Aspects of the neuroanatomy and physiology of sleep in African mole rats
Date
2012-03-06
Authors
Bhagwandin, Adhil
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Abstract
Mole rats are a unique family of the rodent order and are known for a
subterranean lifestyle, reduced eye size, regressed visual system and unusual patterns of
circadian rhythmicity (co-existence of rhythmic and arrhythmic chronotypes within a
species has been documented). Such dramatic changes especially that of phenotype, may
lead to the prediction of significant differences in organisation of the brain and
physiology, therefore these unusual phenotypic features form the core rationale providing
the impetus for the present series of studies. Neuroanatomical examination of the mole rat
brain for immunohistochemical markers of the cholinergic, catecholaminergic,
serotonergic, orexinergic, and histaminergic systems revealed neuronal organisation that
was remarkably similar to those previously reported in other rodents and mammals,
despite the notable differences in lifestyle and phenotype. These results indicate a strong
phylogenetic constraint acting at the systems level of neuronal organisation. The study of
sleep and wake in rhythmic and arrhythmic chronotypes of a species of mole rat indicated
the arrhythmic chronotype spent more time awake with a longer average duration of a
waking episode and less time in sleep with a shorter average duration of a SWS episode.
While remaining somewhat similar between mole rat chronotypes, total sleep time in the
mole rats was significantly reduced in comparison to other rodents. These results also
indicate independence of circadian rhythmicity and sleep homeostasis and possible
alteration of specific genes involved in the sleep-wake cycle of the mole rats examined.
Stereological assessment of absolute numbers of orexinergic neurons revealed that the
arrrhythmic chronotype tends to have more orexinergic neurons per gram of body mass
that the rhythmic chronotype, leading to the conclusion that enhanced vigilance and
peripheral metabolism of the arrhythmic chronotype may underlie this difference.
Immunohistochemical identification of nuclei involved with the sleep-wake cycle,
showed no difference in the distribution of these nuclei between circadian chronotypes
and no major differences when compared to other rodents. Some interesting and
potentially functionally important homogeneities were observed in the distribution of
GABAergic interneurons within the pontine region. Furthermore differential orexinergic
terminal network densities were observed between chronotypes within the arcuate
nucleus and the intergeniculate leaflet. Therefore despite unusual features in lifestyle and
phenotype, the organisation of the mole rat brain remains remarkably similar to other
rodents; however, distinctions of circadian chronotype consistently produced subtle
differences in both the anatomy and physiology of these rodents.
Description
Ph.D., Faculty of Science, University of the Witwatersrand, 2011
Keywords
Neuroanatomy, Anatomy, Sleep, Physiology, Sleep, physiological aspects