Neurons antidepressant mechanisms

In addition to the presumed antidepressant mechanism of these drugs, they exert a multiplicity of effects on other neurotransmitters and neuron receptors, both in the areas that control mood symptoms and elsewhere in the central and peripheral nervous systems. Because medications have effects not only in the areas thought to be related to the disorder being treated but also in other areas in the brain and peripheral nervous system,... 

Laifenfeld D, Klein E, Ben-Shachar D. Norepinephrine alters the expression of genes involved in neuronal sprouting and differentiation relevance for major depression and antidepressant mechanisms. J Neurochem 2002 83 1054-1064. 

Clomipramine is different from the other TCAs, exhibiting preferential selectivity for inhibiting the reuptake of 5-HT at the presynaptic neuronal membrane. Its antidepressant mechanism of action as an inhibitor of the 5-HT transporter is reduced in vivo, however, because of the formation of its active metabolite, N-desmethylclomipramine, which inhibits the reuptake of NE. As a result of its common structure with the other TCAs, clomipramine shares the pharmacological and adverse-effect profile of the other TCAs. 

Bupropion is an atypical antidepressant drug that is the only nonnicotine-based prescription medicine approved for smoking cessation by the FDA. Its mechanism of action is presumed to be mediated by its capacity to block neuronal reuptake of dopamine and/or norepinephrine (Fiore et al. 2000). Relative to other antidepressants, bupropion has a relatively high affinity for the dopamine transporter (Baldessarini 2001). There is also evidence that bupropion acts as a functional nicotine antagonist, suggesting another potential mechanism by which bupropion could reduce smoking rates (Slemmer et al. 2000). 

There are several mechanisms whereby antidepressants can modify intracellular events that occur proximal to the posts)maptic receptor sites. Most attention has been paid to the actions of antidepressants on those pathways that are controlled by receptor-coupled second messengers (such as cyclic AMP, inositol triphosphate, nitric oxide and calcium binding). However, it is also possible that chronic antidepressant treatment may affect those pathways that involve receptor interactions with protein tyrosine kinases, by increasing specific growth factor synthesis or by regulating the activity of proinflammatory cytokines. These pathways are particularly important because they control many aspects of neuronal function that ultimately underlie the ability of the brain to adapt and respond to pharmacological and environmental stimuli. One mechanism whereby antidepressants could increase the s)mthesis of trophic factors is... 

Serotonin mediates many central and peripheral physiological functions, including contraction of smooth muscle, vasoconstriction, food intake, sleep, pain perception, and memory, a consequence of it acting on several distinct receptor types. Although 5-HT may be metabolized by monoamine oxidase, platelets and neurons possess a high-affinity mechanism for reuptake of 5-HT. This mechanism may be inhibited by the widely prescribed antidepressant drugs termed selective serotonin re-uptake inhibitors (SSRl), e.g. fluoxetine (Prozac ), thereby increasing levels of 5-HT in the central nervous system. 

It is believed that tricyclic antidepressants inhibit the (neuronal) reuptake of norepinephrine (noradrenaline) and/or serotonin by presynaptic nerve endings, thus blocking one of the leading mechanisms of their inactivation, and thereby increasing the concentration of the indicated amines potentiating their effects. It should be noted that, as a rule, secondary amines, which are representatives of tricyclic antidepressants, exhibit high activity, blocking the neuronal reuptake of norepinephrine, while tertiary amines act more on the neuronal reuptake of serotonin. 

Pharmacoiogy Nefazodone is an antidepressant with a chemical structure unrelated to available antidepressant agents. The mechanism of action is unknown. Nefazodone inhibits neuronal uptake of serotonin and norepinephrine. Pharmacokinetics ... 

Pharmacology Although the mechanism of the antidepressant and central pain inhibitory action of duloxetine in humans is unknown, it is believed to be related to its potentiation of serotonergic and noradrenergic activity in the CNS. Preclinical studies have shown that duloxetine is a potent inhibitor of neuronal serotonin and norepinephrine reuptake and a less potent inhibitor of dopamine reuptake. 

Our understanding of the mechanism of antidepressant action has evolved over time. In the late 1950s, the first molecules introduced for the treatment of MDD were the so-called tricyclic antidepressants (TCAs), represented by imipramine (7). Subsequent experience with TCAs supported the role of both 5-HT and NE, although these drug molecules act on other neuronal systems as well. Despite their elfectiveness, the use of TCAs was limited due to poor tolerability and safety concerns, in particular, severe toxicity when taken in overdose. 

Kramer MS, Cutler NR, Ballenger JC, Patterson WM, Mendels J (1995) A placebo-controlled trial of L-365,260, a CCK antagonist, in panic disorder. Biol Psychiatry 37 462-466 Kramer MS, Cutler N, Feighner J, Shrivastava R, Carman J, Sramek IJ, Reines SA, Snavely D, Wyatt-Knowles E, Hayle EJ (1998) Distinct mechanism for antidepressant activity by blockade of central substance P receptors. Science 281 1640-1645 Kriegsfeld LJ, Dawson TM, Dawson VL, Nelson RJ, Snyder SH (1997) Aggressive behavior in male mice lacking the gene for neuronal nitric oxide synthase requires testosterone. Brain Res 769 66-70... 

Mechanism of Action An antidepressant that appears to inhibit serotonin and norepinephrine reuptake at CNS neuronal presynaptic membranes is a less potent inhibitor of dopamine reuptake. Therapeutic Effect Relieves depression. Pharmacokinetics Well absorbed from the G1 tract. Protein binding greater than 90%. Extensively metabolized to active metabolites. Excreted primarily in urine and, to a lesser extent, in feces. Half-life 8-17 hr. 

Mechanism of Action An antidepressant and antiobsessive agent that selectively inhibits neuronal reuptake of serotonin. Therapeutic Effect Relieves depression and symptoms of obsessive-compulsive disorder. 

Mechanism of Action A tetracyclic compound that blocks reuptake norepi nephri ne by CNS presynaptic neuronal membranes, increasing availability at postsynaptic neuronal receptor sites, and enhances synaptic activity. Therapeutic Effect Produces antidepressant effect, with prominent sedative effects and low anticholinergic activity. Pharmacokinetics Slowly and completely absorbed after PO administration. Protein binding 88%. Metabolized in liver by hydroxylation and oxidative modification. Excreted in urine. Unknown if removed by hemodialysis. Half-life 27-58 hr. 

Mechanism of Action A tricyclic antidepressant that blocks reuptake of the neu-retransmitters norepinephrine and serotonin at neuronal presynaptic membranes, increasing their availability at postsynaptic receptor sites. Therapeutic Effect Relieves depression. 

A therapeutic decrement may be inherent in the repeated application of antidepressant treatments. In this context, patients who are repeatedly treated with antidepressants appear to become increasingly more resistant to subsequent treatment strategies, including ECT [Amsterdam et al. 1994b]. A number of clinical and biochemical factors, including progressive virulence of recurrent depressive episodes, reduced plasticity of neuronal receptor regulatory mechanisms, and the development of secondary (and even tertiary de-... 

Tricyclic antidepressants are the most commonly used drugs. They produce antidepressant effect by blocking the neuronal uptake of noradrenaline and exert anti-cholinergic activity. They also inhibit neuronal uptake of 5HT and dopamine. The exact mechanism of action is not known. The antidepressant effect is noticed after three to four weeks of drug administration. 

---