Acute effects of intranigral application of MPP+ on nigral and bilateral striatal release of dopamine simultaneously recorded by microdialysis.

Intracerebral microdialysis in freely moving rats was used to investigate the effects of perfusions with the 1-methyl-4-phenylpyridinium ion (MPP+) in the substantia nigra (SN) on the extracellular levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA) in the perfused SN and in the ipsi- and contralateral striata. Following MPP+ perfusion, the release of DA in the SN increased markedly from nondetectable basal levels to about 105 fmoles/min, whereas the output of DOPAC, HVA and 5-HIAA decreased below 25% of basal levels. The intranigral MPP+ application induced, at the same time, an almost immediate, long-lasting decrease in the release of DA in the ipsilateral striatum to less than 20% of basal levels and a moderate increase in the DOPAC and HVA levels, without affecting 5-HIAA output. In the contralateral striatum, the extracellular levels of DA, DOPAC, HVA and 5-HIAA remained unchanged during the entire perfusion experiment. These results suggest that infusion of 10 mM MPP+ into the SN produces an almost immediate blockade of neuronal impulse flow, as shown by the rapid decline in DA release from the ipsilateral striatal nerve terminals. The simultaneously occurring massive increase of the extracellular DA in the SN is, therefore, probably the result of destruction of the nigral cell bodies and/or dendrites following locally applied MPP+. This study clearly illustrates the possibilities of simultaneous microdialysis in various brain areas, allowing pharmacological manipulations on the levels of the cell bodies, while monitoring events in the terminal areas.     

Ethanol alters monoamines in specific mouse brain regions.

Ethanol (3.5 g/kg 60 min post-IP injection) produced the following changes in regional brain monoamine levels and in the respective metabolite/neurotransmitter ratios: for the noradrenergic system, MHPG was decreased in the amygdala and increased in the hypothalamus, while the MHPG/NE ratio was increased in the prefrontal cortex and the hypothalamus. For the dopaminergic system, DA was decreased in the olfactory tubercle, DOPAC was increased in the prefrontal cortex and septum, and DOPAC/DA was increased in the prefrontal cortex, septum, striatum, and hypothalamus. HVA was increased in the prefrontal cortex and septum, while HVA/DA was increased in the same regions plus the olfactory bulb. 3MT was decreased in the olfactory tubercle and striatum. The serotonergic system was not altered. The results demonstrate that ETOH produces selective regional changes in the concentration and utilization of monoamines in mouse brain with a predominant influence on dopaminergic systems and a lesser effect on noradrenergic activity.     

The role of phospholipid methylation in 1-methyl-4-phenyl-pyridinium ion (MPP+)-induced neurotoxicity in PC12 cells

Excessive methylation has been proposed to be involved in the pathogenesis of Parkinson's disease (PD), via mechanisms that involve phospholipid methylation. Meanwhile, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) was found to stimulate phospholipid methylation via the oxidized metabolite, 1-methyl-4-phenyl-pyridinium (MPP+), in the rat brain and liver tissues. In the present study, we investigated the effect of MPP+ on phosphatidylethanolamine N-methyltransferases (PENMT) and the potential role of this pathway in MPP(+)-induced neurotoxicity using PC12 cells. The results obtained indicate that MPP+ stimulated phosphatidylethanolamine (PTE) methylation to phosphatidylcholine (PTC) and correspondingly increased the formation of lysophosphatidylcholine (lyso-PTC). Moreover, the addition of S-adenosylmethionine (SAM) to the cell culture medium increases MPP(+)-induced cytotoxicity. The incubation of 1mM MPP+ and various concentrations of SAM (0-4 mM) decreased the viability of PC12 cells from 80% with MPP+ alone to 38% viability with 4 mM SAM for 4 days incubation. The data also revealed that the addition of S-adenosylhomocysteine (SAH), a methylation inhibitor, offered significant protection against MPP(+)-induced cytotoxicity, indicating that methylation plays a role in MPP(+)-induced cytotoxicity. Interestingly, lyso-PTC showed similar actions to MPP+ in causing many cytotoxic changes with at least 10 times higher potency. Lyso-PTC induced dopamine release and inhibited dopamine uptake in PC12 cells. Lyso-PTC also caused the inhibition of mitochondrial potential and increased the formation of reactive oxygen species in PC12 cells. These results indicate that phospholipid methylation pathway might be involved in MPP+ neurotoxicity and lyso-PTC might play a role in MPP(+)-induced neurotoxicity.     

