Department of Life Sciences and Biotechnology, University of Ferrara, Ferrara, Italy.
Institute of Biological and Chemical Systems, Biological Information Processing (IBCS-BIP), Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany.
Horm Behav. 2022 Sep;145:105244. doi: 10.1016/j.yhbeh.2022.105244. Epub 2022 Aug 18.
Teleosts display the highest level of brain plasticity of all vertebrates. Yet we still know little about how seasonality affects fish behaviour and the underlying cognitive mechanisms since the common neurobehavioral fish models are native to tropical environments where seasonal variation is absent or reduced. The medaka, Oryzias latipes, which inhabits temperate zone habitats, represents a promising model in this context given its large phenotypic changes associated with seasonality and the possibility to induce seasonal plasticity by only manipulating photoperiod. Here, we report the first extended investigation of seasonal plasticity in medaka behaviour and cognition, as well as the potential underlying molecular mechanisms. We compared medaka exposed to summer photoperiod (16 h light:8 h dark) with medaka exposed to winter photoperiod (8 h light:16 h dark), and detected substantial differences. Medaka were more active and less social in summer photoperiod conditions, two effects that emerged in the second half of an open-field and a sociability test, respectively, and might be at least in part related to habituation to the testing apparatus. Moreover, the cognitive phenotype was significantly affected: in the early response to a social stimulus, brain functional lateralisation shifted between the two hemispheres under the two photoperiod conditions, and inhibitory and discrimination learning performance were reduced in summer conditions. Finally, the expression of genes encoding key pituitary hormones, tshß and gh, and of the tshß regulatory transcription factor tef in the brain was increased in summer photoperiod conditions. This work reveals remarkable behavioural and cognitive phenotypic plasticity in response to photoperiod in medaka, and suggests a potential regulatory role for the same hormones involved in seasonal plasticity of other vertebrates.
硬骨鱼类表现出所有脊椎动物中最高水平的大脑可塑性。然而，由于常见的神经行为鱼类模型原产于热带环境，那里的季节性变化不存在或减少，我们仍然不太了解季节性如何影响鱼类的行为和潜在的认知机制。由于与季节性相关的大量表型变化以及仅通过操纵光周期即可诱导季节性可塑性，因此栖息在温带栖息地的青鳉（Oryzias latipes）是一种很有前途的模式生物。在这种情况下，我们首次对青鳉的行为和认知的季节性可塑性进行了扩展研究，并探讨了潜在的潜在分子机制。我们将暴露于夏季光周期（16 小时光照：8 小时黑暗）的青鳉与暴露于冬季光周期（8 小时光照：16 小时黑暗）的青鳉进行了比较，并发现了明显的差异。青鳉在夏季光周期条件下更活跃，社交性更低，这两种效应分别出现在开放场和社交性测试的后半部分，并且至少部分可能与对测试仪器的习惯化有关。此外，认知表型也受到显著影响：在对社交刺激的早期反应中，两个光周期条件下大脑功能的偏侧化在两个半球之间发生了变化，而在夏季条件下，抑制和辨别学习表现则降低了。最后，在夏季光周期条件下，编码关键垂体激素 tshβ和 gh 以及脑中 tshβ调节转录因子 tef 的基因的表达增加了。这项工作揭示了青鳉对光周期的显著行为和认知表型可塑性，并表明了同一激素在其他脊椎动物季节性可塑性中的潜在调节作用。
