The effect of MDMA (3,4-methylenedioxymethamphetamine) on the 5-HT synthesis rate in the rat brain: an autoradiographic study

Prenatal 3,4-methylenedioxymethamphetamine (ecstasy) alters exploratory behavior, reduces monoamine metabolism, and increases forebrain tyrosine hydroxylase fiber density of juvenile rats

3,4-Methylenedioxymethamphetamine (MDMA; ecstasy) use has risen among women of childbearing age. Consequently, there is a substantial risk for fetal exposure from women who are, or become pregnant while abusing MDMA. However, attempts to demonstrate that prenatal MDMA results in neurochemical alterations in rat models have failed. MDMA administration to neonatal rats (third trimester equivalent) results in significant and persistent neurochemical and behavioral alterations, yet human epidemiologic data suggest that the vast majority of prenatal exposure is limited to the first trimester. The following study was conducted to reexamine the potential for prenatal MDMA administration to produce lasting postnatal neurochemical and behavioral alterations using a new rodent model. Pregnant rats were administered twice-daily injections of MDMA (15 mg/kg sc) or saline from embryonic days (E) 14-20. Prenatally exposed pups were examined on postnatal days (P) 3 and 21. At P3, MDMA offspring showed reductions in the dopamine metabolite homovanillic acid which persisted through P21, along with reductions in the serotonin (5-HT) metabolite, 5-HIAA. Prenatally exposed MDMA animals at P21 also had reduced dopamine and 5-HT turnover in the nucleus accumbens. Increases in tyrosine hydroxylase fiber density were found in the frontal cortex, striatum and nucleus accumbens of MDMA animals. In addition, prenatal MDMA significantly increased locomotor activity of P21 pups in a 20-min novel cage environment. These findings provide the first evidence of lasting neurochemical and behavioral alterations following prenatal MDMA. Further investigation is warranted to elucidate possible mechanisms of action and to monitor children gestationally exposed to MDMA.

Selective decrease in serotonin synthesis rate in rat brainstem raphe nuclei following chronic administration of low doses of amitriptyline: an effect compatible with an anti-migraine effect

The effects of chronic, low-dose amitriptyline on serotonin (5-HT) synthesis rate were measured in rat brain using autoradiography and the trapping of alpha-[14C]-methyl-L-tryptophan (alpha-[14C]-MTrp). Rats received amitriptyline (2 mg/kg per day) or saline via intraperitoneal osmotic minipumps for 21 days. Amitriptyline had no effect on any physiological parameters measured, or on free or total plasma tryptophan levels. However, amitriptyline exerted selective decreases of 15% and 17% (P < 0.001) in serotonin synthesis rates in the dorsal and median raphe nuclei, respectively. There was no reduction in any of the projection areas studied, including the cerebral cortex, hippocampus, thalamus, hypothalamus or striatum. The data suggest that chronic low doses of amitriptyline can lead to sustained 5-HT re-uptake inhibition selectively in the raphe nuclei, an effect compatible with tonic activation of 5-HT(1A) autoreceptors and inhibition of 5-HT synthesis. The failure of chronic amitriptyline treatment to affect 5-HT synthesis rate in the projection areas may ensure an adequate regulation of pain pathways implicated in migraine headache, an effect possibly related to amitriptyline anti-migraine efficacy.

Study of the brain serotonergic system with labeled alpha-methyl-L-tryptophan

alpha-Methyl-L-tryptophan (alpha-MTrp) is an artificial amino acid and an analog of tryptophan (Trp), the precursor of the neurotransmitter serotonin (5-HT). In this article we have summarized available data, which suggest that the measurement of the unidirectional uptake of alpha-MTrp and its conversion to 5-HT synthesis rates is a valid approach for the determination of brain 5-HT synthesis rates. The main feature on which the model is based is the trapping of labeled alpha-MTrp in brain tissue. An overview of opposing opinions, which suggest that there is a need for a metabolic conversion of tracer, is also presented and discussed critically. As with all biological modeling there is likely to be room for improvements of the proposed biological model. In addition, there are a limited number of clearly defined circumstances in which the method is confounded by the metabolism of labeled alpha-MTrp via the kynurenine pathway. Nonetheless, a significant body of evidence suggests that labeled alpha-MTrp is a useful tracer to study brain 5-HT synthesis in most circumstances. Calculation of 5-HT synthesis rates depends on the plasma-free tryptophan concentration, which, according to the balance of arguments in the literature, is a more appropriate parameter than the total-plasma tryptophan. The method, as proposed by us, can be used in conjunction with autoradiographic measurements in laboratory animals, and with positron emission tomography in large animals and humans. We review studies in animals looking at the normal control of 5-HT synthesis and the way in which it is altered by drugs, as well as initial studies investigating healthy humans and patients with neuropsychiatric disorders.

