Basal Ganglia in Health and Disease

National Institute Of Environmental Health Sciences

Investigators

Linked publications & trials

Abstract

Study 1: Spectral fiber-photometry derives hemoglobin-absorption changes for accurate fluorescent sensor activity measurement. Summary: Fiber-photometry is an emerging technique for recording fluorescent sensor activity in the brain. Here we demonstrate significant hemoglobin-absorption artifacts that may be misinterpreted as sensor activity changes. Because hemoglobin exists in nearly every location in the brain and its concentration varies over time, such artifacts could significantly impede the accuracy of photometry recording results. We present a novel use of spectral photometry technique and propose a computational method to quantify photon absorption effect from an activity-independent fluorescent sensor, which can be used to derive oxy- and deoxy-hemoglobin concentration changes and correct target sensor activities across spectra. We further demonstrate the utility of this method for delineating brain regional differences in neurovascular transfer functions and shed light on the interpretation of hemodynamic-based neuroimaging data. Study 2: Dopamine Neuron Challenge Exam (DANCE) for early detection of Parkinsons disease. Summary: Parkinsons disease (PD) is a common neurodegenerative disorder featured with progressive loss of dopamine (DA)-producing neurons (DANs) in the substantia nigra pars compacta and a cohort of continuously worsening motor and non-motor symptoms. Currently, there are no biomarkers or diagnostic tests that can detect early-stage PD before the clinical onset when approximately 60% of DANs have been lost. Here we test the hypothesis that a Dopamine Neuron Challenge Exam (DANCE), whereby we measure the DA metabolites in the cerebrospinal fluid (CSF) and plasma after a drug challenge to transiently perturb the homeostasis in DA signaling pathways, may reveal the hypodopaminergic state that has been masked by homeostatic compensation at the early stage of PD. We first use fiber photometry and a genetically encoded DA sensor to identify the most potent DANCE agents to challenge DANs. We then test DANCE in early PD models using both MitoPark mice and 6-OHDA lesion. Finally, we perform behavioral tests to examine the potential adverse effects associated with DANCE. The baseline levels of the major DA metabolites in the CSF and plasma are indistinguishable between controls and early-stage PD mice. DANCE shows 100% sensitivity and specificity in detecting PD using CSF samples, and 100% sensitivity and 82% specificity using plasma samples in early PD mice with 28% loss of DANs. In ultra-early stage PD mice with no detectable loss of DANs, DANCE can still achieve 91% sensitivity and 80-85% specificity using CSF samples. DANCE causes mild and transient inhibition on locomotor activity. The findings described in this study may lead to a sensitive and practical diagnostic test for detecting prodromal PD in the high-risk population. Study 3: Silencing dopamine neurons during sleep slows the progression of Parkinsons disease in mice. Summary: Parkinsons disease (PD) is a highly debilitating neurodegenerative disorder featured with the progressive loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNc). Currently, there are no disease-modifying treatments that can slow or stop the progression of PD. Though the etiology of PD still remains elusive, it has been suggested that SNc DA neurons are more vulnerable than other neurons because of their high bioenergetic demand. Here we test whether reducing the energy expenditure in DA neurons by silencing them during sleep, when DA is not needed for voluntary movement, can protect DA neurons and slow the progression of PD. We show that silencing DA neurons for 6-8 hours daily, either chemogenetically or pharmacologically, improves motor and cognitive functions and reduces the loss of SNc DA neurons in MitoPark mice, a genetic murine model for PD. We further confirm the protective effect of DA neuron silencing in a 6-OHDA lesion PD model. Moreover, silencing DA neurons during sleep does not cause adverse motor or cognitive side effects. These results suggest that reducing energy expenditure by silencing DA neurons during sleep can be an effective and practical treatment to slow the progression of PD. Study 4: DBS-based chemogenetic gene-therapy rescues motor deficits in mice with advanced Parkinsons disease. Summary: Deep brain stimulation (DBS) is currently the most effective treatment for alleviating motor symptoms in patients with advanced Parkinson's Disease (PD). However, the mechanisms underlying its therapeutic effects remain elusive. In this study, using fiber photometry and genetically encoded fluorescent sensors, we measured DBS-induced changes in pre- and postsynaptic neural activities and neurotransmitter release in the subthalamic nucleus (STN), the most commonly selected target in therapeutic DBS for PD. We found that DBS caused persistent elevation in the presynaptic neural activity from afferent axonal terminals while inhibiting the postsynaptic neural activity after a brief initial excitation in local STN neurons. DBS also caused a decrease in both glutamate and GABA release in STN, with a larger decrease observed in glutamate release than GABA when measured simultaneously. Based on these results, we hypothesized that during high-frequency DBS, prolonged activation of presynaptic terminals may disproportionally deplete glutamate and GABA from the releasable pools, leading to a decrease in the excitation/inhibition ratio of synaptic inputs into STN, which in turn results in a decrease in the neural activity in STN neurons. To further test this hypothesis and to develop a less invasive alternative treatment, we used viral vectors to express GiDREADD in STN neurons bilaterally in MitoPark mice, a progressive mouse PD model. We found that a single i.p. injection of 3mg/kg CNO, which inhibits GiDREADD-expressing neurons, completely rescued the motor deficits in open field and rotarod tests in MitoPark mice injected with GiDREADD. The therapeutic effects lasted for at least 5 hours after a single injection. To further test the therapeutic effect of this new treatment after chronic use, the MitoPark mice were treated with CNO daily for 4 weeks their motor functions were evaluated at 29 weeks old. The efficiency of CNO treatment maintained at the same level. Finally, we directly compared the therapeutic effects of electrical DBS and chemogenetic DBS in the same MitoPark mice treated with either CNO or STN-DBS, and found that CNO treatment and DBS stimulation showed comparable effects inhibiting STN neurons and improving motor functions. Taken together, we have revealed the neural mechanisms underlying the therapeutic effects of DBS, and have developed a novel chemogenetic gene-therapy that may become an alternative treatment for patients with advanced PD.