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Effects of tiletamine on spinal cord synaptic transmission
European Journal of Pharmacology 27 (1974) 346-348 © North-Holland Publishing Company
Short c o m m u n i c a t i o n
EFFECTS OF TILETAMINE ON SPINAL CORD SYNAPTIC TRANSMISSION Chieh-Fu CHEN and Sien-Yao CHOW Department of Biophysics, National Defense Medical Center, Taipei, Taiwan, Republic of China
Received 27 May 1974, accepted 31 May 1974 C.-F. CHEN and S.-Y. CHOW,Effects of tiletamine on spinal cord synaptic transmission, European J. Pharmacol. 27 (1974) 346-348. The effect of tiletamine on synaptic transmission was studied in the dorsal root-ventral root preparation of unanesthetized spinal cats. Tiletamine, 10-20 mg/kg, reduced the evoked monosynaptic response of motoneurons with only slight depression on polysynaptic responses. It also augmented the post-tetanic potentiation (PTP) of monosynaptic responses, which may be related to its seizure-producing property. The effect of tiletamine developed within 5 min after i.v. administration and lasted for more than 1 hr. Tiletamine
Synaptic transmission
Motoneurone
1. Introduction Tiletamine (2-(ethylamino)-2-(2-thienyl)-cyclohexanone HC1, CI-634) is an analog of phencyclidine and ketamine which can produce catalepsy and general anesthesia in a variety of animals. It acts principally on the central nervous system and its pharmacological effects have been briefly described (Chen and Ensor, 1968; Chen et al., 1969). This study was undertaken to investigate the effect of tiletamine on the evoked responses of motoneurons in dorsal root-ventral root preparations of unanesthetized cats.
2. Materials and methods 22 unanesthetized spinal cats of either sex, weighing between 2.2 and 3.5 kg, were used in this study. The general methods described by Esplin (1957) were followed. The spinal cord was. transected at the atlanto-occipital junction under brief ether anesthesia. The animals were maintained on artificial respiration. All experiments were done in dorsal root-ventral root ( D R - V R ) preparations. Ventral root (L7 or $1) monosynaptic (2N) and polysynaptic responses were
Post-tetanic potentiation
elicited by stimulation of the homolateral dorsal root of the same segment with stimuli of twice supramaxireal voltage applied at 0.2 Hz. The duration of the rectangular pulses was 0.2 msec. For the study of post-tetanic potentiation of 2N responses, a 250 Hz stimulus applied for 10 sec 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 quantitation of responses, the mean of 5 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 1 - 2 hr. If the response showed sufficient stability, control recordings were made and the drug was administered. The tests following drug administration were continued for 2 - 4 hr. Tiletamine, dissolved in 0.9% NaC1 solution and prepared immediately before each experiment, was administered i.v. in 3 levels of dosage (5, 10 and
347
C.-F. Chen, S..Y. Chow, Tiletamine and synaptic transmission ,-I 0 140
500
oTilefemine
zIu0 1 2 0 u. 0
5mg/Kg
(N-5)
• Tiletamlne
IOmg/Kg
(N-7)
*
20mg/Kg
(N=4)
Tlletornine
(2: to= 4 0 0 o
I00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Iz
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80Z[
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T
T
~
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l
I
1
l
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1
I
1
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* Control (N=4) • Tlletamlne 5mg/Kg
(N-4)
I * Control (N-4) • Tiletom|ne IOmg/Kg
(N-4}
:500
._1 ~L 2 0 0 =E
I
I
h- I 0 0 1/) Z
Z ..
o
,o 2 o
3'0 4'o 5'o s'o
o 5'o ,60
f~o 260 zso o
5'0 16o ,~o 260 2~o
TIME AFTER TETANUS (SEC) TIME AFTER TILETAMINE (MIN)
Fig. 1. Effect of tiletamine on evoked monosynaptic potential (2N spike) in DR-VR preparations of spinal cats: The 9rdinate shows the 2N spike amplitude as a percentage of pre-drug control amplitude and the abscissa, time in min. Points and brackets are means -+S.E.M. The 2N spike amplitudes in experiments after I0 and 20 mg/kg of tiletamine are significantly different from the controls (p < 0.05).
