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Changes in spontaneous activity of medialis dorsalis thalamic neurones during sleep and wakefulness
Electroencephalography and clinical Neurophysiology, 1988, 69:82-84
82
Elsevier Scientific Publishers Ireland, Ltd. EEG 02095
Short communication
Changes in spontaneous activity of medialis dorsalis thalamic neurones during sleep and wakefulness L. Imeri, M.E. Moneta 1 and M. Mancia Institute of Human Physiology 11, University of Milan, Milan (Italy) (Accepted for publication: 10 September 1987)
Summary In chronic unanaesthetized cats unitary activity of medialis dorsalis (MD) thalamic neurones was recorded during Wakefulness (W), slow wave (SWS) and desynchronized (DS) sleep. The discharge pattern of these neurones changes during SWS compared to W. Comparison between desynchronization of W and DS shows a change in the mean frequency, being higher in W than in DS. The results suggest that MD neurones participate in the organization of the sleep-wakefulness cycle. Key words: Medialis dorsalis; Sleep-wakefulness; Synchronization-desynchronization The stimulation of medial thalamic nuclei induces behavioural sleep (Hess 1944) and electrocortical rhythmic waves (Dempsey and Morrison 1942), while the experimental unilateral lesion of the same nuclei does not modify the sleepwakefulness cycle in any significant way (Angeleri et al. 1969). Microphysiological experiences have demonstrated changes in the unitary frequency and discharge pattern of some thalamic neurones during sleep and wakefulness (Mukhametov et al. 1970; Lamarre et al. 1971; Glenn and Steriade 1982; Steriade and Deschenes 1984; Steriade et al. 1986). Up to now the activity of the medialis dorsalis (MD) thalamic nucleus has only been related to the olfactory functions and to the processes of learning and memorization (Jones 1985). This nucleus has never been considered as a possible mediator of functions related to sleep and wakefulness. However, recent clinical data suggest that MD and anterior thalamic nuclei might have a role in the organization of sleep in man (Lugaresi et al. 1986). The aim of this investigation was to study the unitary activity of MD thalamic neurones during different stages of sleep and wakefulness.
Methods The experiments were performed on 2 adult, unanaesthetized cats, having a chronic implant for EEG, EOG, EMG and 1 Present address: Dept. of Preclinical Sciences, Faculty of Medicine, University of Chile, Santiago, Chile.
Correspondence to: Prof. Mauro Mancia, Director, Institute of Human Physiology II, University of Milan, Via Mangiagalli 32, 1-20133 Milan (Italy).
PGO wave recordings. Under Nembutal anaesthesia (40 mg/kg) the electrodes were implanted and a hole was bored in the calvarium, leaving the dura intact, to allow the penetration of the microelectrode. During recording graduated bars were inserted in 2 plastic cylinders, previously fixed onto the skull with screws and dental cement, in order to permit the head of the animal to be tightly restrained in a stereotaxic position without any pain or pressure. After recovery the animals were deprived of sleep the night preceding each experiment, which was performed placing the animals in a sphinx position and leaving them free to move their limbs. The activity of single neurones was recorded with tungsten microelectrodes (9-12 MI2 impedance) stereotaxicaUy lowered, through the intact dura, in the MD nucleus (A 8.5-9, L 1.5-2, H + 5 - + 1). Ten to 15 descents were made on each animal and only signals twice the amplitude of the background noise were recorded. Microcoagulations on the trace of the last penetration were made in order to verify the exact position of the microelectrode. After the end of the entire experiments the animals, in deep Nembutal anaesthesia were intracardiacally perfused with a solution of aldehydes in phosphate buffer. Histological examination was carried out on frozen frontal sections (50 #m thick), stained with the Nissl method. The signals obtained were recorded on magnetic tape for subsequent computerized analysis. The sleep-wakefulness cycle was divided, using standard polygraphic criteria, in attentive but relaxed wakefulness (W), slow wave sleep (SWS), desynchronized sleep (DS). The cells were recorded for about 20 rain and the analysis of the unitary activity was undertaken for each phase of the cycle for a 2 rain period, chosen far from the transition phases. For each stage of the cycle, the mean discharge frequency and the unitary pattern were studied with interspike interval histograms (ISIHs, bins of 2 msec).
