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Noradrenergic involvement in pinealectomy induced convulsions in gerbils
Neuroscience Letters, 120 (1990)245-248
245
ElsevierScientificPublishers Ireland Ltd. NSL 07366
Noradrenergic involvement in pinealectomy induced convulsions in gerbils T h o m a s H. C h a m p n e y Department of Anatomy, Collegeof Medicine, Texas A &M University, College Station, TX 77843-1114 ( U.S.A. )
(Received29 May 1990;Revisedversionreceived21 August 1990;Accepted27 August 1990) Key words: Pineal;Convulsion;Norepinephrine;ct-Methylparatyrosine;Gerbil
Gerbils treated with various noradrenergic compounds were pinealectomized(PINX) or sham-operated (SHAM) and observed for convulsive activity. Although declinesin cortical and hypothalamicnorepinephrinecontent were found after ct-methylparatyrosine(ctMPT)or PINX, treatment with ctMPTdid not produce convulsions in SHAM gerbils or in gerbils which were PINX one week earlier. Likewise,ctMPTdid not increase the number or severityof convulsionsobservedin acutelyPINX gerbils. Treatment with propranolol or isoproterenoldid not have any effecton convulsive activity of PINX gerbils, except that isoproterenol increased the excitabilityof all the gerbils. In conclusion, reducing catecholaminecontent or modifyingfl-noradrenergicreceptor activitywas not able to alter the convulsiveactivitywhich occurs after acute PINX.
Previous research established that removal of the pineal from gerbils resulted in grand real-type seizures which are characterized by wild running and massive tonic/clonic convulsions [6]. Pinealectomy (PINX) also lowered cerebral norepinephrine (NE) levels, but, at that time, it was not known whether the depressed levels were responsible for the convulsive behavior or a result of the convulsions [7]. Neither cortical serotonin nor cortical dopamine were involved in the PINX-induced convulsions [7]. More recent evidence suggested that the depressed cortical N E levels facilitated PINX-induced convulsive activity [5, 8]. Philo found that treatment of PINX gerbils with L-dihydroxyphenylalanine (L-DOPA) prevented the convulsive activity, while treatment with at-methylparatyrosine (ctMPT) increased seizure activity [5]. He concluded that decreased production o f cortical NE occurred after PINX and that this depression promoted the convulsive activity associated with PINX o f gerbils [5]. It is important to note that depression of NE levels in intact gerbils did not produce convulsions [5] indicating that a decline in N E content is not the only change required to produce convulsions in this seizure model. Male Mongolian gerbils (Meriones unguiculatus), 9 weeks old, were obtained from Tumblebrook Farms, West Brookfield, MA. Thirty gerbils arrived in early Correspondence: T.H. Champney, Department of Anatomy, Collegeof Medicine, Texas A&M University, College Station, TX 77843-1114, U.S.A.
0304-3940/90/$03.50 © 1990ElsevierScientificPublishers Ireland Ltd.
May, 1989, and were allowed to acclimate for 3 weeks with food and water continuously available. The gerbils were exposed to long photoperiods (14L:10D, lights on at 05.00h) and constant temperatures (22___2°C). Ten gerbils were PINX [2] and allowed to recover for 1 week ( C H R O N I C PINX). Of the 10 gerbils PINX, 1 died while under pentobarbital anesthesia and another died approximately 5 h after surgery. Another 10 gerbils were sham-operated (SHAM) at the same time and also allowed to recover for 1 week. On the day of experimentation, 2 unoperated gerbils were pinealectomized (ACUTE PINX) and injected with either saline or ~tMPT methyl ester (250 mg/kg, i.p.), 2 SHAM gerbils were injected with saline or 0tMPT and 2 C H R O N I C PINX gerbils were injected with saline or ~MPT. These 6 gerbils were monitored for convulsive activity for 3 h [2]. At the end of the observation period, the gerbils were killed by decapitation while anesthetized with metofane. The completeness of the surgical treatments was checked and portions of the parietal cortex and the medial basal hypothalamus were collected, weighed and frozen. Six additional gerbils (2 from each treatment group) were studied each day for 4 additional days to provide at least 4 gerbils in each treatment group. This complete experimental design was repeated with an additional 30 gerbils which were obtained in early June, 1989. The only difference in this new protocol was that the SHAM operations were performed at the time of A C U T E PINX and not when the C H R O N I C PINX were performed. Since the results from the 2 experiments
