DREADD Activation of Pedunculopontine Cholinergic Neurons Reverses Motor Deficits and Restores Striatal Dopamine Signaling in Parkinsonian Rats

Abstract

The brainstem-based pedunculopontine nucleus (PPN) traditionally associates with motor function, but undergoes extensive degeneration during Parkinson's disease (PD), which correlates with axial motor deficits. PPN-deep brain stimulation (DBS) can alleviate certain symptoms, but its mechanism(s) of action remains unknown. We previously characterized rats hemi-intranigrally injected with the proteasomal inhibitor lactacystin, as an accurate preclinical model of PD. Here we used a combination of chemogenetics with positron emission tomography imaging for in vivo interrogation of discrete neural networks in this rat model of PD. Stimulation of excitatory designer receptors exclusively activated by designer drugs expressed within PPN cholinergic neurons activated residual nigrostriatal dopaminergic neurons to produce profound motor recovery, which correlated with striatal dopamine efflux as well as restored dopamine receptor 1-and dopamine receptor 2-based medium spiny neuron activity, as was ascertained with c-Fos-based immunohistochemistry and stereological cell counts. By revealing that the improved axial-related motor functions seen in PD patients receiving PPN-DBS may be due to stimulation of remaining PPN cholinergic neurons interacting with dopaminergic ones in both the substantia nigra pars compacta and the striatum, our data strongly favor the PPN cholinergic-midbrain dopaminergic connectome as mechanism for PPN-DBS's therapeutic effects. These findings have implications for refining PPN-DBS as a promising treatment modality available to PD patients.

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

“…Based on this evidence, we expected dual lesion to reduce forepaw stepping and L-DOPA-mediated motor improvement. Whereas others using a less severe PD phenotype observed effects of stimulating PPN cholinergic neurons on akinesia (Pienaar et al, 2015;Sharma et al, 2020), we observed no effects of lesion on stepping at baseline or on L-DOPA. Unlike research by Pienaar et al (2015), in our severe 6-OHDA lesion model, PPN control of SNc DA release is likely lost.…”

“…PPN cholinergic neurons stimulate locomotion (Xiao et al., 2016) and ameliorate deficits in forepaw akinesia by normalizing nigrostriatal DA transmission (Pienaar et al., 2015; Sharma et al., 2020). Furthermore, combining SNc DA lesion and PPN ACh lesion produces more severe lesion than either technique alone (Bensaid et al., 2016).…”

“…PPN neurons may also be involved in L-DOPA-and DAagonist-mediated behaviors like motor improvement and dyskinesia (Bastide et al, 2014;Chambers et al, 2019Chambers et al, , 2020Inglis et al, 1994). Despite evidence of PPN involvement in motor deficits and freezing (MacLaren et al, 2014(MacLaren et al, , 2018Pienaar et al, 2015;Sharma et al, 2020;Xiao et al, 2017), a causal role for PPN cholinergic neurons on specific gait parameters, L-DOPA efficacy, and dyskinesia remains unproven.…”

“…Stimulating PPN cholinergic neurons decreases akinesia in parkinsonian rats by normalizing nigrostriatal DA transmission (Pienaar et al., 2015; Sharma et al., 2020). Similarly, PPN neurons may contribute to L‐DOPA’s motor efficacy, as patients undergoing chronic PPN deep brain stimulation reduced their L‐DOPA dose (Mazzone et al., 2014), and showed additional motor benefit beyond L‐DOPA alone (Nandi et al., 2008; Pereira et al., 2011; Stefani et al., 2007).…”

Novel 1-hydroxypyridin-2-one metal chelators prevent and rescue ubiquitin proteasomal-related neuronal injury in an in vitro model of Parkinson’s disease

“…However, such further studies may be best placed by utilizing an in vivo system, since the balance of iron homeostasis is maintained through a dynamic equilibrium between systemic tissues, and hence an animal system will allow for a comparison between various body compartments, while molecular iron regulators identified so far have been shown to operate in man as well as rodents (Wallace 2016). In this regard, our previous work showed that rats that had received a unilateral nigral stereotaxic injection of lactacystin accurately mirror the behavioural and neuropathological deficits shown by PD patients (Pienaar et al 2015a, b;Sharma et al 2020).…”