Comparative antidopaminergic properties of thioridazine, mesoridazine and sulforidazine on the corpus striatum

The functional antidopaminergic potencies of the atypical antipsychotic drug thioridazine (THD), as well as its active metabolites mesoridazine (MES) and sulforidazine (SUL), were assessed by testing their blockade of the inhibitory effects of endogenous dopamine (DA) or apomorphine on the electrically evoked release of radiolabeled DA and acetylcholine (ACh) from perfused rabbit striatal slices. These functional comparisons (reflecting presynaptic and postsynaptic DA receptors, respectively) were correlated with potency estimations of these drugs in competing for D2 DA receptors (i.e., [3H]spiperone binding sites) in rabbit striatal homogenates. Similar orders of potency (SUL greater than MES much greater than THD) were found for blockade of pre- and postsynaptic DA receptors modulating DA and ACh release, respectively, as well as in competing for [3H]spiperone binding sites in the striatum. MES, SUL and haloperidol were 2 to 3 times more potent at DA release modulatory receptors than postsynaptic DA receptors. In contrast, THD was 8 times more potent at antagonizing the apomorphine-induced inhibition of DA release than against apomorphine's effect on ACh release. THD was virtually inactive in antagonizing the inhibition of ACh release induced when nomifensine was used to increase endogenous synaptic DA, despite significantly antagonizing these effects on DA release in the same slices. Together, these data indicate that: 1) MES and SUL are responsible for a significant part of the antidopaminergic effects attributed to THD; 2) THD should produce less cholinergic activation than other neuroleptics; and 3) that nonreceptor-mediated effects at high THD concentrations may mask effects due to receptor blockade.     

Phorbol esters and D2-dopamine receptors

4-beta-Phorbol-12,13-dibutyrate (PDBu), a powerful activator of protein kinase C (PKC), enhanced dopamine (DA) release evoked by electrical stimulation (1 Hz, 2 min) from the striatum and the prefrontal cortex of the rabbit. However, acetylcholine (ACh) release from the striatum (1 Hz, 2 min), was only enhanced slightly by PDBu. The increase in DA release induced by PDBu was reduced markedly at higher frequencies of stimulation. Sulpiride (10 microM) alone, a D2 DA-receptor antagonist, or combined with nomifensine (3 microM), a neuronal-uptake inhibitor, did not prevent PDBu-induced facilitation of DA release from prefrontal cortex or striatum. The D2 DA agonists (LY-171555, bromocriptine and apomorphine) inhibited in a concentration-dependent manner the stimulation-evoked overflow of DA and ACh from the striatum, and of DA from the prefrontal cortex. Pretreatment with PDBu antagonized the inhibitory effect of the three agonists on DA and ACh release. A reduction both in Emax and IC50 was observed in PDBu-treated slices. Removal of endogenous DA by pretreatment with reserpine and alpha-methyl-p-tyrosine, failed to prevent PDBu-induced antagonism of apomorphine effects on ACh release, indicating that the antagonism of agonist effects was not due to higher synaptic levels of endogenous DA. The inactive enantiomer of PDBu, 4-alpha-12,13-dibutyrate did not enhance DA release and failed to modify the effects of D2 agonists on DA release.(ABSTRACT TRUNCATED AT 250 WORDS)     

止颤汤干预神经干细胞移植帕金森病大鼠脑内多巴胺及其代谢产物的变化

背景:如何促进脑内多巴胺含量的增加以及减少多巴胺的代谢,是治疗帕金森病的热点所在.目的:从多巴胺代谢途径角度观察止颤汤对神经干细胞移植帕金森病大鼠的脑黑质中多巴胺及其代谢产物含量的变化.方法:以大鼠脑立体定位和1-甲基-4-苯基-1,2,3,6-四氢吡啶建立帕金森病大鼠模型.应用高效液相色谱法测定帕金森病大鼠中脑多巴胺及其代谢产物的含量.结果与结论:止颤汤可以提高神经干细胞移植后帕金森病大鼠中脑多巴胺及其代谢产物双羟苯乙酸的含量,但对代谢产物高香草酸无明显影响.通过促进帕金森病大鼠干细胞移植后神经干细胞的存活,使之定向分化为多巴胺能神经元并分泌多巴胺,同时抑制多巴胺分解达到治疗作用.     

