Abstract: Objective To investigate the effect of di-(2-ethylhexyl) phthalate(DEHP) on dendritic and synaptic morphology of hippocampal neurons in rats.Methods Cultured hippocampal neurons of rats at day 5 in vitro were exposed to DEHP for 5 days.After immunofluorescence staining,the neurons were morphologically observed under confocal laser scanning microscope,and the densities of dendritic filopodia,dendritic spine and synapse were analyzed.Furthermore,the expression level of synapsin was detected with Western blot.Results Exposures to DEHP at 100 nM,1 μM,and 10 μM for 5 days significantly reduced the densities of dendritic filopodia,spine,and synapse in the cultured hippocampal neurons.Compared with the control,the densities of dendritic filopodia,spine,and synapse after DEHP treatment at 1 μmol/L significantly reduced to 6.23±0.19,4.91±0.09,and 4.04±0.13/20 μm,respectively (P<0.01 for all).However,the inhibitive effect was partly rescued by ICI 182,780,an inhibiter of estrogen receptor (P<0.01).DEHP antagonized promotive effect of 17β-estradiol(17β-E2) on the morphological development of dendrite and synapse when DEHP was combined with 17β-E2(P<0.01).Furthermore,decreased expressions of synapsin I (0.53±0.08),post synaptic density protein 95 (PSD-95)(0.75±0.03),N-methyl-D-aspartic acid (NMDA) receptor 2B subunit (NR2B)(0.66±0.06),and phosphorylated extracellular signal-regulated kinase (ERK) 1/2(0.67±0.02)were found after 1 μM of DEHP treatment (P<0.01 for all).Conclusion DEHP may inhibit the development of dendritic and synaptic morphology of hippocampal neurons in rats through estrogen receptors,and decreased expressions of synaptic proteins and NMDA receptors and the inhibition of ERK1/2 signaling may be involved in the inhibitions,suggesting that DEHP has a toxic effect on the development of neurons.