Daily variations in in vivo tryptophan hydroxylation and in the contents of serotonin and 5-hydroxyindoleacetic acid in discrete brain areas of the rat

Summary The in vivo rate of brain tryptophan hydroxylation was determined through 5-hydroxytryptophan accumulation (5-HTPacc) following the administration of NSD 1015, a L-aromatic amino-acid decarboxylase inhibitor. This measurement was performed every 4 h throughout a 24 h hour period in 10 discrete brain areas of rats maintained on a regular 12 h/12 h light-dark cycle. The concentrations of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were also determined in untreated rats. Daily variations in 5-HTPacc were found in all the areas studied, the 5-HTPacc being higher during the dark period in most structures. These results strongly suggest that tryptophan hydroxylation is involved in the control of the 5-HT biosynthesis circadian rhythm. However, various patterns of 5-HT and 5-HIAA daily variations were observed, suggesting that the circadian factors affecting serotonin metabolism can be different among brain areas.     

Behavioral mechanisms for the anorectic action of the serotonin (5-HT) uptake inhibitor sertraline in rats: Comparison with directly acting 5-HT agonists

The 5-HT uptake inhibitor, sertraline (5-40 mumol/kg, IP) reduced the volume of milk consumed by food-deprived rats during a 30-min test (ID50 = 12 mumol/kg). Observations using a time-sampling method revealed that sertraline shortened meal duration (ID50 = 14 mumol/kg) by decreasing feeding and increasing resting without altering nonfeeding activity or the overall sequence of behavior that characterizes normal satiety. In separate experiments, analysis of videotapes demonstrated that sertraline (10 mumol/kg) decreased not only the time that rats fed but also their actual rate of intake. In comparison, doses of the direct 5-HT agonists, mCPP (1-[3-chlorophenyl]piperazine), RU 24969 (5-methoxy-3-[1,2,3,6-tetrahydropyridin-4-yl]-1H-indole), and DOI (1-[2,5-dimethoxy-4-iodophenyl]-2-amino-propane) that produced similar anorectic effects altered either feeding time or rate but not both. DOI also disrupted the continuity of feeding and the 5-HT agonist, 8-OH-DPAT (8-hydroxy-di-N-propylamino tetralin) produced marked stereotypy at anorectic doses. Together, these results imply that stimulating a number of different serotonergic mechanisms can reduce food intake in rats. Sertraline appears to accelerate the onset of normal satiety, presumably by enhancing physiological actions of endogenous 5-HT.     

Effect of sertraline treatment on benzodiazepine receptors in the rat brain

Summary In this paper we describe the modification of benzodiazepine (BDZ) binding sites in the rat brain after different times of treatment with the 5-hydroxytryptamine-(5HT) uptake blocker sertraline. We investigated the effect of 8, 15 and 30 days sertraline treatment (10 mg/kg/day, i.p.) on³H-flunitrazepam binding sites. In order to describe the anatomical site of action of the drug, the experiment has been carried out by means of quantitative receptor autoradiography. After 8 days of sertraline treatment, an increase of BDZ receptor density is found in the olfactory tubercle. This effect is reversed at 15 and 30 days. At 15 days of treatment, an increase is found in the anterior cingulate cortex. This increase is still present after 30 days of treatment. At 30 days of treatment, we also found an increase of BDZ receptor density in the frontoparietal motor cortex and in the septal nuclei. The Scatchard plots obtained from the saturation experiments indicate that this increase of the receptor density is due to an increase of both the receptor number and affinity. All the other investigated areas are unaffected by the sertraline treatment. The possible neurochemical basis of these BDZ receptor regulation by sertraline and its influence in the therapeutical profile are discussed.     

Effects of biogenic aldehydes and aldehyde dehydrogenase inhibitors on rat brain tryptophan hydroxylase activity in vitro

The effect of indole-3-acetaldehyde, 5-hydroxyindole-3-acetaldehyde, disulfiram, diethyldithiocarbamate, coprine, and 1-amino-cyclopropanol on tryptophan hydroxylase activity was studied in vitro using high performance liquid chromatography with electro-chemical detection. With the analytical method developed, 5-hydroxytryptophan, serotonin, and 5-hydroxyindole-3-acetic acid could be measured simultaneously. Indole-3-acetaldehyde (12-1200 microM) was found to cause a 6-33% inhibition of the enzyme. Dependent upon the nature of the sulfhydryl- or reducing-agent (dithiotreitol, glutathione, or ascorbate) present in the incubates, the degree of inhibition by disulfiram varied, probably due to the formation of various mixed disulfides. Also the presence of diethyldithiocarbamate (160-1600 microM) was found to inhibit tryptophan hydroxylase (28-91%), while 5-hydroxyindole-3-acetaldehyde, coprine, or 1-aminocyclopropanol appeared to have no effect on the enzyme activity.     

