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Age-related changes in striatal dopamine activity following nigral muscimol infusions
Developmental Brain Research, 31 (1987) 129-132 Elsevier
129
BRD 60184
Age-related changes in striatal dopamine activity following nigral muscirnol infusions Solomon L. Mosh61'2, Ellen F. Sperber 1, John N.D. Wurpel 1 and Nansie S. Sharpless 1'3 l Department of Neurology, Albert Einstein College of Medicine, Bronx, NY10461 (U.S.A.), 2Departmentof Pediatrics, Albert Einstein College of Medicine, Bronx, NY 10461 (U.S.A.) and 3Departmentof Psychiatry, Albert Einstein College of Medicine, Bronx, NY10461 (U.S.A.) (Accepted 12 August 1986)
Key words: Basal ganglion;Muscimol; Catecholamine; Seizure; Rat; Animal, newborn
Microinfusions of muscimol into the substantia nigra pars reticulata produced marked increases in striatal dopamine (DA) utilization without affecting striatal DA concentration in adult rats. In contrast, muscimol increased striatal DA concentration and decreased DA utilization in 16-day-oldrat pups. The striatal norepinephrine concentration was not altered in either group. Since previous studies have shown that similar infusions of muscimoiare anticonvulsant in adults and proconvulsant in rat pups, our results suggest that the nigrostriatal pathway may play an important role in mediating the nigral effects on seizures.
The substantia nigra (SN) and especially its pars reticulata (SNR) has been recently identified as a crucial site involved in the modification of seizures 7'13. In adult animals bilateral microinfusions of the G A B A agonist muscimol into the SNR can suppress a variety of experimental seizures suggesting that the GABA-sensitive nigral system may be instrumental in the control of seizures 7'13A6. However, in immature rats, infusions of muscimol into the SNR can enhance the development of seizures 16. These observations indicate that the functional activity of the GABA-sensitive nigral system changes with age from proconvulsant early in life to anticonvulsant later on. We have hypothesized 14 that the SN effects on seizures must be mediated via one of its efferent systems which include the nigrothalamic, nigroreticular, nigrotectal and nigrostriatal pathways 5. In this study we report age-related differences in the effects of muscimol infusions into the SNR on the functional activity of striatal dopamine (DA) neurons. Sprague-Dawley albino rat pups and adult male rats (275-300 g) were used. The pups remained with their natural mothers prior to and after surgery which
took place at 14 days of age (the day of birth was counted as day 0). After age-appropriate anesthesia, bilateral guide cannulae were implanted in the SNR in both age groups using the following stereotaxic coordinates; pups: 5.2 mm posterior and 3.5 mm lateral to bregma, 6.5 mm deep from the skull at an angle of 15°; adults: 5.3 mm posterior and 4.0 mm lateral to bregma, 7.7 mm deep at an angle of 15°. The incisor bar was 3.5 mm below the horizontal plane. Two days after surgery the rats were infused with muscimol (100 ng/0.25 ktl per site) or an equal volume of saline via a 33-gauge inner cannula. Muscimol was dissolved in saline and infused into each SNR consecutively over a period of 2 min per site. Thirty min after the completion of the infusion, the rats were decapitated, and the brains were removed and placed on their dorsal surface on ice. A cut was made perpendicularly downward from the ventral surface of the brain just posterior to the olfactory tubercles. The striata were removed from the rostral piece. The tissues were immediately frozen on dry ice, and then stored at -80 °C until analyzed for D A and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) using high-
Correspondence: S.L. Mosh6, Albert Einstein College of Medicine, 1300Morris Park Avenue, Bronx, NY 10461, U.S.A. 0165-3806/87/$03.50© 1987Elsevier Science Publishers B.V. (BiomedicalDivision)
13~) TABLE I Striatal concentrations o f norepinephrine ( NE). DA and DA metabolites as a )unction o/'age
The rats were infused with 0.25/tl of saline into the SNR. The values are means _+S.E.M. in ng/g wet tissue.
