Change in serotonin metabolism in the rat brain in response to the repeated stimulus presentation

The content of serotonin (5-HT), its metabolite 5-hydroxyindoleacetic acid (5-HIAA), monoamine oxidase (MAO) activity and kinetic parameters (K(m) and Vmax) for the reaction of 5-HT deamination, were examined in various regions of the rat brain after repeated presentation of a contextual stimulus. Habituation to the stimulus was accompanied by an increase of 5-HT metabolism and active transport of 5-HIAA in the amygdala, striatum and midbrain, while these changes were not found in the prefrontal cortex and hippocampus. Kinetic studies have revealed that the enhancement of 5-HT deamination by MAO in the brain structures was mediated by different catalytic mechanisms. A significant decrease in K(m) value for 5-HT deamination in the amygdala indicated an increase in the affinity of enzyme towards 5-HT. In the striatum the enhanced MAO activity was provided by increasing maximal rate of 5-HT deamination. It is concluded that an activation of presynaptic mechanisms of the serotonergic transmission in the amygdala and striatum is involved in the inhibition of biological significance and attention to repeated presentation of stimulus.     

Changes in brain monoamine oxidase activity in conditioned passive avoidance reaction in rats]

Activity of the enzyme monoamine oxidase (MAO) and kinetic parameters (Km, Vmax) for the 5-hydroxytryptamine (5-HT) and dopamine deamination were examined in the brain of rats with conditioned passive avoidance recall. Changes of the 5-HT and dopamine deamination were found in amygdala, striatum and frontal cortex. MAO activity was not changed in hippocampus. In amygdala the rate of 5-HT deamination was significantly increased and kinetic studies revealed increased affinity of the enzyme for 5-HT. The metabolism of dopamine in amygdala was unchanged. In frontal cortex the deamination of 5-HT was not changed, but the dopamine deamination significantly decreased. This decrease was due to lowering of MAO affinity for dopamine. In striatum the metabolism of both 5-HT and dopamine was reduced, and kinetic studies showed the lowering of Vmax for 5-HT and dopamine deamination.     

Monoaminoxidase activity and serotonin metabolism in the brain of rats during latent inhibition]

The monoamine oxidase (MAO) activities and the concentrations of 5-HT and 5-hydroxyindoleacetic acid were investigated in four brain regions in rats during the acquisition of latent inhibition in one-trial passive avoidance task. 5-HT metabolism was not altered in the hippocampus. Changes of 5-HT metabolism were found in the frontal cortex during testing of latent inhibition and were accompanied by lowering of MAO activity. No change of 5-HT metabolism was observed in this structure at the stage of pre-exposition to conditioned stimulus. 5-HT metabolism was activated at the stage of pre-exposition to conditioned stimulus in the amygdala and striatum and was maintained on high level, in these structures during testing of latent inhibition. The data presented here indicate that serotoninergic system in various brains regions is specifically involved in the formation of different stages of latent inhibition.     

Stress-Related Changes in Cerebral Catecholamine and Indoleamine Metabolism: Lack of Effect of Adrenalectomy and Corticosterone

The concentrations of catecholamine and indoleamine metabolites were measured in intact and adrenalectomized mice to determine whether adrenal hormones mediate or modulate the stress-induced responses. Thirty minutes of footshock resulted in significant increases of the ratios of the dopamine (DA) catabolite, dihydroxyphenylacetic acid (DOPAC), to DA in prefrontal cortex, nucleus accumbens, striatum, hypothalamus, and brainstem, and of homovanillic (HVA)/DA ratios in nucleus accumbens, striatum, amygdala, and hypothalamus. Ratios of 3-methoxy-4-hydroxyphenylethyleneglycol to norepinephrine (NE) were also increased in prefrontal cortex, nucleus accumbens, septum, amygdala, hypothalamus, hippocampus, and brainstem. The concentration of NE was decreased in amygdala. 5-Hydroxyindoleacetic acid (5-HIAA)/5-hydroxytryptamine (5-HT, serotonin) ratios and free tryptophan were also increased in every brain region. Very similar data were obtained from mice restrained for 30 min. Adrenalectomy resulted in increased HVA/DA ratios in prefrontal cortex and striatum, and 5-HIAA/5-HT in septum. The stress-related changes were largely similar in adrenalectomized mice. Significant interactions between adrenalectomy and footshock treatment occurred in prefrontal cortical DOPAC/DA and hypothalamic NE which was depleted only in adrenalectomized mice, suggesting tendencies for these measures to be more responsive in adrenalectomized mice. Corticosterone administration (0.5-2.0 mg/kg s.c.) which resulted in plasma concentrations in the physiological range did not alter the concentrations of the cerebral metabolites measured in any region. We conclude that adrenal hormones do not mediate cerebral catecholamine or indoleamine metabolism in stress, although adrenalectomy may affect HVA and 5-HIAA metabolism, and there was a tendency for catecholamines to be more sensitive to stress in adrenalectomized animals.     

