180
Brain Research, 174 (1979) 180-183 © Elsevier/North-Holland Biomedical Press
Enhancement during REM sleep of extracellular potassium ion activity in the reticular formation
TOYOHIKO SATOH, KAZUSHIGE WATABE and KUNIHIRO EGUCHI Department of Physiology, School of Dental Medicine, Aichi-Gakuin University, Nagoya 464 (Japan)
(Accepted May 31st, 1979)
During paradoxical sleep (PS), especially in association with the burst of rapid eye movements (REM), the extracellular microelectrode located in the reticular formation (RF) often shows a tremendous increase in discharge rate of single neurons. Furthermore, it usually picks up also a rush of activity of many nearby neurons which were so far silent even when the animal was moving and the discharge rate of a single neuron was as high as during REM. Another different aspect of the above observations will be the fact that the multiple unit activity (MUA) led from the RF is increased tonically during PS and further intensified phasically at the moment of the burst of REM 1. It has been reported that during ictal discharge of the epileptic focus the extracellular potassium ion activity (Ke) may be enhanced to reach a level which is high enough to depolarize substantially the neuronal membrane potential 2, though the threshold and the rate of firing are not a linear function of the Ke 9. Less marked enhancement of the Ke has been reported to occur in the neuronal structures activated by the afferent volleys4,~,s, 10-12. The present experiment was undertaken to measure the extent of the accumulation of K + ions after burst discharge of the reticular neurons during REM. It will allow to examine under physiological condition the possibility of modulation by the Ke of the activity of local neuronal network. Experiments were performed on 3 adult cats carrying chronically implanted electrodes for monitoring sleep-wakefulness cycle. The head of the animal was restrained by clamping the acrylic mound made on the skull. The electrode for measuring the Ke was stereotaxically lowered in each experiment through the incised dura mater. The electrode was composed of two glass pipettes of 2-3 # m in tip diameter glued together in parallel to have an intertip distance of about 0.1 mm. A short column (0.2-1.0 mm) of potassium ion exchanging resin (Coming 477317) was sucked up into the siliconized tip of one barrel which was filled with 0.1 M KC1. The reference barrel was filled with an artificial cerebrospinal fluid (Fig. 1). The output of these two barrels was amplified differentially so as to cancel the DC potential in the field. The same output was also fed through the band-pass filter (0.5-1.0 kHz) into the
18l
Fig. 1. K+-sensitiveelectrodes photographed after the use for experiment. Lower pipette in each pair contains K+-exchanging resin. Electrode with thicker column of resin (lower pair) gave generally more stable record. integration circuit to record the MUA. The electrode responded with a change of about 35-50 mV to a 10-fold increase in [K +] in the calibration solution. The identification of the recorded sites was made by inserting stereotaxically a stainless steel electrode into the place where the K+-sensitive electrode had been positioned. Electrolytic lesions were made under deep anesthesia and histological examination was made on serial sections stained with Kliiver-Barrera method. The Ke which was measured during wakefulness in the midbrain and pontine R F and the cerebellum, corresponded to [K +] of 3.1-4.1 (mostly 3.6-3.9) mM. When the alert animal moved, the record of Ke was often contaminated with artifacts. However, in most cases where the record was relatively free from artifact, there did not seem to be an appreciable change in the Ke. Only in a few cases the Ke in the RF was observed to increase by about 0.05 mM for a few sec. An increase up to 0.2 mM was encountered only in one occasion. The transition from quiet wakefulness to slow wave sleep, or of opposite direction, was not associated with a measurable change in the Ke. When the recording was made from the pontine or midbrain RF during PS, the Ke was consistently enhanced by 0.2-0.5 mM (Fig. 2). The time course and the intensity of this enhancement were in good parallelism with the increase in the M U A which was phasically accentuated concurrently with the burst of REM. The enhancement tended to be more intense in the core of the R F than in its peripheral part. In a more peripheral part of the brain stem which was close to the pyramidal tract, the change in the Ke during PS was markedly diminished in spite of the persistence of the increase in the MUA. In the cerebellum, the recording which was made in an area with many spikes discharging at a high frequency, presumably the cerebellar cortex, showed during PS an enhancement of Ke which was similar, though slightly less intense, to that observed in the RF. However, in the cerebellar structure without large spike activity, presumably the white matter, neither the M U A nor the Ke was increased during PS.
