Dopamine And 3,4-dihydroxyphenylacetic Acid Research Articles

Nerve growth factor increases survival of dopaminergic graft, rescue nigral dopaminergic neurons and restores functional deficits in rat model of Parkinson's disease

In the present study, an attempt has been made to explore the neuroprotective and neurorescue effects of nerve growth factor (NGF) on grafted cells and on host nigral dopaminergic neurons, respectively. NGF was co-transplanted with fetal ventral mesencephalic cells (VMC) in the striatum of 6-hydroxydopamine (6-OHDA) lesioned rat model of Parkinson's disease (PD). In the other groups fetal VMC and NGF were transplanted alone. Twelve weeks post-transplantation, a significant restoration was observed in d-amphetamine induced rotations (stereotypy), spontaneous locomotor activity, striatal and nigral dopamine (DA) and 3,4-dihydroxy-phenyl acetic acid (DOPAC) levels in co-transplanted rats as compared to VMC alone transplanted rats. Higher number of surviving tyrosine hydroxylase immunoreactive (TH-ir) neurons and significantly increased fiber outgrowth from graft was evident in co-transplanted rats as compared to VMC alone transplanted rats. Further, a significant increase was also observed in substantia nigra TH-ir neurons count in co-transplanted rats, exhibiting a potential neuroprotective and neurorescue effects of NGF on nigrostriatal dopaminergic neurons. The results suggest that NGF at the time of transplantation exhibits neuroprotective effect on transplanted VMC as well as neurorescue effect on remaining host nigral dopaminergic neurons, leading to better functional restoration.

Effect of estrogen upon methamphetamine-induced neurotoxicity within the impaired nigrostriatal dopaminergic system

In the present study, we investigated whether estrogen remains effective as a neuroprotectant within an impaired nigrostriatal dopaminergic (NSDA) system of gonadectomized female and male mice. In Experiment 1, mice were treated with four different regimens of methamphetamine (MA) to establish a protocol for an impaired NSDA system to be used in subsequent experiments. Based upon the results of Experiment 1, in Experiment 2 gonadectomized female mice received a treatment with either control (saline), low- or high-dose of MA to produce an initial NSDA impairment. At one week post-MA, mice received either estradiol benzoate (10 microg) or vehicle followed 24 h later with low-MA or saline. Estrogen altered the toxic effects of the second invasion of MA as indicated by a significant decrease in striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations. In addition, DA and DOPAC depletion was greater in high- vs. low-dose MA. In gonadectomized male mice (Experiment 3), striatal DA and DOPAC concentrations showed greater decreases following high-, vs. low-doses of MA; however, estrogen did not alter these responses. These results demonstrate that the capacity for estrogen to protect or worsen MA-induced neurotoxicity of dopaminergic neurons is limited to female mice and depends on the condition of the NSDA system.

Effect of MAO A knockout on catecholamines in mouse brain regions: dopamine and norepinephrine in the cortex are unaffected by MAO A deficiency

The effect of a lack of the gene encoding monoamine oxidase A (MAO A) in transgenic Tg8 mice on the levels of norepinephrine (NE), dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the midbrain, hypothalamus, hippocampus, striatum, amygdala, and frontal cortex was studied. It was shown that mice with a genetic MAO A knockout differed from those of the initial C3H/HeJ strain by a higher level of NE in all brain regions but the frontal cortex. The increased dopamine level in the striatum, a lower level of its metabolite DOPAC and decreased DOPAC/DA ratio in the midbrain, hypothalamus, hippocampus, and striatum of Tg8 mice was found. There were no changes in the DOPAC level or in the DOPAC/DA ratio in the frontal cortex and amygdala.The substantial (2.4 to 4.8-fold) decrease in the level of DOPAC in the midbrain, hypothalamus, hippocampus, and striatum shows significant impairment of dopamine oxidative deamination in MAO A-knockout mice. At the same time, the lack of any changes in the dopamine level in most of brain regions studied indicates rather effective compensation of the deficit in DA metabolism in Tg8 mice and explains the lack of severe behavioral and pathological consequences in MAO A genetic deficiency. The data show that DA and NE metabolism in brain regions is differently affected by the MAO A deficiency, and that catecholamines in the mouse frontal cortex are unaffected by the lack of MAO A. The results suggest that in different brain regions the relative roles of MAO A, MAO B and COMT in metabolism of catecholamines are different.

