Median Forebrain Bundle Research Articles

Quantifying changes in local basal ganglia structural connectivity in the 6-hydroxydopamine model of Parkinson's Disease using correlational tractography.

In recent years, tractography based on diffusion magnetic resonance imaging (dMRI) has become a popular tool for studying microstructural changes resulting from brain diseases like Parkinson's Disease (PD). Quantitative anisotropy (QA) is a parameter that is used in deterministic fiber tracking as a measure of connection between brain regions. It remains unclear, however, if microstructural changes caused by lesioning the median forebrain bundle (MFB) to create a Parkinsonian rat model can be resolved using tractography based on ex-vivo diffusion MRI. This study aims to fill this gap and enable future mechanistic research on structural changes of the whole brain network rodent models of PD. Specifically, it evaluated the ability of correlational tractography to detect structural changes in the MFB of 6-hydroxydopamine (6-OHDA) lesioned rats. The findings reveal that correlational tractography can detect structural changes in lesioned MFB and differentiate between the 6-OHDA and control groups. Imaging results are supported by behavioral and histological evidence demonstrating that 6-OHDA lesioned rats were indeed Parkinsonian. The results suggest that QA and correlational tractography is appropriate to examine local structural changes in rodent models of neurodegenerative disease. More broadly, we expect that similar techniques may provide insight on how disease alters structure throughout the brain, and as a tool to optimize therapeutic interventions.

LONG-TERM EFFECTS OF SHAM SURGERY ON PHAGOCYTE FUNCTIONS IN RATS

Animal models of inflammatory disorders, including those of the nervous system are commonly used to explore the pathophysiological role of immune cell response in disease triggering and course and to develop biotechnology products for therapeutic use. Modeling some of these disorders, particularly neurodegenerative diseases, implies surgical manipulations for the intracerebral introduction of disease-initiating substances (toxins, amyloids etc.). Design of these experiments involves the use of sham-operated animals as a control of non-specific intrinsic side-effects elicited by surgical manipulations per se, including local and systemic inflammation, where phagocytic cells are key participants. Short-term post-surgical immunomodulatory effects are widely reported. However, no study thus far has examined the long term effects of sham-surgery on phagocyte functions. The purpose of this study was to evaluate the effect of sham-surgery, commonly used for modeling neurodegenerative diseases, on phagocyte functions in the far terms after the surgical manipulations. Materials and Methods. Adult male Wistar rats were used in the study. Sham surgery consisted of stereotactic unilateral injection of saline solution into the median forebrain bundle (sham-operated 1, SO1) or directly into the substantia nigra (sham-operated 2, SO2). Before the placebo surgery, animals were anaesthetized using nembutal and ketamine/xylazine correspondingly. Functional characteristics (phagocytic activity, oxidative metabolism, CD80/86 and CD206 expression) of phagocytes (microglia, peritoneal macrophages, circulating monocytes and granulocytes) were examined by flow cytometry. Differential leukocyte count was conducted using hematological analyzer. Results. Phagocytes from animals underwent of different protocols of placebo surgery, demonstrated various patterns of functional changes on day 29 after the manipulations. In animals from SO1 group, we observed signs of residual neuroinflammation (pro-inflammatory shift of microglia functional profile) along with ongoing resolution of systemic inflammation (anti-inflammatory metabolic shift of circulating phagocytes and peritoneal macrophages). In rats from SO2 group, pro-inflammatory polarized activation of peritoneal phagocytes was registered along with anti-inflammatory shift in microglia and circulating phagocytes. Conclusions. Sham surgery influences functions of phagocytic cells of different locations even in the far terms after the manipulations. These effects can be considered as combined long-term consequences of surgical brain injury and the use of anesthetics. Our observations evidences, that sham associated non-specific immunomodulatory effects should always be taken into consideration in animal models of inflammatory central nervous system diseases.

Spreading of Aggregated α-Synuclein in Sagittal Organotypic Mouse Brain Slices.

