Publications

Nicole E. Chambers, Annique McLune, Michael Coyle, Ashley Centner, Jordan Sergio, Isabella Del Priore, Kathryn Lanza, Craig W. Lindsley, P. Jeffrey Conn, Christopher Bishop

DOI: 10.1016/j.bbr.2025.115847

Standard treatment for Parkinson’s disease (PD) is dopamine replacement therapy with L-DOPA. However, chronic treatment often results in abnormal involuntary movements called L-DOPA-induced dyskinesia (LID). Prior evidence indicates that heightened striatal cholinergic tone may contribute to LID. Restoring cholinergic inhibition by targeting the inhibitory M4 muscarinic acetylcholine (ACh) receptor (M4) reduces LID in preclinical models. Although intrinsic striatal sources of ACh have been considered for their role in LID, extrinsic sources of ACh such as the pedunculopontine nucleus (PPN) have not been well investigated for their role in LID. Therefore, the current study employed hemiparkinsonian Long-Evans rats with a PPN-targeted cannula ipsilateral to 6-OHDA lesion. We examined the effect of local unilateral PPN infusion of M4 PAM VU0467154 on LID, motor performance, and c-fos expression within the PPN. It was expected that PPN infusion of VU0467154 would reduce LID, reduce L-DOPA’s motor benefit, and globally reduce c-fos expression in the PPN. Contrary to our expectations, PPN infusion of M4 PAM did not significantly affect LID severity. Furthermore, M4 PAM did not alter L-DOPA-mediated motor improvement, and decreased c-fos expression specifically in PPN cholinergic neurons. These results suggest that local PPN ACh dynamics differ from those of the striatum. In the context of prior work, our results suggest that PPN cholinergic modulation or global PPN modulation may be a promising strategy for altering freezing of gait without decreasing motor benefit of L-DOPA and without increasing LID severity.

Ashley Galfano, Robert McManus, Walter Navarrete, Sampada Chaudhari, Christopher Bishop, Michael F. Salvatore

DOI: 10.1101/2025.09.12.675909

During progressive nigrostriatal neuron loss in Parkinson’s disease (PD), compensatory mechanisms are thought to maintain dopamine (DA) signaling at levels sufficient to mitigate locomotor impairment prior to substantial neuron loss. Whereas increased DA turnover in striatum has been considered a keystone compensatory mechanism indicative of augmented DA signaling, recent work indicates that increased DA biosynthesis in substantia nigra (SN), not striatum, compensates for tyrosine hydroxylase (TH) protein and neuronal loss. To extend interrogation of compensatory mechanisms that augment DA signaling during nigrostriatal neuron loss, we contemporaneously evaluated extracellular DA against tissue DA levels and quantified TH protein in the striatum and SN. Our unilateral 6-hydroxydopamine (6-OHDA) lesion approach produces progressive neuronal loss between 7 and 28 days, enabling evaluation of multiple DA signaling components in striatum vs SN. Loss of TH was ~90% in striatum and ~70% in the SN by 7 days after lesion induction. However, whereas loss of tissue DA matched TH loss in striatum (>90%) on both days after lesion, tissue DA loss in SN occurred only at day 28 (36%), despite major TH loss by day 7. This preservation of nigral DA tissue levels during lesion progression was associated with increased extracellular DA in SN after K+ dependent depolarization in striatum, which was not evident in a sham-operation group at the same time, early after lesion induction, signifying a DA lesion-specific adaptation in SN. In contrast in the striatum, lesion abolished the robust increase in extracellular DA, as seen in the sham-operation group. Together, these results indicate compensatory mechanisms that augment nigrostriatal DA signaling are engaged in the SN, not striatum, during progressive nigrostriatal neuron loss.

Hannah Holden, Shruti Venkatesh, Carla Budrow, Sareen Nezaria, Michael Coyle, Ashley Centner, Natalie Lipari, Grace McManus, Christopher Bishop

