In vivo fast scan cyclic voltammetry reveals that restricted diffusion maintains discrete dopamine domains in the dorsal striatum.

摘要

Dopamine is an important neurotransmitter involved in a variety of physiological functionality such as motor control, cognition, sexual arousal and reward. Furthermore, dysfunction in the dopaminergic system can lead a number of devastating neurological disorders including Parkinson’s disease, schizophrenia, Alzheimer’s, and substance abuse. Therefore, understanding the real-time mechanisms of dopamine signaling is of utmost importance. ud Real-time analysis of in vivo dopamine poses an interesting analytical challenge. Dopamine is released into the extracellular space deep below the cortical surface in nanomolar to micromolar concentrations on a sub-second timeframe. Because of these conditions, effective dopamine quantification requires a small selective detector that exhibits high temporal resolution and a low limit of detection. Fast scan cyclic voltammetry at carbon fiber microelectrodes has proven to be ideal for this task. The work detailed in this dissertation pairs in vivo voltammetry with electrical stimulation of dopaminergic axonal projections to controllably study dopamine kinetics.ud Previously our laboratory discovered the existence of two discrete dopamine domains in the rat dorsal striatum that exhibit unique dopamine kinetic responses to electrical stimulation. This dissertation is built on the foundation of that work. First, we discovered that the effect of a competitive inhibitor of the dopamine transporter is domain dependent. The kinetics of these domain dependent effects allowed us to predict that dopamine signaling in the extracellular space is subjected to restricted diffusion. We continued on to show that restricted diffusion prevents cross-talk between domains, thus maintaining a strict physical segregation between domains. Further work resulted in the discovery of five discrete dopamine domains. These domains exhibit differing extents of regulation, resulting in unique kinetic responses to electrical stimulation. Finally, we discovered the existence of long-term dopamine signaling. Following electrically stimulated dopamine release, free dopamine in the extracellular space is not completely cleared as previously believed. Instead, the free dopamine establishes a new steady state elevated baseline concentration. These discoveries provide new insight into the complex mechanisms that regulate dopamine signaling, and have the potential to explain the multiple functionalities of the dopaminergic system.ud