16-Day-old pups Adults % of adult value
NE
DA
DOPA (
H VA
146.2 ± 13.2 220.2 _+ 24.4 66c~
3158.5 __+242 8323.4 ± 356 37.9%
538.6 _+32 1558.3 _+95 34.6%
65(/.4 + 36 818.8 ± 44 79.4%
p e r f o r m a n c e liquid c h r o m a t o g r a p h y with electrochemical detection (column: Biophase O D S , 5 p m from Bioanalytical Systems; mobile phase: 0.1 M chloroacetate, p H 3.2, 1 m M N a 2 E D T A , 0.20 m M sodium octylsulfate, and 8% methanol at 1.0 ml/min). The frozen tissues were weighed, h o m o g e n i z e d in icecold 0.1 N HC104, and centrifuged. A n aliquot of the clear s u p e r n a t a n t fluid was injected directly onto the column. Q u a n t i t a t i o n was p e r f o r m e d by d e t e r m i n a tion of p e a k heights relative to the heights of external standards. The striatai concentrations of n o r e p i n e p h rine ( N E ) were m e a s u r e d in both age groups as previously described 2. The caudal piece was frozen in freon and liquid nitrogen. Using s t a n d a r d techniques, 20-~m sections were o b t a i n e d for histological examination. Only those rats in which the cannulae placements were verified histologically to be in the S N R were used in the analyses of the data. These included 10 adult rats (5 in each group) and 21 rat pups (12 infused with muscimol and 9 saline controls). The pup experiments were p e r f o r m e d twice with similar results and therefore the data were combined. H o w e v e r , in the first e x p e r i m e n t the striata from each rat pup were analyzed together; this group consisted of 6 muscimol-infused rats and 5 saline controls. In the second
experiment each striatum was analyzed separately as it was done in the adults. In the saline groups, the striatal concentrations of both catecholamines and D A metabolites differed with age (Table I) as previously r e p o r t e d 4"I1. Indeed in the pups the D A concentrations were very similar to those r e p o r t e d by Coyle and C a m p o c h i a r o 4 (37.9% of the adult value). Microinfusions of muscimol into the S N R produced stereotypies such as sniffing, gnawing and turning in both age groups. These behavioral symptoms were present 30 min after the muscimol microinfusions when the rats were sacrificed. There were no behavioral differences b e t w e e n the two age groups. In the adult rats, microinfusion of muscimol into the S N R induced significant increases in the striatal concentrations of both D O P A C and H V A (Table II) while the D A concentration did not differ from that in the saline control group. F u r t h e r m o r e , there were m a r k e d increases in D A utilization as reflected in the D O P A C / D A and H V A / D A ratios 1°. These ratios were + 1 4 7 % and + 1 2 2 % c o m p a r e d to the saline controls respectively. Microinfusion of muscimol into the S N R p r o d u c e d dramatically different results in the 16-day-old pups.
TABLE II Effects o f intranigral muscimol infusions on striatal DA metabolism in adult rats
Infusions were 100/tg/0.25 pl/site. The values are means + S.E.M. in ng/g wet tissue. Each striatum with a correct ipsilateral SNR cannula placement was analyzed. Thus, the data include one or both striata from 5 rats per group. The statistical analysis used was the one way analysis of variance; n.s., not significant.
Saline Muscimol
DA
DO PA C
HVA
DO PA C/ DA
HVA/ DA
8323.4 + 356 9004.7 + 322 FH5 = 0.46 n.s.
1558.3 _+95 2338.3 + 283
818.8 _+44 1017.6 _+75
1/.09 _+I).003 0.1l _+0.01
FI,14 = 7 . 2
FI,I2 = 5 . 2
P < 11.02
P < 0.05
0.19 + 0.008 0.28 _+0.04 FI,14 = 4.6 P < 0.05
FI.I~ = l. 1
n.s.
131 TABLE III Effects of intranigral muscimol infusions on striatal DA metabolism in 16-day-old rat pups
Infusions were 100 ng/0.25/A/site. The values are means + S.E.M. in ng/g wet tissue and depict the concentrations of DA and its metabolites from only those striata with a correct ipsilateral SNR placement; n.s., not significant.