246
were virtually identical, the data from both experiments were combined to yield between 7 and 11 gerbils for each of the 6 treatment groups. In a third experiment, 30 gerbils, obtained in October, 1988, were randomly assigned to 6 groups in a 2 × 3 factorial design. The gerbils were either acutely SHAM or ACUTE PINX and received saline, isoproterenol (1 mg/ kg, ip) or propranolol (5 mg/kg, i.p.). Six sessions of 5 gerbils per session were examined for seizure activity for 4 h [2] and their cortical and hypothalamic tissues were collected at the end of the examination period. The gerbils in each session were from a random mix of the 6 treatment groups to eliminate or reduce intersession error or investigator bias. High-pressure liquid chromatography with electrochemical detection was utilized to determine catecholamine content in various neural regions of the gerbils [1]. The catecholamine data were analyzed by two-way analysis of variance with the student Neuman-Keuls test used as a post hoc test. Differences in convulsive activity between saline and ~MPT-treated gerbils were determined by t-test. Sham PINX (acute or chronic) and C H R O N I C PINX did not produce convulsive activity, except for one minor convulsive episode observed in a SHAM gerbil which received 0~MPT (Table 1). It is not known why this animal displayed mild convulsive behavior, but the convulsion was of a markedly different nature than the wild running convulsions observed after ACUTE PINX. This gerbil displayed a seizure similar to that observed in seiTABLE I CONVULSIVE ACTIVITY IN MALE MONGOLIAN GERBILS AFTER SHAM PINEALECTOMY, CHRONIC PINEALECTOMY (PERFORMED ONE WEEK EARLIER) OR ACUTE PINEALECTOMY The gerbils also received a single acute injection of saline or ct-methylparatyrosine (~tMPT) (250 mg/kg, i.p.). Values are means + S.E.M.
zure-sensitive gerbils [4]. Over 75 % of the acutely pinealectomized gerbils exhibited spontaneous wild running convulsions, irrespective of saline or ~MPT treatment (Table I). Interestingly, the number of convulsions was significantly (P < 0.05) reduced in ~MPT treated gerbils (Table I). Cortical NE levels were depressed (45 %) in all gerbils injected with ~MPT and were decreased (44 %) in gerbils ACUTE PINX and injected with saline (Fig. 1). Cortical dopamine (DA) levels were not affected by PINX or ~MPT treatment (data not presented). Hypothalamic NE and DA levels were reduced (38 % and 78 %, respectively) by ~MPT treatment and NE levels were also reduced (32%) by ACUTE PINX (Fig. 2). It is interesting to note that PINX produced nearly identical depressions in NE levels as ~MPT treatment and that PINX plus 0~MPT treatment did not produce additional reductions in NE (Figs. 1 and 2). In the third experiment, neither isoproterenol nor propranolol altered cortical NE levels in SHAM gerbils (Table II). Likewise, these compounds did not prevent the PINX-induced decrease in cortical NE levels (Table II). Similar results were observed in hypothalamic NE levels as were found in the cortical NE levels (data not presented). Convulsive activity produced by PINX was not significantly altered by propranolol or isoproterenol administration. However, isoproterenol increased the excitability of the gerbils and produced back rolls, occasional hind-limb extensions and other characteristic behaviors. An independent, 'blind' investigator was able to distinguish isoproterenol-injected gerbils from salineinjected animals by the gerbils' overt behavioral changes. Totals of PINX gerbils: 7 of 15 convulsed, average minutes to onset: 63 + 10, average number of convulsions: 2, i---l SALINE
t,
aMPT
300]
,,p(O.O01 vs SHAM/SALINE
Treatment
Animals convulsed/ total (%)
Minutes to onset
Sham pinealectomy Saline :(MPT
0/11 (0%) 1/9 (11%)
-30
Chronic pinealectomy Saline ~MPT
0/7 (0%) 0/8 (0%)
Acute pinealectomy Saline ~MPT
9/10 (90%) 7/9 (78 %)
*P < 0.05 vs acute pinealectomy/saline.
No. of convulsions
Death
-L
.~c~ ~ 200
~i
I T00
z
SHAM
58 + 9 71 + 14
6_+ I 2 _+ 1"
2 2
--CHRONIC PINX
ACUTE PINX
Fig. I. Norepinephrine content (ng/g) within the parietal cortex of male Mongolian gerbils after sham pinealectomy (SHAM), chronic pinealectomy (CHRONIC PINX) (performed one week earlier) or acute pinealectomy (ACUTE PINX). The gerbils also received a single acute injection of saline or ct-methylparatyrosine (~MPT; 250 mg/kg, i.p.). Values are means +_ S.E.M. with at least 7 gerbils in each group.
