Neurotoxicity of different amyloid beta subspecies in mice and their interaction with isoflurane anaesthesia

Abstract

Background: The aim of this study was to assess different amyloid beta subspecies' effects on behaviour and cognition in mice and their interaction with isoflurane anaesthesia.

Methods: After governmental approval, cannulas were implanted in the lateral cerebral ventricle. After 14 days the mice were randomly intracerebroventricularly injected with Aβ 1-40 (Aβ40), Aβ 1-42 (Aβ42), 3NTyr10-Aβ (Aβ nitro), AβpE3-42 (Aβ pyro), or phosphate buffered saline. Four days after the injection, 30 mice (6 animals per subgroup) underwent general anaesthesia with isoflurane. A "sham" anaesthetic procedure was performed in another 30 mice (6 animals per subgroup, 10 subgroups in total). During the next eight consecutive days a blinded assessor evaluated behavioural and cognitive performance using the modified hole-board test. Following the testing we investigated 2 brains per subgroup for insoluble amyloid deposits using methoxy staining. We used western blotting in 4 brains per subgroup for analysis of tumour-necrosis factor alpha, caspase 3, glutamate receptors NR2B, and mGlu5. Data were analysed using general linear modelling and analysis of variance.

Results: Aβ pyro improved overall cognitive performance (p = 0.038). This cognitive improvement was reversed by isoflurane anaesthesia (p = 0.007), presumably mediated by decreased exploratory behaviour (p = 0.022 and p = 0.037). Injection of Aβ42 was associated with increased anxiety (p = 0.079). Explorative analysis on a limited number of brains did not reveal insoluble amyloid deposits or differences in the expression of tumour-necrosis factor alpha, NR2B, mGlu5, or caspase 3.

Conclusions: Testing cognitive performance after intracerebroventricular injection of different amyloid beta subspecies revealed that Aβ pyro might be less harmful, which was reversed by isoflurane anaesthesia. There is minor evidence for Aβ42-mediated neurotoxicity. Preliminary molecular analysis of biomarkers did not clarify pathophysiological mechanisms.

Fig 1. Neurocognitive function after anaesthesia in mice injected with different Aβ subspecies compared to control.

A: Time Trial (overall cognitive performance), B: Wrong choices total (declarative memory); mean of all tests on two days and standard error (whiskers).

Fig 2. Anxiety-related behavioural changes after anaesthesia in mice injected with different Aβ subspecies compared to control.

A: Time on Board, B: Latency First Board Entry (both anxiety); mean of all tests on two days and standard error (whiskers).

Fig 3. Behavioural parameters of mice injected with different Aβ subspecies after anaesthesia compared to control.

A: Correct Hole Visits (exploratory motivation), B: Line Crossings (locomotor activity); mean of all tests on two days and standard error (whiskers).

Fig 4. Total protein amount in sensory cortex and hippocampus.

A: Tumor necrosis factor alpha (TNF alpha), B: Caspase 3, C: N-methyl-D-aspartate receptor subunit 2B (NR2B); D: Metabotropic glutamate receptor 5 (mGlu5); median (horizontal lines), interquartile range (box) and range (whiskers).