Developmental Changes in Early Sharp Waves in the Hippocampus of Neonatal Rats
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Developmental Changes in Early Sharp Waves in the Hippocampus of Neonatal Rats V. V. Shumkova,1 V. R. Sitdikova,1 D. S. Suchkov,1 and M. G. Minlebaev1,2
UDC 612.82
Translated from Zhurnal Vysshei Nervnoi Deyatel’nosti imeni I. P. Pavlova, Vol. 70, No. 3, pp. 351–359, May–June, 2020. Original article submitted July 18, 2019. Revised version received December 2, 2019. Accepted December 16, 2019. Synchronized activity the hallmark of neural networks. Early sharp waves (eSPW) form one type of synchronized activity – these are synchronized network discharges of neuronal ensembles seen in the developing hippocampus. Despite the fact that eSPW may play a central role in coordinating neural activity and forming hippocampal functions, little is known of changes in eSPW during early postnatal development. Our experiments on neonatal rat pups using multichannel extracellular electrodes showed that during the first two weeks of postnatal life, along with reductions in the duration of eSPW, there were increases in their frequency and amplitude. We also found an increase in extracellular recorded activity of neurons in the pyramidal layer of the hippocampus. These data lead to the suggestion that the dynamics of changes in eSPW and overall network hippocampal activity are associated with the development of the hippocampal neural network and bottom-up neuromodulator projections. Keywords: early activity rhythms, hippocampus, development, neural network, early sharp waves, rats.
al., 2002; Sullivan et al., 2011; Laurent et al., 2015; Valeeva et al., 2019]. While in adult animals SPW is accompanied by high-frequency oscillations in the field potential in the pyramidal layer of the hippocampus (ripple) [Buzsáki et al., 1992; Traub and Bibbig, 2000], eSPW in the immature brain are often accompanied by multiple spikes in cells in the pyramidal layer, forming a so-called “tail” following eSPW for several seconds [Leinekugel et al., 2002]. eSPW are first detected from postnatal day 2 [Karlsson et al., 2006; Mohns et al., 2007; Mohns and Blumberg 2008]. Adult activity rhythms (θ, and δ, ripple) appear from week 2 [Buzsáki et al., 2003; Buhl and Buzsáki, 2005]. Despite the fact that the early postnatal period is characterized by the active formation of hippocampal neural networks and establishment of its functions, little is known about developmental changes in hippocampal activity patterns during this period. We report here an attempt to describe the developmental profile of eSPW in the first two weeks after birth in rodents. The data showed that aging of the animals was accompanied by a gradual increase in eSPW amplitude, seen both in the marginal (oriens) and radial (radiatum) layers of hippocam-
Sharp-wave events, or sharp waves (SPW) constitute the most synchronized rhythm of network activity in the adult hippocampus [Buhl and Buzsáki, 2005]. SPW are seen during slow-wave sleep, immobility, and when animals wash or take food [Lebovitz et al., 1971; MacVicar and Dudek, 1980]. Despite the fact that at the early stages of postnatal
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