Assessment of recovery in the hemiparkinson rat: Drug-induced rotation is inadequate

Striatal inhibition of calpains prevents levodopa-induced neurochemical changes and abnormal involuntary movements in the hemiparkinsonian rat model

Pharmacological dopamine replacement with l-3,4-dihydroxyphenylalanine (L-DOPA) remains the most effective approach to treat the motor symptoms of Parkinson's disease (PD). However, as the disease progresses, the therapeutic response to L-DOPA gradually becomes erratic and is associated with the emergence of dyskinesia in the majority of patients. The pathogenesis of L-DOPA-induced dyskinesia (LID) is still unknown. In the current study, using the 6-hydroxydopamine (6-OHDA)-lesioned rat model of PD, we demonstrated that the calcium-dependent proteins calpains and cdk5 of the striatum play a critical role in the behavioral and molecular changes evoked by L-DOPA therapy. We first confirmed that L-DOPA reversed PD symptoms, assessed by the cylinder, stepping and vibrissae-elicited reaching tests in this animal model, and elicited robust abnormal involuntary movements (AIMs) reminiscent of LID. Interestingly, intrastriatal infusion of the calpains inhibitor MDL28170, and to a lower extent the cdk5 inhibitor roscovitine, reduced the severity and amplitude of AIMs without affecting L-DOPA's antiparkinsonian effects. Notably, the calpains and cdk5 inhibitors totally reversed the striatal molecular changes attributed to L-DOPA therapy, such as ERK1/2 and dynamin phosphorylation. Another fascinating observation was that L-DOPA therapy, in combination with intrastriatal infusion of MDL28170, augmented tyrosine hydroxylase levels in the striatum of lesioned rats without affecting the number of dopaminergic cells in the substantia nigra. These findings disclose a novel mechanism underlying the maladaptive alterations induced by L-DOPA therapy in the 6-OHDA rat model of PD.

Role of dopamine D3 and serotonin 5-HT 1A receptors in L: -DOPA-induced dyskinesias and effects of sarizotan in the 6-hydroxydopamine-lesioned rat model of Parkinson's disease

Sarizotan, a 5-HT(1A) agonist with additional affinity for D(3) and D(4) receptors, has been demonstrated to have anti-dyskinetic effects. The mechanism by which these effects occur is not clear. Using unilateral 6-hydroxydopamine-lesioned rats that received chronic intraperitoneal (ip) administration of L: -3,4-dihydroxyphenylalanine (L: -DOPA) we investigated the involvement of D(3) and 5-HT(1A) receptors in the effects of sarizotan on contraversive circling and abnormal involuntary movements (AIMs). Before sensitization by chronic L: -DOPA treatment (12.5 with 3.25 mg/kg benserazide ip, twice daily for 21 days), no effect of the selective D(3) agonist, PD128907 (1 or 3 mg/kg ip), or the selective D(3) antagonist, GR103691 (0.5 or 1.5 mg/kg ip), was observed. Treatment with sarizotan (1 or 5 mg/kg ip) dose-dependently inhibited the L: -DOPA-induced contraversive turning and AIMs. In co-treatment with the 5-HT(1A) antagonist, WAY100635 (1 mg/kg ip), sarizotan failed to affect this behaviour, confirming the prominent 5-HT(1A) receptor-mediated mechanism of action. In the presence of PD128907 (3 mg/kg ip), the effects of sarizotan on contraversive turning, locomotive dyskinesia and axial dystonia, but not on orolingual and forelimb dyskinesia, were blocked. On its own, PD128907 had no effect on the behavioural effects of L: -DOPA except that it tended to reduce orolingual and forelimb dyskinesia. GR103691 had no effect on its own or in combination with sarizotan. These data identify an involvement of D(3) receptors in the action of sarizotan on some, but not all L: -DOPA-induced motor side effects. This selective involvement is in contrast to the more general involvement of 5-HT(1A) receptors in the anti-dyskinetic effects of sarizotan.

