Mutations in the SNCA gene, which encodes the α-synuclein protein, were the first discovered genetic causes of familial parkinsonism with Lewy pathology. To date, six different SNCA missense mutations as well as multiplications are known to cause parkinsonism. For this review, we performed a literature search to identify all published cases of SNCA-related parkinsonism to provide an updated summary of the clinical and neuropathological features of parkinsonism due to SNCA mutations. Familial parkinsonism associated with SNCA is rare, but α-synuclein aggregation is a core feature of sporadic parkinsonism, including Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. Research into α-synuclein and parkinsonism has impacted how we define the pathology and understand the pathogenesis of Parkinson's disease and related neurodegenerative disorders. We briefly discuss some of the lessons we have learned from research into the physiological role of α-synuclein and its pathological links to neurodegeneration and parkinsonism.

Postural instability and gait disturbances, common disabilities in the elderly and frequently present in Parkinson's disease (PD), have been suggested to be related to dysfunctional cholinergic signaling in the brainstem. We investigated how long-term loss of cholinergic signaling from mesopontine nuclei influence motor behaviors. We selectively eliminated the vesicular acetylcholine transporter (VAChT) in pedunculopontine and laterodorsal tegmental nuclei cholinergic neurons to generate mice with selective mesopontine cholinergic deficiency (VAChT ). VAChT mice did not show any gross health or neuromuscular abnormality on metabolic cages, wire-hang and grip-force tests. Young VAChT mice (2-5 months-old) presented motor learning/coordination deficits on the rotarod; moved slower, and had smaller steps on the catwalk, but showed no difference in locomotor activity on the open field. Old VAChT mice (13-16 months-old) showed more pronounced motor learning/balance deficits on the rotarod, and more pronounced balance deficits on the catwalk. Furthermore, old mutants moved faster than controls, but with similar step length. Additionally, old VAChT-deficient mice were hyperactive. These results suggest that dysfunction of cholinergic neurons from mesopontine nuclei, which is commonly seen in PD, has causal roles in motor functions. Prevention of mesopontine cholinergic failure may help to prevent/improve postural instability and falls in PD patients. Read the Editorial Highlight for this article on page 688.

The pedunculopontine tegmental nucleus (PPT) and laterodorsal tegmental nucleus (LDT) are heterogeneous brainstem structures that contain cholinergic, glutamatergic, and GABAergic neurons. PPT/LDT neurons are suggested to modulate both cognitive and noncognitive functions, yet the extent to which acetylcholine (ACh) signaling from the PPT/LDT is necessary for normal behavior remains uncertain. We addressed this issue by using a mouse model in which PPT/LDT cholinergic signaling is highly decreased by selective deletion of the vesicular ACh transporter (VAChT) gene. This approach interferes exclusively with ACh signaling, leaving signaling by other neurotransmitters from PPT/LDT cholinergic neurons intact and sparing other cells. VAChT mutants were examined on different PPT/LDT‐associated cognitive domains. Interestingly, VAChT mutants showed no attentional deficits and only minor cognitive flexibility impairments while presenting large deficiencies in both spatial and cued Morris water maze (MWM) tasks. Conversely, working spatial memory determined with the Y‐maze and spatial memory measured with the Barnes maze were not affected, suggesting that deficits in MWM were unrelated to spatial memory abnormalities. Supporting this interpretation, VAChT mutants exhibited alterations in anxiety‐like behavior and increased corticosterone levels after exposure to the MWM, suggesting altered stress response. Thus, PPT/LDT VAChT‐mutant mice present little cognitive impairment per se, yet they exhibit increased susceptibility to stress, which may lead to performance deficits in more stressful conditions.—Janickova, H., Kljakic, O., Rosborough, K., Raulic, S., Matovic, S., Gros, R., Saksida, L. M., Bussey, T. J., Inoue, W., Prado, V. F., Prado, M. A. M. Selective decrease of cholinergic signaling from pedunculopontine and laterodorsal tegmental nuclei has little impact on cognition but markedly increases susceptibility to stress. FASEB J. 33, 7018–7036 (2019). http://www.fasebj.org

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