Dopamine In Rat Brain Research Articles

6‐[18F]Fluoro‐L‐DOPA probes dopamine turnover rates in central dopaminergic structures

6-[18F]Fluoro-L-DOPA (FDOPA) cerebral kinetics and metabolism were correlated in normal primates (Macaca nemestrina) and primates with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced unilateral Parkinsonism. Application of a tracer kinetic model to positron emission tomography (PET) data indicated that the model allows reliable estimation of FDOPA blood brain barrier transport, decarboxylation and release of stored 6-[18F]fluorodopamine (FDA) radioactivity in normal striatum (k4 = 0.005/min, turnover half-time greater than or equal to 2 hr), in agreement with biochemical data. PET scans of MPTP treated monkeys revealed 40-50% reduction in total striatal activity in comparison with pre-MPTP scans. Monkey brain biochemical analysis revealed that the reduction in activity was mainly due to a decrease in FDA and its metabolites, 6[18F]fluorohomovanillic (FHVA) and 6-[18F]fluoro-3, 4-dihydroxyphenylacetic acid (FDOPAC). The remaining activity in tissue was 3-0-methyl-6-[18F]fluoro-L-DOPA (3-OMFD) of peripheral origin. The (FHVA + FDOPAC)/FDA ratio was 1:2 in normal putamen and greater than or equal to 6:1 in the lesioned putamen, indicative of a dramatic increase in turnover of FDA. Both kinetic and biochemical data indicate that FDOPA labels a slow turnover rate pool of dopamine in rat and primate brain. This turnover rate for stored dopamine (DA) is accelerated with dopaminergic cell losses (e.g., MPTP-induced Parkinsonism).

In vivo interaction of cabergoline with rat brain dopamine receptors labelled with [ 3H]N-n-propylnorapomorphine

Cabergoline is a potent dopaminergic agent that interacts with agonists and antagonists of dopamine receptors in vitro. We studied the binding of [ 3H]N-n-propylnorapomorphine ([ 3H]NPA) to dopamine receptors after i.v. and oral administration of cabergoline to determine whether cabergoline crosses the blood-brain barrier; bromocriptine was used as a reference drug. Cabergoline and/or its active metabolite(s) did cross the blood-brain barrier and reach dopamine receptors. Comparative time-course analysis of the regional inhibition of [ 3H]NPA binding showed that cabergoline was more potent than bromocriptine in inhibiting [ 3H]NPA binding and that it occupied the receptor for longer. These effects were observed in all areas of the rat brain studied (striatum, olfactory tubercles, adeno- and neurohypophysis, thalamus and hypothalamus). Further studies in the striatum and adenohypophysis showed that cabergoline receptor occupancy was dose-dependent and still detectable 72 h after i.v. administration of the drug. While cabergoline was more potent in the striatum than in the adenohypophysis when administered i.v., the reverse administration, as determined 1 and 8 h later.

The effect of amperozide on uptake and release of [3H]‐dopamine in vitro from perfused rat striatal and limbic brain areas

Amperozide, a putatively antipsychotic drug, was studied for its effects on uptake and release of [3H]-dopamine in rat brain in vitro. Amperozide inhibited uptake of [3H]-dopamine in striatal chopped tissue in vitro with an IC50 of 18 microM. It also increased basal release of [3H]-dopamine from perfused rat striatal and limbic tissue in vitro at concentrations above 5 microM. Release of [3H]-dopamine from perfused rat striatal and limbic tissue stimulated with 5 microM amphetamine, was inhibited by 1 microM amperozide to 46%. No significant difference was found for the effect of amperozide on in vitro release of [3H]-dopamine from corpus striatum compared to tissue from limbic brain regions; neither on basal release nor an amphetamine-stimulated release of dopamine.

