Abstract
Dopamine is a neurotransmitter that plays a critical role both peripherally and centrally in vital functions such as cognition, reward, satiety, voluntary motor movements, pleasure, and motivation. Optimal dopamine bioavailability is essential for normal brain functioning and protection against the development of neurological diseases. Emerging evidence shows that gut microbiota have significant roles in maintaining adequate concentrations of dopamine via intricate, bidirectional communication known as the microbiota-gut-brain axis. The vagus nerve, immune system, hypothalamus–pituitary–adrenal axis, and microbial metabolites serve as important mediators of the reciprocal microbiota-gut-brain signaling. Furthermore, gut microbiota contain intrinsic enzymatic activity that is highly involved in dopamine metabolism, facilitating dopamine synthesis as well as its metabolite breakdown. This review examines the relationship between key genera of gut microbiota such as Prevotella, Bacteroides, Lactobacillus, Bifidobacterium, Clostridium, Enterococcus, and Ruminococcus and their effects on dopamine. The effects of gut dysbiosis on dopamine bioavailability and the subsequent impact on dopamine-related pathological conditions such as Parkinson’s disease are also discussed. Understanding the role of gut microbiota in modulating dopamine activity and bioavailability both in the periphery and in the central nervous system can help identify new therapeutic targets as well as optimize available methods to prevent, delay, or restore dopaminergic deficits in neurologic and metabolic disorders.
Highlights
Dopamine is a neurotransmitter that plays a critical role both peripherally and centrally in vital functions such as cognition, reward, satiety, voluntary motor movements, pleasure, and motivation
We focused on key microbial genera, Prevotella, Bacteroides, Lactobacillus, Bifidobacterium, Clostridium, Enterococcus, and Ruminococcus, that are intricately intertwined with dopaminergic pathways via myriad effects on dopamine precursors, enzymes, receptors, transporters, and metabolites
States of intestinal dysbiosis involving these key genera disrupt microbiota-gut-brain signaling, leading to dopaminergic deficits that manifest in neuropathological conditions like Parkinson’s disease (PD)
Summary
The human gastrointestinal (GI) tract is host to trillions of commensal microbes, which play an integral role in the maintenance of the host immune and homeostatic mechanisms. It is not surprising that significant research efforts have been directed toward better understanding the effects that various microbes may have on both normal and pathophysiological processes in humans and their potential therapeutic implications. The regulation of these intricate processes involves a complex and dynamic bidirectional communication between the gut and the brain via the so-called gut–brain axis [16,17,18]. We present evidence showing the ability of gut microbes belonging to Prevotella, Bacteroides, Lactobacillus, Bifidobacterium, Clostridium, Enterococcus, and Ruminococcus to modulate dopaminergic activity and how subsequent alterations contribute to the pathogenesis of dopamine-related disorders. This review highlights the link between the gut microbiota and the dopaminergic system by presenting current evidence while identifying gaps and proposing future research directions to elucidate the potential contribution of gut microbiota to neurodegenerative disorders affecting dopaminergic neurons
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