Ascorbate reduces morphine-induced extracellular DOPAC level in the nucleus accumbens: A microdialysis study in rats

Most drugs of abuse increase dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) release in the shell of the nucleus accumbens. The effects of ascorbate, which is known to modulate dopamine neurotransmission, on the extracellular level of DOPAC in the nucleus accumbens of naive rats and of rats treated acutely with morphine were studied by using in vivo microdialysis and high performance liquid chromatography with electrochemical detection (HPLC-ECD). Acute morphine (20 mg/kg ip) treatment increased the level of DOPAC in the nucleus accumbens to approximately 170% of basal level. Acute treatment with ascorbate (500 mg/kg ip) alone did not alter nucleus accumbens' DOPAC level, but pretreatment with ascorbate (500 mg/kg ip) 30 min before morphine administration attenuated the effects of acute morphine on the level of DOPAC. These results suggest that ascorbate modulates the mesolimbic dopaminergic pathway.

Gender differences in modulatory effects of tamoxifen upon the nigrostriatal dopaminergic system

It has been demonstrated that the gonadal steroid hormone estrogen can exert neuroprotective effects upon the nigrostriatal dopaminergic (NSDA) system against methamphetamine (MA)-induced neurotoxicity in female, but not male, mice. In contrast, the anti-estrogen, tamoxifen (TMX) can function as a NSDA neuroprotectant within both female and male mice. In an attempt to understand these effects of TMX, the effects of this anti-estrogen upon both behavioral and neurochemical indices of NSDA function were examined within female and male mice following treatment with MA. In general, TMX exerted markedly different (bi-directional) effects upon NSDA function between female and male mice. Notably, treatment with TMX resulted in a relative decrease in striatal dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations within male mice and a relative increase in female mice when treated with MA to produce a significant gender difference. Similar effects were obtained for locomotor behaviors related with NSDA function. That is, TMX produced increases in horizontal activity, number of movements and total distance traveled within MA-treated female mice resulting in statistically significant gender differences for the two former parameters. For non-locomotor behaviors, like time occupying the center and margin of the cage, TMX-treated male mice showed statistically significant increases and decreases compared within TMX-treated female mice, respectively. These results show that in contrast to the similar neuroprotective effects of TMX upon MA-induced NSDA neurotoxicity, a number of other NSDA indices induced by MA show markedly different response profiles between TMX-treated female and male mice.

Neuroprotective effect of the angiotensin-converting enzyme inhibitor perindopril in MPTP-treated mice

The angiotensin -converting enzyme (ACE) inhibitor perindopril has been shown to exert benefical effects on the dopaminergic system. Here, we investigated the effects of perindopril on the dopaminergic system in mice after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment, in comparison with a Ca2+ antagonist, amlodipine. Administration of perindopril showed dose-dependent neuroprotective effects against MPTP-induced striatal dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) depletion. However, administration of amlodipine showed no significant effects on striatal dopamine depletion after MPTP treatment. In our immunohistochemical studies with antibodies against tyrosine hydroxylase (TH), microtubule-associated protein 2a, b (MAP2), dopamine transporter (DAT), parvalbumin (PV), glial fibrillary acidic protein (GFAP) and Cu/Zn-superoxide dismutase (Cu/Zn-SOD), the administration of perindopril significantly attenuated MPTP-induced substantia nigra and striatal damage. This drug also blocked the increases in GFAP-positive astrocytes in the striatum and substantia nigra after MPTP treatment. Furthermore, the administration of perindopril showed a protective effect against the intense Cu/Zn-SOD immunoreactivity in the neurons and glial cells in both the striatum and substantia nigra after MPTP treatment. These results indicated that the ACE inhibitor perindopril can protect against MPTP-induced striatal dopamine and DOPAC depletion in mice. The protective effect may be, at least in part, caused by the reduction of free radicals caused by MPTP. The present study also demonstrated that perindopril is effective against MPTP-induced neurodegeneration of the nigro-striatal dopaminergic pathway. Furthermore, our results provided further evidence that free radical scavengers may be effective in the treatment of neurodegenerative diseases such as Parkinson's disease.

