Urinary testosterone levels in the male blind mole rat (Spalax ehrenbergi) affect female preference

This study investigated the sexual attraction of female blind mole rats to four groups of male mole rats: (a) intact males raised in captivity; (b) intact males trapped in the field; (c) captive males injected with testosterone; (d) captive castrated males. In the first part we measured blood testosterone, androstenedione, and dihydrotestosterone (DHT) levels, by radioimmunoassay; and urine testosterone levels, measured by GC-MS. The second part examined the relationship between urine testosterone levels in males and their attractiveness to females. Higher blood and urine testosterone levels were found in the field animals and in those injected with testosterone compared to captive intact or castrated animals: urine testosterone levels in the two other groups were not detectable. Blood androstenedione levels were also higher in the field animals and in those injected with testosterone compared to captive intact or castrated mole rats. Blood dihydrotestosterone levels were not detectable in all four experimental groups. Female mole rats chose to spend a longer period of time next to males with high blood and urine testosterone levels and high blood androstenedione levels than next to those with lower levels of these hormones. Because courtship and sexual behavior are influenced both by high levels of blood and urine testosterone and high levels of blood androstenedione, we suggest that the low levels of courtship and other sexual behavior in captive mole rats may be related to the lack of female attraction to these males, which display low levels of all three parameters.     

Circadian rhythm and theper ACNGGN repeat in the mole rat,Spalax ehrenbergi

Individual variability in circadian locomotor activity has recently been discovered in the blind mole rat,Spalax ehrenbergi. An interesting association was found between different circadian activity types and two DNA fragments, 5.6 and 5.9 kb long, that contain the ACNGGN repeat sequence, homologous to a part of theperiod gene ofDrosophila. Nine of 12 arrythmic animals showed the 5.6-kb band, while 13 of 17 circadian rhythmic animals had the 5.9-kb band. This repeat exists also in the brain RNA of the mole rat, apparently in higher quantities during the sleeping phase, suggesting that an unusual protein(s), composed of a poly-Thr-Gly segment, affects its circadian rhythm.     

Morphology and cytology of the nasal cavity and vomeronasal organ in juvenile and adult blind mole rats (Spalax ehrenbergi)

The blind mole rat (Spalax ehrenbergi) is a fossorial solitary rodent which exhibits extensive intraspecific aggression and uses scent markings to deter contraspecific invaders. Mole rats of different ages were captured near Tel Aviv, Israel, and sacrificed by an overdose of Xylazine hydrochloride. Olfactory epithelium sites from the nasal cavity (NC) and the vomeronasal organ (VNO) were dissected and fixed for light and electron microscopy. The mole rat's olfactory epithelium of the NC consists of several cell types, of which two types are supporting cells that comprise both microvilli and cilia but differ in staining and the presence of rough endoplasmic reticulum. The third type has no cilia. Secretory goblet cells were frequent among supporting cells of adults alone. Two types of receptor cells protrude into the NC with olfactory knobs at their apical region; one type has up to 177.6 ± 9.4 cilia per knob plus microvilli, while the other type has only microvilli. The third type of sensory cell has no knob and contains microvilli only. The basal epithelium layer consists of short-bodied cells with round nuclei. The VNO of the mole rat is situated beneath the nasal septum, consisting of supporting, sensory, and basal cell types, with many cilia at the apical portion. At its anterior part, the VNO is connected to the NC by narrow canals. The abundance of cilia and microvilli in the mole rat olfactory cells provides the first anatomical evidence for their olfactory acuity. Such acuity is important in mole rats, compensating for their loss of vision and enabling them to detect and avoid rivals prior to potential aggressive encounters as well as to select food plants during foraging. Anat. Rec. 251:460–471, 1998. © 1998 Wiley-Liss, Inc.     

Sexual pheromones in lipids and other fractions from urine of the male mole rat, Spalax ehrenbergi.

Spalax ehrenbergi mole rats are blind, solitary, territorial, aggressive, subterranean rodents with a yearly breeding season that peaks in December and January. We confirm here an earlier report that estrous females are attracted to substances present in the urine of homospecific as compared to heterospecific adult males. We have also found that nonestrous female mole rats show avoidance behavior to the same homospecific urine. Our objective was to ascertain the nature of the pheromone(s) and gain insight as to its possible role in reproductive isolation and speciation. An active principle, detected in either two- or three-choice behavior tests, was found to be extractable from urine by methylene chloride (CH2Cl2) and mainly found in the neutral lipid fraction. Total lipids were chromatographed by thin layer chromatography on silica gel G60 plates. Most of the activity was found in a zone bounded by Rfs 0.2 and 0.7. Cholesterol, other sterols, and ethyl esters of fatty acids chromatographed in this zone as determined by standards and staining. Ethyl esters of fatty acids were also detected in this fraction by GC/MS analysis. Although a large amount of activity was found in lipids, it only accounted for about 1% of that found in urine. Some activity may have been destroyed or lost during the extraction procedure and some may remain in a lipid insoluble form. Preliminary tests of lipid extracts of various portions of the male urogenital tract revealed pheromonal activity present, particularly in tissues associated with testes, epididymis, prostate, and bladder.     