Chronic treatment with clozapine or haloperidol differentially regulates dopamine and serotonin receptors in rat brain

Long-term administration of the atypical neuroleptic clozapine (CLZ) poses a much lower risk of extrapyramidal side effects (EPS) than does the use of typical neuroleptics such as haloperidol (HAL). To investigate the neural mechanisms of the differing CNS activities of these two drugs, we used quantitative autoradiography to measure changes in dopamine and serotonin receptors in rats after injection with CLZ or HAL for 21 days at clinically relevant dose ratios. Levels of D1, D2, and 5-HT2 receptors were determined in frontal cortex, caudate-putamen, and nucleus accumbens. Rats that received CLZ chronically showed CNS receptor changes markedly different from those in chronic HAL-treated animals. Whereas rats treated chronically with HAL showed enhanced striatal D2 binding (average increase of 42%), those treated with CLZ did not. In contrast, chronic CLZ, but not chronic HAL, induced enhanced striatal D1 binding (average increase of 43%). Finally, CLZ treatment decreased 5-HT2 receptor binding by an average of 37%, while HAL had no significant effect. The effects of chronic HAL or CLZ treatment on receptors were similar in all forebrain areas examined. However, since D1 and 5-HT2 receptors are more abundant than D2 sites in limbic and neocortical areas, the preferential modulation of D1 and 5-HT2 receptors by CLZ suggests a greater impact of this atypical neuroleptic on activity of the limbic system than that achieved by the typical neuroleptic, HAL. These findings suggest that the clinical profile of atypical neuroleptics such as CLZ may be attributed to their effects on a receptor profile differing in pharmacological characteristics and anatomical distribution from that affected by typical neuroleptics.

Cognition enhancement by the acetylcholine releaser DuP 996

AbstractDuP 996, 3,3,‐Bis(4‐pyridinylmethyl)‐1‐phenylindolin‐2‐one, a potent in vitro and in vivo releaser of acetylcholine (ACh), dopamine (DA), and serotonin (5HT) in rat brain, significantly enhanced the performance of rats and mice in several behavioral test procedures. At doses of 0.01–0.1 mg/kg s.c. DuP 996 protected against a hypoxia‐induced passive avoidance deficit in rats. In active avoidance procedures, DuP 996 enhanced acquisition of responses: in rats, at doses between 0.085 and 0.85 mg/kg s.c. and 0.25 and 0.85 mg/kg p.o.; in mice, at doses between 0.85 and 2.5 mg/kg s.c. These effects occurred without any alteration of sensitivity to foot‐shock. In addition, Dup 996 prevented a CO2‐induced retention deficit of a passive avoidance response when administered prior to acquisition testing. In a test for acquisition of lever pressing for food in the rat, DuP 996 increased the proportion of animals acquiring this response. Thus, DuP 996 was active in both the shock‐ and appetitive‐motivated procedures and was shown to enhance performance levels when administered post‐training as well as before training trials. These results suggest that DuP 996 may be useful in the treatment of cognition dysfunction.

Methylphenidate and pemoline do not cause depletion of rat brain monoamine markers similar to that observed with methamphetamine

Methyl-phenidate (Ritalin) and pemoline (Cylert) are central nervous system stimulants which are widely prescribed for attention deficit and other psychiatric disorders. Several other related stimulants, including amphetamine and methamphetamine, have been shown to cause long lasting decreases in monoamine markers in rat brain, characteristic of axonal degeneration. To assess the neurotoxic potential of methylphenidate and pemoline, we compared the effects of multiple injections (sc, bid for up to 4 days) of methylphenidate (21 and 50 mg/kg) and pemoline (20 and 70 mg/kg) with methamphetamine (5 and 15 mg/kg) on rat brain norepinephrine, dopamine, and serotonin levels and transport sites. While decreases were observed in all brain monoamine markers measured in rats treated with methamphetamine, no changes were observed in animals treated with methylphenidate as compared to saline-treated controls. Pemoline failed to induce significant changes in the level of monoamine transport sites; however, a wide array of changes were observed in the levels of 5-hydroxyindoleacetic acid, dopamine, and norepinephrine in various brain areas after a 3-day treatment regimen with a high dose (70 mg/kg) of pemoline. The lack of changes in monoamine transport sites following the repeated administration of high doses of methylphenidate and pemoline suggests that these drugs do not affect axonal integrity. However, the pattern of changes observed in the levels of monoamines after pemoline treatment may have relevance to the self-injurious behavior seen in these animals.

