Acute Temperature Stress On Stream Salamander Brain C-fos And 5-ht <sub> 1a </ Sub> Receptor Expression,

Temperature as an important factor to thermoregulation, has more enormous impact on the survival of animals than any other environmental factors. In general, endothermic species such as mammals, birds, can maintain a constant body temperature (Tb) by autonomic and behavioural mechanisms in fluctuant thermal environment. Most of the knowledge on thermoregulatory physiology are from the studies on mammalian species, such as rats. Recently, more and more ectotherm species have been useed as model animals for investigating the mechanisms of thermoregulation since their thermoregulation mainly rely on behavior. The data obtained from a variety of studies will certainly help us further understand the mechanisms that underlie the thermoregulation (anapyrexia and fever).Stream salamander Batrachuperus tibetanus (Schmidt, 1925) (Amphibia: Hynobiidae), a kind of aquatic amphibian, lives in the montane areas with high-altitude and low-temperature.The temperature gradient apparatus was used to measure the optimum temperature, the critical high temperature and the critical low temperature of Batrachuperus tibetanus in our experiment. The results showed that the optimal temperature of this species ranged from 6 to 18℃, the critical high and the critical low temperature were 21.2℃and 0.6℃respectively. HE staining was used to observe the brain structure, and the results showed that the brain in Batrachuperus tibetanus remained at a primitive state.Immunohistochemistry method was used to determine the expressions of c-fos and 5-HT_1A receptors in various brain regions respectively under acute cold and acute heat stress. The subject animals are randomly divided into three groups: the control group exposed to 11.5℃for 2 hrs, the cold stress group exposed to 0.6℃for 2 hrs, the heat stress group exposed to 21.2℃for 2 hrs. We investigated the induction of Fos neuronal activity expression under acute temperature stress, the role of 5-HT_1A receptors in thermoregulation in Batrachuperus tibetanus. The results are listed as follows:1.The number of the positive Fos immunoreactive neurons significantly decreased in the cerebral hemisphere after acute heat stress and acute cold stress, which suggested that the acute temperature stimulation (heat or cold) could inhibite the activities of neurons in cerebral hemisphere of Batrachuperus tibetanus.2. After acute heat stress and acute cold stress, there were more positive Fos immunoreactive neurons in the diencephalon than in the control group (p<0.05).The group exposed to heat stress was significantly different from the control group (p<0.01). These results suggested that the diencephalon of Batrachuperus tibetanus may play an important role in thermoregulation and that the diencephalon is thermosensitive.3. After acute heat stress and acute cold stress, there was not significant change in the number of the positive Fos immunoreactive neurons in mesencephalon of the subject animals in the group exposed to stress groups (p>0.05), which indicated that the mesencephalon of Batrachuperus tibetanus might not play an important role in thermoregulation.4. After acute heat stress and acute cold stress, the number of the positive Fos immunoreactive neurons in the medulla oblongata in the group exposed to hot stress, compared with the control group, didn't change significantly, but decreased in the gourp exposed to cold stress( p<0.05). These results suggested that the activity of medulla oblongata neurons may be inhibited and that the this species may have different thermosensitive units.5. After acute heat stress and acute cold stress, the number of 5-HT_1A receptors in the cells with positive expression in the cerebral hemisphere, in the group exposed to heat stress significantly increased (p<0.01) when compared with the control group, while in the group exposed to cold stress, the number of the receptors did not change significantly. These results suggested that Batrachuperus tibetanus has the basic ability in thermoregulation, the 5-HT_1A receptors participated in thermoregulation.6. After acute heat stress and acute cold stress, the number of 5-HT_1A receptors in the cells with positive expression in the diencephalon, in the group exposed to heat stress significantly increased (p<0.01) when compared with the control group. These results further proved that the diencephalon of Batrachuperus tibetanus played an important role in thermoregulation.7. After acute heat stress and acute cold stress, 5-HT_1A receptors expression in the mesencephalon in the group exposed to stress didn't significantly change (p>0.05), indicating that the temperature stress did not influence the activity of the mesencephalon.8. After acute heat stress and acute cold stress, 5-HT_1A receptors expression in the medulla oblongata,in the group exposed to heat stress significantly increased (p<0.01) when compared with the control group While the group exposed to cold stress showed no significant change. These results suggested that the medulla oblongata of Batrachuperus tibetanus also play a role in thermoregulation. The increase of 5-HT_1A receptors in heat stress group further explained that Batrachuperus tibetanus is relatively primitive, but it has a basical ability in thermoregulation.