Saline Muscimol
DA
DO PA C
HVA
DO PA C/ DA
H V A / DA
3158.5 + 242 5688.5 + 475
538.6 + 32 632.9 + 74 F1,23= 1.2 n.s.
650.4 + 36 592.6 + 60 FI,23 = 0.6 n.s.
0.17 +_.0.008 0.11 + 0.01 F1,23 = 17.3 P < 0.001
0.21 + 0.01 0.11 + 0.006 F1,23 = 66.7 P < 0.001
F1.23 = 2 1 . 4
P < 0.001
The striatai D A concentration was markedly elevated by muscimol (Table III) while the concentrations of D O P A C and H V A remained unaffected. Consequently there were significant decreases in the D A utilization as reflected by the D O P A C / D A and H V A / D A ratios ( - 6 5 % and - 5 2 % from the respective saline controls). In contrast to the D A data, nigral microinfusions of muscimol had no effect on striatal N E concentrations in the two age groups. Thus, in the adults the striatal N E concentration was 220.2 + 28.1 ng/g wet tissue following saline infusions and 210 + 24.4 ng/g after muscimol infusions (F1,15 = 0.05, P > 0.5); in the pups the N E concentrations were 146.1 _+ 13.2 ng/g and 144.3 _+ 17.15 ng/g, respectively (F1.23 = 0.5, P > 0.5). The main finding of this study is that infusions of muscimol into the S N R produced opposite effects on striatal D A and its metabolites as a function of age. In adult rats muscimol increased D A utilization. This is consistent with the data of Kilpatrick et al. 1°, and W o o d TM and is compatible with previous observations indicating that infusions of muscimol in the SNR can paradoxically activate nigral D A neurons 9. This paradoxical activation is indirect; it occurs because the cells of the SNR are more sensitive to the effects of G A B A - m i m e t i c agents than the D A cells of the pars compacta 17. Infusions of G A B A agonists decrease the firing rate of the SNR cells thus disinhibiting the D A neurons leading to increases in striatal D A utilization. In rat pups, infusions of muscimol into the SNR increased the striatal D A concentrations but decreased D A utilization. These data imply that in rat pups, the D A cells of the pars compacta are also disinhibited by the infusions of muscimol into the SNR leading to the
increments of striatal D A concentrations but there may be an immaturity of D A release. Alternatively, the enzymes responsible for the breakdown of D A may not be fully functional and thus not capable of augmenting the catabolism of D A when its synthesis is enhanced. In either case, the final product is a net increase in striatal D A concentration in the pups. Yet, despite the differences in striatal D A metabolism, stereotypies and turning occurred in both age groups. These results support the suggestion of Kilpatrick et al. 1° that D A cell activity or D A utilization cannot be used to predict these behaviors in rats. We have reported 15 that intermittent electrical stimulation of the SN metabolically activates the nigrostriatal pathway (as determined by the deoxyglucose technique) in both adults and rat pups. These findings suggest that the nigrostriatal pathway is at least drivable in 16-day-old rat pups and are compatible with the present findings. Indeed, the nigrostriatal pathway is functional at 16 days of age 3 and since its function requires energy as in adults 1, its metabolic activity can be depicted by the deoxyglucose technique in both groups. Yet the end result of the functional activation may be in the opposite direction as is the case following nigral muscimol infusions. Previous studies in adult rats have implied that the striatum may exert an anticonvuisant influence 5,6,12. However, there is no definitive evidence that a fully functional nigrostriatal pathway is involved in seizures in adult rats 2,7,13 although there is a recent report indicating that one or more monoamines may participate in the mediation of the nigral effects on seizures 8. Our data suggest a role for D A and the nigrostriatal pathway at least in pups if not in both age groups. The muscimol-induced developmental changes in striatal D A utilization and metabolism
132 parallel the muscimol-induced age-related differ-
effects of muscimol.
