Temporal-Spatial Profiling of Pedunculopontine Galanin-Cholinergic Neurons in the Lactacystin Rat Model of Parkinson’s Disease

Abstract

Parkinson's disease (PD) is conventionally seen as resulting from single-system neurodegeneration affecting nigrostriatal dopaminergic neurons. However, accumulating evidence indicates multi-system degeneration and neurotransmitter deficiencies, including cholinergic neurons which degenerate in a brainstem nucleus, the pedunculopontine nucleus (PPN), resulting in motor and cognitive impairments. The neuropeptide galanin can inhibit cholinergic transmission, while being upregulated in degenerating brain regions associated with cognitive decline. Here we determined the temporal-spatial profile of progressive expression of endogenous galanin within degenerating cholinergic neurons, across the rostro-caudal axis of the PPN, by utilizing the lactacystin-induced rat model of PD. First, we show progressive neuronal death affecting nigral dopaminergic and PPN cholinergic neurons, reflecting that seen in PD patients, to facilitate use of this model for assessing the therapeutic potential of bioactive peptides. Next, stereological analyses of the lesioned brain hemisphere found that the number of PPN cholinergic neurons expressing galanin increased by 11%, compared to sham-lesioned controls, and increasing by a further 5% as the neurodegenerative process evolved. Galanin upregulation within cholinergic PPN neurons was most prevalent closest to the intra-nigral lesion site, suggesting that galanin upregulation in such neurons adapt intrinsically to neurodegeneration, to possibly neuroprotect. This is the first report on the extent and pattern of galanin expression in cholinergic neurons across distinct PPN subregions in both the intact rat CNS and lactacystin-lesioned rats. The findings pave the way for future work to target galanin signaling in the PPN, to determine the extent to which upregulated galanin expression could offer a viable treatment strategy for ameliorating PD symptoms associated with cholinergic degeneration.

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

“…In our previous studies [10][11][12][13], we demonstrated that the unilateral nigral lactacystin model of PD not only produced a partial lesion of the DAergic nigrostriatal pathway, but also cholinergic neuronal loss in the PPN, thereby mirroring what is observed in PD patients, and hence highlighting the suitability of this model for the current study. Intracranial injections of ChAT::Cre rats with hM3Dq DREADD were carried out while the animal remained anesthetized for the lesion surgery ( Fig.…”

“…Low-frequency DBS can be targeted to the pedunculopontine nucleus (PPN), leading to an improvement in motor-related symptoms, particularly gait and postural abnormalities, which affect a significant number of PD patients [2][3][4][5]. The PPN, located in the dorso-lateral mesopontine tegmentum, is a highly heterogeneous neuronal structure, primarily composing of cholinergic, glutamatergic, and gamma-aminobutyric acid (GABA)ergic neurons [6][7][8][9][10][11][12][13]. Clinical interest in the PPN as a DBS target stems from the partial denervation of PPN cholinergic neurons (where in the intact brain, such neurons innervate the basal ganglia motor loop [9,14]) observed in Puneet K. Sharma…”

Mitochondrial abnormalities in Parkinson's disease and Alzheimer's disease: can mitochondria be targeted therapeutically?

“…The above animal models focus on recapitulating the loss of dopaminergic neurons from the substantia nigra; a recent animal model however, has concentrated on the cholinergic system in PD [109,110] . This model utilises stereotactic injection of lactocystin in the substantia nigra pars compacta, however the authors then concentrate on investigating the effects on the pedunculopontine nucleus, an area which is a promising target for therapy via deep brain stimulation [111] .…”

Characterization of functional subgroups among genetically identified cholinergic neurons in the pedunculopontine nucleus

“…Besides neurochemical groups based on neurotransmitter content [ 12 , 14 , 15 ], differences in distribution of calcium-binding proteins (rostrocaudal gradient of calbindin and calretinin; [ 16 ]) or the presence of certain neuropeptides (e.g., galanin, [ 5 , 17 ]) were also suggested to define subgroups of PPN neurons. NADPH diaphorase, neuronal nitric oxide synthetase (bNOS) and choline acetyltransferase were investigated as putative cholinergic PPN neuron markers [ 18 – 20 ], from which bNOS was recently proven to be a highly selective marker for cholinergic neurons [ 21 ].…”