0013-4649/88/$03.50 © 1988 Elsevier Scientific Publishers Ireland, Ltd.
M D NI3URONES D U R I N G SLEEP
83
Results
The activity of 63 neurones was recorded. Statistical analysis was performed in 27 cells recorded in W, 51 in SWS, 21 in DS, 25 both in W and SWS, 20 both in SWS and in DS, 11 in all 3 conditions. The mean discharge frequency for the cells recorded in all 3 phases of the sleep-wakefulness cycle was 9.0 _ 8.7 spikes/sec (average + S.D.) in W, 5.0 + 2.9 spikes/see in SWS, 6.3 + 6.8 spikes/sec in DS. The comparison between the mean frequencies in W and DS was the only one which proved to be statistically significant ( P < 0.05, Wilcoxon test). The discharge pattern of M D neurones changed in relation to the different phases of sleep and wakefulness (Fig. 1). During
A
W the neuronal discharge was continuous, unclustered and well spaced (Fig. la). Bursts of high frequency spikes characterized the neuronal activity during SWS (Fig. lb): each burst was formed by 3-15 spikes. The intraburst frequency in most cases ranged between 250 and 500 Hz and in other cases between 166 and 250 Hz. The bursts were irregularly spaced, with intervals ranging between 20 msec and over 1 sec. In DS the neuronal discharge again became continuous and fairly regular (Fig. lc). The analysis of the ISIHs (Fig. 1A, B, C) showed that in SWS (unlike what happened in W and DS) the events fell into the shortest intervals. During W only 12.2% of the intervals fell into the frequency range of 166-500 Hz, whereas in SWS 47.4% of the intervals were grouped into this range. This difference was statistically significant ( P < 0.01, Friedman test) and due to the discharge pattern during SWS.
w.sw.
W
C
@ > @ q-
o o
dr
2
o
200
msec
is°1 B
SWS b
8
10
12
14
16
18
20
I s w s [ ] os
o..o
. , i .............
msec
6
B p_
Z
o
4
°t
0 . 2 . 4. . 6 . .8 . 10. .12 .
14
16
14
16
~20.
18
200
D$ d , , ,lliit l.il ~.Li,J C r;;,,;,.--: ;,;,..,.,,,,r,,,m,,,,, q,_ 0
0
i
2
.
4
i
6
8
10
•
12
INTERSPIKE • Signlficative
dC 0
msec
200
Fig. 1. Interspike interval histograms (ISIHs, bins of 2 msec) of spontaneous activity of a single M D thalamic neurone, during wakefulness (A), slow wave (B) and desynchronized (C) sleep. Samples of spontaneous activity in the same neurone represented by the ISIH are shown during wakefulness (a), slow wave (b) and desynchronized (c) sleep. Calibration: 20 msec.
differences
INTERVALS
(Wilcoxon
test
i
18
i
20
(MSEC)
: p ¢ .05)
Fig. 2. Comparison of average interspike interval histograms (ISIHs) of different neurones recorded during wakefulness (W), slow wave (SWS) and desynchronized (DS) sleep. Only the first 10 interval classes (from 2 to 20 msec) are shown. A: comparison made on 25 neurones between W and SWS. B: comparison made on 20 neurones between SWS and DS. C: comparison made on 11 neurones between W and DS. Asterisks indicate the interval classes where the comparisons are statistically significant ( P < 0.05, Wilcoxon test).