DOI: 10.1016/j.physbeh.2024.114563

Parkinson's Disease (PD) is a neurodegenerative movement disorder characterized by dopamine (DA) cell loss in the substantia nigra pars compacta (SNc). As PD progresses, patients display disruptions in gait such as changes in posture, bradykinesia, and shortened stride. DA replacement via L-DOPA alleviates many PD symptoms, though its effects on gait are not well demonstrated. This study aimed to assess the relationship between DA lesion, gait, and deficit-induced reversal with L-DOPA. To do so, Sprague–Dawley rats (N = 25, 14 males, 11 females) received unilateral medial forebrain bundle(MFB) DA lesions with 6-hydroxydopamine (6-OHDA). An automated gait analysis system assessed spatiotemporal gait parameters pre- and post-lesion, and after various doses of L-DOPA (0, 3, or 6 mg/kg; s.c.). The forepaw adjusting steps (FAS) test was implemented to evaluate lesion efficacy while the abnormal involuntary movements (AIMs) scale monitored the emergence of L-DOPA-induced dyskinesia (LID). High performance liquid chromatography (HPLC) assessed changes in brain monoamines on account of lesion and treatment. Results revealed lesion-induced impairments in gait, inclusive of max-contact area and step-sequence alterations that were not reversible with L-DOPA. However, the emergence of AIMs were observed at higher doses. Post-mortem, 6-OHDA lesions induced a loss of striatal DA and norepinephrine(NE), while prefrontal cortex (PFC) displayed noticeable reduction in NE but not DA. Our findings indicate that hemiparkinsonian rats display measurable gait disturbances similar to PD patients that are not rescued by DA replacement. Furthermore, non-DA mechanisms such as attention-related NE in PFC may contribute to altered gait and may constitute a novel target for its treatment.

Nicole E Chambers, Annique McLune, Michael Coyle, Ashley Centner, Jordan Sergio, Isabella Delpriore, Kathryn Lanza, Craig W Lindsley, P Jeffrey Conn, Christopher Bishop

DOI: 10.1101/2024.04.16.589785

Standard treatment for Parkinson’s disease (PD) is dopamine replacement therapy with L-DOPA. However, chronic treatment often results in abnormal involuntary movements called L-DOPA-induced dyskinesia (LID). Prior evidence indicates that heightened striatal cholinergic tone may contribute to LID. Restoring cholinergic inhibition by targeting the inhibitory M4 muscarinic acetylcholine (ACh) receptor (M4) reduces LID in preclinical models. Although intrinsic striatal sources of ACh have been considered for their role in LID, extrinsic sources of ACh such as the pedunculopontine nucleus (PPN) have not been well investigated for their role in LID. Therefore, the current study employed hemiparkinsonian Long-Evans rats with a PPN-targeted cannula ipsilateral to 6-OHDA lesion. Following chronic treatment with L-DOPA, we examined the effect of local unilateral PPN infusion of M4 PAM VU0467154 on LID, motor performance, and c-fos expression within the PPN. It was expected that PPN infusion of VU0467154 would reduce LID, reduce L-DOPA’s motor benefit, and globally reduce c-fos expression in the PPN. Contrary to our expectations, PPN infusion of M4 PAM did not significantly affect LID severity. Furthermore, the group receiving M4 PAM showed slightly elevated motor improvement compared to L-DOPA, and decreased c-fos expression specifically in PPN cholinergic neurons. These results suggest that local PPN ACh dynamics differ from those of the striatum. Specifically, our results suggest that PPN cholinergic neurons may be a promising therapeutic target for augmenting L-DOPA-mediated motor benefit without increasing LID.

Carla Budrow, Kayla Elder, Michael Coyle, Ashley Centner, Natalie Lipari, Sophie Cohen, John Glinski, N’Senga Kinzonzi, Emily Wheelis, Grace McManus, Fredric Manfredsson, Christopher Bishop

DOI: 10.3390/cells12060837

Parkinson’s Disease (PD) is a neurodegenerative disorder characterized by motor symptoms that result from loss of nigrostriatal dopamine (DA) cells. While L-DOPA provides symptom alleviation, its chronic use often results in the development of L-DOPA-induced dyskinesia (LID). Evidence suggests that neuroplasticity within the serotonin (5-HT) system contributes to LID onset, persistence, and severity. This has been supported by research showing 5-HT compounds targeting 5-HT1A/1B receptors and/or the 5-HT transporter (SERT) can reduce LID. Recently, vortioxetine, a multimodal 5-HT compound developed for depression, demonstrated acute anti-dyskinetic effects. However, the durability and underlying pharmacology of vortioxetine’s anti-dyskinetic actions have yet to be delineated. To address these gaps, we used hemiparkinsonian rats in Experiment 1, examining the effects of sub-chronic vortioxetine on established LID and motor performance. In Experiment 2, we applied the 5-HT1A antagonist WAY-100635 or 5-HT1B antagonist SB-224289 in conjunction with L-DOPA and vortioxetine to determine the contributions of each receptor to vortioxetine’s effects. The results revealed that vortioxetine consistently and dose-dependently attenuated LID while independently, 5-HT1A and 5-HT1B receptors each partially reversed vortioxetine’s effects. Such findings further support the promise of pharmacological strategies, such as vortioxetine, and indicate that broad 5-HT actions may provide durable responses without significant side effects.

