- Email: [email protected]
Ethanol, baclofen, and kainic acid neurotoxicity
EXPERIMENTAL
NEUROLOGY
Ethanol,
69, 359-364 (1980)
Baclofen,
and Kainic Acid Neurotoxicity
EDITH G. MCGEER, ALEXANDERJAKUBOVIC, EDITH A. SINCH Kinsmen
Laboratory of Neurological Vancouver, British Received
November
AND
Research, University of British Columbia. Canada V6T I W5
20, 1979; revision
received
February
Columbia,
19. 1980
The neurotoxicity induced by intrastriatal injections of kainic acid was greater in rats drinking approximately 4 ml ethanol per day for 16 days before injection than in controls. Intraperitoneal injection of 5 mgikg baclofen (parachlorophenyl GABA), 30 min before the kainic acid injections had a slight protective action. These results have implications in connection with reported effects of ethanol and baclofen on glutamate systems in the brain.
INTRODUCTION Kainic acid, a structural analog of glutamate, produces local neuronal damage when intracerebrally injected. The neurotoxicity of kainic acid in both the striatum and the hippocampus has been shown to depend on innervation by intact excitatory (glutamate and, possibly, aspartate) afferent fibers (6, 8). In particular, striatal injections of kainic acid are not neurotoxic following lesions of the glutamate-containing corticostriatal tract. Moreover, coinjections of kainic acid and glutamate are neurotoxic in such animals and the development of kainic acid neurotoxicity in the striata of newborn rats parallels the development of glutamate innervation as evidenced by high-affinity glutamate uptake (3). It was therefore hypothesized that kainic acid exerts its local neurotoxicity through some cooperative interaction with endogenously released glutamate. On this hypothesis, agents which inhibit the release of glutamate might decrease the toxic effects of kainic acid, whereas agents which enhance the activity of glutamate systems might have the opposite effect. Michaelis et al. (10) suggested that both pharmacologic and binding data indicate “a probable Abbreviations:
GAD-glutamic
acid decarboxylase. CAT-choline
acetyltransferase
359 0014-4886/80/080359-06$02.00/O Copyright All rights
0 1980 by Academic Press. Inc. of reproduction in any form reserved
360
MCGEER,
JAKUBOVIC,
AND
SINGH
hyperactivity of the glutamate excitatory system in the central nervous system during chronic ethanol intoxication.” Acute treatment with baclofen (parachlorophenyl GABA), on the other hand, has been said to inhibit the synaptic release of glutamate (4, 12). It seemed possible therefore that such treatments might alter kainic acid neurotoxicity. Because intrastriatal injections of kainic acid destroy local cholinergic and GABA neurons, measurements of glutamic acid decarboxylase (GAD) and choline acetyltransferase (CAT) in injected compared with control striata were found useful indices of the extent of neuronal damage (7). We therefore studied striatal GAD and CAT activities after local injections of kainic acid in animals pretreated with ethanol or baclofen and compared them with those of controls. METHODS Male Wistar rats weighing about 250 g at the time of injection were housed singly in a room with a 12-h light:dark cycle during both pre- and post-injection periods. The ethanol group was given free access for 16 days to a 6% solution of ethanol in Metrecal liquid, chocolate flavor (manufactured by Mead-Johnson, Canada); controls for this group were similarly offered Metrecal with an isocaloric amount of sucrose added. The daily average ethanol intake was 3.5 to 4.3 ml/rat. Rats injected with baclofen (5 mg/kg, i.p., 30 min before the kainic acid injection) and controls for this group were given standard laboratory chow. All kainic acid injections were done stereotaxically under Nembutal anesthesia, as previously described (7), with the total injection volume of 1 ~1 being injected into the striatum during a IO-min period. The contralateral striatum in each rat served as control. The rats were killed 8 to 10 days after injection, and striata were dissected, homogenized, and assayed for protein, CAT, GAD, and tyrosine hydroxylase by previously reported procedures (7). Injections and assays were always done in parallel on control and drug-treated groups. In a separate series of experiments, rats were similarly offered ethanolMetrecal or sucrose-Metrecal for 16 days and killed at the time corresponding to the kainic acid injections. The striata were dissected, then homogenized in 0.32 M sucrose, and portions of the homogenates were used to assay high-affinity glutamate accumulation and kainic acid binding by previously reported methods (9, 14). RESULTS There were no significant differences between any of the groups in the enzyme or protein values in the noninjected striatum, suggesting that the drug treatments per se did not have a significant effect on the enzyme activities measured.
