Effect of chronic administration of phenytoin on regional monoamine levels in rat brain

Phenytoin (DPH) is a widely used anticonvulsant drug but a conclusive mode of action is not yet clear. This study was undertaken to assess the effects of chronic administration of DPH on monoamine levels. DPH (50 mg/kg body weight) was administered to adult male Wistar rats by intraperitoneal injections for 45 days and the regional brain levels of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) were assayed using high performance liquid chromatographic (HPLC) method. The experimental rats revealed no behavioral deficits of any kind nor body and brain weight deficits were observed. Increased NE levels were observed after DPH administration in motor cortex (P<0.05), striatum-accumbens (P<0.01) and hippocampus (P<0.01), whereas, NE level was decreased in brain stem (P<0.05). DA levels were increased in striatum-accumbens (P<0.05), hypothalamus (P<0.001) and cerebellum (P<0.001) but decreased in brainstem (P<0.01). In DPH treated rats, 5-HT levels were increased in motor cortex (P<0.001) but decreased in cerebellum (P<0.001) when compared to control group of rats. The present study suggest that chronic administration of DPH induces alterations in monoamine levels in specific brain regions. DPH seems to mediate, its anticonvulsant action by selectively altering the monoamine levels in different brain regions.     

Alterations in monoamine levels in discrete regions of rat brain after chronic administration of carbamazepine

Carbamazepine (25 mg/kg body weight) was administered intraperitoneally to adult male Wistar rats for 45 days and norepinephrine (NE), dopamine (DA) and serotonin (5-HT) levels were simultaneously assayed in discrete brain regions by high performance liquid chromatographic (HPLC) method. Experimental rats displayed no behavioral abnormalities. Body and brain weights were not significantly different from control group of rats. After exposure it was observed that norepinephrine levels were elevated in motor cortex (P<0.01) and cerebellum (P<0.05), while dopamine levels were decreased in these two regions (P<0.001, P<0.05). However, dopamine levels were increased in hippocampus (P<0.01). Serotonin levels were significantly decreased in motor cortex (P<0.001) and hypothalamus (P<0.001) but increased in striatum-accumbens (P<0.001) and brainstem (P<0.001). These results suggest that carbamazepine may mediate its anticonvulsant effect by differential alterations of monoamine levels in discrete brain regions particularly in motor cortex and cerebellum.     

Effect of Long-Lasting Diabetes Mellitus on Rat and Human Brain Monoamines

Experimental alloxan- or streptozotocin-produced diabetes in rats was accompanied by an increase in the levels of norepinephrine, dopamine, and serotonin, whereas the contents of metabolites, i.e., 5-hydroxyindoleacetic acid and homovanillic acid, in the whole brain gradually decreased with the duration of diabetes. Among the striatum, thalamus, and hypothalamus of alloxan diabetic rats, monoamine alterations were observed only in the hypothalamus; after 1 week an increase of norepinephrine content and after 13 weeks an increase of norepinephrine and dopamine contents were found. Tissues of 11 brain regions of 10 diabetic and 12 control patients post mortem were investigated for monoamine concentrations. Patients were all male, of similar age and interval between death and autopsy. Diabetic patients had an increase in the content of serotonin in the medial and lateral hypothalamus. The content of dopamine increased in the medial hypothalamus, putamen, and medial and lateral pallidus. In diabetic patients, the content of norepinephrine increased in the lateral pallidus and decreased in the nucleus accumbens and claustrum. Thus, it seems that diabetes mellitus in rats, as well as in humans is associated with regionally specific changes in brain monoamines.     

Effects of cholecystokinin octapeptide and its fragments on brain monoamines and plasma corticosterone

The effects of intracerebroventricular administration of an 80 pmole dose of cholecystokinin octapeptide sulphate ester, unsulphated cholecystokinin octapeptide and their fragments were tested on the dopamine, norepinephrine and serotonin contents of the rat hypothalamus, mesencephalon, amygdala, septum, cerebral cortex and striatum, as well as on the plasma corticosterone level.Cholecystokinin octapeptide sulphate ester and the tyrosine-sulphate-methionine and tyrosine-sulphate-methionine-glycine fragments increased the dopamine and norepinephrine contents of the hypothalamus and mesencephalon. The same compounds increased the dopamine content of the amygdala, while they decreased the dopamine and norepinephrine concentrations in the striatum. The plasma corticosterone level was also increased. The unsulphated cholecystokinin octapeptide and its fragments had no effects on the brain monoamine contents and slight but not significant effect on the plasma corticosterone level.The data suggest that the presence of the tyrosine-sulphate-methionine dipeptide is essential in the effects of cholecystokinin octapeptide sulphate ester on the monoamine contents of different brain areas, as well as on the plasma corticosterone level.     