Modeling of the presymptomatic stage of parkinsonism in mice: Analysis of dopamine release in the striatum

We revised our hypothesis that the absence of motor behavior impairments at the presymptomatic stage of Parkinsonism, when degeneration of nigrostriatal dopaminergic neurons has already occurred, is the result of compensatory maintenance of a normal extracellular dopamine (DA) concentration in the striatum. We used microdialysis to measure extracellular levels of DA, its precursor L-dihydroxyphenylalanine (L-DOPA), and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in mouse striatum in a model of the presymptomatic stage of Parkinsonism. This stage was induced by a single subcutaneous injection of the neurotoxin precursor 1-methyl-4-phenyl-1,2,3,4-tetrahydropyridine (MPTP) at a dose of 12 mg/kg. At 14 days after MPTP injection, the extracellular DA content substantially decreased as compared to the control; however, it did not result in alterations of motor behavior, probably due to compensatory processes directed, not to the maintenance of extracellular DA at the normal level, but rather to the elevation of neuronal sensitivity to DA. The extracellular L-DOPA content remained at the normal level. We did not find any changes in the DOPAC and HVA contents.     

Methamphetamine generates peroxynitrite and produces dopaminergic neurotoxicity in mice: protective effects of peroxynitrite decomposition catalyst

Methamphetamine (METH)-induced dopaminergic neurotoxicity is believed to be produced by oxidative stress and free radical generation. The present study was undertaken to investigate if METH generates peroxynitrite and produces dopaminergic neurotoxicity. We also investigated if this generation of peroxynitrite can be blocked by a selective peroxynitrite decomposition catalyst, 5, 10,15, 20-tetrakis(N-methyl-4'-pyridyl)porphyrinato iron III (FeTMPyP) and protect against METH-induced dopaminergic neurotoxicity. Administration of METH resulted in the significant formation of 3-nitrotyrosine (3-NT), an in vivo marker of peroxynitrite generation, in the striatum and also caused a significant increase in the body temperature. METH injection also caused a significant decrease in the concentration of dopamine (DA), 3, 4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) by 76%, 53% and 40%, respectively, in the striatum compared with the control group. Treatment with FeTMPyP blocked the formation of 3-NT by 66% when compared with the METH group. FeTMPyP treatment also provided significant protection against the METH-induced hyperthermia and depletion of DA, DOPAC and HVA. Administration of FeTMPyP alone neither resulted in 3-NT formation nor had any significant effect on DA or its metabolite concentrations. These findings indicate that peroxynitrite plays a role in METH-induced dopaminergic neurotoxicity and also suggests that peroxynitrite decomposition catalysts may be beneficial for the management of psychostimulant abuse.     

Effects on dopamine metabolism of MPTP and MPP+ infused through a push-pull cannula into the caudate nucleus of awake adult male rats

Our previous data demonstrated that both 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 1-methyl-4-phenylpyridinium ion (MPP+) exerted potent inhibition on endogenous 3,4-dihydroxyphenylacetic acid (DOPAC) output and potent stimulation on endogenous dopamine (DA) release from the rat corpus striatum superfused in vitro. In this report, using a push-pull perfusion technique, we examined in vivo the acute effects of MPTP and MPP+ on DA metabolism in the rat caudate nucleus (CN). MPTP or MPP+ in modified Krebs-Ringer phosphate buffer at concentrations of 10(-6), 10(-5) and 10(-4) M was administered directly into the CN for 15 min, each 90 min apart. Thirty minutes after the infusion of 10(-6) M MPP+, DOPAC output was reduced to a significantly lower value and subsequent infusions of high concentrations of MPP+ further decreased DOPAC output. Homovanillic acid (HVA) output was also decreased by MPP+ infusions, however, at higher concentrations. In respect to DA release, 1 of 10, 4 of 10 and 7 of 10 animals responded with significant increases to 10(-6), 10(-5) and 10(-4) M MPP+, respectively. On the other hand, MPTP was effective in reducing DOPAC output only at 10(-4) M and ineffective in altering DA and HVA output at all doses tested. In addition, neither drugs had a significant effect on 5-hydroxyindoleacetic acid. Accompanying the dramatic changes in DA metabolism caused by MPP+, two uncommon behavioral syndromes were also observed; tremor-body twist and body shaking.(ABSTRACT TRUNCATED AT 250 WORDS)     

Acute and prolonged effects of ibogaine on brain dopamine metabolism and morphine-induced locomotor activity in rats.