84 In DS 16.6% of the events fell into the range 166-500 Hz. This value was significantly different ( P < 0.05, Friedman test) from only the one observed in SWS. For the first 10 interval classes (from 2 to 20 msec) the number of intervals observed in the various cells was compared in the different experimental phases. The histograms in Fig. 2 show the average intervals for each class, comparing W to SWS (Fig. 2A), SWS to DS (Fig. 2B) and W to DS (Fig. 2C). The asterisks indicate the interval classes where there was a statistically significant comparison ( P < 0.05, Wilcoxon test). The histogram in Fig. 2A shows that moving from W to SWS the number of shorter intervals increased, while that of the longer ones decreased. In DS, compared to SWS (Fig. 2B), there was a shift in the opposite direction: the number of intervals in the shorter classes decreased whilst it increased in the longer ones. The interval changes in W, compared to DS (Fig. 2C), did not prove to be statistically significant in any case.
Discussion The results suggest that MD thalamic neurones have a role in the organization of the different phases of sleep and wakefulness in the cat. Particularly the discharge pattern of these neurones changes when the animal moves from wakefulness to the synchronization of sleep. During desynchronization either in W or in DS the discharge pattern is similar but the average frequency undergoes significant changes, being higher in W as compared to DS. The behaviour of MD neurones during sleep and wakefulness seems different from that observed in ventrolateral (Lamarre et al. 1971), intralaminar (Glenn and Steriade 1982) and reticularis thalami nuclei (Mukhametov et al. 1970; Steriade et al. 1986). In these nuclei both average frequency and discharge pattern change during SWS when compared to W and DS, while the average frequency in W and DS is similar. The results seem to confirm the recent clinical (Lugaresi et al. 1986) and experimental (Marini et al. 1987) observations, which underline the importance of MD thalamic nucleus in the production and regulation of the sleep-wakefulness cycle.
L. IMERI*ET AL. The authors are deeply grateful to Dr. Maurizio Mariotti and Mr. Renato Calcaterra for the technical assistance and help in the elaboration of the data.
References
Angeleri, F., Marchesi, G.F. and Quattrini, A. Effects of chronic thalamic lesions on the electrical activity of the neocortex and on sleep. Arch. ital. Biol., 1969, 107: 633-667. Dempsey, E.W. and Morris,an, R.S. The production of rhythmically recurrent cortical potential after localized thalamic stimulation. Amer. J. Physiol., 1942, 135: 293-300. Glenn, L.L. and Steriade, M. Discharge rate and excitability of cortically projecting intralaminar thalamic neurons during waking and sleep states. J. Neurosci., 1982, 2: 1387-1404. Hess, W.R. Das Schlafsyndrom Ms Folge dienzephaler Reizung. Helv. physiol. Acta, 1944, 2: 305-344. Jones, E.G. The Thalamus. Plenum Press, New York, 1985: 935 pp. Lamarre, Y., Filion, M. and Cordeau, J.P. Neuronal discharge of the ventrolateral nucleus of the thalamus during sleep and wakefulness in the cat. I. Spontaneous activity. Exp. Brain Res., 1971, 12: 480-498. Lugaresi, E., Medori, R., Montagna, P., Baruzzi, A., Cortelli, P., Lugaresi, A., Tinuper, P., Zucconi, M. and Gambetti, P. Fatal familial insomnia and dysautonomia with selective degeneration of thalamic nuclei. New Engl. J. Med., 1986, 315: 997-1003. Marini, M., Imeri, L. and Mancia, M. Changes in sleep-waking cycle induced by lesions of medialis dorsalis nuclei in the cat. Neurosci. Lett., 1987, in press. Mukhametov, L.M., Rizzolatti, G. and Tradardi, V. Spontaneous activity of neurones of nucleus reticularis thalami in freely moving cats. J. Physiol. (Lond.), 1970, 210: 651-667. Steriade, M. and Deschenes, M. The thalamus as a neuronal oscillator. Brain Res. Rev., 1984, 8: 1-63. Steriade, M., Domich, L. and Oakson, G. Reticularis thalami neurons revisited: activity changes during shifts in states of vigilance. J. Neurosci., 1986, 6: 68-81.