Comparison of central effects of noradrenaline and dopamine injected into the lateral brain ventricle in rats.

Noradrenaline and dopamine injected into the lateral brain ventricle exerted a significant effect on the behavior of rats. Both amines caused a slight rise in the basic locomotor activity which was significantly increased in the animals with inhibited monoamine oxidase activity. Besides that, they suppressed the behavior of rats in the open-field test, inhibited the conditioned avoidance response, decreased body temperature and increased amphetamine-induced motor hyperactivity. Noradrenaline, in contrast to dopamine, changed the intensity of amphetamine-induced stereotypy and prolonged the action of hypnotics. The central action of both catecholamines (in higher doses especially) seemed to have a biphasic course: in the first phase after administration depression was observed which was more pronounced after noradrenaline administration, in the second phase a stimulating effect b     

Increased renal dopamine and acute renal adaptation to a high-phosphate diet

The current experiments explore the role of dopamine in facilitating the acute increase in renal phosphate excretion in response to a high-phosphate diet. Compared with a low-phosphate (0.1%) diet for 24 h, mice fed a high-phosphate (1.2%) diet had significantly higher rates of phosphate excretion in the urine associated with a two- to threefold increase in the dopamine content of the kidney and in the urinary excretion of dopamine. Animals fed a high-phosphate diet had a significant increase in the abundance and activity of renal DOPA (l-dihydroxyphenylalanine) decarboxylase and significant reductions in renalase, monoamine oxidase A, and monoamine oxidase B. The activity of protein kinase A and protein kinase C, markers of activation of renal dopamine receptors, were significantly higher in animals fed a high-phosphate vs. a low-phosphate diet. Treatment of rats with carbidopa, an inhibitor of DOPA decarboxylase, impaired adaptation to a high-phosphate diet. These experiments indicate that the rapid adaptation to a high-phosphate diet involves alterations in key enzymes involved in dopamine synthesis and degradation, resulting in increased renal dopamine content and activation of the signaling cascade used by dopamine to inhibit the renal tubular reabsorption of phosphate.     

Stress-induced depression of motor activity correlates with regional changes in brain norepinephrine but not in dopamine

This experiment examined how inescapable tail shock alters the level of dopamine and norepinephrine within various brain regions of the rat and the relationship of these changes to the depression of motor activity produced by the shock. Following exposure to tail shock that is known to interfere with acquisition of active behavioral tasks, animals were briefly tested for spontaneous motor activity and then sacrificed for neurochemical measures. Norepinephrine and dopamine levels in the frontal cortex, brain stem, striatum, olfactory tubercle, hypothalamus, hippocampus, septum, and amygdala were measured by a sensitive radicenzymatic technique. Exposure to 45 min of tail shock did not alter motor activity significantly, but shock sessions of 60 and 75 min duration produced a marked decrease in motor activity. Levels of dopamine were found to be very little changed in all brain regions studied except for the hypothalamus, in which a substantial rise in dopamine level was observed. Norepinephrine levels, in contrast, fell in many brain regions in response to shock. The fall in norepinephrine levels observed in twi brain regions was significantly correlated with the decline in motor activity (brain stemr=+0.70, hypothalamusr=+0.60) These data suggest that deficits in active motor behavior produced by shock parameters similar to those used in this study may reflect concomitant disturbances of noradrenergic function in specific brain regions.     

