- Email: [email protected]
Arousal episodes during sleep in the neonatal rat
Neuroscience Letters, 42 (1983)45--48 Elsevier Scientific Publishers Ireland Ltd.
AROUSAL EPISODES DURING SLEEP IN THE NEONATAL RAT
MICHAEL CORNER and MAJID MIRMIRAN
Netherlands Institute for Brain Research, Postbus, 41850, 1009 DB Amsterdam (The Netherlands) (Received June 16th, 1983; Accepted August 30th, 1983)
Key words: arousal - sleep ontogeny - chloral hydrate - chlorimipramine
Hippocampal EEG and neck EMG activity were recorded in restrained as well as in unrestrained rat pups following treatment with drugs which selectively suppress wakefulness and active sleep, respectively. Chloral hydrate did not affect active sleep but eliminated the bursts of coordinated total-body movements which were seen during sleep, especially under conditions of restraint. Chlorimipramine, in contrast, suppressed active sleep while sparing the coordinated total-body motility. It is concluded that these latter movements represent an episodic arousal phenomenon, against a background of quiet sleep, which becomes intensified under certain postural conditions.
Spontaneous motility during sleep in neonatal rats shows some striking similarities with prenatal vertebrate behavior patterns ;,for review see refs. 2 and 9). Three main classes of movements have been distinguished in the late chick embryo [6], one of which - localized, irregular twitching of the somatic musculature: 'type 1' motility - closely resembles active sleep (AS) both phenomenologically and pharmacologically [10]. In addition, brief bursts of stereotyped rotatory body movements occur frequently at late embryonic stages ('type IW motility), which respond pharmacologically in a manner suggestive of wakefulness [8]. Avian hatching behavior is comprised of strikingly similar movements [2, 3, 6, 81, and these too have been suggested to represent a phenomenon of episodic arousal, against a background of quiet sleep [1]. Indeed, such movements were able to be selectively suppressed, both in embryonic and in hatching chicks, by sedatives such as chloral hydrate while being spared by chlorimipramine, a drug which eliminated muscle twitching along with all other signs of AS [4] (also see ref. 7). Phenomenologically similar bursts of brief rotatory movements occur during sleep in the neonatal tat [2, 4]. It is not known with certainty, however, whether or not this striking form of early postnatal behavior in mammals deserves to be classified as 'arousal', cq. wakefulness. We have therefore examined the effect upon spontaneous motility in a mammalian species (Rattus norvegicus) of drugs which selectively suppress either active sleep or waking. Four 2-day-old Wistar rat pups were implanted with insulated wire electrodes [7]
46
for chronic recording of neck muscle activity (EMG). Either chloral hydrate (200 mg/kg) or chlorimipramine (30 mg/kg) was injected intraperitoneally on the following day. The latter treatment had the effect of completely suppressing local muscle twitching (i.e. type-I motility) for more than 3 h in both cases (also see ref. 7), but spared the frequent startles and rotatory movement bursts (motility types II and Ill) which punctrate behavioral sleep at this age (Fig. 1). Chloral hydrate had the opposite effect in the other two experimental animals, with the type-III movements being absent for several hours. These results support the hypothesis that certain classes of neonatal motility displayed during behavioral sleep (viz., variable twitching vs rotation and/or startles) correspond physiologically to AS and wakefulness, respectively. Stereotyped total-body bursts can be induced during sleep in older rat pups by means of appropriate restraint [5], and the resulting 'quasi-struggling" movements bear a striking resemblance to avian hatch behavior [1, 6]. Since this phenomenon offers an opportunity for further studying the physiological basis of different types of sleep movements, 6 rats were implanted with electrodes for recording hippocampal EEG and neck EMG activity, and were than studied for 4-5 h each at 19 days after birth. Typical AS continued to occur regularly under such restrained conditions but the characteristic hippocampal theta-waves consistently disappeared prior to each episode of quasi-struggle movements (Fig. 2). The struggle bursts, moreover, were always interspersed with EEG epochs resembling quiet (i.e. 'slowwave') rather than active sleep. The observation that this kind of motility disappeared in all three of the animals which were sedated with chloral hydrate, despite the persistence of active sleep, is consistent with its interpretation as a manifestation of wakefulness rather than of sleep mechanisms. Chlorimipramine, on the other hand, caused a long-lasting suppression of AS (also see ref. 7) in the other three restrained animals, without preventing the appearance of episodic struggling movements (Fig. 3). However, the hypotonia which hitherto terminated most such arousals (see Fig. 2B) was replaced by a post-burst
vr
'
"
'
'
r
Fig. 1. Actograms (80 sec stretches from two typical records) illustrating the effect of chlorimipramine on spontaneous motility in a 3-day-old Wistar rat. Motor activity prior to injection of the drug (upper trace) includes continual localized twitching ('type-I' motility) which largely disappears for several hours post-injection (losser tlace), leaving only "startles'; and rotatory movements (types II and 111, respectively).