ETHANOL,
BACLOFEN,
AND KAINIC
TABLE
361
ACID
I
Protein Values and Enzyme Activities in Kainic Acid-Injected Striatum as Percentage of Values in the Contralateral Striatum (Mean t SD) Group and treatment”
N
GAD”
CAT’
Protein
1. Ethanol 2. Controls
282 8 61 2 l3**”
33-+ 8 64 + 13***
942 962
15 IO
3. Baclofen 4. Controls
79 2 20 32 2 7**
73 2 20 25 + lo**
lO7* 952
5 7
5. Baclofen 6. Controls
52 -t 14 35 i- 6*
60 k 24 34 2 9*
98t 962
6 7
7. Baclofen 8. Controls
87 2 21 63 t I2
81 2 22 62 t 11
102+ 98C
3 4
’ Groups 1,2,7. and 8 were injected with 2.5 nmoles and groups 3 through 6 with 5 nmoles kainic acid. Control values in pmol, h-i, 100 mg-’ protein averaged 15.8 ? 1.3 for GAD and 34.8 i 2.9 for CAT. b Glutamic acid decarboxylase. ” Choline acetyltransferase. * P < 0.05. ** P < 0.01. *** P < 0.001.
As indicated in Table 1, both the CAT and the GAD results suggest that the kainic acid injections caused a significantly higher neurotoxicity in the ethanol-treated group than in the controls. Baclofen, on the other hand, seemed to afford a slight protective action, although the greater variability in the baclofen-treated groups rendered the results less significant.Tyrosine hydroxylase values were not significantly affected in any group. Measurements of kainic acid binding showed no significant difference between the ethanol-treated and the control groups, but the sodium-dependent, net accumulation of labeled glutamate at 1O-6 M was significantly greater in synaptosomes from ethanol-treated animals than in those from controls (Table 2). DISCUSSION Chronic ethanol usage would appear to potentiate the neurotoxicity of small doses of kainic acid. This is consistent with the hypothesis that kainic acid is dependent on an interaction with glutamate systems if, as reported by Michaelis et al. (lo), exposure of rats to ethanol under conditions such as used here leads to hyperactive glutamate systems. The results with bac-
362
MCGEER,
JAKUBOVIC,
AND SINGH
TABLE 2 Glutamate Accumulation and Kainic Acid Binding in the Striatum of Rats After Various Drug Treatments (Mean * SD) Treatment
N
Glutamate accumulation (pmol, 5 min-‘, g-l protein)
Kainic acid binding (fmol, mg-1 protein)
Ethanol Controls
10 10
3.03 ?I 0.34 2.58.2 0.22*
196 2 24 193 c 21
Baclofen Controls
10 10
2.34 -t- 0.19 2.62 + 0.37
-
n Accumulation of radioactive glutamate (IO-& M) was measured after a S-min incubation at 37°C of synaptosomal fractions in Krebs-Ringer phosphate with sodium-free incubations used as blanks (9). Specific kainic acid binding to striatal membranes was measured as the difference in binding of labeled kainate (400 mM) observed in the absence and presence of 10m3M unlabeled kainic acid (14). *P < 0.01.
