Vrsrophor,,ia~,,f,,~I.. lY75.14.,41-149.Pergamon
Press Prmted,n
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PRELIMINARY
NOTES
EFFECTS OF KETAMINE ON SYNAPTIC TRANSMISSION IN CAT SPINAL CORD C. F. CHEN and S. Y. CHOW Department of Biophysics. National Defense Medical Center, Taipei, Taiwan, Republic of China (Accepted 22 July 1974)
Summary-Effects of ketamine on the evoked synaptic potentials and on the post-tetanic potentiation (PTP) of synaptic responses were studied in dorsal root-ventral root preparations of unanaesthetized spinal cats. Ketamine, in doses of IO-20 mg/kg, depressed the synaptic transmission, but enhanced the PTP responses in spinal cord. The enhancement of PTP responses after ketamine may be related to its seizure-inducing property.
Ketamine is a derivative of phencyclidine which is a distinct, centrally-acting drug. These drugs can induce amnesia, analgesia, catalepsy, anaesthesia and convulsions. Many investigators have focused their special attention on the epileptogenic properties of these agents (MORI, KAWAMATA, MITANI, YAMAZAKI and FUJITA, 1971; KAYAMAand IWAMA, 1972; WINTERS,FERRAR-ALLADO, GUZMAN-FLORES and ALCARAZ,1972). A progressive transient enhancement of central synaptic transmission during rapid repetitive stimulation, known as post-tetanic potentiation (PTP), is an important factor in the spread and maintenance of seizure activity (ESPLIN, 1957). We, therefore, studied the effects of ketamine upon PTP in spinal cord in unanaesthetized animal preparations. METHODS
Unanaesthetized cats with the spinal cord severed at the atlanto-occipital junction were used in these experiments. The general methods described by ESPLIN (1957) were followed. All experiments were performed in dorsal root-ventral root (DR-VR) preparations. Ventral root (L7 or Sl) monosynaptic (2N spike) and polysynaptic responses were elicited by stimulation of the homolateral dorsal root of the same segment with stimuli of twice supramaxima1 voltage applied at 02 Hz. The duration of the rectangular pulses was 0,2 msec. For study of post-tetanic potentiation of 2N responses, a 250 Hz stimulus applied for a lo-set period was used for conditioning. The stimuli were delivered by a Grass model S-88 stimulator. Recorded potentials were amplified through a type 3A3 differential amplifier and displayed on a Tektronix type RM565 dual-beam oscilloscope. Responses were photographed by a Grass kymograph camera for later measurement. For quantification of responses, the mean of five consecutive evoked responses under test was taken as a measure of the evoked activity. Arterial blood pressure and heart rate were also monitored during the experiment. In each experiment, when the response of the preparation was satisfactory, the stability was checked by observation for a period of l-2 hr. If the response showed sufficient stability, control recordings were made and the drug was administered. Ketamine HCl, dissolved in 0.9% NaCl solution, was administered intravenously in doses between 2 and 20 mg/kg. Each animal received only one dose of ketamine. RESULTS
Ketamine, in doses smaller than 5 mg/kg, produced no significant effects on the compound ventral root potentials elicited by a single shock stimulation applied to the dorsal root of the same segment. When the dosage of ketamine reached 10 mg/kg, the polysynaptic component of the compound potentials as measured by the areas of asynchrous discharges was depressed, while the monosynaptic component (2N spike) showed no significant change. When the dose increased to 20 mg/kg, both polysynaptic and monosynaptic 147
14x
C. F. CHENand S. Y. CHOW
Ketomine
IO mg/kg(N=7)
0 Ketamine
20 mg/kg(N=8)
l
___I___L__K.__r__
10
20 TIME
30
40
AFTER (MINI
50
60
KETAMINE
Fig. 1. Effect of ketamine on the evoked monos~naptic potential (2N spike) in the DR--VR preparation of spinat cats. The ordinate shows the 2N spike amplitude as a percentage of the pre-drug control amplitude and the abscissa shows time. Points and brackets are means and standard errors of means. * P i 0.05 compared with the corresponding smaller dose (IO mg/kg). 2
300’
F 5 v $ *
I * 250
o Control (N-51
’
l
Q Control (N-5)
Ketamlne 10 mg/kg (N-5)
l
Keta~i~e5~ s
mglkg
I *
200.
