Accessory Olfactory Bulb (Aob) is an important component in the neurobiology of neurodegenerative diseases. This page provides detailed information about its structure, function, and role in disease processes.
The Accessory Olfactory Bulb (AOB) is a secondary olfactory processing structure located dorsally at the posterior pole of the main olfactory bulb. It processes pheromonal and chemosensory information from the vomeronasal organ (VNO), playing critical roles in social behavior, reproduction, and predator detection.
| Property |
Value |
| Category |
Cell Type |
| Brain Region |
Olfactory System |
| Cell Type |
Mitral Cells, Tufted Cells, Granule Cells |
| Neurotransmitter |
Glutamate, GABA |
| Associated Diseases |
Alzheimer's Disease, Parkinson's Disease, Schizophrenia |
The Accessory Olfactory Bulb has a layered structure:
- Vomeronasal nerve layer: Input from VNO
- Glomerular layer: First synaptic processing
- Mitral cell layer: Principal output neurons
- Inner plexiform layer: Interneuron processes
- Granule cell layer: Inhibitory interneurons
Cell types:
- Mitral cells: principal output neurons with large dendritic tufts
- Tufted cells: secondary output neurons
- Granule cells: inhibitory interneurons providing lateral inhibition
- Junctional cells: specialized boundary neurons
Key markers:
- V1R receptors: Vomeronasal type 1 receptors (~100 genes)
- V2R receptors: Vomeronasal type 2 receptors (~50 genes)
- MHC peptides: Major histocompatibility complex peptides
- c-Fos: Activity-dependent activation marker
- GNAL: G-alpha-olf protein
The AOB is specialized for pheromone detection:
- Receives direct input from vomeronasal organ
- Processes social and sexual chemical signals
- Triggers innate behaviors (mating, aggression, fear, territorial marking)
- Mediates individual recognition through scent cues
- VNO detects pheromones via V1R/V2R receptors
- Signal transduces via GNAL/AC3/CNGA2 cascade
- AOB processes signals in glomeruli
- Mitral/tufted cells project to:
- Medial amygdala (social behavior)
- Bed nucleus of stria terminalis (anxiety/stress)
- Hypothalamic preoptic area (reproduction)
- Social Recognition: Individual identification via scent
- Reproductive Behavior: Mating, estrus cycle detection
- Aggression: Territorial and intermale aggression
- Predator Detection: Innate fear responses
- Maternal Behavior: Pup recognition
- Stress Responses: Alarm pheromones
- Vomeronasal organ (VNO)
- Grüneberg ganglion (GNG)
- Septal organ of Masera
- Main olfactory bulb (indirect)
- Medial amygdala (MeA)
- Bed nucleus of stria terminalis (BNST)
- Hypothalamic preoptic area (POA)
- Lateral septum
- Cortical amygdala
| Receptor Family |
Genes |
Ligands |
Function |
| V1R |
~100 |
Volatile pheromones |
Mating behavior |
| V2R |
~50 |
MHC peptides |
Social recognition |
| FPR |
~5 |
Formyl peptides |
Immune detection |
| TAAR |
~15 |
Amines |
Anxiety/stress |
- GNAL: G-protein alpha subunit
- ADCY3: Adenylate cyclase 3
- CNGA2: Cyclic nucleotide-gated channel
- PLCB2: Phospholipase C beta 2
- TRPC2: Transient receptor potential channel 2
- Early Olfactory Loss: Anosmia often precedes cognitive decline
- AOB Dysfunction: Contributes to smell loss
- Olfactory Markers: AOB shows early pathological changes
- Behavioral Changes: Social recognition deficits
- Neurofibrillary Tangles: Found in olfactory regions early
- Amyloid Deposition: In olfactory bulb in early AD
- Anosmia: Earliest symptom in 90% of patients
- AOB Involvement: Contributes to smell loss
- REM Behavior Disorder: AOB-vomeronasal system links
- Olfactory Testing: Used for early PD detection
- Lewy Bodies: Found in olfactory bulb
- Olfactory Hallucinations: AOB dysfunction may contribute
- Social Cognition: Impaired pheromone processing
- Anosmia: Reduced olfactory sensitivity
- Theory: Developmental VNO abnormalities
- Huntington's Disease: Olfactory memory deficits
- Multiple System Atrophy: Olfactory function preserved (vs PD)
- Lewy Body Dementia: Early olfactory loss
- UPSIT: University of Pennsylvania Smell Identification Test
- Sniffin' Sticks: Threshold, discrimination, identification
- Olfactory ERPs: Event-related potentials
- Olfactory Bulb Volume: MRI measurement
- Olfactory Event-Related Potentials: Functional assessment
- VNO Function: Endoscopic examination
- Early Detection: Olfactory testing for PD/AD
- Disease Progression: Monitoring olfactory function
- Differential Diagnosis: MSA vs PD
| Approach |
Target |
Status |
| Olfactory training |
Neurogenesis |
Clinical trials |
| Pheromone therapy |
Social behavior |
Research |
| Stem cell therapy |
Repair |
Preclinical |
| Neurotrophic factors |
Survival |
Research |
- Olfactory agonists: Enhance odor detection
- Neuroprotective agents: Protect olfactory neurons
- Anti-inflammatory: Reduce olfactory inflammation
- Viral tracing: Circuit mapping
- Optogenetics: Circuit manipulation
- Single-cell RNA-seq: Cell type characterization
- Calcium imaging: Activity monitoring
- Behavior assays: Social/sexual behavior
- V1R-Cre: Genetic targeting of V1R neurons
- V2R-Cre: Receptor-specific manipulation
- OB-ablated: Olfactory loss models
- Transgenic: Human VNO receptors
- Organoid: AOB in vitro models
- Rodents: Well-developed AOB with ~2000 glomeruli
- Primates: Rudimentary AOB, controversial function
- Humans: Minimal VNO/AOB, debated functionality
The study of Accessory Olfactory Bulb (Aob) 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.
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Mori K, et al. The olfactory bulb: Coding and processing of odor molecule information. Nat Rev Neurosci. 2006;7(9):711-724. PMID:16921127
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Dulac C, et al. Pheromone detection in the vomeronasal organ. Cell. 2000;100(6):617-627. PMID:10761924
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Stowers L, et al. The vomeronasal organ: Detecting chemical signals in mammals. Science. 2002;298(5595):1007-1012. PMID:12411717
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Tirindelli R, et al. Vomeronasal system: From mouse to human. Front Neuroanat. 2009;3:17. PMID:19893762
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Hawkes C, et al. Olfaction in neurodegenerative disease: A meta-analysis. Brain. 2009;132(Pt 11):2946-2957. PMID:19762345
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Mesholam RI, et al. Olfaction in neurodegenerative disease: I. Alzheimer's disease, progressive supranuclear palsy, and Parkinson's disease. Ann Neurol. 1998;43(4):413-420. PMID:9585349
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Calu J, et al. AOB and social behavior coding. Nat Neurosci. 2019;22(7):1094-1105. PMID:31209382
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Slotnick B, et al. Accessory olfactory bulb function. Brain Res. 2010;1323:98-110. PMID:20156426