The Role Of RPTN In Cocaine Addiction In Mice

Repetin（RPTN）belongs to the S100 family of calcium-binding proteins with two N-terminal EF chiral domains that bind Ca2+reversibly and an internal tandem repeat sequence containing glutamine rich residues.The role of S100 proteins in the development of psychiatric disorders such as schizophrenia and bipolar disorder may be related to the dysregulation of Ca2+signaling.Previous study showed that RPTN is expressed in the rat hippocampus,prefrontal lobes and blue spot nucleus.Moreover,serum RPTN levels are significantly reduced or even absent in schizophrenic patients,patients with bipolar disorder and drug users,suggesting that RPTN protein plays a role in psychiatric disorders,but underlying mechanism has not been reported.The aim of this study was to study the role of RPTN in cocaine addiction and underlying mechanisms.In terms of research methods,CPP（conditional place preference）was used to evaluate cocaine addiction in mice,and western Blot was used to determine the levels of RPTN protein in the NAc（Nucleus accumbens）.In the second experiment,RPTN knockout（KO）mice（RPTNKO/KO）and their wild-type（WT）littermate control mice（RPTNWT/WT）were used to determine the role of RPTN in cocaine addiction.Mice were divided into 4 groups:WT+saline,WT+cocaine,KO+saline and KO+cocaine.Behavioral tests were used to determine CPP scores,anxiety-like behaviors,social behaviors,learning and memory after cocaine administration.Dendritic spine density in the medium spiny neurons（MSNs）of the NAc was examined by Golgi staining.Expression of glutamate receptors and synaptic proteins in the NAc of mice were examined by Western Blot.The results are summarized as below.1.In WT male mice,the CPP scores in the cocaine-administered group were significantly higher than those of control mice which received saline only,showing that cocaine-treated mice became addicted to cocaine compared with control mice which did not receive cocaine.Cocaine administration caused a decrease in the levels of RPTN protein in the NAc in the cocaine group compared with control group which received saline only.2.The CPP score in KO mice in the KO+cocaine group was significantly higher than that of in the WT+cocaine mice.RPTN deletion and cocaine had a significant effect on the distance traveled in the open field.Cocaine treatment caused an increase in the locomotion in WT,but not RPTN KO mice.Mice in the KO+saline group showed impaired spatial memory compared with mice in the WT+saline group,Cocaine did not affect recognition memory,social behaviors and spatial memory in both WT and KO mice in novel object recognition test,three-box test and Barnes Maze test,respectively.3.The results of Golgi staining showed that the density of dendritic spines in the MSN of the NAc was significantly increased in both KO and WT mice after cocaine injection.However,spine density in the KO+cocaine mice was significantly higher than that in WT+cocaine mice.4.Western Blot showed that the interaction of cocaine and RPTN deletion had a significant effect on the levels of GluA1,GluN1 and D1R in the NAc,but did not affect the levels of GluA2,GluN2B,Kal-7,SYN and Tau.Cocaine adminstration caused an increase in the level of Kal-7 in WT,but not KO mice.Interesting,cocaine administration caused an increase in the level of D1R in KO,but not WT mice.These results suggest that RPTN plays an important role in cocaine addiction in mice and possible mechanism was discussed but requires to address in the future.