Dopamine-releasing neurons within the Substantia nigra (SN DA) are particularly vulnerable to degeneration compared to other dopaminergic neurons. The age-dependent, progressive loss of these neurons is a pathological hallmark of Parkinson's disease (PD), as the resulting loss of striatal dopamine causes its major movement-related symptoms. SN DA neurons release dopamine from their axonal terminals within the dorsal striatum, and also from their cell bodies and dendrites within the midbrain in a calcium-and activity-dependent manner. Their intrinsically generated and metabolically challenging activity is created and modulated by the orchestrated function of different ion channels and dopamine D2-autoreceptors. Here, we review increasing evidence that the mechanisms that control activity patterns and calcium homeostasis of SN DA neurons are not only crucial for their dopamine release within a physiological range but also modulate their mitochondrial and lysosomal activity, their metabolic stress levels, and their vulnerability to degeneration in PD. Indeed, impaired calcium homeostasis, lysosomal and mitochondrial dysfunction, and metabolic stress in SN DA neurons represent central converging trigger factors for idiopathic and familial PD. We summarize double-edged roles of ion channels, activity patterns, calcium homeostasis, and related feedback/feed-forward signaling mechanisms in SN DA neurons for maintaining and modulating their physiological function, but also for contributing to their vulnerability in PD-paradigms. We focus on the emerging roles of maintained neuronal activity and calcium homeostasis within a physiological bandwidth, and its modulation by PD-triggers, as well as on bidirectional functions of voltage-gated L-type calcium channels and

Primary cilia (PC) are microtubule-based protrusions of the cell membrane transducing molecular signals during brain development. Here, we report that PC are required for maintenance of Substantia nigra (SN) dopaminergic (DA) neurons highly vulnerable in Parkinson’s disease (PD). Targeted blockage of ciliogenesis in differentiated DA neurons impaired striato-nigral integrity in adult mice. The relative number of SN DA neurons displaying a typical auto-inhibition of spontaneous activity in response to dopamine was elevated under control metabolic conditions, but not under metabolic stress. Strikingly, in the absence of PC, the remaining SN DA neurons were less vulnerable to the PD neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridin (MPTP). Our data indicate conserved PC-dependent neuroadaptive responses to DA lesions in the striatum. Moreover, PC control the integrity and dopamine response of a subtype of SN DA neurons. These results reinforce the critical role of PC as sensors of metabolic stress in PD and other disorders of the dopamine system.

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Here we present a deep learning-based image analysis platform (DLAP), tailored to autonomously quantify numbers of neuronal subtypes in defined areas, and of fluorescence signals, derived from RNAscope probes or immunohistochemistry, in defined cellular compartments. As proof-of-principle, we utilized DLAP to analyse subtypes of dopaminergic midbrain neurons in mouse and human brain-sections. These neurons modulate complex behaviour like voluntary movement, and are differentially affected in Parkinson’s and other diseases. DLAP allows the analysis of large cell numbers from different species, and facilitates the identification of small cellular subpopulations, based on differential mRNA- or protein-expression, and anatomical location. Using DLAP, we identified a small subpopulation of dopaminergic midbrain neurons (~5%), mainly located in the very lateral Substantia nigra (SN), that was immunofluorescence-negative for the plasmalemma dopamine transporter (DAT). These results have important implications, as DAT is crucial for dopamine-signalling, and its expression is commonly used as marker for dopaminergic SN neurons.

Here we present a deep learning-based image analysis platform (DLAP), tailored to autonomously quantify numbers of neuronal subtypes in defined areas, and of fluorescence signals, derived from RNAscope probes or immunohistochemistry, in defined cellular compartments. As proof-of-principle, we utilized DLAP to analyse subtypes of dopaminergic midbrain neurons in mouse and human brain-sections. These neurons modulate complex behaviour like voluntary movement, and are differentially affected in Parkinson’s and other diseases. DLAP allows the analysis of large cell numbers from different species, and facilitates the identification of small cellular subpopulations, based on differential mRNA- or protein-expression, and anatomical location. Using DLAP, we identified a small subpopulation of dopaminergic midbrain neurons (~5%), mainly located in the very lateral Substantia nigra (SN), that was immunofluorescence-negative for the plasmalemma dopamine transporter (DAT), with ~30% smaller cell-bodies, and a ~4-fold higher likelihood of calbindin-d28k co-expression. These results have important implications, as DAT is crucial for dopamine-signalling, and its expression is commonly used as marker for dopaminergic SN neurons.