Study On Effects Of +Gz Exposure On Learning And Memory Of Rats And Changes Of Somatostatin

Modern aircrafts with high performance are able to routinely fly in the +9Gz range and high G increase rate for sustained periods (lasting for 45s), which may exceed a person's physiological tolerance. Nowadays, introduced in or self-developed modern aircrafts have been equipped largely in our country. Safety flying is a social question that has aroused general concern. Further studies on the effects of high +Gz exposures on the body, especially on brain are important questions faced by aerospace medical workers.When exposed to +Gz, blood shifts to lower body, which results blood pressure and blood volume of brain declined, so cerebral ischemia occurred. As an indispensable function of brain, learning and memory related parts of brain such as cerebral cortex, hippocampus, thalamencephalon, corpus striatum, are sensitive to ischemia, even transient ischemia can harm these areas. Researches nowadays are mostly concentrated on brain structure changes and their mechanisms; little has been focused on changes of brain function. Behavior methodis one important means to discuss effects of different stresses on brain function. Researches have show that memory of rat had been impaired after +Gz exposure, but no such effect on learning has been reported. Learning and memory is regulated by many factors. Somatostatin (SS) is a neuropeptide, which is involved in cognitive progress. SS deficits in the central nervous system (CNS) have been demonstrated to be one of the factors related to impairment of learning and memory introduced by cerebral ischemia. Brain ischemic preconditioning (BIP) can alleviate pathologic damages and function impairments induced by severe ischemia. Lower +Gz preconditioning can bring the similar protection effects as BIP. So, do high +Gz exposures impair learning of rat? Does content of SS in CNS change in this duration? Can lower +Gz preconditioning improve learning and memory of rats? To clarify these questions, it is important for further studies on brain damage and its mechanisms induced by high +Gz exposure; also it is beneficial to develop high efficient defending measures.In this study, animal centrifuge was used to simulate + Gz exposure. Open field test, Y-maze test and step through test were used to explore effects of + Gz exposure on learning and memory of rats. Radioimmunoassay (RIA), in Situ Hybridization Histochemistry (ISHH) were used to observe changes of SS and SS mRNA in brain after + Gz exposure. Protective effects of lower + Gz preconditioning were evaluated by using the three kinds of behavior tests, and changes of SS during this course were observed too.The main findings of the study are as follows:1. Effects of +6 Gz/3min and +10 Gz/3min exposures on learning and memory of rats In open field test, compared to control group, summation of crossing and rearing(SCR) declinedsignificantly in +6 Gz/3min group at Od (P<0.01) , time stay in center grille(TSC) had a tendency to improve, SCR declined significantly in +10 Gz/3min group at 0 d and 2 d (P<0.05) , TSC increased significantly at 0d(P<0.01); compared to +6 Gz/3min group, TSC in +10Gz/3min group increased significantly at 2 d(P<0.05). In Y-maze test, there is no apparent changes of right reaction number(RR) and time of reaction(TR) in +6Gz/3min group compared to control group at 0 d, but at 2 d,4 d and 6 d, RR decreased significantly (P<0.01) , and TR increased significantly(P<0.01) ; RR and TR in +10Gz/3min group had significant changes at all time points compared to control group (P<0.01) ; compared to +6 Gz/3min group, RR and TR in +10 Gz/3min group only had significant changes at 0 d (P<0.01 or P<0.05) . In step-through test, latent time(LT) at 0 d in +6 Gz/3min and +10 Gz/3min group increased significantly compared to control group(P<0.05) , LT at 6 d shortened significantly in +6 Gz/3min and +10 Gz/3min group (P<0.01) ; compared to +6 Gz/3min group, total time, LT at 0 d and LT at 6 d changes significantly in +10 Gz/3min group (P<0.05 ) .The results suggested that, +Gz exposure induced serious a...