T*T,
z
2 1 1, 2 150' lsT T % TTT w"100. hns$ x a (: N 50< t. 0
SO
100
150
TIME
200
AFTER
ee5 P *5 22m6 4. 250
0
50
TETANUS
100
150
200
250
(SEC)
Fig. 2. Effect of ketamine on spinal cord PTP. DR-VR preparation. tetanus 25O/sec for 10 sec. The ordinate shows the potentiated 2N spike amplitude as a percentage of the control amplitude and the abscissa shows time in sec. 0: initial PTP responses (control): 0: PTP responses after IO mg/kg (A) and 20 mg/kg (B) of ketamine. Post-tetanic potentiation curves were determined between 15 and 20 min after the administration of ketamine. Points and brackets are means and standard errors of means. Number of animals. five cats for each dose level. * P < 0.05. when compared with corresponding control point.
responses to a single shock stimulation were decreased. This decrease developed in less than 5 min, but it was not statistically significant until 30 min after the injection of ketdmine. This depression lasted more than 60 min. Results are shown in Figures I and 3. Effects of ketamine on the PTP in motor neurones of isolated spinal cord preparation are shown in Figures 2 and 3. It is apparent that ketamine in doses of 10 and 20 mg/kg enhanced the PTP responses in cat spinal cord. The enhancement in PTP responses could be observed 5 min after the injection of ketamine and this enhancement lasted about 30 min. When smaller doses (less than 5 mg/kg) were given, no apparent potentiation or slight enhancement was observed. DISCUSSION
Behavioural and EEG changes representing seizure activity after ketamine administration have been observed in both experimental animals and in man (DOMINO, CHOWFF and CORSSEN,1965; WINTERSet al., 1972; KAYAM and IWAMA. 1972). From this
Ketamine
A
and synaptic
transmission
I49
C
B
J-L
D _L,
L
AA-
L
A_/._ (5mv AL__ L_ IOmsrc
E L
F AA-
I
G AL
H -‘LX__
Fig. 3. Effects of ketamine on the ventral root responses evoked by supramaximal stimulation on the ipsilateral dorsal root. For parameters of stimulation, see Results and Figure 2. A and E: control synaptic potentials. B and F: initial (control) post-tetanic potentiation responses. C and G: synaptic potentials determined at 15 min after 10 mg/kg (C) and 20 mg/kg (G) of ketamine. D and H: post-tetanic potentiation responses determined at 15 min after 10 mg/kg (D) and 20 mg/kg (H) of ketamine.
study it is clear that ketamine, in doses of l&20 mg/kg, significantly enhanced the PTP responses in spinal cord preparations. This effect could partially explain the seizure-inducing property of ketamine, since PTP is a general synaptic property and appears to be a normal consequence of synaptic excitation (ECCLES, 1953). The role of PTP in the spread of seizure discharge has been discussed by ESPLIN (1957). This concept is also supported by the fact that diphenylhydantoin, which is capable of modifying the pattern of maximal seizures, has a striking effect on PTP in spinal cats (ESPLIN, 1957). In addition to exerting a marked effect on PTP responses, ketamine also depressed the synaptic transmission in DR-VR preparations of the spinal cat. The polysynaptic component of the evoked potentials seems more sensitive than the monosynaptic component to the depressive effects of the ketamine. Similar results have been reported by TANG and SCHROEDER (1973). Acknowledgrnlrnts~This research was supported in part by grants from the National Science Council, Republic of China and the China Medical Board of New York, Inc., U.S.A. The authors are indebted to Dr. GRAHAM CHLN for the generous supply of ketamine HCI used in this study. REFERENCES DOMINO, E. F., CHOWFF, P. and CORSSEN. G. (1965). Pharmacological effects of CI-581, a new dissociative anesthetic, in man. Clin. Pharn~uc. Thrr. 6: 279-291. ECCLES, J. C. (1953). The Neurophysiological Basis ofMind, pp. 193-202. Oxford University Press, London. ESPLIN, D. W. (1957). Effects of diphenylhydantoin on synaptic transmission in cat spinal cord and stellate ganglion. J. Pharmac. up. Ther. 120: 301-323. KAYAMA, Y. and IWAMA, K. (1972). The EEG, evoked potentials, and single-unit activity during ketamine anesthesia in cats. Anesthesiology 36: 31&328. MORI, K., KAWAMATA, M., MITANI, H., YAMAZAKI. Y. and FUJITA, M. (1971). A neurophysiologic study of ketamine anesthesia in the cat. Anrsthesiology 35: 373-383. TANG. A. H. and SCHROEDER, L. A. (1973). Spinal-cord depressant effects of ketamine and etoxadrol in cat and the rat. Anesthesiology 39: 37-43. WINTERS, W. D., FERRAR-ALLADO, T., GUZMAN-FLORES, C. and ALCARAZ. M. (1972). The cataleptic state induced by ketamine: a review of the neuropharmacology of anesthesia. Nruropharmacology 11: 303-315.
