19Background 20 Protection of organismal integrity involve physiological stress responses and behavioral 21 defenses. Recent studies in the roundworm Caenorhabditis elegans have shown that pathogen 22 and toxin exposure simultaneously stimulate cellular stress and detoxification responses and 23 aversive behavior. However, whether a coordinate regulation exists between cellular and 24 neurobehavioral defenses remains unclear.
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Results
26Here we show that exposure of C. elegans to high concentrations of naturally attractive food-27 derived odors, benzaldehyde and diacetyl, induces toxicity and aversive behavior. 28 Benzaldehyde preconditioning activates systemic cytoprotective stress responses involving 29 DAF-16/FOXO, SKN-1/Nrf and Hsp90 in somatic cells, which confer behavioral tolerance to 30 benzaldehyde and cross-tolerance to the structurally similar methyl-salicylate, but not to the 31 structurally unrelated diacetyl. In contrast, diacetyl preconditioning augments diacetyl 32 avoidance and does not induce apparent molecular defenses. Reinforcement of the experiences 33 using massed training forms relevant associative memories. Memory retrieval by the odor 34 olfactory cues leads to avoidance of food contaminated by diacetyl and context-dependent 35 behavioral decision to avoid benzaldehyde only if there is an alternative, food-indicative odor. 36 Conclusions 37 Our findings reveal a regulatory link between physiological stress responses and learned 38 behavior which facilitates self-protection in real and anticipated stresses. The potential 39 conservation of this somato-neuronal connection might have relevance in maladaptive avoidant 40 human behaviors.41 3 Background 42Adequate, coordinated responses of multicellular organisms are key to adapt to and 43 overcome fundamental alterations of the environment (1-3). These responses originate from 44 intracellular molecular defenses, such as the oxidative, xenobiotic, metabolic and proteotoxic 45 stress responses, which guard homeostasis and confer cytoprotection against the respective 46 stresses, promoting physiological adaptation, fitness and longevity at the organismal level (4).
47Adaptation also involve complex behavioral responses orchestrated by the neuroendocrine 48 system (5-7). For instance, sensory cues representing danger evoke aversive behavior as a result 49 of perception of multiple sensory stimuli, neuronal processing and decision making both in 50 humans and in other species (8-10). In some cases, the neural impulse of perceived danger is 51 so intense that the organism decides to avoid co-occurring cues representing life-sustaining 52 qualities such as food (6, 11). Besides external sensory cues, decision making is modulated by 53 neural context like arousal, motivation, and reward (12, 13). Importantly, behavioral decisions 54 are also influenced by sensory cues that evoke associative memories of past events (14).
55Moreover, exaggerated, inadequate avoidant behavior is characteristic to human anxiety 56 disorders such as phobias (11)...