Synthesis and Release of Dopamine in Rat Brain: Comparison Between Substantia Nigra Pars Compacta, Pars Reticulata, and Striatum

Dopamine (DA) is synthesized and released not only from the terminals of the nigrostriatal dopaminergic neuronal pathway, but also from the dendrites in the substantia nigra. We have investigated the regulation of the DA turnover, the DA synthesis rate, and the DA release in the substantia nigra pars compacts (SNpc) and pars reticulata (SNpr) in vivo. As a measure of DA turnover, we have assessed the concentrations of 3,4-dihydroxyphenylacetic acid and homovanillic acid. As a measure of the DA synthesis rate, we have determined the 3,4-dihydroxyphenylalanine accumulation after inhibition of aromatic L-amino acid decarboxylase by 3-hydroxybenzylhydrazine. As a measure of DA release, we have investigated the disappearance rate of DA after inhibition of its synthesis by alpha-methyl-p-tyrosine and the 3-methoxytyramine accumulation following monoamine oxidase inhibition by pargyline. Both the DA turnover and the DA synthesis rate increased following treatment with the DA receptor antagonist haloperidol and decreased following treatment with the DA receptor agonist apomorphine in the SNpc and in the SNpr, but the effects of the drugs were less pronounced than in the striatum. gamma-Butyrolactone treatment, which suppresses the firing of the dopaminergic neurons, increased the DA synthesis rate in the striatum (165%), but had no such effect in the SNpc or SNpr. Haloperidol, apomorphine, and gamma-butyrolactone increased, decreased, and abolished, respectively, the DA release in the striatum, but the drugs had no or only slight effects on the alpha-methyl-p-tyrosine-induced DA disappearance and on the pargyline-induced 3-methoxytyramine accumulation in the SNpc or SNpr. Taken together, these results indicate that the DA synthesis rate, but not the DA release, are influenced by DA receptor activity and neuronal firing in the SNpc and SNpr. This is in contrast to the situation in the striatum, where both the DA synthesis rate and the DA release are under such control.

Effects of CI-926 (3-[4-[4-(3-Methylphenyl)-l-Piperazinyl] Butyl]-2,-4-Imidazolidinedione), an Antihypertensive Agent, on Rat Brain Catecholamine and Serotonin Turnover

The effects of the antihypertensive drug CI-926 on rat brain norepinephrine (NE), dopamine (DA), and serotonin (5-HT) turnover and its in vitro affinity for several receptors were investigated. CI-926 (3-30 mg/kg intraperitoneally, i.p.) caused a dose-dependent increase in the rate of brain stem NE synthesis and increased the decline in NE after inhibition of its synthesis by alpha-methyl-p-tyrosine. These findings indicated that CI-926 increased brain NE turnover, probably as a compensatory response to central adrenoceptor blockade based on its nanomolar affinity for alpha 1-adrenoceptors and micromolar affinity for alpha 2-adrenoceptors. CI-926 also increased the rate of DA synthesis and DA metabolite levels; this indicates an increase in DA turnover. The latter effect of CI-926 is attributed to a compensatory response to DA-2 receptor blockade because no affinity for DA-1 relative to DA-2 receptors was found and the effect was antagonized by the DA agonist pergolide. CI-926 decreased brain 5-HT turnover, as indicated by reduced concentrations of the 5-HT metabolite 5-hydroxyindoleacetic acid and a reduced rate of 5-HT synthesis, effects characteristic of centrally acting 5-HT agonists. Based on its affinity for 5-HT-1A receptors versus 5-HT-1B and 5-HT-2, the decrease in 5-HT synthesis and release is interpreted as evidence of 5-HT-1A receptor activation. These findings indicate that besides peripheral alpha 1-adrenergic blockade, an interference of CI-926 with central adrenergic and serotoninergic neurotransmission may contribute in part to an explanation of its antihypertensive properties.

