Objective:

2

To investigate the effects and mechanisms of olfactory three-needle (OTN) electroacupuncture (EA) stimulation of the olfactory system on cognitive dysfunction

synaptic plasticity

and the gut microbiota in senescence-accelerated mouse prone 8 (SAMP8) mice.

Methods:

2

Thirty-six SAMP8 mice were randomly divided into the SAMP8 (P8)

SAMP8+OTN (P8-OT)

and SAMP8+nerve transection+OTN (P8-N-OT) groups according to a random number table (

n

=12 per group)

and 12 accelerated senescence-resistant (SAMR1) mice were used as the control (R1) group. EA was performed at the Yintang (GV 29) and bilateral Yingxiang (LI 20) acupoints of SAMP8 mice for 4 weeks. The Morris water maze test

transmission electron microscopy

terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) staining

Nissl staining

Golgi staining

Western blot

and 16S rRNA sequencing were performed

respectively.

Results:

2

Compared with the P8 group

OTN improved the cognitive behavior of SAMP8 mice

inhibited neuronal apoptosis

increased neuronal activity

and attenuated hippocampal synaptic dysfunction (

P

<

0.05 or

P

<

0.01). Moreover

the expression levels of synaptic plasticity-related proteins N-methyl-D-aspartate receptor 1 (NMDAR1)

NMDAR2B

synaptophysin (SYN)

and postsynaptic density protein-95 (PSD95) in hippocampus were increased by OTN treatment (

P

<

0.05 or

P

<

0.01). Furthermore

OTN greatly enhanced the brain-derived neurotrophic factor (BDNF)/cAMP-response element binding (CREB) signaling and phosphatidylinositol 3-kinase/protein kinase B/mammalian target of ra

pamycin (PI3K/AKT/mTOR) signaling compared with the P8 group (

P

<

0.05 or

P

<

0.01). However

the neuroprotective effect of OTN was attenuated by olfactory nerve truncation. Compared with the P8 group

OTN had a very limited effect on the fecal microbial structure and composition of SAMP8 mice

while specifically increased the genera

Oscillospira and Sutterella

(

P

<

0.05). Interestingly

the P8-N-OT group showed an abnormal fecal microbiota with higher microbial α-diversity

Firmicutes

/

Bacteroidetes

ratio and pathogenic bacteria (

P

<

0.05 or

P

<

0.01).

Conclusions:

2

OTN improved cognitive deficits and hippocampal synaptic plasticity by stimulating the olfactory nerve and activating the BDNF/CREB and PI3K/AKT/mTOR signaling pathways. Although the gut microbiota was not the main therapeutic target of OTN for Alzheimer's disease

the olfactory nerve was essential to maintain the homeostasis of gut microbiota.