Ibogaine, an indolalkylamine, proposed for use in treating opiate and stimulant addiction, has been shown to modulate the dopaminergic system acutely and one day later. In the present study we sought to systematically determine the effects of ibogaine on the levels of dopamine (DA) and the dopamine metabolites 3,4 dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in tissue at several time points, between 1 h and 1 month post-injection. One hour after ibogaine-administration (40 mg/kg i.p.) a 50% decrease in DA along with a 37-100% increase in HVA were observed in all 3 brain regions studied: striatum, nucleus accumbens and prefrontal cortex. Nineteen hours after ibogaine-administration a decrease in DOPAC was seen in the nucleus accumbens and in the striatum. A week after administration of ibogaine striatal DOPAC levels were still reduced. A month after ibogaine injection there were no significant neurochemical changes in any region. We also investigated the effects of ibogaine pretreatment on morphine-induced locomotor activity, which is thought to depend on DA release. Using photocell activity cages we found that ibogaine pretreatment decreased the stimulatory motor effects induced by a wide range of morphine doses (0.5-20 mg/kg, i.p.) administered 19 h later; a similar effect was observed when morphine (5 mg/kg) was administered a week after ibogaine pretreatment. No significant changes in morphine-induced locomotion were seen a month after ibogaine pretreatment. The present findings indicate that ibogaine produces both acute and delayed effects on the tissue content of DA and its metabolites, and these changes coincide with a sustained depression of morphine-induced locomotor activity.     

Effects of 250 mg% ethanol on monoamine and amino acid release from rat striatal slices

A single IP injection of 2.5 g ethanol/kg body weight into the rat increased the striatal levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) one hour later to 133 and 141% of control values, respectively. Blood alcohol concentrations at this time were approximately 250 mg%. The increased striatal tissue levels of DOPAC and HVA found after IP administration did not appear to be due to a direct effect of ethanol on the efflux of these two metabolites or on the release of dopamine (DA) since in vitro studies with striatal slices demonstrated that 250 mg% ethanol had no effect on the endogenous release of DOPAC, HVA, or DA. However, ethanol did enhance the K+-stimulated, Ca2+-dependent release of glutamate and aspartate from striatal slices to 168 and 214% of control values, respectively. The release of glutamate and aspartate from slices of midbrain (minus colliculi) was also increased by 250 mg% ethanol. On the other hand, the release of GABA, NE and 5-HT did not appear to be significantly altered by 250 mg% ethanol. The in vitro findings have led to the hypothesis that the elevated DOPAC and HVA levels observed in the striatum following an acute IP injection of 2.5 g/kg of ethanol are due to increased release of DA produced by the excitatory actions of glutamate (and/or aspartate) on dopaminergic neurons.     

Bilateral augmentation of dopaminergic and serotonergic activity in the striatum and nucleus accumbens induced by conditioned circling

The involvement of dopaminergic (DA) and serotonergic (5-HT) systems in circling was assessed by determining the neurochemical correlates of circling induced and maintained by two different schedules of water reinforcement. The conditioned circling paradigm was employed in an attempt to replicate reports that levels of DA and 3,4-dihydroxyphenylacetic acid (DOPAC) were increased in the striatum and nucleus accumbens septi (NAS) contralateral to the direction of circling. Rats trained to circle using a continuous schedule of reinforcement did not exhibit any changes in concentrations of DA, DOPAC, or homovanillic acid (HVA). Bilateral increases in 5-HT concentrations were observed in the striatum. Use of an intermittent schedule of reinforcement (FR-2) produced higher rates of circling. In rats maintained on the FR-2 schedule, no changes in DA or its metabolites were observed in the striatum. The ratio of HVA to DA was, however, increased bilaterally, suggesting a bilateral augmentation of DA utilization. Concentrations of DA were lower in the NAS contralateral to direction of turning. While NAS levels of HVA were elevated bilaterally when compared to non-circling controls, HVA was lower in the NAS contralateral to the direction of circling. DA utilization, as estimated by HVA: DA ratios, was increased bilaterally in the NAS. None of the measures of DA activity within the olfactory tubercle (OT) were influenced by circling. Turnover of 5-HT, as estimated by the ratio of 5-HT to 5-hydroxyindoleacetic acid (5-HIAA), was increased bilaterally in the striatum, NAS, and OT.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of neurotensin on regional brain concentrations of dopamine, serotonin and their main metabolites.

