Specialized mechanoreceptor systems in rodent glabrous skin

Rodents use their forepaws to actively interact with their tactile environment. Studies on the physiology and anatomy of glabrous skin that makes up the majority of the forepaw are almost non-existent in the mouse. Here we developed a preparation to record from single sensory fibers of the forepaw and compared anatomical and physiological receptor properties to those of the hind paw glabrous and hairy skin. We found that the mouse forepaw skin is equipped with a very high density of mechanoreceptors; > 3 fold more than hind paw glabrous skin. In addition, rapidly adapting mechanoreceptors that innervate Meissner's corpuscles of the forepaw were several-fold more sensitive to slowly moving mechanical stimuli compared to their counterparts in the hind paw glabrous skin. All other mechanoreceptors types as well as myelinated nociceptors had physiological properties that were invariant regardless of which skin area they occupied. We discovered a novel D-hair receptor innervating a small group of hairs in the middle of the hind paw glabrous skin in mice. These glabrous skin D-hair receptors were direction sensitive albeit with an orientation sensitivity opposite to that described for hairy skin D-hair receptors. Glabrous skin hairs do not occur in all rodents, but are present in North American and African rodent species that diverged more than 65 million years ago. The function of these specialized hairs is unknown, but they are nevertheless evolutionarily very ancient. Our study reveals novel physiological specializations of mechanoreceptors in the glabrous skin that likely evolved to facilitate tactile exploration. This article is protected by copyright. All rights reserved

Seasonal variation in gonadal steroids of males and females in the Cape mole-rat (Georychus capensis): The potential for opportunistic breeding

Urinary testosterone concentrations in males and urinary progesterone and oestradiol concentrations in females were measured in the Cape mole-rat (Georychus capensis) and compared for the summer and winter periods. The Cape mole-rat breeds  seasonally, with sexual activity and subsequent pregnancy recorded during the winter months in the southern hemisphere.  Despite the fact that it has a distinct breeding season, seasonal differences in urinary hormone concentrations of both male and female Cape mole-rats were not statistically significant. This finding supports the notion the Cape mole-rat may have the  opportunity to operate as an opportunistic breeder if fortuitous  environmental conditions arise, such as unseasonal rainfall,  occurring at these normally non-favourable times of the year.Key words: Cape mole-rat, progesterone, testosterone, oestrogen, seasonal breeding

Lights out, let’s move about: locomotory activity patterns of Wagner’s gerbil from the desert of Saudi Arabia

We investigated the circadian activity rhythm in the little-studied Wagner’s gerbil  (Gerbillus dasyurus) from the Raydah Protected Area, southwestern Saudi Arabia. In order to assess whether these animals possess an endogenous rhythm of locomotor activity that entrains to the light:dark cycle, they were subjected to three distinct light cycles: an LD cycle (12 h light/12 h dark), a DD cycle (constant darkness) and a DL light cycle (an inverse of the LD light cycle). All eight individuals studied  exhibited entrainment of their activity to the light cycles. Under LD, the total  percentage of activity during the dark phase was 93.7 ± 1.8%. Activity was distributed throughout the night (mean peak activity 22:46 ± 0:14). All eight animals expressed distinct endogenous free-running rhythms of locomotor activity (mean í = 23:55 ± 0:36). During constant darkness, animals still displayed more activity during the subjective night (75.6 ± 0.4%). Under the DL light cycle, the total percentage of activity was 92.7 ± 1.8% during the dark phase. In conclusion, the daily locomotor activity rhythm ofWagner’s gerbil is strongly entrained by the light:dark cycle with the most activity concentrated during the night and consequently this desert-dwelling mammal may thus be considered truly nocturnal.Keywords: circadian rhythm, light:dark cycle, locomotor activity, Saudi  Arabia,Wagner’s gerbil

Circadian rhythms of locomotor activity in the reddish-grey musk shrew (Eulipotyphla: Soricidae) from South Africa

The circadian rhythm of locomotor activity in a southern African shrew, the reddish-grey musk shrew Crocidura cyanea was investigated. Thirteen individuals were subjected to three successive light cycles, each cycle lasting approximately 2 weeks: an LD cycle (12 h light/12 h dark), a DD cycle (constant darkness) and a DL cycle (an inverse of the LD cycle). All of the animals exhibited entrainment of their activity to the LD and DL lighting regimes. Locomotor activity of C. cyanea occurred predominantly during the dark phases of the LD cycle and the DL cycle. Under LD, the mean active phase (α) of C. cyanea was 10.8±0.3 h and the total percentage of activity was 78.9% during the dark phase. When subjected to constant darkness, the mean active phase increased to 13.2±01.8 h and all animals expressed free-running rhythms of locomotor activity (mean± 1 SD=23.0±0.55 h; range=22.4–23.7 h). On the reverse LD cycle, the mean active phase was lowest (09.3±0.16 h) and the total percentage of activity was 71.5% during the dark phase of the cycle. The reddish-grey musk shrew possesses a strong circadian rhythm of locomotor activity that predominantly occurs during the dark phase and consequently the musk shrew may essentially be considered a nocturnal mammal

