Periaqueductal Gray (PAG) Neurons
Introduction <table class="infobox infobox-cell">
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Periaqueductal Gray (PAG) Neurons
Introduction <table class="infobox infobox-cell">
The [periaqueductal gray](/cell-types/periaqueductal-gray) (PAG) is a midbrain gray matter structure surrounding the cerebral aqueduct. It plays crucial roles in [pain modulation](/cell-types/raphe-magnus-pain-modulation-neurons), [emotional processing](/mechanisms/emotional-regulation), [autonomic control](/mechanisms/autonomic-dysfunction), and defensive behaviors. It is increasingly recognized as vulnerable in several [neurodegenerative diseases](/diseases/neurodegeneration). [@fields2000]
Overview
Mermaid diagram (expand to render)
The [brainstem](/brain-regions/brainstem) contains several key nuclei that play critical roles in modulating neurological function and are implicated in [neurodegenerative diseases](/diseases/neurodegeneration). These nuclei serve as focal points where pathological changes can disrupt widespread neural circuits, contributing to disease progression and symptom manifestation. [@bandler1994]
The Periaqueductal Gray (PAG) is a midbrain gray matter structure surrounding the cerebral aqueduct. It plays crucial roles in [pain modulation](/cell-types/raphe-magnus-pain-modulation-neurons), [emotional processing](/mechanisms/emotional-regulation), [autonomic control](/mechanisms/autonomic-dysfunction), and defensive behaviors. It is increasingly recognized as vulnerable in several [neurodegenerative diseases](/diseases/neurodegeneration). [@behbehani1995]
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Multi-Taxonomy Classification
Taxonomy Database Cross-References
External Database Links
[Allen Brain Cell Atlas](https://portal.brain-map.org/atlases-and-data/bkp/abc-atlas)
[CellxGene Census](https://cellxgene.cziscience.com/)
[Human Cell Atlas](https://www.humancellatlas.org/)
Morphology and Markers
Cell Type : Mixed neuronal populations ([glutamatergic](/cell-types/excitatory-neurons), [GABAergic](/cell-types/gabaergic-neurons), [serotonergic](/cell-types/serotonergic-neurons-raphe))Key Markers : Glutamatergic: VGLUT2, VGAT
Serotonergic: TPH2 (subpopulation)
Neuromodulatory: Substance P (NK1R), Enkephalin
Neurotransmitters : [Glutamate](/grik1---glutamate-receptor-kainate-type-subunit-1), [GABA](/cell-types/gaba-receptors-neurons), [Serotonin](/serotonin-receptor-2b-protein), [Opioid peptides](/oprm1-—-mu-opioid-receptor)Columns : dorsolateral (dlPAG), lateral (lPAG), ventrolateral (vlPAG), dorsal (dPAG)Normal Function
Columnar Organization:
Dorsolateral/lPAG : Active coping, fight-or-flight, [emotional pain](/mechanisms/emotional-regulation)Ventrolateral (vlPAG) : Passive coping, quiescence, analgesia, [reward](/mechanisms/reward-system)Dorsal PAG : Vocalization, ocular responses
Key Functions:
[Pain Modulation](/cell-types/raphe-magnus-pain-modulation-neurons) : Descending inhibition of nociception via rostral ventromedial medulla [1][Autonomic Regulation](/mechanisms/autonomic-dysfunction) : Heart rate, blood pressure, breathing[Emotional Responses](/mechanisms/emotional-regulation) : Fear, anxiety, panic attacks [2]Defensive Behaviors : Freezing, flight, fightVocalization : Species-specific calls[Sexual Behavior](/mechanisms/sexual-behavior) : Mating postures
Circuitry The PAG integrates information from multiple brain regions [1][3]: [@fuentes2016]
Output projections: [@knyihrcsillik2005]
[Rostral ventromedial medulla](/cell-types/raphe-nuclei) (RVM): Pain modulation
[Locus coeruleus](/cell-types/locus-coeruleus-noradrenergic): Stress response
[Periaqueductal gray](/cell-types/periaqueductal-gray) spinal cord: Autonomic control
Vulnerability in Disease
[Parkinson's Disease](/diseases/parkinsons-disease)
Early dysfunction : vlPAG shows abnormal activity [4]Freezing of gait : PAG connectivity deficits [5]Pain : Enhanced pain perception due to descending inhibition loss [6]Anxiety/panic : Associated with lPAG dysfunction [7]PD with dementia : Reduced PAG volume on MRI [8][Alzheimer's Disease](/diseases/alzheimers-disease)
