Priming of rotational behavior by a dopamine receptor agonist in Hemiparkinsonian rats: movement-dependent induction

Increased emissions of 50-kHz ultrasonic vocalizations in hemiparkinsonian rats repeatedly treated with dopaminomimetic drugs: A potential preclinical model for studying the affective properties of dopamine replacement therapy in Parkinson's disease

Dopamine replacement therapy used in Parkinson's disease (PD) may induce alterations in the emotional state that can underlie the manifestation of iatrogenic psychiatric-like disturbances. The preclinical investigation of these disturbances is limited, also because few reliable paradigms are available to study the affective properties of dopaminomimetic drugs in parkinsonian animals. To provide a relevant experimental tool in this respect, we evaluated whether dopaminomimetic drugs modified the emission of 50-kHz ultrasonic vocalizations (USVs), a behavioral marker of positive affect, in rats bearing a unilateral lesion with 6-hydroxydopamine in the medial forebrain bundle. Apomorphine (2 or 4 mg/kg, i.p.), L-3,4-dihydroxyphenilalanine (L-DOPA, 6 or 12 mg/kg, i.p.), or pramipexole (2 or 4 mg/kg, i.p.) were administered in a test cage (× 5 administrations) on alternate days. Seven days after treatment discontinuation, rats were re-exposed to the test cage to measure conditioned calling behavior and thereafter received a drug challenge. Hemiparkinsonian rats treated with either apomorphine or L-DOPA, but not pramipexole, markedly vocalized during repeated treatment and after challenge, and showed conditioned calling behavior. Moreover, apomorphine, L-DOPA and pramipexole elicited different patterns of 50-kHz USV emissions and rotational behavior, indicating that calling behavior in hemiparkinsonian rats treated with dopaminomimetic drugs is not a byproduct of motor activation. Taken together, these results suggest that measuring 50-kHz USV emissions may be a relevant experimental tool for studying how dopaminomimetic drugs modify the affective state in parkinsonian rats, with possible implications for the preclinical investigation of iatrogenic psychiatric-like disturbances in PD.

Regulation of dopamine neurotransmission from serotonergic neurons by ectopic expression of the dopamine D2 autoreceptor blocks levodopa-induced dyskinesia

Levodopa-induced dyskinesias (LID) are a prevalent side effect of chronic treatment with levodopa (L-DOPA) for the motor symptoms of Parkinson’s disease (PD). It has long been hypothesized that serotonergic neurons of the dorsal raphe nucleus (DRN) are capable of L-DOPA uptake and dysregulated release of dopamine (DA), and that this “false neurotransmission” phenomenon is a main contributor to LID development. Indeed, many preclinical studies have demonstrated LID management with serotonin receptor agonist treatment, but unfortunately, promising preclinical data has not been translated in large-scale clinical trials. Importantly, while there is an abundance of convincing clinical and preclinical evidence supporting a role of maladaptive serotonergic neurotransmission in LID expression, there is no direct evidence that dysregulated DA release from serotonergic neurons impacts LID formation. In this study, we ectopically expressed the DA autoreceptor D2R_s (or GFP) in the DRN of 6-hydroxydopamine (6-OHDA) lesioned rats. No negative impact on the therapeutic efficacy of L-DOPA was seen with rAAV-D2R_s therapy. However, D2R_s treated animals, when subjected to a LID-inducing dose regimen of L-DOPA, remained completely resistant to LID, even at high doses. Moreover, the same subjects remained resistant to LID formation when treated with direct DA receptor agonists, suggesting D2R_s activity in the DRN blocked dyskinesogenic L-DOPA priming of striatal neurons. In vivo microdialysis confirmed that DA efflux in the striatum was reduced with rAAV-D2R_s treatment, providing explicit evidence that abnormal DA release from DRN neurons can affect LID. This is the first direct evidence of dopaminergic neurotransmission in DRN neurons and its modulation with rAAV-D2R_s gene therapy confirms the serotonin hypothesis in LID, demonstrating that regulation of serotonergic neurons achieved with a gene therapy approach offers a novel and potent antidyskinetic therapy.

Interactions of the tricyclic antidepressant drug amitriptyline with L-DOPA in the striatum and substantia nigra of unilaterally 6-OHDA-lesioned rats. Relevance to motor dysfunction in Parkinson's disease