Altered Neurocircuitry in the Dopamine Transporter Knockout Mouse Brain

The plasma membrane transporters for the monoamine neurotransmitters dopamine, serotonin, and norepinephrine modulate the dynamics of these monoamine neurotransmitters. Thus, activity of these transporters has significant consequences for monoamine activity throughout the brain and for a number of neurological and psychiatric disorders. Gene knockout (KO) mice that reduce or eliminate expression of each of these monoamine transporters have provided a wealth of new information about the function of these proteins at molecular, physiological and behavioral levels. In the present work we use the unique properties of magnetic resonance imaging (MRI) to probe the effects of altered dopaminergic dynamics on meso-scale neuronal circuitry and overall brain morphology, since changes at these levels of organization might help to account for some of the extensive pharmacological and behavioral differences observed in dopamine transporter (DAT) KO mice. Despite the smaller size of these animals, voxel-wise statistical comparison of high resolution structural MR images indicated little morphological change as a consequence of DAT KO. Likewise, proton magnetic resonance spectra recorded in the striatum indicated no significant changes in detectable metabolite concentrations between DAT KO and wild-type (WT) mice. In contrast, alterations in the circuitry from the prefrontal cortex to the mesocortical limbic system, an important brain component intimately tied to function of mesolimbic/mesocortical dopamine reward pathways, were revealed by manganese-enhanced MRI (MEMRI). Analysis of co-registered MEMRI images taken over the 26 hours after introduction of Mn²⁺ into the prefrontal cortex indicated that DAT KO mice have a truncated Mn²⁺ distribution within this circuitry with little accumulation beyond the thalamus or contralateral to the injection site. By contrast, WT littermates exhibit Mn²⁺ transport into more posterior midbrain nuclei and contralateral mesolimbic structures at 26 hr post-injection. Thus, DAT KO mice appear, at this level of anatomic resolution, to have preserved cortico-striatal-thalamic connectivity but diminished robustness of reward-modulating circuitry distal to the thalamus. This is in contradistinction to the state of this circuitry in serotonin transporter KO mice where we observed more robust connectivity in more posterior brain regions using methods identical to those employed here.     

Learning in rats with differing emotional responsiveness and its relation to brain monoamines

The ability for learning was studied in two groups of Wistar line rats divided by susceptibility to the audiogenic stress-stimulation as compared with the monoamines level in various brain structures. The best ability to learn avoidance reaction in a shuttlebox was shown by animals non-resistant to the stress stimulus as compared with the resistant rats, which correlated positively with the exploratory activity in "the open field". The distinct feature of the animals non-resistant to the stress stimulation consisted in a higher reactivity of the monoamine systems, mainly of the noradrenergic system. This group of animals was also characterized by a higher dopamine content and a lower noradrenaline content in the brain-stem. Decreased activity of the brain dopamine-beta-hydroxylase in animals non-resistant to the stress stimulus, has been suggested.     

Effects of copper metabolism on neurological functions in Wistar and Wilson's disease model rats

Behavioral functions of Wistar and Long-Evans Cinnamon (LEC) rats, Wilson's disease animal model, were compared by measuring the open-field, acoustic startle reflex and prepulse inhibition (PPI), and shuttle-box avoidance learning tests with or without oral supplementation with copper or D-penicillamine, copper chelator. All of the LEC rats, irrespective of the treatment, exhibited higher locomotor activity, a decreased habituation to startle response or a lower PPI, compared with Wistar rats. The copper content of all brain regions examined, except for the medulla oblongata of LEC rats, was significantly lower than those in Wistar rats. Besides, in the region of the striatum and the nucleus accumbens of the LEC rats, lower content of norepinephrine, and higher content of dopamine and serotonin were observed compared with Wistar rats. Although copper supplementation did not affect the brain copper content, it reduced the PPI in both Wistar and LEC rats. In contrast, D-penicillamine supplementation decreased both the brain copper content and locomotor activity, and enhanced the startle amplitude only in Wistar rats. These findings suggest that an imbalance in copper homeostasis affects monoamine metabolism and behavioral functions.     

EFFECT OF COPPER STATUS ON BRAIN NEUROTRANSMITTER METABOLISM IN THE LAMB

Abstract— Ataxic and non-ataxic lambs reared under field conditions which gave rise to low copper status were treated with copper intravenously. Untreated ataxic animals served as controls. The neurotransmitter amines, dopamine, norepinephrine and serotonin, were determined in the anterior and posterior regions of the brain stem. Dopamine levels in the anterior region, including the corpus striatum, were significantly lower in the untreated animals than in those treated with copper. Norepinephrine levels were also lower but serotonin concentrations were not different. Plasma amine oxidase activity was markedly higher in the copper treated animals but monoamine oxidase activity in brain stem homogenates was not significantly affected. The monoamine oxidase activity in cortical and cerebellar homogenates was significantly lower in the treated animals than in the untreated animals.     

