Abstract:
In the present study, orexinergic cell bodies within
the brains of rhythmic and arrhythmic circadian chronotypes
from three species of African mole rat (Highveld mole rat—
Cryptomys hottentotus pretoriae, Ansell’s mole rat—Fukomys
anselli and the Damaraland mole rat—Fukomys damarensis)
were identified using immunohistochemistry for
orexin-A. Immunopositive orexinergic (Orx ) cell bodies
were stereologically assessed and absolute numbers of orexinergic
cell bodies were determined for the distinct circadian
chronotypes of each species of mole rat examined. The aim
of the study was to investigate whether the absolute numbers
of identified orexinergic neurons differs between distinct circadian
chronotypes with the hypothesis of elevated hypothalamic
orexinergic neurons in the arrhythmic chronotypes
compared with the rhythmic chronotypes. We found statistically
significant differences between the circadian chronotypes
of F. anselli, where the arrhythmic group had higher
mean numbers of hypothalamic orexin neurons compared
with the rhythmic group. These differences were observed
when the raw data was compared and when the raw data was
corrected for body mass (Mb) and brain mass (Mbr). For the
two other species investigated, no significant differences
were noted between the chronotypes, although a statistically
significant difference was noted between all rhythmic and
arrhythmic individuals of the current study when the counts
of orexin neurons were corrected for Mb—the arrhythmic
individuals had larger numbers of orexin cells.
