Serotonin blockers

Serotonin has been found to influence sleeping, the regulation of body temperature, and sensory perception, but its exact role in mental illness is not yet clear. Unusually low levels of 5-hydroxyindoleacetic acid, a product of serotonin utilization, are characteristically found in the spinal fluid of victims of violent suicide. Drugs that mimic serotonin are sometimes used to treat depression, anxiety, and obsessive-compulsive disorder. Serotonin blockers are used to treat migraine headaches and relieve the nausea that accompanies cancer chemotherapy. A better understanding of the biochemistry of the brain may lead to better medications for treating various forms of mental illness. 

Since the neurotoxic effects of drugs such as parachloroamphetamine on serotonin neurons can be prevented by serotonin uptake blockers (Ross 1976 Sanders-Bush and Steranka 1978). the possibility that serotonin uptake carrier protein was likewise involved in the neurotoxic effects of MDMA was investigated. As shown in figure 4, pretreatment of rats with the seleetive serotonin uptake blocker citalopram (10 ml/kg), prior to each injection of 10 mg/kg MDMA, resulted in nearly complete protection against the neurotoxic effects of MDMA. Citalopram-pretreated rats exhibited only a 15 pereent decrease in serotonin uptake sites. No significant alterations in the eontent of serotonin and 5-HIAA were observed following MDMA treatment, in eomparison with 60 to 80 percent reductions in the serotonergie parameters observed in rats treated with an identical dose of MDMA alone. 

The data deseribed above demonstrate that destruction of serotonin axons by MDMA involves the serotonin aetive uptake carrier and that administration of citalopram, a selective serotonin uptake blocker, prior to administration of MDMA, ean prevent the decreases in serotonin markers elicited by MDMA alone. These data are eonsistent with previous reports for other potent serotonin neurotoxins, demonstrating that pretreatment with serotonin uptake blockers can prevent the neurotoxic effects of parachloroamphetamine (Ross 1976 Sanders-Bush and Steranka 1978). Furthermore, it has been shown that MDMA-induced neurotoxicity can be prevented or reversed if a serotonin uptake blocker such as fluoxetine is administered no later than 12 hours after MDMA treatment (Schmidt 1986). 

In addition to its relatively high affinity at postsynaptic 5-HT receptors, MDMA exhibited high affinity for 5-HT uptake sites and has been shown to increase the release of [ H]5-HT and block [ H]5-HT uptake in vitro. These data suggest that some of the actions of MDMA may be mediated at presynaptic binding sites. With respect to [ H]5-HT release, MDMA has been reported to increase the release of [ H]5-HT from brain synaptosomes (Nichols et al. 1982) and hippocampal slices (Johnson et al. 1986). With respect to uptake blockade, MDMA has been reported to competitively inhibit H-5-HT uptake in vitro (Shulgin 1986). Furthermore, the neurotoxic effects of in vivo administration of MDMA on serotonin terminals can be blocked by concomitant administration of the 5-HT uptake blocker citalo-pram (Battaglia et al. 1988b Schmidt and Taylor 1987). Additional evidence in support of the hypothesis that MDMA produces some of its... 

Opioids, benzodiazepines, barbiturates, corticosteroids, dopamine agonists (e.g., amantadine, bromocriptine, levodopa, pergolide, pramipexole, ropinirole), H2-receptor antagonists, anticholinergics (e.g., diphenhydramine, trihexylphenidyl), P-adrenergic blockers, clonidine, methyldopa, carbamazepine, phenytoin, baclofen, cyclobenzaprine, lithium, antidepressants (e.g., tricyclic antidepressants, selective serotonin reuptake inhibitors), and interleukin-2... 

Drugs that target other sites of platelet action include thromboxane synthetase inhibitors, serotonin or 5-hydroxytryptamine (5-HT2) receptor blockers, and thromboxane A2 receptor blockers, in addition to cyclooxygenase inhibitors and prostaglandin analogues. 

The answer is a. (Hardman, pp 228-229.) Phentolamine is a non-selective a-adrenergic receptor blocker (i.e., it has affinity for both - and ct2-adrenergic receptor sites). It also has a prominent direct relaxant (musculotropic spasmolytic) effect on arterioles, which results in vasodilation and reflex tachycardia. In addition, phentolamine can block the effects of serotonin and will increase hydrochloric acid and pepsin secretion from the stomach. Phentolamine is used for the short-term control of hypertension in patients with pheochromocytoma (i.e., a type of secondary hypertension) because of the high incidence of tachycardia associated with the compound, it is not used chronically for the treatment of essential hypertension... 

The behavioural effects of two antidepressants with opposite molecular actions, ie. tianeptine (a serotonin reuptake enhancer) and fluoxetine (a serotonin reuptake blocker) have been assessed and it was concluded that, apart from the effects on serotonin reuptake, these dmgs have other mechanisms playing an important role in the anti-depressant action <00AF5>. 

Apomorphine is a nonergot dopamine agonist given as a subcutaneous rescue injection. For patients with advanced PD with intermittent off episodes despite optimized therapy, subcutaneous apomorphine triggers an on response within 20 minutes, and duration of effect is up to 100 minutes. Most patients require 0.06 mg/kg. Prior to injection, patients should be premedicated with the antiemetic trimethobenzamide. It is contraindicated with the serotonin-3-receptor blockers (e.g., ondansetron). 

Hwang, E. C., and Van Woert, M. H. (1980) Acute versus chronic effects of serotonin uptake blockers on potentiation of the "serotonin syndrome." Commun. PsychopharmacoL, 4 161-167. 

SSRI = selective serotonin reuptake inhibitor SNRI = serotonin norepinephrine reuptake inhibitor ARB = angiotensin receptor blocker ACE = angiotensin converting enzyme COX-2 = cyclooxygenase 2 ADHD = attention deficit hyperactivity disorder. 

Tremaine LM, Joerg FA. 1989. Automated gas chromatography-electron-capture assay for the selective serotonin uptake blocker sertraline. J Chromatogr B 496 423. 

Listing of antidepressants grouped by principal mechanism of action in the synapse. Abbreviations MAOI—irreversible = irreversible monoamine oxidase inhibitor MAOI—reversible = reversible monoamine oxidase inhibitor NDRl = norepinephrine/ dopamine reuptake inhibitor NRI = norepinephrine reuptake inhibitor NSRl = norepinephrine/serotonin reuptake inhibitor NSSA = norepinephrine/specific serotonin agonist SRI = serotonin reuptake inhibitor SRl/serotonin-2 blocker = serotonin reuptake inhibitor and serotonin-2 receptor antagonist. 

Pindolol (Visken). A beta blocker known to potentiate serotonin activity via a distinct action on serotonin autoreceptors, pindolol has been reported in a controlled study to augment SSRl treatment in OCD patients who are partial responders. Pindolol is administered at a dose of 2.5 mg three times daily. It is generally well tolerated but low blood pressure, dizziness, and sedation can occur. 

---