Synergistic effects of memantine and alpha7 nicotinic acetylcholine receptor agonist PHA-543613 to improve memory of aged rats

Abstract

Background: Combination treatments based on pharmacological interactions at α7 nicotinic acetylcholine receptors (nAChRs) are promising therapeutic approaches for neurocognitive disorders.

Methods: Here, we tested the cognitive efficacy of combinations of memantine with an α7 nAChR-selective agonist (PHA-543613) in naturally aged rats. Age-related changes in the expression of some key genes and proteins were also measured using quantitative polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA).

Results: Aged rats showed marked cognitive decline in the novel object recognition test, and they also exhibited cholinergic changes such as mRNA upregulation of α7 nAChRs. Upregulation of interleukin-1β, macrophage inflammatory protein 1α, CX3CL1, intercellular adhesion molecule 1, and ciliary neurotrophic factor mRNA was also detected in aged rats. Combination treatment of memantine and PHA-543613 successfully alleviated the age-related decline of recognition memory of rats by exceeding the effects of the corresponding monotreatments.

Conclusions: Results indicate a positive interaction between memantine and PHA-543613, which also reflects a putative role of α7 nAChRs in the cognitive enhancer effects of memantine. These findings may facilitate the development of combination therapies for age-related neurocognitive disorders.

Keywords: aging; alpha7 nicotinic acetylcholine receptor; behavior; cytokine; neurocognitive disorder.

Figure 1.

Comparison of the performance of aged and young animals in the NOR test (n_aged = 11, n_young = 12). (A) Young rats spent significantly more time exploring the novel object compared to the familiar one, while aged rats did not discriminate between the novel and the familiar objects. (B) Discrimination index (DI) of aged rats was significantly lower compared to young rats. Asterisks mark significant differences in the time spent with the exploration of the novel and the familiar objects: ***P < .001 (paired samples T-test). Hash indicates a significant difference between the DI of aged and young animals: #P < .05 (independent samples T-test). NOR, novel object recognition.

Figure 2.

Effects of monotreatments with memantine and PHA-543613 on the performance of aged rats in the NOR test. (A) Aged rats (n = 12) that received memantine in the lowest (0.1 mg/kg) and in the highest (1.0 mg/kg) doses showed preference toward the exploration of the novel object compared to the familiar one. (B) DI was not significantly increased by memantine treatment. (C) Aged rats (n = 13) that received PHA-543613 in 0.3 mg/kg and 1.0 mg/kg doses explored the novel object for a significantly longer time compared to the familiar one. (D) PHA-543613 in the lowest dose (0.3 mg/kg) improved DI of aged rats compared to the corresponding vehicle treatment. Asterisks mark significant differences in the time spent with the exploration of the novel and the familiar objects: ***P < .001, *P < .05 (paired samples T-test). Hash indicates significantly different DI compared to the corresponding vehicle treatment: #P < .05 (linear mixed-effect model + post hoc LSD). DI, discrimination index; NOR, novel object recognition.

Figure 3.

Effects of combination treatments with memantine and PHA-543613 on the performance of aged rats in the NOR test (n = 12). (A) Aged rats that received memantine alone and in combination with PHA-543613 spent more time exploring the novel object compared to the familiar one. (B) The memantine-PHA-543613 combination treatment significantly improved the DI of aged rats compared to the vehicle treatment. Asterisks mark significant differences between the exploration time of the novel and the familiar objects: **P < .01, *P < .05 (paired samples T-test). Hash indicates significantly different DI compared to the corresponding vehicle treatment: #P < .05 (linear mixed-effect model + post hoc LSD). DI, discrimination index; NOR, novel object recognition.

Figure 4.

Brain mRNA expression levels of inflammatory markers, neurotrophic factors, and the α7 nAChR in young, and cognitively unimpaired (AU) or impaired (AI) aged rats. (A-C) Neocortical (n_young = 5, n_AU = 4, n_AI = 5), striatal (n_young = 5, n_AU = 4, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) IL-1β mRNA levels. (D-F) Neocortical (n_young = 5, n_AU = 5, n_AI = 5), striatal (n_young = 5, n_AU = 5, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) MIP-1α mRNA levels. (G-I) Neocortical (n_young = 5, n_AU = 5, n_AI = 5), striatal (n_young = 5, n_AU = 4, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) CX3CL1 mRNA levels. (J-L) Neocortical (n_young = 5, n_AU = 4, n_AI = 5), striatal (n_young = 5, n_AU = 4, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) ICAM-1 mRNA levels. (M-O) Neocortical (n_young = 5, n_AU = 4, n_AI = 5), striatal (n_young = 5, n_AU = 5, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) CNTF mRNA levels. (P-R) Neocortical (n_young = 5, n_AU = 5, n_AI = 5), striatal (n_young = 5, n_AU = 5, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) BDNF mRNA levels. (S-U) Neocortical (n_young = 5, n_AU = 4, n_AI = 5), striatal (n_young = 5, n_AU = 4, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) α7 nAChR mRNA levels. Asterisks mark significant changes in mRNA expression levels compared to young animals: ***P < .001, **P < .01, *P < .05 (univariate ANOVA + post hoc LSD). CHRNA7, α7 nicotinic acetylcholine receptors; BDNF, brain-derived neurotrophic factor; CNTF, ciliary neurotrophic factor; ICAM-1, intercellular adhesion molecule 1; IL-1β, interleukin-1β; MIP-1α, macrophage inflammatory protein 1α.

Figure 5.

Brain protein expression levels (pg/µg protein) of inflammatory markers, neurotrophic factors, and α7-nAChRs in young, and cognitively unimpaired (AU) or impaired (AI) aged rats. (A-C) Neocortical (n_young = 4, n_AU = 3, n_AI = 3), striatal (n_young = 5, n_AU = 5, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) IL-1β protein levels. (D-F) Neocortical (n_young = 4, n_AU = 3, n_AI = 3), striatal (n_young = 5, n_AU = 5, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) MIP-1α protein levels. (G-I) Neocortical (n_young = 4, n_AU = 3, n_AI = 3), striatal (n_young = 4, n_AU = 6, n_AI = 4), and hippocampal (n_young = 5, n_AU = 6, n_AI = 5) CX3CL1 protein levels. (J-L) Neocortical (n_young = 4, n_AU = 3, n_AI = 3), striatal (n_young = 4, n_AU = 6, n_AI = 4), and hippocampal (n_young = 5, n_AU = 6, n_AI = 5) ICAM-1 protein levels. (M-O) Neocortical (n_young = 4, n_AU = 3, n_AI = 3), striatal (n_young = 5, n_AU = 5, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) CNTF protein levels. (P-R) Neocortical (n_young = 4, n_AU = 3, n_AI = 3), striatal (n_young = 5, n_AU = 5, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) BDNF protein levels. (S-U) Neocortical (n_young = 4, n_AU = 3, n_AI = 3), striatal (n_young = 5, n_AU = 5, n_AI = 5), and hippocampal (n_young = 5, n_AU = 5, n_AI = 5) α7 nAChR protein levels. Asterisks mark significant changes in protein expression levels compared to young animals: ** P < 0.01, * P < 0.05 (univariate ANOVA + post hoc LSD). α7 nAChR, α7 nicotinic acetylcholine receptors; BDNF, brain-derived neurotrophic factor; CNTF, ciliary neurotrophic factor; ICAM-1, intercellular adhesion molecule 1; IL-1β, interleukin-1β; MIP-1α, macrophage inflammatory protein 1α.