Effects of amitriptyline and isocarboxazid on 5-hydroxytryptophan induced head twitches in mice

Effects of amitriptyline and isocarboxazid on brain 5-HT and 5-HIAA were examined in relation to their action on 5-HTP induced head twitches. Amitriptyline reduced 5-HTP induced head twitches but isocarboxazid increased them. Both amitriptyline and isocarboxazid caused a significant increase of brain 5-HT concentration in 5-HTP treated mice. Amitriptyline also caused a significant increase of 5-HIAA concentration, while isocarboxazid reduced 5-HIAA concentration in the brains of 5-HTP treated mice. Probenecid, which significantly increased 5-HIAA concentration without affecting brain 5-HT concentration in 5-HTP treated mice, reduced 5-HTP induced head twitches. These results suggest that 5-HTP induced head twitches might be induced by an increase of 5-HT concentration, and reduced by an increase of 5-HIAA or a decrease of 5-HT concentration in the brains of mice.     

Effects of 5-hydroxytryptophan, iproniazid and p-chlorophenylalanine on lidocaine seizure threshold of mice

The effects of 5-hyroxytryptophan (5-HTP), iproniazid and p-chlorophenylalanine (p-CPA) on the lidocaine seizure threshold of mice were studied. The median i.p. convulsant dose (CD₅₀) of lidocaine in control (saline-treated) mice was 76.0 mg/kg. Pretreatment with 5-HTP (100 mg/kg i.p.) lowered the CD₅₀ to 61.0 mg/kg. Similar results (CD₅₀ of 58.0 mg/kg) were observed in the iproniazid (100 mg/kg i.p.) pretreated group. In the iproniazid—5-HTP treated group, a more pronounced and significant (p < 0.01) drop of the CD₅₀ to 45.0 mg/kg was observed. In p-CPA pretreated mice (300 mg/kg i.p. for 3 days), the CD₅₀ increased slightly to 90.0 mg/kg. The duration of seizures increased in 5-HTP and iproniazid pretreated groups. These results suggest the possibility of an involvement of 5-HT in the lidocaine-induced convulsive process.     

5-羟色胺酸对吗啡诱导小鼠行为敏化的影响

研究中枢5-羟色胺能系统对吗啡诱导小鼠行为敏化的介导作用。选用雄性昆明小鼠，每天2次注射生理盐水或吗啡10mg／kg，连续3天。停药5天后，于第9天，进行吗啡激发试验，测定小鼠的自主活动60min，观察行为敏化效应。此外，选用5-羟色胺前体物质5-羟色氨酸作为工具药，分别在吗啡处理阶段（形成期），吗啡停药阶段（转换期）以及吗啡激发试验前腹腔注射20-80mg／kg5-羟色氨酸。激发试验给予吗啡后，立即测定小鼠的自主活动。实验第9天激发试验数据表明，每天2次反复给予吗啡的小鼠，其自主活动明显高于生理盐水对照组，说明小鼠对吗啡产生了行为敏化效应。5-羟色氨酸可以选择性抑制吗啡对小鼠行为敏化的诱导作用，其抑制作用呈剂量依赖性。然而，5-羟色氨酸对小鼠吗啡行为敏化的转换和表达无明显药理作用。因此，中枢5-羟色胺能系统的功能水平上调可能对吗啡诱导小鼠行为敏化效应具有一定的抑制作用。     

p-Chlorophenylalanine-induced alterations in the behavioral effects of 5-hydroxytryptophan

Pretreatment of rats with p-chlorophenylalanine methyl ester (PCPA-ME) causes a normally non-effective dose of 5-hydroxytryptophan (5-HTP) to disrupt bar-pressing at times when serotonin (5-HT) concentration is depleted. There does not appear to be any correlation between the initial, behaviorally-distruptive effects of PCPA-ME and the action of this compound on 5-HT biosynthesis.     

Differential uptake, metabolism and behavioral effects of the D and L isomers of 5-hydroxytryptophan.

