The Effects Of Bilateral Prostriata Lesions On Spatial Learning And Memory And Anxiety-Like Behaviors In Rats

BackgroundArea prostriata(prostriata)is one of the major limbic brain structures that responds rapidly to the visual stimuli in the far peripheral visual field.Recent studies have shown that area prostriata receives its inputs not only from the visual and auditory cortices,but also from many structures that are important for spatial information processing and navigation(such as presubiculum,retrosplenial cortex,etc).The prostriata is strongly connected with medial orbitofrontal cortex(ORBm)and the lateroposterior nucleus–pulvinar complex(LP-Pul),which are involved in emotional change and fear processing,respectively.Recent research on area prostriata has focused on its neural circuits and chemoarchitecture.However,data about its roles in spatial learning and memory as well as in anxiety-like behaviors is very lacking.Recent studies have revealed the existence of the prostriata in the rats and mice.Compared with the prostriata in human and monkey brains,the location of the prostriata in rodent brains is more superficial and easier to access for injections and lesion.The prsent study aims to investigate aforementioned roles of area prostriata in rats.ObjectiveTo explore the effect of bilateral lesion of the prostriata on spatial learning and memory and anxiety-like behaviors of the rats,and to examine the changes of neuronal activity in the downstream target regions.MethodsThe exact location of the bilateral prostriata was determined by Nissl and CalbindinD28 K immunohistochemical staining.Then the rats were divided into blank control group,sham group and experimental group.The bilateral prostriata regions of the rats in the sham group were injected with 0.9% sterile saline.Those in the experimental group were injected with 10mg/ml ibotenic acid in order to destroy most of the neurons in the prostriata without affecting the adjacent brain areas.Subsequently,open-field test(OFT),elevated plus maze test(EPM)and Morris water maze test(MWM)were conducted to study the changes in motor ability,anxiety-like behaviors and spatial learning and memory ability of the three groups of rats.Finally,c-fos positive neurons were quantified in some downstream target regions of the prostriata to study the changes of neuronal activity in these regions of the rats in the three groups.ResultsThe findings of the present study indicate that the spatial learning ability and memory ability of rats with bilateral prostriata lesion were significantly reduced compared with the control group and the sham group.In addition,the results of the open-field test and the elevated plus maze test showed that bilateral prostriata lesion did not affect the motor ability of the rats,but the rats with the lesion showed less interest in exploring strange space and more anxiety-like behaviors.Finally,compared with the sham group,decreased neuronal activity was observed in some of the downstream target regions of area prostriata,including the presubiculum,laterodorsal nuclei and lateroposterior nucleus–pulvinar complex,in the experimental group.However,the activity of neurons in some other target regions such as the pretectal nucleus(PTN)and the ventral lateral geniculate nucleus(VLG)did not change.Meanwhile,the neuronal activity in brain regions that are not directly connected with area prostriata,such as substantia nigra(SN)and zona incerta(ZI),was not affected.ConclusionBilateral prostriata lesion does not produce significant effect on the motor ability of the rats,but it reduces the spatial learning and memory ability and the interest in exploring new environment and leads to anxiety-like behaviors.In addition,the lesion of area prostriata also leads to decreased neuronal activity in some downstream target brain regions.