Adult neurogenesis mediates forgetting of multiple types of memory in the rat

Abstract

The formation and retention of hippocampus-dependent memories is impacted by neurogenesis, a process that involves the production of new neurons in the dentate gyrus of the hippocampus. Recent studies demonstrate that increasing neurogenesis after memory formation induces forgetting of previously acquired memories. Neurogenesis-induced forgetting was originally demonstrated in mice, but a recent report suggests that the same effect may be absent in rats. Although a general species difference is possible, other potential explanations for these incongruent findings are that memories which are more strongly reinforced become resilient to forgetting or that perhaps only certain types of memories are affected. Here, we investigated whether neurogenesis-induced forgetting occurs in rats using several hippocampus-dependent tasks including contextual fear conditioning (CFC), the Morris Water Task (MWT), and touchscreen paired associates learning (PAL). Neurogenesis was increased following training using voluntary exercise for 4 weeks before recall of the previous memory was assessed. We show that voluntary running causes forgetting of context fear memories in a neurogenesis-dependent manner, and that neurogenesis-induced forgetting is present in rats across behavioral tasks despite differences in complexity or reliance on spatial, context, or object memories. In addition, we asked whether stronger memories are less susceptible to forgetting by varying the strength of training. Even with a very strong training protocol in the CFC task, we still observed enhanced forgetting related to increased neurogenesis. These results suggest that forgetting due to neurogenesis is a conserved mechanism that aids in the clearance of memories.

Neurogenesis mediated plasticity is associated with reduced neuronal activity in CA1 during context fear memory retrieval

“…Post-natal neurogenesis in the hippocampus is strongly dependent on the age of the animal. Juvenile mice have significantly greater levels of neurogenesis than do aged mice, and the decrease in neurogenesis begins early in life 14 , 42 . Therefore, we sought to use age as an additional natural modulator of postnatal neurogenesis to examine differences in PNN expression.…”

Enhancement of neurogenesis and cognition through intranasal co-delivery of galanin receptor 2 (GALR2) and neuropeptide Y receptor 1 (NPY1R) agonists: a potential pharmacological strategy for cognitive dysfunctions

“…This aligns with the understanding that DCX expression in adult hippocampal neurogenesis is confined to the neuronal lineage. Therefore, the assessment of DCX-positive cells can serve as an indicator of the neurogenic effects induced by a specific treatment [ 57 , 58 ]. The procedure was performed as described for BrdU immunohistochemistry.…”

Nicotinic acetylcholine receptors and learning and memory deficits in Neuroinflammatory diseases

“…Some scientists in the field argued that there is insufficient evidence to sustain the existence of adult neurogenesis in humans, and that generation of neurons and their migration are limited to early childhood ( Curtis et al, 2012 ; Kumar et al, 2019a , 2020 ). Despite these suggestions, the research on adult neurogenesis continues growing, holding great promise for brain rehabilitation, and helping to modifying stressful memories ( Scott et al, 2021 ). Stimulating endogenous brain repair mechanisms would be more effective from an immunological and physiological point of view than using exogenous cell implantation approaches ( Sun, 2014 ; Poulose et al, 2017 ; Scott et al, 2021 ).…”

“…Despite these suggestions, the research on adult neurogenesis continues growing, holding great promise for brain rehabilitation, and helping to modifying stressful memories ( Scott et al, 2021 ). Stimulating endogenous brain repair mechanisms would be more effective from an immunological and physiological point of view than using exogenous cell implantation approaches ( Sun, 2014 ; Poulose et al, 2017 ; Scott et al, 2021 ). Opening opportunities stimulate scientists to study Neurogenesis in various aspects, including the search for controlling and modulating signals ( Shabani et al, 2021 ).…”