Molecular mechanisms in the actions of morphine and viminol (R2) on rat striatum.

Analgesic doses of morphine and viminol R2 increase the turnover rate of dopamine (DA) in rat striatum but fail to increase the striatal concentration of adenosine 3',5'-monophosphate (cAMP) or the affinity of tyrosine hydroxylase (TH) for the pteridine cofactor. When morphine is added to striatal homogenates, it changes neither the basal activity of adenylate cyclase nor the enzyme activation by DA. Similarly to morphine, haloperidol enhances the turnover rate of striatal DA, but unlike morphine it increases the affinity of TH for the pteridine cofactor and blocks the in vitro activation of striatal adenylacte cyclase by DA. Morphine (52 mumol/kg i.p.), viminol R2 (7 mumol/kg i.p.) or haloperidol (2.6 mumol/kg i.p.) fails to increase the striatal cAMP contrations. However (+)-amphetamine (4.8 mumol/kg i.p.) increases DA turnover rate and the striatal cAMP content, but, in doses up to 12.8 mumol/kg i.p., it fails to change the affinity of TH for the pteridine cofactor. This study shows that although (+)-amphetamine, haloperidol and morphine increase the turnover rate of striatal DA each drug possesses a specific profile in its action on molecular mechanisms that control the function of striatal dopaminergic synapses.     

Comparative dopamine-cholinergic mechanisms in the olfactory tubercle and the striatum: effects of metoclopramide

The olfactory tubercle (OT) is a limbic structure containing high dopamine (DA) and acetylcholine (ACh) concentrations. We performed a comparative study of the DA-ACh interactions, the efficacy of autoreceptor control and the effects of metoclopramide in the OT and the nucleus caudate (striatum). Rabbit brain slices from both regions of the same animal were prelabeled with radioactive DA and/or choline and then superfused. Comparable magnitude of DA and ACh release was evoked by electrical stimulation from both regions. DA release was unaltered, whereas ACh release was inversely related to the stimulation frequency, both in OT and striatum. Apomorphine (APO), a D1-D2 agonist, an LY-171555 (LY), a D2 agonist, inhibited DA and ACh release from OT and striatum with similar EC50 and Emax (maximal percentage of inhibition). However, the maximal degree of inhibition of ACh release achieved with APO, LY or DA in the OT was only one-half that observed in the striatum. In both regions, the inhibitory effects of DA agonists on DA and ACh release were reduced markedly when the number of electrical pulses and/or the frequency of stimulation were increased. l-Sulpiride, a DA D2 antagonist, increased the evoked release of DA and ACh from OT in direct relationship with the frequency of stimulation. In the OT, increases in synaptic DA achieved by administration of amphetamine or by blockade of the neuronal uptake pump with nomifensine inhibited the evoked release of ACh. Again these drug treatments produced only a 40 to 50% inhibition of ACh release. SKF 38393, a D1 agonist, had no effect per se on DA or ACh release in OT slices from control or from reserpine-treated animals (2 mg/kg s.c. for 3 or 7 days). With the exception of one specific dose combination, coadministration of SKF 38393 and LY produced no additive or synergistic effects on DA or ACh release from OT. APO- and LY-induced inhibition of DA and ACh release were antagonized by l-sulpiride. However, 300 nM SCH 23390, a D1 antagonist, reduced APO inhibition of DA and ACh release without affecting the inhibitory action of LY on DA and ACh release. Metoclopramide, "a DA antagonist with poor limbic activity", had a similar affinity for OT (pA2: 7.59) and striatal (pA2: 7.59) DA autoreceptors. Its antidopaminergic efficacy on DA receptors modulating ACh release from OT and striatum was also compared.(ABSTRACT TRUNCATED AT 400 WORDS)     

S33084, a novel, potent, selective, and competitive antagonist at dopamine D(3)-receptors: I. Receptorial, electrophysiological and neurochemical profile compared with GR218,231 and L741,626