Effect of angiotensin-converting enzyme inhibitor perindopril on interneurons in MPTP-treated mice

We examined the effects of perindopril on the dopaminergic system in mice after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. The mice received four intraperitoneal injections of MPTP at 1-h intervals. Administration of perindopril showed dose-dependent neuroprotective effects against striatal dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) depletion 3 days after MPTP treatment. Our immunohistochemical study showed that MPTP can severe damage in tyrosine hydroxylase (TH)-immunoreactive neurons after MPTP treatment. The administration of perindopril significantly attenuated MPTP-induced substantia nigra and striatal damage. The present study also showed that the immunoreactivity of parvalbumin (PV)- or neuronal nitric oxide synthase (nNOS)-positive cells in the substantia nigra was decreased 7 days after MPTP treatment, whereas no significant changes were observed in these cells of the striatum throughout the experiments. The administration of perindopril significantly attenuated MPTP-induced decrease of the PV- or nNOS-immunoreactivity in the nigral cells. In double-labeled immunostaining with anti-PV and anti-nNOS antibody, PV-immunoreactive cell bodies and fibers were not double-labeled for nNOS-immunoreactive cell bodies and fibers in both the striatum and substantia nigra after MPTP treatment. Furthermore, PV- or nNOS-immunoreactive cell bodies and fibers in both the striatum and substantia nigra were not double-labeled for TH-immunoreactive cell bodies and fibers. These results demonstrate that the ACE inhibitor perindopril has a dose-dependent protective effect against MPTP-induced striatal dopamine, DOPAC and HVA depletion in mice. The present study also demonstrates that perindopril is effective against MPTP-induced degeneration of the nigral neurons and interneurons. Furthermore, our immunohistochemical study suggests that PV-immunoreactive cells and nNOS-immunoreactive cells are different interneurons in both the striatum and substantia nigra. Thus, our results provide further evidence that the ACE inhibitor perindopril may offer a novel therapeutic strategy for Parkinson's disease (PD).

Cerebrospinal fluid monoamine and metabolite concentrations and aggression in rats

In humans and other primates low cerebrospinal fluid (CSF) levels of the major serotonin (5-HT) metabolite 5-hydroxyindoleacetic acid (5-HIAA) have been correlated to high aggressiveness. This finding forms the basis of the 5-HT deficiency hypothesis of aggression. Surprisingly, this correlation has not been confirmed in rodents so far, while manipulation studies aimed to investigate the link between 5-HT and aggressive behaviour are mostly carried out in rodents. In this study the relation between aggression and CSF monoamine and metabolite concentrations was investigated in male Wildtype Groningen rats. In sharp contrast to the hypothesis and our expectation, a clear positive correlation was found between the individual level of trait-like aggressiveness and CSF concentrations of 5-HT, 5-HIAA, norepinephrine (NE), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOPAC). Shortly after the acute display of aggressive behaviour (as a state-like phenomenon), decreased 5-HT levels and an increase in 5-HIAA/5-HT ratio and NE concentrations were found. Surprisingly, pharmacological challenges known to influence 5-HT transmission and aggressive behaviour did not affect CSF 5-HT and 5-HIAA concentrations, only the NE level was increased. Lesioning 5-HT terminals by 5,7-dihydroxytryptamine (5,7-DHT) administration caused a decrease in CSF 5-HT and 5-HIAA, but without affecting aggressive behaviour. The observed positive correlation between CSF 5-HIAA and trait aggressiveness makes it questionable whether a direct extrapolation of neurobiological mechanisms of aggression between species is justified. Interpretation of CSF metabolite levels in terms of activity of neural substrates requires a far more detailed knowledge of the dynamics and kinetics of a neurotransmitter after its release.

Alpha-1B adrenergic receptor knockout mice are protected against methamphetamine toxicity.