The accumulation of α-synuclein (α-syn) in the brain plays a role in synucleinopathies and it is hypothesized to spread in a prion-like fashion between connected brain regions. In the present study, we aim to investigate this spreading in well-characterized sagittal organotypic whole brain slices taken from postnatal wild type (WT) and transgenic mice overexpressing human α-syn under the promoter of proteolipid protein (PLP). Collagen hydrogels were loaded with monomers of human α-syn, as well as human and mouse pre-formed fibrils (PFFs), to allow local application and slow release. The spreading of α-syn was evaluated in different brain regions by immunohistochemistry for total α-syn and α-syn phosphorylated at the serine129 position (α-syn-P). The application of human and mouse PFFs of α-syn caused the aggregation and spreading of α-syn-P in the brain slices, which was pronounced the most at the region of hydrogel application and surrounding striatum, as well as along the median forebrain bundle. The organotypic slices from transgenic mice showed significantly more α-syn pathology than those from WT mice. The present study demonstrates that seeding with α-syn PFFs but not monomers induced intracellular α-syn pathology, which was significantly more prominent in brain slices with α-syn overexpression. This is consistent with the prion-like spreading theory of α-syn aggregates. The sagittal whole brain slices characterized in this study carry the potential to be used as a novel model to study α-syn pathology.

Electric stimulation of the medial forebrain bundle influences sensorimotor gaiting in humans

BackgroundPrepulse inhibition (PPI) of the acoustic startle response, a measurement of sensorimotor gaiting, is modulated by monoaminergic, presumably dopaminergic neurotransmission. Disturbances of the dopaminergic system can cause deficient PPI as found in neuropsychiatric diseases. A target specific influence of deep brain stimulation (DBS) on PPI has been shown in animal models of neuropsychiatric disorders. In the present study, three patients with early dementia of Alzheimer type underwent DBS of the median forebrain bundle (MFB) in a compassionate use program to maintain cognitive abilities. This provided us the unique possibility to investigate the effects of different stimulation conditions of DBS of the MFB on PPI in humans.ResultsSeparate analysis of each patient consistently showed a frequency dependent pattern with a DBS-induced increase of PPI at 60 Hz and unchanged PPI at 20 or 130 Hz, as compared to sham stimulation.ConclusionsOur data demonstrate that electrical stimulation of the MFB modulates PPI in a frequency-dependent manner. PPI measurement could serve as a potential marker for optimization of DBS settings independent of the patient or the examiner.

Deep brain stimulation for obsessive compulsive disorder: A review of results by anatomical target.

Studies suggest deep brain stimulation (DBS) as a treatment modality for the refractory obsessive-compulsive disorder (OCD). It is unclear where to place the DBS. Various sites are proposed for placement with the ventral capsule/ventral striatum (VC/VS) among the most studied. Herein, we aim to summarize both quantitative Yale-Brown Obsessive-Compulsive Scale (YBOCS) data and qualitative descriptions of the participants’ symptoms when given. A literature search conducted via PubMed yielded 32 articles. We sought to apply a standard based on the utilization of YBOCS. This yielded 153 distinct patients. The outcome measure we focused on in this review is the latest YBOCS score reported for each patient/cohort in comparison to the location of the DBS. A total of 32 articles were found in the search results. In total, 153 distinct patients’ results were reported in these studies. Across this collection of papers, a total of 9 anatomic structures were targeted. The majority of studies showed a better response at the last time point as compared to the first time point. Most patients had DBS at nucleus accumbens followed by VC/VS and the least patients had DBS at the bilateral superolateral branch of the median forebrain bundle and the bilateral basolateral amygdala. The average YBOCS improvement did not seem to directly correlate with the percentile of patients responding to the intervention.Well-controlled, randomized studies with larger sample sizes with close follow up are needed to provide a more accurate determination for placement of DBS for OCD.

Deep brain stimulation for obsessive compulsive disorder: A review of results by anatomical target

Studies suggest deep brain stimulation (DBS) as a treatment modality for the refractory obsessive-compulsive disorder (OCD). It is unclear where to place the DBS. Various sites are proposed for placement with the ventral capsule/ventral striatum (VC/VS) among the most studied. Herein, we aim to summarize both quantitative Yale-Brown Obsessive-Compulsive Scale (YBOCS) data and qualitative descriptions of the participants' symptoms when given. A literature search conducted via PubMed yielded 32 articles. We sought to apply a standard based on the utilization of YBOCS. This yielded 153 distinct patients. The outcome measure we focused on in this review is the latest YBOCS score reported for each patient/cohort in comparison to the location of the DBS. A total of 32 articles were found in the search results. In total, 153 distinct patients' results were reported in these studies. Across this collection of papers, a total of 9 anatomic structures were targeted. The majority of studies showed a better response at the last time point as compared to the first time point. Most patients had DBS at nucleus accumbens followed by VC/VS and the least patients had DBS at the bilateral superolateral branch of the median forebrain bundle and the bilateral basolateral amygdala. The average YBOCS improvement did not seem to directly correlate with the percentile of patients responding to the intervention. Well-controlled, randomized studies with larger sample sizes with close follow up are needed to provide a more accurate determination for placement of DBS for OCD.

