Serotonin depression

Stabel S, Parker PJ Protein kinase C. Pharmacol Ther 51 71-95, 1991 Stagno SJ, Smith ML, Hassenbusch SJ Reconsidering psychosurgery issues of informed consent and physician responsibility. J Clin Ethics 5 217-223, 1994 Stahl SM Is serotonin receptor down regulation linked to the mechanism of action of antidepressant drugs Psychopharmacol Bull 30 39-43, 1994 Stahl SM Mixed anxiety and depression serotonin 1A receptors as a common pharmacological link. J Chn Psychiatry (in press)... 

Monoamine oxidase exists in two subtypes, A and B. Both forms are inhibited by the original MAO inhibitors, which are therefore nonselective. The A form metabolizes the neurotransmitter monoamines most closely linked to depression (serotonin and norepinephrine). 

Several theories have attempted to explain the pathology of depression. One of these theories is the monoamine theory of depression (Heninger et al., 1996). This theory proposes that impaired monoaminergic function is the central basis behind depression. Serotonin and norepinephrine are the two monoamines that have been primarily implicated in the disease. Pharmacological treatment of depression has focused on increasing synaptic levels of these two neurotransmitters (Table 3). 

This diverse collection has been grouped together mostly because they do not operate as selective serotonin reuptake inhibitors. Instead, each one interacts differently with neurotransmitters that are tied to depression serotonin, norepinephrine, or dopamine. For instance, one of the more popular non-SSRIs, Effexor (venlafaxine), selectively inhibits the uptake of serotonin and norepinephrine, acting on the same molecular machinery as tricyclic antidepressants (TCAs). But, in contrast to TCAs, Effexor shows no affinity for other neurotransmitter receptors and thus has far fewer side effects than the... 

W. Poldinger, et al., A Functional-Dimensional Approach to Depression Serotonin Deficiency as a Target Syndrome in a Comparison of 5-HTP and Fluvoxamine. Psychopathobgy 24 (1991) 53-81. 

Serotonin is a key transmitter in CNS function. Altered serotonergic function has been implicated in many CNS disorders including depression, feeding behavior, sleep disorders, schizophrenia, and Alzheimer s disease. 

Treatment of Major Depression. Dmgs commonly used for the treatment of depressive disorders can be classified heuristicaHy iato two main categories first-generation antidepressants with the tricycHc antidepressants (TCAs) and the irreversible, nonselective monoamine—oxidase (MAO) inhibitors, and second-generation antidepressants with the atypical antidepressants, the reversible inhibitors of monoamine—oxidase A (RIMAs), and the selective serotonin reuptake inhibitors (SSRIs). Table 4 fists the available antidepressants. 

Future Outlook for Antidepressants. Third-generation antidepressants are expected to combine superior efficacy and improved safety, but are unlikely to reduce the onset of therapeutic action in depressed patients (179). Many dmgs in clinical development as antidepressive agents focus on estabhshed properties such as inhibition of serotonin, dopamine, and/or noradrenaline reuptake, agonistic or antagonistic action at various serotonin receptor subtypes, presynaptic tt2-adrenoceptor antagonism, or specific monoamine—oxidase type A inhibition. Examples include buspirone (3) (only... 

Selected for clinical trials as a compound to calm agitated patients, imipramine was relatively ineffective. However, it was observed to be effective in the treatment of certain depressed patients (38). Early studies on the mechanism of action showed that imipramine potentiates the effects of the catecholamines, primarily norepinephrine. This finding, along with other evidence, led to the hypothesis that the compound exerts its antidepressant effects by elevating norepinephrine levels at central adrenergic synapses. Subsequent studies have shown that the compound is a potent inhibitor of norepinephrine reuptake and, to a lesser extent, the uptake of serotonin, thus fitting the hypothesis that had been developed to explain the antidepressant actions ofMAOIs. 

Two recently introduced antidepressants are notable m that they are selective serotonin uptake inhibitors Citalopram (19) is reported to be as effective as amitriptyline m the treatment of endogenous depression [75, 16] Fluoxetine (20) as the hydrochlonde is approved for major depressive disorders mcludmg those with concomitant anxiety Interestmgly, it also appears useful m the treatment of obesity [17]... 

Ubiquitous mitochondrial monoamine oxidase [monoamine oxygen oxidoreductase (deaminating) (flavin-containing) EC 1.4.3.4 MAO] exists in two forms, namely type A and type B [ monoamine oxidase (MAO) A and B]. They are responsible for oxidative deamination of primary, secondary, and tertiary amines, including neurotransmitters, adrenaline, noradrenaline, dopamine (DA), and serotonin and vasoactive amines, such as tyramine and phenylethylamine. Their nonselec-tive and selective inhibitors ( selective MAO-A and -B inhibitors) are employed for the treatment of depressive illness and Parkinson s disease (PD). 

S100A10 was found to interact with the serotonin IB receptor increasing its presence at the cell membrane. S100A10 was found to be closely associated with the pathophysiology of depression. 

