Qinghua Jin

The gut microbiome regulates multiple physiological processes of the host and plays a significant role in the adaptation of wild animal hosts to extreme environments. The saxaul sparrow (Passer ammodendri) is a typical bird species found in the northwest of China, characterized by its strong adaptability to extreme environments. Studying it can help reveal the microbial adaptation mechanisms of the host to extreme environments. Therefore, we conducted a comparative analysis of the intestinal microbial community characteristics and functions of the saxaul sparrow in high-altitude (Pamir Plateau) and desert (Tazhong Town) habitats in Xinjiang. The results of full-length 16S rRNA sequencing and species annotation indicated that the bacterial species composition (relative abundance > 0.1%) of the intestinal microbiota community of the saxaul sparrow was Candidatus Arthromitus sp. SFB rat Yit, Escherichia coli, Enterococcus faecium, Enterococcus faecalis, and Klebsiella pneumoniae, in sequence. In addition, Lysinibacillus sphaericus is a unique strain specific to the Tazhong group, while Stenotrophomonas maltophilia has a much higher abundance in the Tazhong group than in the Pamir Plateau group. It is worth noting that both groups of samples contain potential opportunistic pathogenic bacteria, such as Escherichia coli and Klebsiella pneumoniae. The Shannon index of the Pamir Plateau group was lower than that of the Tazhong Town group (p = 0.0026), indicating that the intestinal microbial diversity of the Pamir Plateau group was lower than that of the Tazhong Town group. However, there was no significant difference in the ACE index between the two groups and it was not statistically significant (p > 0.05). The Beta diversity analysis revealed that the distance between the two groups of samples was considerable (p = 0.001), indicating a significant separation. The functional annotation results indicated that the Pamir Plateau group exhibited enhanced capabilities in carbohydrate metabolism, energy metabolism, and DNA damage repair, while the Tazhong Town group demonstrated enhanced lipid metabolism and detoxification abilities. These findings will help reveal the possible impact of the living environment on the composition and function of the intestinal microbiota of the saxaul sparrow, fill the gap in comparative studies of the intestinal microbiota characteristics of the saxaul sparrow in two extreme environments, and provide new theoretical support for subsequent related research.

Obesity has been linked with the impairment of spatial memory and synaptic plasticity but the molecular mechanisms remained unidentified. Since glutamatergic transmission and NMDA receptor neural pathways in hippocampal dentate gyrus (DG) are essential in the learning and memory, we aimed to investigate glutamate (Glu) and NMDA receptor signaling of DG in spatial learning and memory in diet-induced obesity (DIO) rats. Spatial learning and memory were assessed via Morris water maze (MWM) test on control (Ctr) and DIO rats. Extracellular concentration of Glu in the DG was determined using in vivo microdialysis and HPLC. The protein expressions of NMDA receptor subunit 2B (NR2B), brain-derived neurotrophic factor (BDNF), the activation of calcium/calmodulin-dependent kinase II (CaMKII) and cAMP-response-element-binding protein (CREB) in the DG were observed by western blot. Spatial learning and memory were impaired in DIO rats compared to those of Ctr. NR2B expression was increased, while BDNF expression and CaMKII and CREB activation were decreased in DG of DIO rats. Extracellular concentration of Glu was increased in Ctr on the 3rd and 4th days of the MWM test, but significant further increment was observed in DIO rats. Microinjection of an NMDA antagonist (MK-801) into the DG reversed spatial learning and memory impairment. Such effects were accompanied by greater BDNF expression and CaMKII/CREB activation in the DG of DIO rats. In conclusion, the enhancement of Glu-NMDA receptor transmission in the hippocampal DG contributes to the impairment of spatial learning and memory in DIO rats, maybe via the modulation of CaMKII-CREB-BDNF signaling pathway.

The role of norepinephrine of the hippocampal dentate gyrus in spatial learning and memory alteration induced by chronic restraint stress (CRS, 3 h/day, 6 weeks) was investigated in aged rats. Spatial learning and memory were assessed by the Morris water maze (MWM), and the extracellular concentration of norepinephrine and amplitude of field excitatory postsynaptic potential (fEPSP) were measured in the dentate gyrus during MWM test in freely-moving rats. Next, the involvement of β-adrenoceptors in spatial learning and memory of CRS rats was examined by microinjection of its antagonist (propranolol) into the dentate gyrus. In addition, we observed the expression of brain-derived neurotrophic factor (BDNF) protein and activation of cAMP-response element binding protein (CREB) in the dentate gyrus. Compared with the control group, the basal level of norepinephrine, BDNF expression and CREB activation in the dentate gyrus were increased, and the spatial learning and memory abilities were enhanced in CRS rats. In the control group, the norepinephrine concentration and fEPSP amplitude in the dentate gyrus were increased on the second to fourth days of MWM test, and these responses were significantly enhanced in CRS rats. Furthermore, in CRS rats, propranolol significantly decreased the spatial learning and memory abilities, and attenuated the fEPSP response during MWM test, and the BDNF expression and CREB activation in the dentate gyrus. Our results suggest that norepinephrine activation of β-adrenoceptors in the hippocampal dentate gyrus is involved in spatial learning and memory enhancement induced by CRS in aged rats, in part via modulations of synaptic efficiency and CREB-BDNF signaling pathway.