Restoration of 3,4-methylenedioxymethamphetamine-induced 5-HT depletion by the administration of L-5-hydroxytryptophan

BACKGROUND: 3,4-Methylenedioxymethamphetamine (MDMA) causes persistent decreases in brain 5-HT content and 5-HT transporter (SERT) binding, with no detectable changes in SERT protein. Such data suggest that MDMA impairs 5-HT transmission but leaves 5-HT nerve terminals intact. To further test this hypothesis, we carried out two types of experiments in rats exposed to high-dose MDMA. First, we examined the effects of MDMA on SERT binding and function using different in vitro assay conditions. Next, we treated rats with the 5-HT precursor, l-5-hydroxytryptophan (5-HTP), in an attempt to restore MDMA-induced depletions of 5-HT. METHODS: Rats received three i.p. injections of saline or MDMA (7.5 mg/kg), one injection every 2 h. Rats in one group were decapitated, and brain tissue was assayed for SERT binding and [(3)H]5-HT uptake under conditions of normal (100 or 126 mM) and low (20 mM) NaCl concentration. Rats from another group received saline or 5-hydroxytryptophan/benserazide (5-HTP-B), each drug at 50 mg/kg i.p., and were killed 2 h later. RESULTS: MDMA reduced SERT binding to 10% of control when assayed in 100 mM NaCl, but this reduction was only 55% of control in 20 mM NaCl. MDMA decreased immunoreactive 5-HT in caudate and hippocampus to about 35% of control. Administration of 5-HTP-B to MDMA-pretreated rats significantly increased the 5-HT signal toward normal levels in caudate (85% of control) and hippocampus (66% of control). CONCLUSION: 1) Following high-dose MDMA treatment sufficient to reduce SERT binding by 90%, a significant number of functionally intact 5-HT nerve terminals survive. 2) The degree of MDMA-induced decreases in SERT binding depends on the in vitro assay conditions. 3) 5-HTP-B restores brain 5-HT depleted by MDMA, suggesting that this approach might be clinically useful in abstinent MDMA users.     

Relationship between central and peripheral serotonin 5-HT2A receptors: a positron emission tomography study in healthy individuals

5-HT2A receptors on platelet membranes are often measured as indirect markers of the central 5-HT2A receptors. However, the 5-HT2A receptors on the platelets and those in the brain have never been assessed simultaneously in humans. The purpose of this study was to evaluate the relationship between platelet membrane and neocortical 5-HT2A receptors measured simultaneously in normal healthy volunteers. Twelve healthy volunteers had the 5-HT2A receptors on their platelet membranes assessed in vitro using [3H]lysergic acid diethylamide ([3H]LSD) and their central 5-HT2A receptors measured in vivo using [18F]setoperone and positron emission tomography (PET) imaging. We find no significant correlation between the binding potential (Bmax/Kd) of 5-HT2A receptors on platelets and in brain in the same individual (F1,10 = 0.7, P = 0.42). The study was limited by a small sample and the fact the two different ligands were used (i.e. LSD for platelets and setoperone for brain); nonetheless, the findings suggest that changes in platelet 5-HT2A receptors may not indicate similar changes in central 5-HT2A receptors.     

Conditions for the formation of cyclic compounds between pyridoxal phosphate and 5-hydroxytryptamine or 5-hydroxytryptophan

5-Hydroxytryptamine (5HT) and 5-hydroxytryptophan (5HTP) form cyclic compounds (probably of the tetrahydro--carboline type) with pyridoxal phosphate (PLP). In the first step of reaction a Schiff's base is formed; during incubation it is transformed into a cyclic compound with a maximum absorption spectrum at 330 nm. The degree of cyclization depends on pH and substrate concentrations. One mole of 5HT or 5HTP reacts with one mole of coenzyme. The velocity of cyclization increased with an excess of either 5HT (5HTP) or PLP, without any change in the mole to mole ratio. The formation of cyclic compounds was confirmed by the use of isotopes, separation from substrates being achieved by high-voltage electrophoresis.     

Somatostatin induced apnoea: prevention by central and peripheral administration of the opiate receptor blocking agent naloxone