Dopamine D 2 and muscarinic receptor binding characteristics in rat brain after withdrawal of subchronic fluphenazine and sulpiride treatment

1. The effects of subchronic (10 days) treatment with two antischizophrenic drugs, fluphenazine and sulpiride, on rat brain dopamine and muscarinic receptor sites were studied at various time points after withdrawal from the drug treatments. Striatal D-2 dopamine receptors and cortical muscarinic receptors were characterized with the radioligands 3H-spiperone and 3H-quinuclidinyl benzilate ( 3HQNB), respectively. 2. Neither drug treatment affected significantly the number or affinity of cortical muscarinic receptors during the withdrawal time of 18 days. 3. The number of D-2 receptors in striatum was not altered after 4 or 8 fluphenazine-free days, but after 18 days fluphenazine caused an increase of 55 % in the density of D-2 receptors. Sulpiride caused a slight increase in Bmax of striatal D-2 receptors after 4 and 8 withdrawal days but the maximum increase of 29 % was observed after 18 withdrawal days. 4. Fluphenazine treatment caused an increase in the apparent dissociation constant 4 days after the termination of the treatment suggesting that residual neuroleptic levels may have been retained after this dose regimen, since the Kd returned near control levels as the withdrawal time passed. Sulpiride, however, caused a moderate increase in Kd throughout the withdrawal time. 5. In conclusion, these results suggest that even a rather short treatment with fluphenazine or sulpiride, a classical and an atypical neuroleptic, respectively, can induce pronounced changes in striatal dopamine receptor characteristics after a drug washout period of almost three weeks. Thus, possible delayed actions of classical as well as novel neuroleptic drugs on neurotransmitter function should be considered in studies examining the neuroleptic withdrawal effects.

Formula omitted] release of dopamine, acetylcholine, and cholecystokinin in rat brain under freely moving condition : Takeshi Kato, Department of Life Chemistry, Tokyo Institute of Technology, Yokohama 227, Japan

formula omitted] release of dopamine, acetylcholine, and cholecystokinin in rat brain under freely moving condition : Takeshi Kato, Department of Life Chemistry, Tokyo Institute of Technology, Yokohama 227, Japan

Effects of acute and subacute administration of bicuculline on dopamine and muscarinic receptors in rat brain

The changes of characteristics of dopamine (D1 and D2) and muscarinic receptors after acute and subacute administration of bicuculline were examined in rat brain. The results demonstrated that in striatal region, the B max of D2 receptor was significantly increased with no change of affinity after subacute administration of bicuculline. However, neither B max nor K d or the D2 receptor was changed after single administration. The characteristics of D1 receptor were not changed by either acute or subacute administration. The B max of muscarinic receptor in striatal area was significantly increased without changes of affinity after both a single and repeated administration of bicuculline. However, in hippocampus, the B max of muscarinic receptor was significantly decreased after subacute administration of bicuculline. The results suggest that the interactions among GABAergic, dopaminergic and cholinergic neuron exist in central nerve system.

Decrease in the number of rat brain dopamine and muscarinic receptors after chronic alcohol intake.

The effect of 32 weeks' alcohol treatment on the number and affinity of dopamine and muscarinic receptor sites in rat striatum were measured using 3H-spiperone and 3H-quinuclidinylbenzilate (3H-QNB) as radioligands. The number of dopamine receptor sites was 38 per cent and the number of muscarinic receptor sites 36 per cent lower in the alcohol group than in control rats. The differences in receptor affinities were less marked. In conclusion, a long-term alcohol intake with rather moderate doses seems to induce a pronounced down-regulation in dopamine and muscarinic receptor systems in rat striatum.

N,N-Dialkylated monophenolic trans-2-phenylcyclopropylamines: novel central 5-hydroxytryptamine receptor agonists.

N,N-Dialkylated monophenolic derivatives of trans-2-phenylcyclopropylamine were synthesized and tested for central 5-hydroxytryptamine (5-HT) and dopamine (DA) receptor stimulating activity by use of a biochemical test method in rats. A hydroxy substituent in the 2- or 3-position of the phenyl ring was required for 5-HT-receptor stimulation. N,N-Diethyl or N,N-di-n-propyl substitution gave the most potent 5-HT-receptor agonists. The 4-hydroxy and 3,4-dihydroxy derivatives of trans-2-phenyl-N,N-di-n-propylcyclopropylamine were inactive at central DA and 5-HT receptors. In contrast, the corresponding 3-hydroxy derivative 18 and some of its derivatives weakly affected both DA and NE synthesis. Two of the most potent 5-HT-receptor agonists, trans-2-(2-hydroxyphenyl)-N,N-di-n-propylcyclopropylamine (8) and the 3-hydroxy isomer 18 were resolved into the enantiomers. The 1R,2S enantiomers of 8 and 18 displayed 5-HT activity, while the 1S,2R enantiomers were inactive. Compound (1R,2S)-18, but not (1R,2S)-8, weakly affected rat brain DA and NE synthesis.

