Inhibition of striatal dopamine release by the L-type calcium channel inhibitor isradipine co-varies with risk factors for Parkinson's

Ca2+ entry into nigrostriatal dopamine (DA) neurons and axons via L-type voltage-gated Ca2+ channels (LTCCs) contributes, respectively, to pacemaker activity and DA release and has long been thought to contribute to vulnerability to degeneration in Parkinson's disease. LTCC function is greater in DA axons and neurons from substantia nigra pars compacta than from ventral tegmental area, but this is not explained by channel expression level. We tested the hypothesis that LTCC control of DA release is governed rather by local mechanisms, focussing on candidate biological factors known to operate differently between types of DA neurons and/or be associated with their differing vulnerability to parkinsonism, including biological sex, α-synuclein, DA transporters (DATs) and calbindin-D28k (Calb1). We detected evoked DA release ex vivo in mouse striatal slices using fast-scan cyclic voltammetry and assessed LTCC support of DA release by detecting the inhibition of DA release by the LTCC inhibitors isradipine or CP8. Using genetic knockouts or pharmacological manipulations, we identified that striatal LTCC support of DA release depended on multiple intersecting factors, in a regionally and sexually divergent manner. LTCC function was promoted by factors associated with Parkinsonian risk, including male sex, α-synuclein, DAT and a dorsolateral co-ordinate, but limited by factors associated with protection, that is, female sex, glucocerebrosidase activity, Calb1 and ventromedial co-ordinate. Together, these data show that LTCC function in DA axons and isradipine effect are locally governed and suggest they vary in a manner that in turn might impact on, or reflect, the cellular stress that leads to parkinsonian degeneration

Striatal Dopamine Transporter Function Is Facilitated by Converging Biology of α-Synuclein and Cholesterol

Striatal dopamine transporters (DAT) powerfully regulate dopamine signaling, and can contribute risk to degeneration in Parkinson’s disease (PD). DATs can interact with the neuronal protein α-synuclein, which is associated with the etiology and molecular pathology of idiopathic and familial PD. Here, we tested whether DAT function in governing dopamine (DA) uptake and release is modified in a human-α-synuclein-overexpressing (SNCA-OVX) transgenic mouse model of early PD. Using fast-scan cyclic voltammetry (FCV) in ex vivo acute striatal slices to detect DA release, and biochemical assays, we show that several aspects of DAT function are promoted in SNCA-OVX mice. Compared to background control α-synuclein-null mice (Snca-null), the SNCA-OVX mice have elevated DA uptake rates, and more pronounced effects of DAT inhibitors on evoked extracellular DA concentrations ([DA] ) and on short-term plasticity (STP) in DA release, indicating DATs play a greater role in limiting DA release and in driving STP. We found that DAT membrane levels and radioligand binding sites correlated with α-synuclein level. Furthermore, DAT function in Snca-null and SNCA-OVX mice could also be promoted by applying cholesterol, and using Tof-SIMS we found genotype-differences in striatal lipids, with lower striatal cholesterol in SNCA-OVX mice. An inhibitor of cholesterol efflux transporter ABCA1 or a cholesterol chelator in SNCA-OVX mice reduced the effects of DAT-inhibitors on evoked [DA] . Together these data indicate that human α-synuclein in a mouse model of PD promotes striatal DAT function, in a manner supported by extracellular cholesterol, suggesting converging biology of α-synuclein and cholesterol that regulates DAT function and could impact DA function and PD pathophysiology

Axo-glial interactions between midbrain dopamine neurons and oligodendrocyte lineage cells in the anterior corpus callosum

Oligodendrocyte progenitor cells (OPCs) receive synaptic innervation from glutamatergic and GABAergic axons and can be dynamically regulated by neural activity, resulting in activity-dependent changes in patterns of axon myelination. However, it remains unclear to what extent other types of neurons may innervate OPCs. Here, we provide evidence implicating midbrain dopamine neurons in the innervation of oligodendrocyte lineage cells in the anterior corpus callosum and nearby white matter tracts of male and female adult mice. Dopaminergic axon terminals were identified in the corpus callosum of DAT-Cre mice after injection of an eYFP reporter virus into the midbrain. Furthermore, fast-scan cyclic voltammetry revealed monoaminergic transients in the anterior corpus callosum, consistent with the anatomical findings. Using RNAscope, we further demonstrate that ~ 40% of Olig2 + /Pdfgra + cells and ~ 20% of Olig2 + /Pdgfra- cells in the anterior corpus callosum express Drd1 and Drd2 transcripts. These results suggest that oligodendrocyte lineage cells may respond to dopamine released from midbrain dopamine axons, which could affect myelination. Together, this work broadens our understanding of neuron-glia interactions with important implications for myelin plasticity by identifying midbrain dopamine axons as a potential regulator of corpus callosal oligodendrocyte lineage cells

GABA uptake transporters support dopamine release in dorsal striatum with maladaptive downregulation in a parkinsonism model

