Document Detail

Anatomy and forebrain projections of the olfactory and vomeronasal organs in axolotls (Ambystoma mexicanum).
MedLine Citation:
PMID:  7953608     Owner:  NLM     Status:  MEDLINE    
We examined the anatomy of the nasal cavity and forebrain in the axolotl (Ambystoma mexicanum) to determine whether the olfactory and vomeronasal systems are present in this neotenic aquatic salamander. The current study was motivated by two considerations: (a) little is known of the anatomy of the vomeronasal system in aquatic vertebrates, and (b) the presence of both olfactory and vomeronasal systems in larval amphibians has broad implications for the evaluation of these systems in vertebrates. From cresyl-violet-stained sections of snouts we determined that the nasal cavity of axolotls is much like that of terrestrial salamanders. The main chamber of the nasal cavity contains an olfactory epithelium, which is confined to grooves between longitudinal ridges of connective tissue covered in a nonsensory epithelium which lacks goblet cells. Using transmission electron microscopy, we found morphologically distinct olfactory receptor cells: many receptor cells terminate in microvillar dendrites, and fewer terminate in motile cilia with the 9 + 2 microtubule array typical of vertebrate olfactory receptor cells. The ciliated and microvillar cells occur in clusters with little intermingling. Horseradish peroxidase labeling revealed that axons of the olfactory receptor cells terminate in large glomeruli in the main olfactory bulb at the rostral end of the telencephalon. Lateral to the main chamber of the nasal cavity is a diverticulum that is entirely lined with a vomeronasal epithelium containing basal cells, microvillar receptor cells, sustentacular cells that lack specialized processes on the apical surface, and large ciliated cells that may function to move fluid across the vomeronasal epithelium. Unlike the olfactory epithelium, the vomeronasal epithelium lacks Bowman's glands. Using horseradish peroxidase, we determined that the axons of the vomeronasal receptor cells project to the accessory olfactory bulb, a distinct structure dorsal and caudal to the main olfactory bulb. The presence of both olfactory and vomeronasal systems in axolotls and other neotenic salamanders implies that both systems are pleiomorphic in larval amphibians; we therefore suggest that the vomeronasal system may not have originated as an adaptation to terrestrial life.
H L Eisthen; D R Sengelaub; D M Schroeder; J R Alberts
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Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Brain, behavior and evolution     Volume:  44     ISSN:  0006-8977     ISO Abbreviation:  Brain Behav. Evol.     Publication Date:  1994  
Date Detail:
Created Date:  1994-12-20     Completed Date:  1994-12-20     Revised Date:  2006-04-04    
Medline Journal Info:
Nlm Unique ID:  0151620     Medline TA:  Brain Behav Evol     Country:  SWITZERLAND    
Other Details:
Languages:  eng     Pagination:  108-24     Citation Subset:  IM    
Program in Neural Science, Indiana University, Bloomington.
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MeSH Terms
Ambystoma mexicanum / anatomy & histology*
Brain Mapping
Microscopy, Electron
Nasal Mucosa / innervation*
Nasal Septum / innervation*
Olfactory Bulb / anatomy & histology*
Olfactory Nerve / anatomy & histology
Olfactory Pathways / anatomy & histology
Olfactory Receptor Neurons / anatomy & histology*
Prosencephalon / anatomy & histology*
Species Specificity

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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