Antidepressant drugs are recommended for the treatment of Parkinson's disease (PD)-associated depression but their role in the modulation of L-DOPA-induced behavioral and neurochemical markers is poorly explored. The aim of the present study was to examine the impact of the tricyclic antidepressant amitriptyline and L-DOPA, administered chronically alone or in combination, on rotational behavior, monoamine levels and binding of radioligands to their transporters in the dopaminergic brain structures of unilaterally 6-OHDA-lesioned rats. Binding of [³H]nisoxetine to noradrenaline transporter (NET), [³H]GBR 12,935 to dopamine transporter (DAT) and [³H]citalopram to serotonin transporter (SERT) were analyzed by autoradiography. Amitriptyline administered alone did not induce rotational behavior but in combination with L-DOPA increased the number of contralateral rotations much more strongly than L-DOPA alone. The combined treatment also significantly increased the tissue dopamine (DA) content in the ipsilateral striatum and substantia nigra (SN) vs. L-DOPA alone. 6-OHDA-mediated lesion of nigrostriatal DA neurons drastically reduced DAT and NET bindings in the ipsilateral striatum. In the ipsilateral SN, DAT binding decreased while NET binding rose. SERT binding increased significantly mainly in the SN. Amitriptyline administered alone or jointly with L-DOPA had no effect on DAT binding on the lesioned side, significantly decreased SERT binding in the striatum and SN while NET binding only in the SN. Since in the DA-denervated striatum, SERT is mainly responsible for reuptake of L-DOPA-derived DA while in the SN, SERT and NET are involved, the inhibition of these transporters by antidepressant drugs may improve dopaminergic transmission and consequently motor behavior.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

Role of movement in long-term basal ganglia changes: implications for abnormal motor responses

Abnormal involuntary movements (AIMs) and dyskinesias elicited by drugs that stimulate dopamine receptors in the basal ganglia are a major issue in the management of Parkinson’s disease (PD). Preclinical studies in dopamine-denervated animals have contributed to the modeling of these abnormal movements, but the precise neurochemical and functional mechanisms underlying these untoward effects are still elusive. It has recently been suggested that the performance of movement may itself promote the later emergence of drug-induced motor complications, by favoring the generation of aberrant motor memories in the dopamine-denervated basal ganglia. Our recent results from hemiparkinsonian rats subjected to the priming model of dopaminergic stimulation are in agreement with this. These results demonstrate that early performance of movement is crucial for the manifestation of sensitized rotational behavior, indicative of an abnormal motor response, and neurochemical modifications in selected striatal neurons following a dopaminergic challenge. Building on this evidence, this paper discusses the possible role of movement performance in drug-induced motor complications, with a look at the implications for PD management.

The role of neuroplasticity in dopaminergic therapy for Parkinson disease

Dopamine replacement is a mainstay of therapeutic strategies for Parkinson disease (PD). The motor response to therapy involves an immediate improvement in motor function, known as the short-duration response (SDR), followed by a long-duration response (LDR) that develops more slowly, over weeks. Here, we review evidence in patients and animal models suggesting that dopamine-dependent corticostriatal plasticity, and retention of such plasticity in the absence of dopamine, are the mechanisms underlying the LDR. Conversely, experience-dependent aberrant plasticity that develops slowly under reduced dopamine levels could contribute substantially to PD motor symptoms before initiation of dopamine replacement therapy. We place these findings in the context of the role of dopamine in basal ganglia function and corticostriatal plasticity, and provide a new framework suggesting that therapies that enhance the LDR could be more effective than those targeting the SDR. We further propose that changes in neuroplasticity constitute a form of disease modification that is distinct from prevention of degeneration, and could be responsible for some of the unexplained disease-modifying effects of certain therapies. Understanding such plasticity could provide novel therapeutic approaches that combine rehabilitation and pharmacotherapy for treatment of neurological and psychiatric disorders involving basal ganglia dysfunction.

Abnormal involuntary movement (AIM) expression following D2 dopamine agonist challenge is determined by the nature of prior dopamine receptor stimulation (priming) in 6-hydroxydopamine lesioned rats

Rats with unilateral 6-hydroxydopamine (6-OHDA) lesions show sensitization (priming) of rotational behavior upon repeated treatment with dopamine agonists. To relate these observations to dyskinesias exhibited by Parkinson's Disease patients, we assessed abnormal involuntary movements (AIMs) in 6-OHDA rats, which were primed with three injections of either the following: water, D1/D2 agonist apomorphine (Apo) (0.5mg/kg), D1 agonist SKF38393 (SKF) (10mg/kg) or D2 agonist quinpirole (Quin) (1 or 2.5mg/kg). The rats were challenged one week later with Quin (0.25mg/kg). Axial, limb, orolingual, locomotor, and grooming AIMs were scored (0-4) every 5min. Priming with water did not produce AIMs. Priming with Quin (1mg/kg) produced axial and locomotor AIMs, while priming with Apo, SKF or Quin (2.5mg/kg) produced axial, locomotor, limb, and grooming AIMs. The disparity in AIM profiles between Quin (1mg/kg) and (2.5mg/kg) was not the result of D1 receptor stimulation since there was little striatal Fos expression following the third priming injection with Quin (1 or 2.5mg/kg) compared to following SKF, which led to robust striatal Fos expression. Challenge with Quin (0.25mg/kg) essentially reproduced the categories of AIMs exhibited during priming, with no AIMs in water-primed 6-OHDA rats, mild, non-significant, axial and locomotor AIMs in Quin (1 and 2.5mg/kg)-primed 6-OHDA rats, and axial, limb, locomotor, and grooming AIMs in Apo- and SKF-primed 6-OHDA rats. These data suggest that the types of AIMs expressed following challenge with Quin depend on the dopamine receptor subtype and dose of dopamine agonist used during priming.

