, 2008) which is an activator of RGS4 (Huang et al., 2007), whose inhibition increases the efficacy of muscarinic autoreceptor function (Ding et al., 2006) (Figure 8C). Lowered cholinergic tone, a reduction of striatal GDNF levels due to progressive degeneration of ACh neurons, and a lack of functional adaptations by surviving ACh neurons should all influence the physiology of surviving

DA neurons in Shh-nLZC/C/Dat-Cre mice. Consistent with this expectation, we observe highly dynamic distortions in DA tissue content in both the vMB and the striatum. Hence, our results suggest that surviving DA neurons, but not surviving ACh neuron, are able to adapt their physiology dynamically in the face of progressive neurodegeneration and decreased ACh and GDNF/Ret signaling during early adulthood. EX527 However, by 10 months of age, we find the manifestation of discrete locomotion and gait disturbances,

indicating that the progressive deterioration of the mesostriatal circuit surpasses the compensatory capacity of DA neurons in aged Shh-nLZC/C/Dat-Cre mice ( Figure 8D). Archetypes of basal ganglia models imply that an imbalance of cholinergic and dopaminergic signaling in the striatum is responsible for the hyper- and hypokinetic manifestations of progressive movement disorders such as PD (Obeso et al., 2010). Our work describes a mouse paradigm that recapitulates many of the key features of the progressive cellular, neurochemical, and functional pathologies observed in PD with BYL719 nmr apparent face-, construct-, and predictive-validity since the functional phenotype that is associated with progressive neuronal loss can be ameliorated with DA supplementation or a muscarinic antagonist also used in the of management of PD. Yet, the resemblance of the phenotype of Shh-nLZC/C/Dat-Cre mice with PD does not extend to the absolute direction of alterations in cholinergic tone. In PD, ACh tone is increased (Wooten, 1990), while in our paradigm ACh tone is decreased

in the absence of Shh signaling from DA neurons, which also must occur in PD. How can these findings be reconciled? Our data points to the possibility that Shh production is increased in still functioning DA neurons in response to the mounting pathophysiological cell stress in the basal ganglia of PD patients. This notion is supported by several in vivo experiments described herein: we demonstrate that the transcription of Shh in DA neurons is strongly upregulated upon (1) injection of 6-OHDA into the mFB, (2) induction of cholinergic dysfunction in the striatum, (3) induction of cholinergic dysfunction in the PPTg, and (4) the genetic ablation of part of the Shh locus which abrogates the production of functional Shh by DA neurons.