The effects of systemic glucose concentration on brain metabolism following repeated brain ischemia

Since systemic glucose concentration is an important determinant of ischemic brain metabolism in neonates, we sought to determine if the systemic glucose concentration influences brain metabolic alterations following repeated partial ischemia. A group of hyperglycemic pigles (n = 12) were compared to a group of modestly hypoglycemic piglets (n = 12) using in vivo²H and ³¹P magnetic resonance spectroscopy to simultaneously measure cerebral blood flow and phosphorylated metabolites before, during and 30 min after two 10-min episodes of ischemia (i.e. Recovery 1 and 2). For both groups, β-ATP levels at Recovery 1 and 2 were lower than Control (91 ± 11and83 ± 15% of Control, respectively for both groups combined, P = 0.002 vs Control). Inorganic phosphorus was elevated in hyperglycemic piglets at Recovery 1 and 2 (117 ± 15and118 ± 10% of Control). In contrast, in modestly hypoglycemic piglets inorganic phosphorus progressively rose from Recovery 1 (131 ± 24% of Control) to Recovery 2 (149 ± 37% of Control), and differed from the hyperglycemic group (P = 0.02). These changes did not correlate with post-ischemic cerebral blood flow, cerebral O₂ delivery or cerebral glucose delivery. In both groups phosphocreatine and intracellular pH returned to Control values during Recovery 1 and 2. The progressive increase in inorganic phosphorus post-ischemia in hypoglycemic piglets suggests that modest hypoglycemia during and following repeated partial ischemia adversely affects immediate brain metabolic recovery.     

Effect of chronic administration of duloxetine on serotonin and norepinephrine transporter binding sites in rat brain.

BACKGROUND: Chronic treatment of rats with certain selective serotonin or norepinephrine reuptake inhibitors produces significant decreases, respectively, in serotonin and norepinephrine transporter binding sites in brain. Duloxetine may be a dual serotonin/norepinephrine reuptake inhibitor, as it is only a slightly more potent inhibitor of serotonin than norepinephrine uptake in vitro. Consequently, we hypothesized that chronic duloxetine treatment, at doses producing serum levels within its therapeutic range, would affect both monoamine transporters dose-dependently, with a higher dose causing greater reductions of binding sites for both transporters. METHODS: Rats were treated with either 4 or 8 mg/kg/d of duloxetine, paroxetine, desipramine, or vehicle via subcutaneous osmotic minipumps for 21 days. Binding sites for serotonin and norepinephrine transporters were measured in amygdala and hippocampus using quantitative autoradiography. RESULTS: Both doses of duloxetine and paroxetine produced equivalent and significant decreases in [3H] cyanoimipramine binding to serotonin transporters, but only desipramine treatment significantly reduced [3H] nisoxetine binding to norepinephrine transporters. CONCLUSIONS: At doses producing rat serum concentrations in the range achieved in patients at recommended daily doses of the drug, duloxetine behaves in vivo more as a selective serotonin reuptake inhibitor than a dual reuptake inhibitor in its capacity to selectively reduce serotonin transporter density.     

Alterations of noradrenaline and serotonin uptake and metabolism in chronic cobalt-induced epilepsy in the rat

The high affinity uptake of noradrenaline and serotonin, and the concentrations of these monoamines and their metabolites, have been measured in the perifocal cortical area at various stages of the evolution of cobalt-induced epilepsy in the rat. Noradrenaline uptake was maximally reduced at days 8-10 after cortical cobalt application, a time corresponding to the onset of epileptic discharges; it remained diminished during the spiking activity period of the focus (days 14-20) and was back to normal values at day 40, at which time the epileptic syndrome had disappeared. Serotonin uptake was also diminished at days 8-10 but to a lesser extent than was noradrenaline uptake. In the homotopic cerebral cortex contralateral to cobalt application, noradrenaline uptake was reduced at day 10 only and to a lesser extent than in the perifocal area, whereas serotonin uptake was unaffected. Kinetic analysis of the cobalt-induced monoamine uptake alterations at day 10 revealed a diminution of the maximal velocity with no change in the Km. Noradrenaline and dihydroxyphenylethyleneglycol concentrations in the perifocal area were also maximally reduced at days 8-10 but were unaffected at day 2 and day 40 post cobalt application. A reduction of serotonin levels in the perifocal area was observed only at days 8-10 while 5-hydroxyindoleacetic acid remained unaffected throughout the time period studied. The levels of these monoamines and their metabolites were unchanged in the homotopic contralateral cortex 2-40 days after cobalt application. These results indicate that cortical cobalt application induces alterations of the biochemical indices of the density of noradrenaline-containing terminals that closely parallel the evolution of the epileptic syndrome. These data further emphasize the important role of the cortical noradrenergic system in cobalt-induced epilepsy.     