The benzopyranopyrrole S33084 displayed pronounced affinity (pK(i) = 9.6) for cloned human hD(3)-receptors, and >100-fold lower affinity for hD(2) and all other receptors (>30) examined. S33084 concentration dependently, potently, and competitively (pA(2) = 9.7) antagonized dopamine (DA)-induced [(35)S]guanosine-5'- O-(3-thio)triphosphate (GTPgammaS) binding at hD(3)-receptors. It also concentration dependently abolished stimulation by DA of hD(3)-receptor-coupled mitogen-activated protein kinase. Administered alone, S33084 did not modify dialysate levels of DA in the frontal cortex, nucleus accumbens, or striatum of freely moving rats, nor the firing rate of ventrotegmental dopaminergic cell bodies. Furthermore, it had minimal effect on DA turnover in mesocortical, mesolimbic, and nigrostriatal projection regions. However, S33084 dose dependently blocked the suppressive influence of the preferential D(3)-agonist PD128,907 on frontocortical release of DA. Furthermore, it likewise antagonized the inhibitory influence of PD128,907 on the electrical activity of ventrotegmental dopaminergic neurons. Although less potent than S33084, GR218,231 likewise behaved as a selective hD(3)- versus hD(2)-receptor antagonist and its neurochemical and electrophysiological profiles were similar. In contrast, L741,626 was a preferential antagonist at hD(2) versus hD(3) sites. In vivo, on administration alone, L741,626 increased frontocortical, mesolimbic, and (more potently) striatal DA release, enhanced the firing rate of dopaminergic perikarya, and accelerated cerebral DA synthesis. It also blocked the actions of PD128,907. In conclusion, S33084 is a novel, potent, selective, and competitive antagonist at hD(3)-receptors. Although GR218,231 behaves similarly, L741,626 is a preferential D(2)-receptor antagonist. DA D(2)- but not D(3)-(auto) receptors tonically inhibit ascending dopaminergic pathways, although the latter may contribute to phasic suppression of DA release in frontal cortex.     

Effects of acute and chronic clozapine and haloperidol on in vitro release of acetylcholine and dopamine from striatum and nucleus accumbens

The purpose of this investigation was to determine if striatal or nucleus accumbens dopamine (DA) release, ACh release or DA receptor function were altered by acute and chronic haloperidol or clozapine treatment in a manner consistent with the reported pharmacological effects of each drug on A9 and A10 DA cell bodies and projection areas, when experiments were performed without a drug-free, or washout, period after drug treatment. The release of neurotransmitters reported here was evaluated using a slice-superfusion assay system. Transmitter release was induced either by an electrical field (for DA and ACh) or by application of either amphetamine or amfonelic acid (DA only). Dopaminergic receptor function was assessed by inhibiting electrically stimulated ACh release with in vitro TL-99 (a dopaminergic agonist) and by reversing that inhibition with in vitro neuroleptics or with ex vivo experimental paradigms (the in vitro analysis of transmitter release subsequent to in vivo drug administration). These data suggest that although there are differences between haloperidol and clozapine, there is no difference between the degree of postsynaptic DA receptor blockade produced that can be attributed to the duration of neuroleptic treatment. Chronic clozapine (20 mg/kg x 21 days) reversed TL-99-induced inhibition of ACh release in the nucleus accumbens only, whereas chronic haloperidol (0.5 mg/kg x 21 days) produced a similar reversal in both brain areas. One possible explanation for the lack of effect of chronic clozapine treatment in the striatum is that carrier-mediated (amphetamine-stimulated) DA release is enhanced in the striatum but not in the nucleus accumbens, suggesting that the potential DA receptor block in the striatum may be compromised by enhanced striatal DA levels. Acute haloperidol (0.5 mg/kg) was found to increase electrically stimulated ACh release in the striatum and DA release in the nucleus accumbens. Tolerance developed in the striatum, but not the nucleus accumbens, with repeated administration. However, acute clozapine had no effect on ACh release in either area, but it was found to enhance DA release in the striatum, an effect to which tolerance developed with chronic administration. Further, comparison of these data with data obtained using haloperidol and clozapine in vitro suggests that it is unlikely that these effects are due to residual drug still present in these tissues at the time of experimentation. These data are discussed with regard to electrophysiological and pharmacological differences observed between clozapine and haloperidol on the activity of A9 and A10 DA cells after chronic neuroleptic treatment.     

