Physiology & Behavior, Vol. 19, pp. 355-358. Pergamon Press and Brain Research Publ., 1977. Printed in the U.S.A.
Sleep Induced by Intestinal Stimulation in Cats TIBOR KUKORELLI AND GJ~BOR JUH~.SZ
Department of Comparative Physiology, E(~tviSs Lordnd University and Institute of Psychology of the Hungarian Academy of Sciences 1088 Budapest, Muzeum krt 4/A., Hungary
(Received 7 June 1976) KUKORELLI, T. AND G. JUH,~SZ. Sleep induced by intestinal stimulation in cart. PHYSIOL. BEHAV. 19(3) 355-358, 1977. - The influence of afferent impulses of intestinal origin on the sleep stages was studied in fed and starved cats. Low-frequency electrical stimulation of the mucosal surface in a small intestinal fistula reduced the latency of sleep onset. The number of slow wave sleep episodes decreased, but their mean duration increased during stimulation. Conversely, the number of paradoxical sleep episodes increased, but their mean duration was not significantly modifmd by the intestinal stimulation. The role of viscerosensory events in the control of sleep is discussed in relationship to these results. Sleep induction Intestinal stimulation Low frequency Starvation Sleep-wakefulness cycle EEG Slow wave sleep Paradoxical sleep
Sleepduration
At ]east 6 weeks was allowed for recovery before electrode implantation. Stainless steel screws which were threaded bilaterally into the skull over the frontal, parietal, temporal and occipital areas of the cortex served to record EEG activity. A bipolar Nicrotan electrode was stereotaxically inserted into the right dorsal hippocampus. Additional screws were placed into the upper wall of right orbit to monitor electrooculographic (EOG) activity. Electromyogram (EMG) electrodes were inserted subdermally over the dorsal neck muscles. A bipolar electrode was inserted into the lumen of the isolated intestinal loop to stimulate the mucosa. The tip was composed of Plexiglas which measured 0.5 x 2.5 cm, and two 0.5 cm 2 gold-plate caps separated by a distance of 8 mm served as conducting surfaces. Squarewave pulses, 0.5 msec in duration with a frequency of l Hz and 2 - 6 V were used for stimulation. To each eat, the minimum stimulus intensity was applied which would induce sleep onset by EEG criteria in the drowsy state without overt behavioral sequelae [6,7]. EEG, EMG, and EOG activity were continuously recorded at 8 - 1 0 cm/min. Simultaneously, direct obse.rvation of behavior was made. These animals were placed individually into a recording cage 0.8 m long, 0.7 m wide × 0.7 m tall in a sound-attenuated and electrostatically shielded room. The cage was illuminated by a 0.3 W light bulb with the temperature maintained at 23 ± I°C. The animals were placed on a 12:12 light/dar k cycle with illumination from 0 6 . 0 0 - 1 2 . 0 0 hr. Each day 1.5 kg of beef and 1 kg milk were fed to 5 cats at 08.30 hr, to 5 at 13.30 hr. Water was provided ad lib. Polygraphic recording was via a multistrand cable which contained leads attached to a plug on the cat's head.