247
two gerbils died due to convulsions. The reason for the reduction in the number of gerbils which convulsed after PINX in this experiment is not known, although recent results suggest that there is a seasonal rhythm in gerbil convulsive behavior after PINX (Champney, unpublished observations). These findings indicate that gerbils which were ACUTE PINX and received 0tMPT were as sensitive to seizures as PINX, saline-injected gerbils. The present data suggest that gerbils injected with ctMPT have fewer convulsions than saline injected animals, while previous results produced the opposite conclusion [5]. It is difficult to reconcile these differences. However, in both repetitions of the present studies, the PINX/ctMPTinjected gerbils exhibited fewer convulsions which were apparent to the 'blind' observer. PINX in rats also produces convulsions if the rats have been previously parathyroidectomized [9]. Recent results have shown that 0tMPT treatment reduced the number of convulsions in this model to the same degree as seen in the present studies [10]. However, in the rat model, timolol administration (a fl-adrenergic antagonist) increased the number of I"--'1 SALINE
2000
P'271 =MPT *p(O.01 vs SHAM/SALINE ,,, _~z
1500
!i,ooo z
..V
500.
SHAM
CHRONIC PINX
ACUTE PINX
CHRONIC PINX
ACUTE PINX
1000-
_L 500
SHAM
Fig. 2. Norepinephrine and dopamine contents (ng/g) within the hypothalamus of male Mongolian gerbils after sham pinealectomy (SHAM), chronic pinealectomy (CHRONIC PINX) (performed o n e week earlier) or acute pinealectomy (ACUTE PINX). The gerbils also received a single acute injection of saline or ct-methylparatyrosine (~tMPT; 250 mg/kg, i.p.). Values are means + S.E.M. with at least 7 gerbils in each group.
TABLE II PARIETAL CORTEX NOREPINEPHRINE CONTENT (ng/g) IN MALE GERBILS FOUR HOURS AFTER BEING PINEALECTOMIZED OR SHAM-PINEALECTOMIZED AND RECEIVING SALINE, PROPRANOLOL OR ISOPROTERENOL IMMEDIATELY AFTER SURGERY Values are means __+ S.E.M. with 5 gerbils in each group. Two-way analysis of variance: F (row variable) = 10.21, P<0.01; F (column variable) = 1.23, N.S.; F (interaction) = 0.93, N.S.
Sham pinealectomy Pinealectomy
Saline
Propranolol (5 mg/kg, i.p.)
Isoproterenol (1 mg/kg, i.p.)
275 _ 24 187+31
254 + 6 201+27
273 _+ 18 244+13
PINX-induced convulsions [10]. These authors tested a number of adrenergic compounds on this animal model and did not find consistent results to implicate the noradrenergic system. They suggested that the timolol may be acting at serotonin receptors or may produce its effects by other non-specific mechanisms [10]. The lack of an affect of isoproterenol, a fl-adrenergic receptor agonist, or propranolol, a fl-adrenergic receptor antagonist, indicates that a fl-adrenergic receptor mechanism is not acutely involved in the convulsions produced by PINX. The present studies did not examine ~-adrenergic involvement in seizure state, although previous research has suggested that ct-adrenergic mechanisms may modulate air blast-induced convulsions in seizure sensitive gerbils [3]. Another important observation from the present studies is that gerbils which had been able to recover from PINX (CHRONIC PINX) and had depressed cortical NE levels (produced by 0tMPT) did not convulse. Therefore, convulsions produced by PINX may be transient and may not be solely due to depressed cortical NE levels and the lack of a pineal gland. This finding provides evidence for a 'window' of sensitivity to convulsions produced by removal of the pineal gland which is somehow compensated for within one week after PINX. In conclusion, it appears that the involvement of NE in PINX-induced convulsions in gerbils is not as straightforward as has been suggested. A consistent depression in cortical NE is observed during the convulsive episodes and the magnitude of the depression is significantly correlated to the severity of the convulsions [2]. However, pharmacologic manipulations of NE levels or beta receptor activation does not produce a marked affect on the convulsions produced by PINX. The technical help of Leah Matthews and Khenu Singh is appreciated as is the secretarial support of Sher-
