Emotionality modulates the impact of chronic stress on memory and neurogenesis in birds

Abstract

Chronic stress is a strong modulator of cognitive processes, such as learning and memory. There is, however, great within-individual variation in how an animal perceives and reacts to stressors. These differences in coping with stress modulate the development of stress-induced memory alterations. The present study investigated whether and how chronic stress and individual emotionality interrelate and influence memory performances and brain neurogenesis in birds. For that, we used two lines of Japanese quail (Coturnix japonica) with divergent emotionality levels. Highly (E+) and less (E−) emotional quail were submitted to chronic unpredictable stress (CUS) for 3 weeks and trained in a spatial task and a discrimination task, a form of cue-based memory. E + and E− birds were also used to assess the impact of CUS and emotionality on neurogenesis within the hippocampus and the striatum. CUS negatively impacted spatial memory, and cell proliferation, and survival in the hippocampus. High emotionality was associated with a decreased hippocampal neurogenesis. CUS improved discrimination performances and favored the differentiation of newborn cells into mature neurons in the striatum, specifically in E+ birds. Our results provide evidence that CUS consequences on memory and neural plasticity depends both on the memory system and individual differences in behavior.

Training level reveals a dynamic dialogue between stress and memory systems in birds

“…CC-BY-NC-ND 4.0 International license made available under a (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is The copyright holder for this preprint this version posted January 6, 2021. ; https://doi.org/10.1101/2021.01.05.425468 doi: bioRxiv preprint reporting chronic stress that can negatively impact this memory system [1,3,6,7,15]. Moreover, the lowering of chronic stress effects on spatial memory performances after overtraining may be explained by a progressive acquisition of a predominant cue-based strategy to solve the spatial test over days of training.…”

“…To improve the unpredictability of the stressor delivery and decrease habituation to the stress procedure, each stressor occurred at unpredictable times each day during both night and day. The CUS procedure has been fully described and was shown to induce a state of chronic stress in quail [15,[26][27][28][29][30]. Briefly, some stressors were delivered directly in the home cage of the quail: confinement of the bird in the corner of its home cage for 30min, food frustration by placing transparent devices on the feeder just before light on for 30min, soft home cage shaking (2×15 min interspaced by 15 min), unexpected sounds (100 dB) composed of different sounds having or not biological signification for quail.…”

“…The following procedures and the arena used for the task were previously used and validated by our group in chickens and quails [13,15,32,33].…”

“…The third occasion of both tests (spatial and displacement tests) was conducted after an emotional challenge. This emotional challenge consisted of exposing the birds to an open field test, which is known to provoke anxiety-like quail behaviors [15,34,35]. Each quail was individually placed in the centre of a square arena (80 × 80 × 80 cm) of white wood with a beige linoleum floor.…”

“…As the cues from the environment are treated in relation to each other, the spatial memory is considered to be more complex than the cue-based memory, a non-declarative form of memory that results from a simple association between a salient cue and the target and is based on the striatum [9,12,13]. Studies have shown that chronic stress has a strong and negative impact on declarative memory, such as spatial memory [1,3,6,7,14,15], whereas it spares or even improves forms of non-declarative memory [5,6,15,16].…”