The chronobiology of the natal mole-rat, Cryptomys hottentotus natalensis

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Ananlysis of gonadotrophin-releasing hormone-1 and kisspeptin neuronal systems in the nonphotoregulated seasonally breeding eastern rock elephant-shrew (Elephantulus myurus)

Of the 18 sub-Saharan elephant-shrew species, only eastern rock elephant-shrews reproduce seasonally throughout their distribution, a process seemingly independent of photoperiod. The present study characterizes gonadal status and location/intensity of gonadotrophin-releasing hormone-1 (GnRH-1) and kisspeptin immunoreactivities in this polyovulating species in the breeding and nonbreeding seasons. GnRH-1-immunoreactive (ir) cell bodies are predominantly in the medial septum, diagonal band, and medial preoptic area; processes are generally sparse except in the external median eminence. Kisspeptin-ir cell bodies are detected only within the arcuate nucleus; the density of processes is generally low, except in the septohypothalamic nucleus, ventromedial bed nucleus of the stria terminalis, arcuate nucleus, and internal and external median eminence. Kisspeptin-ir processes are negligible at locations containing GnRH-1-ir cell bodies. The external median eminence is the only site with conspicuously overlapping distributions of the respective immunoreactivities and, accordingly, a putative site for kisspeptin's regulation of GnRH-1 release in this species. In the nonbreeding season in males, there is an increase in the rostral population of GnRH-1-ir cell bodies and density of GnRH-1-ir processes in the median eminence. In both sexes, the breeding season is associated with increased kisspeptin-ir process density in the rostral periventricular area of the third ventricle and arcuate nucleus; at the latter site, this is positively correlated with gonadal mass. Cross-species comparisons lead us to hypothesize differential mechanisms within these peptidergic systems: that increased GnRH-1 immunoreactivity during the nonbreeding season reflects increased accumulation with reduced release; that increased kisspeptin immunoreactivity during the breeding season reflects increased synthesis with increased release

Sociality and the telencephalic distribution of corticotrophin-releasing factor, urocortin 3, and binding sites for CRF type 1 and type 2 receptors: A comparative study of eusocial naked mole-rats and solitary Cape mole-rats

Various aspects of social behavior are influenced by the highly conserved corticotrophin-releasing factor (CRF) family of peptides and receptors in the mammalian telencephalon. This study has mapped and compared the telencephalic distribution of the CRF receptors, CRF1 and CRF2, and two of their ligands, CRF and urocortin 3, respectively, in African mole-rat species with diametrically opposed social behavior. Naked mole-rats live in large eusocial colonies that are characterized by exceptional levels of social cohesion, tolerance, and cooperation in burrowing, foraging, defense, and alloparental care for the offspring of the single reproductive female. Cape mole-rats are solitary; they tolerate conspecifics only fleetingly during the breeding season. The telencephalic sites at which the level of CRF1 binding in naked mole-rats exceeds that in Cape mole-rats include the basolateral amygdaloid nucleus, hippocampal CA3 subfield, and dentate gyrus; in contrast, the level is greater in Cape mole-rats in the shell of the nucleus accumbens and medial habenular nucleus. For CRF2 binding, the sites with a greater level in naked mole-rats include the basolateral amygdaloid nucleus and dentate gyrus, but the septohippocampal nucleus, lateral septal nuclei, amygdalostriatal transition area, bed nucleus of the stria terminalis, and medial habenular nucleus display a greater level in Cape mole-rats. The results are discussed with reference to neuroanatomical and behavioral studies of various species, including monogamous and promiscuous voles. By analogy with findings in those species, we speculate that the abundance of CRF1 binding in the nucleus accumbens of Cape mole-rats reflects their lack of affiliative behavior. © 2015 Wiley Periodicals, Inc

Ambient Temperature as a Strong Zeitgeber of Circadian Rhythms in Response to Temperature Sensitivity and Poor Heat Dissipation Abilities in Subterranean African Mole-Rats

Mammals have evolved circadian rhythms in internal biological processes and behaviors, such as locomotor activity (LA), to synchronize to the environmental conditions they experience. Photic entrainment of LA has been well established; however, non-photic entrainment, such as ambient temperature (Ta), has received much less attention. To address this dearth of knowledge, we exposed two subterranean endothermic-homeothermic African mole-rat species, the solitary Cape mole-rat (Georychus capensis [GC]) and social Mahali mole-rat (Cryptomys hottentotus mahali [CHM]), to varying Ta cycles in the absence of light. We showed that the LA rhythms of these two species entrain to Ta cycles and that the majority of LA occurred during the coolest 12-h period. LA confined to the coolest Ta periods may be the direct consequence of the poor heat dissipation abilities of African mole-rats brought about by physiological and ecological constraints. Recently, it has been hypothesized that Ta is only a strong zeitgeber for circadian rhythms in species whose thermoregulatory abilities are sensitive to changes in Ta (i.e., heterotherms and ectotherms), which previously has excluded endothermic-homeothermic mammals. However, this study demonstrates that Ta is a strong zeitgeber or entrainer for circadian rhythms of LA in subterranean endothermic-homeothermic mammals as a consequence of their sensitivity to changes in Ta brought about by their poor heat dissipation abilities. This study reinforces the intimate link between circadian rhythms and thermoregulation and conclusively, for the first time, provides evidence that Ta is a strong zeitgeber for endothermic-homeothermic mammals