Nicotine-Induced Neuroprotection in Rotenone In Vivo and In Vitro Models of Parkinson's Disease: Evidences for the Involvement of the Labile Iron Pool Level as the Underlying Mechanism.

Parkinson's disease (PD) is characterized by the degeneration of the dopaminergic neurons in the substantia nigra pars compacta (SNpc). Clinical and experimental evidence suggest that the activation of the nicotinic acetylcholine receptor (nAChR) could be protective for PD. In this study, we investigated the neuroprotective capacity of nicotine in a rat PD model. Considering that iron metabolism has been implicated in PD pathophysiology and nicotine has been described to chelate this metal, we also studied the effect of nicotine on the cellular labile iron pool (LIP) levels. Rotenone (1μg) was unilaterally injected into the median forebrain bundle to induce the degeneration of the nigrostriatal pathway. Nicotine administration (1mg/K, s.c. daily injection, starting 5days before rotenone and continuing for 30days) attenuated the dopaminergic cell loss in the SNpc and the degeneration of the dopaminergic terminals provoked by rotenone, as assessed by immunohistochemistry. Furthermore, nicotine partially prevented the reduction on dopamine levels in the striatum and improved the motor deficits, as determined by HPLC-ED and the forelimb use asymmetry test, respectively. Studies in primary mesencephalic cultures showed that pretreatment with nicotine (50μM) improved the survival of tyrosine hydroxylase-positive neurons after rotenone (20nM) exposure. Besides, nicotine induced a reduction in the LIP levels assessed by the calcein dequenching method only at the neuroprotective dose. These effects were prevented by addition of the nAChRs antagonist mecamylamine (100μM). Overall, we demonstrate a neuroprotective effect of nicotine in a model of PD in rats and that a reduction in iron availability could be an underlying mechanism.

Ventricular fibrillation cardiac arrest produces a chronic striatal hyperdopaminergic state that is worsened by methylphenidate treatment.

Cardiac arrest survival rates have improved with modern resuscitation techniques, but many survivors experience impairments associated with hypoxic-ischemic brain injury (HIBI). Currently, little is understood about chronic changes in striatal dopamine (DA) systems after HIBI. Given the common empiric clinical use of DA enhancing agents in neurorehabilitation, investigation evaluating dopaminergic alterations after cardiac arrest (CA) is necessary to optimize rehabilitation approaches. We hypothesized that striatal DA neurotransmission would be altered chronically after ventricular fibrillation cardiac arrest (VF-CA). Fast-scan cyclic voltammetry was used with median forebrain bundle (MFB) maximal electrical stimulations (60Hz, 10s) in rats to characterize presynaptic components of DA neurotransmission in the dorsal striatum (D-Str) and nucleus accumbens 14days after a 5-min VF-CA when compared to Sham or Naïve. VF-CA increased D-Str-evoked overflow [DA], total [DA] released, and initial DA release rate versus controls, despite also increasing maximal velocity of DA reuptake (Vmax ). Methylphenidate (10mg/kg), a DA transporter inhibitor, was administered to VF-CA and Shams after establishing a baseline, pre-drug 60Hz, 5s stimulation response. Methylphenidate increased initial evoked overflow [DA] more-so in VF-CA versus Sham and reduced D-Str Vmax in VF-CA but not Shams; these findings are consistent with upregulated striatal DA transporter in VF-CA versus Sham. Our work demonstrates that 5-min VF-CA increases electrically stimulated DA release with concomitant upregulation of DA reuptake 2weeks after brief VF-CA insult. Future work should elucidate how CA insult duration, time after insult, and insult type influence striatal DA neurotransmission and related cognitive and motor functions.