抑郁模型大鼠脑内色氨酸及5-羟色胺的改变

目的研究慢性轻度不可预见性应激抑郁模型大鼠脑内色氨酸(TP)及5-羟色胺(5-HT)含量的变化,探讨抑郁障碍可能发病机制。方法将大鼠随机分为抑郁模型组(10只,以下简称抑郁组)和对照组(10只),对抑郁组大鼠进行连续21d的慢性应激。进行行为学观察;用高效液相色谱-荧光检测法测定大鼠脑内海马、前额叶、下丘脑和纹状体4个部位的5-HT及TP含量。结果(1)抑郁组大鼠慢性应激后的自主活动为(35±9)分,明显低于对照组的(73±9)分,差异有统计学意义(P<0.001)。(2)抑郁组大鼠海马、前额叶5-HT含量分别为(0.34±0.08)ng/mg组织和(0.55±0.06)ng/mg组织,均低于对照组[分别为(0.46±0.06)ng/mg组织和(0.66±0.09)ng/mg组织],差异均有统计学意义(P均<0.01);TP含量分别为(3.76±0.34)ng/mg组织和(4.08±0.51)ng/mg组织,均高于对照组[分别为(3.23±0.38)ng/mg组织和(3.49±0.44)ng/mg组织],差异均有统计学意义(P均<0.05)。两组大鼠下丘脑和纹状体5-HT及TP含量的差异均无统计学意义(P均>0.05)。结论脑内5-HT的合成功能降低是抑郁障碍的可能发病机制之一。     

Sertraline induced parkinsonim. A case report and an in-vivo study of the effect of sertraline on dopamine metabolism

Summary. We report a patient with a parkinsonian syndrome induced by sertraline (Zoloft?), an SSRI antidepressant, whose symptoms resolved after the drug was discontinued. This case prompted us to investigate the effect of sertraline on dopamine metabolism in animals. Sertraline (30 mg/kg, IP) or placebo (vehicle) was administered to two groups of six normal, anesthetized rats and using cerebral microdyalisis extracellular striatal levels of dopamine, the dopamine metabolites (HVA and DOPAC), as well as the serotonin metabolite 5-HIIA were monitored. In animals pre-treated with sertraline, DOPAC, HVA, and 5-HIAA levels were significantly decreased compared to control animals (p < 0.01). These data indicate that sertraline has an effect on dopamine metabolism, which may alter function in the striatum and induce a parkinsonian syndrome. Received October 3, 1997 / Accepted December 20, 1997     

In vivo studies on the enhancement of serotonin reuptake by tianeptine

The present study investigates the in vivo effects of the serotonin uptake enhancer tianeptine. The serotonin metabolite, 5-hydroxy-indolacetic acid (5-HIAA) was measured by in vivo voltammetry and carbon fiber electrodes chronically implanted in different brain areas of freely moving rats. Tianeptine (10 mg/kg i.p.) increased extracellular 5-HIAA in the hippocampus and hypothalamus. The interaction between tianeptine and drugs known to interfere with the uptake or release of serotonin (sertraline, buspirone, D-norfenfluramine) was then studied and, to ascertain the in vivo pharmacological relevance of tianeptine's effects, its ability to reduce the serotoninergic syndrome was evaluated. Both the biochemical and behavioral data indicate that in vivo tianeptine's effects on the serotoninergic system are likely to be due to serotonin uptake enhancement.     

Effects of fluoxetine administration on mu-opoid receptor immunostaining in the rat forebrain

Fluoxetine is a selective serotonin reuptake inhibitor. Analysis of mu-opioid receptor immunostaining after chronic fluoxetine administration in rats revealed an increase in the density of cells expressing mu-opioid receptors in the caudatus-putamen, the dentate gyrus, the lateral septum and the frontal, parietal and piriform cortices. These data suggest that mu-opioid receptor expression in the rat forebrain is altered by in vivo chronic fluoxetine treatment.     