Oral tremor induced by the muscarinic agonist pilocarpine is suppressed by the adenosine A2A antagonists MSX-3 and SCH58261, but not the adenosine A1 antagonist DPCPX

Tremulous jaw movements in rats, which can be induced by dopamine (DA) antagonists, DA depletion, and cholinomimetics, have served as a useful model for studies of tremor. Although adenosine A(2A) antagonists can reduce the tremulous jaw movements induced by DA antagonists and DA depletion, there are conflicting reports about the interaction between adenosine antagonists and cholinomimetic drugs. The present studies investigated the ability of adenosine antagonists to reverse the tremorogenic effect of the muscarinic agonist pilocarpine. While the adenosine A(2A) antagonist MSX-3 was incapable of reversing the tremulous jaw movements induced by the 4.0mg/kg dose of pilocarpine, both MSX-3 and the adenosine A(2A) antagonist SCH58261 reversed the tremulous jaw movements elicited by 0.5mg/kg pilocarpine. Systemic administration of the adenosine A(1) antagonist DPCPX failed to reverse the tremulous jaw movements induced by either an acute 0.5mg/kg dose of the cholinomimetic pilocarpine or the DA D2 antagonist pimozide, indicating that the tremorolytic effects of adenosine antagonists may be receptor subtype specific. Behaviorally active doses of MSX-3 and SCH 58261 showed substantial in vivo occupancy of A(2A) receptors, but DPCPX did not. The results of these studies support the use of adenosine A(2A) antagonists for the treatment of tremor.

Amphetamine-evoked rotation requires newly synthesized dopamine at 14 days but not 1 day after intranigral 6-OHDA and is consistently dissociated from sensorimotor behavior

Immediately after unilateral, intranigral 6-hydroxydopamine (6-OHDA), amphetamine (AMPH) evokes "paradoxical" contraversive rotation, whereas 14 days later, AMPH evokes the traditional ipsiversive rotation used to model the chronic Parkinsonian state. In this study, the hypothesis was that accelerated dopamine (DA) synthesis ipsilateral to the lesion augments cytoplasmic DA to produce paradoxical rotation. Therefore, the sensitivity to synthesis inhibition of AMPH-evoked rotation at 1 or 14 days after 6-OHDA was assessed. To determine the functional status that might be reflected by paradoxical rotation, sensorimotor abilities were examined at 1 and 14 days following unilateral 6-OHDA using the elevated swing, paw placement, grip strength, ladder walking, somatosensory neglect, and cylinder tests. At 14 days after 6-OHDA when AMPH-evoked ipsiversive rotation is mediated by the intact hemisphere, rotation was dose-dependently reduced by tyrosine hydroxylase (TH) inhibition with alpha-methyl-p-tyrosine (alpha-MPT) or dopa decarboxylase (DDC) inhibition with 3-hydroxybenzyl hydrazine (NSD-1015), indicating dependence upon newly synthesized DA. Conversely, at 1 day after 6-OHDA, paradoxical rotation, presumably mediated by the treated hemisphere, was completely resistant to synthesis blockade, indicating an abundant supply of intracellular DA that is independent from synthesis rates. Sensorimotor behaviors were not correlated with AMPH-evoked rotation. The present data do not support the hypothesis that enhanced DA synthesis is required to express paradoxical rotation. Therefore, alternative mechanisms that may enhance cytoplasmic DA to produce paradoxical rotation are discussed.

Effects of coincident 5-HT1A receptor stimulation and NMDA receptor antagonism on L-DOPA-induced dyskinesia and rotational behaviors in the hemi-parkinsonian rat

RATIONALE

Serotonin 1A receptor (5-HT1AR) agonists reduce L-DOPA-induced dyskinesia and enhance motor function in experimental and clinical investigations of Parkinson's disease (PD). While the mechanism(s) by which these effects occur are unclear, recent research suggests that modulation of glutamate neurotransmission contributes.

OBJECTIVE

To further delineate the relationship between 5-HT1A receptors and glutamate, the current study examined the effects of the 5-HT1AR agonist, +/-8-OH-DPAT and the N-methyl-D-aspartic acid receptor (NMDAR) antagonist, MK-801, on L-DOPA-induced motor behavior.

MATERIALS AND METHODS

Unilateral 6-hydroxydopamine lesioned male Sprague-Dawley rats were rendered dyskinetic with 1 week of daily L-DOPA (12 mg/kg, i.p.) + benserazide (15 mg/kg, i.p.). On test days, one group of rats received pretreatments of: +/-8-OH-DPAT (0, 0.03, 0.1, 0.3 mg/kg, i.p.) or MK-801 (0, 0.03, 0.1, 0.3 mg/kg, i.p.). A second group was administered combined +/-8-OH-DPAT (0, 0.03 or 0.1 mg/kg, i.p.) + MK-801 (0, 0.1 mg/kg, i.p.). Pretreatments were followed by L-DOPA administration, after which, abnormal involuntary movements (AIMs) and rotations were monitored. To investigate effects on motor performance, subthreshold doses of +/-8-OH-DPAT (0.03 mg/kg, i.p.) + MK-801 (0.1 mg/kg, i.p.) were administered to L-DOPA-naïve hemiparkinsonian rats before the forepaw adjusting steps test.