Effects of fluoxetine and its complexes with glycyrrizhinic acid on behavior and brain monoamine levels in rats

Effects of serotonin uptake inhibitor fluoxetine (F) and it's complexes with glycyrrizhinic acid (GA) in molar proportions 1GA : 1F (FGA-1) and 4GA : 1F (FGA-4) on rat behavior in elevated plus-maze and brain monoamine concentrations were studied. Drugs (25 mg/kg) were administered per os 1 h before investigations. F-treated rats showed increased anxiety and reduced locomotor activity, whereas FGA-1 and FGA-4 had no effects on the behaviors. None of the compounds modified brain tissue serotonin content, but all of them decreased the level of its metabolite 5-hydroxyindole-3-acetic acid level in the hypothalamus, and FGA-4 also decreased it in the cortex. Noradrenaline levels were increased in the hypothalamus of rats treated with F in both combinations with GA. In the striatum, F increased dopamine and its metabolite DOPAC levels, but their ratio (an indicator of the neurotransmitter turnover) was not altered by this drug. Unlike F, FGA-1 significantly activated dopamine turnover in the striatum. The data obtained suggested that application of F in complexes with GA significantly modified the drug behavioral effects and these alterations may be related to specific effects of the pure compound and its complexes on the functions of the brain monoaminergic systems that regulate investigated behavior.     

Motor deficits and decreased striatal dopamine receptor 2 binding activity in the striatum-specific Dyt1 conditional knockout mice

DYT1 early-onset generalized dystonia is a hyperkinetic movement disorder caused by mutations in DYT1 (TOR1A), which codes for torsinA. Recently, significant progress has been made in studying pathophysiology of DYT1 dystonia using targeted mouse models. Dyt1 ΔGAG heterozygous knock-in (KI) and Dyt1 knock-down (KD) mice exhibit motor deficits and alterations of striatal dopamine metabolisms, while Dyt1 knockout (KO) and Dyt1 ΔGAG homozygous KI mice show abnormal nuclear envelopes and neonatal lethality. However, it has not been clear whether motor deficits and striatal abnormality are caused by Dyt1 mutation in the striatum itself or the end results of abnormal signals from other brain regions. To identify the brain region that contributes to these phenotypes, we made a striatum-specific Dyt1 conditional knockout (Dyt1 sKO) mouse. Dyt1 sKO mice exhibited motor deficits and reduced striatal dopamine receptor 2 (D2R) binding activity, whereas they did not exhibit significant alteration of striatal monoamine contents. Furthermore, we also found normal nuclear envelope structure in striatal medium spiny neurons (MSNs) of an adult Dyt1 sKO mouse and cerebral cortical neurons in cerebral cortex-specific Dyt1 conditional knockout (Dyt1 cKO) mice. The results suggest that the loss of striatal torsinA alone is sufficient to produce motor deficits, and that this effect may be mediated, at least in part, through changes in D2R function in the basal ganglia circuit.     

STIMULATION OF BRAIN DOPAMINE SYNTHESIS BY GAMMA-HYDROXYBUTYRATE

Abstract— Gamma-hydroxybutyrate administration produces a marked selective increase of brain dopamine in different animal species. Following γ -hydroxybutyrate administration, dopamine accumulated in the basal ganglia of the rat and in the caudate nucleus of the rabbit at a rate which greatly exceeded the normal synthesis rate of the amine in these species. Dopamine accumulation was prevented by α -methyltyrosine. These data indicate that γ -hydroxybutyrate stimulates dopamine synthesis. In addition, γ -hydroxybutyrate increased the homovanillic acid level in the rat basal ganglia to a maximum of about 300 per cent of the normal level indicating that γ -hydroxybutyrate inhibits neither monoamine oxidase nor catechol O -methyltransferase in vivo. The possible mechanisms of dopamine accumulation following γ -hydroxybutyrate administration are discussed.     