Comparison of voluntary and forced exercise effects on motor behavior in 6-hydroxydopamine-lesion rat model of Parkinson’s disease

Parkinson’s disease (PD) is one of the most common neurodegenerative disorders. This study compared the effects of two types of exercises on motor dysfunction in characterizing adult male Wistar rats with unilateral 6-hydroxydopamine lesions placed in the median forebrain bundle. Sixty adult male Wistar rats were randomly assigned to six groups: the control intact and Parkinson group (no exercise), the forced group (sham, PD), the voluntary group (sham, PD). The effects of 4 weeks of forced treadmill running and voluntary wheel running on motor behavior were investigated in the open field, Rotarod and hanging tests. The outcomes showed that although the length moved by the voluntary exercise group was more than that in the forced exercise, the forced exercise resulted in better performance in Rotarod (P = 0.01), whereas voluntary exercise was found to increase rearing behavior (P = 0.01). Both exercise groups were the same in the open field (p > 0.05), grooming frequency (P = 0.12), and hanging test (P = 0.181). We found that wheel running and treadmill running exercise protocols improved the motor impairments in the 6-OHDA-lesioned rat model of Parkinson’s disease; therefore, our result suggests that both exercise methods could be beneficial for PD patients to reduce their motor dysfunction.

Protective efficacy of P7C3-S243 in the 6-hydroxydopamine model of Parkinson's disease.

Background:There are currently no therapeutic options for patients with Parkinson's disease that prevent or slow the death of dopaminergic neurons. We have recently identified the novel P7C3 class of neuroprotective molecules that blocks neuron cell death.AIMS:The aim of this study was to determine whether treatment with highly active members of the P7C3 series blocks dopaminergic neuron cell death and associated behavioral and neurochemical deficits in the rat 6-hydroxydopamine (6-OHDA) model of Parkinson's disease.Methods:After unilateral injection of 6-OHDA into the median forebrain bundle, rats were assessed for behavioral function in the open field, cylinder test, and amphetamine-induced circling test. Thereafter, their brains were subjected to neurochemical and immunohistochemical analysis of dopaminergic neuron survival. Analysis was conducted as a function of treatment with P7C3 compounds, with administration initiated either before or after 6-OHDA exposure.Results:Animals administered P7C3-A20 or P7C3-S243, two of the most advanced agents in the P7C3 series of neuroprotective compounds, both before and after 6-OHDA exposure showed evidence of protective efficacy in all measures. When P7C3-S243 administration was initiated after 6-OHDA exposure, rats also showed protective efficacy in all measures, which included blocking dopaminergic neuron cell death in ipsilateral substantia nigra pars compacta, preservation of dopamine and its metabolites in ipsilateral striatum, and preservation of normal motor behavior.Conclusions:The P7C3 series of compounds may form the basis for developing new therapeutic agents for slowing or preventing progression of Parkinson's disease.

The 6-OHDA mouse model of Parkinson's disease – Terminal striatal lesions provide a superior measure of neuronal loss and replacement than median forebrain bundle lesions

Unilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal pathway produce side-biased motor impairments that reflect the motor deficits seen in Parkinson's disease (PD). This toxin-induced model in the rat has been used widely, to evaluate possible therapeutic strategies, but has not been well established in mice. With the advancements in mouse stem cell research we believe the requirement for a mouse model is essential for the therapeutic potential of these and other mouse-derived cells to be efficiently assessed.This aim of this study focused on developing a mouse model of PD using the 129 P2/OLA Hsd mouse strain as this is widely used in the generation of mouse embryonic stem cells. Both unilateral 6-OHDA medial forebrain bundle (MFB) and striatal lesion protocols were compared, with mice analysed for appropriate drug-induced rotational bias. Results demonstrated that lesioned mice responded to d-amphetamine with peak rotation dose at 5mg/kg and 10mg/kg for MFB and striatal lesions respectively. Apomorphine stimulation produced no significant rotational responses, at any dose, in either the MFB or striatal 6-OHDA lesioned mice. Analysis of dopamine neuron loss revealed that the MFB lesion was unreliable with little correlation between dopamine neuron loss and rotational asymmetry. Striatal lesions however were more reliable, with a strong correlation between dopamine neuron loss and rotational asymmetry. Functional recovery of d-amphetamine-induced rotational bias was shown following transplantation of E13 mouse VM tissue into the lesioned striatum; confirming the validity of this mouse model.

Nobiletin protects dopaminergic neurons in the 1-methyl-4-phenylpyridinium-treated rat model of Parkinson's disease.