ences on seizure susceptibility 16. While it is possible that similar age-related parallel changes may exist for other nigral output systems, to date none have been demonstrated. We therefore propose that the altered function of the nigrostriatal pathway early in life may be important in mediating the proconvulsant
1 Ackermann, R.F., Finch, D.M., Babb, T,L. and Engel, J., Jr., Increased glucose metabolism during long duration recurrent inhibition of hippocampal pyramidal cells, J. Neurosci., 4 (1984) 251-264. 2 Albala, B.J., Mosh6, S.L., Cubells, J.F., Sharpless, N.S. and Makman, M.H., Unilateral peri-substantia nigra catecholaminergic lesion and amygdala kindling, Brain Res., 370 (1986) 388-392. 3 Cheronis, J.C., Erinoff, L., Heller, A. and Hoffmann, P.C., Pharmacological analysis of the functional ontogeny of the nigrostriatal dopaminergic neurons, Brain Res., 169 (1979) 545-560. 4 Coyle, J.T. and Campochiaro, P., Ontogenesis of dopaminergic-cholinergic interactions in the rat striatum: a neurochemical study, J. Neurochem., 27 (1976) 673-678. 5 Dray, A., The physiology and pharmacology of mammalian basal ganglia, Progr. Neurobiol., 14 (1980) 221-335. 6 Fariello, R., Forebrain influences on an amygdaloid acute focus in the cat, Exp. Neurol., 51 (1976) 515-528. 7 Gale, K., Mechanisms of seizure control mediate by gamma-aminobutyric acid: role of the substantia nigra, Fed. Proc. Fed. Am. Soc. Exp. Biol., 44 (1985) 2414-2424. 8 Gellman, R.L. and McNamara, J.O., Reserpine reverses the anticonvulsant effect of gamma-vinyl GABA microinjected into the substantia nigra of kindled rats, Soc. Neurosci. Abstr., 11 (1985) 39. 9 Grace, A.A, and Bunney, B.S., Paradoxical GABA excitation of nigral dopaminergic cells: indirect mediation through reticulata inhibitory neurons, Eur. J. Pharmacol., 59 (1979) 211-218. 10 Kilpatrick, I.C., Starr, M.S. and Summerhayes, M., Brain dopamine activity following intranigral or intrathalamic
Supported in part by G r a n t NS 20253 from the NINCDS. We thank Ms. Mariann Downing for her expert technical assistance and Ms. D o n n a Platyan for typing the manuscript.
drug injections in the rat, Brain Res. Bull., t5 (1985) 553-561. 11 Lanier, L.P., Dunn, A.J. and Van Hartesveldt, C., Development of neurotransmitters and their function in brain. In S. Ehrenpreis and I.J. Kopin (Eds.), Reviews of Neuroscience, Vol. 2, Raven, New York, 1976, pp. 195-256. 12 LaGrutta, V., Amato, G. and Zagami, M.T., The importance of the caudate nucleus in the control of convulsive activity in the amygdaloid complex and the temporal cortex of the rat, Electroencephal. Clin. Neurophysiol., 3I (1971) 57-69. 13 McNamara, J.O., Galloway, M.T., Rigsbee. L.C. and Shin, C., Evidence implicating substantia nigra in regulation of kindled seizure threshold, J. Neurosci., 4 (1984) 2410-2417. 14 Mosh6, S.L., Ackermann, R.F., Albala, B.J. and Okada, R., The role of the substantia nigra in seizures of developing animals. In J.A. Wada (Ed.), Kindling 3, Raven, New York, 1986, pp. 91-104. 15 Mosh6, S.L., Brown, L.L., Albala, B.J. and Okada, R., Age related substantia nigra mediated modulation of seizures, Soc. Neurosci. Abstr., 10 (1984) 186. 16 Okada, R., Mosh6, S.L., Wong, B.Y., Sperber, E.F. and Zhao, D., Age related substantia nigra mediated seizure facilitation, Exp. Neurol., 93 (1986) 180-187. 17 Waszczak, B.L., Eng, N. and Wakers, J.R., Effects of muscimol and picrotoxin on single unit activity of substantia nigra neurons, Brain Res., 188 (1980) 185-197. 18 Wood, P.L., Actions of GABAergic agents on dopamine metabolism in the nigrostriatal pathway of the rat, J. Pharmacol. Exp. Ther., 222 (1982) 674-679.