The relative contribution of the D and L isomers of 5-hydroxytryptophan (5-HTP) to the uptake and metabolism of 5-HTP and their associated behavioral effects were investigated. For the metabolic study, an injection of 25 mg/kg of D or L-5-HTP was administered IP and the rats killed 15, 30, 45 or 60 min later. Endogenous levels of 5-HTP, serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were measured in the telencephalon following D- or L-5-HTP administration. Levels of 5-HTP, 5-HT and 5-HIAA were also measured in the brain stem (including diencephalon) following L-5-HTP administration. In the behavioral study, the effects of IP injections of D-5-HTP, L-5-HTP and D,L-5-HTP upon operant responding on a VI 1 schedule were investigated. Compared to vehicle controls, L-5-HTP significantly increased the levels of 5-HTP, 5-HT and 5-HIAA in the telencephalon and brain stem at all time points investigated. Behaviorally, 25 mg/kg of L-5-HTP and 50 mg/kg of D,L-5-HTP produced similar changes. Following the injection of either compound there was a large decrease in response rate with a duration of about 1 hr which paralleled the neurochemical changes. Injections of D-5-HTP produced an increase in the levels of 5-HTP and 5-HIAA in the telencephalon at 15 min but no change in the level of 5-HT was observed. In the operant situation, following D-5-HTP injections, a brief decrease in responding occurred in some animals which did not correlate with the neurochemical data. It was concluded that the L isomer is mainly responsible for the neurochemical and behavioral effects seen when D,L-5-HTP is administered.     

Effects of 5-hydroxytryptophan,oxotremorine, and tetrahydroaminoacridine on apomorphine-induced stereotypy

The stereotyped behavior induced by apomorphine in rats was inhibited by oxotremorine and tetrahydroaminoacridine (THA). 5-Hydroxytryptophan (5-HTP) did not change stereotypy scores. These data show influence of cholinergic mechanisms on such behavior. Possible clinical applications are discussed.     

Morinda officinalis oligosaccharides increase serotonin in the brain and ameliorate depression via promoting 5-hydroxytryptophan production in the gut microbiota

Morinda officinalis oligosaccharides (MOO) are an oral drug approved in China for the treatment of depression in China. However, MOO is hardly absorbed so that their anti-depressant mechanism has not been elucidated. Here, we show that oral MOO acted on tryptophan → 5-hydroxytryptophan (5-HTP) → serotonin (5-HT) metabolic pathway in the gut microbiota. MOO could increase tryptophan hydroxylase levels in the gut microbiota which accelerated 5-HTP production from tryptophan; meanwhile, MOO inhibited 5-hydroxytryptophan decarboxylase activity, thus reduced 5-HT generation, and accumulated 5-HTP. The raised 5-HTP from the gut microbiota was absorbed to the blood, and then passed across the blood–brain barrier to improve 5-HT levels in the brain. Additionally, pentasaccharide, as one of the main components in MOO, exerted the significant anti-depressant effect through a mechanism identical to that of MOO. This study reveals for the first time that MOO can alleviate depression via increasing 5-HTP in the gut microbiota.     

In vivo increase in hypothalamic cyclic AMP following 5-hydroxytryptophan administration in rats

Summary The administration of 5-hydroxytryptophan (5-HTP, 100 mg/kg, i.p.) consistently increased hypothalamic cyclic AMP levels in rats treated 10 days earlier with the serotonin neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), to produce 5-HT receptor supersensitivity. However 5-HTP (100 mg/kg), failed to cause an increase in hypothalamic cyclic AMP in rats not pretreated with 5,7-DHT. The 5-HTP-induced increase in cyclic AMP was blocked by the decarboxylase inhibitor, benserazide (RO 44602, 800 mg/kg) and by the 5-HT antagonist metergoline (5 mg/kg). Other treatments that caused a significant elevation of hypothalamic cyclic AMP included: (a) l-Tryptophan plus the monoamine oxidase inhibitor, tranylcypromine, and (b) the serotonin agonist, 1-(m-trifluromethylphenyl)-1-piperazine.The 5-HT antagonist, methysergide, blocked the serotonin receptor mediated behavioral syndrome, but failed to prevent the increase in hypothalamic cyclic AMP. Moreover, the 5-HT agonist, 5-methoxy-N, N-dimethyltryptamine, (5-Me-DMT), induced a strong behavioral syndrome but failed to significantly increase hypothalamic cyclic AMP. These findings suggest that activation of 5-HT receptors some-where in the brain causes an increase in hypothalamic cyclic AMP, but further studies will be needed to determine whether this is a direct result of activation of the 5-HT receptors in the hypothalamus.     

Effects of dl-para-chlorophenylalanine on sucrose preference and intake: reversal by 5-hydroxytryptophan and 6-methoxy 1,2,3,4,-tetrahydro-beta-carboline

In two experiments involving 12- or 4-hr two-bottle preference tests, rats depleted of brain serotonin by dl-para-chlorophenylalanine (pCPA) injections consumed larger amounts of sucrose and had a higher preference for sucrose solutions over distilled water than vehicle-injected control animals. Injection of 5-hydroxytryptophan (5-HTP) or 6-methoxy-1,2,3,4-tetrahydro-β-carboline (6-MeO-THBC) was found to reverse the effects of pCPA on brain serotonin as well as reverse the increased sucrose preference produced by pCPA.     

