fluoxetine-induced anxiety-like behaviors are unknown.

OBJECTIVES

The current studies tested the hypothesis that acute administration of the SSRI fluoxetine would produce behaviors in rats resembling those produced by uncontrollable stress and that these behaviors would be blocked by prior wheel running.

RESULTS

Adult, male Fisher 344 rats administered moderate (10 mg/kg) or high (20 mg/kg) doses of fluoxetine demonstrated exaggerated shock-elicited freezing and an interference with shuttle box escape compared to rats given either saline or low-dose fluoxetine (2.5 mg/kg). Fluoxetine-induced behaviors were similar to, but smaller in magnitude than, those produced by uncontrollable stress and were blocked by pretreatment with the 5-HT(2C) receptor antagonist SB 242084 (1 mg/kg). Rats allowed access to running wheels for 6 weeks were protected against the anxiety-like behaviors produced by a single injection of fluoxetine (10 mg/kg).

CONCLUSIONS

Behavioral effects of acute fluoxetine administration resemble those produced by uncontrollable stress. Results are consistent with the idea that exercise can produce resistance against the anxiogenic effects of acute increases in 5-HT and suggest that acute behavioral effects of antidepressants can depend on history of physical activity.

Rehabilitation of decreased motor performance in patients with chronic fatigue syndrome: should we treat low effort capacity or reduced effort tolerance?

Aim: The aetiology, pathophysiology, diagnostic delineation and treatment of chronic fatigue syndrome (CFS) remain a matter of debate. Here some aspects of the debate are elucidated, with a particular focus on the patients' decreased motor performance.

Hypothesis: The pathophysiological basis of decreased motor performance in CFS may, theoretically, involve three components: (1) a peripheral energetic deficit (impaired oxidative metabolism and/or physical deconditioning); (2) a central perceptual disturbance (higher effort sense or increased `interoception'); and (3) a fundamental failure of the neurobiological stress system, leading to an abnormal `sickness response'. It is proposed that the first two components may lead to low effort capacity, while the third component may lead to reduced effort tolerance. Although there is evidence for low effort capacity influencing symptoms and functional limitations in CFS, it is assumed that reduced effort tolerance might be the primary disturbance in CFS.

Diagnostic implications: Distinguishing low effort capacity and reduced effort tolerance may contribute to a refinement of current diagnostic criteria of CFS and the identification of subgroups.

Therapeutic implications: The above-mentioned distinction may make it possible to formulate a rationale for an effective implementation and adequate outcome evaluation of rehabilitation strategies in CFS.

Research implications: This new heuristic framework may inform future research aimed at disentangling the complex determination of impaired motor performance in CFS, as well as studies aimed at customizing treatment to different subtypes of patients.

Monitoring and Titrating Symptoms

A key challenge to optimising marathon running performance is to train with adequate frequency, duration and intensity as well as get enough recovery to optimise biological adaptations underlying performance. Some marathon runners train inadequately and underperform, while others perform poorly because they become injured or develop staleness in response to overtraining. Staleness, a depression-like syndrome, could plausibly be caused by overtraining-induced molecular and cellular changes in brain circuits involved in depression or other related mood states such as anger, fatigue, vigor and confusion. The central thesis of this paper is that easily assessed resting and/or exercise symptoms, valid markers of either difficult-to-access, expensive-to-assess or unmeasurable brain circuits, can be used to optimise marathon running performance by helping to avoid either inadequate training or excessive training resulting in staleness. Available models of human performance and relevant data, admittedly incomplete at the present time, suggest that marathon runners may benefit from systematically using symptom responses to training in order to aid in adjusting training loads for the purpose of optimising training. As this approach is better linked with neuroscience and neuroimaging findings, it could be refined and prove to be useful for elite as well as non-elite marathon runners.

Mind and muscle: the cognitive-affective neuroscience of exercise

There is growing basic-science interest in the mechanisms underpinning the positive effects of exercise on brain function and cognitive-affective performance. There is also increasing clinical evidence that exercise may prevent and treat various neuropsychiatric disorders. At the same time, there is growing awareness that athletic performance is mediated in crucial ways by central nervous system mechanisms. The relevant mechanisms in all these cases requires further exploration, but likely includes neurotrophic, neuroendocrine, and neurotransmitter systems, which in turn are crucial mediators of psychopathology and resilience. The hypothesis that Homo sapiens evolved as a specialist endurance runner provides an intriguing context against which to research the proximal mechanisms relevant to a cognitive-affective neuroscience of exercise.

