1. Effects of hippocampal damage on pain perception in a rat model of Alzheimer's disease induced by amyloid-β and ibotenic acid injection into the hippocampus.
- Author
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Hayashi M, Kudo C, Hanamoto H, Maegawa H, Usami N, and Niwa H
- Subjects
- Animals, Male, Rats, Maze Learning drug effects, Maze Learning physiology, Proto-Oncogene Proteins c-fos metabolism, Pain Measurement, Memory Disorders etiology, Alzheimer Disease pathology, Alzheimer Disease metabolism, Alzheimer Disease chemically induced, Alzheimer Disease physiopathology, Amyloid beta-Peptides metabolism, Ibotenic Acid toxicity, Hippocampus metabolism, Hippocampus drug effects, Hippocampus pathology, Disease Models, Animal, Pain Perception drug effects, Pain Perception physiology, Rats, Sprague-Dawley, Peptide Fragments toxicity
- Abstract
Patients with Alzheimer's disease (AD) present with a variety of symptoms, including core symptoms as well as behavioral and psychological symptoms. Somatosensory neural systems are generally believed to be relatively unaffected by AD until late in the course of the disease; however, somatosensory perception in patients with AD is not yet well understood. One factor that may complicate the assessment of somatosensory perception in humans centers on individual variations in pathological and psychological backgrounds. It is therefore necessary to evaluate somatosensory perception using animal models with uniform status. In the current study, we focused on the hippocampus, the primary site of AD. We first constructed a rat model of AD model using bilateral hippocampal injections of amyloid-β peptide 1-40 and ibotenic acid; sham rats received saline injections. The Morris water maze test was used to evaluate memory impairment, and the formalin test (1 % or 4 % formalin) and upper lip von Frey test were performed to compare pain perception between AD model and sham rats. Finally, histological and immunohistochemical methods were used to evaluate tissue damage and neuronal activity, respectively, in the hippocampus. AD model rats showed bilateral hippocampal damage and had memory impairment in the Morris water maze test. Furthermore, AD model rats exhibited significantly less pain-related behavior in phase 2 (the last 50 min of the 60-minute observation) of the 4 % formalin test compared with the sham rats. However, no significant changes were observed in the von Frey test. Immunohistochemical observations of the trigeminal spinal subnucleus caudalis after 4 % formalin injection revealed significantly fewer c-Fos-immunoreactive cells in AD model rats than in sham rats, reflecting reduced neuronal activity. These results indicate that AD model rats with hippocampal damage have reduced responsiveness to persistent inflammatory chemical stimuli to the orofacial region., Competing Interests: Declaration of competing interest None., (Copyright © 2024. Published by Elsevier Inc.)
- Published
- 2024
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