The Role Of Hippocampal Thyroid Hormone Receptor Signaling In The Learning And Memory Impairment Of The Offspring And Its Transgenerational Effect Induced By Paternal Fenvalerate Exposure

ObjectivesMore and more studies showed that paternal experience affected the neurophenotype of offspring.However,the effects of paternal fenvalerate exposure on neurobehavioral development in offspring are still blank.In the current study,we established a model of paternal fenvalerate exposure in mice.We explore the effects of paternal fenvalerate exposure on hippocampal neuron density and the TR signaling.MethodsTo establish a model of neurobehavioral development impairment in offspring induced by paternal fenvalerate exposure.Previous studies showed that mice were orally administered with 20 mg/kg fenvalerate did not produce significant toxic effects.In this study,we selected 20 mg/kg of fenvalerate,as the high dose（FEN-H）.And 2 mg/kg,1/10 of the high dose,was chosen as the low dose（FEN-L）.In fenvalerate-exposed groups,all male mice were orally administered with fenvalerate（2 or 20 mg/kg）daily for 5 weeks.In control group,all male mice were orally administered with corn oil daily for 5weeks.The body weight and food consumption were measured daily.After gavage,one male was mated with one untreated-female mouse to generate F1 offspring.All pregnant mice gave birth naturally on GD18.Within 12 h after birth,each dam was adjusted to four male pups and four female pups.According to previous studies,neurobehavioral and growth development was measured during lactation period（PND1～PND21）.Male and female offspring were separated into different cages on PND21.Adult F1 offspring were divided into three subgroups randomly.In the first group,mice were used for behavioral tests.In the second group,mice were sacrificed for molecular analysis.And in the last group,F1 males were mated with F1 females from control group to produce F2 offspring.Neurobehavioral and growth development were examined during lactation period.F2 males and F2 females were separated into different cages on PND21.Adult F2 males and F2 females were divided into two subgroups randomly.In the first group,mice were used for behavioral tests.In the second group,mice were sacrificed for molecular analysis.HE staining was used on brain sections of F1 and F2offspring to explore the effects of paternal fenvalerate exposure on hippocampal neurons.RT-PCR was used to detect the levels of TRα1,TRβ1,BDNF,Trk B and p75^NTRin F1 and F2 offspring.ResultsThere was no change on body weight and food intake of F0 males in different groups.Besides,paternal fenvalerate exposure did not alter body weight of F0 and F1pregnant mice.There was no difference on neurobehavioral and physical development in F1 offspring during lactation period among different groups.In Morris water maze,there was no difference on escape time among F1 males in the spatial training.Escape latency on the fifth day was increased in F1 females from the FEN-H group.Repeated measures showed that escape latency was longer in F1 females from FEN-H group than those from control group,whereas no difference on escape latency in F1 males was observed among different groups.No change was found on swimming speed between different groups.For probe test on the sixth day,F1 females from FEN-H group showed fewer times on crossing objective quadrants compared to controls.There was no change on swimming distance and time proportion in different groups.Hippocampal histopathology was assessed among F1 offspring.Despite of no difference on neural density in CA1 region,neural density in CA3 region was reduced in F1 females but not F1 males.In RT-PCR,no change on the expressions of TRα1and TRβ1 m RNAs was observed in F1 males among different groups.Moreover,there was no significant change on m RNA levels of BDNF,Trk B and p75^NTR,three downstream genes of TR pathway,in F1 males from different groups.Despite of no significant change on TRβ1 m RNA in F1 females,the expression of TRα1 m RNA was downregulated in F1 females from fenvalerate-exposed mice.Despite of no significant change on Trk B m RNA in F1 females,the expressions of BDNF and p75^NTRm RNAs,two downstream genes of TR pathway,were downregulated in F1females from fenvalerate-exposed mice.For F2 offspring,there was no difference on neurobehavioral and physical development in F2 offspring during lactation period among different groups.For spatial training trail in Morris water maze,no significant change on escape latency was observed among F2 males.Escape time on the fourth and fifth day was increased in F2 females from the FEN-H group.Further analysis showed that escape latency was longer in F2 females from FEN-H group than those from control group,whereas no change on escape latency in F2 males was observed among different groups（analyzed by repeated-measures ANOVA）.No change was found on swimming speed between different groups.For probe test on the sixth day,F2 females from FEN-H group showed less time proportion in the objective quadrant compared to controls.There was no change on swimming distance and times on crossing objective quadrants in different groups.Hippocampal histopathology was assessed among F2 males.No significant change on the number of neurons in hippocampal CA1 and CA3 regions was observed between different groups.Hippocampal histopathology was then assessed among F2 females.Despite of no difference on neural density in CA1 region,neural density in CA3 region was reduced in F2 females but not F2 males.In RT-PCR,no significant change on the expressions of TRα1 and TRβ1 m RNAs in F2 males was observed among different groups.Moreover,there was no significant change on m RNA levels of BDNF,Trk B and p75^NTR,three downstream genes of TR pathway,in F2 males from different groups.Despite of no significant change on TRβ1 m RNA in F2 females,the expression of TRα1 m RNA was downregulated in F2 females from fenvalerate-exposed mice.Accordingly,the expressions of BDNF,Trk B and p75^NTRm RNAs,three downstream genes of TR pathway,were downregulated in F2 females from fenvalerate-exposed mice.ConclusionsPaternal fenvalerate exposure impairs learning and memory partially through disturbing hippocampal TR signaling in female offspring.