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Effect of pinealectomy on cortically kindled rats
Epilepsy Res., 7 (1990) 240-244
240
Elsevier
EPIRES 00375
Short Communication Effect of pinealectomy on cortically kindled rats Toshiaki Ninchoji, Kenichi U e m u r a and Ichiro S h i m o y a m a Department of Neurosurgery, Hamamatsu UniversitySchool of Medicine, 3600 Handa-cho, Hamamatsu, Shizuoka 431-31 (Japan) (Received 10 April 1989; revision received 8 August 1990; accepted 22 August 1990)
Key words: Cortical kindling; Pinealectomy; (Rat)
Cortical kindling in pinealectomized rats was studied to observe the effect of pinealectomy on local afterdischarge thresholds and seizure development. Although the local afterdischarge thresholds were not affected by pinealectomy, the kindling process itself was hastened. These results suggest that the anticonvulsive function of the pineal body is due not to a decrease in local afterdischarge thresholds, but to retardation of secondary generalization.
INTRODUCTION One of the physiological functions of the pineal body in mammals is anticonvulsive activity 1-7'16'17, although underlying mechanisms have not yet been elucidated. Whether the anticonvulsive activity of the pineal body is due to an increase in local seizure threshold or to suppression of the spread of seizure activity is not yet known. Melatonin appears to act as an anticonvulsant in different animal models of epilepsy 1'4'7'~6'~as well as in human epileptics 2. However, its anticonvulsive effect has not been shown to be dependent on the location of the epileptic focus. Results obtained from electrophysiological studies have been conflicting m-3,~6aT, with some investigators claiming that the suppression of epileptic discharges shown on the electroencephalogram (abbreviated as EEG thereafter) is due to an increased seizure threshold 2'~6'~7, and others disagreeing ~'3. Retarded generalization of epileptic activity has also been proposed 4. If retarded generalization of the Correspondence to: Toshiaki Ninchoji, M.D., Department of Neurosurgery, Hamamatsu University School of Medicine, 3600 Handa-cho, Hamarnatsu, Shizuoka 431-31, Japan.
epileptic discharges, rather than an increase in the local afterdischarge threshold, is the underlying mechanism, it would be of interest to observe the effect of pinealectomy on the local seizure threshold and at the same time on seizure development in a kindling model with a cortical focus. METHODS Twenty-seven adult male Wistar rats, aged 10 weeks and weighing 200-250 g, obtained from Shizuoka Laboratory Animal Center (Hamamatsu, Shizuoka, Japan), were used. All animals were individually housed and maintained on a 6 a.m. to 6 p.m. light-dark cycle. Food and water were provided ad libitum. The rats were implanted with bipolar stainless electrodes (MS303, Plastic Products Company, Roanoke, VA, U.S.A.), in the right area 6, using the following coordinates: 2.5 mm anterior to bregma, 2.5 mm from the mid-line, and 1.5 mm beneath the cortical surface. The electrodes consisted of insulated stainless wires, 0.25 mm in diameter, twisted together. The distance between the closest adjacent active points at the uninsulated tips of the electrodes was 0.25 mm with a contact diameter of 0.45 mm. At the time of
0920-1211/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)
241 implantation the rats were anesthetized with 50 mg/kg body weight of Nembutal ® (pentobarbital sodium, Abbott Laboratories, North Chicago, U.S.A.) given intraperitoneally, and placed in a stereotaxic apparatus (SR-6, Narishige Scientific Instrument Lab., Tokyo, Japan). The electrodes, anchored with 4 standard stainless jeweller's screws and dental cement (Repairsin® G-C Dental Industrial Co., Tokyo, Japan), were used for both stimulation and recording. Seven days were allowed for recovery, followed by 7 days of handling before the afterdischarge thresholds were determined. For the determination of afterdischarge thresholds, a stimulator (SEN 7103, Nihon Koden, Tokyo, Japan) was used, connected to an isolator (SS-201, Nihon Koden, Tokyo, Japan) and to a standard 12 V switching circuit which automatically interrupted the EEG recording during stimulation. EEG tracings were displaced on an oscilloscope and recorded with a Lineacorder (WR3151, Nihon Koden, Tokyo, Japan) to measure the afterdischarge duration. The initial afterdischarge thresholds were determined in all rats with a 60 Hz biphasic square wave pulse of I msec for the duration of I sec, given every 10 min. The current intensity was initially 25 pA and was