Press Prmted,n
Gt. Br~tam
PRELIMINARY
NOTES
EFFECTS OF KETAMINE ON SYNAPTIC TRANSMISSION IN CAT SPINAL CORD C. F. CHEN and S. Y. CHOW Department of Biophysics. National Defense Medical Center, Taipei, Taiwan, Republic of China (Accepted 22 July 1974)
Summary-Effects of ketamine on the evoked synaptic potentials and on the post-tetanic potentiation (PTP) of synaptic responses were studied in dorsal root-ventral root preparations of unanaesthetized spinal cats. Ketamine, in doses of IO-20 mg/kg, depressed the synaptic transmission, but enhanced the PTP responses in spinal cord. The enhancement of PTP responses after ketamine may be related to its seizure-inducing property.
Ketamine is a derivative of phencyclidine which is a distinct, centrally-acting drug. These drugs can induce amnesia, analgesia, catalepsy, anaesthesia and convulsions. Many investigators have focused their special attention on the epileptogenic properties of these agents (MORI, KAWAMATA, MITANI, YAMAZAKI and FUJITA, 1971; KAYAMAand IWAMA, 1972; WINTERS,FERRAR-ALLADO, GUZMAN-FLORES and ALCARAZ,1972). A progressive transient enhancement of central synaptic transmission during rapid repetitive stimulation, known as post-tetanic potentiation (PTP), is an important factor in the spread and maintenance of seizure activity (ESPLIN, 1957). We, therefore, studied the effects of ketamine upon PTP in spinal cord in unanaesthetized animal preparations. METHODS
Unanaesthetized cats with the spinal cord severed at the atlanto-occipital junction were used in these experiments. The general methods described by ESPLIN (1957) were followed. All experiments were performed in dorsal root-ventral root (DR-VR) preparations. Ventral root (L7 or Sl) monosynaptic (2N spike) and polysynaptic responses were elicited by stimulation of the homolateral dorsal root of the same segment with stimuli of twice supramaxima1 voltage applied at 02 Hz. The duration of the rectangular pulses was 0,2 msec. For study of post-tetanic potentiation of 2N responses, a 250 Hz stimulus applied for a lo-set period was used for conditioning. The stimuli were delivered by a Grass model S-88 stimulator. Recorded potentials were amplified through a type 3A3 differential amplifier and displayed on a Tektronix type RM565 dual-beam oscilloscope. Responses were photographed by a Grass kymograph camera for later measurement. For quantification of responses, the mean of five consecutive evoked responses under test was taken as a measure of the evoked activity. Arterial blood pressure and heart rate were also monitored during the experiment. In each experiment, when the response of the preparation was satisfactory, the stability was checked by observation for a period of l-2 hr. If the response showed sufficient stability, control recordings were made and the drug was administered. Ketamine HCl, dissolved in 0.9% NaCl solution, was administered intravenously in doses between 2 and 20 mg/kg. Each animal received only one dose of ketamine. RESULTS
Ketamine, in doses smaller than 5 mg/kg, produced no significant effects on the compound ventral root potentials elicited by a single shock stimulation applied to the dorsal root of the same segment. When the dosage of ketamine reached 10 mg/kg, the polysynaptic component of the compound potentials as measured by the areas of asynchrous discharges was depressed, while the monosynaptic component (2N spike) showed no significant change. When the dose increased to 20 mg/kg, both polysynaptic and monosynaptic 147
14x
C. F. CHENand S. Y. CHOW
Ketomine
IO mg/kg(N=7)
0 Ketamine
20 mg/kg(N=8)
l
___I___L__K.__r__
10
20 TIME
30
40
AFTER (MINI
50
60
KETAMINE
Fig. 1. Effect of ketamine on the evoked monos~naptic potential (2N spike) in the DR--VR preparation of spinat cats. The ordinate shows the 2N spike amplitude as a percentage of the pre-drug control amplitude and the abscissa shows time. Points and brackets are means and standard errors of means. * P i 0.05 compared with the corresponding smaller dose (IO mg/kg). 2
300’
F 5 v $ *
I * 250
o Control (N-51
’
l
Q Control (N-5)
Ketamlne 10 mg/kg (N-5)
l
Keta~i~e5~ s
mglkg
I *
200.