The psychostimulant methamphetamine (MA) is toxic to nigro-striatal dopaminergic terminals in both experimental animals and humans. In mice, three consecutive injections of MA (5 mg/kg, i.p. with 2 h of interval) induced a massive degeneration of the nigro-striatal pathway, as reflected by a 50% reduction in the striatal levels of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC), by a substantial reduction in striatal tyrosine hydroxylase and high-affinity DA transporter immunostaining, and by the development of reactive gliosis. MA-induced nigro-striatal degeneration was largely attenuated in mice lacking alpha1b-adrenergic receptors (ARs). MA-stimulated striatal DA release (measured by microdialysis in freely moving animals) and locomotor activity were also reduced in alpha1b-AR knockout mice. Pharmacological blockade of alpha-adrenergic receptors with prazosin also protected wild-type mice against MA toxicity. These results suggests that alpha1b-ARs may play a role in the toxicity of MA on nigro-striatal DA neurons.

Effect of one-week ethanol treatment on monoamine levels and dopaminergic receptors in rat striatum.

We studied the effects of ethanol on the levels of norepinephrine, dopamine, serotonin (5-HT) and their metabolites as well as on D1- and D2-like receptors in the rat striatum. Ethanol (2 or 4 g/kg, po) was administered daily by gavage to male Wistar rats and on the 7th day, 30 min or 48 h after drug administration, the striatum was dissected for biochemical assays. Monoamine and metabolite concentrations were measured by HPLC and D1- and D2-like receptor densities were determined by binding assays. Scatchard analyses showed decreases of 30 and 43%, respectively, in D1- and D2-like receptor densities and no change in dissociation constants (Kd) 48 h after the withdrawal of the dose of 4 g/kg. Ethanol, 2 g/kg, was effective only on the density of D2-like receptors but not on Kd of either receptor. Thirty minutes after the last ethanol injection (4 g/kg), decreases of D2 receptor density (45%) as well as of Kd values (34%) were detected. However, there was no significant effect on D1-like receptor density and a 46% decrease was observed in Kd. An increase in dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC), a decrease in norepinephrine, and no alteration in 5-HT levels were demonstrated after 48-h withdrawal of 4 g/kg ethanol. Similar effects were observed in dopamine and DOPAC levels 30 min after drug administration. No alteration in norepinephrine concentration and a decrease in 5-HT levels were seen 30 min after ethanol (4 g/kg) administration. Our findings indicate the involvement of the monoaminergic system in the responses to ethanol.

N-methyl-norsalsolinol modulates serotonin metabolism in the rat caudate nucleus: correlation with behavioural changes.

In earlier studies the dihydroxylated tetrahydroisoquinoline derivative 2(N)-methyl-norsalsolinol (NMNorsal) was identified in patients with Parkinson's disease. In the present study, NMNorsal (20 or 40 mg/kg) was given intraperitoneally to rats kept under normal light-dark cycles. Using brain microdialysis technique, serotonin (5-HT), 5-hydroxyindolacetic acid (HIAA), dopamine (DA), and 3,4-dihydroxyphenylacetic acid (DOPAC) were determined in the dialysate from caudate nucleus in vivo and from tissue in vitro at various times following NMNorsal administration. Even after high-dose NMNorsal administration (40 mg/kg) and measurements up to 48 h after administration, levels of DA and its metabolite DOPAC were not modified. In contrast to the DA metabolism, 5-HT levels in the dialysate increased to approx. 2-fold during the 48 h following administration of a single high-dose of NMNorsal while HIAA decreased to approx. 50%. These changes of 5-HT and HIAA were nearly identical in the homogenate preparation of the caudate nucleus when compared to the amounts present in the dialysate. During assessment controls and low-dose-treated animals were almost always sleeping. Only high-dose NMNorsal-treated rats were active, with maximum activity after 48 h, however, behavioural activity was clearly different to the classical 5-HT behavioural syndrome. Taken together, increased 5-HT levels in the striatum found in our studies seem to be linked to the behavioural activity induced by high-dose NMNorsal, and NMNorsal appeared to perturb normal diurnal rhythms of spontaneous locomotor activity. The precise mechanism by which NMNorsal acts on 5-HT metabolism and behaviour is, however, unclear and further investigation is required.