RESULTS

Individually, both +/-8-OH-DPAT and MK-801 dose-dependently decreased L-DOPA-induced AIMs without affecting rotations. Combined subthreshold doses of +/-8-OH-DPAT+MK-801 reduced L-DOPA-induced AIMs and potently enhanced contralateral rotations without altering L-DOPA-induced motor improvements.

CONCLUSIONS

The current results indicate a functional interaction between 5-HT1AR and NMDAR that may improve pharmacological treatment of PD patients.

Blockade of globus pallidus adenosine A(2A) receptors displays antiparkinsonian activity in 6-hydroxydopamine-lesioned rats treated with D(1) or D(2) dopamine receptor agonists

We have recently demonstrated how antagonism of adenosine A(2A) receptors within the globus pallidus (GP) ipsilateral to dopaminergic denervation potentiates contralateral rotational behavior induced by the dopamine precursor L-DOPA in 6-hydroxydopamine-lesioned hemiparkinsonian rats. To further characterize the influence of pallidal A(2A) receptor blockade on the motor stimulant effects elicited by dopamine receptor activation, hemiparkinsonian rats were infused with the water-soluble A(2A) antagonist SCH BT2 in the GP, alone or in combination with systemic administration of either SKF 38393 or quinpirole, to stimulate dopamine D(1) or D(2) receptors, respectively. SCH BT2 alone (5 mug/1 mul) neither altered motor behavior nor produced postural asymmetry. In contrast, the contralateral rotations elicited by SKF 38393 (1.5 mg/kg) as well as quinpirole (0.05 mg/kg) were potentiated by the concomitant intrapallidal infusion of SCH BT2. The results of this study demonstrate that blockade of pallidal A(2A) receptors exerts a facilitatory influence on the motor effects produced by the selective stimulation of either D(1) or D(2) dopamine receptors in hemiparkinsonian rats and suggest an involvement of GP in the antiparkinsonian activity of A(2A) receptor antagonists.

Human retinal pigment epithelial cell implants ameliorate motor deficits in two rat models of Parkinson disease

Intrastriatal transplantation of gelatin microcarrier-attached human retinal pigment epithelial cells (hRPE-GM) may represent an alternative source for cell therapy in Parkinson disease (PD). The use of human retinal pigment epithelial (hRPE) cells in PD relies on the capacity of these cells to produce l-dopa as an intermediate product in the eumelanin synthesis pathway. We investigated the behavioral effects of hRPE-GM implants on forelimb use asymmetries and hindlimb motor deficits in unilateral and bilateral 6-hydroxydopamine (6-OHDA) rat models of PD. We report that intrastriatal unilateral implantation of hRPE-GM in rats with 6-OHDA nigrostriatal lesions produce an amelioration of the contralateral forelimb disuse and the contralateral hindlimb deficits. These results further support the possibility that implantation of cultured hRPE cells may be a promising therapeutic option for patients with PD.

The partial 5-HT1A agonist buspirone reduces the expression and development of l-DOPA-induced dyskinesia in rats and improves l-DOPA efficacy

Dopamine (DA) replacement therapy with l-DOPA remains the standard pharmacotherapy for Parkinson's disease (PD). Unfortunately, chronic l-DOPA treatment is accompanied by development of motor fluctuations and l-DOPA-induced dyskinesia (LID). While serotonin (5-HT)(1A) agonists acutely reduce these complications, their prophylactic and long-term effects are not well-delineated. To test this, male Sprague-Dawley rats received unilateral 6-hydroxydopamine (6-OHDA) lesions. In experiment 1, l-DOPA-primed rats were pre-treated with Vehicle (0.9% NaCl), various doses of the partial 5-HT(1A) agonist, buspirone (0.25, 1.0 or 2.5 mg/kg, ip) or buspirone (2.5 mg/kg, ip)+the 5-HT(1A) antagonist, WAY100635 (0.5 mg/kg, ip) 5 min prior to l-DOPA (12 mg/kg+15 mg/kg benserazide, ip). Rats were tested for LID using the abnormal involuntary movements (AIMs) scale and motor performance using the forepaw adjusting steps test (FAS). In experiment 2, l-DOPA-naïve rats received co-administration of l-DOPA+buspirone (1.0 or 2.5 mg/kg, ip) for 2 weeks. AIMs and FAS were measured throughout. In l-DOPA-primed rats, buspirone dose-dependently reduced LID and improved l-DOPA-related motor performance due to action at the 5-HT(1A) receptor. In l-DOPA-naïve rats, buspirone delayed LID development while improving l-DOPA's anti-parkinsonian efficacy indicating the potential long-term benefits of 5-HT(1A) agonists for reduction of l-DOPA-related side effects.