T*T,
z
2 1 1, 2 150' lsT T % TTT w"100. hns$ x a (: N 50< t. 0
SO
100
150
TIME
200
AFTER
ee5 P *5 22m6 4. 250
0
50
TETANUS
100
150
200
250
(SEC)
Fig. 2. Effect of ketamine on spinal cord PTP. DR-VR preparation. tetanus 25O/sec for 10 sec. The ordinate shows the potentiated 2N spike amplitude as a percentage of the control amplitude and the abscissa shows time in sec. 0: initial PTP responses (control): 0: PTP responses after IO mg/kg (A) and 20 mg/kg (B) of ketamine. Post-tetanic potentiation curves were determined between 15 and 20 min after the administration of ketamine. Points and brackets are means and standard errors of means. Number of animals. five cats for each dose level. * P < 0.05. when compared with corresponding control point.
responses to a single shock stimulation were decreased. This decrease developed in less than 5 min, but it was not statistically significant until 30 min after the injection of ketdmine. This depression lasted more than 60 min. Results are shown in Figures I and 3. Effects of ketamine on the PTP in motor neurones of isolated spinal cord preparation are shown in Figures 2 and 3. It is apparent that ketamine in doses of 10 and 20 mg/kg enhanced the PTP responses in cat spinal cord. The enhancement in PTP responses could be observed 5 min after the injection of ketamine and this enhancement lasted about 30 min. When smaller doses (less than 5 mg/kg) were given, no apparent potentiation or slight enhancement was observed. DISCUSSION
Behavioural and EEG changes representing seizure activity after ketamine administration have been observed in both experimental animals and in man (DOMINO, CHOWFF and CORSSEN,1965; WINTERSet al., 1972; KAYAM and IWAMA. 1972). From this
Ketamine
A
and synaptic
transmission
I49
C
B
J-L
D _L,
L
AA-
L
A_/._ (5mv AL__ L_ IOmsrc
E L
F AA-
I
G AL
H -‘LX__
Fig. 3. Effects of ketamine on the ventral root responses evoked by supramaximal stimulation on the ipsilateral dorsal root. For parameters of stimulation, see Results and Figure 2. A and E: control synaptic potentials. B and F: initial (control) post-tetanic potentiation responses. C and G: synaptic potentials determined at 15 min after 10 mg/kg (C) and 20 mg/kg (G) of ketamine. D and H: post-tetanic potentiation responses determined at 15 min after 10 mg/kg (D) and 20 mg/kg (H) of ketamine.
study it is clear that ketamine, in doses of l&20 mg/kg, significantly enhanced the PTP responses in spinal cord preparations. This effect could partially explain the seizure-inducing property of ketamine, since PTP is a general synaptic property and appears to be a normal consequence of synaptic excitation (ECCLES, 1953). The role of PTP in the spread of seizure discharge has been discussed by ESPLIN (1957). This concept is also supported by the fact that diphenylhydantoin, which is capable of modifying the pattern of maximal seizures, has a striking effect on PTP in spinal cats (ESPLIN, 1957). In addition to exerting a marked effect on PTP responses, ketamine also depressed the synaptic transmission in DR-VR preparations of the spinal cat. The polysynaptic component of the evoked potentials seems more sensitive than the monosynaptic component to the depressive effects of the ketamine. Similar results have been reported by TANG and SCHROEDER (1973). Acknowledgrnlrnts~This research was supported in part by grants from the National Science Council, Republic of China and the China Medical Board of New York, Inc., U.S.A. The authors are indebted to Dr. GRAHAM CHLN for the generous supply of ketamine HCI used in this study. REFERENCES DOMINO, E. F., CHOWFF, P. and CORSSEN. G. (1965). Pharmacological effects of CI-581, a new dissociative anesthetic, in man. Clin. Pharn~uc. Thrr. 6: 279-291. ECCLES, J. C. (1953). The Neurophysiological Basis ofMind, pp. 193-202. Oxford University Press, London. ESPLIN, D. W. (1957). Effects of diphenylhydantoin on synaptic transmission in cat spinal cord and stellate ganglion. J. Pharmac. up. Ther. 120: 301-323. KAYAMA, Y. and IWAMA, K. (1972). The EEG, evoked potentials, and single-unit activity during ketamine anesthesia in cats. Anesthesiology 36: 31&328. MORI, K., KAWAMATA, M., MITANI, H., YAMAZAKI. Y. and FUJITA, M. (1971). A neurophysiologic study of ketamine anesthesia in the cat. Anrsthesiology 35: 373-383. TANG. A. H. and SCHROEDER, L. A. (1973). Spinal-cord depressant effects of ketamine and etoxadrol in cat and the rat. Anesthesiology 39: 37-43. WINTERS, W. D., FERRAR-ALLADO, T., GUZMAN-FLORES, C. and ALCARAZ. M. (1972). The cataleptic state induced by ketamine: a review of the neuropharmacology of anesthesia. Nruropharmacology 11: 303-315.