Cocaine

Cocaine HCl (0, 10, or 50 mg/kg) was injected into adult male ICR mice ip. Thirty minutes later, the brains were removed, and nine regions were isolated: olfactory bulbs, olfactory tubercles, prefrontal cortex, septum, striatum, amygdala, hypothalamus, hippocampus, and thalamus. Using high-performance liquid chromatography, concentrations of norepinephrine, dopamine, serotonin, and their major metabolites and the metabolite/neurotransmitter ratios were determined as an indicator of utilization. Serotonergic systems responded most dramatically. 5HIAA/5-HT decreases were seen in all the brain regions, except the septum, hippocampus, and olfactory bulbs. In most instances, the alterations were dose-dependent. The most profound changes were seen in the amygdala, prefrontal cortex, hypothalamus, and thalamus. For noradrenergic systems, significant responses were seen only in the amygdala, prefrontal cortex, and hypothalamus, but then only at the lower dose. The dopaminergic responses were more complex and not always dose-dependent. The DOPAC/DA ratio was decreased only in the amygdala and striatum at the lower dose, and the olfactory tubercles at the higher dose. It was increased in the septum. The HVA/DA ratios were decreased in the amygdala, prefrontal cortex, and hypothalamus, but only at the lower dose (like MHPG/NE). The 3MT/DA ratio was decreased in the thalamus at the lower dose and in the olfactory tubercles at the higher dose, whereas it was increased in the prefrontal cortex at the lower dose. The HVA and DOPAC routes of degradation were both utilized only by the amygdala. Thus, cocaine produced its most comprehensive effects in this nucleus, as well as the greatest absolute percentage changes for all three of the monoamine systems studied.     

Interactions of Phencyclidine Receptor Agonist MK-801 with Dopaminergic System: Regional Studies in the Rat

Interactions of the potent phencyclidine receptor agonist MK-801 with the dopaminergic system were examined in various brain regions in the rat. MK-801 increased dopamine (DA) metabolism in the pyriform cortex, entorhinal cortex, prefrontal cortex, striatum, olfactory tubercle, amygdala, and septum without affecting DA metabolism in the cingulate cortex and nucleus accumbens. In pyriform cortex and amygdala, MK-801 was more potent than phencyclidine at increasing DA metabolism. Local injections of MK-801 into ventral tegmental area and into the amygdala/pyriform cortex interface indicated that MK-801 may act at the cell body as well as the nerve terminal level to increase DA metabolism and that ongoing dopaminergic neuronal activity is a prerequisite for full drug action.     

Specificity of endogenous substrates for types A and B monoamine oxidase in rat striatum