Reversed palatal perforation by upper incisors in ageing blind mole-rats (Spalax ehrenbergi)

Blind mole-rats ( Spalax ehrenbergi ) are fossorial solitary rodents that present striking morphological, physiological and behavioural adaptations to the subterranean environment in which they live. Previous studies have shown that mole-rats are specialised in tooth-digging. The rapid eruption-rate of their incisors has evolved to compensate for their excessive wear by excavation. Males use their incisors more than females for digging and fighting, and their rate of incisor eruption is significantly more rapid than in females. Since mole-rats use their incisors for digging throughout the year, we suggest that continuous mechanical pressure on their oral tissues concentrated at the apical sites of the upper incisors leads to cell and tissue fatigue. We provide evidence for 5 stages of palatal perforation by the upper incisors at their apical sites, with maximum perforation characterising aged males. Interspecies comparisons with 7 other fossorial and semi-fossorial rodent species, and with beavers, which expose their incisors to enormous mechanical pressure, revealed that this palatal perforation is unique to the male mole-rat. We suggest that while the fast eruption rate of incisors in the mole-rat compensates for the rapid wear resulting from digging, evolutionary adaptation to continuous tooth-digging is still ongoing, since the physical pressure of digging at the apical sites of the upper incisors leads to tissue destruction, breakage of the palatal bone and possibly to death, as a result of maxillary inflammation.     

Activity pattern and rhythm in the subterranean mole rat superspeciesSpalax ehrenbergi

Good candidates for naturally occurring variability in circadian rhythms may be subterranean herbivores, since they are not normally subjected to entraining light stimulation. To test this possibility, we selected the blind mole ratSpalax ehrenbergi superspecies in Israel and tested it in short- and long-term experiments. Short-term experiments showed that the animals exhibited three patterns of activity: a regular circadian rhythm (26.6%), an altered circadian rhythm (shorter or longer than normal, 53.1%), and an arrhythmic pattern (20.3%). A long-term experiment showed that the arrhythmic pattern indeed reflected a genuine arrhythmic genotype. The mole rats were found to be active less than 25% of the day and exhibited a multiphasic mode of activity, both diurnally and nocturnally. The number of activity periods and the level of activity were negatively correlated: Animals that exhibited a high level of activity per unit of time showed low numbers of activity periods, while animals that exhibited a lower level of activity showed higher numbers.     

Cancer-free aging: Insights from Spalax ehrenbergi superspecies

Cancer and ageing can be regarded as two different manifestations of the same underlying process—accumulation of cellular damage—and therefore both are closely linked. Nowadays, the ageing of populations worldwide is leading to an unprecedented increase in cancer cases and fatalities, and therefore the understanding of links between cancer and ageing is more important than ever. Spalax is considered an excellent model for ageing and, additionally, for cancer research, due to not show clear age-related phenotypic changes and not develop spontaneous tumours, despite its relatively long lifespan (∼20 years in captivity). Thereby, the purpose of this review is to summarize the recent knowledge on Spalax, with a particular emphasis on the molecular mechanisms associated with their longevity and cancer resistance.     

Adaptive features of skeletal muscles of mole rats (Spalax ehrenbergi) to intensive activity under subterranean hypoxic conditions

Mole rats of the Spalax ehrenbergi superspecies are blind subterranean rodents that live under fluctuating oxygen supply, reduced to a measured 6% O₂, and mostly probably lower, during the rainy season. Fiber typing of muscles of the neck (trapezius) and leg (gastrocnemius, quadriceps) using standard histochemical techniques (succinic dehydrogenase, myosin ATPase) showed that the muscle fibers of mole rats in natural settings, as well as after extended captivity, were predominantly type IIa. The same muscles in laboratory rats showed the full range of fiber types. In contrast, the hearts of the mole rats and the laboratory rats were very similar. Our results indicate that skeletal muscle in the mole rats appears to have evolved in response to specific environmental demands to permit intensive endurance burrowing activities under conditions of severe or chronic hypoxia.     

The mechanism of digging in Arvicola terrestris and Spalax ehrenbergi: functional and evolutional studies

The cineradiographic study of the digging modalities in Arvicola terrestris and Spalax erenbergi showed important convergences in the mechanisms used by both species. Head and incisors are the burrowing tools, acting as a "scraping-shovel" in Spalax and as a "scratching-shovel" in Arvicola. They are moved forward by a force originated by the pressure of the hind limbs against the ground, and transmitted through the vertebral axis. The myological study of these species revealed the increase of the insertional areas for the cephalic muscles. However, the adaptative answer of the cervical vertebrae to the mechanical constraints of digging are different in Arvicola and Spalax; the former developed high resistance moments and the latter increased vertebral stiffness. The characters of the post-cranial skeleton in the digging rodents tend to constitute a morphocline in which Spalax is the final stage and Arvicola an intermediate stage. Then, the adaptative divergences noted above between these animals might reflect their phyletic distance.     