Somatostatin (SRIF) (6 nmol) given intracisternally (i.c.) into the alpha-chloralose anaesthetized rat has recently been shown to cause apnoea with a latency of 5-10 minutes (Kalia et al. 1984a). The apnoea produced by SRIF is very rapid, irreversible and leads to the death of the animal. In view of the existence of SRIF nerve cell bodies and terminals in medullary respiratory nuclei such as the ventral and ventrolateral subnuclei of the nucleus of the tractus solitarius (nTS) (Kalia et al. 1984b, Johanson et al. 1984), we have proposed the existence of somatostatinergic mechanisms in the respiratory nuclei of the medulla oblongata involved in mediating apnoeic conditions (Kalia et al. 1984a). In the present study, we have analysed whether the SRIF induced apnoea could be counteracted by a previous i.c. administration of the highly selective alpha 2-adreno-receptor blocking agent RX 781094 (2-(2-(I,4 benzodioxanyl]2-imi-dazoline HCl) (Doxey et al. 1983), or an opiate receptor blocking agent such as naloxone. Thus, both alpha 2-adrenoreceptor agonists and opiates induce respiratory depression, and opiates in high doses cause apnoea (Bolme et al. 1974, Hassen et al. 1982, Sitsen et al. 1982). In addition, catecholamine (CA) and enkephalin immuno-reactive nerve terminal networks exist in high densities within the nucleus tractus solitarius (nTS) of the medulla oblongata and may therefore interact with somatostatin nerve terminals in regulation of respiratory activity (Kalia et al. 1984b).     

Antidepressant potentiation of 5-hydroxytryptophan by L-deprenil in affective illness

In an open trial study, L-Deprenil, an irreversible selective MAO-B inhibitor without 'chesse effect' was given to 14 patients with unipolar and bipolar depression receiving L-5-Hydroxytryptophan (L-5-HTP) and benzerazide. Ten out of 14 patients showed a good response to the combination of drugs and a correlation was found between the degree of platelet MAO inhibition and clinical response. In a double-blind controlled study, 18 affectively ill patients were randomly allocated to L-Deprenil plus L-5-HTP and benzerazide, 21 patients were treated with L-5-HTP and benzerazide and 19 patients with placebo only. Patients treated with the combination of L-Deprenil and L-5-HTP showed a significantly greater clinical improvement than placebo patients but this was not the case for patients treated with 5-HTP alone. A positive relationship was demonstrated between mood improvement and degree of platelet MAO inhibition in patients treated with L-Deprenil.     

Baroreceptor-mediated inhibition of respiration after peripheral and central administration of a 5-HT1A receptor agonist in neonatal piglets

Inhibition of neurones in the ventral medulla accentuates the respiratory inhibition associated with acute blood pressure elevation in piglets. Activation of presynaptic 5-HT(1A) receptors inhibits serotonergic neurones in the ventral medulla and caudal raphé, and we tested the hypothesis that administration of 8-hydroxydipropylaminotetralin (8-OH-DPAT), a 5-HT(1A) agonist, within the rostroventral medulla and caudal raphé would enhance baroreceptor-mediated inhibition of respiratory activity in decerebrate, neonatal piglets. Baroreceptor stimulation was achieved by inflating a balloon in the distal aorta to elevate carotid blood pressure. After two to four control trials of baroreceptor stimulation, each piglet was given either a single intravenous (i.v.) dose of 10 microg kg(-1) 8-OH-DPAT or treated by adding 10 or 30 mm 8-OH-DPAT to the dialysate for approximately 10 min to inhibit serotonergic neurones, after which the baroreceptor stimulation trials were repeated. Baroreceptor stimulation reduced respiratory activity, particularly the respiratory frequency, which diminished from 35.7 +/- 3.3 to 33.8 +/- 3.1 breaths min(-1) (P < 0.02) and, following i.v. 8-OH-DPAT, baroreceptor-mediated inhibition of respiratory output was significantly accentuated (P < 0.05); the respiratory frequency declined from 34.5 +/- 3.6 to 26.5 +/- 2.9 breaths min(-1). Increasing aortic blood pressure reduced the respiratory frequency (P < 0.01), but focal dialysis of 10 or 30 mm 8-OH-DPAT had, on average, no effect on the ventilatory inhibition associated with an acute elevation of blood pressure. We conclude that activation of 5-HT(1A) receptors after systemic administration of 8-OH-DPAT enhanced baroreflex-mediated inhibition of ventilation, but this effect cannot be attributed to 5-HT(1A) receptor activation within the rostroventral medulla and caudal raphé.     

Reversibility of para-chlorophenylalanine-induced insomnia by intrahypothalamic microinjection of L-5-hydroxytryptophan

Para-chlorophenylalanine, a blocker of serotonin biosynthesis by inhibiting tryptophan hydroxylase, induced total insomnia which was accompanied in cat by a permanent discharge of ponto-geniculo-occipital activity. L-5-Hydroxytryptophan microinjection (1-4 micrograms/0.5 microliters) in the anterior hypothalamus 72 h after para-chlorophenylalanine administration, restored both slow wave sleep and paradoxical sleep with variable latencies for each state of sleep. On the contrary, ponto-geniculo-occipital activity was never suppressed. The hypnogenic effects of L-5-hydroxytryptophan were always followed by a return of the para-chlorophenylalanine-induced insomnia. On the other hand, the temperature recording did not show any alteration of the cerebral temperature after para-chlorophenylalanine treatment but the subsequent L-5-hydroxytryptophan microinjection was followed by hyperthermia. Using immunohistochemistry for serotonin after intrahypothalamic L-5-hydroxytryptophan microinjection in parachlorophenylalanine-pretreated cat, we defined a restricted region of the anterior hypothalamus possibly responsible for the hypnogenic effect. This region included the lateral hypothalamus and the anterior hypothalamic area. It is suggested that the reversible hypersomnia after L-5-hydroxytryptophan microinjection in the anterior hypothalamus in para-chlorophenylalanine-pretreated cat is due to a neurohormonal action of serotonin: serotonin could act upon the anterior hypothalamus which secondarily inhibits a waking system located in the ventrolateral hypothalamus leading to the appearance of paradoxical sleep.     