increased in 25 ~tA increments until afterdischarges were obtained on the EEG. The animals then were randomly divided into 3 groups, namely the pinealectomy, sham-operated, and non-surgical groups. The animals in the first two groups were re-anesthetized with similar doses of Nembutal ®, and their heads fixed in a stereotaxic apparatus. The removal of the pineal bodies was accomplished with a parasagittal occipital approach under microscopic magnification (Konan Operation Microscope K-280TM, Konan Camera Co., N; hinomiya, Japan). After shaving the dorsum of their heads, a longitudinal skin incision was made. Right parieto-occipitai craniectomy was performed to expose the angle made by the dorsal sagittal and transverse sinuses. The dura mater was incised. A small part of the occipital lobe with an approximate volume of 2 x 2 x 1.5 mm 3 was suctioned. The pineal body, located underneath the confluence, came into view under the microscope and was entered with microscissors. The parenchyma of the pineal body was sucked
out without disturbing the surrounding venous sinuses. In the sham-operated group, only part of the occipital lobe was resected. The dura mater was left open and the skin was closed with 3-0 silk in both groups. Because resection of the occipital lobe was unavoidable in both the pinealectomy and the shamoperated group, a third, non-surgical group was added. Two weeks were allowed for recovery from surgery, after which the afterdischarge thresholds were determined in all 3 groups to observe the effect of the pinealectomy. Subsequently, kindling was started with the current intensity fixed at the afterdischarge threshold for each animal. Kindling stimulations were given between 7.00 and 8.00 a.m. every day. Because of the unstable state of 'full kindling' in cortical kindling, it was arbitrarily defined as more than 4 clonic-tonic-clonic general seizures in which afterdischarges lasted more than 20 sec in 5 consecutive kindling stimulations in any of above-mentioned groups. At the end of the study, all of the animals under Nembutal ® were perfused through the heart with physiological saline solution followed by 10% formalin solution, after which the whole brain from each animal was removed for later histological examination. Histological studies with hematoxylin-eosin staining were performed to confirm the position of the electrode tips, as well as to observe the completeness of the pinealectomy. In the pinealectomy group in particular, the cranial vault was resected with a Rongeur under the microscope, so as not to disturb the dura mater over the confluence. In this way, the adequacy of the surgery was confirmed before histological examination. Studem's t test was used to te~t the significance of changes in afterdischarge thresholds before and after the surgical procedures. Analysis of variance was used to test the significance of differences in kindling rates among the groups. RESULTS Ten, 8 and 9 rats were used for the pinealectomy, sham-operated and non-surgical groups, respectively. Removal of a small piece of the occipital lobe did
242
N-group(n=9
I-- . . . . . . . . . .
)
"0- ..........
I
S-group(n=
I- . . . . .
)
8
P-group (n = 10)
•
"0" .....
I- . . . .
|
4
-4
..0- . . . .
~-
.!
-4
"
afterdlscharge
threshold
800 ,A before surgery "after
surgery
Fig. 1. Effect of surgical procedures on the local afterdischarge thresholds (expressed as mean + S.D./~A). The original aRerdischarge thresholds (425 + 20"/) did not differ significantly from those (472 :!: 284) measured 2 weeks later in the non-surgical group (N-group). Afterdischatg~," thresholds before surgical procedures, 209 :t: 132 in the sham-operated group (S-group) and 254 :J: 114 in the pinealectomy (P-group) group, also did not differ significantly from those measured 2 weeks after the surgical procedures 322:1:245 in the Sgroup and 235 _-4"82 in the P-group.
not result in any significant changes in behavior or any EEG changes, as compared with the non-surgical group. There were no significant differences in body weight gain between the groups after the surgical procedures. The effect of pinealectomy on the local cortical afterdischarge thresholds was observed. No significant changes in the local afterdischarge thresholds were observed in any of the 3 groups (Fig. 1), even after surgery. As for the effect of pinealectomy on the kindling rate, in the pinealectomy group the animals reached full kindling with 25.6 -4- 4.8 stimulations, whereas 41.0 _+ 9.8 stimulations were required in the sham-
N-group(n= 9)
S-group(n= 0)
P-group(n=10)
;
~
:
!
