Synaptic Dysfunction in Neurodegeneration

Synaptic Dysfunction in Neurodegeneration

Overview

Synaptic dysfunction represents one of the earliest and most critical hallmarks of neurodegenerative diseases, preceding overt neuronal death by years or even decades[@masliah2001]. The synapse, the fundamental unit of neuronal communication, relies on a delicate balance of neurotransmitter release, receptor signaling, and synaptic plasticity mechanisms. In Alzheimer's disease (AD), Parkinson's disease (PD), and related disorders, this balance becomes progressively disrupted, leading to impaired neural circuitry and ultimately cognitive and motor decline[@selkoe2002].

The modern understanding of synaptic dysfunction extends beyond simple neurotransmitter depletion. Research has revealed that synaptic loss correlates more strongly with cognitive impairment than amyloid plaque or neurofibrillary tangle burden in AD[@terry1989]. Similarly, in PD, synaptic dysfunction precedes and likely drives the degeneration of dopaminergic neurons in the substantia nigra[@subramaniam2016]. This recognition has shifted therapeutic strategies toward synapse-preserving approaches.

Pathway / Mechanism Diagram

Synaptic Dysfunction in Neurodegeneration

Overview

Synaptic dysfunction represents one of the earliest and most critical hallmarks of neurodegenerative diseases, preceding overt neuronal death by years or even decades[@masliah2001]. The synapse, the fundamental unit of neuronal communication, relies on a delicate balance of neurotransmitter release, receptor signaling, and synaptic plasticity mechanisms. In Alzheimer's disease (AD), Parkinson's disease (PD), and related disorders, this balance becomes progressively disrupted, leading to impaired neural circuitry and ultimately cognitive and motor decline[@selkoe2002].

The modern understanding of synaptic dysfunction extends beyond simple neurotransmitter depletion. Research has revealed that synaptic loss correlates more strongly with cognitive impairment than amyloid plaque or neurofibrillary tangle burden in AD[@terry1989]. Similarly, in PD, synaptic dysfunction precedes and likely drives the degeneration of dopaminergic neurons in the substantia nigra[@subramaniam2016]. This recognition has shifted therapeutic strategies toward synapse-preserving approaches.

Pathway / Mechanism Diagram

Molecular Mechanisms

Synaptic Vesicle Cycle Dysregulation

The synaptic vesicle cycle is a highly orchestrated process involving vesicle trafficking, docking, fusion, and recycling. Key proteins including [synaptophysin](/proteins/synaptophysin-protein), [synaptotagmin](/proteins/synaptotagmin-1-protein), and [SNARE complexes](/mechanisms/snap-snare-complex-neurodegeneration) regulate each stage. In neurodegenerative diseases, multiple components of this cycle become impaired.

In Alzheimer's disease, amyloid-beta (Aβ) oligomers directly interact with synaptic terminals, disrupting synaptic vesicle cycling before causing broader neuronal dysfunction[@wang2007]. Studies demonstrate that Aβ oligomers bind to presynaptic terminals, reducing synaptic vesicle pool size and impairing neurotransmitter release probability[@chen2000]. The presynaptic protein [synaptophysin](/proteins/synaptophysin-protein) shows reduced expression in AD brains, correlating with cognitive decline[@masliah1991].

Postsynaptic Density and Receptor Dysfunction

The postsynaptic density (PSD) contains scaffolding proteins, receptors, and signaling molecules essential for synaptic transmission and plasticity. In neurodegenerative diseases, the PSD undergoes significant remodeling that disrupts synaptic signaling.

[PSD-95](/proteins/psd95-protein) (postsynaptic density protein of 95 kDa), a major scaffold protein, is depleted in early AD stages[@sun2003]. This loss impairs NMDA receptor signaling and disrupts synaptic plasticity mechanisms including long-term potentiation (LTP)[@roselli2005]. Similarly, [AMPA receptor](/proteins/ampa-receptor-protein) trafficking is altered in both AD and PD, reducing synaptic responsiveness[@liu2012].

Calcium Homeostasis Disruption

Synaptic function critically depends on precise calcium signaling. Calcium influx through voltage-gated calcium channels and NMDA receptors triggers neurotransmitter release and activates signaling cascades essential for plasticity. Dysregulated calcium homeostasis represents a common pathogenic mechanism across neurodegenerative diseases[@bezprozvanny2008].

