No abstract

The dysregulation of dopamine, a neuromodulator, is associated with a broad spectrum of brain disorders, including Parkinson's disease, addiction, and schizophrenia. Quantitative measurements of dopamine are essential for understanding dopamine functional dynamics. Fast-scan cyclic voltammetry (FSCV) is the most widely used electrochemical technique for measuring real-time in vivo dopamine level changes. Standard FSCV has only been used to analyze "phasic dopamine" (changes in seconds), because the gradual generation of background charging current is inevitable, and acts as the main noise source in the low-frequency band. Although "tonic dopamine" (changes in minutes to hours) is key for understanding the dopamine system, an electrochemical technique capable of simultaneously measuring phasic and tonic dopamine in an in vivo environment has not been established. Several modified voltammetric techniques have been developed for measuring tonic dopamine, but the sampling rates (0.1-0.05 Hz) are too low to be useful. Further investigation of the in vivo applicability of previously developed background drift removal methods for measuring tonic dopamine levels is required. We developed a second-derivative-based background removal (SDBR) method for simultaneously measuring phasic and tonic neurotransmitter levels in real-time. The performance of this technique was tested via in silico and in vitro tonic dopamine experiments. Furthermore, its applicability was tested in vivo. SDBR is a simple, robust, post-processing technique that can extract tonic neurotransmitter levels from all FSCV data. As SDBR is calculated in individual-scan voltammogram units, it can be applied to any real-time closed-loop system that uses a neurotransmitter as a biomarker.

Dopamine (DA) homeostasis influences emotions, neural circuit development, cognition, and the reward system. Dysfunctions in DA regulation can lead to neurological disorders, including depression, developmental disorders, and addiction. DA homeostasis disruption is a primary cause of Parkinson's Disease (PD). Therefore, understanding the relationship between DA homeostasis and PD progression may clarify the mechanisms for pharmacologically treating PD. This study developed a novel in vitro DA homeostasis platform which consists of three main parts:(1) a microfluidic device for culturing DAergic neurons, (2) an optical detection system for reading DA levels, and (3) an automatic closed-loop control system that establishes when and how much medication to infuse; this uses a microfluidic device that can cultivate DAergic neurons, perfuse solutions, perform in vitro PD modeling, and continuously monitor DA concentrations. The automatically controlled closed-loop control system simultaneously monitors pharmacological PD treatment to support long-term monitoring of DA homeostasis. SH-SY5Y neuroblastoma cells were chosen as DAergic neurons. They were cultivated in the microfluidic device, and real-time cellular DA level measurements successfully achieved long-term monitoring and modulation of DA homeostasis. When applied in combination with multiday cell culture, this advanced system can be used for drug screening and fundamental biological studies.

Tuft dendrites of pyramidal neurons housed in layer 1 of the neocortex form extensive excitatory synaptic connections with long-range cortical and high-order thalamic axons, along with diverse inhibitory inputs. Recently, we reported that synapses from the vibrissal primary motor cortex (vM1) and posterior medial thalamic nucleus (POm) are spatially clustered together in the same set of distal dendrites, suggesting a close functional interaction. In this study, we evaluated how these two types of synapses interact with each other using in vivo two-photon Ca2+ imaging and electrophysiology. We observed that dendritic Ca2+ responses could be efficiently evoked by electrical stimulation of POm or vM1 in the overlapping set of dendritic branches, rejecting the idea of branch-wise origin-selective synaptic wiring. Surprisingly, the Ca2+ responses upon coincident POm and vM1 stimulation summed sublinearly. We attribute this sublinearity to mutual inhibition via inhibitory neurons because synaptic currents generated by POm and vM1 also integrated sublinearly, but pharmacologically isolated direct synaptic currents summed linearly. Inhibitory neurons receiving POm inputs in the superficial cortical layer negatively regulated vM1-evoked responses. Finally, POm and vM1 innervated overlapping but distinct populations of somatostatin-expressing inhibitory neurons. Thus, POm and vM1 inputs negatively modulate each other in the mouse somatosensory cortex.