Abstract
BackgroundData indicates anti-oxidant, anti-inflammatory and pro-cognitive properties of noradrenaline and analyses of post-mortem brain of Alzheimer's disease (AD) patients reveal major neuronal loss in the noradrenergic locus coeruleus (LC), the main source of CNS noradrenaline (NA). The LC has projections to brain regions vulnerable to amyloid deposition and lack of LC derived NA could play a role in the progression of neuroinflammation in AD. Previous studies reveal that intraperitoneal (IP) injection of the noradrenergic neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) can modulate neuroinflammation in amyloid over-expressing mice and in one study, DSP-4 exacerbated existing neurodegeneration.MethodsTASTPM mice over-express human APP and beta amyloid protein and show age related cognitive decline and neuroinflammation. In the present studies, 5 month old C57/BL6 and TASTPM mice were injected once monthly for 6 months with a low dose of DSP-4 (5 mg kg-1) or vehicle. At 8 and 11 months of age, mice were tested for cognitive ability and brains were examined for amyloid load and neuroinflammation.ResultsAt 8 months of age there was no difference in LC tyrosine hydroxylase (TH) across all groups and cortical NA levels of TASTPM/DSP-4, WT/Vehicle and WT/DSP-4 were similar. NA levels were lowest in TASTPM/Vehicle. Messenger ribonucleic acid (mRNA) for various inflammatory markers were significantly increased in TASTPM/Vehicle compared with WT/Vehicle and by 8 months of age DSP-4 treatment modified this by reducing the levels of some of these markers in TASTPM. TASTPM/Vehicle showed increased astrocytosis and a significantly larger area of cortical amyloid plaque compared with TASTPM/DSP-4. However, by 11 months, NA levels were lowest in TASTPM/DSP-4 and there was a significant reduction in LC TH of TASTPM/DSP-4 only. Both TASTPM groups had comparable levels of amyloid, microglial activation and astrocytosis and mRNA for inflammatory markers was similar except for interleukin-1 beta which was increased by DSP-4. TASTPM mice were cognitively impaired at 8 and 11 months but DSP-4 did not modify this.ConclusionThese data reveal that a low dose of DSP-4 can have varied effects on the modulation of amyloid plaque deposition and neuroinflammation in TASTPM mice dependent on the duration of dosing.
Highlights
Data indicates anti-oxidant, anti-inflammatory and pro-cognitive properties of noradrenaline and analyses of post-mortem brain of Alzheimer's disease (AD) patients reveal major neuronal loss in the noradrenergic locus coeruleus (LC), the main source of CNS noradrenaline (NA)
high performance liquid chromatography (HPLC) analyses At 8 months of age the level of NA in hippocampus or cortex of WT mice was not altered by DSP-4 treatment compared with vehicle treatment
The readouts we examined included NA levels and LC tyrosine hydroxylase (TH), Aβ protein deposition, neuroinflammation and behaviour following monthly intraperitoneal DSP-4 administration for either 3 or 6 months duration
Summary
Data indicates anti-oxidant, anti-inflammatory and pro-cognitive properties of noradrenaline and analyses of post-mortem brain of Alzheimer's disease (AD) patients reveal major neuronal loss in the noradrenergic locus coeruleus (LC), the main source of CNS noradrenaline (NA). Acute intraperitoneal (IP) administration of low-doses (50 μg kg-1) of the selective noradrenergic neurotoxin N(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4), in rat, potentiates the expression of pro-inflammatory genes in response to beta amyloid protein (Aβ) injection into the brain [15]. Higher doses of DSP-4 (two injections of 50 mg kg-1 spaced by a week,) have been assessed in APP23 mice, resulting in an exacerbation of AD relevant readouts at 6 months postinjection [21] These data suggest that NA release in the projection areas may underlie a protective mechanism, as well as an involvement in cognitive processes. As the LC NA system is compromised in AD [6], it is possible that this down-regulation of brain NA can contribute to the progression of disease
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