Long-term behavioral effects of social separation during early life in a social mammal, Octodon degus.

Social separation is thought to induce a strong stress response in social juvenile mammals, but little is known about how this response might vary throughout the development. The present study examines the long-term effects of early-life stress (ELS) induced by social separation on individual behaviors later in life using the social and precocious species Octodon degus. Four experimental groups were established a positive control group of mothers and siblings from six litters comprised the socially housed (SH) group, while pups from seven litters were randomly assigned to three treatments: pups experiencing no separation (NS) treatment while their siblings did; repeated bouts of consecutive separation (CS); intermittent separation (IS). We analyzed the effects of separation treatment on the frequency and duration of freezing, rearing and grooming behaviors. ELS was correlated with higher hyperactivity, and hyperactivity increased with more frequent separation. However, the behavioral trend of the NS group changed to hyperactive in long-term observation. The findings suggest that the NS group was indirectly affected by ELS. In addition, suggesting ELS acts to converge an individual's behavioral tendencies in a certain direction.

Message to researchers: the characteristic absence of a posterior communicating artery is easily lost in the gerbil.

The Mongolian gerbil has historically been useful for brain ischemia experiments, owing to the gerbil's uniquely underdeveloped circle of Willis (CoW). This led to a gerbil model of cochlear ischemia being generated in our unit. However, we have found that the usual severe hearing loss seen in this model was not being induced consistently in recent experiments using the MON/Jms/GbsSlc gerbil (the sole commercially available gerbil in Japan). We set out to evaluate the posterior communicating artery (PcomA) in MON/Jms/GbsSlc, to re-establish whether this strain is appropriate for ischemia models. Having found that this unique feature is often lost, we then attempted to breed for the characteristic absent PcomA. India-ink perfusion revealed that the percentage of intact bilateral PcomA ("communicating type") in the MON/Jms/GbsSlc gerbil was 57%; unilateral only ("unilateral communicating type") was 39%; and completely absent PcomA ("non-communicating type") was 4%. We were able to obtain few examples of the indigenous old aged Japanese UNG/Mz gerbil strain (at University of Miyazaki). Unfortunately, the pure UNG/Mz female was too elderly for mating. Therefore, selective breeding crosses between MON/Jms/GbsSlc and male UNG/Mz were carried out. After five generations of selective breeding, the percentage of non-communicating type gerbils was significantly higher in the newly generated strain, MON/Jms/SlcMz (F6 generation; 63%) than in the MON/Jms/GbsSlc gerbil. Bilateral common carotid artery occlusion surgery demonstrated that the cerebral blood flow was significantly reduced in MON/Jms/SlcMz compared with MON/Jms/GbsSlc (p < 0.0001) and induced more hippocampal injuries in MON/Jms/SlcMz than in MON/Jms/GbsSlc (p < 0.01). In conclusion, the commercially available MON/Jms/GbsSlc gerbil can easily regain PcomA, and we established a new gerbil strain (MON/Jms/SlcMz) displaying non-PcomA.

Comparison of the gut microbiotas of laboratory and wild Asian house shrews (Suncus murinus) based on cloned 16S rRNA sequences.

The Asian house shrew, Suncus murinus, is an insectivore (Eulipotyphla, Mammalia) and an important laboratory animal for life-science studies. The gastrointestinal tract of Suncus is simple: the length of the entire intestine is very short relative to body size, the large intestine is quite short, and there are no fermentative chambers such as the forestomach or cecum. These features imply that Suncus has a different nutritional physiology from those of humans and mice, but little is known about whether Suncus utilizes microbial fermentation in the large (LI) or small (SI) intestine. In addition, domestication may affect the gastrointestinal microbial diversity of Suncus. Therefore, we compared the gastrointestinal microbial diversity of Suncus between laboratory and wild Suncus and between the SI and LI (i.e., four groups: Lab-LI, Lab-SI, Wild-LI, and Wild-SI) using bacterial 16S rRNA gene library sequencing analyses with a sub-cloning method. We obtained 759 cloned sequences (176, 174, 195, and 214 from the Lab-LI, Lab-SI, Wild-LI, and Wild-SI samples, respectively), which revealed that the gastrointestinal microbiota of Suncus is rich in Firmicutes (mostly lactic acid bacteria), with few Bacteroidetes. We observed different bacterial communities according to intestinal region in laboratory Suncus, but not in wild Suncus. Furthermore, the gastrointestinal microbial diversity estimates were lower in laboratory Suncus than in wild Suncus. These results imply that Suncus uses lactic acid fermentation in the gut, and that the domestication process altered the gastrointestinal bacterial diversity.

Individual differences in torpor expression in adult mice are related to relative birth mass.

Daily torpor is a physiological adaptation in small mammals and birds, characterised by drastic reductions in metabolism and body temperature. Energy-constraining conditions, such as cold and starvation, are known to cause the expression of daily torpor. However, the reason for high degrees of inter- and intra-individual variation in torpor expression (TE) in similar situations is not clear. As littermates of altricial animals are exposed to an uneven allocation of maternal resources from conception to weaning, we tested whether early nutritional experiences have long-term effects on TE in adults. We used full-sibling littermates of laboratory mice that as adults were starved overnight to induce torpor. We measured body mass from birth until adulthood as an indicator of nutritional status, and calculated the relative body mass (RBM) as an indicator of the difference in nutritional status within a litter. After maturation, we subjected mice to five repeated torpor induction trials involving 24 h of fasting and 5 days of recovery. Half of the female mice displayed great individual variation in TE whereas male mice rarely exhibited daily torpor. In females, RBM at birth influenced TE, irrespective of body mass in adulthood; thus, female mice born with low RBMs displayed high TE in adulthood. In conclusion, we provide evidence that TE in mice differs among littermates, and that this variation is linked closely to heterogeneous nutritional experiences during the fetal period.

Protein restriction does not affect body temperature pattern in female mice.

Daily torpor is a physiological adaptation in mammals and birds characterized by a controlled reduction of metabolic rate and body temperature during the resting phase of circadian rhythms. In laboratory mice, daily torpor is induced by dietary caloric restriction. However, it is not known which nutrients are related to daily torpor expression. To determine whether dietary protein is a key factor in inducing daily torpor in mice, we fed mice a protein-restricted (PR) diet that included only one-quarter of the amount of protein but the same caloric level as a control (C) diet. We assigned six non-pregnant female ICR mice to each group and recorded their body weights and core body temperatures for 4 weeks. Body weights in the C group increased, but those in the PR group remained steady or decreased. Mice in both groups did not show daily torpor, but most mice in a food-restricted group (n=6) supplied with 80% of the calories given to the C group exhibited decreased body weights and frequently displayed daily torpor. This suggests that protein restriction is not a trigger of daily torpor; torpid animals can conserve their internal energy, but torpor may not play a significant role in conserving internal protein. Thus, opportunistic daily torpor in mice may function in energy conservation rather than protein saving.