Receptor Mechanism Of Abnormal Dopamine Regulation In Heterozygous Reeler Mice

BackgroundSchizophrenia（SZ）is a significant public health and social problem threatening human health,which is a severe mental disease with complex etiology.It has abnormal neural network function and cognitive impairment,which is related to polygenic abnormalities.Reelin gene has been identified as the preferred candidate gene related to schizophrenia.Studies showed that heterozygous reeler mice（HRM）have dopamine（DA）dysfunction similar to schizophrenia,but the mechanism is unclear.ObjectivesThe present study aimed to perform behavioral experiments,electrophysiological techniques and molecular approaches to observe whether the cognitive function,EEG activity and the expression and function of dopamine receptor of HRM have changed and to explore its molecular mechanism.MethodsThe animals used in the experiment were male HRM and wild-type littermates（WT）aged 4-6 months,weighing about 25-35 g,with 20 animals in each group.The following animal experiments were carried out.1.Behavioral experimentOpen field test,Morris water maze test,elevated plus maze test and three-chamber social approach test were conducted to assess the ability of learning and memory and cognitive function of wild-type mice（WT）and HRM.2.Western blotAfter anesthetized,animals were sacrificed and fixed via cardiac perfusion with physiological saline and the hippocampus was isolated from the brain.The total protein of hippocampus was extracted and the expression levels of dopamine receptors in hippocampus of WT and HRM were detected.3.Extracellular field recording of extracorporeal hippocampal slicesAnimals were anesthetized and sacrificed for brain.Horizontal slices of the mouse brain were cut in chilled sucrose-ACSF,and then transferred to the Haas-type recording chamber to record local field potentials of hippocampus.γ oscillations were induced by carbamoylcholine chloride（5μM）.The effect of dopamine and different dopamine receptor blockers on γ oscillations were detected after steady-state γ power was reached.Results1.In the elevated plus maze experiment,WT tended to enter the open arms more frequently and spend more time in the open arms than HRM;In three-chamber social approach test,HRM showed slightly decreased social ability and social novelty preference;The open field experiment showed that the motor function of mice was normal;The learning and memory ability of HRM was not impaired in the water maze experiment;2.In the comparison between WT and HRM,there was no significant difference in γpower.Peak frequency of oscillations in HRM were decreased.DA can increase the hippocampal γ oscillations of WT,but did not increase hippocampal γ oscillations of HRM,suggesting dopamine dysfunction in HRM;3.Compared with WT,the expression of dopamine D3 receptor in hippocampus of HRM increased,but the expression of other receptors did not change.4.Effects of dopamine receptor blockers on hippocampal γ oscillations of WT and HRM are different.We found that the D3 receptor（D3R）antagonist GR103691 caused a large increase of γ power in HRM but had no effect on WT;the D2 receptor（D2R）antagonist phenothiazine caused a large increase of γ power in WT but had no effect on HRM;The selective antagonist for different D1-type dopamine receptor（SKF-83566）and D4-type dopamine receptor（L-745870）had little or small effect in WT or HRM.5.After blocking dopamine D2 receptor,the effect of Phenothiazine + DA on γ power in WT and HRM was not different from that of Phenothiazine alone.After blocking dopamine D3 receptor,DA had no effect on γ power in hippocampus of WT,but increasedγ power of HRM.ConclusionsHRM has anxiety and abnormal social behavior,which are similar to schizophrenia.The deletion of RELN will lead to dysregulation of DA system in mice.Abnormal dopamine regulation may be related to the dysfunction of dopamine D2 receptor and the overexpression of dopamine D3 receptor.