47
EEG
,
A=I
+
,
-.,
--,.
,.r . . . . .
" - ~ "
:
,
'" ""+ ..... "'"
-~:
+"'~
:,
-
-
~''~~~~~~+*+/::~I
T
200 uv /
1
11 s e c
EEG iill EMG::-~::
.;--,: . . . . . . . . . . . . . . . . . . : . . . .
~+![" ,
!tit
, + It-
-
--
--
. . . . . . . .
:-
-----~::
__lll.Lr~ip
,,
.,,,
Fig. 2. Spontaneous movements during sleep in a 19-day-old Wistar rat. A(I,2): active sleep under unrestrained conditions, showing characteristic theta waves in the hippocampal EEG (upper traces) which are interrupted during bursts of gross body movements; slow-wave sleep typically follows each of these brief arousal episodes. B(l,2): sleep during restraint in the same animal, confirming the occurrence of active as well as slow-wave sleep under such conditions; hippocampal theta-waves are invariably replaced by a slow-wave sleep EEG pattern at the onset of stereotyped struggling behavior, while EMG hypotonia occurs inbetween the motor bursts (lower trace).
f
,!
Fig. 3. Spontaneous quasi-struggle movements in a restrained Wistar rat pup (19 days old) following injection of chlorimipramine. The hippocampal EEG (upper trace) is now devoid of visible theta-wave activity throughout sleep, and the EMG (lower trace) no longer shows muscle atonia following any of the arousal episodes. A l-min stretch from a typical record is shown.
48
EMG pattern which mimicked that seen in unrestrained sleeping animals (see Fig. 2A). This last finding suggests that AS brain mechanisms, while clearly not involved in the actual triggering of arousal episodes during sleep, may nevertheless account for their exceedingly abrupt termination under conditions of severe restraint. 1 Bakhuis, W.L. and Bour, H.L., Climax (hatching) behavior, and its relation to sleep and wakefulness, in T. Ookawa (Ed.), Brain and Behavior of the Fowl, Japan Sci. Soc. Press, Tokyo, 1983, pp. 159- i 69. 2 Corner, M.A., Spontaneous motility rhythms during early development - phenomenological and neurophysiological considerations. In M.A. Corner et al. (Eds.), Maturation of the Nervous System, Progr. Brain Res., Vol. 48. Elsevier, Amsterdam, 1978, pp. 349-366. 3 Corner, M.A. and Bakhuis, W.L., Cerebral electrical activity, forebrain function and behavior in the chick at the time of hatching, Brain Res., 13 (1969), 541-555. 4 Corner, M.A., Bour. H.L. and Mirmiran, M., Development of spontaneous motility, and its physiological interpretation in the rat, chick and frog. in E. Meisami and M. Brazier (Eds.), Neural Growth and Differentiation, Raven Press, New York, 1979, pp. 253-267. 5 Corner. M.A. and Kwee, P., Cyclic EEG and motility patterns during sleep in restrained infant rats, Electroenceph. clin. Neurophysiol., 41 (1976) 64-72. 6 Hamburger, V. and Oppenhei~a, R.W., Prehatching motility and hatching behavior in the chick, J. exp. Zool., 166 (1967) 171-204. 7 Mirmiran, M., Van de Poll, N., Corner, M., Van Oyen, H. and Bour, H., Suppression of active sleep by chronic treatment with chlorimipramine during early postnatal development: effects upon adult sleep and l;-havior in the rat, Brain Res., 204 (1981) 129-146. 80ppenheim, R.V~., Experimental studies on hatching behavior in the chick, IV. Evidence for the role of a noradrenergic mechanism, J. exp. Zool., 204 (1978)95-112. 90ppenheim, R.W., The neuroembryological study of behavior: progress, problems, perspectives, in R.K. Hunt (Ed.), Neural Development (Ill): Neuronal Specificity, Plasticity and Patterns; Current Topics in Developmental Biology, Vol. 17, Academic Press, New York, 1982, pp. 257-310. i0 Sedlacek, .I. and Corner, M.A., Monoaminergic regulation of spontaneous motility in the chick embryo. In T. Ookawa (Ed.), Brain and Behavior in the Fowl, Japan Sci. Soc. Press, Tokyo, 1983, pp. 61-70.