248 rie H u g h e s . T h e s e studies w e r e s u p p o r t e d by a r e s e a r c h g r a n t f r o m the E p i l e p s y F o u n d a t i o n o f A m e r i c a . 6 1 Champney, T.H., Steger, R.W., Christie, D.S. and Reiter, R.J., Alterations in components of the pineal melatonin synthetic pathway by acute insulin stress in the rat and Syrian hamster, Brain Res., 338 (1985) 25-32. 2 Champney, T.H., Transection of the pineal stalk produces convulsions in male Mongolian gerbils (Meriones unguiculatus), Epilepsy Res., 4 (1989) 14-19. 3 Lfscher, W. and Czuczwar, S.J., Comparison of drugs with different selectivity for central ~-, and ~2-adrenoceptors in animal models of epilepsy, Epilepsy Res., 1 (1987) 165 172. 4 Loskota, W.J., Lomax, P. and Rich, S.T., The gerbil as a model for study of the epilepsies, Epilepsia, 15 (1974) 109-119. 5 Philo, R., Catecholamines and pinealectomy-induced convulsions in the gerbil (Meriones unguiculatus). In R.J. Reiter (Ed.), The
7
8
9
10
Pineal and Its Hormones, Alan R. Liss, New York, 1982, pp. 233 241. Philo, R. and Reiter, R.J., Characterization of pinealectomyinduced convulsions in the Mongolian gerbil (Meriones unguiculatus), Epilepsia, 19 (1978) 485-492. Philo, R., Reiter, R.J. and McGill, J.R., Changes in brain dopamine, norepinephrine and serotonin associated with convulsions induced by pinealectomy in the gerbil, J. Neural Transm., 46 (1979) 239-252. Philo, R., Reiter, R.J., The involvement of brain amines in pinealectomy-induced convulsions in the gerbil: I. Serotonin, Behav. Brain Res., 3 (1981) 71 82. Reiter, R.J. and Morgan, W.M., Attempts to characterize the convulsive response of parathyroidectomized rats to pineal gland removal, Physiol. Behav., 9 (1972) 203 208. Stockmeier, C.A. and Blask, D.E., Neuropharmaeological modification of central catecholamines: effects of pinealectomy-induced convulsions, J. Pineal Res., 3 (1986) 67-76.
245
ElsevierScientificPublishers Ireland Ltd. NSL 07366
Noradrenergic involvement in pinealectomy induced convulsions in gerbils T h o m a s H. C h a m p n e y Department of Anatomy, Collegeof Medicine, Texas A &M University, College Station, TX 77843-1114 ( U.S.A. )
(Received29 May 1990;Revisedversionreceived21 August 1990;Accepted27 August 1990) Key words: Pineal;Convulsion;Norepinephrine;ct-Methylparatyrosine;Gerbil
Gerbils treated with various noradrenergic compounds were pinealectomized(PINX) or sham-operated (SHAM) and observed for convulsive activity. Although declinesin cortical and hypothalamicnorepinephrinecontent were found after ct-methylparatyrosine(ctMPT)or PINX, treatment with ctMPTdid not produce convulsions in SHAM gerbils or in gerbils which were PINX one week earlier. Likewise,ctMPTdid not increase the number or severityof convulsionsobservedin acutelyPINX gerbils. Treatment with propranolol or isoproterenoldid not have any effecton convulsive activity of PINX gerbils, except that isoproterenol increased the excitabilityof all the gerbils. In conclusion, reducing catecholaminecontent or modifyingfl-noradrenergicreceptor activitywas not able to alter the convulsiveactivitywhich occurs after acute PINX.
Previous research established that removal of the pineal from gerbils resulted in grand real-type seizures which are characterized by wild running and massive tonic/clonic convulsions [6]. Pinealectomy (PINX) also lowered cerebral norepinephrine (NE) levels, but, at that time, it was not known whether the depressed levels were responsible for the convulsive behavior or a result of the convulsions [7]. Neither cortical serotonin nor cortical dopamine were involved in the PINX-induced convulsions [7]. More recent evidence suggested that the depressed cortical N E levels facilitated PINX-induced convulsive activity [5, 8]. Philo found that treatment of PINX gerbils with L-dihydroxyphenylalanine (L-DOPA) prevented the convulsive activity, while treatment with at-methylparatyrosine (ctMPT) increased seizure activity [5]. He concluded that decreased production o f cortical NE occurred after PINX and that this depression promoted the convulsive activity associated with PINX o f gerbils [5]. It is important to note that depression of NE levels in intact gerbils did not produce convulsions [5] indicating that a decline in N E content is not the only change required to produce convulsions in this seizure model. Male Mongolian gerbils (Meriones unguiculatus), 9 weeks old, were obtained from Tumblebrook Farms, West Brookfield, MA. Thirty gerbils arrived in early Correspondence: T.H. Champney, Department of Anatomy, Collegeof Medicine, Texas A&M University, College Station, TX 77843-1114, U.S.A.