Quantitative measurement of neurological deficit after mild (30 min) transient middle cerebral artery occlusion in rats

Although 30-min transient middle cerebral artery occlusion (30-min tMCAo) causes reproducible subcortical infarction in rats, it is difficult to evaluate the resulting neurological deficit using common behavioral tests such as the rota-rod test, adhesive-removal test, or narrow beam test. Establishment of a method of quantitative evaluation would help to develop a novel therapeutic approach to treat cerebral infarction. To solve this problem, we examined whether the neurological deficit could be detected by the Montoya staircase test or methamphetamine-induced rotation, which are commonly used in a Parkinson disease model induced by intrastriatal injection of 6-hydroxydopamine (6-OHDA). From 10 to 14 days after tMCAo, the Montoya staircase test showed significant clumsiness in forelimb tasks contralateral to the lesion side, whereas sham-operated rats showed no significant clumsiness in both forelimbs. The number of ipsilateral rotations induced by methamphetamine was also increased in tMCAo-rats at 21 days after tMCAo. Although Pearson's correlations coefficient showed that the results of these tests were correlated with the infarction volume, there was no significant correlation between the results of these two tests. These findings imply that the neurological deficit detected by both tests might reflect the severity of ischemic injury, but each test might evaluate different aspects of neurological deficit. Thus, the Montoya staircase test and methamphetamine-induced rotation are useful to evaluate neurological deficit in the chronic stage of subcortical infarction induced by 30-min tMCAo.

MDMA and fenfluramine reduce L-DOPA-induced dyskinesia via indirect 5-HT1A receptor stimulation

Chronic L-3,4-dihydroxyphenylalanine (L-DOPA) pharmacotherapy in Parkinson's disease is often accompanied by the development of abnormal and excessive movements known as dyskinesia. Clinical and experimental studies indicate that indirect serotonin agonists can suppress dyskinesia without affecting the efficacy of L-DOPA. While the mechanism by which these effects occur is not clear, recent research suggests that serotonin 5-HT1A receptors may play a pivotal role. To test this, male Sprague-Dawley rats with unilateral 6-hydroxydopamine medial forebrain bundle lesions received 1 week of daily treatment with L-DOPA (12 mg/kg, i.p.) plus benserazide (15 mg/kg, i.p.). Beginning on the 8th day of treatment and every 3rd or 4th day thereafter, rats were pretreated with vehicle (0.9% NaCl), the serotonin and dopamine releaser 3,4-methylenedioxymethamphetamine (MDMA; 0.25 or 2.5 mg/kg, i.p.) or the serotonin releaser fenfluramine (FEN; 0.25 or 2.5 mg/kg, i.p.) 5 min prior to L-DOPA, after which abnormal involuntary movements (AIMs) and rotations were quantified every 20th minute for 2 h. Pretreatment with 2.5 mg/kg of either MDMA or FEN reduced AIMs. To determine the contribution of the 5-HT1A receptor to these effects, another group of L-DOPA-primed 6-hydroxydopamine-lesioned rats were pretreated with the 5-HT1A antagonist WAY100635 (0.5 mg/kg, i.p.), MDMA + WAY100635 (2.5 + 0.5 mg/kg, i.p.) or FEN + WAY100635 (2.5 + 0.5 mg/kg, i.p.) 5 min prior to L-DOPA and subsequent AIMs and rotation tests. The antidyskinetic effects of MDMA and FEN were reversed by cotreatment with WAY100635. These results suggest that 5-HT-augmenting compounds such as MDMA and FEN probably convey antidyskinetic properties in part via stimulation of 5-HT1A receptors.