Early changes in neuropeptide mRNA expression in the striatum following reserpine treatment

Altered profile and D2-dopamine receptor modulation of high voltage-activated calcium current in striatal medium spiny neurons from animal models of Parkinson's disease

In the present work we analyzed the profile of high voltage-activated (HVA) calcium (Ca2+) currents in freshly isolated striatal medium spiny neurons (MSNs) from rodent models of both idiopathic and familial forms of Parkinson's disease (PD). MSNs were recorded from reserpine-treated and 6-hydroxydopamine (6-OHDA)-lesioned rats, and from DJ-1 and PINK1 (PTEN induced kinase 1) knockout (-/-) mice. Our analysis showed no significant changes in total HVA Ca2+ current. However, we recorded a net increase in the L-type fraction of HVA Ca2+ current in dopamine-depleted rats, and of both N- and P-type components in DJ-1-/- mice, whereas no significant change in Ca2+ current profile was observed in PINK1-/- mice. Dopamine modulates HVA Ca2+ channels in MSNs, thus we also analyzed the effect of D1 and D2 receptor activation. The effect of the D1 receptor agonist SKF 83822 on Ca2+ current was not significantly different among MSNs from control animals or PD models. However, in both dopamine-depleted rats and DJ-1-/- mice the D2 receptor agonist quinpirole inhibited a greater fraction of HVA Ca2+ current than in the respective controls. Conversely, in MSNs from PINK1-/- mice we did not observe alterations in the effect of D2 receptor activation. Additionally, in both reserpine-treated and 6-OHDA-lesioned rats, the effect of quinpirole was occluded by the selective L-type Ca2+ channel blocker nifedipine, while in DJ-1-/- mice it was mostly occluded by ω-conotoxin GVIA, blocker of N-type channels. These results demonstrate that both dopamine depletion and DJ-1 deletion induce a rearrangement in the HVA Ca2+ channel profile, specifically involving those channels that are selectively modulated by D2 receptors.

Further evidence for an involvement of nociceptin/orphanin FQ in the pathophysiology of Parkinson's disease: a behavioral and neurochemical study in reserpinized mice

The contribution of nociceptin/orphanin FQ (N/OFQ) to reserpine-induced Parkinsonism was evaluated in mice. A battery of motor tests revealed that reserpine caused dose-dependent and long-lasting motor impairment. Endogenous N/OFQ sustained this response because N/OFQ peptide (NOP) receptor knockout (NOP(-/-) ) mice were less susceptible to the hypokinetic action of reserpine than wild-type (NOP(+/+) ) animals. Microdialysis revealed that reserpine elevated glutamate and reduced GABA levels in substantia nigra reticulata, and that resistance to reserpine in NOP(-/-) mice was accompanied by a milder increase in glutamate and lack of inhibition of GABA levels. To substantiate this genetic evidence, the NOP receptor antagonist 1-[(3R,4R)-1-cyclooctylmethyl-3-hydroxymethyl-4-piperidyl]-3-ethyl-1,3-dihydro-2H benzimidazol-2-one (J-113397) simultaneously reduced akinesia and nigral glutamate levels in reserpinized NOP(+/+) mice, being ineffective in NOP(-/-) mice. Moreover, repeated J-113397 administration in reserpinized mice resulted in faster recovery of baseline motor performance which was, however, accompanied by a loss of acute antiakinetic response. The short-term beneficial effect of J-113397 was paralleled by normalization of nigral glutamate levels, whereas loss of acute response was paralleled by loss of the ability of J-113397 to inhibit glutamate levels. We conclude that endogenous N/OFQ contributes to reserpine-induced Parkinsonism, and that sustained NOP receptor blockade produces short-term motor improvement accompanied by normalization of nigral glutamate release.

An Automated Method for Scanning LC−MS Data Sets for Significant Peptides and Proteins, Including Quantitative Profiling and Interactive Confirmation

Differential quantification of proteins and peptides by LC-MS is a promising method to acquire knowledge about biological processes, and for finding drug targets and biomarkers. However, differential protein analysis using LC-MS has been held back by the lack of suitable software tools. Large amounts of experimental data are easily generated in protein and peptide profiling experiments, but data analysis is time-consuming and labor-intensive. Here, we present a fully automated method for scanning LC-MS/MS data for biologically significant peptides and proteins, including support for interactive confirmation and further profiling. By studying peptide mixtures of known composition, we demonstrate that peptides present in different amounts in different groups of samples can be automatically screened for using statistical tests. A linear response can be obtained over almost 3 orders of magnitude, facilitating further profiling of peptides and proteins of interest. Furthermore, we apply the method to study the changes of endogenous peptide levels in mouse brain striatum after administration of reserpine, a classical model drug for inducing Parkinson disease symptoms.

