| Small mammals living in the temperate and polar regions produce a set of adaptivestrategies, including anatomy, physiology and behavior aspects to cope with the variations inphotoperiod, ambient temperature, food and social factors in the long-term evolution process.The environmental factors have effects on rodents in their reproduction period, especially duringtheir lactation. The ambient temperature in cave would affect the plasticity of the nervous system,including physiology and behavior aspects, resulting in the variation of conformity. We used thetypical species Brandt’s vole (Lasiopodomys brandtii) as our subject. They are captured whichacquired from Inner Mongolian steppe as reared population. Based on the research for manyyears in our group, there are two experiments in our study.In experiment1, we explored the effect of environmental temperature on neurogenesis andmetabolic regulation during lactation in Brandt’s vole. We hypothesized that the metabolicphenotypes induced by high temperature experience during lactation may be relative with thealteration in adult neurogenesis in Brandt’s voles. This study shed light in explaining whyoffspring born in different seasons have various life experiences and the nervous mechanism inwild population.The detailed program of experiment1was as follows.We randomly assigned the subjects into two groups after they had given birth (postnatal1day, P1). Animals were housed in the control group (n=8,23±1℃) and high temperature group(n=8,30±1℃) until weaning (week3), then all of them would be moved to control temperaturegroup (23±1℃) with2-3same-sex partners. Voles from each group were reared incold-acclimated room(5±1℃)for3weeks after injected with BrdU(100mg per kg body weight,intraperitoneally(i.p.), once per day for2weeks). Animals were sacrificed after the treatment, thebrain were then removed and cut at40μm thickness on a freezing microtome.Experiment1protocols were as follows.Litter mass and body mass (±0.1g) were recorded every week during lactation. Then foodintake and body mass were measured every two weeks after weaning until when they reached toadulthood. Metabolic measurements were conducted using an open circuit respirometer on the day after the low temperature acclimation. We tested the number of BrdU-positive cells inhypothalamus (related to metabolic regulation), including arcuate hypothalamic nucleus (ARC),paraventricular hypothalamic nucleus (PVN), lateral hypothalamic nucleus (LH),(dorsomedialhypothalamic nucleus (DMH) and ventromedial hypothalamic nucleus (VMH). We also recordedthe number of BrdU-positive cells in the dentate gyrus of the hippocampus (DG, related tolearning and memory behaviors) and amygdala nucleus (AMY, related to emotion behavior) ofanimals. Next we tested the cell type during neurogenesis in those areas by BrdU/NeuNdouble-labeled immunohistochemistry (NeuN, a marker of mature neurons).The results of experiment1were as follows.1. The body mass of Brandt’s voles in high temperature group showed no significance fromthat of the control group during the period from lactation to adult period, though the body massof animals in high temperature group is slight lower than the control group.2. There was no difference in food intake between the two groups.3. There was no difference between the two groups in RMR either.4. There were no differences in the number of cell survival (BrdU-positive cells) in ARCand PVN between the two groups. However, the number of BrdU-positive cells in LH, DMH andVMH in high temperature group was higher than the control group.5. The number of BrdU-positive cells in DG and AMY in high temperature group washigher than that of the control group.6. The number of BrdU/NenN double-labeled cell (BrdU/NeuN-positive cells) in ARC,DMH, VMH and DG shows no significant difference either.In conclusion, different environmental temperatures not only affect the developmentalpattern in Brandt’s voles during their early life, but also have a long-term impact in theneurogenesis in hypothalamus, hippocampus and amygdala. These results shed lights on theexplanation why offspring born in different seasons have different life experience and theunderlying nervous mechanism in the wild population.In experiment2, we explored the effect of low temperature on neurogenesis in adultBrandt’s vole. We hypothesized that cold exposure experience may affect on neurogenesis,accordingly impacting the energy metabolic regulation, memory and cognition behaviors in adultBrandt’s voles.The detailed program of experiment2was as follows. We randomly assigned the adult subjects (P60-P70) into two groups. Animals were housedin the control group (n=8,23±1℃) and low temperature group (n=8,5±1℃) for3weeks afterinjected with BrdU(100mg per kg body weight, intraperitoneally (i.p.), once per day for2weeks). Animals were sacrificed after the treatment, the brain were then removed and cut at40μm thickness on a freezing microtome.Experiment2protocols were as follows.We tested the number of BrdU-positive cells in hypothalamus, including ARC, PVN, DMHand VMH. We also recorded the number of BrdU-positive cells in the DG of animals. Next wetested the cell type during neurogenesis in those areas by BrdU/NeuN double-labeledimmunohistochemistry (NeuN, a marker of mature neurons).The results of experiment2were as follows.1. There were no differences in the number of cell survival (BrdU-positive cells) in PVN,DMH and VMH between the two groups. However, the number of BrdU-positive cells in ARCand DG in low temperature group was less than that of the control group.2. The number of BrdU/NenN double-labeled cell (BrdU/NeuN-positive cells) in PVN,DMH, VMH and DG shows no significant difference either. Nevertheless, The number ofBrdU/NenN double-labeled cell (BrdU/NeuN-positive cells) in ARC in low temperature group ishigher than that of the control group.In a word, cold exposure have a impact in the neurogenesis in hypothalamus, hippocampus.The change of environment will affect the plasticity of the nervous system, which play animportant role in promoting the ability of adapting the stimulus environments in animals. Theseresults reveal that the explanation in hostile environment have different physiology and behaviorexpression and the underlying nervous mechanism in the wild population. |
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