Abstract: Studies were designed to evaluate specificity of the transmitter amines serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA), as well as the trace amines p -tyramine ( p -TA) and β -phenylethylamine (PEA) for types A and B monoamine oxidase (MAO) in rat striatum. 5-HT was found to be a specific substrate for the type A enzyme. However, the specificity of PEA for the type B enzyme was found to be concentration-dependent. When low concentrations of PEA and 5-HT were used to measure type B and type A activities, respectively, both clorgyline and deprenyl were highly selective for the sensitive form of MAO in vivo. However, as the concentration of PEA was increased, the type B inhibitor deprenyl became less effective in preventing deamination of PEA. Conversely, the type A inhibitor clorgyline became more effective in this regard. Kinetic analysis following selective in vivo inhibition showed PEA deamination by both forms of MAO with a 13-fold greater affinity for the type B enzyme. In vivo dose-response curves obtained with the common substrates DA and p -TA showed approximately 20% deamination by the B enzyme. Kinetic values for DA and p -TA deamination in in vivo -treated tissue possessing only type A or type B MAO activity, revealed a 2.5-fold greater affinity for the type A enzyme. These studies show the importance of concentration on substrate specificity in striatal tissue. The results obtained characterize the common substrate properties of DA and p -TA as well as of PEA in rat striatum. In addition, the presence of regional specificity for 5-HT deamination by only type A MAO is demonstrated.     

Monoamine Oxidase Activity and Monoamine Metabolism in Brains of Parkinsonian Patients Treated with l-Deprenyl

Monoamine oxidase (MAO) type A and type B were measured using kynuramine, 3,4-dihydroxyphenylethylamine (dopamine, DA), and 5-hydroxytryptamine (5-HT, serotonin) in 20 brain areas. The highest activities were found in the striatum (caudate nucleus, putamen, globus pallidus, and substantia nigra), hypothalamus, and c-mammilare. The ratio of DA to 5-HT deamination varied in the different regions, being in favor of DA in the striatum. With kynuramine as the substrate IC50 values of a number of inhibitors indicated that l-deprenyl was far more potent an inhibitor of human brain MAO than clorgyline or harmaline. N-Desmethylpropargylindane hydrochloride (AGN 1135) was also shown to have MAO-B inhibitory selectivity similar to that of l-deprenyl. Brains obtained at autopsy from l-deprenyl-treated Parkinsonian patients showed that, whereas MAO-B was fully inhibited by the therapeutic doses of l-deprenyl, substantial MAO-A activity was still evident. These results are matched by the significant increases of DA noted in caudate nucleus, globus pallidus, putamen, and substantia nigra and the unaltered 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the same regions. These data indicate that the therapeutic actions of l-deprenyl may lie in its selective inhibition of MAO-B resulting in increased brain levels of DA formed from L-dihydroxyphenylacetic acid (L-DOPA).     

Effect of intrastriatal injection of soman on acetylcholine, dopamine and serotonin metabolism

Intrastriatal injection of soman (14.85 nmol) inhibits cholinesterase (ChE) activity in the striatum with much smaller decreases in ChE activity in other brain areas of the rat. As would be expected, there is a substantial increase in striatal acetylcholine (ACh) content shortly after soman injection. However, this increase is no longer significant 1 h following intrastriatal injection. There is no change in striatal KACh 20 min, 1 h or 24 h following soman injection. ACh content is not affected in the parietal cortex, hippocampus, or medulla/pons following intrastriatal soman injection. However, KACh and/or ACh turnover are reduced in these brain areas following soman injection. There is no consistent effect on dopamine (DA) metabolism in any of the brain areas studied. However, serotonin (5-HT) metabolism appears to be affected in the cortex, hippocampus and medulla/pons following intrastriatal injection of soman. Possible mechanisms of the actions of local injection of soman on brain Ach and 5-HT metabolism are discussed, as well as the differences observed between the effects of local and peripheral administration of soman on DA metabolism in the striatum.     

Guinea Pig Striatum as a Model of Human Dopamine Deamination: The Role of Monoamine Oxidase Isozyme Ratio, Localization, and Affinity for Substrate in Synaptic Dopamine Metabolism