Monoclonal antibodies against glutaraldehyde-conjugated dopamine.

Four mice were immunized with dopamine (DA)-glutaraldehyde (G)--protein conjugates over a period of 8-10 weeks. Polyclonal antisera, obtained at various intervals, were tested using an enzyme-linked immunosorbent assay (ELISA). All had anti-conjugated DA antibodies. As soon as good antibody affinity was detected between 10(-10) and 10(-6) M, the mouse yielding the highest apparent affinity was killed, and the spleen was dissected out. Hybridomas were obtained from spleen cells fused with SP2/O/Ag myeloma cells. Supernatant culture media of hybridomas were tested for the presence of anti-conjugated DA antibodies with the ELISA method. Selected hybridomas giving good antibody affinity and specificity were then cloned by the limiting dilution technique. The resulting supernatant culture media were again tested by ELISA. Clones that gave a high antibody affinity (10(-10)-10(-8)M) for G-conjugated DA were used for histochemical localization of DA in rat brain. G-fixed rat brains were sectioned from the telencephalon to the mesencephalon, reduced with sodium borohydride, and prepared for peroxidase-antiperoxidase immunocytochemistry using supernatant (diluted 1:100) or ascites fluid (diluted 1:50,000). Dense networks of very fine fibers were observed in the striatum, septum, and cortex. Numerous immunoreactive cell bodies were found in the ventral tegmental area, the substantia nigra, the hypothalamus, and the dorsal raphe. The ELISA tests and adsorption controls suggested that the monoclonal antibody allowed highly specific detection of DA in tissues.

Effect of combined exposure to lead and ethanol on some biochemical indices in the rat

We investigated the effect of daily oral administration to young rats of lead (10 mg/kg) and ethanol (10%, v/v, in drinking water), either alone or in combination, for 8 weeks on the uptake of lead in tissues, brain biogenic amines, hepatic alcohol dehydrogenase and cytosolic and mitochondrial aldehyde dehydrogenase and some selected lead-sensitive variables. Lead given in combination with ethanol produced more pronounced inhibition in the activities of hepatic glutamic oxalacetic transaminase (GOT) and glutamic pyruvic transaminase (GPT) as compared to lead alone treatment. Simultaneous exposure to lead and ethanol produced a greater depression of dopamine (DA) and 5-hydroxytryptamine (5-HT) levels in the whole brain of rats, compared to rats treated with lead alone. The concentrations of lead in blood, liver and brain were significantly higher in rats exposed simultaneously to lead and ethanol. Though ethanol treatment alone inhibited the activities of hepatic alcohol dehydrogenase and cytosolic and mitochondrial aldehyde dehydrogenase, no effect of lead treatment alone on these variables was observed. The results suggested that animals exposed to ethanol and lead are more vulnerable to the neurologic and hepatotoxic effects and the systemic toxicity of lead.

Supplemental dietary tyrosine in sepsis and acute hemorrhagic shock.

Previous studies showed that dopamine and norepinephrine levels in rat brain are reduced following stress and that rats fed supplemental tyrosine do not exhibit these reductions. We hypothesized that dietary supplementation with tyrosine would enhance resistance to acute hemorrhagic shock and sepsis by increasing substrate (tyrosine) availability for catecholamine synthesis. Rats were fed either a standard rat chow (6.8 g of tyrosine per kilogram of chow), which supports normal growth, fertility, and longevity, or the same chow supplemented with 10 g of tyrosine per kilogram of chow. Seven days later, the rats underwent cecal ligation and perforation while under intraperitoneal pentobarbital anesthesia. There was a significant increase in survival in the tyrosine-supplemented group. Similarly, in another experiment, tyrosine-supplemented rats were able to tolerate acute fulminant hemorrhagic shock better than were nonsupplemented control animals.

3H]-domperidone labels only a single population of receptors which convert from high to low affinity for dopamine in rat brain.