* number of ,~tlmulatlons
10
io
•
i,
i0
Fig. 2. Kindling rate (expressed as mean + S.D.). Animals reached full kindling with 25,6 ± 5.0 stimulations in the pinealectomy group (P-group), significantly fewer than the 41.0 ± 10.5 stimulations in the sham-operated group (S-group), although no significant difference in the number of stimulations required to reach full kindling was observed between the Sgroup and the non-surgical group (N-group). The asterisk indicates a statistically significant difference.
operated group and 47.4 _+ 19.0 in the non-surgical group (Fig. 2). There was a significant difference between the pinealectomy and sham-operated groups (P < 0.05), but no significant difference between the sham-operated and non-surgical groups, indicating that removal of the pineal body hastened the kindling process. Histological studies confirmed the lack of any damage to the midbrain tectum and the complete removal of the superficial pineal bodies in the pine,,!. . . . my group. DISCUSSION The antiepileptic property of the pineal body has been examined in different animals in which excessive neuronal excitement or clinical seizures are observed when the pineal body is removed 3' 6,9,H,n, and in different models of epilepsy in which suppression of epileptic discharges on the EEG or clinical seizures is found when melatonin is given l'4's'7't6,lT,All investigators are in basic agreement that melatonin has antiepileptic properties, though the underlying mechanisms are not clear. The question has arisen as to whether the local afterfiischarge threshold is increased or not, with considerable controversy existing about the effect of melatonin on the local afterdischarge thresh-
243 o | d 1-3'16'17. Some authors have claimed that the
antiepileptic property of melatonin may be due to an increase, in the local seizure threshold 2'16'~7, while others have not been able to find any such increase ~'3. Another question is whether this antiepileptic property depends upon location of the epileptic focus in animal models of epilepsy. The antiepileptic property of melatonin has been reported in animal models of epilepsy with both subcortical 1-3 and cortical loci 4-6'16. Cortical kindling was selected as an experimental model to observe the effect of pinealectomy on the local afterdischarge threshold, and also to investigate how the elimination of circulating melatonin affected seizure development. This antiepileptic property of melatonin has been investigated in a kindling ~nodel with an amygdaloid focus ~, and in that study it was found that administration of melatonin caused reduction in the seizure rank score as well as shortened afterdischarge duration in fully kindled rats. However, in this study, the effect of melatonin on the local afterdischarge thresholds and on seizure development was not investigated. A number of studies using animal models of epilepsy other than kindling model have been conducted to investigate the effect of melatonin on the local afterdischarge threshold. Roldan et al. ~6 found an increase in the local afterdiseharge threshold for electrical stimulation in the cerebral cortex, although the threshold for topical applica-
REFERENCES 1 Albertson, T.E. et al., The anticonvulsant properties of melatonin on kindled seizures in rats, Neuropharmacology, 20 (1981) 61-66. 2 Anton-Tay, F. et al., On the effect of melatonin upon human brain. Its possible therapeutic implications, Life Sci., 10 (1971) 841-850. 3 Bindoni, M. et al., Hippocampal evoked potentials and convulsive activity after electrolytic lesions of the pineal body, in chronic experiments on rabbits, Arch. Sci. Biol., 49 (1965) 223-233. 4 Brailowsky, S., Effects of melatonin on the photosensitive epilepsy of the baboon, Papio papio, Eiectroenceph. Clin. Neurophysiol., 41 (1976) 314-319. 5 Fariello, R.G. et al., Melatonin.induced changes in the sensory activation of acute epileptic foci, Neurosci. Lett., 3 (1976) 151-155.
tion of chemical irritant was unchanged. On the other hand, other investigators 3,s observed no effect of melatonin administration on the local afterdischarge threshold. Pinealectomy9 and intraventricular injection of antimelatonin antibody 6 induced cortical epileptic discharges in the EEG in rats, although negative findings were obtained in chickens ~°. In our study, pinealectomy did not cause any changes in the baseline EEG, nor did it affect the local afterdischarge threshold. As circulating melatonin is abolished in pinealectomized rats s, a lack of melatonin does not seem to affect the local afterdischarge threshold. Philo et al. and Reiter et al. developed new experimental epilepsy models in Mongolian gerbils by pinealectomy 12'~3and in rats by a combination of parathyroidectomy and pinealectomy n'~4'~s and suggested that the pineal body may exibit its antiepileptic property by stabilizing brain amines n'~3, although it was not clear whether the decrease in monoamines was caused by pinealectomy. Brailowsky presented an interesting suggestion in a study using photosensitive baboons; namely that the anticonvulsive property of melatonin is due to the suppression of generalization of seizure activity 4. This is in agreement with our results, which showed that pinealectomy hastened secondary generalization without affecting the afterdischarge threshold of the cortical focus.
