The Neurobiology Mechanisms Of Rat Food Foraging Behavior

Part Ⅰ A method for detection of food foraging behavior in the ratObjective To establish laboratory model for detection of rat food foraging behavior that can mimic the corresponding environment in nature.Methods After12h of food deprivation (no water deprivation), rats were removed from their home cages and placed in an open field which was constructed with black wood with dimensions of150cm×150cm×50cm (length×width×height). After habituating for2h in the field, the test rat was allowed to forage food freely from7:00P.M. to7:00A.M.of the next day. For testing competitive food foraging activity, one rat was placed in a small plastic home cage (30cm×18cm×16cm) with a metal wire cover with250g of standard food pellets on the wire mesh, and a test rat which had been deprived of food for12h was placed in the open field. The rat residing in the small cage and the test rat with the same gender and did not have any interaction with each other before the test. The test rat was allowed navigate to the cage and foraged food freely from7:00P.M. to7:00A.M. the next day. The amount of food moved to the open field was calculated and as an indicator of food foraging ability. For testing the non-competitive food foraging activity, the test rat was placed in the open field and allowed to navigate to the cage without any residing rat in the cage. The other parts of procedures were conducted in the same manner as in the test session of the competitive food foraging paradigm. During no-hurdle foraging test,250g of standard food pellets were placed in transparent bright Plexiglas tray (30cm×18cm×2cm) instead of a small wire-topped plastic home cage, and the tray was placed within the open field close to one side of the wall. The other parts of the procedure were conducted in the same manner as in the test session of the competitive and non-competitive food foraging behavior. After this we evaluated the effects of several variables on the competitive food foraging behavior. The variables include fasting versus non-fasting, clean floor versus floor with bedding materials, the procedures were conducted for five consecutive days in a rat and a high degree of difficulty on the competitive and non-competitive food foraging tests in rats.Results We found that naive rat without training or manipulation foraged most of food pellets from the food container to the field in three procedures. No effects of test type (competitive, non-competitive and no-hurdle food foraging tests) and animal gender or their interaction on the amount of food foraged per night. The activities in animals with fasting were increased in the competitive food foraging behavior test compared with non-fasting rats. There was no significant difference in the amount of food foraged in the presence or absence of bedding materials. The amount of foraged food was consistent each day for five consecutive days with a slight increase in following days. After adding the difficulty, the foraged food per night was no significant changing in non-competitive food foraging test. In the competitive food foraging test, the foraged food per night was significantly decreased after adding the level of difficulty.Conclusion We successfully created a simple and practical laboratory model that can quantitatively detect the natural food foraging behaviour without any artificial intervention or training in rat. Part II Involvement of anterior cingulate cortex in the food foraging behavior of the ratObjective To evaluate the effect of anterior cingulate cortex (ACC) on the rat food foraging behavior.Method The kanic acid (KA) was administrated into the rat ACC or OFC bilaterally to injure ACC or OFC, the sham lesion rat microinjection of saline into the ACC or OFC.3weeks after lesion surgery, behavioral performance were done including food foraging tests, emotional behavior tests (assessed by elevated plus-maze test (EPM), open field test (OFT), forced swimming test (FST), and sucrose preference test) and exploratory activities. Following the completion of behavioral testing, brain tissue were processed for Nissl staining to determine the extent and location of the KA-induced lesion.Results Bilateral microinjections of KA into ACC or OFC produced an obvious lesion of brain tissue. In contrast to the sham lesion group, bilateral complete ACC chemical lesion significantly decrease the amount of foraged food in the competitive food foraging test, non-competitive food foraging test and no-hurdle food foraging test. Moreover, the deficit of food foraging activity is more prominent in the competitive food foraging test than in the non-competitive and no-hurdle food foraging test after ACC lesion. But after OFC lesion, rats foraged the same amount of food in all the three experiments as the control group. No alteration after ACC lesion are found in other behaviours including EPM, OFT, FST, sucrose preference test and exploratory behaviour.Conclusion The integrality of ACC is important in the food foraging-related behaviours. Part Ⅲ The effect of Dopaminergic and Glutaminergic neurotransmitter systems on the rat food foraging behaviorObjective To explore the role of dopamine D2receptor and non-competitive NMDA receptor in food foraging behavior of ratMethod Rats were injected subcutaneously with MK-801(a highly selective non-competitive NMDA receptor antagonist), haloperidol (dopamine D2receptor antagonist) or vehicle, competitive, non-competitive and no-hurdle food foraging behavior were studied30min after injection of MK-801, haloperidol or vehicle, and the amount of food eaten per night was also observed.Results A dramatic decrease of foraged food was found in the rats after administration of haloperidol in competitive, non-competitive and no-hurdle food foraging tests. Treatment with MK-801reduced the foraged food in the competitive food foraging test, but did not affect the foraged food in the non-competitive and no-hurdle food foraging tests. The haloperidol and MK-801treatment did not induced any effect on eaten activity of per night.Conclusion Our study suggests that dopaminergic and glutaminergic systems are differentiatlly involved in the rat food foraging behaviours.