Abstract
As an endogenous neuromodulator, hydrogen sulfide (H2S) exerts multiple biological effects in the brain. Previous studies have shown that H2S is involved in the regulation of neural synaptic plasticity and cognition in healthy rodents. It is well known that there is a progressive decline of cognitive function that occurs with increased age. The purpose of this study was to investigate the role of H2S in aging-associated amygdalar synaptic plasticity and cued fear memory deficits as well as to explore the underlying mechanisms. We found that H2S levels in the amygdala were significantly lower in aged rats when compared with healthy adult rates, which displayed significant deficits in long-term potentiation (LTP) in the thalamo-lateral amygdala (LA) pathway and amygdala-dependent cued fear memory. Bath application of an H2S donor, sodium hydrogen sulfide (NaHS), significantly reversed the impaired LTP in brain slices from aged rats, and intra-LA infusion of NaHS restored the cued fear memory in aged rats. Mechanismly, we found that H2S treatment significantly enhanced NMDAR-mediated synaptic responses in the thalamo-LA pathway of aged rats. Notably, GluN2B-containing NMDARs, but not GluN2A-containing NMDARs, contributed to the effects of H2S on aging-associated impairments of amygdalar LTP and fear memory, because applying GluN2B antagonist could abolish the beneficial effects of NaHS treatment on amygdalar LTP and cognitive performance in aged rats. Collectively, these results show that H2S can reverse aging-associated amygdalar synaptic plasticity and fear memory deficits by restoring the function of GluN2B-containing NMDARs, suggesting that supplement of H2S might be a therapeutic approach for aging-related cognitive disorders.
Highlights
Cognitive decline is a natural part of aging (Corey-Bloom et al, 1996; Bishop et al, 2010) and memory is normally the first cognitive domains to decline as individuals age (Singh-Manoux et al, 2012)
There was no significant difference in Paired-pulse facilitation (PPF) between the two groups (p > 0.05; Figure 1F), suggesting that impairment of amygdalar long-term potentiation (LTP) in aged rats should attribute to a modification in postsynaptic responsiveness, but not be from the altered release of the presynaptic neurotransmitter
Our primary finding was that supplementing aged rats with H2S can reverse deficits in cued fear memory and amygdalar N-methyl-d-aspartate receptor (NMDAR)-dependent LTP, which is a validated model of memory and learning
Summary
Cognitive decline is a natural part of aging (Corey-Bloom et al, 1996; Bishop et al, 2010) and memory is normally the first cognitive domains to decline as individuals age (Singh-Manoux et al, 2012). Mounting evidence has indicated that aging is associated with hypofunction of NMDARs in regions of the brain associated with synaptic plasticity, memory, and learning (Kumar, 2015). It is generally accepted that hypofunction of NMDARs contributes to impediments in memory and learning that occur with increased age (Das and Magnusson, 2011; Foster, 2012; Kumar and Foster, 2013; Li et al, 2017) and augmenting the expression and functional activity of the NMDAR subunit could overcome the cognitive impairments in aged animals (Slutsky et al, 2010; Robillard et al, 2011; Brim et al, 2013; Wang et al, 2014)
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