0304-3940/90/$03.50 © 1990ElsevierScientificPublishers Ireland Ltd.
May, 1989, and were allowed to acclimate for 3 weeks with food and water continuously available. The gerbils were exposed to long photoperiods (14L:10D, lights on at 05.00h) and constant temperatures (22___2°C). Ten gerbils were PINX [2] and allowed to recover for 1 week ( C H R O N I C PINX). Of the 10 gerbils PINX, 1 died while under pentobarbital anesthesia and another died approximately 5 h after surgery. Another 10 gerbils were sham-operated (SHAM) at the same time and also allowed to recover for 1 week. On the day of experimentation, 2 unoperated gerbils were pinealectomized (ACUTE PINX) and injected with either saline or ~tMPT methyl ester (250 mg/kg, i.p.), 2 SHAM gerbils were injected with saline or 0tMPT and 2 C H R O N I C PINX gerbils were injected with saline or ~MPT. These 6 gerbils were monitored for convulsive activity for 3 h [2]. At the end of the observation period, the gerbils were killed by decapitation while anesthetized with metofane. The completeness of the surgical treatments was checked and portions of the parietal cortex and the medial basal hypothalamus were collected, weighed and frozen. Six additional gerbils (2 from each treatment group) were studied each day for 4 additional days to provide at least 4 gerbils in each treatment group. This complete experimental design was repeated with an additional 30 gerbils which were obtained in early June, 1989. The only difference in this new protocol was that the SHAM operations were performed at the time of A C U T E PINX and not when the C H R O N I C PINX were performed. Since the results from the 2 experiments
246
were virtually identical, the data from both experiments were combined to yield between 7 and 11 gerbils for each of the 6 treatment groups. In a third experiment, 30 gerbils, obtained in October, 1988, were randomly assigned to 6 groups in a 2 × 3 factorial design. The gerbils were either acutely SHAM or ACUTE PINX and received saline, isoproterenol (1 mg/ kg, ip) or propranolol (5 mg/kg, i.p.). Six sessions of 5 gerbils per session were examined for seizure activity for 4 h [2] and their cortical and hypothalamic tissues were collected at the end of the examination period. The gerbils in each session were from a random mix of the 6 treatment groups to eliminate or reduce intersession error or investigator bias. High-pressure liquid chromatography with electrochemical detection was utilized to determine catecholamine content in various neural regions of the gerbils [1]. The catecholamine data were analyzed by two-way analysis of variance with the student Neuman-Keuls test used as a post hoc test. Differences in convulsive activity between saline and ~MPT-treated gerbils were determined by t-test. Sham PINX (acute or chronic) and C H R O N I C PINX did not produce convulsive activity, except for one minor convulsive episode observed in a SHAM gerbil which received 0~MPT (Table 1). It is not known why this animal displayed mild convulsive behavior, but the convulsion was of a markedly different nature than the wild running convulsions observed after ACUTE PINX. This gerbil displayed a seizure similar to that observed in seiTABLE I CONVULSIVE ACTIVITY IN MALE MONGOLIAN GERBILS AFTER SHAM PINEALECTOMY, CHRONIC PINEALECTOMY (PERFORMED ONE WEEK EARLIER) OR ACUTE PINEALECTOMY The gerbils also received a single acute injection of saline or ct-methylparatyrosine (~tMPT) (250 mg/kg, i.p.). Values are means + S.E.M.