20 mg/kg). Each animal received only 1 injection o f tiletamine.
3. Results Tiletamine, 5 to 20 mg/kg, consistently depressed monosynaptic responses in cat spinal preparations. The degree o f depression on the evoked monosynaptic potentials was directly related to the dose o f tiletamine (fig. 1). The depression was noticed in less than 5 min after i.v. injection o f the drug and lasted for more than 1 hr. The evoked polysynaptic response was consistently, but not significantly, reduced. The post-tetanic potentiation of monosynaptic responses (PTPP in motoneurones of isolated spinal cord preparation was modified after tiletamine. Although some degree of augmentation in PTP was observed at all three dose levels, it was only significant at 10 mg/kg (fig. 2). Like the effect On monosynaptic responses, the effect of tiletamine on PTP developed prompt!y, becoming maximal at about 15 min after drug administration and lasted for more than 1 hr.
Fig. 2. Effect of tiletamine on spinal PTP. DR-VR preparation, tetanus 250/see for 10 sec. The ordinate shows the potentiated 2N spike amplitude as a percentage of the control amplitude and abscissa, time in see. o, Initial PTP responses (control); e, PTP responses after 5 mg/kg or 10 mg/kg of tiletamine. PTP curves were determined between 15 and 20 min after administration of tiletamine. Points and brackets are means -+S.E.M. *p < 0.05 when compared with its control.
4. Discussion It has been shown (Domino et al., 1965; Winters and Ferrar-AUado, 1972; Kayama and Iwama, 1972) that phencyclidine and ketamine induce behavioral and electroencephalographic changes representative o f seizure activity in b o t h experimental animals and men. Chen et al. (1969) have also noted brief and mild clonic seizure in some cats and monkeys after large doses of tiletamine. Results in this study demonstrated that tiletamine augmented the PTP and depressed the monosynaptic responses in the D R - V R preparation o f spinal cats. Since PTP is an important factor in the spread of seizure activity (Esplin, 1957), enhanced PTP responses could explain the epileptogenic properties o f ,this compound. Preliminary experiments revealed that ketamine exhibited similar effects in the same preparation of spinal cats (unpublished observations).
Acknowledgements This research was supported in part by a grant from the National Science Council, Republic of China. The authors are
348
C.-F. Chen, S.- Y. Chow, Tiletamine and synaptic transmission
indebted to Dr. Alexander M. Moore, Director of Research Information Services of Parke, Davis & Company, for the generous supply of tiletamine HC1 used in this study.
References Chen, G. and C.R. Ensor, 1968, 2-(Ethylamino)-2(2-thienyl)cyclohexanone" HC1 (CI-634), a taming, incapacitating and anesthetic agent for the cat, Amer. J. Vet. Res. 29, 863. Chert, G., C.R. Ensor and B. Bohner, 1969, The pharmacology of 2-(ethylamino)-2-(2-thienyl)-cyclohexanone HCI (CI634), J. Pharmacol. Expfl. Therap. 168, 171.
Domino, E.F., P. Chodoffjand G. Corssen, 1965, Pharmacological effects of CI-581, a new dissociative anesthetic, in man, Clin. Pharmacol. Therap. 6,279. Esplin, D.W., 1957, Effects of diphenylhydantoin on synaptic transmission in cat spinal cord and stellate ganglion, J. Pharmacol. Exptl. Therap. 120,301. Kayama, Y. and K. Iwama, 1972, The EEG, evoked potentials, and single-unit activity during ketamine anesthesia in cats, Anesthesiology 36,316. Winters, W.D. and T. Ferrar-Allado, 1972, The cataleptic state induced by ketamine: A review of the neuropharmacology of anesthesia, Neuropharmacology 11,303.