Extra‐cellular dopamine increases in the paraventricular nucleus of male rats during sexual activity

Dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) concentrations were measured in the dialysate obtained with vertical microdialysis probes implanted into the paraventricular nucleus of the hypothalamus of sexually potent male rats. Animals showed noncontact erections when put in the presence of, and copulated with a receptive (ovarietomized oestrogen and progesterone primed) female rat. Dopamine and DOPAC concentrations in the paraventricular dialysate increased 140% and 19%, respectively, above baseline values during exposure to the receptive female and 280% and 31%, respectively, during copulation. No changes in dopamine and DOPAC concentrations were detected in the paraventricular dialysate when sexually potent male rats were exposed to nonreceptive (ovariectomized not oestrogen plus progesterone primed) female rats. These results confirm the involvement of the paraventricular nucleus in control of erectile function and copulatory behaviour and show for the first time that dopamine neurotransmission is increased in this hypothalamic nucleus when erection occurs in physiological contexts.

A comparison of the effects of risperidone and its major metabolite, 9-hydroxy-risperidone, on dopamine release in the rat prefrontal cortex

The effects of intraperitoneally (IP) injected phencyclidine (phencyclohexyl piperidine; PCP) on the metabolism of dopamine (DA) and cholecystokinin-like immunoreactivity (CCK-LI) in the rat brain were investigated in connection with PCP-induced behavioral changes. The predominant behavior change elicited by 2.5 mg/kg PCP was locomotion, while with higher doses (5 and 10 mg/kg) sniffing, swaying and falling were observed in addition to the enhanced locomotor activity. Backpedaling and rotation were observed in 10 mg/kg PCP-treated rats. IP injection of PCP caused a dose-related increase in the levels of DA and 3,4-dihydroxy-phenylacetic acid (DOPAC) in the medial frontal cortex (MFC) and anterior cingulate cortex (ant.CC) without any changes in the nucleus accumbens (NAc) or striatum. CCK-LI in the MFC, ant.CC and NAc was decreased in a dose-dependent manner following IP injection of PCP. These findings support the evidence that PCP selectively activates the mesocortical DA systems. Furthermore, our results indicate a functional relationship between the mesocortical DA neurons and intrinsic CCK containing cortical neurons, and the change in the activity of the intrinsic CCK-containing cortical neurons in these two areas, perhaps due to an alteration in DA transmission, might be involved in behavioral changes after PCP injection.

Effect of sulpiride on the amphetamine-induced changes in extracellular dopamine, DOPAC, and hydroxyl radical generation in the rat striatum.

The neurotoxic effects of psychostimulants are mediated by several mechanisms, which together lead to neuronal damage. These mechanisms include an increase in the extracellular content of dopamine, stimulation of dopamine oxidation, accumulation of extracellular glutamate, and an increase in body temperature. In the present study, the dopamine receptor antagonist sulpiride proved able to prevent the delayed loss of dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) and depressed the gradual generation of hydroxyl radicals induced in the rat striatum by D-amphetamine. However, sulpiride at a dose of 75 mg/kg x 2, coadministered with D-amphetamine (7.5 mg/kg x 4), potentiated the increase in extracellular dopamine and initially slightly enhanced D-amphetamine-induced stereotypy. The gradual increase in hydroxyl radical generation predicts the depletion of dopamine and DOPAC in the rat striatum after D-amphetamine administration, but the increase in extracellular dopamine is not a pivotal factor in the enhanced production of hydroxyl radicals.

Semichronic Inhibition of Glutathione Reductase Promotes Oxidative Damage to Proteins and Induces both Transcription and Translation of Tyrosine Hydroxylase in the Nigrostriatal System

We have evaluated the effect of N,N-bis (2-chloroethyl)-N-nitrosourea (BCNU), an inhibitor of glutathione reductase (GR), on the oxidative status along with the integrity of the nigrostriatal dopaminergic system of the rat. The oxidative status was studied by the quantification of carbonyl groups coupled to protein homogenates. Moreover, the specific oxidations in glial fibrillary acidic protein (GFAP) and neurofilament-200 (NF-200) were also measured. The results show that oxidative damage in proteins in the nigrostriatal system is confined to the striatum. Specific carbonyl groups coupled to native NF-200 and GFAP were also increased. These changes were accompanied by reactive astrocytosis in striatum but not in substantia nigra. In substantia nigra, decreased levels of dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) were observed following BCNU treatment. In contrast, DA levels were increased in the striatum along with an overall decrease in the ratios of DA metabolites to DA. We also studied the mRNA levels for tyrosine hydroxylase (TH) and the dopamine transporter (DAT) by in situ hybridization. TH mRNA but not DAT mRNA was significantly induced in substantia nigra following BCNU treatment, which was consistent with significant elevations in TH enzyme amount and activity and unchanged DA uptake in striatum. All these results support the DA free radical hypothesis and the key role of the striatal glutathione system in protecting the striatal system against oxidative stress.