182 EEG Lh..~.,a.,.,,k,,,~,L.,,,_.
EOG ~
I LU
. . . . .
~,
~
!
Ik,.
EEG _,,InJ"°~. /
~'L~'~'Y-':'L : '
"~
.......
~". . . . .
r
ii~..
. . . . . . . . . . . . . .
-a~
~
,u~..
JI..~A
k,,a
/
". . . . . . . . . . . . .
I
"
~ ' ~ ;~" " " ' J" '
II
;
3.6
4.1
lO sec
Fig. 2. Typical polygram of PS with REM in the EOG and flat neck EMG. K; potassium ion activity, high frequency filtered at 100 Hz. Calibration in mM. Record from pontine RF (P 7.8, R 0.6, V 4 . 3 ) in close vicinity to a neuron slowly discharging during wakefulness and slow wave sleep. Note enhanced Ke and MUA at the moment of large REM. After PS the animal moved and gave artifacts to both Ke and MUA channels.
The p r e s e n t results have d e m o n s t r a t e d t h a t a n a c c u m u l a t i o n o f K + ions in the extracellular space occurs d u r i n g PS in the cell-rich area. H o w e v e r , as the a c c u m u l a t i o n was small in a m o u n t , its influence u p o n the n e u r o n a l m e m b r a n e p o t e n t i a l will be quite limited. It has been r e p o r t e d t h a t the increase in K e i n d u c e d in the cerebral cortex a,s,11, t h a l a m u s 10 a n d spinal c o r d 5 b y electrical or sensory s t i m u l a t i o n o f the afferent i n p u t s c o r r e s p o n d s to the change in [K +] b y 0.3-3.0 m M in anesthetized animals. The e n h a n c e m e n t o f K e d u r i n g R E M o b s e r v e d in the present e x p e r i m e n t was relatively weak, b u t was greater t h a n the change m e a s u r e d d u r i n g s p o n t a n e o u s spike b u r s t in the mesencephalic R F o f curarized rats ( a b o u t 0.1 m M ) 12. A r o u s a l f r o m slow wave sleep was n o t associated with a detectable change in Ke, whereas an enhancem e n t o f K e has been r e p o r t e d to occur in the cerebral cortex o f anesthetized r a t u p o n externally i n d u c e d E E G desynchronization4, 8. This difference might be due in p a r t to the effect o f the anesthetic. The e n h a n c e m e n t o f K e d u r i n g PS t e n d e d to be less intense in the p e r i p h e r a l p a r t o f the R F a n d was a l m o s t a b s e n t in the areas close to o r p r e s u m a b l y in the fiber tract. I n o r d e r to realize an a c c u m u l a t i o n o f K + ions the a m o u n t o f release f r o m the cells will be the m o s t i m p o r t a n t factor. H o w e v e r , local difference o f the n e u r o n a l tissue in the a b i l i t y to r e m o v e K + ions f r o m the extracellular space is a n o t h e r i m p o r t a n t factor3,6,L T h e role o f the latter factor is currently u n d e r investigation.
1 Barzano, E. et Jeannerod, M., Activit6 multi-unitaire de structures sous-corticales pendant le cycle veille-sommeil chez le chat, Electroenceph. clin. NeurophysioL, 28 (1970) 136-145. 2 Fertziger, A. P. and Ranck, J. B. Jr., Potassium ~iccumulation in interstitial space during epileptiform seizures, Exp. Neurol., 26 (1970) 571-585.