Effects of selective 5-HT1A receptor antagonists on regional serotonin synthesis in the rat brain: an autoradiographic study with alpha-[14C]methyl-L-tryptophan

The effects of acute and chronic administration of WAY100635 and WAY100135, serotonin (5-HT)1A antagonists, on 5-HT synthesis rates, calculated from the trapping of alpha-[14C]methyl-L-tryptophan (alpha-MTrp), were evaluated in the rat brain using autoradiography. In the acute treatment studies, WAY100635 (1 mg/kg) induced a significant increase in 5-HT synthesis in the median raphe nucleus and some nerve terminal structures (range between 18 and 53%), while WAY100135 (10 mg/kg) produced a significant decrease of synthesis, in the range between 16 and 33%, in the raphe magnus nucleus and several projection areas. The action of WAY100635 given acutely was likely a result of antagonist actions at the 5-HT1A somato-dendritic autoreceptors. WAY100135 probably acted acutely as a partial agonist. In the chronic treatment studies, WAY100635 (1 mg/kg/day) and WAY100135 (10 mg/kg/day) were administered for 7 days as s.c. injections once a day. Chronic treatment with both compounds significantly reduced the rate of 5-HT synthesis in the nerve terminal structures and produced a significant increase in the raphe nuclei. These treatments did not have any effect on the plasma free or total tryptophan.

Brain net unidirectional uptake of alpha-[14c]methyl-L-tryptophan (alpha-MTrp) and its correlation with regional serotonin synthesis, tryptophan incorporation into proteins, and permeability surface area products of tryptophan and alpha-MTrp

The uptake and trapping constants for labeled tryptophan (Trp) via the serotonin (5-hydroxytryptamine; 5-HT) metabolic pathway and for the incorporation of Trp into proteins, and alpha-[14C]methyl-L-tryptophan (alpha-MTrp) were measured. Measurements were done in rats treated with either saline or probenecid (200 mg/kg). In addition, the blood-brain barrier (BBB) permeability surface area products for Trp (PS(T)) and alpha-MTrp (PSalpha) were measured in normal rats. The results suggest that, in both groups of rats, there is a highly significant correlation (p < 0.05; Pearson Product Moment Correlation (PPMC) between the brain uptake and trapping constants for alpha-MTrp and those of Trp via the 5-HT metabolic pathway, but there is no significant correlation (p > 0.05; PPMC) between either of these constants and the PS products of either compound. There is also no significant correlation (p > 0.05; PPMC) between the constant for the Trp incorporation into proteins with any of the other parameters. For all parameters, except Trp incorporation into proteins (alpha-MTrp is not incorporated into proteins), there was a highly significant correlation (p < 0.001) between the quantities measured for Trp and alpha-MTrp. The data presented here strongly suggests that the brain uptake and trapping of alpha-MTrp relates to brain 5-HT synthesis, and does not relate to the BBB transport or protein incorporation of Trp. On the basis of these results, as well as those previously reported, we concluded that trapping (unidirectional uptake) of alpha-MTrp can be converted to the 5-HT synthesis rates in the brain. From this also follows that labeled alpha-MTrp is a good tracer for in vivo evaluation of the brain 5-HT synthesis.

Correlation between 5-HT content and uptake site density following (S)-MDMA and dexfenfluramine-induced depletion, and with neuroprotection by the glycine site-specific NMDA antagonist ACEA 1021

3,4-Methylenedioxymethamphetamine (MDMA) and fenfluramine are amphetamine analogues that both cause long-term depletion of serotonin (5-HT) and 5-HT uptake sites in brain tissue. Depletion caused by these amphetamines is commonly measured by labeling 5-HT uptake sites using 3H-paroxetine combined with autoradiography or, alternatively measuring the concentration of 5-HT in tissue using high-performance liquid chromatography (HPLC). A close correlation between the 5-HT concentration measured in micropunch samples and the density of 3H-paroxetine-labeled 5-HT uptake sites measured in corresponding 20 micron coronal slices was determined (R2 = 0.92). These methods combined demonstrated that the glycine-site specific NMDA antagonist ACEA 1021 (4 x 30 mg/kg, i.p., 2 hourly) given 30 minutes before (S)-MDMA (4 x 10 mg/kg, i.p., 2 hourly) was able to prevent the depletion of both 5-HT content and uptake site density but unable to prevent the depletion of 5-HT content and uptake site density caused dexfenfluramine (4 x 15 mg/kg, i.p., 2 hourly).