Striatal dopamine (DA) is critical for action and learning. Recent data show that DA release is under tonic inhibition by striatal GABA. Ambient striatal GABA tone on striatal projection neurons can be determined by plasma membrane GABA uptake transporters (GATs) located on astrocytes and neurons. However, whether striatal GATs and astrocytes determine DA output are unknown. We reveal that DA release in mouse dorsolateral striatum, but not nucleus accumbens core, is governed by GAT-1 and GAT-3. These GATs are partly localized to astrocytes, and are enriched in dorsolateral striatum compared to accumbens core. In a mouse model of early parkinsonism, GATs are downregulated, tonic GABAergic inhibition of DA release augmented, and nigrostriatal GABA co-release attenuated. These data define previously unappreciated and important roles for GATs and astrocytes in supporting DA release in striatum, and reveal a maladaptive plasticity in early parkinsonism that impairs DA output in vulnerable striatal regions

Investigating the control of striatal dopamine neurotransmission by axonal calcium channels and by striatal neuromodulators: Insights for Parkinson's disease

Dopamine (DA) is a key striatal neuromodulator which is central to processes including action selection and reward-related learning. DA dysfunction is associated with a number of psychomotor disorders, most notably of which is Parkinson's disease (PD). This thesis uses fast-scan cyclic voltammetry in acute mouse striatal slices to detect DA release at carbon fibre microelectrodes with subsecond temporal resolution, to investigate factors affecting the presynaptic control of DA release. In this thesis, I have investigated the roles of voltage dependent calcium channels (VDCCs) and the neuromodulator, substance P (SP), in the presynaptic control of DA, in the presence of nicotinic acetylcholine receptor (nAChR) blockade. This is because ACh has profound modulatory and driving effects on DA release, via activation of nAChRs on DA terminals. In CPu, blockers for N-, P/Q-, T- or L-type VDCCs (ω-Conotoxin GVIA, ω-Agatoxin IVA, NNC 55-0396, isradipine) reduced DA release to varying degrees (N&gt;P/Q&gt;T&gt;L). Furthermore, L-type function was eliminated by α-synuclein knockout. In NAc, only N and P/Q-blockers modified DA release (N&gt;P/Q) and more weakly than in CPu. Frequency-specific effects of some VGCCs were reproduced by changes to extracellular Ca2+ or release probability, consistent with Ca2+ entry governing the relationship between DA release probability and its short-term plasticity. Finally I have shown that SP can directly modulate striatal DA release in a manner that depends on striosome-matrix location. To date there is much conflict in the literature on the role of SP in a number of striatal processes, this finding may help to resolve these conflicts and shed light on the little understood role of the striosome-matrix division of the striatum.</p

Data from: "Inhibition of striatal dopamine release by the L-type calcium channel inhibitor isradipine co-varies with risk factors for Parkinson's"

Ca2+ entry into nigrostriatal dopamine (DA) neurons and axons via L-type voltage-gated Ca2+ channels (LTCCs) contributes respectively to pacemaker activity and DA release, and has long been thought to contribute to vulnerability to degeneration in Parkinson’s disease. LTCC function is greater in DA axons and neurons from substantia nigra pars compacta than from ventral tegmental area, but this is not explained by channel expression level. We tested the hypothesis that LTCC-control of DA release is governed rather by local mechanisms, focussing on candidate biological factors known to operate differently between types of DA neurons and/or be associated with their differing vulnerability to parkinsonism, including biological sex, α-synuclein, DA transporters (DATs), and calbindin-D28k (Calb1). We detected evoked DA release ex vivo in mouse striatal slices using fast-scan cyclic voltammetry, and assessed LTCC support of DA release by detecting the inhibition of DA release by the LTCC inhibitors isradipine or CP8. Using genetic knockouts or pharmacological manipulations we identified that striatal LTCC support of DA release depended on multiple intersecting factors, in a regionally and sexually divergent manner. LTCC function was promoted by factors associated with Parkinsonian risk, including male sex, α-synuclein, DAT, and a dorsolateral co-ordinate, but limited by factors associated with protection i.e. female sex, glucocerebrosidase activity, Calb1, and ventromedial co-ordinate. Together, these data show that LTCC function in DA axons, and isradipine effect, are locally governed and suggest they vary in a manner that in turn might impact on, or reflect, the cellular stress that leads to parkinsonian degeneration.Funding: Parkinson's UK G-1803 Wellcome Trust 223202/Z/21/

Investigating the control of striatal dopamine neurotransmission by axonal calcium channels and by striatal neuromodulators: Insights for Parkinson's disease