82
Elsevier Scientific Publishers Ireland, Ltd. EEG 02095
Short communication
Changes in spontaneous activity of medialis dorsalis thalamic neurones during sleep and wakefulness L. Imeri, M.E. Moneta 1 and M. Mancia Institute of Human Physiology 11, University of Milan, Milan (Italy) (Accepted for publication: 10 September 1987)
Summary In chronic unanaesthetized cats unitary activity of medialis dorsalis (MD) thalamic neurones was recorded during Wakefulness (W), slow wave (SWS) and desynchronized (DS) sleep. The discharge pattern of these neurones changes during SWS compared to W. Comparison between desynchronization of W and DS shows a change in the mean frequency, being higher in W than in DS. The results suggest that MD neurones participate in the organization of the sleep-wakefulness cycle. Key words: Medialis dorsalis; Sleep-wakefulness; Synchronization-desynchronization The stimulation of medial thalamic nuclei induces behavioural sleep (Hess 1944) and electrocortical rhythmic waves (Dempsey and Morrison 1942), while the experimental unilateral lesion of the same nuclei does not modify the sleepwakefulness cycle in any significant way (Angeleri et al. 1969). Microphysiological experiences have demonstrated changes in the unitary frequency and discharge pattern of some thalamic neurones during sleep and wakefulness (Mukhametov et al. 1970; Lamarre et al. 1971; Glenn and Steriade 1982; Steriade and Deschenes 1984; Steriade et al. 1986). Up to now the activity of the medialis dorsalis (MD) thalamic nucleus has only been related to the olfactory functions and to the processes of learning and memorization (Jones 1985). This nucleus has never been considered as a possible mediator of functions related to sleep and wakefulness. However, recent clinical data suggest that MD and anterior thalamic nuclei might have a role in the organization of sleep in man (Lugaresi et al. 1986). The aim of this investigation was to study the unitary activity of MD thalamic neurones during different stages of sleep and wakefulness.
Methods The experiments were performed on 2 adult, unanaesthetized cats, having a chronic implant for EEG, EOG, EMG and 1 Present address: Dept. of Preclinical Sciences, Faculty of Medicine, University of Chile, Santiago, Chile.
Correspondence to: Prof. Mauro Mancia, Director, Institute of Human Physiology II, University of Milan, Via Mangiagalli 32, 1-20133 Milan (Italy).
PGO wave recordings. Under Nembutal anaesthesia (40 mg/kg) the electrodes were implanted and a hole was bored in the calvarium, leaving the dura intact, to allow the penetration of the microelectrode. During recording graduated bars were inserted in 2 plastic cylinders, previously fixed onto the skull with screws and dental cement, in order to permit the head of the animal to be tightly restrained in a stereotaxic position without any pain or pressure. After recovery the animals were deprived of sleep the night preceding each experiment, which was performed placing the animals in a sphinx position and leaving them free to move their limbs. The activity of single neurones was recorded with tungsten microelectrodes (9-12 MI2 impedance) stereotaxicaUy lowered, through the intact dura, in the MD nucleus (A 8.5-9, L 1.5-2, H + 5 - + 1). Ten to 15 descents were made on each animal and only signals twice the amplitude of the background noise were recorded. Microcoagulations on the trace of the last penetration were made in order to verify the exact position of the microelectrode. After the end of the entire experiments the animals, in deep Nembutal anaesthesia were intracardiacally perfused with a solution of aldehydes in phosphate buffer. Histological examination was carried out on frozen frontal sections (50 #m thick), stained with the Nissl method. The signals obtained were recorded on magnetic tape for subsequent computerized analysis. The sleep-wakefulness cycle was divided, using standard polygraphic criteria, in attentive but relaxed wakefulness (W), slow wave sleep (SWS), desynchronized sleep (DS). The cells were recorded for about 20 rain and the analysis of the unitary activity was undertaken for each phase of the cycle for a 2 rain period, chosen far from the transition phases. For each stage of the cycle, the mean discharge frequency and the unitary pattern were studied with interspike interval histograms (ISIHs, bins of 2 msec).
