Effects of pedunculopontine nucleus cholinergic lesion on gait and dyskinesia in hemiparkinsonian rats

Abstract

Pedunculopontine nucleus (PPN) cholinergic neurons are implicated in freezing of gait in Parkinson's disease (PD) and motor stereotypy in normal animals, but the causal role of these neurons on specific gait parameters and treatment‐induced dyskinesia remains speculative. Therefore, we examined whether selective cholinergic lesion of the rostral PPN affects PD motor and gait deficits, L‐DOPA‐induced dyskinesia and motor improvement, and DA‐agonist‐induced dyskinesia. Sprague–Dawley rats were assigned to one unilaterally lesioned group: Sham lesion, PPN cholinergic lesion with diphtheria urotensin II fusion toxin, medial forebrain bundle dopamine lesion with 6‐hydroxydopamine, or dual acetylcholine and dopamine lesion. We used gait analysis and forepaw adjusting steps to examine PD gait and motor deficits. Forepaw adjusting steps were also used to assess motor improvement with L‐DOPA treatment. The abnormal involuntary movements scale measured L‐DOPA and dopamine D1‐ and D2‐receptor agonist‐induced dyskinesia. Lesions, verified via tyrosine hydroxylase and choline acetyltransferase immunohistochemistry reduced an average of 95% of nigral dopamine neurons and 80% of PPN cholinergic neurons, respectively. Rats receiving acetylcholine and dual lesion demonstrated enhanced freezing, and acetylcholine lesioned rats exhibited increased print area and stand index. Dopamine and dual lesion produced similar forepaw adjusting steps task on and off L‐DOPA. Relative to DA lesioned rats, dual lesioned rats displayed reduced L‐DOPA and DA agonist‐induced dyskinesia at specific time points. Our results indicate that PPN cholinergic neurons affect gait parameters related to postural stability. Therefore, therapeutically targeting PPN cholinergic neurons could reduce intractable postural instability in PD without affecting motor benefits or side effects of L‐DOPA treatment.

Rostral Pedunculopontine Nucleus Infusion of M4Positive Allosteric Modulator VU0467154 Augments L-DOPA Effects in Hemiparkinsonian Rats

“…This suggests that PPN cholinergic neurons could be a unique therapeutic target for augmenting L-DOPA-derived motor benefit without affecting LID. Additionally, when combined with our previous findings (Chambers et al, 2021) that PPN cholinergic Running Title: PPN M4 AUGMENTS L-DOPA EFFECTS neurons influence freezing of gait and aspects of gait related to balance and stability, it is possible that PPN cholinergic neurons may also be able to modify PD gait deficits without negatively impacting LID or L-DOPA-mediated motor benefit. Stimulation of PPN cholinergic neurons improves forepaw akinesia in a PD model by normalizing nigrostriatal DA transmission (Pienaar et al, 2015;Sharma et al, 2020).…”

“…Nigral brain slices with TH staining were imaged with a BZ-X series microscope at 10x magnification. For TH cell counts total enumeration was used (Chambers et al, 2021;Sellnow et al, 2019). Data are represented as percent Of the 30 animals receiving microinjections which had successful placement of the injection within the PPN, 2 were excluded due to TH counts above 40%, indicating incomplete lesion, leaving 28 animals remaining for data analysis.…”

Substantia Nigra Pars Reticulata Projections to the Pedunculopontine Nucleus Modulate Dyskinesia

“…67,74,77 It is tempting to speculate that the population of locomotion-activating glutamatergic PPN neurons become hyperactive during LID and are suppressed by increasing GABA release from SNr terminals in our study; however, determining which neuron type(s) are dysregulated during LID will be paramount for understanding how SNr modulation of PPN neurons decreases LID. It is worth noting that targeted ablation of cholinergic PPN neurons yielded only modest changes in LID, 78 supporting a role for the glutamatergic or GABAergic population. Although we showed that stimulation of SNr to PPN fibers was sufficient to reduce LID, we have not excluded contributions of other SNr targets.…”

Comparing tonic and phasic dendritic calcium in cholinergic pedunculopontine neurons and dopaminergic substantia nigra neurons

“…Of particular interest, ~30–60% of cholinergic pedunculopontine nucleus (PPN) neurons are lost in PD patients (Giguère et al, 2018; Jellinger, 1988; Rinne et al, 2008; Sébille et al, 2019). PPN cholinergic neurons directly innervate motor structures in the basal ganglia and lower brainstem (Mena‐Segovia & Bolam, 2017), and their degeneration may contribute to gait and balance impairments (Chambers et al, 2021; Grabli et al, 2013; Karachi et al, 2010; Rinne et al, 2008). However, it is not known why PPN cholinergic neurons and SNc dopaminergic neurons selectively degenerate in PD.…”