Central monoamine oxidase and phenolsulfotransferase activities in spontaneously hypertensive rats

The activities of monoamine oxidase and phenolsulfotransferase in the hypothalamus and anterior pituitary gland of spontaneously hypertensive rats and the normotensive control (Wistar Kyoto rat) rats were investigated. The monoamine oxidase activity (determined using dopamine as substrate) in both these tissues was not significantly different between the normo- and hypertensive animals. Hypothalamic phenolsulfotransferase does not sulfate-conjugate dopamine at pH of 6.5 and pituitary phenolsulfotransferase does not sulfate-conjugate dopamine or 3,4-dihydroxyphenylacetic acid at the same pH. Hypothalamic phenolsulfotransferase activity determined using 3,4-dihydroxyphenylacetic acid as substrate was significantly higher in the spontaneously hypertensive than the Wistar Kyoto rats, while pituitary enzyme (determined using phenol as substrate) was the same in both strains of animals. We proposed that in the spontaneously hypertensive rats the higher level of hypothalamic phenolsulfotransferase could (by removing 3,4-dihydroxyphenylacetic acid as sulfated acid) increase the deamination of dopamine by monoamine oxidase. This could in turn result in the presence of high amount of sulfated 3,4-dihydroxyphenylacetic acid in the anterior pituitary gland reported in our earlier study, and be partly responsible for the reduced central dopaminergic activity found in the hypertensive rats.     

Long-Term L-DOPA Treatment Causes Indiscriminate Increase in Dopamine Levels at the Cost of Serotonin Synthesis in Discrete Brain Regions of Rats

(1) The treatment of choice for Parkinson’s disease (PD) is 3,4-dihydroxyphenylalanine (L-DOPA) with peripheral decarboxylase inhibitor, but long-term therapy leads to motor and psychiatric complications. In the present study we investigated 5-hydroxytryptamine (5-HT) and dopamine concentrations in serotonergic and dopaminergic nuclei following chronic administration of L-DOPA to find whether the neurotransmitter synthesis in these brain areas are compensated. (2) Rats were administered L-DOPA (250 mg/kg) and carbidopa (25 mg/kg) daily for 59 and 60 days, and killed on the 60th day, respectively at 24 h and 30 min after the last dose. L-DOPA, norepinephrine, 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), dopamine, homovanillic acid (HVA), and 3,4-dihydroxyphenylacetic acid (DOPAC) were measured in striatum, nucleus raphe dorsalis (NRD), nucleus accumbens (NAc), substantia nigra, cerebellum, and cortex employing HPLC-electrochemical procedure. (3) Prolonged treatment of L-DOPA caused depression in the animals as revealed in a forced swim test. Serotonin content was significantly decreased in all brain regions studied 30 min after long-term L-DOPA, except in NAc. The cortex and striatum showed lowered levels of this indoleamine 24 h after 59 doses of L-DOPA. Dopamine, HVA, and DOPAC concentrations were significantly higher in all the regions studied after 30 min, and in the cerebellum after 24 h of L-DOPA. The levels of DOPAC were elevated in all the brain areas studied 24 h after prolonged L-DOPA treatment. (4) The present results suggest that long-term L-DOPA treatment results in significant loss of 5-HT in serotonergic and dopaminergic regions of the brain. Furthermore, while L-DOPA metabolism per se was uninfluenced, dopamine synthesis was severely impaired in all the regions. The imbalance of serotonin and dopamine formation may be the cause of overt cognitive, motor, and psychological functional aberrations seen in parkinsonian patients following prolonged L-DOPA treatment.     

Age changes in rat vasomotor reflexes and sympathetic neuron ultrastructure following chemical sympathectomy]

Prolonged administration of guanethidine (20 mg/kg) to newborn rats caused a marked reduction in the number of cells in stellate ganglia. The administration of guanethidine for 14 days decreased the amount of cells to 30% of the normal (partial sympathectomy), and for 28 days--to 0.5% (complete sympathectomy). At the age of two months the blood pressure pressor reflexes to asphyxia and femoral nerve stimulation were absent in both groups of the sympathectomized animals. These responses, however, were restored in the partially sympathectomized animals at the age of four months. No restoration took place in the completely sympathectomized animals. The electron microscopic studies of neurons in the partially sympathectomized animals showed the presence of a great number of neurofibrils. According to literature data this fact was typical of cells in which an active growth of axon fibers took place.     