0013-4649/88/$03.50 © 1988 Elsevier Scientific Publishers Ireland, Ltd.
M D NI3URONES D U R I N G SLEEP
83
Results
The activity of 63 neurones was recorded. Statistical analysis was performed in 27 cells recorded in W, 51 in SWS, 21 in DS, 25 both in W and SWS, 20 both in SWS and in DS, 11 in all 3 conditions. The mean discharge frequency for the cells recorded in all 3 phases of the sleep-wakefulness cycle was 9.0 _ 8.7 spikes/sec (average + S.D.) in W, 5.0 + 2.9 spikes/see in SWS, 6.3 + 6.8 spikes/sec in DS. The comparison between the mean frequencies in W and DS was the only one which proved to be statistically significant ( P < 0.05, Wilcoxon test). The discharge pattern of M D neurones changed in relation to the different phases of sleep and wakefulness (Fig. 1). During
A
W the neuronal discharge was continuous, unclustered and well spaced (Fig. la). Bursts of high frequency spikes characterized the neuronal activity during SWS (Fig. lb): each burst was formed by 3-15 spikes. The intraburst frequency in most cases ranged between 250 and 500 Hz and in other cases between 166 and 250 Hz. The bursts were irregularly spaced, with intervals ranging between 20 msec and over 1 sec. In DS the neuronal discharge again became continuous and fairly regular (Fig. lc). The analysis of the ISIHs (Fig. 1A, B, C) showed that in SWS (unlike what happened in W and DS) the events fell into the shortest intervals. During W only 12.2% of the intervals fell into the frequency range of 166-500 Hz, whereas in SWS 47.4% of the intervals were grouped into this range. This difference was statistically significant ( P < 0.01, Friedman test) and due to the discharge pattern during SWS.
w.sw.
W
C
@ > @ q-
o o
dr
2
o
200
msec
is°1 B
SWS b
8
10
12
14
16
18
20
I s w s [ ] os
o..o
. , i .............
msec
6
B p_
Z
o
4
°t
0 . 2 . 4. . 6 . .8 . 10. .12 .
14
16
14
16
~20.
18
200
D$ d , , ,lliit l.il ~.Li,J C r;;,,;,.--: ;,;,..,.,,,,r,,,m,,,,, q,_ 0
0
i
2
.
4
i
6
8
10
•
12
INTERSPIKE • Signlficative
dC 0
msec
200
Fig. 1. Interspike interval histograms (ISIHs, bins of 2 msec) of spontaneous activity of a single M D thalamic neurone, during wakefulness (A), slow wave (B) and desynchronized (C) sleep. Samples of spontaneous activity in the same neurone represented by the ISIH are shown during wakefulness (a), slow wave (b) and desynchronized (c) sleep. Calibration: 20 msec.
differences
INTERVALS
(Wilcoxon
test
i
18
i
20
(MSEC)
: p ¢ .05)
Fig. 2. Comparison of average interspike interval histograms (ISIHs) of different neurones recorded during wakefulness (W), slow wave (SWS) and desynchronized (DS) sleep. Only the first 10 interval classes (from 2 to 20 msec) are shown. A: comparison made on 25 neurones between W and SWS. B: comparison made on 20 neurones between SWS and DS. C: comparison made on 11 neurones between W and DS. Asterisks indicate the interval classes where the comparisons are statistically significant ( P < 0.05, Wilcoxon test).
