Page 62 - University of Pretoria RESEARCH REVIEW 2018

Nature’s own contraceptive Nigel Bennett, Department of Zoology and Entomology, and MRI
Naked mole-rats live in colonies ranging in size from 70
to up to 300 individuals. The ruler of such a colony is a despotic queen who pushes members around to get them to work, but also to let them know who is boss!
the GnRH neurons and bring about suppression of reproduction. Indeed, elevated PRL is known to suppress fertility in many birds and mammals and it has been found to be an important factor in mediating both alloparental and parental care.
As would be expected for a reproductively active breeding
female mammal, the circulating PRL concentrations detected in naked mole-rat queens were around pregnancy and lactation. These results suggest that elevated PRL in nonbreeders may be an important component of reproductive suppression in nonbreeding males and females, but in promoting helping behaviour in these cooperatively breeding animals. However, how
the queen orchestrates this socially induced infertility still remains unknown.
Recent transcriptome profiling of
the naked mole-rat brain has shown the breeding animals have increased expression of the genes involved in dopamine metabolism (dopamine inhibits prolactin secretion) compared with nonbreeders. This is wholly consistent with the concept of high levels of PRL in nonbreeding naked mole-rats and strongly suggests
a role for hyperprolactinaemia as
a component in socially induced reproductive suppression in the naked mole-rat.
The paper was published in 2018 in the highly prestigious Royal Society journal, Biology Letters.
The naked mole-rat occurs in the eastern horn of Africa in Kenya, Ethiopia, Somalia, and Djibouti. They use an extensive burrow system
in hard clays and live in so-called ‘castles of clay’ where nonbreeders act as helpers. The queen usually has between two and three male consorts who breed with her.
For many years, Professor Nigel Bennett had been puzzled as to why the nonbreeders of both sexes had swollen teats despite the fact that nonbreeding females, and of course males, were not pregnant. The presence of swollen teats in males was especially bizarre, and he suspected that elevated levels of hormone prolactin might be
important. At the time, there was no specific assay for mole-rat prolactin (PRL) available. He approached Professor André Ganswindt (MRI) to see if a guinea pig assay (the guinea pig being a close relative to the naked mole-rat) could be used to measure PRL. After some trouble-shooting at the Endocrine Research Laboratory, and validations by Stefanie Ganswindt, the team was ready to measure the PRL concentrations in the naked mole-rat!
The PRL levels measured in the nonbreeders of both sexes showed that although there is some variability, many values are clinically hyperprolactinaemic. This suggests that the high levels of PRL act on
Vanessa Wanja Kamgang, a PhD student, with Nigel Bennett.
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