Pain perception changes : Altered PAG-mediated analgesia [9]Emotional regulation : Contributes to apathy and depression [10]Sleep disorders : PAG regulates REM sleep - affected early [11]Autonomic dysfunction : Cardiovascular dysregulation [12][Multiple System Atrophy](/diseases/multiple-system-atrophy)
Autonomic failure : vlPAG degeneration contributes to orthostatic hypotension [13]Pain : Neuropathic pain common in MSA [14]Sleep disorders : REM behavior disorder can originate from PAG [15][Amyotrophic Lateral Sclerosis](/diseases/amyotrophic-lateral-sclerosis)
Breathing dysfunction : PAG controls respiratory centers [16]Pseudobulbar affect : Emotional lability linked to PAG [17]Pain modulation : May be affected by disease progressionMolecular Markers and Neurochemistry
Neurotransmitter Systems The PAG contains diverse neurotransmitter populations [1][2]: [@fanciulli2015]
Receptor Expression Key receptor populations in PAG [neurons](/entities/neurons):
[Mu-opioid receptors](/oprm1-—-mu-opioid-receptor): Mediate endogenous analgesia
[5-HT1A receptors](/proteins/serotonin-receptor-1a): Anxiolytic effects
[NMDA receptors](/entities/nmda-receptor): Synaptic plasticity
[GABAB receptors](/proteins/gaba-b-receptor): Inhibitory modulation
Animal Models
Parkinson's Disease Models
6-OHDA lesions: Show vlPAG hyperactivity [4]
[α-Synuclein](/proteins/alpha-synuclein) overexpression: PAG pathology [5]
Alzheimer's Disease Models
[APP](/entities/app-protein)/PS1 mice: Altered PAG function [9]
[Tau](/proteins/tau) models: Navigation deficits related to PAG
Pain Models
Chronic constriction injury: PAG neuronal changes [1]
Opioid tolerance: PAG desensitization
Therapeutic Implications
Deep Brain Stimulation
PAG/DBS targets : Emerging therapy for [Parkinson's disease](/diseases/parkinsons-disease-disease) [18]Pain modulation : PAG stimulation for chronic pain [19]Pharmacological Approaches
Opioid analgesics : Act on PAG μ-receptorsSSRI/SNRI : May modulate PAG serotonergic tone [2]GABAergic agents : Anxiolytic effects via PAGNovel Targets
TRPV1 modulation : PAG vanilloid receptorsEndocannabinoid system : PAG CB1 receptor modulation [20]Neurotrophic factors : BDNF delivery to PAGSee Also
[Brainstem](/brain-regions/brainstem)
[Pain Modulation](/cell-types/raphe-magnus-pain-modulation-neurons)
[Parkinson's Disease](/diseases/parkinsons-disease)
[Alzheimer's Disease](/diseases/alzheimers-disease)
[Autonomic Dysfunction](/mechanisms/autonomic-dysfunction)
[Serotonergic Neurons](/cell-types/serotonergic-neurons-raphe)
[Locus Coeruleus](/cell-types/locus-coeruleus-noradrenergic)
[Rostral Ventromedial Medulla](/cell-types/raphe-magnus)
External Links
[<a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3414567/" target="_blank">NCBI PMC: PAG Pain Modulation</a>](/institutions/nih)
[<a href="https://pubmed.ncbi.nlm.nih.gov/30122223/" target="_blank">PubMed: PAG in Parkinson's Disease</a>](/institutions/nih)
Background The study of Periaqueductal Gray (Pag) Neurons has evolved significantly over the past decades. Research in this area has revealed important insights into the underlying mechanisms of neurodegeneration and continues to drive therapeutic development.
Historical context and key discoveries in this field have shaped our current understanding and will continue to guide future research directions.
Brain Atlas Resources
Allen Human Brain Atlas : [Periaqueductal Gray expression search](https://human.brain-map.org/microarray/search/show?search_term=Periaqueductal+Gray)Allen Cell Type Atlas : [Transcriptomic cell type reference](https://portal.brain-map.org/atlases-and-data/rnaseq)Allen Mouse Brain Atlas : [Periaqueductal Gray search](https://mouse.brain-map.org/search/index.html?query=Periaqueductal+Gray)[Periaqueductal Gray - Allen Brain Atlas](https://human.brain-map.org/microarray/search/show?search_term=Periaqueductal+Gray)
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