Objective To investigate the effect of Lactobacillus casei on depressive behavior and the expression of NR1, NR2A receptor in postpartum depression rats induced by maternal separation. Methods Twenty-four Sprague-Dawley female rats were randomly divided into control group( CON group) (n=8),postpartum depression group(PPD group) (n=8),postpartum depression with lactobacillus casei group(PPD+ Lactobacillus casei group) (n=8). Rats of the control group were given no interventions. Rats in PPD group and PPD+Lactobacillus casei group were given maternal separation to establish depression model. And then the rats in PPD+Lactobacillus casei group were treated with Lactobacillus casei ( 8× 108CFU/(kg·d)) for 4 weeks after 14 days of maternal separation. The forced swimming test ( FST) was employed to detect the depressive behaviors. Lactobacillus,Bifidobacterium,Enterococcus faecalis and Esche-richia coli in cecum of rats and the expression of NR1 and NR2A mRNA in hippocampus of rats were detec-ted by real-time fluorescence quantitative PCR. Results Compared with CON group ((157. 50±8. 13) s), the immobility time of PPD group((200. 00±10. 35) s) was significantly longer (t=-3. 23,P<0. 05). Com-pared with PPD group,the immobility time of PPD+ Lactobacillus casei group ((153. 25±7. 41) s) was sig-nificantly shortened (t=3. 67,P<0. 05),and the depressive behavior was improved. Compared with CON group,the mRNA expression of Lactobacillus ((1. 47± 0. 08),t=-5. 87,P<0. 01),Enterococcus faecalis ((1. 23±0. 08),t=-2. 85,P<0. 05) and Escherichia coli( (1. 33±0. 07),t=-4. 96,P<0. 01) in caecum were significantly increased in PPD group, while that of Bifidobacterium decreased significantly (( 0. 65 ± 0. 07),t=5. 18,P<0. 01). Compared with PPD group,the mRNA expression of Lactobacillus ( ( 1. 05 ± 0. 05),t=3. 67,P<0. 01),Enterococcus faecalis ((0. 97±0. 05),t=2. 74,P<0. 05) and Escherichia coli ((1. 06±0. 05),t=3. 31,P<0. 01) were significantly decreased in PPD+ Lactobacillus casei group,while that of Bifidobacterium increased significantly ((0. 98± 0. 04),t=-4. 26,P<0. 01). Compared with CON group,the mRNA expression of NR1 receptor (( 0. 57 ± 0. 04), t=9. 65, P<0. 01) and NR2A receptor ((0. 60±0. 05),t=8. 64,P<0. 05) in hippocampus of rats in PPD group were significantly decreased. Com-pared with PPD group,the expression of NR1 receptor ((1. 01±0. 05),t=-5. 39,P<0. 01) and NR2A re-ceptor ((0. 98±0. 07),t=-3. 91,P<0. 05) in hippocampus were increased significantly in PPD+ Lactoba-cillus casei group. Conclusion Lactobacillus casei can improve the depressive behavior of postpartum depression in rats,and improve the intestinal flora,which affect the expression of NR1 and NR2A in hippocampus.

The opioid system plays an important role in memory processess. Morphine mimics endogenous opioids by acting on opioid receptor in brain to regulate memory. However, the effects of morphine on spatial memory acquisition are controversial. Also, little evidence has suggested that morphine could affect the retrieval of spatial memory. In the current study, effects of pre-training morphine and naloxone on the acquisition vs. retrieval of spatial reference vs. working memory were examined using discrete water maze tasks in C57BL/6 mice. Pre-training morphine administration (7.5 and 15 mg/kg, i.p.) impaired the acquisition of both spatial reference memory and working memory. Motivation to escape from the water maze was not affected by morphine. Pre-test morphine also inhibited the retrieval of spatial working memory but not reference memory. The effects of morphine on the acquisition and retrieval of spatial working memory were eliminated by naloxone pretreatment (1mg/kg). These results indicate that morphine could differentially modulate a variety of aspects of spatial memory and these effects are mediated by the mu-opioid receptor.