129
BRD 60184
Age-related changes in striatal dopamine activity following nigral muscirnol infusions Solomon L. Mosh61'2, Ellen F. Sperber 1, John N.D. Wurpel 1 and Nansie S. Sharpless 1'3 l Department of Neurology, Albert Einstein College of Medicine, Bronx, NY10461 (U.S.A.), 2Departmentof Pediatrics, Albert Einstein College of Medicine, Bronx, NY 10461 (U.S.A.) and 3Departmentof Psychiatry, Albert Einstein College of Medicine, Bronx, NY10461 (U.S.A.) (Accepted 12 August 1986)
Key words: Basal ganglion;Muscimol; Catecholamine; Seizure; Rat; Animal, newborn
Microinfusions of muscimol into the substantia nigra pars reticulata produced marked increases in striatal dopamine (DA) utilization without affecting striatal DA concentration in adult rats. In contrast, muscimol increased striatal DA concentration and decreased DA utilization in 16-day-oldrat pups. The striatal norepinephrine concentration was not altered in either group. Since previous studies have shown that similar infusions of muscimoiare anticonvulsant in adults and proconvulsant in rat pups, our results suggest that the nigrostriatal pathway may play an important role in mediating the nigral effects on seizures.
The substantia nigra (SN) and especially its pars reticulata (SNR) has been recently identified as a crucial site involved in the modification of seizures 7'13. In adult animals bilateral microinfusions of the G A B A agonist muscimol into the SNR can suppress a variety of experimental seizures suggesting that the GABA-sensitive nigral system may be instrumental in the control of seizures 7'13A6. However, in immature rats, infusions of muscimol into the SNR can enhance the development of seizures 16. These observations indicate that the functional activity of the GABA-sensitive nigral system changes with age from proconvulsant early in life to anticonvulsant later on. We have hypothesized 14 that the SN effects on seizures must be mediated via one of its efferent systems which include the nigrothalamic, nigroreticular, nigrotectal and nigrostriatal pathways 5. In this study we report age-related differences in the effects of muscimol infusions into the SNR on the functional activity of striatal dopamine (DA) neurons. Sprague-Dawley albino rat pups and adult male rats (275-300 g) were used. The pups remained with their natural mothers prior to and after surgery which
took place at 14 days of age (the day of birth was counted as day 0). After age-appropriate anesthesia, bilateral guide cannulae were implanted in the SNR in both age groups using the following stereotaxic coordinates; pups: 5.2 mm posterior and 3.5 mm lateral to bregma, 6.5 mm deep from the skull at an angle of 15°; adults: 5.3 mm posterior and 4.0 mm lateral to bregma, 7.7 mm deep at an angle of 15°. The incisor bar was 3.5 mm below the horizontal plane. Two days after surgery the rats were infused with muscimol (100 ng/0.25 ktl per site) or an equal volume of saline via a 33-gauge inner cannula. Muscimol was dissolved in saline and infused into each SNR consecutively over a period of 2 min per site. Thirty min after the completion of the infusion, the rats were decapitated, and the brains were removed and placed on their dorsal surface on ice. A cut was made perpendicularly downward from the ventral surface of the brain just posterior to the olfactory tubercles. The striata were removed from the rostral piece. The tissues were immediately frozen on dry ice, and then stored at -80 °C until analyzed for D A and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) using high-
Correspondence: S.L. Mosh6, Albert Einstein College of Medicine, 1300Morris Park Avenue, Bronx, NY 10461, U.S.A. 0165-3806/87/$03.50© 1987Elsevier Science Publishers B.V. (BiomedicalDivision)
13~) TABLE I Striatal concentrations o f norepinephrine ( NE). DA and DA metabolites as a )unction o/'age
The rats were infused with 0.25/tl of saline into the SNR. The values are means _+S.E.M. in ng/g wet tissue.
