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. 2020 May 21;143(8):2341–2368. doi: 10.1093/brain/awaa072

Figure 4.

Figure 4

Pre-ictal and ictal temporal firing dynamics of absence seizures. (A) Average fluorescence changes indicate a decrease in firing in unidentified cortical layer 5 and 6 (but not layer 4) neurons of the visual cortex of non-anaesthetized, head-restrained stargazer mice that begins more than 2 s before and ends almost 2 s after the electrographic seizure. A similar decrease in total firing rate that start 2 s before seizure onset and terminates at seizure offset also occurs in identified fast-spiking (FS) interneurons of the cortical initiation network (CIN) and in ventrobasal thalamocortical (TC) neurons (blue trace) of freely moving GAERS rats, whereas the total firing GABAergic thalamic reticular neurons (green trace) decreases from 3 s before seizure onset but then show a persistent ictal increase until seizure offset. In contrast, there is an increase in T-channel mediated burst firing in ventrobasal thalamocortical (blue) and thalamic reticular neurons (green) neurons that begins ∼1 s prior to seizure onset and continues until seizure offset. (B) Timing of action potential output with respect to the EEG-spike of different neurons in cortico-thalamo-cortical and basal ganglia pathways are superimposed on a schematic spike-and-wave (light black line). Time zero indicates the peak of the EEG spike and individual brain regions are shown on the right. Data for cortico-thalamic CIN layer 5/6, substantia nigra, ventrobasal thalamocortical and reticular nucleus are from freely moving GAERS rats (Deransart et al., 2003; McCafferty et al., 2018b), whereas data from striatum, subthalamic nucleus, and globus pallidus are from GAERS rats under neurolept anaesthesia (Slaght et al., 2004; Paz et al., 2005, 2007). As the firing time of cortico-thalamic layer 5/6 neurons in the CIN of freely moving GAERS rats occurs about 10 ms earlier than that of the same GAERS neurons recorded under neurolept anaesthesia, the timing of cortico-subthalamic, cortico-striatal, cortico-thalamic CIN layer 2/3 and layer 4 neurons taken from GAERS under neurolept anaesthesia were modified accordingly. FS-INT = fast-spiking GABAergic interneurons; MSN = striatal medium spiny neurons. Open and filled symbols indicate inhibitory GABAergic and excitatory glutamatergic neurons, respectively. (A) Data for CIN FS interneurons are unpublished observations, the others were modified from McCafferty et al. (2018b) and Meyer et al. (2018).