Intensive rehabilitation treatment in parkinsonian patients with dyskinesias: a preliminary study with 6-month followup

A major adverse effect of levodopa therapy is the development of dyskinesia, which affects 30–40% of chronically treated Parkinsonian patients. We hypothesized that our rehabilitation protocol might allow a reduction in levodopa dosage without worsening motor performances, thus reducing frequency and severity of dyskinesias. Ten Parkinsonian patients underwent a 4-week intensive rehabilitation treatment (IRT). Patients were evaluated at baseline, at the end of the rehabilitation treatment and at 6-month followup. Outcome measures were the Unified Parkinson's Disease Rating Scale Sections II, III, and IV (UPDRS II, III, IV) and the Abnormal Involuntary Movement Scale (AIMS). At the end of the IRT, levodopa dosage was significantly reduced (P = 0.0035), passing from 1016 ± 327 to 777 ± 333 mg/day. All outcome variables improved significantly (P < 0.0005 all) by the end of IRT. At followup, all variables still maintained better values with respect to admission (P < 0.02 all). In particular AIMS score improved passing from 11.90 ± 6.5 at admission to 3.10 ± 2.3 at discharge and to 4.20 ± 2.7 at followup. Our results suggest that it is possible to act on dyskinesias in Parkinsonian patients with properly designed rehabilitation protocols. Intensive rehabilitation treatment, whose acute beneficial effects are maintained over time, might be considered a valid noninvasive therapeutic support for Parkinsonian patients suffering from diskinesia, allowing a reduction in drugs dosage and related adverse effects.

The intriguing effects of ecstasy (MDMA) on cognitive function in mice subjected to a minimal traumatic brain injury (mTBI)

RATIONALE

The use of ecstasy (MDMA) among young adults has dramatically increased over the years. Since MDMA may impair the users' driving ability, the risk of being involved in a motor vehicle accident (MVA) is notably increased. Minimal traumatic brain injury (mTBI) a common consequence of MVAs-produces short- and long-term physical, cognitive, and emotional impairments.

OBJECTIVES

To investigate the effects of an acute dose of MDMA in mice subjected to closed head mTBI.

METHODS

Mice received 10 mg/kg MDMA 1 h prior to the induction of mTBI. Behavioral tests were conducted 7 and 30 days post-injury. In addition to the behavioral tests, phosphorylation of IGF-1R, ERK, and levels of tyrosine hydroxylase (TH) were measured.

RESULTS

mTBI mice showed major cognitive impairments in all cognitive tests conducted. No additional impairments were seen if mTBI was preceded by one dose of MDMA. On the contrary, a beneficial effect was seen in these mice. The western blot analysis of TH revealed a significant decrease in the mTBI mice. These decreases were reversed in mice that were subjected to MDMA prior to the trauma.

CONCLUSIONS

The presence of MDMA at the time of mTBI minimizes the alteration of visual and spatial memory of the injured mice. The IGF-1R pathway was activated due to mTBI and MDMA but was not the main contributor to the cognitive improvements. MDMA administration inverted the TH decreases seen after injury. We believe this may be the major cause of the cognitive improvements seen in these mice.

Methamphetamine-induced dopamine-independent alterations in striatal gene expression in the 6-hydroxydopamine hemiparkinsonian rats

Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle are used extensively as a model of Parkinson's disease. The present experiments sought to identify genes that were affected in the dopamine (DA)-denervated striatum after 6-hydroxydopamine-induced destruction of the nigrostriatal dopaminergic pathway in the rat. We also examined whether a single injection of methamphetamine (METH) (2.5 mg/kg) known to cause changes in gene expression in the normally DA-innervated striatum could still influence striatal gene expression in the absence of DA. Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle resulted in METH-induced rotational behaviors ipsilateral to the lesioned side and total striatal DA depletion on the lesioned side. This injection also caused decrease in striatal serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels. DA depletion was associated with increases in 5-HIAA/5-HT ratios that were potentiated by the METH injection. Microarray analyses revealed changes (±1.7-fold, p<0.025) in the expression of 67 genes on the lesioned side in comparison to the intact side of the saline-treated hemiparkinsonian animals. These include follistatin, neuromedin U, and tachykinin 2 which were up-regulated. METH administration caused increases in the expression of c-fos, Egr1, and Nor-1 on the intact side. On the DA-depleted side, METH administration also increased the expression of 61 genes including Pdgf-d and Cox-2. There were METH-induced changes in 16 genes that were common in the DA-innervated and DA-depleted sides. These include c-fos and Nor-1 which show greater changes on the normal DA side. Thus, the present study documents, for the first time, that METH mediated DA-independent changes in the levels of transcripts of several genes in the DA-denervated striatum. Our results also implicate 5-HT as a potential player in these METH-induced alterations in gene expression because the METH injection also caused significant increases in 5-HIAA/5-HT ratios on the DA-depleted side.