<table class="infobox infobox-cell">
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<th class="infobox-header" colspan="2">Vasoactive Intestinal Peptide Expressing Interneurons</th>
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<td class="label">Name</td>
<td><strong>Vasoactive Intestinal Peptide Expressing Interneurons</strong></td>
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<td class="label">Type</td>
<td>Cell Type</td>
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<table class="infobox infobox-cell">
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<th class="infobox-header" colspan="2">Vasoactive Intestinal Peptide Expressing Interneurons</th>
</tr>
<tr>
<td class="label">Name</td>
<td><strong>Vasoactive Intestinal Peptide Expressing Interneurons</strong></td>
</tr>
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<td class="label">Type</td>
<td>Cell Type</td>
</tr>
</table>
Vasoactive Intestinal Peptide (VIP) Expressing Interneurons represent a major class of cortical and hippocampal GABAergic interneurons that play critical roles in regulating disinhibitory circuits, sensory processing, and cognitive functions["@pfeffer2013"]. These [neurons](/entities/neurons) are characterized by their expression of VIP, a neuropeptide that acts as both a neurotransmitter and neuromodulator, and are increasingly recognized for their involvement in neurodegenerative disease processes["@tricoire2011"].
VIP interneurons constitute approximately 10-15% of all cortical interneurons and are strategically positioned to modulate cortical circuit dynamics through their unique disinhibitory mechanisms["@gonchar2007"]. Their dysfunction has been implicated in Alzheimer's disease, Parkinson's disease, and various forms of dementia.
VIP-expressing interneurons are primarily located in cortical layers II/III, with smaller populations in layers V and VI[@rudy2011]. They exhibit characteristic bipolar or bitufted morphology with vertically oriented dendrites and axons that form dense axonal arbors[@kuhlman2013]. In the mouse [cortex](/brain-regions/cortex), VIP neurons represent approximately 10% of all GABAergic neurons, while human cortical tissue shows similar proportions with some regional variation[@defelipe2002].
In the [hippocampus](/brain-regions/hippocampus), VIP interneurons are found throughout the cornu ammonis (CA) regions and dentate gyrus[@acsdy1996]. They are particularly enriched in the stratum lacunosum-moleculare and stratum radiatum, where they modulate entorhinal cortical inputs to CA1 pyramidal neurons[@losonczy2006]. VIP+ cells in the hippocampus include distinct subtypes with varying morphological and physiological properties[@somogyi2005].
VIP-expressing basket cells target the soma and proximal dendrites of pyramidal neurons, providing powerful perisomatic inhibition[@miles1996]. These cells receive excitatory input from layer 2/3 pyramidal neurons and can suppress pyramidal cell firing with high temporal precision[@tams1998].
Bipolar VIP neurons have vertically elongated cell bodies with dendrites extending in opposite directions[@kawaguchi1993]. They preferentially target other interneurons, particularly somatostatin (SST) expressing neurons, creating a disinhibitory circuit motif[@pfeffer2013a].
Ivy cells are a recently characterized VIP+ subtype that expresses neuropeptide Y (NPY) and targets the distal dendrites of pyramidal neurons[@tricoire2010]. These cells provide dendritic inhibition and are thought to modulate calcium signaling in pyramidal cell dendritic compartments[@mller2017].
A subset of VIP neurons specifically targets the dendritic shafts of pyramidal neurons, modulating excitatory inputs at their site of origin[@huang2019]. These cells express the transcription factor Htr2a and are enriched in layer 1[@lee2010].
VIP interneurons form a key disinhibitory module within the cortical microcircuit[@zhang2014]. The canonical circuit involves: (1) excitatory pyramidal neuron activation of VIP interneurons; (2) VIP neuron inhibition of SST-expressing somatostatin neurons; (3) removal of SST-mediated inhibition from pyramidal neurons, resulting in net disinhibition[@fu2014].
This disinhibitory circuit is plasticity-enabled and experience-dependent, allowing cortical circuits to dynamically adjust their processing gain based on behavioral state and learning demands[@kuhlman2014].
VIP neurons co-express corticotropin-releasing hormone (CRH) in many cortical regions, and VIP-CRH interactions play important roles in stress responses and anxiety-related behaviors[@tritsch2014]. The VIP-CRH system modulates hypothalamic-pituitary-adrenal (HPA) axis activity and is dysregulated in stress-related neurodegenerative conditions[@sapolsky2015].
VIP neurons are critical regulators of REM sleep (rapid eye movement sleep), also known as paradoxical sleep[@jones2008]. The ventrolateral preoptic area (VLPO) contains VIP-expressing neurons that promote REM sleep onset and maintenance[@saper2010]. These neurons project to brainstem REM sleep generators in the pontine tegmentum and medulla[@jones2010].
VIP-mediated REM sleep regulation involves complex interactions with other neuromodulatory systems, including cholinergic, GABAergic, and glutamatergic signaling[@brown2011]. Disruption of VIP signaling leads to REM sleep behavior disorder (RBD), a condition characterized by loss of muscle atonia during REM sleep[@schenck1986].
VIP signaling in the suprachiasmatic nucleus (SCN) mediates communication between circadian clock neurons and regulates circadian rhythm entrainment[@welsh2009]. SCN VIP neurons (approximately 10% of SCN neurons) release VIP at night to synchronize cellular clocks throughout the biological clock[@maywood2008]. This VIP-mediated signaling is essential for maintaining coherent circadian rhythms, which are frequently disrupted in neurodegenerative diseases[@videnovic2014].
VIP interneuron dysfunction contributes to hippocampal circuit impairments in Alzheimer's disease (AD)[@palop2016]. Post-mortem studies of AD brain tissue reveal reduced VIP neuron numbers and altered VIP expression patterns in the [entorhinal cortex](/brain-regions/entorhinal-cortex) and hippocampus[@brady1997]. These changes correlate with memory deficits and disease progression[@verret2012].
AD-related [amyloid-beta](/proteins/amyloid-beta) (Aβ) pathology selectively targets VIP interneurons, leading to disinhibitory circuit abnormalities[@hijazi2020]. Aβ-mediated suppression of VIP neuron activity results in excessive somatostatin neuron activity, which impairs hippocampal sharp-wave ripples and memory consolidation[@mably2018]. Restoring VIP neuron function has emerged as a potential therapeutic strategy[@martinezlosa2018].
Targeting VIP signaling represents a novel approach to AD treatment[@gozes2000]. VIP receptor agonists (VPAC1/VPAC2) have shown promise in preclinical models by reducing neuroinflammation and improving cognitive function[@offen2019]. Additionally, VIP-based peptides crossing the [blood-brain barrier](/entities/blood-brain-barrier) are under development for AD therapy[@ganea2002].
VIP interneurons modulate cortical inputs to the basal ganglia in Parkinson's disease (PD)[@goldberg2009]. Changes in cortical VIP neuron activity contribute to abnormal beta-frequency oscillations observed in PD motor cortex[@steiner2015]. These oscillatory abnormalities are linked to bradykinesia and rigidity symptoms[@brown2003].
VIP signaling abnormalities are implicated in REM sleep behavior disorder (RBD), a prodromal marker of synucleinopathies including PD[@iranzo2016]. VIP neurons in the brainstem REM sleep circuit undergo degeneration in RBD, leading to loss of muscle atonia during REM sleep[@boeve2003]. RBD patients have approximately 80-90% likelihood of developing a synucleinopathy such as PD or dementia with Lewy bodies within 10-14 years[@iranzo2013].