Visual system labeled by c-Fos immunohistochemistry after light exposure in the 'blind' subterranean Zambian mole-rat (Cryptomys anselli)

The Zambian mole-rat (Cryptomys anselli) is a rodent that lives and forages underground, and under natural conditions is rarely, if ever, exposed to l ight, Its eye is organized as in other rodents and is prominent but minuscu le. The animals do not seem to react to light behaviorally or to orient vis ually, although exact physiological and/or behavioral experiments have not been conducted to date. Nuclear expression of transcriptional regulatory pr otein (c-Fos) as a marker of cell activity was studied immunohistochemicall y in five mole-rats exposed to bright light for 1 h after 3 days in constan t darkness, and in four non-stimulated control animals that were kept in da rkness for three days and then killed under deep anesthesia. The retinae an d 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, retrospl enial cortex, neocortex] in light-exposed animals. In contrast, the suprach iasmatic nucleus did not seem to be affected by light stimuli during the ex periment. In both light-stimulated and control animals the rudimentary supe rior colliculus exhibited slight immunoreactivity. Interestingly, the oliva ry pretectal nucleus, which in mammals is involved in light/dark discrimina tion, as well as the DLG as part of the image-forming visual system were co nsistently labeled by c-Fos after light stimulation, indicating that vision in Cryptomys possibly plays a more significant role than previously assume d. Copyright (C) 2000 S. Karger AG. Basel.