AROUSAL EPISODES DURING SLEEP IN THE NEONATAL RAT
MICHAEL CORNER and MAJID MIRMIRAN
Netherlands Institute for Brain Research, Postbus, 41850, 1009 DB Amsterdam (The Netherlands) (Received June 16th, 1983; Accepted August 30th, 1983)
Key words: arousal - sleep ontogeny - chloral hydrate - chlorimipramine
Hippocampal EEG and neck EMG activity were recorded in restrained as well as in unrestrained rat pups following treatment with drugs which selectively suppress wakefulness and active sleep, respectively. Chloral hydrate did not affect active sleep but eliminated the bursts of coordinated total-body movements which were seen during sleep, especially under conditions of restraint. Chlorimipramine, in contrast, suppressed active sleep while sparing the coordinated total-body motility. It is concluded that these latter movements represent an episodic arousal phenomenon, against a background of quiet sleep, which becomes intensified under certain postural conditions.
Spontaneous motility during sleep in neonatal rats shows some striking similarities with prenatal vertebrate behavior patterns ;,for review see refs. 2 and 9). Three main classes of movements have been distinguished in the late chick embryo [6], one of which - localized, irregular twitching of the somatic musculature: 'type 1' motility - closely resembles active sleep (AS) both phenomenologically and pharmacologically [10]. In addition, brief bursts of stereotyped rotatory body movements occur frequently at late embryonic stages ('type IW motility), which respond pharmacologically in a manner suggestive of wakefulness [8]. Avian hatching behavior is comprised of strikingly similar movements [2, 3, 6, 81, and these too have been suggested to represent a phenomenon of episodic arousal, against a background of quiet sleep [1]. Indeed, such movements were able to be selectively suppressed, both in embryonic and in hatching chicks, by sedatives such as chloral hydrate while being spared by chlorimipramine, a drug which eliminated muscle twitching along with all other signs of AS [4] (also see ref. 7). Phenomenologically similar bursts of brief rotatory movements occur during sleep in the neonatal tat [2, 4]. It is not known with certainty, however, whether or not this striking form of early postnatal behavior in mammals deserves to be classified as 'arousal', cq. wakefulness. We have therefore examined the effect upon spontaneous motility in a mammalian species (Rattus norvegicus) of drugs which selectively suppress either active sleep or waking. Four 2-day-old Wistar rat pups were implanted with insulated wire electrodes [7]
46
for chronic recording of neck muscle activity (EMG). Either chloral hydrate (200 mg/kg) or chlorimipramine (30 mg/kg) was injected intraperitoneally on the following day. The latter treatment had the effect of completely suppressing local muscle twitching (i.e. type-I motility) for more than 3 h in both cases (also see ref. 7), but spared the frequent startles and rotatory movement bursts (motility types II and Ill) which punctrate behavioral sleep at this age (Fig. 1). Chloral hydrate had the opposite effect in the other two experimental animals, with the type-III movements being absent for several hours. These results support the hypothesis that certain classes of neonatal motility displayed during behavioral sleep (viz., variable twitching vs rotation and/or startles) correspond physiologically to AS and wakefulness, respectively. Stereotyped total-body bursts can be induced during sleep in older rat pups by means of appropriate restraint [5], and the resulting 'quasi-struggling" movements bear a striking resemblance to avian hatch behavior [1, 6]. Since this phenomenon offers an opportunity for further studying the physiological basis of different types of sleep movements, 6 rats were implanted with electrodes for recording hippocampal EEG and neck EMG activity, and were than studied for 4-5 h each at 19 days after birth. Typical AS continued to occur regularly under such restrained conditions but the characteristic hippocampal theta-waves consistently disappeared prior to each episode of quasi-struggle movements (Fig. 2). The struggle bursts, moreover, were always interspersed with EEG epochs resembling quiet (i.e. 'slowwave') rather than active sleep. The observation that this kind of motility disappeared in all three of the animals which were sedated with chloral hydrate, despite the persistence of active sleep, is consistent with its interpretation as a manifestation of wakefulness rather than of sleep mechanisms. Chlorimipramine, on the other hand, caused a long-lasting suppression of AS (also see ref. 7) in the other three restrained animals, without preventing the appearance of episodic struggling movements (Fig. 3). However, the hypotonia which hitherto terminated most such arousals (see Fig. 2B) was replaced by a post-burst
vr
'
"
'
'
r
Fig. 1. Actograms (80 sec stretches from two typical records) illustrating the effect of chlorimipramine on spontaneous motility in a 3-day-old Wistar rat. Motor activity prior to injection of the drug (upper trace) includes continual localized twitching ('type-I' motility) which largely disappears for several hours post-injection (losser tlace), leaving only "startles'; and rotatory movements (types II and 111, respectively).
