Properties of slow oscillation during slow-wave sleep and anesthesia in cats

Abstract

Deep anesthesia is commonly used as a model of slow-wave sleep (SWS). Ketamine-xylazine anesthesia reproduces the main features of sleep slow oscillation: slow, large-amplitude waves in field potential, which are generated by the alternation of hyperpolarized and depolarized states of cortical neurons. However, direct quantitative comparison of field potential and membrane potential fluctuations during natural sleep and anesthesia is lacking, so it remains unclear how well the properties of sleep slow oscillation are reproduced by the ketamine-xylazine anesthesia model. Here, we used field potential and intracellular recordings in different cortical areas in the cat to directly compare properties of slow oscillation during natural sleep and ketamine-xylazine anesthesia. During SWS cortical activity showed higher power in the slow/delta (0.1-4 Hz) and spindle (8-14 Hz) frequency range, whereas under anesthesia the power in the gamma band (30-100 Hz) was higher. During anesthesia, slow waves were more rhythmic and more synchronous across the cortex. Intracellular recordings revealed that silent states were longer and the amplitude of membrane potential around transition between active and silent states was bigger under anesthesia. Slow waves were mostly uniform across cortical areas under anesthesia, but in SWS, they were most pronounced in associative and visual areas but smaller and less regular in somatosensory and motor cortices. We conclude that, although the main features of the slow oscillation in sleep and anesthesia appear similar, multiple cellular and network features are differently expressed during natural SWS compared with ketamine-xylazine anesthesia.

Figure 1.

Calculation of the amplitude of slow oscillation in the membrane potential during transitions from silent to active states. Columns 1 and 3 show recordings during slow-wave sleep and ketamine–xylazine anesthesia with clearly bimodal distribution of membrane potential, whereas columns 2 and 4 show recordings with clear silent and active states but no clear bimodality of the membrane potential distribution. b1–b4, Histograms of membrane potential distribution from 60 s segments from cells shown in a1–a4. c1–c4, Transitions from silent to active states (time 0 corresponding to the time at half-amplitude) and event-triggered average (thick black traces). All transitions of a 60 s segment are displayed in gray. d1–d4, Histograms of all gray segments shown in c (gray histogram). Histograms of event-triggered average are shown in black. Note the bimodal distribution for all recordings with this method.

Figure 2.

Fragments of continuous electrographic recordings during waking, slow-wave sleep, and ketamine–xylazine anesthesia. a, Traces of multiunit activity and local field potential in cortical area 3, EEG from area 5, EOG, and EMG recorded in one cat during indicated conditions. Corresponding recordings were obtained with the same electrodes. b, Autocorrelograms of the unit recording from the neuron shown in a. Insets, Fifty spikes and their average (gray line) of the unit shown in a for the three recorded states. Note a dramatic increase in rhythmicity of cortical activities under ketamine–xylazine anesthesia.

Figure 3.

Typical field potential and intracellular recordings from different cortical areas during natural slow-wave sleep and ketamine–xylazine anesthesia. a, Schematic representation of the location of electrodes for local field potential (black dots with numbers indicate recording sites for traces in b) and for intracellular recordings (pipette drawing, for traces in c–f). b, Field potentials recorded simultaneously in different cortical areas in one cat using the same set of chronically implanted electrodes, either during slow-wave sleep (left column) or under ketamine–xylazine anesthesia (right column). In slow-wave sleep recordings, note the most prominent slow oscillation in suprasylvian gyrus (electrode locations 8–10). In anesthesia recordings, note the high synchrony of slow waves at all locations. c–f, Typical segments of intracellular recordings during slow-wave sleep (left column) or ketamine–xylazine anesthesia (right column). Intracellular recordings: c, precruciate gyrus; d, postcruciate gyrus; e, marginal gyrus; and f, suprasylvian gyrus. The scale is the same for all intracellular traces. Gray dotted lines indicate −60 mV.

Figure 4.