Dopamine (DA) is a key striatal neuromodulator which is central to processes including action selection and reward-related learning. DA dysfunction is associated with a number of psychomotor disorders, most notably of which is Parkinson's disease (PD). This thesis uses fast-scan cyclic voltammetry in acute mouse striatal slices to detect DA release at carbon fibre microelectrodes with subsecond temporal resolution, to investigate factors affecting the presynaptic control of DA release. In this thesis, I have investigated the roles of voltage dependent calcium channels (VDCCs) and the neuromodulator, substance P (SP), in the presynaptic control of DA, in the presence of nicotinic acetylcholine receptor (nAChR) blockade. This is because ACh has profound modulatory and driving effects on DA release, via activation of nAChRs on DA terminals. In CPu, blockers for N-, P/Q-, T- or L-type VDCCs (&omega;-Conotoxin GVIA, &omega;-Agatoxin IVA, NNC 55-0396, isradipine) reduced DA release to varying degrees (N>P/Q>T>L). Furthermore, L-type function was eliminated by &alpha;-synuclein knockout. In NAc, only N and P/Q-blockers modified DA release (N>P/Q) and more weakly than in CPu. Frequency-specific effects of some VGCCs were reproduced by changes to extracellular Ca2+ or release probability, consistent with Ca2+ entry governing the relationship between DA release probability and its short-term plasticity. Finally I have shown that SP can directly modulate striatal DA release in a manner that depends on striosome-matrix location. To date there is much conflict in the literature on the role of SP in a number of striatal processes, this finding may help to resolve these conflicts and shed light on the little understood role of the striosome-matrix division of the striatum.</p

The Striosome and Matrix Compartments of the Striatum: A Path through the Labyrinth from Neurochemistry toward Function

The striatum is a heterogeneous structure with a diverse range of neuron types and neuromodulators. Three decades of anatomical and biochemical studies have established that the neurochemical organization of striatum is not uniformly heterogeneous, but rather, can be differentiated into neurochemically discrete compartments known as striosomes (also known as patches) and matrix. These compartments are well understood to differ in their expression of neurochemical markers, with some differences in afferent and efferent connectivity, and have also been suggested to have different involvement in a range of neurological diseases. However, the functional outcomes of striosome-matrix organization are poorly understood. Now, recent findings and new experimental tools are beginning to reveal that the distinctions between striosomes and matrix have distinct consequences for striatal synapse function. Here, we review recent findings that suggest there can be distinct regulation of neural function in striosome versus matrix compartments, particularly compartment-specific neurochemical interactions. We highlight that new transgenic and viral tools are becoming available that should now accelerate the pace of advances in understanding of these long-mysterious striatal compartments

Communities Setting the Direction for Their Right to Nutritious, Affordable Food: Co-Design of the Remote Food Security Project in Australian Indigenous Communities

Despite long histories of traditional food security, Indigenous peoples globally are disproportionately exposed to food insecurity. Addressing this imbalance must be a partnership led by Indigenous peoples in accordance with the UN Declaration of the Rights of Indigenous Peoples. We report the co-design process and resulting design of a food security research project in remote Australia and examine how the co-design process considered Indigenous peoples’ ways of knowing, being, and doing using the CREATE Tool. Informed by the Research for Impact Tool, together Aboriginal Community Controlled Health Organisation staff, Indigenous and non-Indigenous public health researchers designed the project from 2018–2019, over a series of workshops and through the establishment of research advisory groups. The resulting Remote Food Security Project includes two phases. Phase 1 determines the impact of a healthy food price discount strategy on the diet quality of women and children, and the experience of food (in)security in remote communities in Australia. In Phase 2, community members propose solutions to improve food security and develop a translation plan. Examination with the CREATE Tool showed that employing a co-design process guided by a best practice tool has resulted in a research design that responds to calls for food security in remote Indigenous communities in Australia. The design takes a strengths-based approach consistent with a human rights, social justice, and broader empowerment agenda. Trial registration: The trial included in Phase 1 of this project has been registered with Australian New Zealand Clinical Trials Registry: ACTRN12621000640808

Transcription factors FOXA1 and FOXA2 maintain dopaminergic neuronal properties and control feeding behavior in adult mice

Midbrain dopaminergic (mDA) neurons are implicated in cognitive functions, neuropsychiatric disorders, and pathological conditions; hence understanding genes regulating their homeostasis has medical relevance. Transcription factors FOXA1 and FOXA2 (FOXA1/2) are key determinants of mDA neuronal identity during development, but their roles in adult mDA neurons are unknown. We used a conditional knockout strategy to specifically ablate FOXA1/2 in mDA neurons of adult mice. We show that deletion of Foxa1/2 results in down-regulation of tyrosine hydroxylase, the rate-limiting enzyme of dopamine (DA) biosynthesis, specifically in dopaminergic neurons of the substantia nigra pars compacta (SNc). In addition, DA synthesis and striatal DA transmission were reduced after Foxa1/2 deletion. Furthermore, the burst-firing activity characteristic of SNc mDA neurons was drastically reduced in the absence of FOXA1/2. These molecular and functional alterations lead to a severe feeding deficit in adult Foxa1/2 mutant mice, independently of motor control, which could be rescued by L-DOPA treatment. FOXA1/2 therefore control the maintenance of molecular and physiological properties of SNc mDA neurons and impact on feeding behavior in adult mice