A new poly(ADP-ribose) polymerase inhibitor, FR261529 [2-(4-chlorophenyl)-5-quinoxalinecarboxamide], ameliorates methamphetamine-induced dopaminergic neurotoxicity in mice

Methamphetamine (METH) administration in mice, results in a chronic dopamine (DA) depletion associated with nerve terminal damage, with DA oxidation and generation of reactive oxygen species (ROS) primarily mediating this neurotoxicity. The oxidative stress induced by METH putatively activates nuclear enzyme poly(ADP-ribose) polymerase (PARP), with excessive PARP activation eventually leading to cell death. In this study, we show that prevention of PARP activation by treatment with FR261529 [2-(4-chlorophenyl)-5-quinoxalinecarboxamide], the compound that was recently identified as a novel PARP inhibitor (IC50 for PARP-1 = 33 nM, IC50 for PARP-2 = 7 nM), protects against both ROS-induced cells injury in vitro and METH-induced dopaminergic neuronal damage in an in vivo Parkinson's disease (PD) model. In PC12 cells, exposure of hydrogen peroxide or METH markedly induced PARP activation, and treatment with FR261529 (1 microM) significantly reduced PARP activation and attenuated cell death. In the mouse METH model, METH (15 mg/kg x 2 i.p., 2 h apart) intoxication accelerated DA metabolism and oxidation in the striatum, with subsequent cell damage in nigrostriatal dopaminergic neurons after 4 days. Oral administration of FR261529 (10 or 32 mg/kg) attenuated the damage of dopaminergic neurons via marked reduction of PARP activity and not via changes in dopamine metabolism or body temperature. These findings indicate that the neuroprotective effects of a novel PARP inhibitor, FR261529, were accompanied by inhibition of METH-induced PARP activation, suggesting that METH induces nigrostriatal dopaminergic neurodegeneration involving PARP activation and also orally active and brain-penetrable PARP inhibitor FR261529 could be a novel attractive therapeutic candidate for neurodegenerative disorders such as PD.     

Quantitative [(123)I]FP-CIT pinhole SPECT imaging predicts striatal dopamine levels, but not number of nigral neurons in different mouse models of Parkinson's disease

Single photon emission computed tomography (SPECT) using [(123)I]FP-CIT as radioligand for the dopamine transporter has become a widely used tool to monitor the integrity of the nigrostriatal dopaminergic projection in Parkinson's disease (PD). Previous studies with pinhole SPECT in small animals have demonstrated that the striatal [(123)I]FP-CIT binding indeed correlates with the striatal dopamine transporter protein level. It is unclear, however, if there is a stable relationship between the striatal [(123)I]FP-CIT binding and other functionally important parameters of the nigrostriatal system, such as the striatal dopamine levels and the number of dopaminergic neurons in the substantia nigra. To assess this question experimentally, we studied two different mouse models of PD, namely a mild 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine intoxication paradigm, to model mild nigrostriatal damage and the intrastriatal 6-hydroxydopamine paradigm to model more advanced nigrostriatal damage. Our data demonstrate that the striatal [(123)I]FP-CIT binding measured by SPECT in vivo precisely predicts the striatal dopamine concentrations, but does not necessarily correlate with the nigral dopaminergic cell number. Thus, the present work underscores that FP-CIT SPECT does only allow judging the integrity of the striatal dopaminergic nerve terminals, but not the nigral dopaminergic cells in PD. This finding may have significant impact on the use of [(123)I]FP-CIT SPECT as a surrogate marker for clinical trials aimed at measuring neuroprotection.     

Selective impairment of prediction error signaling in human dorsolateral but not ventral striatum in Parkinson's disease patients: evidence from a model-based fMRI study

Animal studies have found that the phasic activity of dopamine neurons during reward-related learning resembles a “prediction error” (PE) signal derived from a class of computational models called reinforcement learning (RL). An apparently similar signal can be measured using fMRI in the human striatum, a primary dopaminergic target. However, the fMRI signal does not measure dopamine per se, and therefore further evidence is needed to determine if these signals are related to each other. Parkinson's disease (PD) involves the neurodegeneration of the dopamine system and is accompanied by deficits in reward-related decision-making tasks. In the current study we used a computational RL model to assess striatal error signals in PD patients performing an RL task during fMRI scanning. Results show that error signals were preserved in ventral striatum of PD patients, but impaired in dorsolateral striatum, relative to healthy controls, a pattern reflecting the known selective anatomical degeneration of dopamine nuclei in PD. These findings support the notion that PE signals measured in the human striatum by the BOLD signal may reflect phasic DA activity. These results also provide evidence for a deficiency in PE signaling in the dorsolateral striatum of PD patients that may offer an explanation for their deficits observed in other reward learning tasks.     