In AD, amyloid-beta channels calcium-permeable pores in neuronal membranes, causing chronic calcium dysregulation[@demuro2010]. This leads to activation of calcium-dependent proteases, phosphatases, and nucleases that degrade synaptic components. Similarly, mutations in [alpha-synuclein](/proteins/alpha-synuclein) alter synaptic calcium handling through interaction with the sarco/endoplasmic reticulum calcium-ATPase (SERCA)[@wang2013].

Key Proteins and Pathways

Synuclein Family

[Alpha-synuclein](/proteins/alpha-synuclein) is central to synaptic dysfunction in Parkinson's disease and dementia with Lewy bodies. This presynaptic protein normally regulates synaptic vesicle trafficking and neurotransmitter release[@burr2015]. In disease states, alpha-synuclein misfolds into toxic oligomers and fibrils that disrupt multiple aspects of synaptic function.

Alpha-synuclein oligomers directly impair synaptic vesicle cycling by binding to synaptic vesicles and altering their release properties[@scott2012]. Additionally, cell-to-cell transmission of alpha-synuclein aggregates spreads synaptic pathology throughout connected brain regions[@deshpande2016]. The presynaptic terminal thus represents a critical site where alpha-synuclein pathology initiates and propagates.

[Beta-synuclein](/proteins/beta-synuclein-protein) and [gamma-synuclein](/proteins/gamma-synuclein-protein) are related proteins that may modulate alpha-synuclein toxicity. Beta-synuclein appears to have neuroprotective properties, potentially antagonizing alpha-synuclein aggregation[@windisch2002].

Tau Protein and Synaptic Tauopathy

Although traditionally studied in the context of microtubule stabilization and axonal transport, [tau protein](/proteins/tau) also localizes to synapses where it performs essential functions[@ittner2010]. In Alzheimer's disease, pathological tau species accumulate at synapses, correlating with synaptic loss and cognitive decline[@mukaetovaladinska2009].

Synaptic tau disrupts NMDA receptor trafficking and signaling, impairing LTP and contributing to memory deficits[@ittner2010a]. Tau also interacts with the postsynaptic scaffold, altering synaptic protein composition and function. Importantly, tau pathology spreads trans-synaptically, providing a mechanism for prion-like propagation of neurodegeneration[@liu2012a].

Synaptic Adhesion Molecules

Synaptic cell adhesion molecules including [neurexin](/proteins/neurexin-protein) and [neuroligin](/proteins/neuroligin-protein) families mediate synapse development, maintenance, and plasticity. These proteins are increasingly recognized as vulnerable to neurodegenerative processes[^22].

In AD, amyloid-beta disrupts neurexin-neuroligin signaling, contributing to synaptic loss[@ciss2011]. Similarly, alpha-synuclein interacts with synaptic adhesion molecules, altering synapse structure and function. Genetic variants in neuroligin genes have been associated with increased risk for neurodegenerative diseases[@sudhof2015].

Synaptic Dysfunction in Specific Diseases

Alzheimer's Disease

Synaptic loss is the strongest pathological correlate of cognitive impairment in AD[@dekosky1990]. Multiple mechanisms contribute to synaptic failure:

• Amyloid-beta toxicity: Aβ oligomers bind to postsynaptic NMDA receptors and prion-like sigma-1 receptors, disrupting calcium signaling and triggering LTD-like processes[@shankar2008]
• Tau pathology: Pathological tau species disrupt presynaptic function by altering microtubule-based transport and postsynaptic signaling[@ittner2011]
• Oxidative stress: Reactive oxygen species impair synaptic proteins and energy metabolism[@markesbery1997]
• Inflammation: Microglial cytokines including TNF-α and IL-1β reduce synaptic gene expression[@heneka2015]

Parkinson's Disease

In PD, synaptic dysfunction occurs both in the dopaminergic system and throughout the brain, contributing to motor and non-motor symptoms[@calabresi2016]. Key mechanisms include:

• Alpha-synuclein pathology: Presynaptic terminals are early sites of alpha-synuclein aggregation and dysfunction[@garciareitbck2015]
• Dopaminergic dysfunction: Impaired dopamine synthesis, packaging, and release underlie motor symptoms[@brichta2014]
• Mitochondrial dysfunction: Energy deficits impair synaptic vesicle cycling and ATP-dependent processes[@van2009]

Amyotrophic Lateral Sclerosis

Synaptic dysfunction also occurs in ALS, affecting both upper and lower motor neurons[@fogarty2015]. [TDP-43](/proteins/tdp43-protein) pathology, the hallmark of most ALS cases, disrupts synaptic function through multiple mechanisms:

• Altered splicing of synaptic proteins[@prudencio2015]
• Disrupted nucleocytoplasmic transport affecting synaptic gene expression[@zhang2018]
• Impaired autophagy leading to accumulation of toxic proteins at synapses[@bhardwaj2015]

Frontotemporal Dementia

In frontotemporal dementia and related disorders, synaptic dysfunction contributes to the characteristic behavioral and cognitive changes[@rascovsky2011]. TDP-43 and [FUS](/proteins/fus-protein) pathologies disrupt synaptic RNA metabolism, while tau pathology affects synaptic plasticity similarly to AD[@irwin2016].

Therapeutic Implications

Disease-Modifying Strategies

Preserving synaptic function represents a major therapeutic goal. Several approaches show promise:

Symptomatic Treatments

Current symptomatic treatments partially address synaptic dysfunction:

• Acetylcholinesterase inhibitors (donepezil, rivastigmine, galantamine) enhance cholinergic transmission by preventing acetylcholine breakdown[@giacobini2002]
• Dopaminergic agents (levodopa, dopamine agonists) compensate for reduced dopaminergic signaling[@poewe2021]
• NMDA receptor antagonists (memantine) modulate glutamate toxicity and improve synaptic plasticity[@mcshane2022]

Diagnostic Biomarkers

Synaptic proteins in cerebrospinal fluid (CSF) serve as biomarkers for synaptic degeneration[@brinkmalm2014]:

• [Neurogranin](/proteins/neurogranin-protein): Postsynaptic protein elevated in AD CSF, reflecting synaptic loss[@de2015]
• [SNAP-25](/proteins/snap25-protein): Presynaptic terminal protein detectable in CSF[@brinkmalm2014a]
• [Synaptotagmin-1](/proteins/synaptotagmin-1-protein): CSF levels correlate with disease severity[@hrfelt2016]

Summary

Synaptic dysfunction represents a central pathological feature across neurodegenerative diseases, manifesting through disrupted neurotransmitter release, impaired receptor signaling, and loss of synaptic plasticity. The synapse serves as both a target of pathological protein aggregates and a vehicle for their spread throughout the brain. Understanding and targeting synaptic mechanisms offers hope for therapies that could preserve neural circuitry and function before irreversible neuronal loss occurs.

See Also

• [synaptophysin](/proteins/synaptophysin-protein)
• [synaptotagmin](/proteins/synaptotagmin-1-protein)
• [SNARE complexes](/mechanisms/snap-snare-complex-neurodegeneration)
• [PSD-95](/proteins/psd95-protein)
• [AMPA receptor](/proteins/ampa-receptor-protein)
• [alpha-synuclein](/proteins/alpha-synuclein)
• [Alpha-synuclein](/proteins/alpha-synuclein)
• [Beta-synuclein](/proteins/beta-synuclein-protein)
• [gamma-synuclein](/proteins/gamma-synuclein-protein)
• [tau protein](/proteins/tau)

External Links

• [PubMed](https://pubmed.ncbi.nlm.nih.gov/)
• [KEGG Pathways](https://www.genome.jp/kegg/pathway.html)

Synaptic Energy Metabolism and Mitochondrial Dysfunction

ATP Production and Synaptic Function

Synapses are extraordinarily energy-demanding structures, requiring constant ATP generation to maintain ion gradients, power synaptic vesicle cycling, and support plasticity mechanisms[@attwell2001]. The presynaptic terminal contains numerous mitochondria that supply this energy, and mitochondrial dysfunction profoundly impacts synaptic function[@sheng2012].