THE PRESENT study was conducted as part of a larger investigation [6,7] concerned with the activity of intestinal afferents and brain mechanisms regulating behavior. Viscerosensory activity has been shown t o influence the sleep-wakefulness rhythm. We previously [6,7] observed that low-frequency ( 1 - 8 c/see) stimulation of the small intestine and splanchnic nerve produced electroencephalographically (EEG) defined signs of sleep onset in cats. These findings taken together with that of a reduction in sleep stages (slow-wave, paradoxical) observed [ 13] after the abdominal vegetative nerves were severed, raise the possibility of a hypnogenic influence with its origin in the intestinal receptors. Therefore, the objective of the present study was to investigate this as an effective site for influencing the various sleep stages in cats by obtaining polygraphic recordings during chronic intestinal stimulation. Would the sleep cycle be altered by low-frequency stimulation of the small intestinal mucosa? METHOD Ten adult male cats aged 2 - 4 years weighing 3 - 5 kg. were prepared with chronic intestinal fistula and electrodes were implanted for sleep recordings under Nembutal anesthesia. The intestinal fistula were constructed as previously described [7]. Following median laparatomy, a loop of 15 cm long was excised from the upper part of jejunum. The continuity of the intestinal tract was restored by a bilateral anastomosis. Both ends of the isolated intestinal loop were sutured to the abdominal skin 5 cm apart. The loop rested in the abdominal cavity in a U-shaped position, retaining its original innervation and blood vessel connections. 355
356
KUKORELLI AND JUHASZ
fed
starved
The cats were adapted 4 hr/daily for a week to the cable and intestinal-stimulating electrode. Recordings began at 0.900 hr and were terminated 4 hr later. First, continuous polygraphic (control) recordings were obtained for 5 consecutive days "without intestinal stimulation. This was followed by 5 successive recording days when the intestinal mucosa was stimulated continuously during wakefulness (W), drowsiness (D) and slow-wave (SWS), but not in paradoxical sleep (PS). Five animals were fed for about 25 min before each recording period, while the other 5 were starved throughout the 10 days encompassing the experiment. Each 60-sec epoch of the ten 4-hr records per animal (5 control/5 stimulation) was classified'according to previously adopted criteria [2,14] into one of .the following categories: W, D, SWS, and PS. An epoch was assigned to t h a t stage which occupied 30 sec or more of its duration.
6o
40.
20
•
W
O
SWS
W
PS
O
SWS
PS
RESULTS FIG. 1. Distribution of total recording time in the wakefulness and sleep stages before (white columns) and during (dotted columns) intestinal stimulation.
The data derived from the sleep-wake states was compared between groups (fed vs. starved) and with respect to treatment (control vs. stimulation). All statistical analyses were based upon 2-tailed r-tests. The distribution of wakefulness and the sleep stages remained unchanged during the control period. Sleep duration did not increase over consecutive d a y s , but was similar on the first (X = 140.7 min) and last (X = 137.3 rain). Pronounced differences existed between the control data of the starved and satiated cats. There was a statistically significant main effect on the duration of episodes occupied by W, D, and each sleep stage. Table I shows that the mean episode durations of W and D were less while those of PS and SWS were greater in the fed compared with the starved animals (all ps
Sleep Induced by Intestinal Stimulation in Cats TIBOR KUKORELLI AND GJ~BOR JUH~.SZ
Department of Comparative Physiology, E(~tviSs Lordnd University and Institute of Psychology of the Hungarian Academy of Sciences 1088 Budapest, Muzeum krt 4/A., Hungary
(Received 7 June 1976) KUKORELLI, T. AND G. JUH,~SZ. Sleep induced by intestinal stimulation in cart. PHYSIOL. BEHAV. 19(3) 355-358, 1977. - The influence of afferent impulses of intestinal origin on the sleep stages was studied in fed and starved cats. Low-frequency electrical stimulation of the mucosal surface in a small intestinal fistula reduced the latency of sleep onset. The number of slow wave sleep episodes decreased, but their mean duration increased during stimulation. Conversely, the number of paradoxical sleep episodes increased, but their mean duration was not significantly modifmd by the intestinal stimulation. The role of viscerosensory events in the control of sleep is discussed in relationship to these results. Sleep induction Intestinal stimulation Low frequency Starvation Sleep-wakefulness cycle EEG Slow wave sleep Paradoxical sleep
Sleepduration
At ]east 6 weeks was allowed for recovery before electrode implantation. Stainless steel screws which were threaded bilaterally into the skull over the frontal, parietal, temporal and occipital areas of the cortex served to record EEG activity. A bipolar Nicrotan electrode was stereotaxically inserted into the right dorsal hippocampus. Additional screws were placed into the upper wall of right orbit to monitor electrooculographic (EOG) activity. Electromyogram (EMG) electrodes were inserted subdermally over the dorsal neck muscles. A bipolar electrode was inserted into the lumen of the isolated intestinal loop to stimulate the mucosa. The tip was composed of Plexiglas which measured 0.5 x 2.5 cm, and two 0.5 cm 2 gold-plate caps separated by a distance of 8 mm served as conducting surfaces. Squarewave pulses, 0.5 msec in duration with a frequency of l Hz and 2 - 6 V were used for stimulation. To each eat, the minimum stimulus intensity was applied which would induce sleep onset by EEG criteria in the drowsy state without overt behavioral sequelae [6,7]. EEG, EMG, and EOG activity were continuously recorded at 8 - 1 0 cm/min. Simultaneously, direct obse.rvation of behavior was made. These animals were placed individually into a recording cage 0.8 m long, 0.7 m wide × 0.7 m tall in a sound-attenuated and electrostatically shielded room. The cage was illuminated by a 0.3 W light bulb with the temperature maintained at 23 ± I°C. The animals were placed on a 12:12 light/dar k cycle with illumination from 0 6 . 0 0 - 1 2 . 0 0 hr. Each day 1.5 kg of beef and 1 kg milk were fed to 5 cats at 08.30 hr, to 5 at 13.30 hr. Water was provided ad lib. Polygraphic recording was via a multistrand cable which contained leads attached to a plug on the cat's head.
