Effect of acute tryptophan depletion on noradrenaline and dopamine in the rat brain

In human subjects, the acute tryptophan (TRP) depletion (ATD) paradigm has been shown to have effects on mood and cognition. It is assumed that these effects are mediated through the serotonin system. In this study, we have examined the effects of ATD on the central concentrations of the monoamine transmitters, noradrenaline (NA) and dopamine (DA) as well as on serotonin (5-HT). Effects on NA and DA could also affect mood and cognition. Following oral administration of TRP-containing (TRP+) and TRP-free (TRP-) amino acid mixtures, neurotransmitter concentrations and free plasma TRP concentrations were determined by High Performance Liquid Chromatography (HPLC) with electrochemical detection. Free plasma TRP was significantly and substantially reduced (79%) in rats given a TRP- amino acid mixture when compared with those given a TRP+ mixture. ATD also significantly decreased 5-HT and 5-hydroxyindolacetic acid in the frontal cortex, remaining cortex and hippocampus, but did not significantly reduce these in the striatum. Furthermore, ATD did not significantly alter the concentration of NA and DA in any brain region examined. This study demonstrates that the administration of a TRP- amino acid mixture in rats can reduce free plasma TRP to levels comparable to those reported in human studies. These results indicate that behavioural and cognitive changes produced by ATD in preclinical or clinical studies are likely to be due to specific effects on the serotonergic system.     

Fos immunocytochemical studies on the neuroanatomical sites of action of acute tyrosine depletion in the rat brain

Rationale Acute depletion of brain tyrosine using a tyrosine-free amino acid mixture offers a nutritional approach to reduce central catecholamine function. Recent preclinical data suggest that tyrosine-free amino acid mixtures may have region-specific effects through targeting dopamine neurones.Objectives Here we used fos immunocytochemistry to examine the neuroanatomical sites of action of a tyrosine-free amino acid mixture administered either alone or combined with amphetamine.Methods Rats (male, Sprague Dawley, 240–260 g) were administered (IP) either a tyrosine-free amino acid mixture (1 g/kg), or the same mixture supplemented with tyrosine and phenylalanine (1 g/kg). Mixtures were injected twice (1 h apart) followed 1 h later by amphetamine (2 mg/kg SC). Two hours later, cardiac perfusion was performed and brains were processed for fos immunocytochemistry. Fos positive cells were counted using computer imaging software.Results The tyrosine-free amino acid mixture alone did not alter fos expression in ten regions of the rat forebrain compared to saline controls. However, the mixture reduced the increase in fos expression evoked by amphetamine. This effect was region-specific and was greatest in caudate putamen, nucleus accumbens, bed nucleus stria terminalis and lateral habenula, and lacking in other areas including cingulate and insular cortices, lateral septum and central amygdaloid nucleus. Moreover, in most regions the effect of the tyrosine-free mixture was less after tyrosine and phenylalanine supplementation.Conclusions In summary, a tyrosine-free amino acid mixture reduced amphetamine-induced fos expression but this effect was region-specific and included dopamine-rich regions. These data further support the idea that tyrosine depletion strategies have potential as treatments for mania and other hyperdopaminergic states.     

Effect of probenecid on rat brain phenolsulfotransferase activity using dopamine as substrate

Dopamine sulfate (DAS) is formed by the action of phenolsulfotransferase (PST) on dopamine (DA). Since probenecid is often used to investigate the transport of monoamine acidic metabolites such as DAS from the brain, we investigated the effect of probenecid on rat brain PST activity utilizing DA as substrate. In the presence of 30 or 90 microM DA, probenecid had either no effect or a dose-related inhibitory effect on PST activity. PST activity increased at low probenecid concentrations, but decreased at high probenecid concentrations when 360 microM DA was utilized. Several conditions were found where PST activity was not affected by probenecid.     