Sleep and activity rhythms are related to circadian phase in the blind.

STUDY OBJECTIVES: Sleep is controlled by both circadian and homeostatic mechanisms. As the light-dark cycle is the most important time cue in humans, blind individuals may have circadian rhythm disorders including sleep. The aim of the study was to assess sleep with simultaneous measurement of an endogenous marker of the circadian clock, namely 6-sulphatoxymelatonin (aMT6s). SETTING AND PARTICIPANTS: 59 registered blind subjects were studied in their own homes. DESIGN: Subjects completed daily sleep and nap diaries for at least four weeks, wore activity monitors continuously, and collected urine samples over 48 hours each week for 3-5 weeks for assessment of aMT6s rhythms. RESULTS: The most sensitive indicator of a circadian rhythm disorder was day-time napping. Subjects with normally entrained (NE) aMT6s rhythms had fewer naps of a shorter duration than abnormally entrained (AE) or free-running (FR) subjects. The timing of these naps was not random; significantly more naps occurred within a five-hour range before and after the aMT6s acrophase (phi (phi)) than outside this range. Disorders in the timing and duration of night sleep in AE subjects manifested as either a permanent advance (advanced sleep phase syndrome, ASPS) or delay (delayed sleep phase syndrome, DSPS). In FR subjects there were transient advances and delays in sleep timing that paralleled aMT6s timing with increased night sleep duration and reduced number and duration of day-time naps associated with a normal aMT6s phase. CONCLUSIONS: Changes in sleep and activity rhythms reflect changes in circadian phase.     

Sleep patterns and avoidance conditioning in the rat.

For 19 male rats of the Wistar strain, percentages of wakefulness (W), slow sleep (SS) and paradoxical sleep (PS) were determined by recording EEG activity of neo-cortex and EMG of neck muscles, for 48 consecutive hours. After the recording periods, the locomotor activity of the animals was measured in an open-field; then they were trained in a two-way shuttle-box. Statistical analysis showed significant correlations between physiological and behavioral variables. The most interesting correlation was that between percentage of PS and number of shocks received during avoidance conditioning: r = ?0.521. Number of shocks was also significantly correlated with the ratio PS/W (r = ?0.567). On the contrary, percentages of W and SS were not significantly correlated with learning scores. Multivariate analysis of the data showed a direct relationship between PS, avoidance and activity scores. These results may reflect a relationship between individual patterns of central activation and shuttle-box situation as well as a direct involvement of PS in memory processes.     

Sleep deprivation in the rat: IX. Recovery

Eight rats were subjected to total sleep deprivation, paradoxical sleep deprivation, or high amplitude sleep deprivation until they showed major deprivation-induced changes. Then they were allowed to sleep ad lib. Three rats that had shown the largest temperature declines died within two to six recovery days. During the first 15 days of ad lib sleep, surviving rats showed complete or almost complete reversal of the following deprivation-induced changes: debilitated appearance, lesions on the paws and tail, high energy expenditure, large decreases in peritoneal temperature, high plasma epinephrine and norepinephrine levels, and low thyroxine levels. The most prominent features of recovery sleep in all rats were immediate and large rebounds of paradoxical sleep to far above baseline levels, followed by lesser temporally extended rebounds. Rebounds of high amplitude non-rapid eye movement (NREM) sleep occurred only in some rats and were smaller and less immediate.     

Sleep deprivation in the rat: II. Methodology

Methods common to several studies in this series are described. A key feature is a sleep deprivation apparatus in which an experimental and a yoked control rat are housed on opposite sides of a divided disk suspended over shallow water. When the experimental rat enters a "forbidden" sleep stage, the disk is automatically rotated, forcing the experimental rat to walk to avoid being carried into the water. The control rat receives the same physical stimulation but can sleep ad lib when the disk is stationary.     