Fixed ratio discrimination training increases in vivo striatal dopamine in neonatal 6-OHDA-lesioned rats.

Massed training in the conditional discrimination task, the fixed ratio discrimination (FRD) task led to elevated extracellular dopamine (DA) concentrations in the neonatal 6-hydroxydopamine (6-OHDA)-treated rat, a model of Lesch-Nyhan disease (LND). Rats neonatally treated with 6-OHDA or its vehicle were, as adults, implanted with microdialysis probes and assessed for basal pretraining concentrations of DA and its major metabolites. Subsequently, microdialysis samples were collected each day following three separate FRD training periods (trained group) or three separate periods of noncontingent food presentations (untrained group). The present study found that there were significant increases in extracellular DA in the caudate-putamen from basal pretraining concentrations in the repeated sample collections of trained 6-OHDA-lesioned animals but not in the samples of untrained 6-OHDA-lesioned animals. Consistent with previous studies [Brain Res. 508 (1990) 30.], there was an increase in the extracellular concentrations as compared to tissue concentrations of DA and 3,4-dihydroxyphenylacetic acid (DOPAC). Similar to our previous studies with long-term FRD training [Pharmacol. Biochem. Behav. 51 (1995) 861; Brain Res. 713 (1996) 246.], there was also an indication of an increase in cortical and striatal tissue concentration of DA in the trained 6-OHDA-lesioned animals as compared to the untrained 6-OHDA-lesioned animals. The elevations in striatal DA concentrations following operant performance in the present study illustrate how operant procedures of the behavior therapy used with individuals with LND and other mental retardation syndromes may interact with the modulation of dopaminergic function by the pharmaceutical application of DA antagonists to suppress aberrant behaviors.

Inhibition of protein kinase C but not protein kinase A attenuates morphine withdrawal excitation of rat hypothalamus–pituitary–adrenal axis

Our previous studies have shown an enhanced activity of the hypothalamus–pituitary–adrenocortical axis response in rats withdrawn from morphine, which results from an increase in the hypothalamic paraventricular nucleus noradrenergic activity that is dependent on α-adrenoceptor activation. The first objective of this work was to examine the effect of protein kinase A (PKA) and protein kinase C (PKC) inhibitors on morphine withdrawal-induced changes in corticosterone release (an index of the hypothalamus–pituitary–adrenocortical axis activity) and in catecholaminergic turnover in the paraventricular nucleus. Plasma corticosterone levels as well as the concentration of noradrenaline, 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), dopamine and 3,4-dihydroxyphenylacetic acid (DOPAC) in the paraventricular nucleus were determined. The second purpose of the study was to assess whether kinase inhibitors, administered continuously through s.c. osmotic minipumps, get into the brain. Chronic pretreatment for 7 days with the selective PKA inhibitor N-(2′guanidinoethyl)-5-isoquinolinesulfonamide (HA-1004) concomitantly with morphine did not affect the increase in corticosterone release observed after naloxone-precipitated morphine withdrawal. However, pretreatment with the selective PKC inhibitor, calphostin-C significantly antagonized the corticosterone hypersecretion in morphine-withdrawn rats. Neither HA-1004 nor calphostin-C co-administered with morphine for 7 days did modify the morphine withdrawal-induced increase in noradrenaline turnover. Pretreatment with HA-1004 inhibits the increase in dopamine turnover during morphine withdrawal, whereas calphostin-C did not affect the DOPAC/dopamine ratio. Our results might indicate that expression of morphine dependence for hypothalamus–pituitary–adrenocortical axis hyperactivity involves PKC but not PKA signaling mechanisms. It is suggested that in rats PKC may be up-regulated during morphine dependence. High-performance liquid chromatography (HPLC) analysis of hypothalamic tissue from rats perfused with kinase inhibitors demonstrates that both calphostin-C and HA-1004 can cross the blood–brain barrier when administered peripherally.

