Nokia Miriam S, Lensu Sanna, Lehtonen Suvi-Maaria, Harjupatana Tero, Penttonen Markku
Department of Psychology and Centre for Interdisciplinary Brain Research, University of Jyväskylä, Jyväskylä, Finland.
Department of Physics, Nanoscience Center, University of Jyväskylä, Jyväskylä, Finland.
Hippocampus. 2025 Sep;35(5):e70035. doi: 10.1002/hipo.70035.
Neural activity and bodily functions are inherently rhythmic and related to each other. The occurrence of hippocampal sharp-wave ripples (SPW-Rs) and dentate spikes (DSs) supporting memory consolidation is regulated by the overall state of the brain, and they also seem to aggregate to a certain phase of the breathing cycle in naturally sleeping mice. Further, SPW-Rs and DSs synchronize to a variable degree between hemispheres, but how this is affected by the neural and bodily state is unclear. Here, we recorded dorsal hippocampal local-field potentials, electrocardiogram, and respiration for several hours under urethane anesthesia in adult male Sprague-Dawley rats. For a subset of rats, we injected atropine (50 mg/kg, i.p.) halfway into the recording to decrease cholinergic and parasympathetic tone. We found variable relation of hippocampal oscillations to breathing phase and none to the cardiac cycle phase. A decrease in breathing rate implying increased parasympathetic tone preceded the start of SPW-R bouts. Roughly 90% of DSs and half of SPW-Rs were unilateral. In most rats, SPW-Rs were more often bilateral during slow breathing compared to faster breathing. Atropine reduced the proportion of bilateral SPW-Rs. Both nonrapid eye movement sleep-like state and atropine increased the proportion of bilateral DSs under urethane anesthesia. Finally, in naturally sleeping rats, both DSs and SPW-Rs were bilateral ~60% of the time. In sum, urethane seems to desynchronize DSs but not SPW-Rs, and a low cholinergic and/or parasympathetic tone seems to dissociate SPW-Rs and to synchronize DSs in the two hippocampi. Whether these findings have relevance in terms of memory consolidation and behavior should be investigated in the future.
神经活动和身体功能本质上具有节律性且相互关联。支持记忆巩固的海马体尖波涟漪（SPW-Rs）和齿状回尖峰（DSs）的出现受大脑整体状态调节，并且在自然睡眠的小鼠中它们似乎聚集到呼吸周期的特定阶段。此外，SPW-Rs和DSs在半球之间以不同程度同步，但尚不清楚神经和身体状态如何影响这种同步。在此，我们在成年雄性Sprague-Dawley大鼠的乌拉坦麻醉下记录了数小时的背侧海马局部场电位、心电图和呼吸。对于一部分大鼠，我们在记录过程中中途注射阿托品（50 mg/kg，腹腔注射）以降低胆碱能和副交感神经张力。我们发现海马体振荡与呼吸相位之间存在可变关系，与心动周期相位无关。呼吸频率降低意味着副交感神经张力增加，这先于SPW-R发作的开始。大约90%的DSs和一半的SPW-Rs是单侧的。在大多数大鼠中，与快速呼吸相比，慢呼吸时SPW-Rs更常为双侧。阿托品降低了双侧SPW-Rs的比例。在乌拉坦麻醉下，非快速眼动睡眠样状态和阿托品都增加了双侧DSs的比例。最后，在自然睡眠的大鼠中，DSs和SPW-Rs大约60%的时间是双侧的。总之，乌拉坦似乎使DSs不同步，但不影响SPW-Rs，低胆碱能和/或副交感神经张力似乎使SPW-Rs分离并使两个海马体中的DSs同步。这些发现是否与记忆巩固和行为相关，有待未来研究。