Effect of tryptophan, 5-hydroxytryptophan,serotonin, histidine,and histamine on peroxidation of lipids in liver mitochondrial membranes

The effect of tryptophan, 5-hydroxytryptophan, serotonin, histidine, and histamine on peroxidation of lipids in rat liver mitochondrial membranes in the presence of Fe⁺⁺ ions which induce this process was studied by recording very weak chemiluminescence. 5-Hydroxytryptophan and serotonin in concentrations of 10^–5–10^–4 M (protein concentration 1.8 mg/ml mitochondrial suspension) inhibit this process. By studying the kinetics of the initial part of the ascending branch of the slow burst constants of antioxidative activity were calculated: For 5-hydroxytryptophan and serotonin these were 2.2·10³ and 9.8·10³M^–1 respectively. The antioxidant action is linked with the presence of a phenol group in the molecule of the compound tested. It is postulated that the action of 5-hydroxytryptophan and serotonin on peroxidation of lipids in membranes, besides their effect on other membrane processes, is also an important factor in the regulation of permeability of biological membranes.Department of Molecular Pharmacology and Radiobiology, Medicobiological Faculty, N. I. Pirogov Second Moscow Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR S. S. Debov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 81, No. 2, pp. 169–171, February, 1976.     

Control of central and peripheral tolerance by Aire

The negative selection of self-reactive thymocytes depends on the expression of tissue-specific antigens by medullary thymic epithelial cells. The autoimmune regulator (Aire) protein plays an important role in turning on these antigens, and the absence of even one Aire-induced tissue-specific antigen in the thymus can lead to autoimmunity in the antigen-expressing target organ. Recently, Aire protein has been detected in peripheral lymphoid organs, suggesting that peripheral Aire plays a complementary role here. In these peripheral sites, Aire was found to regulate the expression of a group of tissue-specific antigens that is distinct from those expressed in the thymus. Furthermore, transgenic antigen expression in extrathymic Aire-expressing cells (eTACs) can mediate deletional tolerance, but the immunological relevance of Aire-dependent, endogenous tissue-specific antigens remains to be determined.     

Comparison of central and peripheral nervous system lesions caused by high-dose short-term and low-dose subchronic acrylamide treatment in rats

The effects of high-dose subacute acrylamide treatment of up to 50 mg/kg/day for 4 or 10 d were compared to those of subchronic exposure, up to 12 mg/kg/day for 90 d. In the subacute study, Purkinje cells, long ascending tracts of the spinal cord, optic tract terminal or preterminal regions in superior colliculus, sensory ganglion cells, and distal large-caliber peripheral axons were severely affected. Purkinje cells and fasciculus gracilis changes were the earliest lesions. In the subchronic study, the dominant lesion was confined to the distal peripheral axon, with only minor changes occurring in spinal cord and medulla. Paranodal swellings with the characteristic appearance of neurofilament aggregations were not seen. This morphological study suggests a significant difference between high- and low-dose acrylamide-induced lesions. If there is a reduced tendency for long-term low-dose acrylamide exposure to produce CNS lesions, the risk of irreversible nervous system damage would be less than that predicted from subacute studies.     

Effects of acute central and peripheral ACTH1-24 administration on lordosis behavior

The role of adrenocorticotropic hormone (ACTH) in the control of the lordosis reflex of female rats was investigated. Experiment 1 examined the effects of ACTH^1–24 infused into the ventricular system of the brain. ACTH treatment lowered the performance of both ovariectomized (ovx) and adrenalectomized-ovariectomized (adx-ovx) extrogen-primed females. ACTH-treated females also showed evidence of spontaneous stretching, yawning, and grooming. Experiment 2 examined the effects of ACTH^1–24 administered subcutaneously. Here ACTH elevated performance of ovx but not adx-ovx estrogen-primed females. There was no evidence of spontaneous stretching, yawning, and grooming movements in females given peripheral ACTH. In both experiments, untreated adx-ovx females showed a higher level of lordosis than untreated ovx females. These results suggest that the central effect of acute ACTH elevation differs from the peripheral effect, and that the peripheral effect is probably mediated by the adrenal.