The effects of neurotensin, 7.5 or 30 micrograms, on concentrations of DA, DOPAC, (HVA), serotonin 5-HT and 5-HIAA were measured in 8 regions of the rat brain either 5 or 30 min following intracerebroventricular administration. Regions examined include the frontal cortex, striatum, nucleus accumbens, amygdala, septum, hypothalamus, ventral tegmentum and substantia nigra. Results indicate that both doses of neurotensin significantly elevated concentrations of dopamine in the striatum and amygdala 5 min following injection. The effects of the peptide on DOPAC and HVA were more pervasive and enduring, with significant increases in metabolite levels occurring in both mesolimbic and nigrostriatal terminal regions. In order to assess effects on turnover of dopamine, the ratios of each metabolic to dopamine concentrations were examined. Results indicate that, while the DOPAC/DA ratio was elevated in many regions, the HVA/DA ratio was increased in all regions examined. The effects of neurotensin on serotoninergic parameters were less pervasive and more variable, with both increases and decreases in 5-HT and 5-HIAA concentrations being observed. The effects of the peptide on 5-HIAA/5-HT were limited to the nucleus accumbens, where this ratio was increased, and the ventral tegmentum, where 5-HIAA/5-HT was decreased. These findings reveal that the effects of the neurotensin on dopaminergic transmission are more widespread than previously reported in that all major dopamine pathways are affected by the peptide. Also, the observed changes in the ratios of both DOPAC and HVA to DA suggest that neurotensin enhances the turnover of this transmitter.     

Dopamine synthesis in inbred mouse strains which differ in numbers of dopamine neurons

BALB/cJ and CBA/J mice have been shown to have different numbers of dopamine (DA) neurons in the central nervous system, with BALB/cJ mice having 20–50% more DA neurons in each dopaminergic cell group which is reflected in a difference in tyrosine hydroxylase activity in these cell groups. The present study compared the levels of DA and the rate of DA synthesis between these two inbred mouse strains. Three measures were used to reflect the rate of DA synthesis: the levels of DA metabolites (DOPAC and HVA) in the striatum, the rate of disappearance of DA following inhibition of tyrosine hydroxylase withα-methyl-P-tyrosine, and the rate of accumulation of DOPA following inhibition of aromatic amino acid decar☐ylase with NSD-1015. Striatal DA levels were slightly higher in CBA/J mice than BALB/cJ mice. The rate of DA synthesis in the striatum, as estimated from the accumulation of DOPA following NSD-1015 injection or from the decline of DA levels followingα-methyl-p-tyrosineinjection, was from 30–50% greater in the BALB/cJ mice compared to the CBA/J mice. In striatum, DOPAC levels were higher, HVA levels lower, and DOPAC plus HVA levels equal in CBA/J mice compared to BALB/cJ mice. The results show that BALB/cJ mice, with more DA neurons than CBA mice, also synthesize more DA. In addition, the data suggest that DA levels do not necessarily reflect numbers of DA neurons, and that catecholamine metabolite levels are not a good measure for comparing catecholamine synthesis between inbred animal strains.     