Recovery From Experimental Parkinsonism by Semaphorin-guided Axonal Growth of Grafted Dopamine Neurons

Cell therapy in animal models of Parkinson''s disease (PD) is effective after intrastriatal grafting of dopamine (DA) neurons, whereas intranigral transplantation of dopaminergic cells does not cause consistent behavioral recovery. One strategy to promote axonal growth of dopaminergic neurons from the substantia nigra (SN) to the striatum is degradation of inhibitory components such as chondroitin sulphate proteoglycans (CSPG). An alternative is the guidance of DA axons by chemotropic agents. Semaphorins 3A and 3C enhance axonal growth of embryonic stem (ES) cell–derived dopaminergic neurons in vitro, while Semaphorin 3C also attracts them. We asked whether intranigral transplantation of DA neurons, combined with either degradation of CSPG or with grafts of Semaphorin 3–expressing cells, towards the striatum, is effective in establishing a new nigrostriatal dopaminergic pathway in rats with unilateral depletion of DA neurons. We found depolarization-induced DA release in dorsal striatum, DA axonal projections from SN to striatum, and concomitant behavioral improvement in Semaphorin 3–treated animals. These effects were absent in animals that received intranigral transplants combined with Chondroitinase ABC treatment, although partial degradation of CSPG was observed. These results are evidence that Semaphorin 3–directed long-distance axonal growth of dopaminergic neurons, resulting in behavioral improvement, is possible in adult diseased brains.     

Inflammatory process in Parkinson disease: neuroprotection by neuropeptide Y

Parkinson's disease (PD) is characterized by the degeneration of dopaminergic neurons in the nigro‐striatal pathway. Interestingly, it has already been shown that an intracerebral administration of neuropeptide Y (NPY) decreases the neurodegeneration induced by 6‐hydroxydopamine (6‐OHDA) in rodents and prevents loss of dopamine (DA) and DA transporter density. The etiology of idiopathic PD now suggest that chronic production of inflammatory mediators by activated microglial cells mediates the majority of DA‐neuronal tissue destruction. In an animal experimental model of PD, the present study shows that NPY inhibited the activation of microglia evaluated by the binding of the translocator protein (TSPO) ligand [3H]PK11195 in striatum and substantia nigra of 6‐OHDA rats. These results suggest a potential role for inflammation in the pathophysiology of the disease and a potential treatment by NPY in PD.     

Effects of d-amphetamine and dopamine synthesis inhibitors on dopamine and acetylcholine neurotransmission in the striatum. II. Release in the presence of vesicular transmitter stores

The release of endogenous dopamine (DA) elicited by electrical stimulation and by d-amphetamine (AMPH) from superfused striatal slices of untreated rabbits was examined. AMPH (0.3-10 microM) produced a concentration-dependent increase in basal DA efflux (30-fold increase at 10 microM) and stimulation-evoked (SE) DA overflow (11-fold increase at 10 microM). Although AMPH had little effect on the basal efflux of dihydroxyphenylacetic acid (DOPAC), the drug was an effective inhibitor of the SE overflow of the DA metabolite (66% inhibition at 0.3 microM). AMPH increased significantly the total basal efflux of endogenous compounds (DA + DOPAC) only at high concentrations (3-10 microM) whereas the total SE overflow of total endogenous compounds was decreased at all concentrations of AMPH tested. AMPH inhibited SE [3H]acetylcholine (ACh) release in a concentration-dependent manner (71% inhibition at 10 microM). Inhibition of DA synthesis with alpha-methyl-p-tyrosine (100 microM) or 3-iodotyrosine (100 microM) reduced both the basal efflux and SE overflow of endogenous DA and DOPAC; synthesis inhibition had greater effects on the SE overflow. Neither synthesis inhibitor altered SE [3H]ACh release. alpha-Methyl-p-tyrosine and 3-iodotyrosine reduced the absolute values of the basal efflux and SE overflow of DA elicited by AMPH by approximately 60%; however, the inhibition of SE [3H]ACh release produced by AMPH was attenuated only slightly (approximately 20%). Synthesis inhibitors also reduced tissue DA levels (approximately 30%). These results suggest that: basal efflux of endogenous DA from superfused rabbit striatal slices may derived both from DA newly synthesized in the cytoplasm and from spontaneous leakage of DA from storage vesicles. In addition, synthesis may provide a continuous supply of DA to vesicles that are used for exocytotic DA release during electrical stimulation. However, the depletion of tissue DA produced by synthesis inhibitors as well as other extraneous pharmacological actions of these drugs makes firm conclusions difficult. AMPH increases the synaptic concentration of DA by accelerating the basal efflux as well as the SE overflow of unchanged DA. At concentrations less than 1 microM AMPH has no effect on basal efflux of DA or DOPAC but reduces SE overflow of DOPAC via an unknown mechanism. At higher concentrations (greater than or equal to 1 microM) acceleration of carrier-mediated DA efflux coupled with displacement of DA from vesicular stores, as well as interference with the uptake of exocytotically released DA produces a marked increase in synaptic DA which in turn inhibits SE ACh release.(ABSTRACT TRUNCATED AT 400 WORDS)     