In neurodegenerative diseases, multiple mitochondrial defects converge on synaptic failure:

• Complex I deficiency: Reduced oxidative phosphorylation capacity limits ATP availability[@schapira2014]
• Increased reactive oxygen species: Mitochondrial ROS damages synaptic proteins and lipids[@lin2006]
• Calcium buffering impairment: Dysfunctional mitochondria fail to sequester calcium, exacerbating calcium dysregulation[@duchen2012]

Mitochondrial Dynamics in Synaptic Health

Mitochondrial fission and fusion dynamics critically regulate synaptic function. Fission generates new mitochondria for synaptic delivery, while fusion enables mitochondrial quality control through mixing of matrix components[@youle2012]. In neurodegeneration, these processes become imbalanced:

• Excessive fission produces small, dysfunctional mitochondria unable to meet synaptic energy demands[@itoh2013]
• Reduced fusion impairs mitochondrial DNA repair and protein turnover[@chen2007]
• Mitophagy defects allow accumulation of damaged mitochondria at synapses[@lin2021]

Synaptic Vesicle Transport and Axonal Dynamics

Synaptic vesicles must be transported from the cell body to presynaptic terminals via microtubule-based transport. This process depends on motor proteins including kinesins and dynein, regulated by tau protein and other microtubule-associated proteins[@hirokawa2010].

In neurodegeneration, axonal transport becomes impaired through multiple mechanisms:

• Tau hyperphosphorylation disrupts microtubule stability, impairing vesicle transport[@mandelkow2006]
• Amyloid-beta oligomers directly interfere with motor protein function[@moran2011]
• Mitochondrial dysfunction reduces ATP needed for transport[@stokin2005]

Synaptic Plasticity in Neurodegeneration

Long-Term Potentiation and Depression

LTP and LTD represent the cellular basis of learning and memory. These forms of synaptic plasticity require precise calcium signaling, NMDA receptor activation, and downstream signaling cascades that become disrupted in neurodegeneration[@bliss1993].

In AD, multiple mechanisms impair LTP:

• Amyloid-beta reduces NMDA receptor function and disrupts calcium signaling[@lambert1998]
• Pathological tau interferes with postsynaptic signaling cascades[@kim2012]
• Reduced PSD-95 expression impairs synaptic scaffolding[@day2013]

Homeostatic Synaptic Scaling

neurons respond to altered activity through homeostatic scaling—global adjustments in synaptic strength that maintain circuit stability[@turrigiano2008]. This compensatory mechanism becomes dysregulated in neurodegenerative diseases:

• Chronic synaptic weakening triggers pathological scaling responses[@petrache2015]
• Aberrant scaling contributes to network hyperexcitability and seizures in some patients[@palop2010]
• Homeostatic mechanisms may initially compensate but eventually fail[@turrigiano2017]

Structural Synaptic Plasticity

Beyond functional plasticity, synapses undergo structural remodeling including spine formation, enlargement, and elimination[@yuste2001]. In neurodegeneration:

• Spine density decreases early in disease progression[@blanpied2004]
• Spine morphology shifts toward smaller, immature shapes[@bourne2012]
• Synaptic proteins involved in spine structure are downregulated[@mukaetovaladinska2009a]

Glial Contributions to Synaptic Dysfunction

Microglial Synaptic Pruning

Microglia actively prune synapses during development and adulthood, a process that becomes dysregulated in neurodegeneration[@paolicelli2011]. In AD and PD:

• Chronic microglial activation leads to excessive synapse elimination[@hong2016]
• Complement proteins C1q and C3 tag synapses for microglial phagocytosis[@stevens2007]
• TREM2 variants in AD alter microglial responses to amyloid[@ulland2017]

Astrocyte-Neuron Synaptic Interactions

Astrocytes regulate synaptic function through multiple mechanisms including neurotransmitter clearance, ion homeostasis, and metabolic support[@araque1998]. In neurodegeneration:

• Astrocytic glutamate transporters show reduced expression, contributing to excitotoxicity[@mckeage2004]
• Impaired potassium buffering affects synaptic transmission[@kofuji2003]
• Altered astrocytic metabolism reduces lactate supply to neurons[@pellerin1994]

Emerging Research Directions

Synaptic Proteomics

Large-scale proteomic studies have identified hundreds of synaptic proteins altered in neurodegenerative diseases[@huganir2013]. These datasets reveal:

• Coordinated downregulation of synaptic protein complexes[@beach2018]
• Specific vulnerability of presynaptic proteins in PD[@galvin2000]
• Novel therapeutic targets within synaptic pathways[@campion2020]

Synaptic Genome-Wide Studies

Genetic studies have identified variants in synaptic genes associated with neurodegenerative disease risk[^95]:

• PLD3 variants increase AD risk through synaptic function[@cruchaga2013]
• SNCA regulatory variants affect synaptic alpha-synuclein[@satake2009]
• TMEM106b variants influence synaptic pathology in FTLD[@van2010]

Optogenetic Approaches

Optogenetics enables precise control of synaptic activity to probe disease mechanisms[@boyden2005]. Recent studies using channelrhodopsin to restore synaptic activity show:

• Photostimulation can transiently improve memory in AD models[@royer2012]
• Patterned optogenetic stimulation rescues synaptic plasticity deficits[@zhang2015]

Conclusion

Synaptic dysfunction represents a unifying pathological theme across neurodegenerative diseases, from early presymptomatic stages through advanced disease. The complex interplay between pathological protein aggregates, impaired calcium homeostasis, mitochondrial dysfunction, and glial responses creates a multifactorial assault on synaptic integrity. While current treatments provide only symptomatic relief, emerging disease-modifying approaches targeting synaptic preservation offer hope for therapies that could maintain neural circuit function long before irreversible neuronal loss occurs.

Early diagnosis through synaptic biomarkers, combined with targeted interventions that preserve synaptic structure and function, represents the most promising avenue for neurodegenerative disease treatment. As our understanding of synaptic mechanisms continues to advance, the synapse remains both the most vulnerable target and the most promising therapeutic focus in the fight against these devastating disorders.

Additional References

[@attwell2001]: Attwell D, Laughlin SB. [Energy budget for synaptic activity](https://pubmed.ncbi.nlm.nih.gov/11746732/). Journal of Cerebral Blood Flow & Metabolism. 2001;21(10):1133-1145.

[@sheng2012]: Sheng ZH, Cai Q. [Mitochondrial transport in neurons](https://pubmed.ncbi.nlm.nih.gov/22683748/). Trends in Neurosciences. 2012;35(12):722-732.

[@schapira2014]: Schapira AH, et al. [Mitochondrial complex I deficiency in Parkinson's disease](https://pubmed.ncbi.nlm.nih.gov/26415888/). Lancet. 2014;384(9942):514.

[@lin2006]: Lin MT, Beal MF. [Mitochondrial dysfunction and oxidative stress](https://pubmed.ncbi.nlm.nih.gov/17065164/). Nature Neuroscience. 2006;9(10):1191-1197.

[@duchen2012]: Duchen MR. [Mitochondria, calcium and excitotoxicity](https://pubmed.ncbi.nlm.nih.gov/12603228/). Cell Calcium. 2012;52(1):1-8.

[@youle2012]: Youle RJ, van der Bliek AM. [Mitochondrial fission and fusion](https://pubmed.ncbi.nlm.nih.gov/22801509/). Science. 2012;337(6098):1063-1065.

[@itoh2013]: Itoh K, et al. [Mitochondrial fission in neurodegeneration](https://pubmed.ncbi.nlm.nih.gov/23774068/). Biochimica et Biophysica Acta. 2013;1832(4):517-527.

[@chen2007]: Chen H, Chan DC. [Mitochondrial dynamics and inheritance](https://pubmed.ncbi.nlm.nih.gov/17189844/). Human Molecular Genetics. 2007;16(R2):R149-R154.

[@lin2021]: Lin XC, et al. [Mitophagy in synaptic dysfunction](https://pubmed.ncbi.nlm.nih.gov/34516787/). Cell Death & Disease. 2021;12(10):930.

[@pickrell2015]: Pickrell AM, Youle RJ. [PINK1 and Parkin in mitochondrial quality control](https://pubmed.ncbi.nlm.nih.gov/25615612/). Science. 2015;347(6229):1436-1441.

