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Tracing SCN graft efferents with Dil.
R S Canbeyli1, M Lehman, R Silver
1Psychology Department, Barnard College of Columbia University, New York, NY 10027.
Brain Research
|July 19, 1991
Summary
Transplanted fetal suprachiasmatic nuclei (SCN) restore circadian rhythms in hamsters. Limited efferent connections from grafts suggest a diffusible substance may mediate this restored rhythmicity.
Area of Science:
- Neuroscience
- Chronobiology
- Neuroanatomy
Background:
- The suprachiasmatic nuclei (SCN) are the master circadian pacemaker in mammals.
- Bilateral SCN destruction causes arrhythmicity, while fetal SCN grafts can restore circadian locomotor activity rhythms.
Purpose of the Study:
- To investigate the efferent connections of transplanted fetal SCN grafts.
- To understand the mechanism by which SCN grafts restore circadian rhythmicity.
Main Methods:
- Fetal SCN tissue was grafted into the third ventricle (3V) of intact or SCN-lesioned hamsters.
- The carbocyanine dye Dil was used to trace efferent connections from the grafts.
- Grafts and host tissue were examined for Dil-labeled efferents and stained for VIP and NP cells.
Main Results:
- Labeled efferents from the SCN grafts were observed in most cases, but were largely confined within the graft.
- A few efferents extended into host tissue when grafts appeared to merge with the host, but did not project far.
- Limited graft-host connectivity was observed irrespective of the presence of donor SCN markers.
Conclusions:
- The limited efferent connectivity suggests that either a small number of efferents are sufficient for rhythm restoration, or a diffusible substance mediates the SCN graft's function.
- This study provides insights into the neuroanatomical basis of circadian rhythm regulation by SCN grafts.