The Role Of The Prostaglandins And The Hypothalamus In Thermoregulation In The Lizard, Phrynocephalus Przewalskii (Agamidae)

It is a basic demand for animals to maintain body temperature within the optimal range for their metabolism and normal physiological activities. Recent years, many studies were focused on the pattern of thermoregulation in reptiles and they considered that most reptiles regulate body temperature by behavioral and physiological means. However, only a few attempts have been made to elucidate the physiological mechanisms of thermoregulation in reptiles, particularly in the central nerve system and cardiovascular regulation. With the deeply study, numerous studies on different groups of reptiles have shown different heart rates in warming and cooling (the 'hysteresis' pattern), which allow reptiles to control rates of transient heat transfer and peripheral flow between the environment and their core. The physiological mechanisms of hysteresis have some reports, but the results are different. In vivo and in vitro experiments, this study aims to clarify the role of prostaglandins in physiological mechanisms of hysteresis and provide evidence of the mechanisms in cardiovascular regulation. The hypothalamus has been conclusively identified as the central nerve system in the thermoregulation, receives and senses various informations from peripheral thermoreceptors, acts and antagonizes with its receptors, sends efferent signals to different effector organs. This experiment studies the location of different neurotransmitters in the hypothalamus and analyses the immunoreactivity, aiming to clarify the probability of various neurotransmitters in the thermoregulation in reptiles and make a base for further studying the mechanisms of neurotransmitters in thermoregulation.This experiment consists of two parts. One part is the role of prostaglandins in the thermoregulation in reptiles. In vivo and in vitro experiments, heart rates during heating and subsequent cooling were shown a hysteresis pattern. On administration of COX inhibitor, there were no differences in heart rate between heating and cooling at any body temperature. Administration of agonist prostaglandins only produced a significant effect on heart rate below 25℃. Another part is the role of thehypothalamus in the thermoregulation in reptiles. Fibers immunoreactive (IR) for antibody raised against 5-HT and SP were only found in the SON and SCN. Furthermore, in the SON, many 5-HT immunoreactive neurons were observed when ambient temperature (Ta) at 40 °C, otherwise, the relatively moderate 5-HT-IR neurons were observed when Ta at 10°C, very few immunoreactive neurons were found at 25 °C. In the SON, many SP immunoreactive neurons were observed when ambient temperature (Ta) at 10°C, whereas, the relatively moderate SP-IR neurons were found when Ta at 40 °C, very few immunoreactive neurons were observed at 25 °C. These results showed temperature-related changes in 5-HT and SP immunoreactivity. A remarkable seasonal alternation was found in iNOS-IR. There were only sparse NOS-IR neurons in the PO/AH of the hypothalamus of control animals. In contrast, in hibernation-induced animals iNOS-IR significantly increased in both intensity and number of immunostained cells in the PO/AH. In the hibernating lizards, P. przewalskii, an intraperitoneal injection of PGE2 at doses of 40 nmol Kg'1, caused no significant iNOS-IR response in all lizards after 30 min period. The iNOS-IR responses to 100 nmol Kg"1 and 200 nmol Kg"1 were larger than 40 nmol Kg"1, caused remarkable decline, but the difference between 100 nmol Kg"1 and 200 nmol Kg"1 group was not statistically significant. Moreover, there were barely discernable iNOS-IR neurons in the hypothalamus or only occasional lightly immunostained cells were observed after an intraperitoneal injection of PGE2 at doses of 260 nmol Kg"1. Lizards received an intraperitoneal injection of PGE2 at doses of 40, 100, 200, 260 nmol Kg"1 and iNOS-IR was examined at 15, 30, 60, 90 min respectively after the injection. It showed that iNOS-IR caused a slightly increase after 60 min, especially remarkable when an intraperitoneal injection of PGE2 at doses of 200 nmol Kg"1 after 90 min. Fibers immunoreactive (IR) for antibody raised against VIP were only found in the SCN. Furthermore, many VIP immunoreactive neurons were observed at ZT6, and there were remarkable differences with ZT0, ZT12 and ZT18.We concluded that prostaglandins play only a limited role in modulating heart activity in P. przewalskii. It appears that reptiles have evolved an intrinsic regulatory mechanism devoid of neural and humoral input to adapt to the thermal environment orby pacemaker cell activity. The neurotransmitters of the hypothalamus probably take part in the thermoregulation in reptiles. These results also suggest that the PGE2 induces iNOS-IR and overexpression of iNOS-IR requires at least 1 -2 h to be induced in cold-adapted lizard. VIP is likely to be involved in the translation of photic inputs in the SCN and acts as a primary pacemaker in the driving daily and circadian rhythms.