Effect of dopamine on tyrosine hydroxylase in cultured rat adrenal medulla

Explants of rat adrenal medulla were cultured in defined medium for up to 22 hr. Addition of dopamine to the medium led to a diminution in the activity of tyrosine hydroxylase (tyrosine 3-monooxygenase; EC 1.14.16.2) in the tissue. The enzyme activity was inversely proportional to the concentration of dopamine in the culture medium. The extent of loss of tyrosine hydroxylase, as measured by immunochemical titration, corresponded to the degree of loss in enzyme activity under the same conditions. The decreased amount of enzyme protein was due to a decrease in the rate of synthesis of tyrosine hydroxylase. However, this effect was not specific in that the relative rate of tyrosine hydroxylase synthesis was not decreased. Metabolites of dopamine when added to the medium did not affect tyrosine hydroxylase activity. Two other adrenal medullary enzymes, monoamine oxidase (EC 1.4.3.4) and acid phosphatase (EC 3.1.3.2), were not affected by addition of dopamine to the medium. The results indicate that elevated cytoplasmic levels of dopamine decrease the concentration of tyrosine hydroxylase by inhibiting protein synthesis.     

Effect of desipramine and amphetamine on noradrenergic neurotransmission: electrophysiological studies in the rat brain.

The present electrophysiological experiments were undertaken to investigate the effect of desipramine and d-amphetamine on noradrenergic neurotransmission in the rat central nervous system. The effectiveness of electrical stimulation of the locus coeruleus and of microiontophoretic application of norepinephrine (NE) in suppressing the firing activity of CA3 pyramidal neurons was studied in the dorsal hippocampus. Desipramine (0.5 and 5 mg/kg i.v.) and d-amphetamine (0.25 and 5 mg/kg i.v.) decreased the effectiveness of locus coeruleus stimulation and prolonged the effect of microiontophoretically applied NE on the same pyramidal neurons. Subsequent i.v. administration of idazoxan, an alpha 2-adrenoceptor antagonist, reversed the effects of desipramine and d-amphetamine on the effectiveness of locus coeruleus stimulation and decreased that of microiontophoretically applied NE. In addition, idazoxan prevented the effect of subsequent administration of desipramine (5 mg/kg i.v.) on the effectiveness of locus coeruleus stimulation. High doses of d-amphetamine (5 and 10 mg/kg i.v.) decreased the firing activity of hippocampus pyramidal neurons by 70 and 98%, respectively, whereas low doses of desipramine (0.5 mg/kg i.v.) or of d-amphetamine (0.25 mg/kg i.v.) were without effect. After lesioning of NE projections with 6-hydroxydopamine, the effect of the 5 mg/kg dose of d-amphetamine on the firing activity of hippocampus pyramidal neurons was markedly reduced, whereas the cumulative 10 mg/kg dose of d-amphetamine completely suppressed, as in control rats, the firing activity of these neurons. This effect of d-amphetamine in 6-hydroxydopamine-pretreated rats was reversed by the administration of the 5-HT1A receptor antagonist BMY 7378. These data provide evidence that acute administration of desipramine and d-amphetamine decreases the effectiveness of locus coeruleus stimulation by increasing the activation of terminal alpha 2-adrenoceptor autoreceptors. In addition, acute administration of high doses of d-amphetamine decreases the firing rate of hippocampus pyramidal neurons by increasing NE and serotonin release.     

多巴胺耗竭对大鼠纹状体缺血DARPP-32蛋白的影响(英文)

目的:研究多巴胺(DA)耗竭对纹状体缺血后DARPP-32蛋白磷酸化水平、细胞内分布和mRNA表达的影响,探讨DA在缺血性纹状体损伤中的作用机制。方法:采用6-羟基多巴胺损毁大鼠黑质和四血管阻断全脑缺血模型,用放射自显影、免疫组化和原位杂交的方法观察DARPP-32的含量、磷酸化水平及mRNA表达情况的变化。结果:缺血后体外测定DARPP-32[~(32)P]的掺入量降低。黑质损毁后再缺血,损毁侧纹状体DARPP-32[λ-~(32)P]掺入量有明显升高,且DARPP-32免疫反应阳性神经元及mRNA表达均明显强于对照侧。结论:纹状体缺血时DARPP-32体内磷酸化增加,而耗竭DA可抑制这种作用。黑质损毁可升高纹状体缺血时DARPP-32免疫反应性及DARPP-32mRNA的表达水平。     

Effect of electroshock on dopamine metabolism in rat brain

Summary A single electroshock stimulation (EST) by means of a conventional clinical EST apparatus was administered to 40 rats. Ten minutes after the start of general convulsions the animals were sacrificed. Corpus striatum was analyzed for dopamine (DA) and homovanillic acid (HVA). A statistically not significant increase of DA and a highly significant increase of HVA was noted in the EST group compared to the control animals. The data indicate an acceleration of the DA synthesis induced by EST. The results are discussed in relation to the action of antidepressive drugs on the monoaminergic neurons and a supposed biochemical correlate of endogenous depression.     