Effect of morphine applied by intrapallidal microdialysis on the release of dopamine in the nucleus accumbens

The effect of morphine, administered intrapallidally, on extracellular concentrations of DA, DOPAC, and HVA in the nucleus accumbens and striatum was studied in the behaving rat using the in vivo microdialysis technique. Unilateral application of morphine hydrochloride was perfomed through microdialysis probes into the rat ventral pallidum (10 μ1 of 0 2.6 4.0, 13.0, and 26.0 mM) or globus pallidus (10 μ1 of 0 and 26.0 mM). The levels of DA, DOPAC, and HVA were measured using the HPLC with EC detection in dialysates collected from the nucleus accumbens, anteromedial, and anterolateral striatum. Samples were taken every 45 min over 3 h before and over 5 h after morphine or vehicle administration. Administration of morphine into the ventral pallidum resulted in increased DOPAC and HVA concentrations in the nucleus accumbens. Pretreatment with naloxone (1 mg/kg, SC) abolished this effect of morphine. Administration of morphine into the globus pallidus resulted in increased DA, DOPAC, and HVA concentrations in the nucleus accumbens and DA in the anteromedial striatum. The levels of DA and metabolites in anterolateral striatum remained rather unchanged following morphine administered into the ventral pallidum or the globus pallidus. The changes in DA neurotransmission into the nucleus accumbens induced by morphine application into the ventral pallidum and globus pallidus are reminiscent of a phasic and tonic release of DA respectively. The results show that intrapallidal morphine increases DA neurotransmission in nucleus accumbens and suggest that the effect of morphine is mediated by ventral pallidum/mesolimbic and globus pallidus/thalamocortical pathways, depending on the site of injection.     

Enhanced response to the inhibitory action of LY171555, a dopamine D2-agonist, on in vivo striatal dopamine release in DOCA/NaCl-hypertensive rats

Our previous studies have demonstrated that LY171555 (quinpirole), a specific dopamine (DA) D₂-receptor agonist, has a pressor effect in the conscious rat which is accompanied by increased sympathetic outflow and arginine vasopressin release. To test the hypothesis that LY171555 inhibits in vivo release of DA and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), from central dopaminergic neurons of the conscious, freely moving rat by activation of presynaptic DA receptors in the central nervous system and that this mechanism may be altered in the desoxycorticosterone acetate (DOCA)/NaCl model of hypertension, we used the in vivo push-pull perfusion method to study the effect of LY171555 on central DA release in normotensive and DOCA/NaCl-hypertensive rats. Levels of the DOPAC and HVA were measured in striatal perfusates by HPLC before and after administration of LY171555 (1 mg/kg, i.v.) of conscious, unrestrained 4-week DOCA/NaCl hypertensive and uninephrectomized H₂O control rats. There were no significant differences in basal striatal HVA (80 ± 12 vs 89 ± 11 pg/min; DOCA/NaCl vs control) or DOPAC levels (37 ± 5 vs 17 pg/min; DOCA/NaCl vs control) during the entire 240-min collection period. LY171555 significantly reduced HVA and DOPAC levels in perfused striatum in both normotensive control and DOCA/NaCl-hypertensive rats. The LY 17555-induced suppression in HVA levels was significantly greater in DOCA/NaCl rats (Δ = 60.7 ± 3.6%) than in H₂O controls (Δ = 49.0 ± 3.5%, P < 0.05). Pretreatment with metoclopramide (10 mg/kg, i.v.), a specific central and peripheral DA D₂-receptor antagonist, completely blocked the suppressive effects of LY171555 on HVA and DOPAC levels. These observations provide direct evidence for the presence of functionally significant presynaptic inhibitory DA D₂-receptors which modulate dopaminergic neuro-transmission in the striatum of conscious, freely moving rats. This regulatory mechanism appears to be altered in the DOCA/NaCl model of hypertension. These results support the concept that DOCA/NaCl-hypertensive rats have altered central dopaminergic activity.     

Conjugated HVA increase in rat urine after insulin-induced hypoglycemia: Involvement of central dopaminergic structures but not of adrenal medulla

