Central visual system of the naked mole‐rat (Heterocephalus glaber)

Abstract

Naked mole-rats are fossorial rodents native to eastern Africa that spend their lives in extensive subterranean burrows where visual cues are poor. Not surprisingly, they have a degenerated eye and optic nerve, suggesting they have poor visual abilities. However, little is known about their central visual system. To investigate the organization of their central visual system, we injected a neuronal tracer into the eyes of naked mole-rats and mice to compare the neural structures mediating vision. We found that the superior colliculus and lateral geniculate nucleus were severely atrophied in the naked mole-rat. The olivary pretectal nucleus was reduced but still retained its characteristic morphology, possibly indicating a role in light detection. In addition, the suprachiasmatic nucleus is well innervated and resembles the same structure in other rodents. The naked mole-rat appears to have selectively lost structures that mediate form vision while retaining structures needed for minimal entrainment of circadian rhythms. Similar results have been reported for other mole-rat species. Taken together, these data suggest that light detection may still play an important role in the lives of these "blind" animals: most likely for circadian entrainment or setting seasonal rhythms. © 2006 Wiley-Liss, Inc.Key words: brain; evolution; vision; superior colliculus; eye; blind A well-developed visual system is metabolically costly, so one would expect a reduction in the visual systems of subterranean rodents where light levels are minimal. However, animals with occasional access to the surface can make use of brief light exposure for setting circadian and seasonal rhythms. Studies of both Ansell's mole-rat (Cryptomys anselli) and the blind mole-rat (Spalax ehrenbergi) have revealed severe atrophy of many of the structures involved in form vision, yet some of the structures involved in other types of light detection appear unchanged. This has led to the suggestion that light cues are still used to mediate aspects of behavior in at least some fossorial species (Cooper et al., 1993;Nemec et al., 2004).Naked mole-rats ( Fig. 1) are fossorial rodents from eastern Africa in the same family (Bathyergidae) as Ansell's mole-rat. Naked mole-rats live underground in large eusocial colonies with division of labor and separate castes that have different social, morphological, and behavioral characteristics. Only a few colony members are reproductively active, which results in a high level of genetic similarity in the colony due to inbreeding (Jarvis, 1981).In addition to social and physiological adaptations to life underground, mole-rats exhibit several sensory modifications. Sound attenuates rapidly underground, and presumably because of this environmental constraint, molerats have degraded hearing with poor sound localization abilities (Heffner and Heffner, 1993;Brittan-Powell et al., 2001). However, naked mole-rats are somatosensory specialists with a novel array of somatic vibrissae for guiding orienting behavior (Crish et al...

Distal axonopathy with structural persistence in glaucomatous neurodegeneration

“…These include the nucleus of the optic tract (see Fig. 1), the ventral lateral geniculate nuclei (LGN; vLGN) and dorsal LGN (dLGN), and the olivary pretectal nucleus (OPT), all of which derive input from collaterals of RGC axons projecting to the SC (18,19,28). In a 10-mo DBA/2 SC with full CTB (Fig.…”

“…CTB is an established marker for active uptake and transport and has been used successfully to assess the retinal projection to the SC in injury (21,22,45). Animals were transcardially perfused with 4% paraformaldehyde in PBS solution and tissues removed after 48 h of CTB activity, an established period for complete retinotopic mapping of the SC for mice and other small mammals (28). CTB signal in serial coronal brain sections (50 μm) was photographed digitally on an Olympus AX-70 microscope.…”

Retinorecipient areas in the diurnal murine rodent Arvicanthis niloticus: A disproportionally large superior colliculus

“…It is substantial in hamster (Pickard and Silverman, 1981;Johnson et al, 1988;Youngstrom et al, 1991;Elliott et al, 1995;Ling et al, 1998;Muscat et al, 2003) and some primates (Mick et al, 1993). It is also present in blind mole rat and mole-lemming (Herbin et al, 1994) but absent in other fossorial species (Nemec et al, 2004(Nemec et al, , 2008Crish et al, 2006). It is limited to the horizontal limb of the diagonal band of Broca in the mink (Martinet et al, 1992).…”

Is Cerebellar Architecture Shaped by Sensory Ecology in the New Zealand Kiwi <b><i>(Apteryx mantelli)</i></b><b>?</b>

“…Both species have evolved a well-developed somatosensory system and a rudimentary visual system in order to occupy a subterranean niche [Catania, 1999[Catania, , 2011Catania and Remple, 2002;Crish et al, 2006;Henry et al, 2006]. It has been suggested that these animals show a distinct pattern of expression of the molecular marker zebrin II (ZII, also known as aldolase C) [Ahn et al, 1994] in the cerebellum [Marzban et al, , 2015.…”