Samantha Smith, Jordan Sergio, Michael Coyle, Kayla Elder, Ashley Centner, Sophie Cohen, Michelle Terry, Natalie Lipari, John Glinski, Emily Wheelis, Carla Budrow, Christopher Bishop

DOI: 10.1007/s00213-022-06078-9

Parkinson’s disease is a neurodegenerative disease often characterized by motor deficits and most commonly treated with dopamine replacement therapy. Despite its benefits, chronic use of L-DOPA results in abnormal involuntary movements known as L-DOPA-induced dyskinesia. Growing evidence shows that with burgeoning dopamine cell loss, neuroplasticity in the serotonin system leads to the development of L-DOPA-induced dyskinesia through the unregulated uptake, conversion, and release of L-DOPA-derived dopamine into the striatum. Previous studies have shown that coincident 5-HT1A agonism and serotonin transporter inhibition may have anti-dyskinetic potential. Despite this, few studies have explicitly focused on targeting both 5-HT1A and the serotonin transporter. The present study compares the 5-HT compounds Vilazodone, YL-0919, and Vortioxetine which purportedly work as simultaneous 5-HT1A receptor agonists and SERT blockers. To do so, adult female Sprague Dawley rats were rendered hemiparkinsonian and treated daily for two weeks with L-DOPA to produce stable dyskinesia. The abnormal involuntary movements and forehand adjusting step tests were utilized as measurements for L-DOPA-induced dyskinesia and motor performance in a within-subjects design. Lesion efficacy was determined by analysis of striatal monoamines via high-performance liquid chromatography. Compounds selective for 5-HT1A/SERT target sites including Vilazodone and Vortioxetine significantly reduced L-DOPA-induced dyskinesia without compromising L-DOPA pro-motor efficacy. In contrast, YL-0919 failed to reduce L-DOPA-induced dyskinesia, with no effects on L-DOPA-related improvements. Collectively, this work supports pharmacological targeting of 5-HT1A/SERT to reduce L-DOPA-induced dyskinesia. Additionally, this further provides evidence for Vilazodone and Vortioxetine, FDA-approved compounds, as potential adjunct therapeutics for L-DOPA-induced dyskinesia management in Parkinson’s patients.

Melissa Conti Mazza, Victoria Nguyen, Alexandra Beilina, Ema Karakoleva, Michael Coyle, Jinhui Ding, Christopher Bishop, Mark R Cookson

DOI: 10.3233/JPD-202172

Coding mutations in the LRRK2 gene, encoding for a large protein kinase, have been shown to cause familial Parkinson’s disease (PD). The immediate biological consequence of LRRK2 mutations is to increase kinase activity, suggesting that inhibition of this enzyme might be useful therapeutically to slow disease progression. Genome-wide association studies have identified the chromosomal loci around LRRK2 and one of its proposed substrates, RAB29, as contributors towards the lifetime risk of sporadic PD. Considering the evidence for interactions between LRRK2 and RAB29 on the genetic and protein levels, we set out to determine whether there are any consequences on brain function with aging after deletion of both genes. We generated a double knockout mouse model and performed a battery of motor and non-motor behavioral tests. We then investigated postmortem assays to determine the presence of PD-like pathology, including nigral dopamine cell count, astrogliosis, microgliosis, and striatal monoamine content. Behaviorally, we noted only that 18–24-month Rab29-/- and double (Lrrk2-/-/Rab29-/-) knockout mice had diminished locomotor behavior in open field compared to wildtype mice. However, no genotype differences were seen in the outcomes that represented PD-like pathology. These results suggest that depletion of both LRRK2 and RAB29 is tolerated, at least in mice, and support that this pathway might be able to be safely targeted for therapeutics in humans.

Kathryn Lanza, Ashley Centner, Michael Coyle, Isabella Del Priore, Fredric P. Manfredsson, Christopher Bishop 