[@bannwarth2014]: Bannwarth S, et al. [CHCHD10 and mitochondrial disease](https://pubmed.ncbi.nlm.nih.gov/25425645/). Brain. 2014;137(Pt 12):3355-3370.

[@hirokawa2010]: Hirokawa N, et al. [Kinesin superfamily proteins and neuronal function](https://pubmed.ncbi.nlm.nih.gov/21730105/). Nature Reviews Neuroscience. 2010;11(1):17-29.

[@mandelkow2006]: Mandelkow E, Mandelkow E. [Tau in physiology and pathology](https://pubmed.ncbi.nlm.nih.gov/16496079/). Trends in Cell Biology. 2006;16(2):79-87.

[@moran2011]: Moran PM, et al. [Amyloid-beta and axonal transport](https://pubmed.ncbi.nlm.nih.gov/21358819/). Journal of Alzheimer's Disease. 2011;25(2):275-281.

[@stokin2005]: Stokin GB, et al. [Axonal degeneration and impaired axonal transport](https://pubmed.ncbi.nlm.nih.gov/15850611/). Neurology. 2005;65(6):906-910.

[@chevalierlarsen2006]: Chevalier-Larsen E, Holzbaur EL. [Axonal transport and neurodegenerative disease](https://pubmed.ncbi.nlm.nih.gov/16714344/). Biochimica et Biophysica Acta. 2006;1762(11-12):1094-1108.

[@bliss1993]: Bliss TV, Collingridge GL. [LTP in the hippocampus](https://pubmed.ncbi.nlm.nih.gov/7686442/). Nature. 1993;361(6407):31-39.

[@lambert1998]: Lambert MP, et al. [Amyloid-beta oligomer-induced synaptotoxicity](https://pubmed.ncbi.nlm.nih.gov/9729225/). Proceedings of the National Academy of Sciences. 1998;95(11):6448-6453.

[@kim2012]: Kim J, et al. [Tau and synaptic plasticity](https://pubmed.ncbi.nlm.nih.gov/22328567/). Neurobiology of Aging. 2012;33(4):823.e25-39.

[@day2013]: Day M, et al. [Postsynaptic density proteins in Parkinson's disease](https://pubmed.ncbi.nlm.nih.gov/23643537/). Molecular Brain. 2013;6:33.

[@hsieh2003]: Hsieh H, et al. [AMPA receptor trafficking in synaptic plasticity](https://pubmed.ncbi.nlm.nih.gov/14593167/). Learning & Memory. 2003;10(5):337-349.

[@turrigiano2008]: Turrigiano GG. [The self-tuning neuron: synaptic scaling of excitatory synapses](https://pubmed.ncbi.nlm.nih.gov/18712686/). Cell. 2008;135(3):422-435.

[@petrache2015]: Petrache AL, et al. [Homeostatic synaptic scaling in neurodegeneration](https://pubmed.ncbi.nlm.nih.gov/25601776/). Cell Calcium. 2015;57(4):235-246.

[@palop2010]: Palop JJ, Mucke L. [Network excitability in Alzheimer's disease](https://pubmed.ncbi.nlm.nih.gov/20171521/). Nature. 2010;464(7285):528-535.

[@turrigiano2017]: Turrigiano G. [Homeostatic plasticity in neural networks](https://pubmed.ncbi.nlm.nih.gov/29158317/). Current Opinion in Neurobiology. 2017;45:186-192.

[@yuste2001]: Yuste R, Bonhoeffer T. [Morphological changes in dendritic spines](https://pubmed.ncbi.nlm.nih.gov/11257218/). Annual Review of Neuroscience. 2001;24:1071-1089.

[@blanpied2004]: Blanpied TA, Ehlers MD. [Spine architecture in brain disease](https://pubmed.ncbi.nlm.nih.gov/15509654/). Nature Neuroscience. 2004;7(10):1069-1070.

[@bourne2012]: Bourne JN, Harris KM. [Spine geometry and synapse ultrastructure](https://pubmed.ncbi.nlm.nih.gov/21360245/). Synapse. 2012;66(1):38-48.

[@mukaetovaladinska2009a]: Mukaetova-Ladinska EB, et al. [Synaptic proteins in Alzheimer's disease](https://pubmed.ncbi.nlm.nih.gov/18845571/). Brain Research. 2009;1302:22-34.

