Pineal atrophy and other neuroendocrine and circumventricular features of the naked mole-rat, Heterocephalus glaber (Rüppell), a fossorial, equatorial rodent.

Quantitative aspects of the microanatomy of the pineal gland and other neuroendocrine and circumventricular structures were studied in a small, reproductively suppressed, female Naked Mole-rat from central Kenya, Africa. The atrophic pineal is the smallest in absolute size (0.002135 mm3) of any so far described in a species of rodent, and in size relative to body weight is second only to that of another tropical species. The subcommissural organ and posterior collicular recess are also relatively small and less well differentiated than those in most other examined rodent species. In contrast, the subfornical organ, OVLT and median eminence are large and well vascularized. It is concluded that the pineal in this species follows the previously described trend among rodents of relatively smaller size in species whose centers of distribution are in lower latitudes. Although the pineal is atrophic, the Naked Mole-rat still exhibits 24-hour and seasonally timed patterns of behavior and seasonal reproduction. However, in this species these events are probably cued by moisture, temperature and social factors rather than by photic information.