The kinetic properties of type A and type B monoamine oxidase (MAO) were examined in guinea pig striatum, rat striatum, and autopsied human caudate nucleus using 3,4-dihydroxyphenylethylamine (dopamine, DA) as the substrate. MAO isozyme ratio in guinea pig striatum (28% type A/72% type B) was similar to that in human caudate nucleus (25% type A/75% type B) but different from that in rat striatum (76% type A/24% type B). Additional similarities between guinea pig striatum and human caudate nucleus were demonstrated for the affinity constants (Km) of each MAO) isozyme toward DA. Endogenous concentrations of DA, 3-methoxytyramine, 3,4-dihydroxyphenylacetic acid, and homovanillic acid were also measured in guinea pig and rat striatum following selective type A (clorgyline-treated) and type B (deprenyl-treated) MAO inhibition. In guinea pig, DA metabolism was equally but only partially affected by clorgyline or deprenyl alone. Combined treatment with clorgyline and deprenyl was required for maximal alterations in DA metabolism. By contrast, DA metabolism in rat striatum was extensively altered by clorgyline but unaffected by deprenyl alone. Finally, the deamination of DA in synaptosomes from guinea pig striatum was examined following selective MAO isozyme inhibition. Neither clorgyline nor deprenyl alone reduced synaptosomal DA deamination. However, clorgyline and deprenyl together reduced DA deamination by 94%. These results suggest that the isozyme localization and/or isozyme affinity for DA, rather than the absolute isozyme content, determines the relative importance of type A and type B MAO in synaptic DA deamination. Moreover, based on the enzyme kinetic properties of each MAO isozyme, guinea pig striatum may serve as a suitable model of human DA deamination.     

Different roles of dopamine and serotonin in conditioned passive avoidance response of rats

Deamination of dopamine and serotonin by monoamine oxidase was studied in the prefrontal cortex, striatum, hippocampus and amygdaloid complex of the brain of rats during retrieval of conditioned passive avoidance response. Changes in the dopamine and serotonin metabolism were observed in different brain structures. A decrease in dopamine-deaminating activity of monoamine oxidase was found in the hippocampus, striatum and prefrontal cortex. At the same time, serotonin-deaminating activity of the enzyme was decreased in the striatum and increased in the amygdaloid complex, whereas it did not change in the prefrontal cortex and hippocampus. The observed changes in dopamine metabolism in the prefrontal cortex and hippocampus and serotonin metabolism in the amygdaloid complex indicate that dopamine and serotonin are involved in the regulation of two different processes mediating the memory trace retrieval. Dopamine is involved in neuronal mechanisms of information processes providing the strategy of behavior, whereas serotonin is related to emotional mechanisms of memory.     

Effects of muscimol and baclofen on levels of monoamines and their metabolites in the El mouse brain

We compared the changes in monoamines and their metabolites in the El mouse brain induced by GABA-A and GABA-B receptor agonists. Muscimol was used as a GABA-A receptor agonist, and baclofen as a GABA-B receptor agonist. Muscimol (3 mg/kg) significantly increased the DOPAC level in all parts of the mouse brain and the HVA level in the cortex, striatum, and midbrain. No significant change was observed in the dopamine (DA) level. These findings suggest that muscimol may accelerate both the synthesis and catabolism of DA. Baclofen (20 mg/kg) increased the DA level in the hippocampus and midbrain, and the DOPAC level in the hippocampus. Muscimol increased 5-HIAA levels and decreased 5-HT levels. This result suggests that 5-HT metabolism is accelerated by muscimol. No change in 5-HT or 5-HIAA levels was induced by baclofen. The GABA-A receptor system seems to have a potent effect not only on DA neurons, but on 5-HT neurons. However, the GABA-B receptor system appears to have almost no effect on 5-HT neurons, though it appears to have some effect on DA neurons.     

Changes in brain serotonin metabolism and [3H]-serotonin receptor binding during recall of conditioned passive avoidance in rats