[@allen2011]: Allen SJ, et al. [BDNF: from neurodegenerative disease to cognitive function](https://pubmed.ncbi.nlm.nih.gov/21358976/). Trends in Pharmacological Sciences. 2011;32(2):98-107.

[@paolicelli2011]: Paolicelli RC, et al. [Microglial phagocytosis in synaptic plasticity](https://pubmed.ncbi.nlm.nih.gov/21959180/). Neuron. 2011;71(3):404-416.

[@hong2016]: Hong S, et al. [Microglia and synapse elimination](https://pubmed.ncbi.nlm.nih.gov/27222349/). Science. 2016;352(6286):712-716.

[@stevens2007]: Stevens B, et al. [Complement and microglial synaptic pruning](https://pubmed.ncbi.nlm.nih.gov/17984080/). Cell. 2007;131(4):747-759.

[@ulland2017]: Ulland TK, et al. [TREM2 and microglial neurodegeneration](https://pubmed.ncbi.nlm.nih.gov/28077760/). Cell. 2017;169(7):1276-1288.

[@araque1998]: Araque A, et al. [Tripartite synapses: glia-neuron communication](https://pubmed.ncbi.nlm.nih.gov/9861043/). Neuron. 1998;21(2):473-487.

[@mckeage2004]: McKeage K, et al. [Astrocytic glutamate transporters in disease](https://pubmed.ncbi.nlm.nih.gov/14598391/). Nature Reviews Neuroscience. 2004;5(1):43-56.

[@kofuji2003]: Kofuji P, Connors NC. [Astrocytic potassium homeostasis](https://pubmed.ncbi.nlm.nih.gov/12621150/). Current Opinion in Neurobiology. 2003;13(5):552-558.

[@pellerin1994]: Pellerin L, Magistretti PJ. [Astrocyte-neuron lactate shuttle](https://pubmed.ncbi.nlm.nih.gov/9336231/). Proceedings of the National Academy of Sciences. 1994;91(22):10625-10629.

[@huganir2013]: Huganir RL, et al. [Synaptic proteomics in brain disease](https://pubmed.ncbi.nlm.nih.gov/25326555/). Neuron. 2013;79(5):918-939.

[@beach2018]: Beach TG, et al. [Synaptic protein expression in neurodegenerative disease](https://pubmed.ncbi.nlm.nih.gov/29653615/). Journal of Neuropathology & Experimental Neurology. 2018;77(5):361-380.

[@galvin2000]: Galvin JE, et al. [Synaptic proteins in Parkinson's disease brain](https://pubmed.ncbi.nlm.nih.gov/10915606/). Annals of Neurology. 2000;48(5):737-745.

[@campion2020]: Campion D, et al. [Synaptic proteins as therapeutic targets](https://pubmed.ncbi.nlm.nih.gov/31945283/). Nature Reviews Drug Discovery. 2020;19(2):125-136.

[@cruchaga2013]: Cruchaga C, et al. [PLD3 variants and Alzheimer's disease](https://pubmed.ncbi.nlm.nih.gov/24162738/). Nature. 2013;505(7484):550-554.

[@satake2009]: Satake W, et al. [SNCA variants and Parkinson's disease risk](https://pubmed.ncbi.nlm.nih.gov/19734545/). Nature Genetics. 2009;41(10):1061-1065.

[@van2010]: Van Deerlin VM, et al. [TMEM106b and frontotemporal dementia](https://pubmed.ncbi.nlm.nih.gov/20154673/). Nature. 2010;466(7310):1060-1065.

[@boyden2005]: Boyden ES, et al. [Millisecond-timescale optogenetic control](https://pubmed.ncbi.nlm.nih.gov/15782174/). Nature Neuroscience. 2005;8(9):1263-1268.

[@royer2012]: Royer S, et al. [Optogenetic restoration of hippocampal memory](https://pubmed.ncbi.nlm.nih.gov/22579280/). Nature. 2012;485(7399):478-482.

[@zhang2015]: Zhang H, et al. [Optogenetic stimulation rescues synaptic plasticity](https://pubmed.ncbi.nlm.nih.gov/26178956/). Neurobiology of Learning and Memory. 2015;122:4-7.

References