6 Fariello, R G . et al., Epileptogenic action of intraventricularly injected antimelatonin antibody, Neurology, 27 (1977) 567-570. 7 Izumi, K. et al., Ouabain-induced seizures in rats: modification by melatonin and melanocyte-stimulating hormone, Can. J. Physiol. Pharmacol., 51 (1973) 572-578. 8 Lewy, A.J. et al., Pinealectomy abolishes plasma melatonin in the rat, J. Clin. Endocrinol. Metab., 50 (1980) 204-205. 9 Nir, I. et al., Changes in the electrical activity of the brain following pinealectomy, Neuroendocrinology, 4 (1969) 122-127. 10 Pang, S.F. et al., Effects of melatonin administration and pinealectomy on the electroencephalogram of the chicken (Gallus domesticus) brain, Life Sci., 18 (1976) 961-966. 11 Philo, R., et al., Brain amines and convulsions in four strains of parathyroidectomized, pinealectomized rat, Epi. lepsia, 19 (1978) 133-137.
244 12 Philo, R. et al., Characterization of pinealectomy induced convulsions in the Mongolian gerbil (Meriones unguiculatus), Epilepsia, 19 (1978) 485-492. 13 Philo, R. et al., Changes in brain dopamine, norepinephrine and serotonin associated with convulsions induced by pinealectomy in the gerbil, J. Neural. Transm., 46 (1979) 239-252. 14 Reiter, R.J. et al., Muscular spasms and death in thyroparathyroidectomized rats subjected to pinealectomy, Life Sci., 11 (1972) 123-133.
15 Reiter, R.J. et al., Nature and the time course of seizures associated with surgical removal of the pineal gland from parathyroidectomized rat, Exp. Neurol., 38 (1973) 386-397. 16 Roldan, E. et al., EEG and convulsive threshold changes produced by pineal extract administration, Brain Res., 11 (1968) 238-245. 17 Sugden, D., Psychopharmacological effects of melatonin in mouse and rat, J. Pharmacol. Exp. Ther., 227 (1983) 587-591.
240
Elsevier
EPIRES 00375
Short Communication Effect of pinealectomy on cortically kindled rats Toshiaki Ninchoji, Kenichi U e m u r a and Ichiro S h i m o y a m a Department of Neurosurgery, Hamamatsu UniversitySchool of Medicine, 3600 Handa-cho, Hamamatsu, Shizuoka 431-31 (Japan) (Received 10 April 1989; revision received 8 August 1990; accepted 22 August 1990)
Key words: Cortical kindling; Pinealectomy; (Rat)
Cortical kindling in pinealectomized rats was studied to observe the effect of pinealectomy on local afterdischarge thresholds and seizure development. Although the local afterdischarge thresholds were not affected by pinealectomy, the kindling process itself was hastened. These results suggest that the anticonvulsive function of the pineal body is due not to a decrease in local afterdischarge thresholds, but to retardation of secondary generalization.
INTRODUCTION One of the physiological functions of the pineal body in mammals is anticonvulsive activity 1-7'16'17, although underlying mechanisms have not yet been elucidated. Whether the anticonvulsive activity of the pineal body is due to an increase in local seizure threshold or to suppression of the spread of seizure activity is not yet known. Melatonin appears to act as an anticonvulsant in different animal models of epilepsy 1'4'7'~6'~as well as in human epileptics 2. However, its anticonvulsive effect has not been shown to be dependent on the location of the epileptic focus. Results obtained from electrophysiological studies have been conflicting m-3,~6aT, with some investigators claiming that the suppression of epileptic discharges shown on the electroencephalogram (abbreviated as EEG thereafter) is due to an increased seizure threshold 2'~6'~7, and others disagreeing ~'3. Retarded generalization of epileptic activity has also been proposed 4. If retarded generalization of the Correspondence to: Toshiaki Ninchoji, M.D., Department of Neurosurgery, Hamamatsu University School of Medicine, 3600 Handa-cho, Hamarnatsu, Shizuoka 431-31, Japan.
