Function and Regulation of ALDH1A1-positive Nigrostriatal Dopaminergic Neurons in Motor Control and Parkinson's disease

National Institute On Aging

Investigators

Linked publications, trials & patents

Abstract

To investigate the activity patterns of ALDH1A1+ DANs during motor skill learning and sensorimotor behavioral control, we will conduct single-unit spiking activity recordings from DANs in the ventral SNc of Aldh1a1CreERT2 mice. We will utilize optotrodes equipped with either silicone laminar arrays or microwire bundles during an adaptive motor learning task, where head-fixed mice learn to walk on a spheric treadmill. Subsequently, mice will undergo a sensorimotor operant task of virtual navigation on the treadmill with precise sensory cues and feedback to forage for rewards. To identify ALDH1A1+ DANs during recordings, we will employ the optogenetic tagging method. Our aim is to examine how the activity of ALDH1A1+ and ALDH1A1-negative (ALDH1A1) DANs is modulated at different epochs and stages of motor learning. We will also investigate burst activity related to classic reward prediction errors in these neurons, particularly in response to predictive sensory cues and various trial outcomes. These results will help determine how DAN activity from molecularly defined classes contributes to motor learning and behavioral control. To achieve high temporal resolution, crucial for conveying critical behavioral information, we will record spiking activity from DANs. Alternatively, we will use deep brain calcium two-photon imaging, a recently acquired technique, which will allow us to investigate plasticity in ALDH1A1+ DANs during learning. This method will enable us to follow the activity of the same ALDH1A1+ DAN ensemble throughout the entire learning process. The subcellular spatial resolution offered by calcium imaging will aid in identifying sources of learning-related signals to these neurons, including changes in specific input strength in dendritic compartments during learning and task performance. Although calcium signals have slower dynamics than spikes, certain aspects of DAN activity in the sub-second scale may be sufficient for behavioral control, such as changes in tonic spike rate or magnitude of their axonal dopamine release. To establish causality between ALDH1A1+ DAN activity and motor learning performance, we will manipulate somatic spiking activity and axonal dopamine release using optogenetics and chemogenetics methods. By expressing light-gated chloride channels, such as JAWS, in these neurons via Cre-dependent viral vectors, we can transiently inhibit somatic activity using light delivered through implanted optic fibers in the SNc. Precise temporal patterns of ALDH1A1+ DAN spiking activity, especially burst firing, will be time-locked to specific behavioral epochs to determine their causal contribution to learning. Additionally, facilitatory or inhibitory chemogenetic receptors, known as DREADDs, will be expressed in these neurons to allow bidirectional control of their excitability during task performance. As axonal dopamine release often has region-specific regulation mechanisms independent from somatic spiking, we will transiently suppress axonal dopamine release of ALDH1A1+ DANs in one of their projected areas using light-activated Gi/o-coupled receptors expressed in ALDH1A1+ DAN axons. The resulting learning efficacy and behavioral changes from these manipulations will be compared with corresponding sham control mice to draw conclusions. This approach will enable us to determine the causal roles of specific aspects of ALDH1A1+ DAN neuronal activity in motor learning and behavioral control. For example, reduced excitability of these neurons may delay motor learning, while increased excitability could expedite learning. Timing of burst activity in ALDH1A1+ DANs may be pivotal for learning, as inhibiting these neurons at the movement initiation could result in more motor errors, while inhibition during the presence of sensory cues may lead to failure in reward association. Suppression of their dopamine release in the striatum is also expected to affect learning, potentially in a learning-stage dependent manner. To gain further circuit insight, we will genetically manipulate specific inputs to these neurons. By crossbreeding Aldh1a1CreERT2 mice with Grin1-LoxP KI mice, we can selectively disrupt glutamate-mediated excitatory inputs to the ALDH1A1+ DANs. Preliminary results from the resulting Grin1 cKO mice suggest that the glutamatergic afferent activity at ALDH1A1+ DANs may not be required for motor skill learning but could still be involved in other aspects of learning. As ALDH1A1+ SNc DANs display distinct rebound activity in response to GABA-B receptor (Gabbr1)-mediated inhibitory inputs from dSPNs, we are currently developing Gabbr1 cKO mice to selectively disrupt Gabbr1 expression in ALDH1A1+ DANs. These Gabbr1 cKO mice will provide critical insights into the contribution of Gabbr1-mediated rebound and burst activity in ALDH1A1+ DAN-dependent motor skill learning.