47
EEG
,
A=I
+
,
-.,
--,.
,.r . . . . .
" - ~ "
:
,
'" ""+ ..... "'"
-~:
+"'~
:,
-
-
~''~~~~~~+*+/::~I
T
200 uv /
1
11 s e c
EEG iill EMG::-~::
.;--,: . . . . . . . . . . . . . . . . . . : . . . .
~+![" ,
!tit
, + It-
-
--
--
. . . . . . . .
:-
-----~::
__lll.Lr~ip
,,
.,,,
Fig. 2. Spontaneous movements during sleep in a 19-day-old Wistar rat. A(I,2): active sleep under unrestrained conditions, showing characteristic theta waves in the hippocampal EEG (upper traces) which are interrupted during bursts of gross body movements; slow-wave sleep typically follows each of these brief arousal episodes. B(l,2): sleep during restraint in the same animal, confirming the occurrence of active as well as slow-wave sleep under such conditions; hippocampal theta-waves are invariably replaced by a slow-wave sleep EEG pattern at the onset of stereotyped struggling behavior, while EMG hypotonia occurs inbetween the motor bursts (lower trace).
f
,!
Fig. 3. Spontaneous quasi-struggle movements in a restrained Wistar rat pup (19 days old) following injection of chlorimipramine. The hippocampal EEG (upper trace) is now devoid of visible theta-wave activity throughout sleep, and the EMG (lower trace) no longer shows muscle atonia following any of the arousal episodes. A l-min stretch from a typical record is shown.
48
EMG pattern which mimicked that seen in unrestrained sleeping animals (see Fig. 2A). This last finding suggests that AS brain mechanisms, while clearly not involved in the actual triggering of arousal episodes during sleep, may nevertheless account for their exceedingly abrupt termination under conditions of severe restraint. 1 Bakhuis, W.L. and Bour, H.L., Climax (hatching) behavior, and its relation to sleep and wakefulness, in T. Ookawa (Ed.), Brain and Behavior of the Fowl, Japan Sci. Soc. Press, Tokyo, 1983, pp. 159- i 69. 2 Corner, M.A., Spontaneous motility rhythms during early development - phenomenological and neurophysiological considerations. In M.A. Corner et al. (Eds.), Maturation of the Nervous System, Progr. Brain Res., Vol. 48. Elsevier, Amsterdam, 1978, pp. 349-366. 3 Corner, M.A. and Bakhuis, W.L., Cerebral electrical activity, forebrain function and behavior in the chick at the time of hatching, Brain Res., 13 (1969), 541-555. 4 Corner, M.A., Bour. H.L. and Mirmiran, M., Development of spontaneous motility, and its physiological interpretation in the rat, chick and frog. in E. Meisami and M. Brazier (Eds.), Neural Growth and Differentiation, Raven Press, New York, 1979, pp. 253-267. 5 Corner. M.A. and Kwee, P., Cyclic EEG and motility patterns during sleep in restrained infant rats, Electroenceph. clin. Neurophysiol., 41 (1976) 64-72. 6 Hamburger, V. and Oppenhei~a, R.W., Prehatching motility and hatching behavior in the chick, J. exp. Zool., 166 (1967) 171-204. 7 Mirmiran, M., Van de Poll, N., Corner, M., Van Oyen, H. and Bour, H., Suppression of active sleep by chronic treatment with chlorimipramine during early postnatal development: effects upon adult sleep and l;-havior in the rat, Brain Res., 204 (1981) 129-146. 80ppenheim, R.V~., Experimental studies on hatching behavior in the chick, IV. Evidence for the role of a noradrenergic mechanism, J. exp. Zool., 204 (1978)95-112. 90ppenheim, R.W., The neuroembryological study of behavior: progress, problems, perspectives, in R.K. Hunt (Ed.), Neural Development (Ill): Neuronal Specificity, Plasticity and Patterns; Current Topics in Developmental Biology, Vol. 17, Academic Press, New York, 1982, pp. 257-310. i0 Sedlacek, .I. and Corner, M.A., Monoaminergic regulation of spontaneous motility in the chick embryo. In T. Ookawa (Ed.), Brain and Behavior in the Fowl, Japan Sci. Soc. Press, Tokyo, 1983, pp. 61-70.