Dopamine recognized and competed for a single population of [3H]-domperidone-binding sites in rat striatum and olfactory tubercle when tested in the presence of sodium ions and guanine nucleotide [Gpp(NH)p]. In the absence of Na+ and Gpp(NH)p, however, dopamine recognized two components of [3H]-domperidone binding. Thus, [3H]-domperidone labelled only a single population of dopamine receptors (type D2) which fully converted from high to low affinity for dopamine. These results agree with those found previously using [3H]-spiperone and [3H]-YM-09151-2.

Alteration of the turnover of dopamine and 5-hydroxytryptamine in rat brain associated with hypothermia

The alteration of monoamines and their metabolites in the brain in response to hypothermia was studied using rats subjected to a cold and immobilization stress. The experiments were designed to compare the responses in the “hypothermal” rats with those in the “normothermal” ones which received the same stress except for the change in body temperature. It has been found that the contents of norepinephrine (NE) and 5-hydroxytryptamine (5-HT) in various cerebral regions were significantly decreased during hypothermia. These decreases were readily reversed by the rewarming of animals. Moreover, the increase in the content of 5-hydroxyindole-3-acetic acid (5-HIAA), the metabolite of 5-HT, was also detected in some cerebral regions where the decrease of 5-HT was observed. Although the dopamine (DA) contents in all cerebral regions examined were found to be unaltered, its metabolites, 3,4-dihydroxyphenlacetic acid (DOPAC) and/or homovanillic acid (HVA) contents in most regions in the brain showed a significant elevation elevation during and/or after the occurrence of hypothermia. These results suggest that the metabolic turnovers of 5-HT and DA in various cerebral regions may be accelerated during hypothermia.

Development of specificity and stereoselectivity of rat brain dopamine receptors

Prenatal exposure to the neuroleptic haloperidol has been reported to produce an enduring decrement in the number of dopamine D2 receptors in rat striatum and a persistent diminution of a dopamine dependent behavior, stereotypy.17 The ontogeny of rat brain dopamine binding sites has been studied in terms of the kinetic properties and phenotypic specificity in rat fetal brain through early postnatal development. Sites showing some properties of the D2 binding site can be found prior to gestational day (GD) 18, can be labeled with [3H]dopamine or [3H]spiroperidol and can he displaced with dopaminergic agonists and antagonists.5 Saturation kinetics for specific [3H]spiroperidol has previously been found to occur on or about GD 18.1.5 It is of interest that the critical period for the prenatal effect of haloperidol to reduce striatal D2 binding sites. CD's 15–18.18 coincides with the period during which dopamine binding sites lack true specificity, but can be labeled with dopaminergic ligands.In these experiments the development of stereoselectivity of brain dopamine binding sites has been examined. When rat mothers were given either the neuroleptic (+)-butaclamol or its therapeutically inactive isomer (−)-butaclamol during the critical period CD's 15–18. the number of [3H]spiroperidol binding sites in striata of offspring was significantly reduced by both stereoisomers. This is in marked contrast to the postnatal treatment effect by a neuroleptic in which upregulation of striatal D2 binding sites occurs only by treatment with the therapeutically active isomer (+)-butaclamol. In vitro studies of the direct effect of the stereoisomers of butaclamol indicate that the recognition sites detected during fetal brain development with [3H]spiroperidol do not distinguish between the isomers of butaclamol. The point at which stereoselectivity is apparent also appears to be the point at which the prenatal neuroleptic effect is no longer operative and the mature response to increase the number of dopamine binding sites occurs.

Brain dopamine and serotonin receptor sites revealed by digital subtraction autoradiography.

Autoradiography combined with image analysis permitted quantitative visualization of dopamine (D2) and serotonin (S2) binding sites in rat brain. Forebrain sections were incubated with tritiated spiroperidol alone or with tritiated spiroperidol plus unlabeled compounds that saturated the D2 or S2 sites. By subtracting the digitized image of an autoradiograph derived from the latter sections from that of the former, the D2 or S2 sites were specifically revealed. The resulting quantitative images demonstrate the differing anatomical distributions of these sites. The D2 site is largely restricted to the striatal complex (caudate-putamen, nucleus accumbens septi, and olfactory tubercle), whereas the S2 site is enriched in layer 5 of motor cortex, the perirhinal and cingulate cortices, and the claustrum.