Allopregnanolone increases the number of dopaminergic neurons in substantia nigra of a triple transgenic mouse model of Alzheimer's disease

Abstract

More than a third of Alzheimer's disease (AD) patients show nigrostriatal pathway disturbances, resulting in akinesia (inability to initiate movement) and bradykinesia (slowness of movement). The high prevalence of this dysfunction of dopaminergic neuron in the nigrostriatal pathway in AD suggests that the risk factors for AD appear also significant risk factors for substantia nigra pars compacta (SNpc) lesions. Previously, we have demonstrated that allopregnanolone (APα) promotes neurogenesis and improves the cognitive function in a triple transgenic mouse model of AD (3xTgAD). In this study, we sought to exam 1) the SNpc lesions in 3xTgAD mice and 2) the impact of APα on promoting the regeneration of new dopaminergic neurons in SNpc of the 3xTgAD mice. The number of Nissl-stained total neurons, tyrosine hydroxylase (TH) positive neurons, and BrdU/TH double positive newly formed neurons were analyzed with unbiased stereology. In the SNpc of 3xTgAD mice, TH positive neurons was 47+- 18 % (p = 0.007), total neurons was 62 +-11.6 % (p = 0.016), of those in the SNpc of non-Tg mice, respectively. APα treatment increased the TH positive neurons in the SNpc of 3xTgAD mice to 93.2 +- 18.5 (p = 0.021 vs. 3xTgAD vehicle) and the total neurons to 84.9+- 6.6 (p = 0.046 vs. 3xTgAD vehicle) of non-Tg mice. These findings indicate that there is a loss of neurons, specifically the TH positive neurons in SNpc of 3xTgAD mice, and that APα reverses the lesion in SNpc of 3xTgAD by increasing the formation of new TH neurons.

Fig. (1)

Allopregnanolone reverses the decline of total neurons and tyrosine hydroxylase expressing neurons in substantia nigra of 3 month old male 3xTgAD mice. Representative immunofluorescent images of TH positive cells are presented in A. The representative Nissl-stained neurons and the optical fractionator counting frame are presented in B. The countable Nissl-stained neuron is marked with *. Scale bars = 50μm. The results of unbiased stereological counting of Nissl-stained neurons and TH neurons in SNpc are presented as mean ± SD and the statistical significance between groups is indicated. The ANOVA analysis indicated F(3,20) = 3.33; p = 0.04.

Fig. (2)

(A) Allopregananolone increases the newly formed (BrdU positive) TH expressing cells in SNpc of 3xTgAD mice. The representative BrdU (red) and TH (green) double positive (indicated by an arrow) immunofluorescent images are presented in A. The 3D volume-view of z-series images of the double immune-stained newly formed TH neuron in A demonstrates a co-localization of BrdU incorporation (nuclear) and TH (cytoplasm) IR in the same cell. Scale bar = 50μm. The number of BrdU/TH double positive cells are presented as mean ± SD and the statistical significance between groups are indicated. (B) The ANOVA analysis indicated F(3,20) = 3.20; p = 0.026.