THE PRESENT study was conducted as part of a larger investigation [6,7] concerned with the activity of intestinal afferents and brain mechanisms regulating behavior. Viscerosensory activity has been shown t o influence the sleep-wakefulness rhythm. We previously [6,7] observed that low-frequency ( 1 - 8 c/see) stimulation of the small intestine and splanchnic nerve produced electroencephalographically (EEG) defined signs of sleep onset in cats. These findings taken together with that of a reduction in sleep stages (slow-wave, paradoxical) observed [ 13] after the abdominal vegetative nerves were severed, raise the possibility of a hypnogenic influence with its origin in the intestinal receptors. Therefore, the objective of the present study was to investigate this as an effective site for influencing the various sleep stages in cats by obtaining polygraphic recordings during chronic intestinal stimulation. Would the sleep cycle be altered by low-frequency stimulation of the small intestinal mucosa? METHOD Ten adult male cats aged 2 - 4 years weighing 3 - 5 kg. were prepared with chronic intestinal fistula and electrodes were implanted for sleep recordings under Nembutal anesthesia. The intestinal fistula were constructed as previously described [7]. Following median laparatomy, a loop of 15 cm long was excised from the upper part of jejunum. The continuity of the intestinal tract was restored by a bilateral anastomosis. Both ends of the isolated intestinal loop were sutured to the abdominal skin 5 cm apart. The loop rested in the abdominal cavity in a U-shaped position, retaining its original innervation and blood vessel connections. 355
356
KUKORELLI AND JUHASZ
fed
starved
The cats were adapted 4 hr/daily for a week to the cable and intestinal-stimulating electrode. Recordings began at 0.900 hr and were terminated 4 hr later. First, continuous polygraphic (control) recordings were obtained for 5 consecutive days "without intestinal stimulation. This was followed by 5 successive recording days when the intestinal mucosa was stimulated continuously during wakefulness (W), drowsiness (D) and slow-wave (SWS), but not in paradoxical sleep (PS). Five animals were fed for about 25 min before each recording period, while the other 5 were starved throughout the 10 days encompassing the experiment. Each 60-sec epoch of the ten 4-hr records per animal (5 control/5 stimulation) was classified'according to previously adopted criteria [2,14] into one of .the following categories: W, D, SWS, and PS. An epoch was assigned to t h a t stage which occupied 30 sec or more of its duration.
6o
40.
20
•
W
O
SWS
W
PS
O
SWS
PS
RESULTS FIG. 1. Distribution of total recording time in the wakefulness and sleep stages before (white columns) and during (dotted columns) intestinal stimulation.
The data derived from the sleep-wake states was compared between groups (fed vs. starved) and with respect to treatment (control vs. stimulation). All statistical analyses were based upon 2-tailed r-tests. The distribution of wakefulness and the sleep stages remained unchanged during the control period. Sleep duration did not increase over consecutive d a y s , but was similar on the first (X = 140.7 min) and last (X = 137.3 rain). Pronounced differences existed between the control data of the starved and satiated cats. There was a statistically significant main effect on the duration of episodes occupied by W, D, and each sleep stage. Table I shows that the mean episode durations of W and D were less while those of PS and SWS were greater in the fed compared with the starved animals (all ps