16-Day-old pups Adults % of adult value
NE
DA
DOPA (
H VA
146.2 ± 13.2 220.2 _+ 24.4 66c~
3158.5 __+242 8323.4 ± 356 37.9%
538.6 _+32 1558.3 _+95 34.6%
65(/.4 + 36 818.8 ± 44 79.4%
p e r f o r m a n c e liquid c h r o m a t o g r a p h y with electrochemical detection (column: Biophase O D S , 5 p m from Bioanalytical Systems; mobile phase: 0.1 M chloroacetate, p H 3.2, 1 m M N a 2 E D T A , 0.20 m M sodium octylsulfate, and 8% methanol at 1.0 ml/min). The frozen tissues were weighed, h o m o g e n i z e d in icecold 0.1 N HC104, and centrifuged. A n aliquot of the clear s u p e r n a t a n t fluid was injected directly onto the column. Q u a n t i t a t i o n was p e r f o r m e d by d e t e r m i n a tion of p e a k heights relative to the heights of external standards. The striatai concentrations of n o r e p i n e p h rine ( N E ) were m e a s u r e d in both age groups as previously described 2. The caudal piece was frozen in freon and liquid nitrogen. Using s t a n d a r d techniques, 20-~m sections were o b t a i n e d for histological examination. Only those rats in which the cannulae placements were verified histologically to be in the S N R were used in the analyses of the data. These included 10 adult rats (5 in each group) and 21 rat pups (12 infused with muscimol and 9 saline controls). The pup experiments were p e r f o r m e d twice with similar results and therefore the data were combined. H o w e v e r , in the first e x p e r i m e n t the striata from each rat pup were analyzed together; this group consisted of 6 muscimol-infused rats and 5 saline controls. In the second
experiment each striatum was analyzed separately as it was done in the adults. In the saline groups, the striatal concentrations of both catecholamines and D A metabolites differed with age (Table I) as previously r e p o r t e d 4"I1. Indeed in the pups the D A concentrations were very similar to those r e p o r t e d by Coyle and C a m p o c h i a r o 4 (37.9% of the adult value). Microinfusions of muscimol into the S N R produced stereotypies such as sniffing, gnawing and turning in both age groups. These behavioral symptoms were present 30 min after the muscimol microinfusions when the rats were sacrificed. There were no behavioral differences b e t w e e n the two age groups. In the adult rats, microinfusion of muscimol into the S N R induced significant increases in the striatal concentrations of both D O P A C and H V A (Table II) while the D A concentration did not differ from that in the saline control group. F u r t h e r m o r e , there were m a r k e d increases in D A utilization as reflected in the D O P A C / D A and H V A / D A ratios 1°. These ratios were + 1 4 7 % and + 1 2 2 % c o m p a r e d to the saline controls respectively. Microinfusion of muscimol into the S N R p r o d u c e d dramatically different results in the 16-day-old pups.
TABLE II Effects o f intranigral muscimol infusions on striatal DA metabolism in adult rats
Infusions were 100/tg/0.25 pl/site. The values are means + S.E.M. in ng/g wet tissue. Each striatum with a correct ipsilateral SNR cannula placement was analyzed. Thus, the data include one or both striata from 5 rats per group. The statistical analysis used was the one way analysis of variance; n.s., not significant.
Saline Muscimol
DA
DO PA C
HVA
DO PA C/ DA
HVA/ DA
8323.4 + 356 9004.7 + 322 FH5 = 0.46 n.s.
1558.3 _+95 2338.3 + 283
818.8 _+44 1017.6 _+75
1/.09 _+I).003 0.1l _+0.01
FI,14 = 7 . 2
FI,I2 = 5 . 2
P < 11.02
P < 0.05
0.19 + 0.008 0.28 _+0.04 FI,14 = 4.6 P < 0.05
FI.I~ = l. 1
n.s.
131 TABLE III Effects of intranigral muscimol infusions on striatal DA metabolism in 16-day-old rat pups
Infusions were 100 ng/0.25/A/site. The values are means + S.E.M. in ng/g wet tissue and depict the concentrations of DA and its metabolites from only those striata with a correct ipsilateral SNR placement; n.s., not significant.