The content of serotonin and its metabolite 5-hydroxyindoleacetic acid, monoamine oxidase activity, and [3H]-serotonin radioligand receptor binding were examined in the prefrontal cortex, striatum, amygdala, hippocampus and periaqueductal gray matter at different time after one-trial passive avoidance training of rats. Changes in the serotonergic activity were observed only in rats, which showed retrieval of conditioned passive avoidance response. No serotonergic changes were found immediately and one day after training. Also, there were no changes in trained rats without retrieval of conditioned passive avoidance response or rats with experimental amnesia. The pattern of the involvement of brain structures in the retrieval process was also revealed. [3H]-serotonin binding was decreased in the amygdala, periaqueductal gray matter and striatum, whereas it did not change in the prefrontal cortex and hippocampus. At the same time, the serotonin content in these structures did not differ from that of intact rats. Deamination of serotonin by monoamine oxidase and active transport of 5-hydroxyindoleacetic acid from nerve terminals were increased in the amygdala and periaqueductal gray matter, whereas in the striatum serotonin catabolism was decreased. The obtained differences in serotonin catabo- lism suggest that the decrease in receptor binding of serotonin in these brain structures is provided by different synaptic processes: presynaptic changes in the striatum and postsynaptic receptor changes in the amygdala and periaqueductal gray matter. It is concluded that the decrease in the serotonergic activity in the amygdala and periaqueductal gray matter represents one of the mechanisms activating the emotiogenic system mediating the memory trace retrieval in inhibitory avoidance learning.     

Effect of cholecystokinin octapeptide sulphate ester on brain monoamines in the rat

The effect of different doses of intracerebro-ventricularly administered cholecystokinin octapeptide sulphate ester (CCK-8-SE) was studied on dopamine (DA), norepinephrine (NE) and serotonin (5-HT) contents in the hypothalamus, mesencephalon, amygdala, septum and striatum, 10, 20 and 60 min following administration. The DA and NE content increased and the 5-HT content decreased in the hypothalamus and mesencephalon. A biphasic action was observed in the amygdala of DA, NE and 5-HT depending upon the time and doses used. Similar action was seen on DA and NE in the septum. In the striatum, the DA and 5-HT content decreased while the NE level first increased and then decreased. The data indicate that the CCK-8-SE is able to modify the activity of DA, NE and 5-HT in different brain regions in a time and dose-dependent manner, with a local specific action.     

Post-mortem changes of neurotransmitter concentrations in the rat brain regions

Using High Performance Liquid Chromatography coupled with electrochemical detection the post-mortem stability of noradrenaline (NA), dopamine (DA), serotonin (5-HT) and 5-hydroxy indole acetic acid (5-HIAA) were examined in the rat hypothalamus, amygdala, cerebral cortex, cerebellum and corpus striatum over an 8 hour time period. Changes in concentrations of the different neurotransmitters were less than it might be expected. The significant changes were: a. A fall in NA levels in the cerebral cortex by 4 hours and in the hypothalamus at 8 hours. b. A reduction in DA concentrations in the corpus striatum at 8 hours but a two fold rise of levels in the hypothalamus at 1 and 2 hours. c. A four-fold increase in 5-HT concentrations in the amygdala throughout the 8 hours studied. The results indicate that for comparative studies on post-mortem brain tissue correction factors should be employed to take into account differential changes in the concentrations of the various neurotransmitters.     

Regional Differences in 5-Hydroxytryptamine and Catecholamine Uptake in Primary Astrocyte Cultures

The uptake of 3H-labelled 5-hydroxytryptamine (5-HT, serotonin) norepinephrine ([3H]NE), and 3,4-dihydroxyphenylethylamine ([ 3H]dopamine, [3H]DA) was studied in primary astrocyte cultures prepared from the cerebral cortex, corpus striatum, and hippocampal regions of neonatal rat brain. Na+-dependent uptake showed marked regional differences. For [3H]5-HT the magnitude of uptake was corpus striatum greater than or equal to cerebral cortex greater than hippocampus, whereas for [3H]NE the order was hippocampus greater than corpus striatum greater than cerebral cortex. For [3H]DA, only the hippocampal cultures showed significant Na+-dependent uptake. [3H]5-HT uptake was specifically inhibited by 10(-7) M fluoxetine whereas [3H]NE uptake was preferentially inhibited by 10(-7) M desipramine. These results may reflect regional brain specialization and/or different developmental patterns of high affinity uptake of serotonin and catecholamines by astrocytes in situ.     