zure-sensitive gerbils [4]. Over 75 % of the acutely pinealectomized gerbils exhibited spontaneous wild running convulsions, irrespective of saline or ~MPT treatment (Table I). Interestingly, the number of convulsions was significantly (P < 0.05) reduced in ~MPT treated gerbils (Table I). Cortical NE levels were depressed (45 %) in all gerbils injected with ~MPT and were decreased (44 %) in gerbils ACUTE PINX and injected with saline (Fig. 1). Cortical dopamine (DA) levels were not affected by PINX or ~MPT treatment (data not presented). Hypothalamic NE and DA levels were reduced (38 % and 78 %, respectively) by ~MPT treatment and NE levels were also reduced (32%) by ACUTE PINX (Fig. 2). It is interesting to note that PINX produced nearly identical depressions in NE levels as ~MPT treatment and that PINX plus 0~MPT treatment did not produce additional reductions in NE (Figs. 1 and 2). In the third experiment, neither isoproterenol nor propranolol altered cortical NE levels in SHAM gerbils (Table II). Likewise, these compounds did not prevent the PINX-induced decrease in cortical NE levels (Table II). Similar results were observed in hypothalamic NE levels as were found in the cortical NE levels (data not presented). Convulsive activity produced by PINX was not significantly altered by propranolol or isoproterenol administration. However, isoproterenol increased the excitability of the gerbils and produced back rolls, occasional hind-limb extensions and other characteristic behaviors. An independent, 'blind' investigator was able to distinguish isoproterenol-injected gerbils from salineinjected animals by the gerbils' overt behavioral changes. Totals of PINX gerbils: 7 of 15 convulsed, average minutes to onset: 63 + 10, average number of convulsions: 2, i---l SALINE
t,
aMPT
300]
,,p(O.O01 vs SHAM/SALINE
Treatment
Animals convulsed/ total (%)
Minutes to onset
Sham pinealectomy Saline :(MPT
0/11 (0%) 1/9 (11%)
-30
Chronic pinealectomy Saline ~MPT
0/7 (0%) 0/8 (0%)
Acute pinealectomy Saline ~MPT
9/10 (90%) 7/9 (78 %)
*P < 0.05 vs acute pinealectomy/saline.
No. of convulsions
Death
-L
.~c~ ~ 200
~i
I T00
z
SHAM
58 + 9 71 + 14
6_+ I 2 _+ 1"
2 2
--CHRONIC PINX
ACUTE PINX
Fig. I. Norepinephrine content (ng/g) within the parietal cortex of male Mongolian gerbils after sham pinealectomy (SHAM), chronic pinealectomy (CHRONIC PINX) (performed one week earlier) or acute pinealectomy (ACUTE PINX). The gerbils also received a single acute injection of saline or ct-methylparatyrosine (~MPT; 250 mg/kg, i.p.). Values are means +_ S.E.M. with at least 7 gerbils in each group.
247
two gerbils died due to convulsions. The reason for the reduction in the number of gerbils which convulsed after PINX in this experiment is not known, although recent results suggest that there is a seasonal rhythm in gerbil convulsive behavior after PINX (Champney, unpublished observations). These findings indicate that gerbils which were ACUTE PINX and received 0tMPT were as sensitive to seizures as PINX, saline-injected gerbils. The present data suggest that gerbils injected with ctMPT have fewer convulsions than saline injected animals, while previous results produced the opposite conclusion [5]. It is difficult to reconcile these differences. However, in both repetitions of the present studies, the PINX/ctMPTinjected gerbils exhibited fewer convulsions which were apparent to the 'blind' observer. PINX in rats also produces convulsions if the rats have been previously parathyroidectomized [9]. Recent results have shown that 0tMPT treatment reduced the number of convulsions in this model to the same degree as seen in the present studies [10]. However, in the rat model, timolol administration (a fl-adrenergic antagonist) increased the number of I"--'1 SALINE
2000
P'271 =MPT *p(O.01 vs SHAM/SALINE ,,, _~z
1500
!i,ooo z
..V
500.
SHAM
CHRONIC PINX
ACUTE PINX
CHRONIC PINX
ACUTE PINX
1000-
_L 500
SHAM
Fig. 2. Norepinephrine and dopamine contents (ng/g) within the hypothalamus of male Mongolian gerbils after sham pinealectomy (SHAM), chronic pinealectomy (CHRONIC PINX) (performed o n e week earlier) or acute pinealectomy (ACUTE PINX). The gerbils also received a single acute injection of saline or ct-methylparatyrosine (~tMPT; 250 mg/kg, i.p.). Values are means + S.E.M. with at least 7 gerbils in each group.