Saline Muscimol
DA
DO PA C
HVA
DO PA C/ DA
H V A / DA
3158.5 + 242 5688.5 + 475
538.6 + 32 632.9 + 74 F1,23= 1.2 n.s.
650.4 + 36 592.6 + 60 FI,23 = 0.6 n.s.
0.17 +_.0.008 0.11 + 0.01 F1,23 = 17.3 P < 0.001
0.21 + 0.01 0.11 + 0.006 F1,23 = 66.7 P < 0.001
F1.23 = 2 1 . 4
P < 0.001
The striatai D A concentration was markedly elevated by muscimol (Table III) while the concentrations of D O P A C and H V A remained unaffected. Consequently there were significant decreases in the D A utilization as reflected by the D O P A C / D A and H V A / D A ratios ( - 6 5 % and - 5 2 % from the respective saline controls). In contrast to the D A data, nigral microinfusions of muscimol had no effect on striatal N E concentrations in the two age groups. Thus, in the adults the striatal N E concentration was 220.2 + 28.1 ng/g wet tissue following saline infusions and 210 + 24.4 ng/g after muscimol infusions (F1,15 = 0.05, P > 0.5); in the pups the N E concentrations were 146.1 _+ 13.2 ng/g and 144.3 _+ 17.15 ng/g, respectively (F1.23 = 0.5, P > 0.5). The main finding of this study is that infusions of muscimol into the S N R produced opposite effects on striatal D A and its metabolites as a function of age. In adult rats muscimol increased D A utilization. This is consistent with the data of Kilpatrick et al. 1°, and W o o d TM and is compatible with previous observations indicating that infusions of muscimol in the SNR can paradoxically activate nigral D A neurons 9. This paradoxical activation is indirect; it occurs because the cells of the SNR are more sensitive to the effects of G A B A - m i m e t i c agents than the D A cells of the pars compacta 17. Infusions of G A B A agonists decrease the firing rate of the SNR cells thus disinhibiting the D A neurons leading to increases in striatal D A utilization. In rat pups, infusions of muscimol into the SNR increased the striatal D A concentrations but decreased D A utilization. These data imply that in rat pups, the D A cells of the pars compacta are also disinhibited by the infusions of muscimol into the SNR leading to the
increments of striatal D A concentrations but there may be an immaturity of D A release. Alternatively, the enzymes responsible for the breakdown of D A may not be fully functional and thus not capable of augmenting the catabolism of D A when its synthesis is enhanced. In either case, the final product is a net increase in striatal D A concentration in the pups. Yet, despite the differences in striatal D A metabolism, stereotypies and turning occurred in both age groups. These results support the suggestion of Kilpatrick et al. 1° that D A cell activity or D A utilization cannot be used to predict these behaviors in rats. We have reported 15 that intermittent electrical stimulation of the SN metabolically activates the nigrostriatal pathway (as determined by the deoxyglucose technique) in both adults and rat pups. These findings suggest that the nigrostriatal pathway is at least drivable in 16-day-old rat pups and are compatible with the present findings. Indeed, the nigrostriatal pathway is functional at 16 days of age 3 and since its function requires energy as in adults 1, its metabolic activity can be depicted by the deoxyglucose technique in both groups. Yet the end result of the functional activation may be in the opposite direction as is the case following nigral muscimol infusions. Previous studies in adult rats have implied that the striatum may exert an anticonvuisant influence 5,6,12. However, there is no definitive evidence that a fully functional nigrostriatal pathway is involved in seizures in adult rats 2,7,13 although there is a recent report indicating that one or more monoamines may participate in the mediation of the nigral effects on seizures 8. Our data suggest a role for D A and the nigrostriatal pathway at least in pups if not in both age groups. The muscimol-induced developmental changes in striatal D A utilization and metabolism
132 parallel the muscimol-induced age-related differ-
effects of muscimol.