lofen are less convincing but are at least in the direction predicted on the basis of the prior reports that baclofen inhibits the release of glutamate (4, 12). It must be said, however, that the effects of both ethanol and baclofen on glutamate systems are still not proven and would undoubtedly be only part of the effects of these drugs on various neurotransmitter systems. The increased accumulation of labeled glutamate in the ethanol-treated animals was somewhat surprising in view of prior literature, Michaelis et al. (lo), using concentrations of radioactive glutamate similar to those used here, found an increase in glutamate binding with synaptosomal membranes, but they were studying the sodium-independent binding sites and the amount of binding they found was approximately 1/50th of the sodiumdependent accumulation found in the present study. Roach ef al. (13) found about 16% less sodium-dependent accumulation of radioactive glutamate in whole brain tissue from alcohol-treated compared with control rats. However, they used the supernate of a IOOOg centrifugation and calculation indicates that, if the endogenous glutamate was released into this supernate, the concentration at which Roach et al. were working would have been of the order of 10m4 M. Under those conditions, considerably more low-affinity uptake would be expected than in our studies where we used the synaptosomal fraction. Under our conditions, the increased accumulation in the ethanol-treated animals may not reflect an increase in net uptake as such but rather may be due to an increase in homo exchange consequent to an increased release. Further experiments will be needed to determine whether or not this is the case. Although the binding data of Michaelis et al. (10) might indicate supersensitive postsynaptic receptors (and thus lead one to expect decreased presynaptic release), the field of glutamate
ETHANOL.
BACLOFEN,
AND KAINIC
ACID
363
binding sites is presently too complex to allow any firm interpretation of such data. The kainic acid binding experiments did not indicate any significant abnormality in the kainic acid binding sites after chronic ethanol treatment. As it is becoming increasingly clear, however, that these binding sites are not identical with the postsynaptic glutamate receptors, a supersensitivity of these postsynaptic receptors, such as implied by Michaelis ef cl/. (lo), is not ruled out. It is interesting to speculate on the possible meaning of these results in relation to human disease. The histologic and biochemical patterns seen after injection of kainic acid into the striatum, hippocampus, or cerebellum of rats have been compared with those seen in various human degenerative disorders (2,5, 1 I). Because of this, and because glutamate is itself neurotoxic, it was hypothesized that neuronal death in degenerating disorders such as Huntington’s disease, senile dementia, or some of the ataxias may depend on some pre- or postsynaptic abnormality in glutamatergic systems which results in prolonged, excessive stimulation of the postsynaptic neurons. If there is any validity to this hypothesis, the present data and those of Michaelis et al. (10) might provide a rationale as to why the chronic use of ethyl alcohol would be contraindicated in persons at risk for those diseases. Similarly, ethanol might be expected to have a deleterious effect in epilepsy because glutamate and its analogs have convulsive properties. On the other hand, on the same hypothesis, chronic treatment with an agent which inhibits glutamate release might slow the rate of cell loss in a condition such as Huntington’s disease. Short-term clinical trials of baclofen in Huntington’s disease have been negative (1). but even a potent inhibitor of glutamate release could not be expected, on this hypothesis of its action, to improve established symptomatology. In any case, the present data suggest that any such agent would have to be far more potent than baclofen on glutamate systems. REFERENCES 1. BARBEAU. A. 1973. GABA and Huntington‘s chorea. Li~ncrt 2: 1499-1500. 2. BIZIERE, K.. AND J. T. COYLE. 1978. Infiuence of corticostriatal afferents on striatal kainic acid neurotoxicity. Neurosci. Left. 8: 303-310. 3. COYLE, J. T., E. G. MCGEER, AND P. L. MCGEER. 1978. Neostriatal injections: a model for Huntington’s chorea. Pages 139-161 in E. G. MCGEER, J. W. OLNEY. AND P. L. MCGEER, Eds. Kainic Acid 0.~ a Tool in Neurobiology. Raven Press. New York. 4. Fox, S.. K. KRNJEVIC, M. E. MORRIS, E. PUIL, AND R. WERMAN. 1978. Action of baclofen on mammalian synaptic transmission. Neuroscience 3: 495-5 15. 5. HERNDON, R.M.. AND J. T. COYLE. 1978. Glutamatergic innervation, kainic acid, and selective vulnerability in the cerebellum. Pages 189-200 in E. G. MCGEER, J. W. OLNEY, AND P. L. MCGEER, Eds.. Kainic Acid as cl Tool in Neurobiology. Raven Press. New York.