epileptic discharges, rather than an increase in the local afterdischarge threshold, is the underlying mechanism, it would be of interest to observe the effect of pinealectomy on the local seizure threshold and at the same time on seizure development in a kindling model with a cortical focus. METHODS Twenty-seven adult male Wistar rats, aged 10 weeks and weighing 200-250 g, obtained from Shizuoka Laboratory Animal Center (Hamamatsu, Shizuoka, Japan), were used. All animals were individually housed and maintained on a 6 a.m. to 6 p.m. light-dark cycle. Food and water were provided ad libitum. The rats were implanted with bipolar stainless electrodes (MS303, Plastic Products Company, Roanoke, VA, U.S.A.), in the right area 6, using the following coordinates: 2.5 mm anterior to bregma, 2.5 mm from the mid-line, and 1.5 mm beneath the cortical surface. The electrodes consisted of insulated stainless wires, 0.25 mm in diameter, twisted together. The distance between the closest adjacent active points at the uninsulated tips of the electrodes was 0.25 mm with a contact diameter of 0.45 mm. At the time of
0920-1211/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)
241 implantation the rats were anesthetized with 50 mg/kg body weight of Nembutal ® (pentobarbital sodium, Abbott Laboratories, North Chicago, U.S.A.) given intraperitoneally, and placed in a stereotaxic apparatus (SR-6, Narishige Scientific Instrument Lab., Tokyo, Japan). The electrodes, anchored with 4 standard stainless jeweller's screws and dental cement (Repairsin® G-C Dental Industrial Co., Tokyo, Japan), were used for both stimulation and recording. Seven days were allowed for recovery, followed by 7 days of handling before the afterdischarge thresholds were determined. For the determination of afterdischarge thresholds, a stimulator (SEN 7103, Nihon Koden, Tokyo, Japan) was used, connected to an isolator (SS-201, Nihon Koden, Tokyo, Japan) and to a standard 12 V switching circuit which automatically interrupted the EEG recording during stimulation. EEG tracings were displaced on an oscilloscope and recorded with a Lineacorder (WR3151, Nihon Koden, Tokyo, Japan) to measure the afterdischarge duration. The initial afterdischarge thresholds were determined in all rats with a 60 Hz biphasic square wave pulse of I msec for the duration of I sec, given every 10 min. The current intensity was initially 25 pA and was increased in 25 ~tA increments until afterdischarges were obtained on the EEG. The animals then were randomly divided into 3 groups, namely the pinealectomy, sham-operated, and non-surgical groups. The animals in the first two groups were re-anesthetized with similar doses of Nembutal ®, and their heads fixed in a stereotaxic apparatus. The removal of the pineal bodies was accomplished with a parasagittal occipital approach under microscopic magnification (Konan Operation Microscope K-280TM, Konan Camera Co., N; hinomiya, Japan). After shaving the dorsum of their heads, a longitudinal skin incision was made. Right parieto-occipitai craniectomy was performed to expose the angle made by the dorsal sagittal and transverse sinuses. The dura mater was incised. A small part of the occipital lobe with an approximate volume of 2 x 2 x 1.5 mm 3 was suctioned. The pineal body, located underneath the confluence, came into view under the microscope and was entered with microscissors. The parenchyma of the pineal body was sucked
out without disturbing the surrounding venous sinuses. In the sham-operated group, only part of the occipital lobe was resected. The dura mater was left open and the skin was closed with 3-0 silk in both groups. Because resection of the occipital lobe was unavoidable in both the pinealectomy and the shamoperated group, a third, non-surgical group was added. Two weeks were allowed for recovery from surgery, after which the afterdischarge thresholds were determined in all 3 groups to observe the effect of the pinealectomy. Subsequently, kindling was started with the current intensity fixed at the afterdischarge threshold for each animal. Kindling stimulations were given between 7.00 and 8.00 a.m. every day. Because of the unstable state of 'full kindling' in cortical kindling, it was arbitrarily defined as more than 4 clonic-tonic-clonic general seizures in which afterdischarges lasted more than 20 sec in 5 consecutive kindling stimulations in any of above-mentioned groups. At the end of the study, all of the animals under Nembutal ® were perfused through the heart with physiological saline solution followed by 10% formalin solution, after which the whole brain from each animal was removed for later histological examination. Histological studies with hematoxylin-eosin staining were performed to confirm the position of the electrode tips, as well as to observe the completeness of the pinealectomy. In the pinealectomy group in particular, the cranial vault was resected with a Rongeur under the microscope, so as not to disturb the dura mater over the confluence. In this way, the adequacy of the surgery was confirmed before histological examination. Studem's t test was used to te~t the significance of changes in afterdischarge thresholds before and after the surgical procedures. Analysis of variance was used to test the significance of differences in kindling rates among the groups. RESULTS Ten, 8 and 9 rats were used for the pinealectomy, sham-operated and non-surgical groups, respectively. Removal of a small piece of the occipital lobe did
242
N-group(n=9
I-- . . . . . . . . . .