Striatal delta opioid receptor binding in experimental models of Parkinson's disease and dyskinesia

Enhanced delta opioid receptor transmission may represent an endogenous compensatory mechanism in parkinsonism to reduce the activity of the indirect striatopallidal pathway following dopamine depletion. Furthermore, increased delta opioid receptor transmission may be causative in the production of dyskinesia following repeated dopaminergic treatment in Parkinson's disease. The present study employed radioligand receptor autoradiography, using [3H]naltrindole, a ligand selective for the delta opioid receptor, to assess delta opioid receptor binding sites in forebrain regions of reserpine-treated rats, and in parkinsonian nondyskinetic, and dyskinetic MPTP-lesioned macaques. In reserpine-treated animals, specific delta opioid binding was increased in premotor cortex (+30%), sensorimotor striatum (+20%), and associative striatum (+17%) rostrally, but was not changed in caudal forebrain. In contrast, delta opioid receptor binding was not significantly altered at any region analyzed, in either nondyskinetic or dyskinetic, MPTP-lesioned macaques, compared to normal. These results suggest that transient changes in delta opioid receptor binding may occur in motor circuits following acute dopamine depletion. However, in the more chronic MPTP-lesioned macaque model, simple changes in delta opioid receptor number or affinity are unlikely to contribute to mechanisms for abnormal opioid transmission in Parkinson's disease and dyskinesia.

Rhes, the Ras homolog enriched in striatum, is reduced under conditions of dopamine supersensitivity

Striatal dopamine receptors become supersensitive when dopaminergic input is removed through either surgical denervation or pharmacological depletion. Although alterations such as increased D2 receptor binding and increased receptor-G protein coupling have been described in supersensitive striatal tissue, their roles in the mechanism of supersensitivity remain uncertain. The Ras Homolog Enriched in Striatum (Rhes) is expressed in brain areas that receive dopaminergic input, and here we test whether alterations in its expression accompany treatments that promote dopamine receptor supersensitivity in rats. Removal of dopamine input to the striatum by surgical denervation with 6-hydroxydopamine resulted in a decrease in rhes mRNA expression throughout striatum, as measured with quantitative in situ hybridization. The decrease was detected as early as two weeks and as late as seven months after surgery. Furthermore, a decrease in rhes mRNA was evident after repeated or acute reserpine treatment. Chronic daily injection of rats with the D2 antagonist eticlopride, which is known to up-regulate D2 receptors without inducing profound receptor supersensitivity, did not alter the expression of rhes mRNA in striatum. Thus, changes in rhes mRNA expression are strictly correlated with receptor supersensitivity, perhaps as a result of continuous removal of dopaminergic input. These findings suggest that rhes mRNA expression is maintained by dopamine and may play a role in determining normal dopamine receptor sensitivity.

Opioid-mediated modulation of calcium currents in striatal and pallidal neurons following reserpine treatment: focus on kappa response

Previous work has shown that enkephalins target N-type calcium (Ca2+) channels in striatal and globus pallidus (GP) neurons, principally through activation of mu-like receptors. Here, we examined the effects of selective mu, delta, and kappa agonists on Ca2+ currents in striatal and GP neurons isolated from either control or reserpine-treated rats. In cells from control rats DAMGO and dynorphin (DYN) inhibited high-voltage-activated (HVA) Ca2+ currents preferentially in "medium-to-small" GP cells (likely to correspond to parvalbumin-negative cells). The kappa response was elicited by several agonists (DYN 17, DYN 13, BRL, U50-488-H), U50-488-H being the most effective (>30% maximal inhibition). U50-488-H affected both omega-CgTxGVIA-sensitive and nimodipine-sensitive Ca2+ conductances. The kappa-mediated effect (but not the mu response) was slow and blocked by chelerythrine, supporting the involvement of protein kinase C. In neurons from reserpinized rats we observed modest changes in the mu-inhibited fraction in small GP cells and a dramatic reduction of the kappa-sensitive fraction in principal striatal cells. These data imply that aminergic depletion alters opiate transmission differentially in the indirect and direct pathways. The suppression of the kappa response only in striatum reinforces the notion of an imbalance of endogenous opiates as relevant in extrapyramidal motor dysfunctions.

Ropinirole versus l-DOPA effects on striatal opioid peptide precursors in a rodent model of Parkinson's disease: implications for dyskinesia