Short c o m m u n i c a t i o n
EFFECTS OF TILETAMINE ON SPINAL CORD SYNAPTIC TRANSMISSION Chieh-Fu CHEN and Sien-Yao CHOW Department of Biophysics, National Defense Medical Center, Taipei, Taiwan, Republic of China
Received 27 May 1974, accepted 31 May 1974 C.-F. CHEN and S.-Y. CHOW,Effects of tiletamine on spinal cord synaptic transmission, European J. Pharmacol. 27 (1974) 346-348. The effect of tiletamine on synaptic transmission was studied in the dorsal root-ventral root preparation of unanesthetized spinal cats. Tiletamine, 10-20 mg/kg, reduced the evoked monosynaptic response of motoneurons with only slight depression on polysynaptic responses. It also augmented the post-tetanic potentiation (PTP) of monosynaptic responses, which may be related to its seizure-producing property. The effect of tiletamine developed within 5 min after i.v. administration and lasted for more than 1 hr. Tiletamine
Synaptic transmission
Motoneurone
1. Introduction Tiletamine (2-(ethylamino)-2-(2-thienyl)-cyclohexanone HC1, CI-634) is an analog of phencyclidine and ketamine which can produce catalepsy and general anesthesia in a variety of animals. It acts principally on the central nervous system and its pharmacological effects have been briefly described (Chen and Ensor, 1968; Chen et al., 1969). This study was undertaken to investigate the effect of tiletamine on the evoked responses of motoneurons in dorsal root-ventral root preparations of unanesthetized cats.
2. Materials and methods 22 unanesthetized spinal cats of either sex, weighing between 2.2 and 3.5 kg, were used in this study. The general methods described by Esplin (1957) were followed. The spinal cord was. transected at the atlanto-occipital junction under brief ether anesthesia. The animals were maintained on artificial respiration. All experiments were done in dorsal root-ventral root ( D R - V R ) preparations. Ventral root (L7 or $1) monosynaptic (2N) and polysynaptic responses were
Post-tetanic potentiation
elicited by stimulation of the homolateral dorsal root of the same segment with stimuli of twice supramaxireal voltage applied at 0.2 Hz. The duration of the rectangular pulses was 0.2 msec. For the study of post-tetanic potentiation of 2N responses, a 250 Hz stimulus applied for 10 sec 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 quantitation of responses, the mean of 5 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 1 - 2 hr. If the response showed sufficient stability, control recordings were made and the drug was administered. The tests following drug administration were continued for 2 - 4 hr. Tiletamine, dissolved in 0.9% NaC1 solution and prepared immediately before each experiment, was administered i.v. in 3 levels of dosage (5, 10 and
347
C.-F. Chen, S..Y. Chow, Tiletamine and synaptic transmission ,-I 0 140
500
oTilefemine
zIu0 1 2 0 u. 0
5mg/Kg
(N-5)
• Tiletamlne
IOmg/Kg
(N-7)
*
20mg/Kg
(N=4)
Tlletornine
(2: to= 4 0 0 o
I00 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Iz
o•
80Z[
~_ .d
T
T
T
~
l
l
I
1
l
l
1
I
1
z
z
6°[I
* Control (N=4) • Tlletamlne 5mg/Kg
(N-4)
I * Control (N-4) • Tiletom|ne IOmg/Kg
(N-4}
:500
._1 ~L 2 0 0 =E
I
I
h- I 0 0 1/) Z
Z ..
o
,o 2 o
3'0 4'o 5'o s'o
o 5'o ,60
f~o 260 zso o
5'0 16o ,~o 260 2~o
TIME AFTER TETANUS (SEC) TIME AFTER TILETAMINE (MIN)
Fig. 1. Effect of tiletamine on evoked monosynaptic potential (2N spike) in DR-VR preparations of spinal cats: The 9rdinate shows the 2N spike amplitude as a percentage of pre-drug control amplitude and the abscissa, time in min. Points and brackets are means -+S.E.M. The 2N spike amplitudes in experiments after I0 and 20 mg/kg of tiletamine are significantly different from the controls (p < 0.05).
