Compelling evidence suggests that accumulation and aggregation of alpha-synuclein (α-syn) contribute to the pathogenesis of Parkinson's disease (PD). Here, we describe a novel Bacterial Artificial Chromosome (BAC) transgenic model, in which we have expressed wild-type human α-syn fused to green fluorescent protein (GFP), under control of the mouse α-syn promoter. We observed a widespread and high expression of α-syn-GFP in multiple brain regions, including the dopaminergic neurons of the substantia nigra pars compacta (SNpc) and the ventral tegmental area, the olfactory bulb as well as in neocortical neurons. With increasing age, transgenic mice exhibited reductions in amphetamine-induced locomotor activity in the open field, impaired rotarod performance and a reduced striatal dopamine release, as measured by amperometry. In addition, they progressively developed deficits in an odor discrimination test. Western blot analysis revealed that α-syn-GFP and phospho-α-syn levels increased in multiple brain regions, as the mice grew older. Further, we observed, by immunohistochemical staining for phospho-α-syn and in vivo by two-photon microscopy, the formation of α-syn aggregates as the mice aged. The latter illustrates that the model can be used to track α-syn aggregation in vivo. In summary, this novel BAC α-syn-GFP model mimics a unique set of aspects of PD progression combined with the possibility of tracking α-syn aggregation in neocortex of living mice. Therefore, this α-syn-GFP-mouse model can provide a powerful tool that will facilitate the study of α-syn biology and its involvement in PD pathogenesis.

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, and motor dysfunction has been attributed to loss of dopaminergic neurons. However, motor dysfunction is only one of many symptoms experienced by patients. A neuropathological hallmark of PD is intraneuronal protein aggregates called Lewy pathology (LP). Neuropathological staging studies have shown that dopaminergic neurons are only one of the many cell types prone to manifest LP. Progressive appearance of LP in multiple brain regions, as well as peripheral nerves, has led to the popular hypothesis that LP and misfolded forms of one of its major components - α-synuclein (aSYN) - can spread through synaptically connected circuits. However, not all brain regions or neurons within connected circuits develop LP, suggesting that cell autonomous factors modulate the development of pathology. Here, we review studies about how LP develops and progressively engages additional brain regions. We focus on how connectivity constrains progression and discuss cell autonomous factors that drive pathology development. We propose a mixed model of cell autonomous factors and trans-synaptic spread as mediators of pathology progression and put forward this model as a framework for future experiments exploring PD pathophysiology.

Huntington's disease (HD) is a hereditary disorder characterized by personality changes, chorea, dementia and weight loss. The cause of this weight loss is unknown. The aim of this study was to examine body weight changes and weight-regulating factors in HD using the R6/2 mouse model as a tool. We found that R6/2 mice started losing weight at 9 weeks of age. Total locomotor activity was unaltered and caloric intake was not decreased until 11 weeks of age, which led us to hypothesize that increased metabolism might underlie the weight loss. Indeed, oxygen consumption in R6/2 mice was elevated from 6 weeks of age, indicative of an increased metabolism. Several organ systems that regulate weight and metabolism, including the hypothalamus, the stomach and adipose tissue displayed abnormalities in R6/2 mice. Together, these data demonstrate that weight loss in R6/2 mice is associated with increased metabolism and changes in several weight-regulating factors.

Motor symptoms of Parkinson's disease (PD) are apparent after a high proportion of dopamine neurons in the substantia nigra have degenerated. The vast majority of PD cases are sporadic, and the underlying pathobiological causes are poorly understood. Adults exhibit great variability in the numbers of nigral dopamine neurons, suggesting that factors during embryonic or early life regulate the development and physiology of dopaminergic neurons. Furthermore, exposure to infections and inflammation in utero has been shown to affect fetal brain development in models of schizophrenia and autism. Here, we utilize a mouse maternal infection model to examine how maternal herpesvirus infection impacts dopaminergic neuron-related gene and protein expression in the adult offspring.

Weight loss is the most important non-neurological complication of Huntington's disease (HD). It correlates with disease progression and affects the quality of life of HD patients, suggesting that it could be a valuable target for therapeutic intervention. The mechanism underlying weight loss in HD is unknown. Mutant huntingtin, the protein that causes the disease, is not only expressed in the brain, but also along the gastrointestinal (GI) tract. Here we demonstrate that the GI tract of HD mice is affected. At the anatomical level we observed loss of enteric neuropeptides, as well as decreased mucosal thickness and villus length. Exploring the functions of the GI system we found impaired gut motility, diarrhea, and malabsorption of food. The degree of malabsorption was inversely associated with body weight, suggesting that GI dysfunction plays an important role in weight loss in HD mice. In summary, these observations suggest that the GI tract is affected in HD mice and that GI dysfunction contributes to nutritional deficiencies and weight loss.

In Parkinson's disease, some of the first alpha-synuclein aggregates appear in the olfactory system and the dorsal motor nucleus of the vagus nerve before spreading to connected brain regions. We previously demonstrated that injection of alpha-synuclein fibrils unilaterally into the olfactory bulb of wild type mice leads to widespread synucleinopathy in brain regions directly and indirectly connected to the injection site, consistently, over the course of periods longer than 6 months. Our previously reported observations support the idea that alpha-synuclein inclusions propagates between brain region through neuronal networks. In the present study, we further defined the pattern of propagation of alpha-synuclein inclusions and developed a mathematical model based on known mouse brain connectivity. Using this model, we first predicted the pattern of alpha-synuclein inclusions propagation following an injection of fibrils into the olfactory bulb. We then analyzed the fitting of these predictions to our published histological data. Our results demonstrate that the pattern of propagation we observed in vivo is consistent with axonal transport of alpha-synuclein aggregate seeds, followed by transsynaptic transmission. By contrast, simple diffusion of alpha-synuclein fits very poorly our in vivo data. We also found that the spread of alpha-synuclein inclusions appeared to primarily follow neural connections retrogradely until 9 months after injection into the olfactory bulb. Thereafter, the pattern of spreading was consistent with anterograde propagation mathematical models. Finally, we applied our mathematical model to a different, previously published, dataset involving alpha-synuclein fibril injections into the striatum, instead of the olfactory bulb. We found that the mathematical model accurately predicts the reported progressive increase in alpha-synuclein neuropathology also in that paradigm. In conclusion, our findings support that the progressive spread of alpha-synuclein inclusions after injection of protein fibrils follows neural networks in the mouse connectome.