The dopamine precursor, L-3,4-dihydroxyphenylalanine (L-DOPA), remains the most common treatment for Parkinson's disease. However, following long-term treatment, disabling side effects, particularly L-DOPA-induced dyskinesias, are encountered. Conversely, D2/D3 dopamine receptor agonists, such as ropinirole, exert an anti-parkinsonian effect while eliciting less dyskinesia when administered de novo in Parkinson's disease patients. Parkinson's disease and L-DOPA-induced dyskinesia are both associated with changes in mRNA and peptide levels of the opioid peptide precursors preproenkephalin-A (PPE-A) and preproenkephalin-B (PPE-B). Furthermore, a potential role of abnormal opioid peptide transmission in dyskinesia is suggested due to the ability of opioid receptor antagonists to reduce the L-DOPA-induced dyskinesia in animal models of Parkinson's disease. In this study, the behavioural response, striatal topography and levels of expression of the opioid peptide precursors PPE-A and PPE-B were assessed, following repeated vehicle, ropinirole, or L-DOPA administration in the 6-OHDA-lesioned rat model of Parkinson's disease. While repeated administration of L-DOPA significantly elevated PPE-B mRNA levels (313% cf. vehicle, 6-OHDA-lesioned rostral striatum; 189% cf. vehicle, 6-OHDA-lesioned caudal striatum) in the unilaterally 6-OHDA-lesioned rat model of Parkinson's disease, ropinirole did not. These data and previous studies suggest the involvement of enhanced opioid transmission in L-DOPA-induced dyskinesia and that part of the reason why D2/D3 dopamine receptor agonists have a reduced propensity to elicit dyskinesia may reside in their reduced ability to elevate opioid transmission.

Catecholamine secretory vesicle stimulus-transcription coupling in vivo. Demonstration by a novel transgenic promoter/photoprotein reporter and inhibition of secretion and transcription by the chromogranin A fragment catestatin

Stimulation of chromaffin cell secretion in vitro triggers not only secretion but also resynthesis of just released catecholamines and chromogranin A, the precursor of the catecholamine release-inhibitory, nicotinic cholinergic antagonist peptide catestatin. Does stimulus-transcription coupling occur in vivo? And does catestatin antagonize secretion and transcription in vivo? To answer these questions, we employed a novel mouse strain harboring a chromogranin A promoter/firefly luciferase reporter transgene. Tissue-specific expression of the reporter was established by both luminescence and reverse transcription-PCR. Secretion and transcription in vivo were triggered by either direct nicotinic stimulation or vesicular transmitter depletion. Nicotinic blockade in vivo was attempted with either the classical antagonist chlorisondamine or the novel antagonist catestatin. Luciferase reporter expression was exquisitely sensitive over a large dynamic range, was specific for the transgenic animals, and paralleled typical neuroendocrine distribution of endogenous chromogranin A. Adrenal ontogeny revealed a rise of embryonic transgene expression until embryonal day 18, with an abrupt postnatal decline. Direct nicotinic stimulation of chromaffin cells caused catecholamine release and transgene transcription, each of which was nearly completely blocked by chlorisondamine. Similar adrenal results were obtained during vesicular catecholamine depletion. Both secretion and transcription were substantially blocked in the adrenal gland by catestatin. In brain and sympathetic nerve, stimulation of transcription was more modest, and reserpine responses were only incompletely blocked by chlorisondamine or catestatin, perhaps because of limited blood-brain barrier penetration by these cationic antagonists. Thus, nicotinic cholinergic stimulus-transcription coupling occurs in vivo and can be provoked either directly or indirectly (by vesicular transmitter depletion). Such coupling triggers the biosynthesis of chromogranin A, the precursor of catestatin. Catestatin itself blocks stimulation of both secretion and transcription in vivo. Thus, chromogranin A and its catestatin fragment may lie at the nexus of nicotinic cholinergic signaling in vivo.

D2-mediated modulation of N-type calcium currents in rat globus pallidus neurons following dopamine denervation

We have studied the effects of dopamine and the D2-like agonist quinpirole on calcium currents of neurons isolated from the striatum and the globus pallidus (GP). Experiments were performed in young adult rats, either in control conditions or following lesion of the nigrostriatal pathway by the unilateral injection of 6-hydroxydopamine (6-OHDA) in the substantia nigra. Apomorphine-driven contralateral turning, 15 days after lesioning, assessed the severity of the dopamine denervation. In addition, the loss of tyrosine hydroxylase immunohistochemistry confirmed the extent of the toxin-induced damage. In both striatal medium spiny (MS) and GP neurons of control animals dopamine and quinpirole promoted a very modest inhibition of calcium conductance. Following 6-OHDA, the inhibition was unaltered in MS (from 10 to 12%), but significantly augmented in GP neurons (21% vs. 9%). Interestingly, analogous inhibition was observed in GP neurons dissociated 20 h after reserpine treatment. Further features of the D2 response were thus studied only in neurons isolated from 6-OHDA-lesioned GP. The D2 modulation was G-protein-mediated but not strictly voltage-dependent. omega-Conotoxin-GVIA occluded the response implying the involvement of N-type calcium channels. The effect of quinpirole developed fast and was insensitive to alterations of cytosolic cAMP. The incubation in phorbol esters or OAG blocked the D2 effect, supporting the involvement of PKC. These findings suggest that postsynaptic D2-like receptors are functionally expressed on GP cell bodies and may supersensitize following dopamine-denervation. A direct D2 modulation of calcium conductance in GP may alter GP firing properties and GABA release onto pallidofugal targets.