Summary To examine the possible contribution of Rat adrenal medulla to urinary DOPAC and HVA, we have studied these compounds in adrenals and urine under insulin-induced (5 IU/kg) hypoglycemic stimulation.In the urine samples collected over 16-hour-period following the intravenous insulin injection, there was a great increase in E, NE and their methoxylated derivatives MN and NMN, without change in DA, DOPAC, MHPG and free HVA excretion. In addition, there was a pronounced increase in urinary HVA conjugates (glucuronide and sulfate). Only very low amounts of DOPAC (10±2ng/gland; 0.05% of catechols) and no detectable amounts of HVA (<3 ng/gland) were found in adrenal glands, without no significant change two hours after insulin, thus suggesting that Rat adrenal glands are not meaningful sources for urinary HVA and DOPAC.Since free HVA and total MHPG excretion remained unchanged, HVA contribution from sympathetic neurons seems unlikely in our study.In contrast, highly increased levels of conjugated HVA-and at a lesser extent of conjugated DOPAC-have been found in the striatum, which appears to be the most likely source of urinary HVA increment. The dopaminergic activation following insulin affected too the hypothalamus but not the nucleus accumbens. The role of such central dopaminergic activation has been discussed in terms of feeding behavior.     

The role of dopamine in intracranial self-stimulation of the ventral tegmental area

The role of dopaminergic (DA) neurons in brain stimulation reward produced by electrical stimulation of the ventral tegmental area (VTA) was investigated in the rat. In the first experiment, extensive 6-hydroxydopamine lesions of the ascending fibers of the mesotelencephalic DA projections resulted in significant changes in intracranial self-stimulation (ICS) rate-current intensity functions when the lesion was ipsilateral to the stimulating electrode. Similar contralateral lesions had no effect on these functions, thus ruling out lesion-induced performance deficits as being responsible for the decreases in ICS rates across the wide range of current intensities that occurred after the ipsilateral lesions. In the second experiment, ICS obtained from electrodes in the VTA resulted in significant increases in the DA metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum, nucleus accumbens, and olfactory tubercle ipsilateral to the stimulating electrode. The ratios of DOPAC and HVA to DA, considered to be indices of DA utilization, were also increased in these brain regions ipsilateral to the electrode. No changes were observed in the contralateral striatum, nucleus accumbens, and olfactory tubercle. Similar increases were observed in stimulated "yoked" animals that received brain stimulation at identical rates and currents but did not lever-press for this stimulation. The third experiment examined the effects of lever-pressing for food on an FR8 schedule of reinforcement on DA utilization in the striatum, nucleus accumbens, and olfactory tubercle. Despite high rates of responding, no effects were observed on DOPAC:DA or HVA:DA ratios in these brain regions.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of homocysteine on the dopaminergic system and behavior in rodents

Long-term treatment of levodopa for Parkinson's disease (PD) patients is known to elevate homocysteine level in their plasma. The present study was designed to examine the possible neurotoxic effects of the increased homocysteine level on the dopaminergic system. Homocysteine was administered into Sprague-Dawley male rats intracerebroventricularly or C57BL/6 mice intraperitoneally. Following homocysteine injection the locomotor activities, the levels of dopamine (DA) and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), and immunohistochemistry of dopaminergic neurons were examined. The results obtained indicate that homocysteine administration (1 or 2 micromol, i.c.v.) into the rat brains for 5 days significantly decreased the locomotor activities and dopamine as well as its metabolites, DOPAC and HVA, in the rat striatal regions. Two different doses of homocysteine (50 and 100mg/100g, i.p. daily) were administered into mice for 36 days to evaluate the effect of systemic treatment of homocysteine on the dopaminergic neurons of the brain. The intraperitoneal injections of two doses of homocysteine significantly increased homocysteine levels in the striatal regions of mouse brains by 21.5 and 39.2%, while reducing dopamine turnover rates in the striatal regions by decreasing (DOPAC+HVA)/DA, 23.7 and 51.6%, respectively. Accordingly, homocysteine decreased locomotor activities significantly by decreasing movement time by 29 and 38%, total distance by 32 and 42%, and numbers of movement by 28 and 41%, respectively. Moreover, homocysteine decreased tyrosine hydroxylase immunoreactivity in substantia nigra of mouse brain. The data obtained indicate that the potential of homocysteine to be toxic to the dopaminergic system. Consequently, long-term levodopa therapy for PD may accelerate the progression of PD, at least in part by elevated homocysteine.     