This study investigated the effect of nobiletin, a flavonoid found in citrus fruits, on the degeneration of dopaminergic (DA) neurons in a neurotoxin model of Parkinson's disease (PD). 1-Methyl-4-phenylpyridinium (MPP(+)) was unilaterally injected into the median forebrain bundle of rat brains (to generate a neurotoxin model of PD) with or without daily intraperitoneal injection of nobiletin. Our results showed that nobiletin treatment at 10 mg/kg bw, but not at 1 or 20 mg/kg bw, significantly protected DA neurons in the substantia nigra (SN) of MPP(+)-treated rats. In parallel to the neuroprotection, nobiletin treatment at 10 mg/kg inhibited microglial activation and preserved the expression of the glial cell line-derived neurotrophic factor, which is a therapeutic agent against PD, in the SN. These results suggest that the proper supplementation with nobiletin may protect against the neurodegeneration involved in PD.

6-Hydroxydopamine impairs mitochondrial function in the rat model of Parkinson’s disease: respirometric, histological, and behavioral analyses

Mitochondrial defects have been shown to be associated with the pathogenesis of Parkinson's disease (PD). Yet, experience in PD research linking mitochondrial dysfunction, e.g., deregulation of oxidative phosphorylation, with neuronal degeneration and behavioral changes is rather limited. Using the 6-hydroxydopamine (6-OHDA) rat model of PD, we have investigated the potential role of mitochondria in dopaminergic neuronal cell death in the substantia nigra pars compacta by high-resolution respirometry. Mitochondrial function was correlated with the time course of disease-related motor behavior asymmetry and dopaminergic neuronal cell loss, respectively. Unilateral 6-OHDA injections (>2.5 μg/2 μl) into the median forebrain bundle induced an impairment of oxidative phosphorylation due to a decrease in complex I activity. This was indicated by increased flux control coefficient. During the period of days 2-21, a progressive decrease in respiratory control ratio of up to -58 % was observed in the lesioned compared to the non-lesioned substantia nigra of the same animals. This decrease was associated with a marked uncoupling of oxidative phosphorylation. Mitochondrial dysfunction, motor behavior asymmetry, and dopaminergic neuronal cell loss correlated with dosage (1.25-5 μg/2 μl). We conclude that high-resolution respirometry may allow the detection of distinct mitochondrial dysfunction as a suitable surrogate marker for the preclinical assessment of potential neuroprotective strategies in the 6-OHDA model of PD.

GABA Attenuates L-DOPA-Induced Striatal and Nigral ERK1/2 Signaling in a Rat Model of Parkinson’s Disease

L-DOPA is the primary drug used to treat Parkinson’s disease (PD) symptoms, but motor side effects limit its long term use. Previous experimental studies show that L-DOPA acts on supersensitive D1 receptors in the basal ganglia to induce extracellular signal-regulated kinases 1 and 2 (ERK1/2), a pair of MAP-kinase proteins that may be involved in induction of motor side effects. Since GABA is known to be intimately involved in basal ganglia function, we investigated whether elevating GABA levels via a GABA-transaminase (GABA-T) inhibitor affects the L-DOPA-induced ERK1/2 phosphorylation in the striatum and substantia nigra (SN) using a rat model of PD. Unilateral dopaminergic lesions of median forebrain bundle neurons were done using the neurotoxin 6-hydroxydopamine. Rats were prescreened for the extent of the lesion by apomorphine-induced rotation test. Lesioned rats were treated with aminooxyacetic acid (AOAA, a GABA-T inhibitor), L-DOPA, or in combination. Immunohistochemistry of tyrosine hydroxylase (TH, a direct indicator of dopaminergic lesion), substance P (SP, an indirect marker that decreases after lesion), and phospho-ERK1/2 was done using slices at the level of striatum and SN. Unilateral dopaminergic lesioned rats, as expected, exhibited >90% TH loss and a modest SP loss in the striatum and SN. L-DOPA alone induced a 343% and 330% increase in phospho-ERK1/2 in the striatum and SN, respectively. We report here a novel finding that pretreatment with AOAA attenuated the L-DOPA induced increase in phospho-ERK1/2 by 62% and 68% in the striatum and SN, respectively, suggesting a DA-GABA-ERK1/2 link in the therapeutic and/or side effects of L-DOPA.