止颤汤干预神经干细胞移植帕金森病大鼠脑内多巴胺及其代谢产物的变化

背景：如何促进脑内多巴胺含量的增加以及减少多巴胺的代谢,是治疗帕金森病的热点所在。目的：从多巴胺代谢途径角度观察止颤汤对神经干细胞移植帕金森病大鼠的脑黑质中多巴胺及其代谢产物含量的变化。方法：以大鼠脑立体定位和1-甲基-4-苯基-1,2,3,6-四氢吡啶建立帕金森病大鼠模型。应用高效液相色谱法测定帕金森病大鼠中脑多巴胺及其代谢产物的含量。结果与结论：止颤汤可以提高神经干细胞移植后帕金森病大鼠中脑多巴胺及其代谢产物双羟苯乙酸的含量,但对代谢产物高香草酸无明显影响。通过促进帕金森病大鼠干细胞移植后神经干细胞的存活,使之定向分化为多巴胺能神经元并分泌多巴胺,同时抑制多巴胺分解达到治疗作用。     

Imaging DA release in a rat model of L-DOPA-induced dyskinesias: A longitudinal in vivo PET investigation of the antidyskinetic effect of MDMA

In the context of Parkinson's disease, motor symptoms result from the degeneration of nigrostriatal neurons. Dopamine (DA) replacement using l-3,4-dihydroxyphenylalanine (L-DOPA) has been the treatment of choice in the early stages of the disease. However, with disease progression, patients suffer from motor complications, which have been suggested to arise from DA released from serotonergic terminals according to the false neurotransmitter hypothesis. The synthetic amphetamine derivative (±) 3,4-methylenedioxymethamphetamine (MDMA) has been shown to significantly inhibit dyskinesia in humans and in animal models of PD. In this study, we examined the effect of MDMA on L-DOPA-induced DA release by using [(11)C]raclopride kinetic modeling to assess alterations in DA neurotransmission in a rat model of L-DOPA-induced dyskinesia (LID) in a longitudinal in vivo PET study. Rats were submitted to 6-OHDA lesions, and the lesions were confirmed to be sufficiently severe based on the performance during stepping tests and [(11)C]methylphenidate PET scans. The rats underwent two [(11)C]raclopride PET sessions before (baseline) and after two weeks of chronic L-DOPA treatment (priming). L-DOPA priming led to strong abnormal involuntary movements (AIMs). In group 1, L-DOPA priming reduced L-DOPA-induced DA release in the lesioned striatum with no effect on the healthy side, while the concomitant administration of L-DOPA and MDMA (group 2) increased the DA levels in the lesioned and healthy striatum. In addition, behavioral analysis, which was performed two weeks after the second PET session, confirmed the antidyskinetic effect of MDMA. Our data show that L-DOPA-induced DA release is attenuated in the Parkinsonian striatum after chronic L-DOPA pretreatment and that the antidyskinetic mechanism of MDMA does not depend primarily on dopaminergic neurotransmission.     