3 Futamachi•K.J.•Mutani•R.andPrince•D.A.•P•tassiumactivityinrabbitc•rtex•BrainResearch• 75 (1974) 5-25.
183 4 Korytovfi, H., Arousal-induced increase of cortical [K+] in unrestrained rats, Experientia, (Basel), 33 (1977) 242-244. 5 Kri~, N., Sykovfi, E., Ujec, E. and Vyklick#, L., Changes of extracellular potassium concentration induced by neuronal activity in the spinal cord of the cat, J. PhysioL (Lond.), 238 (1974) 1-15. 6 Lewis, D. V. and Schuette, W. H., NADH fluorescence and [K÷]0 changes during hippocampal electrical stimulation, ,L NeurophysioL, 38 (1975) 405-417. 7 Lux, H. D. and Neher, E., The equilibration time course of [K+]o in cat cortex, Exp. Brain Res., 17 (1973) 190-205. 8 Melnikovov~i, H., Changes in the potassium ion concentration in the extracellular space of rat cerebral cortex during the arousal reaction, Physiol. bohemoslov., 27 (1978) 131-138. 9 Oliver, A. P., Hoffer, B. J. and Wyatt, R. J., Interaction of potassium and calcium in penicillininduced interictal spike discharge in the hippocampal slice, Exp. Neurol., 62 (1978) 510-520. 10 Singer, W. and Lux, H. D., Presynaptic depolarization and extracellular potassium in the cat lateral geniculate nucleus, Brain Research, 64 (1973) 17-33. 11 Singer, W. and Lux, H. D., Extracellular potassium gradients and visual receptive fields in the cat striate cortex, Brain Research, 96 (1975) 378-383. 12 Sykovfi, E., Rothenberg, S. and Krekule, I., Changes of extracellular potassium concentration during spontaneous activity in the mesencephalic reticular formation of the rat, Brain Research, 79 (1974) 333-337.
Brain Research, 174 (1979) 180-183 © Elsevier/North-Holland Biomedical Press
Enhancement during REM sleep of extracellular potassium ion activity in the reticular formation
TOYOHIKO SATOH, KAZUSHIGE WATABE and KUNIHIRO EGUCHI Department of Physiology, School of Dental Medicine, Aichi-Gakuin University, Nagoya 464 (Japan)
(Accepted May 31st, 1979)
During paradoxical sleep (PS), especially in association with the burst of rapid eye movements (REM), the extracellular microelectrode located in the reticular formation (RF) often shows a tremendous increase in discharge rate of single neurons. Furthermore, it usually picks up also a rush of activity of many nearby neurons which were so far silent even when the animal was moving and the discharge rate of a single neuron was as high as during REM. Another different aspect of the above observations will be the fact that the multiple unit activity (MUA) led from the RF is increased tonically during PS and further intensified phasically at the moment of the burst of REM 1. It has been reported that during ictal discharge of the epileptic focus the extracellular potassium ion activity (Ke) may be enhanced to reach a level which is high enough to depolarize substantially the neuronal membrane potential 2, though the threshold and the rate of firing are not a linear function of the Ke 9. Less marked enhancement of the Ke has been reported to occur in the neuronal structures activated by the afferent volleys4,~,s, 10-12. The present experiment was undertaken to measure the extent of the accumulation of K + ions after burst discharge of the reticular neurons during REM. It will allow to examine under physiological condition the possibility of modulation by the Ke of the activity of local neuronal network. Experiments were performed on 3 adult cats carrying chronically implanted electrodes for monitoring sleep-wakefulness cycle. The head of the animal was restrained by clamping the acrylic mound made on the skull. The electrode for measuring the Ke was stereotaxically lowered in each experiment