Sleep deprivation and c-fos expression in the rat brain

SUMMARY  This study examined the effects of sleep deprivation on the expression of the immediate early gene c-fos in the brain with both in situ hybridization and immunocytochemistry. Rats were manually sleep-derived for 3 h, 6 h, 12 h, and 24 h starting at light onset (08.00 hours), and for 12 h starting at dark onset (20.00 hours). c-Fos expression was found to be higher in sleep-deprived rats with respect to control animals in several brain areas. The increase was evident both in terms of c-fos mRNA and Fos protein, although with a different time course. Among the areas that showed a consistent induction of c-fos were many cortical regions, the medial preoptic area and the posterior hypothalamic area, some thalamic nuclei, and several nuclei of the dorsal pontine tegmentum. The pattern of c-fos expression after sleep deprivation was very similar to that observed after comparable periods of spontaneous wakefulness (Pompeiano et al. 1994). In general, the increase in c-fos expression was not simply proportional to the amount of previous wakefulness. In many areas, the highest levels of c-fos were seen after 3 h of sleep deprivation. These observations are discussed with respect to the homeostatic regulation of sleep and to the functional consequences of wakefulness in specific brain areas.     

Postnatal development of the eye in the naked mole rat (Heterocephalus glaber)

The naked mole rat (Heterocephalus glaber) is a subterranean rodent whose eyes are thought to be visually nonfunctional and as such is an ideal animal with which to pursue questions in evolutionary developmental biology. This report is the first in-depth study on the development and morphology of the naked mole rat eye. Using standard histological analysis and scanning and transmission electron microscopy, we describe the structural features of the eye. We further report on the morphological changes that accompany the development of this eye from neonate to adult and compare them with those that occur during mouse eye development. We observed numerous abnormalities in the shape and cellular arrangement of the structures of the anterior chamber, with notable malformations of the lens. Cell proliferation and cell death assays were conducted to investigate the possible causes of lens malformation. We found that neither of these processes appeared abnormal, indicating that they were not responsible for the lens phenotype of the mole rat. In order to investigate the process of lens differentiation, we analyzed the expression of gamma-crystallins using Western blots and immunocytochemistry. At birth, levels of gamma-crystallin appear normal, but soon thereafter, the gamma-crystallin expression is terminated. Absence of detectable gamma-crystallins in adults suggests that there is a gradual degradation and loss of these proteins. The evolutionary factors that could be responsible for the eye morphology of the naked mole rat are discussed. A model for abnormal lens differentiation and the role it plays in the morphogenesis of the rest of the eye in the naked mole rats is proposed.     

Sleep and sleep homeostasis in constant darkness in the rat

According to the two-process model of sleep regulation, a homeostatic Process S increases during waking and decreases during sleep. The time course of Process S can be derived on the basis of changes in vigilance states and changes in electroencephalogram slow-wave activity (SWA, activity below 4 Hz) during non-rapid eye movement (NREM) sleep. In most mouse strains, an optimal fit between S and SWA was achieved with one increasing (active during waking and REM sleep) and one decreasing time constant (active during NREM sleep) for Process S. However, in the rat, systematic deviations in the light and dark periods were observed, which were resolved by introducing different decreasing time constants between the light and dark periods. The present study shows that this difference between the rest (light) and active (dark) phases remains, and may even be larger, after animals are adapted to constant dark conditions for at least a week. In addition, the data show that the build-up rate of SWA at the onset of a NREM sleep episode is slow compared with the increase rate under light–dark conditions, and that this build-up rate changes with the circadian phase. The slow build-up rate introduces a systematic error between the simulation of Process S and SWA in NREM sleep. The circadian modulation of the build-up rate may, together with circadian changes in NREM sleep episode duration, be the source of the necessity of introducing a difference in the decreasing time constant between the rest and active phases.     

Sleep deprivation in the rat: VII. Immune function

Immune function studies were performed on splenic lymphocytes obtained from rats subjected to total or paradoxical sleep deprivation. Spleen cell counts, in vitro lymphocyte proliferation responses to mitogens, and in vitro and in vivo plaque-forming cell responses to antigens were obtained. Sleep-deprived rats were roughly equivalent to both their yoked controls and home-cage controls in all assays. The results do not support the hypothesis that sleep deprivation results in immune suppression as measured by the above-mentioned parameters.     

Sleep and feeding patterns in the ventromedial hypothalamic lesioned rat

Sleep and feeding patterns were recorded in Ventromedial Hypothalamic (VMH) lesioned rats during 10 to 15 consecutive days. During the dynamic phase of hyperphagia, daily Slow Wave Sleep (SWS) and Paradoxical Sleep (PS) were significantly increased compared to normal rats. These increases were exclusively due to a greater duration of SWS and PS episodes and a higher number of PS episodes during the dark period of the day. During the static phase, sleep amounts returned, as did food intake, to normal values but the equal circadian sleep distribution observed during the dynamic phase persisted. During the dynamic phase, the size of a meal was highly correlated with sleep events within the intermeal interval (IMI) preceding it, and only weakly correlated with sleep within the subsequent IMI. Unlike normal rats, there were no significant variations in deprivation and satiety ratios throughout the nycthemeron. These findings suggest that in VMH lesioned rats, physiological parameters determining sleep and feeding are perhaps more important than ecological ones. In addition, possible causative relations and common underlying factors between sleep and feeding are discussed.