〔Abstract〕 To investigate the impact of mandibular retrognathism on brain function in rats and its poten- tial mechanisms．Methods Male SD rats aged 3 to 4 weeks ( w) were randomly divided into control group ( n = 10) and mandible retrusion ( MR) group ( n = 30) ，with the MR group further divided into three subgroups: 1，2， or 4 weeks，with 10 rats in each subgroup．The MR group used modified metal tubes，which were bonded to the lingual side of the maxillary incisors in rats，forcing the mandible to retract by 2－2. 5 mm，thereby achieving the goal of constructing a mandibular retrognathism model; the control group received no interventions．The effects of mandibular retraction on the spatial learning ability and memory ability of rats were explored by behavioral experi- ments such as Morris water maze，Y maze and new object recognition 1，2，and 4 weeks after modeling，respective- ly．Hematoxylin-eosin ( HE) and Nissl staining were employed to observe the histomorphological changes in CA1， CA3，and DG regions of hippocampal tissues．Immunohistochemistry was employed to detect the protein expression levels of tropomyosin receptor kinase B ( TrkB) in the CA1，CA3，and dentate gyrus ( DG) regions of the hippo- campus．Western blot was used to assess the expression changes in the TrkB / phosphoinositide 3-kinase ( PI3K) / protein kinase B ( AKT) pathway in hippocampal tissue．Quantitative analysis of apoptosis-related proteins in the hippocampus，including Bcl-2-associated X protein ( Bax) ，B-cell lymphoma-2 protein ( Bcl-2) ，and Caspase-3， was conducted using qRT-PCR and Western blot．Results Behavioral experiments showed that rats in the MR group，especially the MR 4 w group，were significantly weaker in learning and spatial memory than the control group，MR 1 w，and MR 2 w( P＜0. 05) ．HE staining showed that pyramidal cells in the control group were ar- ranged orderly with regular morphology．In contrast，the MR group exhibited a reduction in the number of cells in the hippocampal CA1，CA3，and dentate gyrus ( DG) regions．The cells were sparsely and irregularly arranged， with nuclear condensation and enlarged cellular spaces． Nissl staining further demonstrated damage to the Nissl bodies in the MR group．Meanwhile，the TrkB / PI3K / AKT signaling pathway was activated in the MR group，and the expression of p-TrkB，PI3K，and p-AKT proteins was up-regulated ( P ＜0. 05) ．Western blot and qRT-PCR indicated that MR up-regulated the expression of pro-apoptotic protein Bax，apoptotic effector protein Caspase-3 ( P＜0. 05) ，and inhibited the expression of anti-apoptotic protein Bcl-2 ( P ＜0. 05) ．Conclusion Mandibular retraction impairs brain function and affects cognition and learning memory in rats．This may be achieved by regula- ting the TrkB / PI3K / AKT signaling pathway to induce apoptosis in hippocampal neurons．