through the incised dura mater. The electrode was composed of two glass pipettes of 2-3 # m in tip diameter glued together in parallel to have an intertip distance of about 0.1 mm. A short column (0.2-1.0 mm) of potassium ion exchanging resin (Coming 477317) was sucked up into the siliconized tip of one barrel which was filled with 0.1 M KC1. The reference barrel was filled with an artificial cerebrospinal fluid (Fig. 1). The output of these two barrels was amplified differentially so as to cancel the DC potential in the field. The same output was also fed through the band-pass filter (0.5-1.0 kHz) into the
18l
Fig. 1. K+-sensitiveelectrodes photographed after the use for experiment. Lower pipette in each pair contains K+-exchanging resin. Electrode with thicker column of resin (lower pair) gave generally more stable record. integration circuit to record the MUA. The electrode responded with a change of about 35-50 mV to a 10-fold increase in [K +] in the calibration solution. The identification of the recorded sites was made by inserting stereotaxically a stainless steel electrode into the place where the K+-sensitive electrode had been positioned. Electrolytic lesions were made under deep anesthesia and histological examination was made on serial sections stained with Kliiver-Barrera method. The Ke which was measured during wakefulness in the midbrain and pontine R F and the cerebellum, corresponded to [K +] of 3.1-4.1 (mostly 3.6-3.9) mM. When the alert animal moved, the record of Ke was often contaminated with artifacts. However, in most cases where the record was relatively free from artifact, there did not seem to be an appreciable change in the Ke. Only in a few cases the Ke in the RF was observed to increase by about 0.05 mM for a few sec. An increase up to 0.2 mM was encountered only in one occasion. The transition from quiet wakefulness to slow wave sleep, or of opposite direction, was not associated with a measurable change in the Ke. When the recording was made from the pontine or midbrain RF during PS, the Ke was consistently enhanced by 0.2-0.5 mM (Fig. 2). The time course and the intensity of this enhancement were in good parallelism with the increase in the M U A which was phasically accentuated concurrently with the burst of REM. The enhancement tended to be more intense in the core of the R F than in its peripheral part. In a more peripheral part of the brain stem which was close to the pyramidal tract, the change in the Ke during PS was markedly diminished in spite of the persistence of the increase in the MUA. In the cerebellum, the recording which was made in an area with many spikes discharging at a high frequency, presumably the cerebellar cortex, showed during PS an enhancement of Ke which was similar, though slightly less intense, to that observed in the RF. However, in the cerebellar structure without large spike activity, presumably the white matter, neither the M U A nor the Ke was increased during PS.
182 EEG Lh..~.,a.,.,,k,,,~,L.,,,_.
EOG ~
I LU
. . . . .
~,
~
!
Ik,.
EEG _,,InJ"°~. /
~'L~'~'Y-':'L : '
"~
.......
~". . . . .
r
ii~..
. . . . . . . . . . . . . .
-a~
~
,u~..
JI..~A
k,,a
/
". . . . . . . . . . . . .
I
"
~ ' ~ ;~" " " ' J" '
II
;
3.6
4.1
lO sec
Fig. 2. Typical polygram of PS with REM in the EOG and flat neck EMG. K; potassium ion activity, high frequency filtered at 100 Hz. Calibration in mM. Record from pontine RF (P 7.8, R 0.6, V 4 . 3 ) in close vicinity to a neuron slowly discharging during wakefulness and slow wave sleep. Note enhanced Ke and MUA at the moment of large REM. After PS the animal moved and gave artifacts to both Ke and MUA channels.