Effects of d-amphetamine and dopamine synthesis inhibitors on dopamine and acetylcholine neurotransmission in the striatum. I. Release in the absence of vesicular transmitter stores

The release of endogenous dopamine (DA) elicited by electrical stimulation and by d-amphetamine (AMPH) from superfused striatal slices of reserpine-pretreated rabbits was examined. Although reserpine pretreatment reduced tissue DA levels by greater than 95%, the basal efflux of DA and the DA metabolite dihydroxyphenylacetic acid (DOPAC) was slightly greater than that observed in untreated slices. DOPAC constituted the large majority of the basal efflux of endogenous compounds. No overflow of endogenous compounds was evoked by electrical stimulation (3 Hz, 3 min) after reserpine pretreatment. Superfusion with alpha-methyl-p-tyrosine (100 microM) abolished the efflux of endogenous DA and DOPAC. AMPH (0.3-10 microM) produced a concentration-dependent increase in the basal efflux of endogenous DA and a concomitant decrease in endogenous DOPAC efflux. The total efflux of endogenous compounds (DA + DOPAC) tended to be decreased by AMPH. No electrically evoked overflow of endogenous compounds was observed in the presence of AMPH. The increase in synaptic DA produced by AMPH was reflected by a concentration-dependent reduction in the electrically evoked overflow of [3H]acetylcholine (ACh). The ability of AMPH to increase DA efflux and inhibit [3H]ACh release was blocked by inhibition of DA synthesis with alpha-methyl-p-tyrosine (100 microM) or by blockade of the DA neuronal uptake carrier with nomifensine (NOM) (10 microM) and was potentiated by inhibition of monoamine oxidase with pargyline (10 microM). NOM also blocked partially the ability of AMPH to reduce endogenous DOPAC efflux. NOM increased the basal efflux of endogenous DA and inhibited electrically evoked [3H]ACh release but these effects were quantitatively much less than those produced by AMPH. NOM had no effect on DOPAC efflux. Pargyline had little effect on endogenous DA efflux or electrically evoked [3H]ACh release but abolished DOPAC efflux and increased tissue DA levels measured at the end of superfusion. When given in combination, NOM and pargyline produced a similar degree of inhibition of [3H]ACh release as AMPH, although the increase in DA efflux produced by this drug combination was less than that produced by AMPH. These results suggest that in the absence of vesicular transmitter stores (reserpine-pretreatment): synthesis provides a continuous supply of DA which is metabolized rapidly within the neuron and is lost as DOPAC; AMPH facilitates the synthesis-dependent efflux of extravesicular DA probably by an accelerated exchange diffusion mechanism.(ABSTRACT TRUNCATED AT 400 WORDS)     

微泵恒速灌注叠氮钠致痴呆大鼠脑内胆碱及单胺类神经递质含量改变

目的 观察线粒体呼吸链复合体IV(线粒体细胞色素C氧化酶)抑制剂叠氮钠对大鼠脑内胆碱及单胺类神经递质的影响，探讨线粒体缺陷导致学习记忆障碍的可能机制。方法 SD大鼠皮下埋植Alzet微泵，连续恒速给予叠氮钠共30天，分为1mg／kg／h和2mg／kg／h两个剂量组。取脑，分区测定皮层和海马胆碱乙酰基转移酶(放射化学法)及乙酰胆碱酯酶(羟胺比色法)的活性，高效液相色谱法测定纹状体内单胺类神经递质及其代谢产物含量。结果 模型大鼠皮层和海马胆碱乙酰基转移酶活性降低，海马区乙酰胆碱酯酶活性升高，皮层和海马胆碱乙酰基转移酶与乙酰胆碱酯酶活性的比值明显降低。纹状体内单胺类神经递质及其代谢产物含量各组间无明显差异。结论 线粒体细胞色素C氧化酶活性的抑制可以导致动物脑内胆碱乙酰基转移酶及乙酰胆碱酯酶活性的异常，是模型大鼠学习记忆能力障碍的基础。微泵恒速灌注叠氮钠仅损伤大鼠脑内胆碱能神经系统，对脑内单胺类神经递质无影响，可作为拟痴呆模型，应用于发病机理及药理学等方面的研究。     