Autoradiographic evidence for differential G-protein coupling of 5-HT1A receptors in rat brain: lack of effect of repeated injections of fluoxetine

The present study examined the distribution of [³H]8-OH-DPAT-labeled 5-HT_1A receptors and their degree of coupling to G proteins in the hypothalamus and several other brain regions. In addition, we also investigated the effects of repeated injections of fluoxetine on the density and G protein coupling of 5-HT_1A receptors in hypothalamic nuclei and other brain regions using autoradiography. Male rats received daily injections of either fluoxetine (10 mg/kg, ip) for 3, 7, 14 and 22 days, or saline for 22 days. 5-HT_1A receptors were labeled by 2 nM [³H]8-hydroxy-2-(dipropylamino)tetralin ([³H]8-OH-DPAT) in the absence or presence of guanylylimidodiphosphate (Gpp(NH)p, 10⁻⁵ M) to determine the percentage of 5-HT_1A receptors coupled to G proteins. 5-HT_1A receptor densities ranged from 7 to 63 fmol/mg tissue equivalent among hypothalamic nuclei. Similarly, the degree of G protein coupling to 5-HT_1A receptors varied markedly among hypothalamic nuclei (from 14% to 61%) and among other brain regions (from 17% to 85%). Fluoxetine did not alter the density or the degree of coupling of 5-HT_1A receptors in any brain regions. These data indicate marked regional differences in the degree of G protein-coupled 5-HT_1A receptors and suggest that fluoxetine-induced desensitization of hypothalamic 5-HT_1A receptors is not mediated by changes in receptor density or G protein coupling.     

The composition of lunch determines afternoon plasma tryptophan ratios in humans

Summary It is well established that the ratio of the plasma tryptophan concentration to those of the other large neutral ammo acids determines the transport of tryptophan into the brain. Brain tryptophan levels, in turn, control production of the neurotransmitter serotonin. Protein-rich meals, when consumed in the morning after an overnight fast, have been shown to decrease the plasma tryptophan ratio, while carbohydrate-rich meals have the opposite effect. We now show that these meals have similar effects when consumed for lunch, even if they are preceded by a small breakfast meal.     

Neuronal damage following non-lethal but repeated cerebral ischemia in the gerbil

Summary Brief, non-lethal transient forebrain ischemia in the gerbil can injure selectively vulnerable neurons when such ischemia is induced repeatedly. The influence of the number and interval of the ischemic insults on neuronal damage, as well as the time course of damage, following repeated 2-min forebrain ischemia were examined. A single 2-min forebrain ischemia were examined. A single 2-min ischemic insult caused no morphological neuronal damage. A moderate number of hippocampal CA1 neurons were destroyed following two ischemic insults with a 1-h interval, and destruction of almost all CA1 neurons resulted from three or five insults at 1-h intervals. Three and five insults also resulted in moderate to severe damage to the striatum and thalamus, depending on the number of episodes. Although three ischemic insults at 1-h intervals caused severe neuronal damage, this number of insults at 5-min and 4-h intervals caused destruction of relatively few neurons, and non neurons were destroyed at 12-h intervals. Following three ischemic insults at 1-h intervals, damage to the striatum, neocortex, hippocampal CA4 subfield and thalamus was observed at 6–24 h of survival, whereas damage to the hippocampal CA1 subfield appeared at 2–4 days. The results indicate that even a brief non-lethal ischemic insult can produce severe neuronal damage in selectively vulnerable regions when it is induced repeatedly at a certain interval. The severity of neuronal damage was dependent on the number and interval of ischemic episodes.     

Neuronal damage following repeated brief ischemia in the gerbil

The effect of repetition of brief ischemia, which causes no morphological brain damage when given as a single insult, was studied. Two-minute forebrain ischmia was induced in gerbils singly and 3 or 5b times at 60-min intervals. Although 2-min ischemia induced no neuronal damage, 3 or 5 repeated ischemic insults caused neuronal damage in the selectively vulnerable regions, the severity being dependent on the number of episodes.     