Indeed, 5-HT is also a substrate for the 5-HT transporter, itself an important player in the treatment of depression, and more recently for the whole range of anxiety disorders spectrum (GAD, OCD, social and other phobias, panic and post-traumatic stress disorders). It is the target for SSRIs (selective serotonin reuptake inhibitors) such as fluoxetine, paroxetine, fluvoxamine, and citalopram or the more recent dual reuptake inhibitors (for 5-HT and noradrenaline, also known as SNRIs) such as venlafaxine. Currently, there are efforts to develop triple uptake inhibitors (5-HT, NE, and DA). Further combinations are possible, e.g. SB-649915, a combined 5-HTia, 5-HT1b, 5-HT1d inhibitor/selective serotonin reuptake inhibitor (SSRI), is investigated for the treatment of major depressive disorder. 

The TCAs, such as amitriptyline (Elavil) and dox-epin (Sinequan), inhibit reuptake of norepinephrine or serotonin at the presynaptic neuron. Drug classified as MAOIs inhibit the activity of monoamine oxidase a complex enzyme system that is responsible for breaking down amines. This results in an increase in endogenous epinephrine, norepinephrine and serotonin in the nervous system. An increase in these neurohormones results in stimulation of the CNS. The action of the SSRIs is linked to their inhibition of CNS neuronal uptake of serotonin (a CNS neurotransmitter). The increase in serotonin levels is thought to act as a stimulant to reverse depression. 

As was previously mentioned, a hangover-like syndrome is common the next day after use of MDMA. MDMA withdrawal, which is thought to be caused by serotonin depletion, can last for weeks and includes symptoms of depression, anxiety, restlessness, and insomnia (Allen et al. 1993 McGuite et al. 1994). No specific treatments are currently indicated fot this withdtawal syndrome, although the antidepressant bupropion may be helpful (Solhkhah... 

Briggs G, Freeman R, Yaffe S Drugs in Pregnancy and Lactation A Reference Guide to Maternal and Fetal Risk. Philadelphia, Lippincott, Williams Wilkins, 2002 Chengappa KN, Kambhampati R, Perkins K, et al Bupropion sustained release as a smoking cessation treatment in remitted depressed patients maintained on neatment with selective serotonin reuptake inhibitor antidepressants. J Clin Psychiatry 62 503—508, 2001... 

The enantiomerically pure 3-arylglutaric ester are precursors for the synthesis of (—)-paroxetine [10], a selective serotonin reuptake inhibitor used in the treatment of depression, obsessive compulsive disorder, and panic, and (i )-Baclofen [11], a GABAb receptor agonist, which is used cHnically in the treatment of spasticity (Chart 5.1). 

Anderson IM, Tomenson BM (1994). The efficacy of selective serotonin reuptake inhibitors in depression a meta-analysis of studies against tricyclic antidepressants. / Psychopharmacol 8, 238 9. 

There is, however, a unique risk in the bipolar form that antidepressant treatment may trigger a switch into mania. This may occur either as the natural outcome of recovery from depression or as a pharmacological effect of the drug. Particular antidepressants (the selective serotonin reuptake inhibitors) seem less liable to induce the switch into mania than other antidepressants or electroconvulsive therapy. Treatment for mania consists initially of antipsychotic medication, for instance the widely used haloperidol, often combined with other less specific sedative medication such as the benzodiazepines (lorazepam intramuscularly or diazepam orally). The manic state will usually begin to subside within hours and this improvement develops further over the next 2 weeks. If the patient remains disturbed with manic symptoms, additional treatment with a mood stabilizer may help. 

Wurtman, RJ and Wurtman, JJ (1995) Brain serotonin, carbohydrate-craving, obesity and depression. Obesity Res. 3 477S-480S. 

Salomon, RM, Miller, HL, Delgado, PL and Charney, D (1993) The use of tryptophan depletion to evaluate central serotonin function in depression and other neuropsychiatric disorders. Int. J. Clin. Psychopharmacol. 8 41-46. 

Weiss, JM, Goodman, PA, Lostito, BG, Corrigan, S, Charry, JM and Bailey, WH (1981) Behavioral depression produced by an uncontrollable stressor relationship to norepinephrine, dopamine and serotonin levels in various regions of rat brain. Brain Res. Rev. 3 167-205. 

QUESTION We have all these theories about serotonin being involved in depression. Do you have any explanation for why depression is not seen in humans if serotonin neurons have been damaged by these drugs ... 

ANSWER I think that elearly it is possible that there is no neurotoxieity in humans. I think all of us would like for this to be the ease. And maybe it is the ease. We have talked about this a lot with fenfluramine, and we have done studies with paraehloroamphetamine in whieh we have given it orally to rats at relatively low doses, but still anoreetie doses, over 90 days. We have seen depletion of serotonin, but that was fully reversible depletion. It eame baek when the drug was stopped. I think there may be no neurotoxieity at the oral doses used in humans. I think that would be great if that is the ease. That would explain why there is no depression or other kinds of symptoms. But I don t feel comfortable about relying on the laek of reporting of depression as real evidence that there is no neurotoxieity. We simply need to have better data on that. 

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