ences on seizure susceptibility 16. While it is possible that similar age-related parallel changes may exist for other nigral output systems, to date none have been demonstrated. We therefore propose that the altered function of the nigrostriatal pathway early in life may be important in mediating the proconvulsant
1 Ackermann, R.F., Finch, D.M., Babb, T,L. and Engel, J., Jr., Increased glucose metabolism during long duration recurrent inhibition of hippocampal pyramidal cells, J. Neurosci., 4 (1984) 251-264. 2 Albala, B.J., Mosh6, S.L., Cubells, J.F., Sharpless, N.S. and Makman, M.H., Unilateral peri-substantia nigra catecholaminergic lesion and amygdala kindling, Brain Res., 370 (1986) 388-392. 3 Cheronis, J.C., Erinoff, L., Heller, A. and Hoffmann, P.C., Pharmacological analysis of the functional ontogeny of the nigrostriatal dopaminergic neurons, Brain Res., 169 (1979) 545-560. 4 Coyle, J.T. and Campochiaro, P., Ontogenesis of dopaminergic-cholinergic interactions in the rat striatum: a neurochemical study, J. Neurochem., 27 (1976) 673-678. 5 Dray, A., The physiology and pharmacology of mammalian basal ganglia, Progr. Neurobiol., 14 (1980) 221-335. 6 Fariello, R., Forebrain influences on an amygdaloid acute focus in the cat, Exp. Neurol., 51 (1976) 515-528. 7 Gale, K., Mechanisms of seizure control mediate by gamma-aminobutyric acid: role of the substantia nigra, Fed. Proc. Fed. Am. Soc. Exp. Biol., 44 (1985) 2414-2424. 8 Gellman, R.L. and McNamara, J.O., Reserpine reverses the anticonvulsant effect of gamma-vinyl GABA microinjected into the substantia nigra of kindled rats, Soc. Neurosci. Abstr., 11 (1985) 39. 9 Grace, A.A, and Bunney, B.S., Paradoxical GABA excitation of nigral dopaminergic cells: indirect mediation through reticulata inhibitory neurons, Eur. J. Pharmacol., 59 (1979) 211-218. 10 Kilpatrick, I.C., Starr, M.S. and Summerhayes, M., Brain dopamine activity following intranigral or intrathalamic
Supported in part by G r a n t NS 20253 from the NINCDS. We thank Ms. Mariann Downing for her expert technical assistance and Ms. D o n n a Platyan for typing the manuscript.
drug injections in the rat, Brain Res. Bull., t5 (1985) 553-561. 11 Lanier, L.P., Dunn, A.J. and Van Hartesveldt, C., Development of neurotransmitters and their function in brain. In S. Ehrenpreis and I.J. Kopin (Eds.), Reviews of Neuroscience, Vol. 2, Raven, New York, 1976, pp. 195-256. 12 LaGrutta, V., Amato, G. and Zagami, M.T., The importance of the caudate nucleus in the control of convulsive activity in the amygdaloid complex and the temporal cortex of the rat, Electroencephal. Clin. Neurophysiol., 3I (1971) 57-69. 13 McNamara, J.O., Galloway, M.T., Rigsbee. L.C. and Shin, C., Evidence implicating substantia nigra in regulation of kindled seizure threshold, J. Neurosci., 4 (1984) 2410-2417. 14 Mosh6, S.L., Ackermann, R.F., Albala, B.J. and Okada, R., The role of the substantia nigra in seizures of developing animals. In J.A. Wada (Ed.), Kindling 3, Raven, New York, 1986, pp. 91-104. 15 Mosh6, S.L., Brown, L.L., Albala, B.J. and Okada, R., Age related substantia nigra mediated modulation of seizures, Soc. Neurosci. Abstr., 10 (1984) 186. 16 Okada, R., Mosh6, S.L., Wong, B.Y., Sperber, E.F. and Zhao, D., Age related substantia nigra mediated seizure facilitation, Exp. Neurol., 93 (1986) 180-187. 17 Waszczak, B.L., Eng, N. and Wakers, J.R., Effects of muscimol and picrotoxin on single unit activity of substantia nigra neurons, Brain Res., 188 (1980) 185-197. 18 Wood, P.L., Actions of GABAergic agents on dopamine metabolism in the nigrostriatal pathway of the rat, J. Pharmacol. Exp. Ther., 222 (1982) 674-679.