Effects of the triple reuptake inhibitor amitifadine on extracellular levels of monoamines in rat brain regions and on locomotor activity

Major depressive disorder is a prevalent disease, and current pharmacotherapy is considered to be inadequate. It has been hypothesized that a triple reuptake inhibitor (TRI) that activates dopamine (DA) neurotransmission in addition to serotonin and norepinephrine (NE) circuitries may result in enhanced antidepressant effects. Here, we investigated the pharmacological effects of a serotonin-preferring TRI-amitifadine (EB-1010, formerly DOV 21947). The effects of amitifadine (10 mg/kg ip.) on extracellular concentrations of monoamines and their metabolites in rat brain regions were investigated using the in vivo microdialysis technique. The effects of amitifadine on locomotor activity and stereotyped behavior were also evaluated. A major metabolite of amitifadine, the 2-lactam compound, was investigated for inhibition of monoamine uptake processes. Amitifadine markedly and persistently increased extracellular concentrations of serotonin, NE, and DA in prefrontal cortex. The extracellular concentrations of DA were also increased in the DA-rich areas striatum and nucleus accumbens. The extracellular concentrations of the metabolites of serotonin, 5-hydroxyindoleacetic acid, and DA, 3,4-dihydroxyphenylacetic and homovanillic acid, were also markedly decreased in brain regions. Amitifadine did not increase locomotor activity or stereotypical behaviors over a broad dose range. The lactam metabolite of amitifadine weakly inhibited monoamine uptake. Thus, amitifadine increased extracellular concentrations of serotonin, NE, and DA, consistent with TRI. Although amitifadine significantly increased DA in the nucleus accumbens, it did not induce locomotor hyperactivity or stereotypical behaviors. The enhancement of serotonin, NE, and DA in rat brain regions associated with depression suggest that amitifadine may have novel antidepressant activity.     

Long-term effects of repeated methylamphetamine administration on dopamine and serotonin neurons in the rat brain: A regional study

Repeated high doses (25 and 100 mg/kg) of methylamphetamine produce long-term depletions of both dopamine (DA) and serotonin (5-HT) in the rat brain. In the DA system, depletions are most pronounced in the neostriatum and substantia nigra, with decreased levels in these two regions being significantly correlated. Within the 5-HT system, levels are most reduced in the amygdala, frontal cortex and neostriatum. When both the DA and 5-HT depleting actions of methylamphetamine are considered, the hypothalamus stands out as one of the more resistant brain regions. The regional pattern of reduced 5-HT levels following methylamphetamine is similar to that seen after p-chloroamphetamine. After both methylamphetamine and p-chloroamphetamine, a loss of 5-HT synaptosomal uptake sites occurs. Serotonergic systems are more sensitive than DA systems to the apparent neurotoxic actions of methylamphetamine.     

Amino acids, serotonin, and 5-hydroxyindoleacetic acid following foot shock in rats

Concentrations of tryptophan, serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in brain and plasma, as well as plasma amino acid composition, were measured after 1-h foot shock. Stress induced a rise in both plasma and brain 5-HIAA, whereas 5-HT concentration was found to be increased only in plasma. A prominent rise in brain tryptophan was observed, whereas in plasma, foot shock caused a significant increase only in tryptophan level. Concentrations of other amino acids were found to be either decreased or unchanged. Ratio of tryptophan to the other long-chain neutral amino acids increased significantly following foot shock. It is possible that stress-related changes in 5-HT turnover are due to increased plasma tryptophan, in turn causing a rise in brain tryprophan, necessary to cope with enhanced 5-HT metabolism, reflected as a rise in 5-HIAA levels.     

Monoamine oxidase: A gene polymorphism,tryptophan hydroxylase gene polymorphism and antidepressant response to fluvoxamine in Japanese patients with major depressive disorder

Monoamine oxidase A (MAOA) and tryptophan hydroxylase (TPH) are the staple enzymes in the metabolism of serotonin (5-HT). The genetic polymorphisms of these two enzymes might individually alter the production, release, reuptake or degradation of 5-HT during the treatment of selective serotonin reuptake inhibitors (SSRIs), leading to the individual differences in the antidepressant effects of SSRIs. The authors investigated whether a functional polymorphism in the MAOA gene promoter (MAOA-VNTR) and a TPH gene polymorphism in intron 7 (TPH-A218C) were associated with the antidepressant response to fluvoxamine in 66 Japanese patients with major depressive disorder during a 6-week study with a specific dosage plan. Fifty-four patients completed the study. The present study fails to demonstrate that the genetic polymorphisms of MAOA-VNTR and TPH-A218C affect the antidepressant effect of fluvoxamine in Japanese patients with major depressive disorder.