Central Nervous System Involvement in the Animal Model of Myodystrophy

Congenital muscular dystrophies present mutated gene in the LARGE mice model and it is characterized by an abnormal glycosylation of α-dystroglycan (α-DG), strongly implicated as having a causative role in the development of central nervous system abnormalities such as cognitive impairment seen in patients. However, the pathophysiology of the brain involvement remains unclear. Therefore, the objective of this study is to evaluate the oxidative damage and energetic metabolism in the brain tissue as well as cognitive involvement in the LARGE^(myd) mice model of muscular dystrophy. With this aim, we used adult homozygous, heterozygous, and wild-type mice that were divided into two groups: behavior and biochemical analyses. In summary, it was observed that homozygous mice presented impairment to the habituation and avoidance memory tasks; low levels of brain-derived neurotrophic factor (BDNF) in the prefrontal cortex, hippocampus, cortex and cerebellum; increased lipid peroxidation in the prefrontal cortex, hippocampus, striatum, and cerebellum; an increase of protein peroxidation in the prefrontal cortex, hippocampus, striatum, cerebellum, and cortex; a decrease of complex I activity in the prefrontal cortex and cerebellum; a decrease of complex II activity in the prefrontal cortex and cerebellum; a decrease of complex IV activity in the prefrontal cortex and cerebellum; an increase in the cortex; and an increase of creatine kinase activity in the striatum and cerebellum. This study shows the first evidence that abnormal glycosylation of α-DG may be affecting BDNF levels, oxidative particles, and energetic metabolism thus contributing to the memory storage and restoring process.     

Distribution of Serotonin Receptor of Type 6 (5-HT6) in Human Brain Post-mortem. A Pharmacology, Autoradiography and Immunohistochemistry Study

The aim of this study was to investigate the distribution of serotonin (5-HT) receptors of type 6 (5-HT(6)) in postmortem human prefrontal cortex, striatum and hippocampus. The brain samples were obtained from 6 subjects who had died for causes not involving primarily or secondarily the CNS. The 5-HT(6) receptor distribution was explored by the [(125)I]SB-258585 binding to brain membranes followed by the pharmacological characterization, where possible, and by autoradiographic, immunohistochemical and immunofluorescence evaluations. A specific and saturable [(125)I]SB-258585 binding was detected in striatum only, with a pharmacological characterization consistent with that of a 5-HT(6) receptor. The autoradiography showed the presence of a specific [(125)I]SB-258585 binding distributed homogeneously in caudate, putamen and accumbens. The immunohistochemistry, carried out in the striatum only, coupled with the immunofluorescence with glial fibrillary acidic protein (GFAP) and parvalbumin (PV) showed the co-localization of 5-HT(6) receptor with PV, while indicating that this receptor subtype was expressed in neurons and not in astrocytes. Taken together, the present findings showed the presence of a higher density of 5-HT(6) receptors, as labeled by [(125)I]SB-258585, in striatum than in hippocampus and prefrontal cortex, and specifically within the neuronal body. In addition, they would suggest that striatum is one of the major potential CNS targets linked to 5-HT(6) receptor modulation.     

合欢花对慢性应激大鼠生长和脑单胺类神经递质含量的影响

为探讨合欢花对慢性应激大鼠生长和脑单胺类神经递质的影响,采用15只大鼠,设置了对照组、应激组和合欢花组3组实验。应激组和合欢花组均接受7天的应激刺激,之后合欢花组再灌胃合欢花10天。实验结束后,取3组大鼠的脑组织,用高效液相色谱法测定高香草酸(HVA)、去甲肾上腺素(NE)、多巴胺(DA)和5-羟色胺(5-HT)的含量。结果表明,应激组大鼠日增重显著低于对照组(P=0.011);而合欢花组大鼠的日增重极显著高于应激组(P=0.002)。应激组大鼠海马、纹状体和前额叶中的HVA含量与对照组相比,虽有升高的趋势,但无显著差异;两组间的NE、DA和5-HT也无显著差异。合欢花组大鼠海马中的HVA、DA含量明显高于应激组,而前额叶中的多巴胺和5-羟色胺,以及纹状体中的5-羟色胺均明显低于应激组。这表明合欢花对慢性应激引起的大鼠生长受抑有缓解作用,对其脑内单胺类神经递质有调节作用。