20 mg/kg). Each animal received only 1 injection o f tiletamine.
3. Results Tiletamine, 5 to 20 mg/kg, consistently depressed monosynaptic responses in cat spinal preparations. The degree o f depression on the evoked monosynaptic potentials was directly related to the dose o f tiletamine (fig. 1). The depression was noticed in less than 5 min after i.v. injection o f the drug and lasted for more than 1 hr. The evoked polysynaptic response was consistently, but not significantly, reduced. The post-tetanic potentiation of monosynaptic responses (PTPP in motoneurones of isolated spinal cord preparation was modified after tiletamine. Although some degree of augmentation in PTP was observed at all three dose levels, it was only significant at 10 mg/kg (fig. 2). Like the effect On monosynaptic responses, the effect of tiletamine on PTP developed prompt!y, becoming maximal at about 15 min after drug administration and lasted for more than 1 hr.
Fig. 2. Effect of tiletamine on spinal PTP. DR-VR preparation, tetanus 250/see for 10 sec. The ordinate shows the potentiated 2N spike amplitude as a percentage of the control amplitude and abscissa, time in see. o, Initial PTP responses (control); e, PTP responses after 5 mg/kg or 10 mg/kg of tiletamine. PTP curves were determined between 15 and 20 min after administration of tiletamine. Points and brackets are means -+S.E.M. *p < 0.05 when compared with its control.
4. Discussion It has been shown (Domino et al., 1965; Winters and Ferrar-AUado, 1972; Kayama and Iwama, 1972) that phencyclidine and ketamine induce behavioral and electroencephalographic changes representative o f seizure activity in b o t h experimental animals and men. Chen et al. (1969) have also noted brief and mild clonic seizure in some cats and monkeys after large doses of tiletamine. Results in this study demonstrated that tiletamine augmented the PTP and depressed the monosynaptic responses in the D R - V R preparation o f spinal cats. Since PTP is an important factor in the spread of seizure activity (Esplin, 1957), enhanced PTP responses could explain the epileptogenic properties o f ,this compound. Preliminary experiments revealed that ketamine exhibited similar effects in the same preparation of spinal cats (unpublished observations).
Acknowledgements This research was supported in part by a grant from the National Science Council, Republic of China. The authors are
348
C.-F. Chen, S.- Y. Chow, Tiletamine and synaptic transmission
indebted to Dr. Alexander M. Moore, Director of Research Information Services of Parke, Davis & Company, for the generous supply of tiletamine HC1 used in this study.
References Chen, G. and C.R. Ensor, 1968, 2-(Ethylamino)-2(2-thienyl)cyclohexanone" HC1 (CI-634), a taming, incapacitating and anesthetic agent for the cat, Amer. J. Vet. Res. 29, 863. Chert, G., C.R. Ensor and B. Bohner, 1969, The pharmacology of 2-(ethylamino)-2-(2-thienyl)-cyclohexanone HCI (CI634), J. Pharmacol. Expfl. Therap. 168, 171.
Domino, E.F., P. Chodoffjand G. Corssen, 1965, Pharmacological effects of CI-581, a new dissociative anesthetic, in man, Clin. Pharmacol. Therap. 6,279. Esplin, D.W., 1957, Effects of diphenylhydantoin on synaptic transmission in cat spinal cord and stellate ganglion, J. Pharmacol. Exptl. Therap. 120,301. Kayama, Y. and K. Iwama, 1972, The EEG, evoked potentials, and single-unit activity during ketamine anesthesia in cats, Anesthesiology 36,316. Winters, W.D. and T. Ferrar-Allado, 1972, The cataleptic state induced by ketamine: A review of the neuropharmacology of anesthesia, Neuropharmacology 11,303.