Related Experiment Videos
The claustrum is not missing from all monotreme brains.
Ken W S Ashwell1, Craig Hardman, George Paxinos
1Department of Anatomy, School of Medical Sciences, The University of New South Wales, Sydney, NSW 2052, Australia. k.ashwell@unsw.edu.au
Brain, Behavior and Evolution
|August 21, 2004
Summary
The claustrum, a brain structure, is present in monotremes like echidnas and possibly platypuses, challenging previous assumptions about mammalian brain evolution.
Area of Science:
- Neuroscience
- Comparative Anatomy
- Mammalian Evolution
Background:
- The claustrum's presence in the mammalian forebrain has been debated, with many believing it absent in monotremes.
- Monotremes, including echidnas and platypuses, represent a unique evolutionary lineage of mammals.
Purpose of the Study:
- To investigate the presence and characteristics of the claustrum in the brains of the short-beaked echidna and the platypus.
- To determine if the claustrum is a feature exclusive to therian mammals or if it predates mammalian divergence.
Main Methods:
- Utilized Nissl and myelin staining techniques.
- Employed enzyme histochemistry for acetylcholinesterase.
- Conducted immunohistochemistry for parvalbumin, calbindin, calretinin, and tyrosine hydroxylase.
Main Results:
- Identified a small but distinct insular claustrum in the echidna, located ventrolaterally to the putamen.
- Observed that echidna insular claustrum neurons share chemical features with adjacent cortex, not the putamen.
- Found evidence suggesting a possible insular claustrum in the platypus, but an endopiriform nucleus was not identified in either species.
Conclusions:
- The claustrum is not exclusive to therian mammals, indicating its presence in the ancestral mammalian brain.
- This study provides crucial evidence for the evolutionary history of the claustrum and mammalian forebrain organization.