TABLE II PARIETAL CORTEX NOREPINEPHRINE CONTENT (ng/g) IN MALE GERBILS FOUR HOURS AFTER BEING PINEALECTOMIZED OR SHAM-PINEALECTOMIZED AND RECEIVING SALINE, PROPRANOLOL OR ISOPROTERENOL IMMEDIATELY AFTER SURGERY Values are means __+ S.E.M. with 5 gerbils in each group. Two-way analysis of variance: F (row variable) = 10.21, P<0.01; F (column variable) = 1.23, N.S.; F (interaction) = 0.93, N.S.
Sham pinealectomy Pinealectomy
Saline
Propranolol (5 mg/kg, i.p.)
Isoproterenol (1 mg/kg, i.p.)
275 _ 24 187+31
254 + 6 201+27
273 _+ 18 244+13
PINX-induced convulsions [10]. These authors tested a number of adrenergic compounds on this animal model and did not find consistent results to implicate the noradrenergic system. They suggested that the timolol may be acting at serotonin receptors or may produce its effects by other non-specific mechanisms [10]. The lack of an affect of isoproterenol, a fl-adrenergic receptor agonist, or propranolol, a fl-adrenergic receptor antagonist, indicates that a fl-adrenergic receptor mechanism is not acutely involved in the convulsions produced by PINX. The present studies did not examine ~-adrenergic involvement in seizure state, although previous research has suggested that ct-adrenergic mechanisms may modulate air blast-induced convulsions in seizure sensitive gerbils [3]. Another important observation from the present studies is that gerbils which had been able to recover from PINX (CHRONIC PINX) and had depressed cortical NE levels (produced by 0tMPT) did not convulse. Therefore, convulsions produced by PINX may be transient and may not be solely due to depressed cortical NE levels and the lack of a pineal gland. This finding provides evidence for a 'window' of sensitivity to convulsions produced by removal of the pineal gland which is somehow compensated for within one week after PINX. In conclusion, it appears that the involvement of NE in PINX-induced convulsions in gerbils is not as straightforward as has been suggested. A consistent depression in cortical NE is observed during the convulsive episodes and the magnitude of the depression is significantly correlated to the severity of the convulsions [2]. However, pharmacologic manipulations of NE levels or beta receptor activation does not produce a marked affect on the convulsions produced by PINX. The technical help of Leah Matthews and Khenu Singh is appreciated as is the secretarial support of Sher-
248 rie H u g h e s . T h e s e studies w e r e s u p p o r t e d by a r e s e a r c h g r a n t f r o m the E p i l e p s y F o u n d a t i o n o f A m e r i c a . 6 1 Champney, T.H., Steger, R.W., Christie, D.S. and Reiter, R.J., Alterations in components of the pineal melatonin synthetic pathway by acute insulin stress in the rat and Syrian hamster, Brain Res., 338 (1985) 25-32. 2 Champney, T.H., Transection of the pineal stalk produces convulsions in male Mongolian gerbils (Meriones unguiculatus), Epilepsy Res., 4 (1989) 14-19. 3 Lfscher, W. and Czuczwar, S.J., Comparison of drugs with different selectivity for central ~-, and ~2-adrenoceptors in animal models of epilepsy, Epilepsy Res., 1 (1987) 165 172. 4 Loskota, W.J., Lomax, P. and Rich, S.T., The gerbil as a model for study of the epilepsies, Epilepsia, 15 (1974) 109-119. 5 Philo, R., Catecholamines and pinealectomy-induced convulsions in the gerbil (Meriones unguiculatus). In R.J. Reiter (Ed.), The
7
8
9
10
Pineal and Its Hormones, Alan R. Liss, New York, 1982, pp. 233 241. Philo, R. and Reiter, R.J., Characterization of pinealectomyinduced convulsions in the Mongolian gerbil (Meriones unguiculatus), Epilepsia, 19 (1978) 485-492. Philo, R., Reiter, R.J. and McGill, J.R., Changes in brain dopamine, norepinephrine and serotonin associated with convulsions induced by pinealectomy in the gerbil, J. Neural Transm., 46 (1979) 239-252. Philo, R., Reiter, R.J., The involvement of brain amines in pinealectomy-induced convulsions in the gerbil: I. Serotonin, Behav. Brain Res., 3 (1981) 71 82. Reiter, R.J. and Morgan, W.M., Attempts to characterize the convulsive response of parathyroidectomized rats to pineal gland removal, Physiol. Behav., 9 (1972) 203 208. Stockmeier, C.A. and Blask, D.E., Neuropharmaeological modification of central catecholamines: effects of pinealectomy-induced convulsions, J. Pineal Res., 3 (1986) 67-76.