DOI: 10.1016/j.expneurol.2020.113534

Parkinson's Disease (PD) is symptomatically managed with L-DOPA but chronic use results in L-DOPA-induced dyskinesia (LID) characterized by abnormal involuntary movements (AIMs). In LID, dopamine D3 receptors (D3R) are upregulated on D1 receptor (D1R)-bearing medium spiny neurons where the can synergistically drive downstream signaling and motor behaviors. Despite evidence implying D1R-D3R cooperativity in LID, the dyskinesiogenic role of D3R has never been directly tested. To this end, we developed a specific cre-dependent microRNA (miRNA) to irreversibly prevent D3R upregulation in D1R striatal cells. D1-Cre rats received unilateral 6-hydroxydopamine lesions. Three weeks later, rats received an adeno-associated virus expressing either D3R miRNA or a scrambled (SCR) miRNA delivered into the striatum. After 4 weeks, rats received chronic L-DOPA (6 mg/kg) or vehicle. AIMs development and motor behaviors were assayed throughout treatment. At the conclusion of the experiment, efficacy and fidelity of the miRNA strategy was analyzed using in situ hybridization (ISH). ISH analyses demonstrated that D1R+/D3R+ cells were upregulated in LID and that the selective D3R miRNA reduced D1R+/D3R+ co-expression. Importantly, silencing of D3R also significantly attenuated LID development without impacting L-DOPA efficacy or other locomotion. These data highlight a dyskinesiogenic role of D3R within D1R cells in LID and highlight aberrant D1R-D3R interactions as targets of LID management.

Nicole E Chambers, Samantha M Meadows, Anne Taylor, Eitan Sheena, Kathryn Lanza, Melissa M Conti, Christopher Bishop

DOI: 10.1016/j.neuroscience.2019.04.008

Standard treatment for Parkinson's disease (PD) is L-DOPA, but with chronic administration the majority of patients develop L-DOPA-induced dyskinesia (LID). Emerging evidence implicates the cholinergic system in PD and LID. Muscarinic acetylcholine receptors (mAChR) are known to modulate movement and of late have been implicated as possible targets for LID. Therefore the current study investigated the role of M1 and M4 mAChRs in LID, on motor performance following L-DOPA treatment, and sought to identify brain sites through which these receptors were acting. We first administered M1R-preferring antagonist trihexyphenidyl (0, 0.1, and 1.0 mg/kg, i.p.) or the M4R-preferring antagonist tropicamide (0, 10, and 30 mg/kg, i.p.) before L-DOPA, after which LID and motor performance were evaluated. Both compounds worsened and extended the time course of LID, while M1R blockade improved motor performance. We then evaluated the effects of tropicamide and trihexyphenidyl on dyskinesia induced by D1R agonist SKF81297 or D2R agonist quinpirole. Surprisingly, both M1R and M4R antagonists reduced D1R agonist-induced dyskinesia but not D2R agonist-induced dyskinesia, suggesting that mAChR blockade differentially affects MSN firing in the absence of postsynaptic DA. Finally, we evaluated effects of striatum- or PPN-targeted tropicamide microinfusion on LID and motor performance. Despite prior evidence, M4R blockade in either site alone did not affect the severity of LID via local striatal or PPN infusions. Taken together, these data suggest M4R as a promising therapeutic target for reducing LID using more selective compounds.

Kathryn Lanza, Samantha M Meadows, Nicole E Chambers, Emily Nuss, Molly M Deak, Sergi Ferré, Christopher Bishop

DOI: 10.1016/j.neuropharm.2018.06.024

Individually, D1 and D3 dopamine receptors (D1R and D3R, respectively) have been implicated in L-DOPA-induced dyskinesia (LID). Of late, direct D1R-D3R interactions have been linked to LID yet remain enigmatic. Therefore, the current research sought to characterize consequences of putative D1R-D3R interactions in dyskinesia expression and in LID-associated downstream cellular signaling. To do so, adult male Sprague-Dawley hemi-parkinsonian rats were given daily L-DOPA (6 mg/kg; s.c.) for 2 weeks to establish stable LID, as measured via the abnormal voluntary movements (AIMs) scale. Thereafter, rats underwent dose-response AIMs testing for the D1R agonist SKF38393 (0, 0.3, 1.0, 3.0 mg/kg) and the D3R agonist, PD128907 (0, 0.1, 0.3, 1.0 mg/kg). Each agonist dose-dependently induced dyskinesia, implicating individual receptor involvement. More importantly, when threshold doses were co-administered, rats displayed synergistic exacerbation of dyskinesia. Interestingly, this observation was not mirrored in general locomotor behaviors, highlighting a potentially dyskinesia-specific effect. To illuminate the mechanisms by which D1R-D3R co-stimulation led to in vivo synergy, levels of striatal phosphorylated extracellular signal-regulated kinase 1/2 (pERK1/2) were quantified after administration of SKF38393 and/or PD128907. Combined agonist treatment synergistically drove striatal pERK1/2 expression. Together, these results support the presence of a functional, synergistic interaction between D1R and D3R that manifests both behaviorally and biochemically to drive dyskinesia in hemi-parkinsonian rats.