Pharmacologic mechanisms of serotonergic regulation of dopamine neurotransmission

The neurotransmitter dopamine (DA) has a long association with normal functions such as motor control, cognition, and reward, as well as a number of syndromes including drug abuse, schizophrenia, and Parkinson's disease. Studies show that serotonin (5-HT) acts through several 5-HT receptors in the brain to modulate DA neurons in all 3 major dopaminergic pathways. There are at least fourteen 5-HT receptor subtypes, many of which have been shown to play some role in mediating 5-HT/DA interactions. Several subtypes, including the 5-HT1A, 5-HT1B, 5-HT2A, 5-HT3 and 5-HT4 receptors, act to facilitate DA release, while the 5-HT2C receptor mediates an inhibitory effect of 5-HT on DA release. Most 5-HT receptor subtypes only modulate DA release when 5-HT and/or DA neurons are stimulated, but the 5-HT2C receptor, characterized by high levels of constitutive activity, inhibits tonic as well as evoked DA release. This review summarizes the anatomical evidence for the presence of each 5-HT receptor subtype in dopaminergic regions of the brain and the neuropharmacological evidence demonstrating regulation of each DA pathway. The relevance of 5-HT receptor modulation of DA systems to the development of therapeutics used to treat schizophrenia, depression, and drug abuse is discussed. Lastly, areas are highlighted in which future research would be maximally beneficial to the treatment of these disorders.

Modulation of dopamine release by striatal 5-HT2C receptors

Previous work has demonstrated that dopamine (DA) transmission is regulated by serotonin-2C (5-HT2C) receptors but the site(s) in the brain where these receptors are localized is not known. The present work utilized in vivo microdialysis to investigate the modulation of DA release by 5-HT2C receptors localized in the nerve terminal regions of the mesocortical and nigrostriatal DA pathways. Microdialysis probes implanted in the striatum or the prefrontal cortex (PFC) measured dialysate DA concentrations, while the selective 5-HT2B/2C inverse agonist SB 206553 was given locally by reverse dialysis into these terminal regions. Additionally, the effects of the 5-HT2C agonist mCPP on striatal DA were measured. Local administration of SB 206553 (0.1-100 microM) into the striatum increased DA efflux in a concentration-dependent manner. Systemic administration of mCPP (1.0 mg/kg i.p.) decreased striatal DA and attenuated the SB 206553-induced increase. In contrast, infusion of SB 206553 (0.1-500 microM) by reverse dialysis into the PFC had no significant effect on basal DA efflux in this region. Additionally, high concentrations of SB 206553 had no effect on high potassium (K(+))-stimulated DA release in the PFC. These data contribute to a body of evidence indicating that 5-HT2C receptors inhibit nigrostriatal dopaminergic transmission. In addition, the results suggest that the nigrostriatal system is regulated by 5-HT2C receptors localized in the dorsal striatum. Elucidating the mechanisms by which serotonin (5-HT) modulates striatal and prefrontocortical DA concentrations may lead to improvements in the treatment of diverse syndromes such as schizophrenia, Parkinson's disease, anxiety, drug abuse, and/or depression.

5-HT1A responsivity in patients with panic disorder before and after treatment with aerobic exercise, clomipramine or placebo

Blunted neuroendocrine and physiological responses to the selective 5-HT(1A) receptor agonist, ipsapirone, have been observed in patients with panic disorder and/or agoraphobia (PDA). In order to examine whether this hyporesponsiveness to ipsapirone is modified by pharmacological or non-pharmacological therapeutic interventions, challenges with an oral dose of ipsapirone (0.3 mg/kg) and placebo were performed in patients with PDA before and after 10 weeks of treatment with clomipramine, aerobic exercise and placebo. Before treatment, administration of ipsapirone was followed by significant increases of cortisol, anxiety and other psychopathological symptoms in comparison to the placebo challenge. In addition, a significant decrease of body temperature was observed. After the 10-week treatment period, the psychological responses to ipsapirone were significantly reduced in the clomipramine and the exercise group. In contrast, there was a non-significant trend towards higher cortisol responses after clomipramine and exercise treatment. The hypothermic response to ipsapirone was significantly reduced by clomipramine treatment. In conclusion, our results demonstrate that effective treatment of panic disorder has divergent effects on the psychological, neuroendocrine and temperature responses to ipsapirone.

Altered states: the clinical effects of Ecstasy

Ecstasy is the second most widely abused illegal drug in Europe. Ecstasy is the colloquial name for 3,4-methylenedioxymethamphetamine (MDMA), but not all Ecstasy tablets contain MDMA. When taken in hot, crowded environments, Ecstasy/MDMA users have developed acute complications that have had fatal consequences. Epidemiological evidence indicates that adverse reactions to Ecstasy/MDMA intoxication are rare and idiosyncratic. Potential mechanisms of action are reviewed. In animal studies, MDMA damages serotonergic fibres and reduces the number of serotonin transporter sites within the CNS. Demonstration of neurotoxicity in human users of Ecstasy is hampered by a number of confounds that the majority of published studies have failed to address. These confounds are reviewed and their impact is discussed.