The p r e s e n t results have d e m o n s t r a t e d t h a t a n a c c u m u l a t i o n o f K + ions in the extracellular space occurs d u r i n g PS in the cell-rich area. H o w e v e r , as the a c c u m u l a t i o n was small in a m o u n t , its influence u p o n the n e u r o n a l m e m b r a n e p o t e n t i a l will be quite limited. It has been r e p o r t e d t h a t the increase in K e i n d u c e d in the cerebral cortex a,s,11, t h a l a m u s 10 a n d spinal c o r d 5 b y electrical or sensory s t i m u l a t i o n o f the afferent i n p u t s c o r r e s p o n d s to the change in [K +] b y 0.3-3.0 m M in anesthetized animals. The e n h a n c e m e n t o f K e d u r i n g R E M o b s e r v e d in the present e x p e r i m e n t was relatively weak, b u t was greater t h a n the change m e a s u r e d d u r i n g s p o n t a n e o u s spike b u r s t in the mesencephalic R F o f curarized rats ( a b o u t 0.1 m M ) 12. A r o u s a l f r o m slow wave sleep was n o t associated with a detectable change in Ke, whereas an enhancem e n t o f K e has been r e p o r t e d to occur in the cerebral cortex o f anesthetized r a t u p o n externally i n d u c e d E E G desynchronization4, 8. This difference might be due in p a r t to the effect o f the anesthetic. The e n h a n c e m e n t o f K e d u r i n g PS t e n d e d to be less intense in the p e r i p h e r a l p a r t o f the R F a n d was a l m o s t a b s e n t in the areas close to o r p r e s u m a b l y in the fiber tract. I n o r d e r to realize an a c c u m u l a t i o n o f K + ions the a m o u n t o f release f r o m the cells will be the m o s t i m p o r t a n t factor. H o w e v e r , local difference o f the n e u r o n a l tissue in the a b i l i t y to r e m o v e K + ions f r o m the extracellular space is a n o t h e r i m p o r t a n t factor3,6,L T h e role o f the latter factor is currently u n d e r investigation.
1 Barzano, E. et Jeannerod, M., Activit6 multi-unitaire de structures sous-corticales pendant le cycle veille-sommeil chez le chat, Electroenceph. clin. NeurophysioL, 28 (1970) 136-145. 2 Fertziger, A. P. and Ranck, J. B. Jr., Potassium ~iccumulation in interstitial space during epileptiform seizures, Exp. Neurol., 26 (1970) 571-585.
3 Futamachi•K.J.•Mutani•R.andPrince•D.A.•P•tassiumactivityinrabbitc•rtex•BrainResearch• 75 (1974) 5-25.
183 4 Korytovfi, H., Arousal-induced increase of cortical [K+] in unrestrained rats, Experientia, (Basel), 33 (1977) 242-244. 5 Kri~, N., Sykovfi, E., Ujec, E. and Vyklick#, L., Changes of extracellular potassium concentration induced by neuronal activity in the spinal cord of the cat, J. PhysioL (Lond.), 238 (1974) 1-15. 6 Lewis, D. V. and Schuette, W. H., NADH fluorescence and [K÷]0 changes during hippocampal electrical stimulation, ,L NeurophysioL, 38 (1975) 405-417. 7 Lux, H. D. and Neher, E., The equilibration time course of [K+]o in cat cortex, Exp. Brain Res., 17 (1973) 190-205. 8 Melnikovov~i, H., Changes in the potassium ion concentration in the extracellular space of rat cerebral cortex during the arousal reaction, Physiol. bohemoslov., 27 (1978) 131-138. 9 Oliver, A. P., Hoffer, B. J. and Wyatt, R. J., Interaction of potassium and calcium in penicillininduced interictal spike discharge in the hippocampal slice, Exp. Neurol., 62 (1978) 510-520. 10 Singer, W. and Lux, H. D., Presynaptic depolarization and extracellular potassium in the cat lateral geniculate nucleus, Brain Research, 64 (1973) 17-33. 11 Singer, W. and Lux, H. D., Extracellular potassium gradients and visual receptive fields in the cat striate cortex, Brain Research, 96 (1975) 378-383. 12 Sykovfi, E., Rothenberg, S. and Krekule, I., Changes of extracellular potassium concentration during spontaneous activity in the mesencephalic reticular formation of the rat, Brain Research, 79 (1974) 333-337.