84 In DS 16.6% of the events fell into the range 166-500 Hz. This value was significantly different ( P < 0.05, Friedman test) from only the one observed in SWS. For the first 10 interval classes (from 2 to 20 msec) the number of intervals observed in the various cells was compared in the different experimental phases. The histograms in Fig. 2 show the average intervals for each class, comparing W to SWS (Fig. 2A), SWS to DS (Fig. 2B) and W to DS (Fig. 2C). The asterisks indicate the interval classes where there was a statistically significant comparison ( P < 0.05, Wilcoxon test). The histogram in Fig. 2A shows that moving from W to SWS the number of shorter intervals increased, while that of the longer ones decreased. In DS, compared to SWS (Fig. 2B), there was a shift in the opposite direction: the number of intervals in the shorter classes decreased whilst it increased in the longer ones. The interval changes in W, compared to DS (Fig. 2C), did not prove to be statistically significant in any case.
Discussion The results suggest that MD thalamic neurones have a role in the organization of the different phases of sleep and wakefulness in the cat. Particularly the discharge pattern of these neurones changes when the animal moves from wakefulness to the synchronization of sleep. During desynchronization either in W or in DS the discharge pattern is similar but the average frequency undergoes significant changes, being higher in W as compared to DS. The behaviour of MD neurones during sleep and wakefulness seems different from that observed in ventrolateral (Lamarre et al. 1971), intralaminar (Glenn and Steriade 1982) and reticularis thalami nuclei (Mukhametov et al. 1970; Steriade et al. 1986). In these nuclei both average frequency and discharge pattern change during SWS when compared to W and DS, while the average frequency in W and DS is similar. The results seem to confirm the recent clinical (Lugaresi et al. 1986) and experimental (Marini et al. 1987) observations, which underline the importance of MD thalamic nucleus in the production and regulation of the sleep-wakefulness cycle.
L. IMERI*ET AL. The authors are deeply grateful to Dr. Maurizio Mariotti and Mr. Renato Calcaterra for the technical assistance and help in the elaboration of the data.
References
Angeleri, F., Marchesi, G.F. and Quattrini, A. Effects of chronic thalamic lesions on the electrical activity of the neocortex and on sleep. Arch. ital. Biol., 1969, 107: 633-667. Dempsey, E.W. and Morris,an, R.S. The production of rhythmically recurrent cortical potential after localized thalamic stimulation. Amer. J. Physiol., 1942, 135: 293-300. Glenn, L.L. and Steriade, M. Discharge rate and excitability of cortically projecting intralaminar thalamic neurons during waking and sleep states. J. Neurosci., 1982, 2: 1387-1404. Hess, W.R. Das Schlafsyndrom Ms Folge dienzephaler Reizung. Helv. physiol. Acta, 1944, 2: 305-344. Jones, E.G. The Thalamus. Plenum Press, New York, 1985: 935 pp. Lamarre, Y., Filion, M. and Cordeau, J.P. Neuronal discharge of the ventrolateral nucleus of the thalamus during sleep and wakefulness in the cat. I. Spontaneous activity. Exp. Brain Res., 1971, 12: 480-498. Lugaresi, E., Medori, R., Montagna, P., Baruzzi, A., Cortelli, P., Lugaresi, A., Tinuper, P., Zucconi, M. and Gambetti, P. Fatal familial insomnia and dysautonomia with selective degeneration of thalamic nuclei. New Engl. J. Med., 1986, 315: 997-1003. Marini, M., Imeri, L. and Mancia, M. Changes in sleep-waking cycle induced by lesions of medialis dorsalis nuclei in the cat. Neurosci. Lett., 1987, in press. Mukhametov, L.M., Rizzolatti, G. and Tradardi, V. Spontaneous activity of neurones of nucleus reticularis thalami in freely moving cats. J. Physiol. (Lond.), 1970, 210: 651-667. Steriade, M. and Deschenes, M. The thalamus as a neuronal oscillator. Brain Res. Rev., 1984, 8: 1-63. Steriade, M., Domich, L. and Oakson, G. Reticularis thalami neurons revisited: activity changes during shifts in states of vigilance. J. Neurosci., 1986, 6: 68-81.