Spectral composition of local field potentials is different during slow-wave sleep and anesthesia. a, Segment of LFP recorded in the right somatosensory cortex (area 3, top trace) and its high-frequency component (30–100 Hz, bottom trace) during SWS (a1) and under ketamine–xylazine anesthesia (a2). Recordings in a1 and a2 are from the same chronically implanted electrode in the same animal. b1, b2, Power spectra (0–100 Hz) of a 20 s epoch of the same recording as in a1, a2. Insets show a zoom-in of slow and delta (0.1–4 Hz), spindle (8–14 Hz), and gamma (30–100 Hz) frequency ranges. c, Mean ratio (ketamine–xylazine anesthesia/SWS) of the integral power in the three frequency ranges (0.1–4, 8–14, and 30–100 Hz). The mean power ratio was calculated from 10 pairs of 20 s epochs of LFP recorded from the same electrodes during anesthesia and SWS in different cortical locations. Note the higher power during SWS in 0.1–4 and 8–14 Hz but the large increase in gamma power under ketamine–xylazine anesthesia. *p < 0.05, **p < 0.01, ***p < 0.001, Wilcoxon's signed rank test for area specific comparisons, one-sample t test for pooled data.

Figure 5.

Rhythmicity of slow waves in local field potential and membrane potential is higher during ketamine–xylazine anesthesia than in SWS. a, b, Autocorrelograms of local field potential (columns 1 and 3) or membrane potential (columns 2 and 4) recorded either during slow-wave sleep (left columns) or during ketamine–xylazine anesthesia (right columns) in the precruciate gyrus. Examples in a and recording 1 of precruciate gyrus in color-coded panels in b show the same data. b, Each panel shows five typical examples of color-coded autocorrelations in four different cortical areas as indicated. Note the strong rhythmicity of both field potential and intracellular activities under ketamine–xylazine anesthesia as evidenced by periodically alternating peaks (red) and troughs (yellow) in the autocorrelograms. c, The magnitude of the second peak in autocorrelation of LFP and membrane potential during SWS and anesthesia in the four cortical areas. In all cases, the magnitude of the second peak was significantly higher under anesthesia (two-tailed Mann–Whitney test, *p < 0.05, **p < 0.01).

Figure 6.

Higher coherence of slow oscillation during ketamine–xylazine anesthesia than in slow-wave sleep. Coherence in the slow/delta frequency range (0.2–4 Hz; a1), in the spindle frequency range (8–14 Hz; a2), and in the gamma frequency range (30–100 Hz; a3) of LFPs recorded during ketamine–xylazine anesthesia plotted against coherence calculated from recordings made with the same electrodes but during slow-wave sleep (LFP recordings shown in Fig. 3b). b, Data from a1–a3 but plotted on the same scale. c, (panels above the diagonal, red–white–blue color code). The difference (anesthesia − slow-wave sleep) in coherence for each pair of recording sites for slow/delta frequencies (c1), spindle frequencies (c2), and gamma frequencies (c3). Blue colors indicate higher coherence during anesthesia; red colors indicate higher coherence during sleep. Note that most pairs show a stronger coherence during ketamine–xylazine anesthesia than during sleep (seen as a positive difference, blue). c (panels below the diagonal, green–yellow–brown), Coherence values for each pair of recording sites under ketamine–xylazine anesthesia. Recording sites are indicated as follows (see Fig. 3a). Somato, postcruciate gyrus; Motor, precruciate gyrus; PFC, frontal gyrus; Marg, marginal gyrus; Supra, suprasylvian gyrus. 1 is the most anterior, and 4 is the most posterior site.

Figure 7.

Silent states are more prominent during anesthesia than in SWS. a1, a2, Mean duration of silent states measured at half-amplitude transitions from active to silent and from silent to active states in intracellular recordings during sleep (black) or anesthesia (gray). a1, Comparison of the mean silent state duration during SWS and under anesthesia for each cortical area and pooled data from all areas. a2, Comparison between different areas during SWS and anesthesia. Note that duration of silent states is significantly longer under anesthesia than during SWS. b1, b2, Mean ratio of time spent in silent state over total time. Comparison scheme as in a. Note the longer time spent in silent states during anesthesia than during SWS. c1, c2, Mean amplitude of membrane potential shift between silent and active state during slow oscillation measured from intracellular recordings. Comparison scheme as in a. Note that pooled data show significantly larger membrane potential transition amplitude under anesthesia compared with SWS. Note that amplitude of membrane potential transition between silent and active states is significantly different between cortical areas during SWS but not during anesthesia. The number of cells recorded in each condition is indicated within each bar in a1. *p < 0.05, **p < 0.01, ***p < 0.001. a1–c1, Mann–Whitney test for n < 15, unpaired t test with Welch's correction for larger samples. a2–c2, Kruskal–Wallis test with Dunn's correction.