Visual System Labeled by c-Fos Immunohistochemistry after Light Exposure in the ‘Blind’ Subterranean Zambian Mole-Rat (Cryptomys anselli)

Abstract

The Zambian mole-rat (Cryptomys anselli) is a rodent that lives and forages underground, and under natural conditions is rarely, if ever, exposed to light. Its eye is organized as in other rodents and is prominent but minuscule. The animals do not seem to react to light behaviorally or to orient visually, although exact physiological and/or behavioral experiments have not been conducted to date. Nuclear expression of transcriptional regulatory protein (c-Fos) as a marker of cell activity was studied immunohistochemically in five mole-rats exposed to bright light for 1 h after 3 days in constant darkness, and in four non-stimulated control animals that were kept in darkness for three days and then killed under deep anesthesia. The retinae and retino-recipient areas of non-stimulated animals remained unlabeled, but many of these structures showed strong c-Fos expression bilaterally [retina, dorsal lateral geniculate body (DLG), olivary pretectal nucleus, retrosplenial cortex, neocortex] in light-exposed animals. In contrast, the suprachiasmatic nucleus did not seem to be affected by light stimuli during the experiment. In both light-stimulated and control animals the rudimentary superior colliculus exhibited slight immunoreactivity. Interestingly, the olivary pretectal nucleus, which in mammals is involved in light/dark discrimination, as well as the DLG as part of the image-forming visual system were consistently labeled by c-Fos after light stimulation, indicating that vision in Cryptomys possibly plays a more significant role than previously assumed.