Article Figures & Data
Figures
- Fig. 1.
Clonazepam (CZP) reversibly suppresses evoked oscillations in rat thalamic slices. Five simultaneous multiunit recordings from a rat thalamic slice in control conditions (left), during CZP application (middle), and after CZP washout (right). In each condition, the top three recordings are from thalamocortical neurons in the ventrobasal complex, and the bottom two recordings are from thalamic reticular neurons. In the top TRN trace, unit amplitude is small, so arrows point to the location of the last detected burst in each oscillation. The stimulus artifact is visible at the left of each recording. Calibration: 1 sec.
- Fig. 2.
Clonazepam (CZP) reversibly suppresses evoked oscillations in thalamic slices from wild-type (WT, top) mice and mice with mutations in the α1 subunit of the GABAA receptor (α1(H101R), middle), but not in slices from mice with mutant α3 subunits (α3(H126R), bottom). For each condition, control (left), CZP (middle), and washout (right), multiunit recordings from the same electrode during two consecutive evoked oscillations are shown. The stimulus artifact is visible at the left of each recording. Calibration: 500 msec.
- Fig. 3.
Comparison of the magnitude and washout of the clonazepam-mediated suppression of spikes during evoked oscillations in slices from rats, wild-type (WT) mice, α1(H101R) mice, and α3(H126R) mice. For each case, the total number of spikes in each evoked oscillation, relative to control, is plotted for various conditions (control, CZP application, and at 5 min intervals during drug washout). For rat slices, data from recordings in the ventrobasal complex (VB, ○) and the thalamic reticular nucleus (TRN, ▪) are plotted separately. In mouse slices, all recordings were made in VB. CZP significantly reduces the number of spikes during evoked oscillations in rat TRN, rat VB, WT mice, and α1 mutant mice but has no effect in α3 mutant mice (*p < 0.05; ***p < 0.001). Error bars indicate ± 1 SEM.
- Fig. 4.
Clonazepam (CZP) both suppresses spikes throughout oscillations and shortens the duration of oscillations.a, The number of spikes suppressed by CZP increases over the course of an oscillation. Each oscillation is divided into five time intervals (quintiles), each of which represents a successively later portion of the oscillation and contains one-fifth of the spikes in control conditions. For each quintile, the number of spikes in CZP relative to that in control is shown. In the VB and TRN of rats, CZP suppresses some spikes (20–30%) early in the oscillation and a much greater fraction (∼50%) late in the oscillation. In the VB of WT and α1(H101R) mice, the CZP-mediated suppression is initially small but grows progressively over the course of the oscillation. b, CZP significantly shortens the duration of evoked oscillations in rat TRN, rat VB, WT mouse VB, and α1(H101R) mouse VB (*p < 0.05; **p < 0.01), and this shortening reverses after CZP washout. In the VB of α3(H126R) mice, CZP prolongs the duration, but this is not statistically significant.
- Fig. 5.
Clonazepam (CZP) suppresses synchronous firing during evoked oscillations. We compared the bursts of synchronous population activity during oscillations in control conditions (solid black) with bursts at similar times during oscillations in CZP (gray) and after CZP washout (dotted black). Each burst shown here is an average computed from several sweeps from several experiments. In recordings from the TRN and VB of rats and from the VB of WT and α1(H101R) mice, the main effect of CZP is to suppress spikes at the peaks of the bursts.
- Fig. 6.
Binned spike counts (ratemeters) during four consecutive evoked oscillations in control (left) and CZP (right) during a recording from WT mouse VB. A single shock to internal capsule elicits a sustained oscillation, consisting of a series of bursts of population firing. The amplitude of early bursts is similar in control and CZP, but the later bursts are strongly suppressed in CZP, so that in the latter condition, oscillations come to a premature end. Each bar (‖) marks the center of a burst near the average time at which the third burst would occur during control oscillations in this recording. Calibration: horizontal, 500 msec; vertical, 5 spikes; bin width, 10 msec.
- Fig. 7.
Clonazepam (CZP) reduces the number of bursts in reticular neurons. Intracellular recordings from a reticular neuron in an α1 receptor mutant slice during evoked oscillations in three different conditions: application of 100 nm CZP (left), washout with control ACSF (middle), and subsequent application of 300 nm CZP (right). For each condition, the activity during four consecutive evoked oscillations is shown. Excluding the initial, stimulus-evoked burst (at left of each trace), this neuron consistently bursts three times in control ACSF, but only once or, rarely, twice in CZP. In the top three panels, bursts indicated by asterisks are shown on an expanded time scale in the insets to confirm that bursts consist of similar numbers of spikes in the three conditions: 100 nm CZP, wash, and 300 nmCZP.
- Fig. 8.
Clonazepam reduces the number of bursts, but not burst morphology, in multiunit activity recorded from TRN. Top, Multiunit recording from TRN in an α1(H101R) mouse in control conditions and after the application of 100 nm CZP (calibration: 1 sec). a and b show a population burst in each of the two conditions on an expanded time scale (calibration: 25 msec). Note the spikes of varying amplitudes and high interspike frequency, suggesting that the population burst contains spikes from multiple bursting RE cells. The top traces together with a and b show that fewer RE cell bursts occur in CZP than in control conditions. cand d show a burst, likely from a single RE cell, in the two conditions (calibration: 10 msec). In this experiment, one to three bursts that had similar spike morphologies and overall burst pattern were discernable in each control sweep compared with at most one burst from this presumed unit that was visible in each CZP sweep (data not shown). In both conditions, these bursts contained four to five spikes, consistent with the idea that although CZP may decrease the number of RE cell bursts, the number of spikes in each burst by this RE cell does not change dramatically.
Tables
Spike count in CZP (% of control) Change in duration after CZP application (msec) Period (msec) Control CZP Rat TRN 68 ± 6*** −359 ± 109** 170 ± 9 177 ± 10 Rat VB 64 ± 4* −417 ± 137** 165 ± 5 169 ± 9 WT mouse (VB) 87 ± 6* −279 ± 95* 139 ± 6 141 ± 7 α1(H101R) mouse (VB) 82 ± 6* −275 ± 102* 152 ± 4 146 ± 5 α3(H126R) mouse (VB) 103 ± 5 117 ± 99 141 ± 5 141 ± 7 * p < 0.05; ** p < 0.01; *** p < 0.001.
α1(H101R) Wild-type 1 Wild-type 2 Control 100 nmCZP Control 100 nm CZP Control 100 nm CZP Bursts/sweep 2.9 ± 0.2 1.3 ± 0.2*** 1.3 ± 0.4 0.3 ± 0.3* 6.0 ± 0 4.3 ± 0.6* Spikes/burst 4.3 ± 0.5 5.6 ± 0.7 2.7 ± 0.4 3 ± 0 1.4 ± 0.1 1.4 ± 0.2 Spikes immediately after intracellular stimulation 7.2 ± 0.2 7.3 ± 0.2 7.7 ± 0.2 8.0 ± 0 5 ± 0 4.8 ± 0.3 CZP reduces the number of bursts, but not spikes per burst, in intracellular recordings from RE cells. The number of bursts per evoked oscillation, the number of spikes per burst, and the number of spikes in the 50–100 msec immediately after internal capsule stimulation are shown for each of three intracellularly recorded RE cells. In every case, the number of bursts per oscillation is significantly reduced, whereas the number of spikes per burst and the number of spikes immediately after internal capsule stimulation remain unchanged. *p < 0.05; ***p < 0.001.