Transient receptor potential vanilloid subtype 1 contributes to mesencephalic dopaminergic neuronal survival by inhibiting microglia-originated oxidative stress

The present study examined whether capsaicin (CAP), an agonist of transient receptor potential vanilloid subtype 1 (TRPV1) can prevent 1-methyl-4-phenylpyridinium (MPP(+))-induced dopaminergic (DA) neuronal death in the substantia nigra (SN). Unilateral injection of MPP(+) into the median forebrain bundle of rat brain resulted in a significant loss of nigral DA neurons, assessed by tyrosine hydroxylase (TH) immunostaining. In parallel, activation of microglia, visualized by OX-42 and OX-6 immunostaining were also observed in the SN, where degeneration of nigral neurons was found. By contrast, MPP(+) neurotoxicity was partially inhibited by co-treatment with MPP(+) and CAP. Interestingly, CAP significantly decreased not only immunoreactivity of OX-42 and OX-6 but also production of microglia-derived reactive oxygen species (ROS) in the SN of MPP(+)-treated rats. In experiments designed to further verify effectiveness of CAP against microglia-derived neurotoxicity, CAP inhibited ROS production and blocked MPP(+)-induced death of DA neurons in co-cultures of mesencephalic neurons and microglia, but not in microglia-free, neuron-enriched mesencephalic cultures. This beneficial effect was reversed by capsazepine, an antagonist of TRPV1, expressed in microglia, indicating TRPV1 involvement. Our data demonstrate for the first time that CAP may inhibit microglial activation-mediated oxidative stress via TRPV1, suggesting that CAP and its analogs may have therapeutic value by inhibiting microglial activation and/or ROS generation that occurs in Parkinson's disease.

Riluzole neuroprotection in a parkinson's disease model involves suppression of reactive astrocytosis but not GLT-1 regulation

BackgroundRiluzole is a neuroprotective drug used in the treatment of motor neurone disease. Recent evidence suggests that riluzole can up-regulate the expression and activity of the astrocyte glutamate transporter, GLT-1. Given that regulation of glutamate transport is predicted to be neuroprotective in Parkinson's disease, we tested the effect of riluzole in parkinsonian rats which had received a unilateral 6-hydroxydopamine injection into the median forebrain bundle.ResultsRats were treated with intraperitoneal riluzole (4 mg/kg or 8 mg/kg), 1 hour before the lesion then once daily for seven days. Riluzole produced a modest but significant attenuation of dopamine neurone degeneration, assessed by suppression of amphetamine-induced rotations, preservation of tyrosine hydroxylase positive neuronal cell bodies in the substantia nigra pars compacta and attenuation of striatal tyrosine hydroxylase protein loss. Seven days after 6-hydroxydopamine lesion, reactive astrocytosis was observed in the striatum, as determined by increases in expression of glial fibrillary acidic protein, however the glutamate transporter, GLT-1, which is also expressed in astrocytes was not regulated by the lesion.ConclusionsThe results confirm that riluzole is a neuroprotective agent in a rodent model of parkinson's disease. Riluzole administration did not regulate GLT-1 levels but significantly reduced GFAP levels, in the lesioned striatum. Riluzole suppression of reactive astrocytosis is an intriguing finding which might contribute to the neuroprotective effects of this drug.

The Time Course of D1 Agonist Induced Striatonigral ERK1/2 Signaling in a Rat Model of Parkinson’s Disease

Using a rat model of hemiparkinsonism, we examined the time-course of D1 agonist, SKF-38393-induced changes in extracellular signaling regulated kinases 1/2 (ERK1/2) phosphorylation in the striatum and substantia nigra (SN). We unilaterally lesioned the rat median forebrain bundle with 6-hydroxydopamine. Dopaminergic lesioned rats were administered with SKF-38393 and perfused at 15, 30, 60, or 120 minutes after the drug. Immunohistochemical analysis of striatum and SN revealed, as expected, a loss of tyrosine hydroxylase and a decrease of substance P in lesioned rats. SKF-38393 induced a robust increase in phospho-ERK1/2 levels in the lesioned striatum, which peaked at 15 min and substantially declined by 120 min. We report for the first time that similar changes were observed in the SN. The time-dependent ERK 1/2 activation in the striatonigral neurons may play a role in the therapeutic and/or side effects such as dyskinesias related to the dopamine agonist treatment for Parkinson’s disease.