)
"0- ..........
I
S-group(n=
I- . . . . .
)
8
P-group (n = 10)
•
"0" .....
I- . . . .
|
4
-4
..0- . . . .
~-
.!
-4
"
afterdlscharge
threshold
800 ,A before surgery "after
surgery
Fig. 1. Effect of surgical procedures on the local afterdischarge thresholds (expressed as mean + S.D./~A). The original aRerdischarge thresholds (425 + 20"/) did not differ significantly from those (472 :!: 284) measured 2 weeks later in the non-surgical group (N-group). Afterdischatg~," thresholds before surgical procedures, 209 :t: 132 in the sham-operated group (S-group) and 254 :J: 114 in the pinealectomy (P-group) group, also did not differ significantly from those measured 2 weeks after the surgical procedures 322:1:245 in the Sgroup and 235 _-4"82 in the P-group.
not result in any significant changes in behavior or any EEG changes, as compared with the non-surgical group. There were no significant differences in body weight gain between the groups after the surgical procedures. The effect of pinealectomy on the local cortical afterdischarge thresholds was observed. No significant changes in the local afterdischarge thresholds were observed in any of the 3 groups (Fig. 1), even after surgery. As for the effect of pinealectomy on the kindling rate, in the pinealectomy group the animals reached full kindling with 25.6 -4- 4.8 stimulations, whereas 41.0 _+ 9.8 stimulations were required in the sham-
N-group(n= 9)
S-group(n= 0)
P-group(n=10)
;
~
:
!
* number of ,~tlmulatlons
10
io
•
i,
i0
Fig. 2. Kindling rate (expressed as mean + S.D.). Animals reached full kindling with 25,6 ± 5.0 stimulations in the pinealectomy group (P-group), significantly fewer than the 41.0 ± 10.5 stimulations in the sham-operated group (S-group), although no significant difference in the number of stimulations required to reach full kindling was observed between the Sgroup and the non-surgical group (N-group). The asterisk indicates a statistically significant difference.
operated group and 47.4 _+ 19.0 in the non-surgical group (Fig. 2). There was a significant difference between the pinealectomy and sham-operated groups (P < 0.05), but no significant difference between the sham-operated and non-surgical groups, indicating that removal of the pineal body hastened the kindling process. Histological studies confirmed the lack of any damage to the midbrain tectum and the complete removal of the superficial pineal bodies in the pine,,!. . . . my group. DISCUSSION The antiepileptic property of the pineal body has been examined in different animals in which excessive neuronal excitement or clinical seizures are observed when the pineal body is removed 3' 6,9,H,n, and in different models of epilepsy in which suppression of epileptic discharges on the EEG or clinical seizures is found when melatonin is given l'4's'7't6,lT,All investigators are in basic agreement that melatonin has antiepileptic properties, though the underlying mechanisms are not clear. The question has arisen as to whether the local afterfiischarge threshold is increased or not, with considerable controversy existing about the effect of melatonin on the local afterdischarge thresh-
243 o | d 1-3'16'17. Some authors have claimed that the
antiepileptic property of melatonin may be due to an increase, in the local seizure threshold 2'16'~7, while others have not been able to find any such increase ~'3. Another question is whether this antiepileptic property depends upon location of the epileptic focus in animal models of epilepsy. The antiepileptic property of melatonin has been reported in animal models of epilepsy with both subcortical 1-3 and cortical loci 4-6'16. Cortical kindling was selected as an experimental model to observe the effect of pinealectomy on the local afterdischarge threshold, and also to investigate how the elimination of circulating melatonin affected seizure development. This antiepileptic property of melatonin has been investigated in a kindling ~nodel with an amygdaloid focus ~, and in that study it was found that administration of melatonin caused reduction in the seizure rank score as well as shortened afterdischarge duration in fully kindled rats. However, in this study, the effect of melatonin on the local afterdischarge thresholds and on seizure development was not investigated. A number of studies using animal models of epilepsy other than kindling model have been conducted to investigate the effect of melatonin on the local afterdischarge threshold. Roldan et al. ~6 found an increase in the local afterdiseharge threshold for electrical stimulation in the cerebral cortex, although the threshold for topical applica-
REFERENCES 1 Albertson, T.E. et al., The anticonvulsant properties of melatonin on kindled seizures in rats, Neuropharmacology, 20 (1981) 61-66. 2 Anton-Tay, F. et al., On the effect of melatonin upon human brain. Its possible therapeutic implications, Life Sci., 10 (1971) 841-850. 3 Bindoni, M. et al., Hippocampal evoked potentials and convulsive activity after electrolytic lesions of the pineal body, in chronic experiments on rabbits, Arch. Sci. Biol., 49 (1965) 223-233. 4 Brailowsky, S., Effects of melatonin on the photosensitive epilepsy of the baboon, Papio papio, Eiectroenceph. Clin. Neurophysiol., 41 (1976) 314-319. 5 Fariello, R.G. et al., Melatonin.induced changes in the sensory activation of acute epileptic foci, Neurosci. Lett., 3 (1976) 151-155.