Effect of p-nitromethylamphetamine on biogenic amines and their amino-acid precursors in rat brain

1. Low doses of p-nitromethylamphetamine caused small increases in the concentrations of brain noradrenaline and dopamine in the rat; a dose of 60 mg/kg however, caused a decrease in the concentrations of both amines. p-Nitromethylamphetamine caused behavioural hyperexcitability only at doses which approximated to half the LD50 (68 mg/kg).2. p-Nitromethylamphetamine potentiated the action of 4,alpha-dimethyl-m-tyramine in depleting brain noradrenaline. This suggests that it may affect brain noradrenaline concentrations by utilizing a reserpine resistant uptake mechanism.3. p-Nitromethylamphetamine decreased the concentration of brain 5-hydroxytryptamine.4. Changes in the blood and brain concentrations of tyrosine and gamma-amino-n-butyric acid concentration in the brain could not be correlated with the changes in brain amines. However, a rise in the concentration of brain tryptophan appeared to be correlated with the fall in brain 5-hydroxytryptamine.     

Brain tyrosine depletion attenuates haloperidol-induced striatal dopamine release in vivo and augments haloperidol-induced catalepsy in the rat

Rationale There are conflicting reports as to whether alterations in tyrosine levels affect functional indices of striatal dopamine (DA) transmission. Since the DA antagonist haloperidol (HAL) increases striatal DA release and induces catalepsy through its actions on striatal DA systems, it provides a useful paradigm to assess both neurochemical and behavioral effects of lowering brain tyrosine levels.Objectives To determine how brain tyrosine depletion affects HAL-induced catalepsy and striatal DA release in awake, freely moving rats.Methods In male rats, a control or tyrosine- and phenylalanine-free neutral amino acid solution NAA(–) (IP) was administered 30–60 min prior to HAL (IP). In one cohort, striatal microdialysate was assayed for DA levels. In a parallel cohort, catalepsy was measured using the bar test.Results NAA (–) reduced striatal tyrosine levels by 60%. The latter did not affect basal striatal DA release, but consistently delayed the attainment of maximal HAL-induced (0.19 mg/kg and 0.25 mg/kg SC) striatal DA release; the latter was abolished by administration of tyrosine. NAA(–) also potentiated HAL-induced catalepsy.Conclusions Acute brain tyrosine depletion attenuates HAL-induced striatal DA release and potentiates haloperidol-induced catalepsy. Both effects can be reversed by administration of tyrosine. Overall, the data indicate that tyrosine depletion affects both neurochemical and behavioral indices of striatal DA release.     

Impacts of stress and sex hormones on dopamine neurotransmission in the adolescent brain

Rationale

Adolescence is a developmental period of complex neurobiological change and heightened vulnerability to psychiatric illness. As a result, understanding factors such as sex and stress hormones which drive brain changes in adolescence, and how these factors may influence key neurotransmitter systems implicated in psychiatric illness, is paramount.

Objectives

In this review, we outline the impact of sex and stress hormones at adolescence on dopamine neurotransmission, a signaling pathway which is critical to healthy brain function and has been implicated in psychiatric illness. We review normative developmental changes in dopamine, sex hormone, and stress hormone signaling during adolescence and throughout postnatal life, then highlight the interaction of sex and stress hormones and review their impacts on dopamine neurotransmission in the adolescent brain.

Results and conclusions

Adolescence is a time of increased responsiveness to sex and stress hormones, during which the maturing dopaminergic neural circuitry is profoundly influenced by these factors. Testosterone, estrogen, and glucocorticoids interact with each other and have distinct, brain region-specific impacts on dopamine neurotransmission in the adolescent brain, shaping brain maturation and cognitive function in adolescence and adulthood. Some effects of stress/sex hormones on cortical and subcortical dopamine parameters bear similarities with dopaminergic abnormalities seen in schizophrenia, suggesting a possible role for sex/stress hormones at adolescence in influencing risk for psychiatric illness via modulation of dopamine neurotransmission. Stress and sex hormones may prove useful targets in future strategies for modifying risk for psychiatric illness.     