The Metabotropic Glutamate Receptor 4-Positive Allosteric Modulator VU0364770 Produces Efficacy Alone and in Combination with l-DOPA or an Adenosine 2A Antagonist in Preclinical Rodent Models of Parkinson's Disease

Parkinson's disease (PD) is a debilitating neurodegenerative disorder associated with severe motor impairments caused by the loss of dopaminergic innervation of the striatum. Previous studies have demonstrated that positive allosteric modulators (PAMs) of metabotropic glutamate receptor 4 (mGlu₄), including N-phenyl-7-(hydroxyimino) cyclopropa[b]chromen-1a-carboxamide, can produce antiparkinsonian-like effects in preclinical models of PD. However, these early mGlu₄ PAMsexhibited unsuitable physiochemical properties for systemic dosing, requiring intracerebroventricular administration and limiting their broader utility as in vivo tools to further understand the role of mGlu₄ in the modulation of basal ganglia function relevant to PD. In the present study, we describe the pharmacologic characterization of a systemically active mGlu₄ PAM, N-(3-chlorophenyl)picolinamide (VU0364770), in several rodent PD models. VU0364770 showed efficacy alone or when administered in combination with L-DOPA or an adenosine 2A (A2A) receptor antagonist currently in clinical development (preladenant). When administered alone, VU0364770 exhibited efficacy in reversing haloperidol-induced catalepsy, forelimb asymmetry-induced by unilateral 6-hydroxydopamine (6-OHDA) lesions of the median forebrain bundle, and attentional deficits induced by bilateral 6-OHDA nigrostriatal lesions in rats. In addition, VU0364770 enhanced the efficacy of preladenant to reverse haloperidol-induced catalepsy when given in combination. The effects of VU0364770 to reverse forelimb asymmetry were also potentiated when the compound was coadministered with an inactive dose of L-DOPA, suggesting that mGlu₄ PAMs may provide L-DOPA-sparing activity. The present findings provide exciting support for the potential role of selective mGlu₄ PAMs as a novel approach for the symptomatic treatment of PD and a possible augmentation strategy with either L-DOPA or A2A antagonists.

Increased efficacy of the 6-hydroxydopamine lesion of the median forebrain bundle in small rats, by modification of the stereotaxic coordinates

The 6-hydroxydopamine (6-OHDA) lesion is the most widely used rat model of Parkinson's disease. A single unilateral injection of 6-OHDA into the median forebrain bundle (MFB) selectively destroys dopamine neurons in the ipsilateral substantia nigra pars compacta (SNc) and ventral tegmental area (VTA), removing more than 95% of the dopamine innervation from target areas. The stereotaxic coordinates used to deliver 6-OHDA to the MFB have been used in our laboratory successfully for more than 25 years. However, in recent years we have observed a decline in the success rate of this lesion. Previously regular success rates of >80% of rats lesioned, have become progressively more variable, with rates as low as 20% recorded in some experiments. Having excluded variability of the neurotoxin and operator errors, we hypothesized that the change seen might be due to the use of smaller rats at the time of first surgery. An attempt to proportionally adjust the lesion coordinates base on head size did not increase lesion efficacy. However, in support of the small rat hypothesis it was observed that, using the standard coordinates, rat's heads had a “nose-up” position in the stereotaxic fame. Adjustment of the nose bar to obtain a flat head position during surgery improved lesion success, and subsequent adjustments of the lesion coordinates to account for smaller head size led to a greatly increased lesion efficacy (>90%) as assessed by amphetamine induced rotation.

Positive association between striatal serotonin level and abnormal involuntary movements in chronic l-DOPA-treated hemiparkinsonian rats

Although l-DOPA represents the standard of care in Parkinson's disease, long-term treatment may be compromised by l-DOPA-induced dyskinesia (LID), with adverse fluctuations in motor responsiveness and progressive loss of control. Here we show that in rats with 6-hydroxydopamine-induced lesions of the median forebrain bundle, LID correlates with 5-HT levels. Rats were treated with l-DOPA (6 mg/kg) and benserazide (15 mg/kg) daily for 3 weeks to induce the development of abnormal involuntary movements (AIMs). After this chronic l-DOPA treatment, the lesion side of the rats displayed significant changes in striatal dopamine (DA) and 5-HT levels. Striatal DA and 5-hydroxytryptamine (5-HT) levels were inversely correlated, and AIMs were strongly positively correlated with DA levels and negatively correlated with 5-HT levels. Axial AIMs were more strongly correlated with DA and 5-HT levels than were the other AIMs subtypes, while locomotive AIMs showed no significant correlation at all. In addition, striatal 5-HT was more strongly (negatively) correlated with the AIMs than striatal DA levels. These results demonstrate that 5-HT contributes to LID and that both striatal DA (positively) and 5-HT (negatively) affect the severity of LID. We suggest that by strategic modification of the serotonin system it may be possible to attenuate the adverse effects of chronic l-DOPA therapy.