Interaction Between Female Mouse Estrous Cycle And Vulnerability To Cocaine And Associated Neuroendocrine Mechanisms

Ovarian hormones,especially estrogens,are key factors influencing the susceptibility of females to addictive drugs.Estrogen levels are associated with the estrous cycle of female animals.Thus,there is a close association between the estrous cycle and the female vulnerability to drug abuse.However,it is not well known about specific neuroendocrine mechanisms on such reciprocal interactions.In this study,using ICR mice,the interaction between estrous cycle and cocaine exposure and putative mechanisms were investigated from the following aspects.1.Comparison on the levels of glucocorticoid receptor(GR),tyrosine hydroxylase(TH),serum estradiol(E2)and corticosterone(CORT)between estrous and diestrus.The results of enzyme-linked immunosorbent assay(ELISA)showed that the serum E2 concentration in estrus was higher than that in diestrus,but the CORT concentration changed.We found that the GR-IR neurons was increased in the CA1 and dentate gyrus in estrous compared to diestrus via immunohistochemistry test;the TH-IR neurons in the hypothalamic paraventricular nucleus(PVN)and ventral tegmental area(VTA)were increased.2.Acute cocaine administration-induced behavioral sensitization in estrous and diestrus.The locomotion and anxiety levels were examined following intraperitoneally acute cocaine injection(20 mg of cocaine /kg body weight,twice a day)using open field test and elevated plus-maze.while the concentrations of serum oxytocin(OT),arginine vasopressin(AVP),E2 and CORT neuronal expression of estrogen receptor alpha(ER?)and OT-IR were also examined.Subjects were assigned to one of four treatment groups:estrous cocaine group(EC),estrous saline group(ES),diestrus cocaine group(DC)and diestrus saline group(DS).The results showed that the EC and DC showed higher locomotion and anxiety levels compared to the ES and DS,respectively.The DC increased anxiety levels compared to the EC.The expression of ER? neurons in the arcuate hypothalamic nucleus(AR)and ventromedial hypothalamic nucleus(VMH)was decreased in the EC and DS compared to the ES.OT-IR neurons were decreased in the PVN whenthe EC compared to the ES,the DC compared to the DS,the DS compared to the ES,the DC compared to EC.The serum E2 and CORT were increased when the EC compared to the ES,the DC compared to the DS.Serum E2 level was decreased and OT level was increased.Serum OT was increased when the EC compared to the ES,the DC compared to the DS,the DC compared to EC.3.The effect of chronic cocaine injection on estrous cycle and behavioral neuroendocrine: The estrous cycle,the anxiety levels,locomotion and the serum E2 concentration and the expression of OT-IR,AVP-IR and ER?-IR neurons were detected after cocaine injection for 7 days(20 mg/kg twice daily,or saline in control).The results showed that compared with the saline group and the blank control group,chronic cocaine treatment shorten the duration of pre-estrus,estrus,diestrus and the whole estrous cycle.Compared to saline group,the anxiety levels and locomotion were increased,the OT-and AVP-IR expression in the PVN was decreased in the cocaine group,and the ER?-IR expression in the nucleus accumbens(NAC),nucleus preoptic area(MPOA),AR and VMH was decreased.4.Effects of cocaine exposure during late pregnancy on offspring's estrous cycle and behavioral neuroendocrine.Dam mice were administered cocaine(20 mg/kg twice daily,or saline in control)for 7 days before delivery,then estrous cycle was examined in offspring on postnatal 55 days(PND55).While locomotion,emotion,and sociality and serum E2 levels,the expression of OT-IR and ER?-IR neurons were compared between estrus,and diestrus.Subjects were assigned to one of four treatment groups: estrous offspring whose mother exposed to cocaine(CE),estrous offspring whose mother exposed to saline(SE),diestrous offspring whose mother exposed to cocaine(CD)and diestrous offspring whose mother exposed to cocaine(SD).The results showed that the pre-estrus,estrous and the estrous cycle were extended in offspring whose mother exposed to cocaine.Compared to the SE group,anxiety level was increased,while affiliative behavior,following,rearing and self-grooming behavior were decreased in the CE group.However,there was no difference in the locomotion between these two groups.Compared to the SD group,affiliative behavior,investigation and locomotion was decreased,but thelocomotion unchanged in the CD group.Serum E2 concentration,the OT-IR expression in the PVN and supraoptic nucleus(SON)was decreased,while the ER?-IR expression in the MPOA,AR and VMH were decreased When the CE group compared with SE group,the CD group compared with SD group.5.Effects of neonatal OT treatment on offspring's estrous cycle and cocaine-induced behavioral neuroendocrine.The neonatal pups were administrated 1.5 ug OT(dissolved in50 ul saline)from PND 4 to PND10.At the age of 55 days,we examined the estrous cycle and the serum E2 level,the expression of OT-IR and ER?-IR neurons in diestrous;acute cocaine-induced emotion,locomotion and sociality.Here,subjects were assigned to one of four treatment groups: saline treated adults who received early OT injection(OS),saline treated adults who received early saline injection(SS),cocaine treated adults who received early OT injection(OC)and cocaine treated adults who received early saline treatment(SC).The results showed that early OT treatment prolonged estrus and serum E2 level was increased,while PVN OT expression,ER expression in the BNST,MPOA,AR and VMH were increased in adulthood.Compared with SS group,locomotion,affiliative behavior and rearing behavior were increased in the OS group.Compared with SC group,locomotion was decreased,but anxiety level unchanged in the OC group.These results indicated that the estrus and diestrus female mice had different activities in stress system and dopaminergic neurons;although acute cocaine exposure induced behavioral sensitization in both estrus and diestrus,expression levels of cocaineinduced neuroendocrine responses were different;chronic cocaine injection interfered with estrus cycles and affected the activity of neuropeptides and estrogen systems;pregnant dams exposed to cocaine influenced offspring's estrus cycles and lowered the locomotion and sociality and increased anxiety level;early OT treatment affected estrus cycles and enhanced sociality,but inhibited cocaine-induced behavioral sensitization in adulthood.In summary,vulnerability to drug abuse and estrus cycles may affect each other in females.OT,estrogen system and stress systems modulate such reciprocal interactions.