Effect of certain GABA-ergic substances on dopamine metabolism in the rat brain

Effect of the GABA-ergic drugs, sodium hydroxybutyrate, n-dipropylacetate (n-DPA) and piracetam, has been studied on the level of homovanillic acid (HVA) and activity of GABA-transaminase in the striate body of the rat brain. It has been established that piracetam in doses of 500 and 400 mg/kg, n-DPA in a dose of 200 mg/kg and sodium hydroxybutyrate in a dose of 500 mg/kg do not affect the HVA level or activity of GABA-transaminase. The data obtained are likely to support a suggestion about a possible relationship between the GABA-ergic and dopaminergic mediator system.     

Effects on mood of acute phenylalanine/tyrosine depletion in healthy women.

Catecholamines have been implicated in the etiology and pathophysiology of mood and anxiety disorders. In the present study, we investigated the effects of experimentally reducing catecholamine neurotransmission by means of acute phenylalanine/tyrosine depletion (APTD). Healthy female volunteers ingested: (1) a nutritionally balanced amino acid (AA) mixture (n = 14); (2) a mixture deficient in the serotonin precursor, tryptophan (n = 15); or (3) one deficient in the catecholamine precursors, phenylalanine and tyrosine (n = 12). Mood was measured at three times: at baseline and both immediately before and after an aversive psychological challenge (public speaking and mental arithmetic) conducted 5 hours after AA mixture ingestion. Acute tryptophan depletion (ATD) lowered mood and energy and increased irritability scores. These effects were statistically significant only after the psychological challenge. The effect of APTD on mood was similar to that of ATD. APTD did not attenuate the anxiety caused by the psychological challenge. These findings suggest that, in healthy women, reduced serotonin and/or catecholamine neurotransmission increases vulnerability to lowered mood, especially following exposure to aversive psychological events.     

人参银杏合剂对抗大鼠脑急性低氧损伤的作用

目的 :观察人参银杏合剂对模拟高原缺氧脑损伤的保护作用并探讨其机理。方法 :将成年SD大鼠随机分为常氧对照组、急性低氧组、人参银杏合剂加低氧组 ,分别观察各组大鼠海马CA1区锥体细胞层神经元形态的变化、脑组织含水量、Na+ K+ ATP酶活性、超氧化物歧化酶 (SOD)活性和丙二醛(MDA)含量。结果 :(1)缺氧 2 4h复氧 72h后 ,海马CA1区锥体层神经元形态发生明显变化 ,细胞数目减少 ,排列紊乱 ,突起消失 ,而人参银杏合剂加低氧组细胞损伤不明显 ,形态与对照组相似。 (2 )与对照组相比 ,急性低氧组的脑含水量显著增高 (P <0 .0 1) ,人参银杏合剂加低氧组脑含水量较急性低氧组明显降低 (P <0 .0 5 )。 (3)急性低氧组脑组织Na+ K+ ATP酶活性与对照组相比明显降低 (P <0 .0 5 ) ,人参银杏合剂加低氧组脑组织Na+ K+ ATP酶活性较低氧组明显升高 (P <0 .0 5 )。 (4)急性低氧组脑组织SOD活性与对照组比较有所下降 ,但无统计学意义 (P >0 .0 5 ) ,人参银杏合剂加低氧组SOD活性较急性低氧组明显上升 (P <0 .0 5 )。 (5 )急性低氧组脑组织MDA含量明显高于对照组 (P <0 .0 1) ,人参银杏合剂加低氧组脑MDA含量较急性对照组显著降低 (P <0 .0 1)。结论 :人参银杏合剂对高原缺氧脑损伤具有保护作用 ,其机理与其抗氧自     

Effect of methamphetamine self-administration on tyrosine hydroxylase and dopamine transporter levels in mesolimbic and nigrostriatal dopamine pathways of the rat