Dopamine release is severely compromised in the R6/2 mouse model of Huntington's disease

Recently, alterations in dopamine signaling have been implicated in Huntington's disease. In this work, dopamine release and uptake was measured in striatal slices from the R6/2 transgenic mouse model of Huntington's disease using fast-scan cyclic voltammetry at carbon-fiber microelectrodes. Dopamine release in brain slices from 6-week-old R6/2 mice is substantially reduced (53% of wild type), while dopamine uptake is unaffected. In agreement with this, R6/2 mice injected with the dopamine uptake inhibitor cocaine exhibited a blunted motor activity response (54% of wild type). At 10 weeks of age, an even more dramatic motor activity decrease in response to cocaine injection (21% of wild type) was observed. Moreover, the pre-drug activity of 10-week-old R6/2 mice was significantly reduced (by 37%) compared with 6-week-old R6/2 mice. Striatal dopamine release decreased with age, indicating that progressive alterations in dopaminergic pathways may affect motor activity. The inhibition constants of cocaine and methamphetamine (METH) determined in brain slices differed little between genotype or age group, suggesting that the decreased responses to cocaine and METH arise from compromised dopamine release rather than differences in uptake or drug action. Collectively, these data demonstrate (i) a reduction in the ability of dopamine terminals to release dopamine and (ii) the importance of this attenuation of release on the motor symptoms of Huntington's disease.     

Histofluorescence studies of monoamine neurons in the rat brain after cobaltous acetate intoxication

The aim was to study changes in brain monoamine neurons in an experimental animal model with an extrapyramidal motor syndrome of the parkinsonian type. The neurological signs were observed in rats after acute cobaltous acetate intoxication under mild ischemic conditions. Histofluorescence studies showed a decrease in catecholamine fluorescence (which signifies a decrease in the amine content) in the hypothalamus and mesencephalic reticular formation, but not in the substantia nigra or basal ganglia. Serotonin fluorescence was increased in nerve cell bodies of the dorsal and median raphe nuclei and in nerve terminals in some thalamic and preoptic regions. Histological staining of sections adjacent to the fluorescent ones showed no neuronal loss and some pathology of myelin. The disturbing effect of cobaltous ions on the neuronal transmission, and/or the imbalance between dopamine and serotonin in the extrapyramidal motor syndrome observed in poisoned rats have been discussed.     

Rapid changes in monoamine levels following administration of corticotropin-releasing factor or corticosterone are localized in the dorsomedial hypothalamus

Monoaminergic systems are important modulators of the neuroendocrine, autonomic, and behavioral responses to stress-related stimuli. The male roughskin newt (Taricha granulosa) was used as a model system to investigate the effects of corticotropin-releasing factor (CRF) or corticosterone administration on tissue concentrations of norepinephrine, epinephrine, dopamine, 3,4-dihydroxyphenylacetic acid, serotonin, and 5-hydroxyindoleacetic acid (5-HIAA) in microdissected brain areas. Intracerebroventricular infusion of 25 or 50 ng of CRF increased locomotor activity and site-specifically increased dopamine concentrations within the dorsomedial hypothalamus 30 min after treatment when compared to vehicle-treated controls. In further studies, male newts were treated as follows: (1) no injection, no handling, (2) saline injection, or (3) 10 microg corticosterone and then placed in a novel environment. Monoamine and monoamine metabolite concentrations were similar in the unhandled and saline-injected controls 20 min after treatment. In contrast, corticosterone-injected newts had elevated concentrations of dopamine, serotonin, and 5-HIAA in the dorsomedial hypothalamus (a region that contains dopamine- and serotonin-accumulating neuronal cell bodies in representatives of all vertebrate classes) but not in several other regions studied. These site-specific neurochemical effects parallel neurochemical changes observed in the dorsomedial hypothalamic nucleus of mammals following exposure to a variety of physical and psychological stress-related stimuli. Therefore, these changes may reflect highly conserved, site-specific neurochemical responses to stress and stress-related neurochemicals in vertebrates. Given the important role of the dorsomedial hypothalamus in neuroendocrine, autonomic, and behavioral responses to stress, and a proposed role for this region in fast-feedback effects of glucocorticoids on the hypothalamo-pituitary-adrenal axis, these stress-related monoaminergic changes are likely to have important physiological or behavioral consequences.