Delayed delivery of AAV-GDNF prevents nigral neurodegeneration and promotes functional recovery in a rat model of Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) is a strong candidate agent in the neuroprotective treatment of Parkinson's disease (PD). We investigated whether adeno-associated viral (AAV) vector-mediated delivery of a GDNF gene in a delayed manner could prevent progressive degeneration of dopaminergic (DA) neurons, while preserving a functional nigrostriatal pathway. Four weeks after a unilateral intrastriatal injection of 6-hydroxydopamine (6-OHDA), rats received injection of AAV vectors expressing GDNF tagged with FLAG peptide (AAV-GDNFflag) or beta-galactosidase (AAV-LacZ) into the lesioned striatum. Immunostaining for FLAG demonstrated retrograde transport of GDNFflag to the substantia nigra (SN). The density of tyrosine hydroxylase (TH)-positive DA fibers in the striatum and the number of TH-positive or cholera toxin subunit B (CTB, neuronal tracer)-labeled neurons in the SN were significantly greater in the AAV-GDNFflag group than in the AAV-LacZ group. Dopamine levels and those of its metabolites in the striatum were remarkably higher in the AAV-GDNFflag group compared with the control group. Consistent with anatomical and biochemical changes, significant behavioral recovery was observed from 4-20 weeks following AAV-GDNFflag injection. These data indicate that a delayed delivery of GDNF gene using AAV vector is efficacious even 4 weeks after the onset of progressive degeneration in a rat model of PD.     

Behavioral recovery in a primate model of Parkinson's disease by triple transduction of striatal cells with adeno-associated viral vectors expressing dopamine-synthesizing enzymes

One potential strategy for gene therapy of Parkinson's disease (PD) is the local production of dopamine (DA) in the striatum induced by restoring DA-synthesizing enzymes. In addition to tyrosine hydroxylase (TH) and aromatic-L-amino-acid decarboxylase (AADC), GTP cyclohydrolase I (GCH) is necessary for efficient DA production. Using adeno-associated virus (AAV) vectors, we previously demonstrated that expression of these three enzymes in the striatum resulted in long-term behavioral recovery in rat models of PD. We here extend the preclinical exploration to primate models of PD. Mixtures of three separate AAV vectors expressing TH, AADC, and GCH, respectively, were stereotaxically injected into the unilateral putamen of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated monkeys. Coexpression of the enzymes in the unilateral putamen resulted in remarkable improvement in manual dexterity on the contralateral to the AAV-TH/-AADC/-GCH-injected side. Behavioral recovery persisted during the observation period (four monkeys: 48 days, 65 days, 50 days, and >10 months, each). TH-immunoreactive (TH-IR), AADC-IR, and GCH-IR cells were present in a large region of the putamen. Microdialysis demonstrated that concentrations of DA in the AAV-TH/-AADC/-GCH-injected putamen were increased compared with the control side. Our results show that AAV vectors efficiently introduce DA-synthesizing enzyme genes into the striatum of primates with restoration of motor functions. This triple transduction method may offer a potential therapeutic strategy for PD.     

Paraquat exposure reduces nicotinic receptor-evoked dopamine release in monkey striatum

Paraquat, an herbicide widely used in the agricultural industry, has been associated with lung, liver, and kidney toxicity in humans. In addition, it is linked to an increased risk of Parkinson's disease. For this reason, we had previously investigated the effects of paraquat in mice and showed that it influenced striatal nicotinic receptor (nAChR) expression but not nAChR-mediated dopaminergic function. Because nonhuman primates are evolutionarily closer to humans and may better model the effects of pesticide exposure in man, we examined the effects of paraquat on striatal nAChR function and expression in monkeys. Monkeys were administered saline or paraquat once weekly for 6 weeks, after which nAChR levels and receptor-evoked [(3)H]dopamine ([(3)H]DA) release were measured in the striatum. The functional studies showed that paraquat exposure attenuated dopamine (DA) release evoked by alpha3/alpha6beta2(*) (nAChR that is composed of the alpha3 or alpha6 subunits, and beta2; the asterisk indicates the possible presence of additional subunits) nAChRs, a subtype present only on striatal dopaminergic terminals, with no decline in release mediated by alpha4beta2(*) (nAChR containing alpha4 and beta2 subunits, but not alpha3 or alpha6) nAChRs, present on both DA terminals and striatal neurons. Paraquat treatment decreased alpha4beta2(*) but not alpha3/alpha6beta2(*) nAChR expression. The differential effects of paraquat on nAChR expression and receptor-evoked [(3)H]DA release emphasize the importance of evaluating changes in functional measures. The finding that paraquat treatment has a negative impact on striatal nAChR-mediated dopaminergic activity in monkeys but not mice indicates the need for determining the effects of pesticides in higher species.