tion of chemical irritant was unchanged. On the other hand, other investigators 3,s observed no effect of melatonin administration on the local afterdischarge threshold. Pinealectomy9 and intraventricular injection of antimelatonin antibody 6 induced cortical epileptic discharges in the EEG in rats, although negative findings were obtained in chickens ~°. In our study, pinealectomy did not cause any changes in the baseline EEG, nor did it affect the local afterdischarge threshold. As circulating melatonin is abolished in pinealectomized rats s, a lack of melatonin does not seem to affect the local afterdischarge threshold. Philo et al. and Reiter et al. developed new experimental epilepsy models in Mongolian gerbils by pinealectomy 12'~3and in rats by a combination of parathyroidectomy and pinealectomy n'~4'~s and suggested that the pineal body may exibit its antiepileptic property by stabilizing brain amines n'~3, although it was not clear whether the decrease in monoamines was caused by pinealectomy. Brailowsky presented an interesting suggestion in a study using photosensitive baboons; namely that the anticonvulsive property of melatonin is due to the suppression of generalization of seizure activity 4. This is in agreement with our results, which showed that pinealectomy hastened secondary generalization without affecting the afterdischarge threshold of the cortical focus.
6 Fariello, R G . et al., Epileptogenic action of intraventricularly injected antimelatonin antibody, Neurology, 27 (1977) 567-570. 7 Izumi, K. et al., Ouabain-induced seizures in rats: modification by melatonin and melanocyte-stimulating hormone, Can. J. Physiol. Pharmacol., 51 (1973) 572-578. 8 Lewy, A.J. et al., Pinealectomy abolishes plasma melatonin in the rat, J. Clin. Endocrinol. Metab., 50 (1980) 204-205. 9 Nir, I. et al., Changes in the electrical activity of the brain following pinealectomy, Neuroendocrinology, 4 (1969) 122-127. 10 Pang, S.F. et al., Effects of melatonin administration and pinealectomy on the electroencephalogram of the chicken (Gallus domesticus) brain, Life Sci., 18 (1976) 961-966. 11 Philo, R., et al., Brain amines and convulsions in four strains of parathyroidectomized, pinealectomized rat, Epi. lepsia, 19 (1978) 133-137.
244 12 Philo, R. et al., Characterization of pinealectomy induced convulsions in the Mongolian gerbil (Meriones unguiculatus), Epilepsia, 19 (1978) 485-492. 13 Philo, R. et al., Changes in brain dopamine, norepinephrine and serotonin associated with convulsions induced by pinealectomy in the gerbil, J. Neural. Transm., 46 (1979) 239-252. 14 Reiter, R.J. et al., Muscular spasms and death in thyroparathyroidectomized rats subjected to pinealectomy, Life Sci., 11 (1972) 123-133.
15 Reiter, R.J. et al., Nature and the time course of seizures associated with surgical removal of the pineal gland from parathyroidectomized rat, Exp. Neurol., 38 (1973) 386-397. 16 Roldan, E. et al., EEG and convulsive threshold changes produced by pineal extract administration, Brain Res., 11 (1968) 238-245. 17 Sugden, D., Psychopharmacological effects of melatonin in mouse and rat, J. Pharmacol. Exp. Ther., 227 (1983) 587-591.