Lead intoxication during intrauterine life and lactation but not during adulthood reduces nucleus accumbens dopamine release as studied by brain microdialysis

Environmentally relevant levels of lead (Pb) have been demonstrated to have a neurotoxic action, especially on children. In this study, Long–Evans rats were continuously exposed to Pb acetate in drinking water from early gestational days (2–6) or from 28 days of age. At the 13th week of age, the functional activity of the nucleus accumbens (NAC) dopaminergic system was studied by means of transversal microdialysis. Neither Pb treatment regimen modified dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) extracellular concentrations, with respect to control rats. However, neuronal depolarisation, induced by perfusion with 60 mM KCl, increased extracellular DA levels to a significantly minor degree in rats exposed to Pb during the intrauterine life, with respect to both control and adult Pb treated rats. The in utero treated rats also responded with a lower DA release to amphetamine (1 mg/kg ip) administration. On the other hand, no difference in NAC DA level was found amongst treatment groups in response to different concentrations of the D 2–D 3 dopaminergic agonist quinpirole, locally administered by means of inverse dialysis. These data indicate a preferential impairment of NAC DA synthesis and/or release in rats exposed to Pb acetate during their intrauterine life.

Biochemical and immunohistological changes in the brain of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mouse

We investigated neurochemically and neuropathologically the utility of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice as a model of Parkinson’s disease. The changes in dopamine D 1 and D 2 receptors and dopamine uptake sites were determined by quantitative autoradiography using [ 3H]SCH23390, [ 3H]raclopride and [ 3H]mazindol, respectively. Dopamine and 3,4-dihydroxyphenyl acetic acid (DOPAC) contents in the striatum were measured by high-performance liquid chromatography. The distribution of nigral neurons and reactive astrocytes was determined by immunohistochemical staining with antibody against tyrosine hydroxylase (TH) and glial fibrillary acidic protein (GFAP). The mice received four intraperitoneal injections of MPTP (10 mg/kg) at 1-h intervals and then the brains were analyzed at 3 and 7 days after the treatments. No significant change in dopamine D 1 receptors was observed in the striatum and substantia nigra after acute treatment with MPTP. Dopamine D 2 receptors were reduced significantly in the substantia nigra only 7 days after the MPTP treatment, whereas striatum showed no significant change in the binding throughout the experiments. In contrast, dopamine uptake sites were reduced markedly in the striatum and substantia nigra 3 and 7 days after the MPTP treatment. Dopamine and DOPAC content were also reduced in the striatum 3 and 7 days after the MPTP treatment. An immunohistochemical study indicated a loss of the number of TH-positive neurons in the substantia nigra 7 days after the MPTP treatment. In contrast, numerous GFAP-positive astrocytes were evident in the striatum 7 days after the MPTP treatment. These results provide valuable information for the pathogenesis of acute stage of Parkinson’s disease.

Effects of melatonin on dopamine metabolism in the hypothalamus and the pituitary of the rainbow trout, Oncorhynchus mykiss

The present paper discusses the effect of a single melatonin treatment (0.5 mg/kg, i.p.) on the dopaminergic metabolism in the hypothalamus and pituitary of the rainbow trout. The effects of exogenous melatonin on dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) contents were compared with the variations in the content of these catecholamines associated to the natural increase in the endogenous melatonin from daytime (3 hr before lights off) to nighttime (3 hr after lights off). Animals treated with melatonin showed a rapid (maximal values at 30 min post-injection) and relatively sustained rise in plasma melatonin levels, which reached supraphysiological ranges. The increase in circulating melatonin was accompanied by a reduction in the amount of DOPAC in both the hypothalamus (30, 60, and 120 min after i.p. melatonin) and the pituitary (120 min after i.p. melatonin) as well as in the pituitary DOPAC/DA ratio (60 and 120 min after i.p. melatonin). Similarly, the increase in circulating melatonin levels from the daytime to nighttime was associated with decreases in the contents of DOPAC in both the hypothalamus and pituitary and in the DOPAC/DA ratio in the pituitary. These data suggest that the inhibition of the hypothalamic–pituitary dopaminergic metabolism may be a specific mechanism of melatonin action in the trout brain that might operate following changes in the secretion of the hormone from the pineal gland. J. Exp. Zool. 287:440–444, 2000. © 2000 Wiley-Liss, Inc.