A pilot study of the predictive value of the probenecid test in application of 5-hydroxytryptophan as antidepressant

In depressions, varying therapeutic effects have been obtained with 5-HT precursors. This is possibly due to the fact that the group of the depressions is pathogenetically heterogeneous; that, specifically, some types do and other types do not entail disturbances in the central 5-HT metabolism; and that only the former types are precursor-sensitive. This hypothesis was tested in a preliminary pilot study, and confirmed. The central 5-HT consumption was assessed on the basis of the probenecid test. In this experiment, 5-HTP was for the first time given in large doses over a considerable period of time.This study was supported by grants from the Netherlands Organization for Pure Research (Z.W.O.), the Preventie Fonds and the Merck Sharp & Dohme Research Laboratories (U.S.A.).     

The interaction of some kynurenine pathway metabolites with 5-hydroxytryptophan and 5-hydroxytryptamine

The kynrenine pathway metabolites kynurenine, 3-hydroxykynurenine and xanthurenic acid have been tested against 5-hydroxytryptamine (5-HT) and 5-hydroxytryptophan (5-HTP)-induced head twitches in the mouse in a dose-range of 0.5–5.0 mg/kg. Kynurenine and 3-hydroxykynurenine were highly active. Low doses caused marked potentiation of the twitch response to both 5-HT and 5-HTP with increased toxicity of 5-HT. High doses caused antagonism of both responses. Xanthurenic acid was inactive over the same dose range. The effects of kynurenine could not be duplicated in the guinea-pig ileum. The relevance of these results to the involvement of kynurenine pathway metabolites in depressive illness is discussed.     

Simultaneous determination of femtomole quantities of 5-hydroxytryptophan, serotonin and 5-hydroxyindoleacetic acid in brain using HPLC with electrochemical detection

A simple rapid method for the determination of 5-hydroxytryptophan, serotonin (5-hydroxytryptamine), and 5-hydroxyindoleacetic acid in brain is presented. Brain proteins are precipitated with Zn(OH)2. The indoles in the supernatant are separated by HPLC in less than than 8 min on a reverse phase column and detected electrochemically. As little as 38 fmol of hydroxyindole compound can be detected and quantitated. Because the method is rapid and uncomplicated many samples can be processed in a day.     

Effects of para-chlorophenylalanine and 5-hydroxytryptophan on alcohol intake in the rat

Para-chlorophenylalanine, the tryptophan hydroxylase inhibitor that depletes serotonin selectively, increased alcohol intake in rats. 5-Hydroxytryptophan, the serotonin percursor, reduced alcohol intake. These findings suggest that alcohol preference in the rat may be related to the brain tryptaminirgic system.     

Effects of para-chlorophenylalanine and 5-hydroxytryptophan on mouse killing behavior in killer rats.

The effects of para-chlorophenylalanine (PCPA) on mouse killing behavior were examined in natural killer rats. Forty-eight hr after injection, this serotonin synthesis inhibitor, at relatively low doses of 75 and 150 mg/kg, facilitated mouse killing, as indicated by a decrease in latency to attack the mouse. This effect was revealed in a test of satiation, in which five successive mice were presented to the rat, and also in a novel cage situation. Other than the shorter latencies to attack and kill mice, the killing response was similar in topography to the natural kill. The increase in killing after PCPA injection was associated with a reliable reduction in brain serotonin and in 5-hydroxyindoleacetic acid, and the time courses of the behavioral and biochemical changes were generally similar. In contrast to PCPA, injection of the serotonin precursor 5-hydroxytryptophan (5-HTP, 100 mg/kg) reliably lengthened attack and kill latencies in killer rats. In rats pretreated with PCPA, 5-HTP not only reversed this drug's facilitation of killing, but completely blocked killing in 67% of the rats tested. These results strengthen the hypothesis that brain serotonergic neurons are involved in the inhibition of mouse killing.     

Serotonergic influences on food intake: effect of 5-hydroxytryptophan on parameters of feeding behaviour in deprived and free-feeding rats.

Three experiments were carried out to examine the effect of the serotonin precursor, 5-hydroxytryptophan, upon food intake and the micro-structure of eating in deprived rats, and on the pattern of meal taking in free-feeding animals. The study also investigated the capacity of a peripheral decarboxylase inhibitor (MK-486) to antagonise the effect of 5-HTP in order to identify a central or peripheral mode of action. In deprived rats 5-HTP brought about a dose related inhibition of food intake which was midly antagonised by MK-486. A detailed analysis of the behavioural changes occurring during eating showed that the inhibition of food intake by 5-HTP was reflected in a reduced number of eating bouts and a slower rate of eating. MK-486 did not antagonise the effect of 5-HTP on eating rate. In free-feeding rats whose food comsumption was continuously monitored for 24-hr periods, 5-HTP gave rise to reduction in meal size and a slowing of the intra-meal rate of eating. These findings are in keeping with the effects of other serotonergic manipulations on the patterns of feeding in rats.     