Metabolism of monoamine neurotransmitters in the evolution of infarction in ischemic striatum

Summary The time course of changes in monoamine metabolism in ischemic striatum was assessed by measurement of levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT) and 5-hydroxy-indole-acetic acid (5-HIAA) 2, 4, 7 and 16 hours after irreversible unilateral carotid ligation in Mongolian gerbils with stroke. DA was reduced to 30% of the level in the contralateral non-ischemic striata by 2 hours after stroke, but DOPAC was significantly elevated (p < 0.01) to 227%, while HVA remained equal to control. At 4 hours after stroke, DOPAC was 86% of the contralateral non-ischemic striata but HVA had risen to 130%. At 7 hours after stroke, DOPAC in the ischemic striata was 148% of control, while HVA remained at 133%. By 16 hours after stroke, DA, DOPAC and HVA were depleted from the ischemic striata, corresponding to the time course for irreversible damage to the neurotransmitter uptake function of nerve terminals. 5-HT levels in the ischemic striata were 30% of control at 2 hours, 46% at 4 hours, 30% at 7 hours and 21% at 16 hours, while 5-HIAA remained equal to control throughout the time course. These studies indicate that monoamine metabolism continues in ischemic striatum for up to 8 hours after the onset of stroke following irreversible unilateral carotid ligation in the Mongolian gerbil, but metabolism of DA is disrupted by 16 hours after stroke while metabolism of 5-HT continues.     

Ceruletide suppresses endogenous dopamine release via vagal afferent system, studied by in vivo intracerebral dialysis

Ceruletide, a cholecystokinin-related decapeptide, has been reported to have some therapeutic effects on tardive dyskinesia and other involuntary movement disorders. In order to clarify the effects of ceruletide on dopaminergic activity in the rat striatum, we measured the release of endogenous dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) after intraperitoneal administration of ceruletide (2, 20, 200 micrograms/kg) using in vivo intracerebral dialysis techniques. After administration of ceruletide (200 micrograms/kg), extracellular DA decreased significantly (P less than 0.05) for 0.5-3 h. The maximal reduction of extracellular DA (by 29%) was observed for 2-2.5 h. Extracellular DA was reduced (21%) by 20 but not by 2 micrograms/kg ceruletide. DOPAC and HVA did not change at any dose of ceruletide. We also demonstrated that bilateral subdiaphragmatic vagotomy blocked this inhibitory effect of ceruletide on DA release. These findings indicate that peripherally administered ceruletide suppresses endogenous DA release via the vagal afferent system.     

Substantia nigra 6-hydroxydopamine lesions alter dopaminergic synaptic markers in the nucleus basalis magnocellularis and striatum of rats

Recent findings have demonstrated the existence of dopaminergic (DA) markers in the nbM of the human brain and a reduction of these markers in both the nbM and the striatum of patients suffering from Alzheimer's disease (AD). To investigate the source of the DA synaptic markers found in the nbM, rats received unilateral 6-OHDA lesions of the substantia nigra pars compacta (SNc). The SNc lesions caused significant reductions in DA and DOPAC but not HVA in the nbM and the striatum; 3H-sulpiride binding to D2 receptors ipsilateral to the SNc lesion was significantly increased in the striatum (16%), consistent with denervation supersensitivity, but single-point analysis showed no significant changes in the nbM. These data suggest that the decreases in DA and 3H-spiperone binding levels observed in the nbM of AD patients may be due to partial destruction of DA nbM afferent projections from the brainstem.     

Free and conjugated 3, 4-dihydroxyphenylacetic acid and homovanillic acid in brain dopaminergic areas at basal state and after pipotiazine activation

Summary We have determined free and conjugated 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in discrete brain areas of rats.Conjugated HVA or DOPAC accounted for 22–38% of total acids in striatum, mesolimbic tissue or prefrontal cortex. Activation of dopamine (DA) metabolism by a single injection of pipotiazine palmitic ester (PPZ), a long-lasting neuroleptic, increased free acid levels (DOPAC and HVA) at either dose and conjugate levels after 32 or 50 mg/kg. 48 hours after PPZ-32 mg/kg, the observed increases of conjugates could exceed in some cases those of corresponding free acids.About half of total DOPAC and HVA were conjugated in hypothalamus, PPZ moderately increased free DOPAC (at 32 mg/kg) but did not elevate significantly the conjugated form.It is concluded that sulfation is an important pathway for DOPAC and HVA metabolism in brain and that the determination of both free and conjugated DOPAC or/and HVA may shed additional lights on regional DA metabolism and the effect of drags thereon.