Locus Coeruleus as a Master Regulator of Diverse Functions in the Central Nervous System: Its Relevance in Ageing and...

The brainstem nucleus locus coeruleus (LC) is a rod-shaped, cylindrical, deeply pigmented neuromelanin (NM)-rich cluster of noradrenergic cells placed bilaterally in the dorsolateral tegmentum of the pons. The main neurotransmitter synthesised by these neurons is norepinephrine (NE), which polymerises to NM. Collectively, it regulates a plethora of activities, including vigilance, synaptic plasticity, memory processing, pain, stress responses, selective attention, cognition, sleep, emotion, capillary wall permeability and cerebral blood flow, thereby holding a 'master key' to several processes. Despite being small in dimensions, it is of enormous significance in diverse functions. Degeneration of the LC occurs early and progressively in both Alzheimer's disease (AD) and Parkinson's disease (PD), with diverse impacts, and is linked to neuropsychiatric entities such as depression, anxiety, cognitive impairment, schizophrenia and rapid eye movement sleep disorders, thereby raising considerable interest in normal physiology as well as in disease.

This review is to better understand the neuroanatomical connections of human LC (master regulator of the central nervous system), pigmentation, cellular types, neurotransmitters/co-transmitters, and its role in ageing and neurodegenerative diseases. Recent and relevant classical research and review articles were referred to from PubMed to prepare a short review of the structure of LC, its projections, NM pigment and neuroprotection. We further examined the details of its cell types, neurotransmitters, co-transmitter functions and its effects in ageing, AD and PD, with emphasis on human studies.

LC is a vital region that offers neuroprotection, assists in the maintenance of cognitive reserve and enhances resilience and neuronal survival, despite the presence of AD and PD pathology for several decades. Further, it synthesises NE and co-transmitters that regulate attention, sleep-wake cycle, mood, cognition and so on. Maintaining its integrity and function promises potential scope to promote its health with normal ageing and improve clinical strategies in patients with neurodegeneration.