Action of two hypothalamic factors (TRH, MIF) and of angiotensin II on the behavioral effects of L-DOPA and 5-hydroxytryptophan in mice

Melanocyte stimulating hormone release-inhibiting factor (MIF), thyrotropin releasing hormone (TRH) and angiotensin II, injected i.p. to mice, potentiate the behavioral effect of L-DOPA and 5-hydroxytryptophan.     

Development of tolerance to the wet-dog shake behaviour but not the increase in seizure threshold induced by l-5-hydroxytryptophan during continued treatment in rats

The time course of different pharmacological effects of l-5-hydroxytryptophan (5-HTP) during continued treatment was studied in rats. 5-HTP was administered three times daily at 100 mg/kg IP in combination with the peripheral decarboxylase inhibitor carbidopa (10 mg/kg) for 14 days. 5-HTP induced a pronounced increase of the threshold for maximal electroconvulsions, decreased body temperature and body weight and induced characteristic wet-dog shake behaviour. Whereas the anticonvulsant effect increased during the 14 days of treatment, tolerance developed to the excitatory and, less rapidly, to the hypothermic and anorexigenic effects of 5-HTP. Biochemical determinations showed marked increases in 5-HTP and its metabolites, 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid, in both plasma and brain throughout the period of treatment. The mechanisms underlying the different time-courses of the functional effects of 5-HTP during continued treatment are not clear, but effects on catecholaminergic systems as well as regional differences in 5-HT increases in the brain might be involved.     

Reduction of the antinociceptive effect of 5-hydroxytryptophan in morphine tolerant rats

The effect of 5-hydroxytryptophan on pain threshold was studied in rats both tolerant and nontolerant to the analgesic action of morphine as assessed using a procedure of electrical stimulation. The compound elevated pain threshold and exhibited an additive effect with morphine analgesia in nontolerant rats. A marked reduction of the antinociceptive action of the serotonin precursor as well as absence of the additive effect with morphine was observed in rats tolerant to the analgesic. These results are discussed in terms of the possible mechanism of action of serotonin on morphine effects.     

Effects of inhibitors of 5-hydroxytryptamine uptake on plasma glucose and their interaction with 5-hydroxytryptophan in producing hypoglycaemia in mice

The effects of various inhibitors of 5-HT uptake on plasma glucose have been studied in normal and monoamine oxidase inhibitor pretreated mice. Additionally their interaction with 5-hydroxytryptophan (5-HTP) in producing hypoglycaemia was studied. Clomipramine, fenfluramine, fluoxetine, ORG 6582 (dl-8-chloro-11-anti-amino-benzo-(b)-bicyclo[3.3.1]nona-3, 6α(10α)-diene hydrochloride), ORG 6997 (dl-4-exo-amino-8-chloro-benzo-(b)-bicyclo[3.3.1]nona-2-6α(10α)-diene hydrochloride), MK 212 and mazindol did not modify the plasma glucose in normal mice but produced hypoglycaemia in mice pretreated with either nialamide or pargyline. Dexamphetamine did not influence plasma glucose in either normal or monoamine oxidase inhibitor pretreated mice. Each of the above drugs except ORG 6997 but including dexamphetamine augmented the hypoglycaemic effect of 5-HTP in normal mice. These responses did not appear to be mediated by insulin since none of the drugs increased the plasma immunoreactive insulin concentration or augmented the hyperinsulinaemic effect of 5-HTP. Moreover, fenfluramine, fluoxetine and ORG 6582 did not augment the hypoglycaemic action of injected insulin although such an augmentation was produced by mazindol.     

Factors modifying the head-twitch response to 5-hydroxytryptophan

Factors modifying the head twitch response to 5-hydroxy d,l-tryptophan (5-HTP) have been investigated in the mouse. Stage of oestrous cycle and time of day had no effect. Local anaesthesia of the pinna region virtually abolished the response. Painting the pinnae with xylene increased the response and also increased the spontaneous head twitch rate. A concurrent variable frequency sound reduced the head twitch rate as did isolation. These results suggest that sensory input from the pinna is a necessary precondition for the head-twitch response to 5-HTP and demonstrate that the rate of twitching is modified by environmental conditions. The suggestion is made that 5-HTP might allow the perception of previously subliminal stimuli from the pinna region.The authors wish to thank Mr. D. Newton for his able technical assistance during the latter part of this work.