Rationale and objectives Many studies have examined the effect of experimenter-delivered methamphetamine on the mesolimbic and nigrostriatal dopamine pathways. In contrast, little is known about the effect of methamphetamine self-administration on these neuronal pathways. We studied the effect of methamphetamine self-administration on two key regulators of dopamine transmission, tyrosine hydroxylase (TH), and dopamine transporter (DAT), in components of the mesolimbic and nigrostriatal dopamine pathways.Methods Rats self-administered methamphetamine (0.1 mg/kg per infusion, fixed-ratio-1 reinforcement schedule) or saline (control condition) for 9 h/day over 10 days. The brains of these rats were collected after 1 or 30 days of forced abstinence and the expression levels of TH and DAT were assayed by in situ, hybridization and western blot.Results TH mRNA and protein levels were increased in the ventral tegmental area (VTA, the cell body region of the mesolimbic dopamine system) and the substantia nigra pars compacta (SNC, the cell body region of the nigrostriatal dopamine system) after 1 day, but not 30 days, of forced abstinence from methamphetamine. In contrast, methamphetamine self-administration had no effect on TH protein levels in dopaminergic terminals located in the nucleus accumbens and caudate–putamen. In addition, methamphetamine self-administration had no effect on DAT mRNA levels in the VTA.Conclusions Results suggest that extended daily access to self-administered methamphetamine results in a transient, short-lasting effect on mesolimbic and nigrostriatal dopamine neurons of the rat brain.     

Lack of effect of acute dopamine precursor depletion in nicotine-dependent smokers.

RATIONALE: Nicotine increases dopamine (DA) release but its role in nicotine dependence remains unclear. OBJECTIVE: To assess the role of DA in nicotine craving and self-administration using acute phenylalanine/tyrosine depletion (APTD). METHODS: Fifteen nicotine-dependent men ingested, a minimum of 3days apart, a nutritionally balanced amino acid (AA) mixture (BAL), a mixture deficient in the catecholamine precursors, phenylalanine and tyrosine, and APTD followed by the immediate DA precursor, L-DOPA. Beginning 3h after ingestion of the AA mixture, subjects smoked 4 cigarettes. Craving, mood, and other aspects of subjective state were assessed with self-report scales. Smoking puff topography was measured with a computerized flowmeter. RESULTS: APTD did not change smoking puff topography, cigarette craving, or subjective effects of smoking. CONCLUSIONS: The findings suggest that in nicotine-dependent smokers craving for cigarettes, subjective effects of nicotine, and the self-administration of freely available cigarettes are largely unrelated to acute changes in DA neurotransmission.     

Effects of the co-administration of mirtazapine and paroxetine on serotonergic neurotransmission in the rat brain.

The alpha(2)-adrenoreceptor antagonist mirtazapine, which is also a 5-HT(2), 5-HT(3) and H(1) receptors antagonist and the selective serotonin (5-HT) reuptake inhibitor paroxetine are effective antidepressant drugs which enhance 5-HT neurotransmission via different mechanisms. The present studies were undertaken to determine whether the mirtazapine-paroxetine combination could induce an earlier and/or a greater effect on the 5-HT system than either drug alone. Using in vivo electrophysiological paradigms, the firing activity of dorsal raphe 5-HT neurons was decreased by 70% in rats treated with paroxetine (10 mg/kg/day, s.c.) for 2 days and was back to normal after 21 days. In contrast, a 2-day treatment with mirtazapine (5 mg/kg/day, s.c.) did not alter the firing of 5-HT neurons whereas it was increased by 60% after 21 days of treatment. A low dose of mirtazapine (5 mg/kg/day, s.c.x2 days) failed to offset the decremental effect of paroxetine on the 5-HT neuron firing activity, but a higher dose (10 mg/kg/day, s.c.x2 days) did attenuate the decremental effect of paroxetine. In the dorsal hippocampus, neither mirtazapine (5 mg/kg/day, s.c.) nor a paroxetine (10 mg/kg/day, s.c.) treatment altered the responsiveness of 5-HT(1A) receptors to microiontophoretically-applied 5-HT. Both in controls and in rats treated for 2 days with paroxetine alone, the administration of the 5-HT(1A) antagonist WAY 100635 (25-100 microg/kg, i.v.) did not change the firing activity of dorsal hippocampus CA(3) pyramidal neurons. However, WAY 100635 increased significantly the firing activity of these neurons in rats treated with mirtazapine alone but to a greater extent with both mirtazapine and paroxetine for 2 days. After 21 days of treatment, WAY 100635 increased to a greater degree the firing rate of CA(3) pyramidal neurons in rats which received the combination over rats given either drug alone. It is concluded that the mirtazapine-paroxetine combination shortened the delay in enhancing the tonic activation of postsynaptic 5-HT(1A) receptors and produced a greater activation of the postsynaptic 5-HT(1A) receptors than either drug given alone. The present results suggested that mirtazapine may have a faster onset of action than a SSRI, and that the co-administration of mirtazapine and paroxetine may accelerate the antidepressant response and as well as being more effective than either drug alone.