364
MCGEER,
JAKUBOVIC,
AND
SINGH
6. K~HLER, C., R. SCHWARCZ, AND K. FUXE. 1978. Perforant path transections protect hippocampal granule cells from kainate lesions. Neurosci. Letr. 10: 241-246. 7. MCGEER, E. G., AND P. L. MCGEER. 1978. Some factors influencing the neurotoxicity of intrastriatal injections of kainic acid. Neurochem. Res. 3: 501-517. 8. MCGEER, E. G., P. L. MCGEER, AND K. SINGH. 1978. Kainic acid-induced degeneration of neostriatal neurons: dependency upon cortico-striatal tract. Bruin Res. 139: 381-383.
9. MCGEER, P. L., E. G. MCGEER, U. SCHERER, AND K. SINGH. 1977. A glutamatergic corticostriatal path? Brain Res. 128: 369-373. 10. MICHAELIS, E. K., M. J. MULVANEY, AND W. J. FREED. 1978. Effects of acute and chronic ethanol intake on synaptosomal glutamate binding activity. Biochem. Pharmacol.
27: 1685-1691.
11. NADLER, J. V., B. W. PERRY, AND C. W. COTMAN. 1978. Preferential vulnerability of hippocampus to intraventricular kainic acid. Pages 219-237 in E. G. MCGEER, J. W. OLNEY, AND P. L. MCGEER , Eds., Kainic Acid as a Tool In Neurobiology. Raven Press, New York. 12. POTASHNER, S. J. 1979. Baclofen: effects on amino acid release and metabolism in slices of guinea pig cerebral cortex. J. Neurochem. 32: 103-109. 13. ROACH, M. K., M. M. KHAN, R. COFFMAN, W. PENNINGTON, AND D. L. DAVIS. 1973. Brain (Na+ + K+)-activated adenosine triphosphatase activity and neurotransmitter uptake in alcohol-dependent rats. Brain Res. 63: 323-329. 14. VINCENT, S. R., AND E. G. MCGEER. 1978. Kainic acid binding to membranes of striatal neurons. Life Sci. 24: 265-270.
NEUROLOGY
Ethanol,
69, 359-364 (1980)
Baclofen,
and Kainic Acid Neurotoxicity
EDITH G. MCGEER, ALEXANDERJAKUBOVIC, EDITH A. SINCH Kinsmen
Laboratory of Neurological Vancouver, British Received
November
AND
Research, University of British Columbia. Canada V6T I W5
20, 1979; revision
received
February
Columbia,
19. 1980
The neurotoxicity induced by intrastriatal injections of kainic acid was greater in rats drinking approximately 4 ml ethanol per day for 16 days before injection than in controls. Intraperitoneal injection of 5 mgikg baclofen (parachlorophenyl GABA), 30 min before the kainic acid injections had a slight protective action. These results have implications in connection with reported effects of ethanol and baclofen on glutamate systems in the brain.
INTRODUCTION Kainic acid, a structural analog of glutamate, produces local neuronal damage when intracerebrally injected. The neurotoxicity of kainic acid in both the striatum and the hippocampus has been shown to depend on innervation by intact excitatory (glutamate and, possibly, aspartate) afferent fibers (6, 8). In particular, striatal injections of kainic acid are not neurotoxic following lesions of the glutamate-containing corticostriatal tract. Moreover, coinjections of kainic acid and glutamate are neurotoxic in such animals and the development of kainic acid neurotoxicity in the striata of newborn rats parallels the development of glutamate innervation as evidenced by high-affinity glutamate uptake (3). It was therefore hypothesized that kainic acid exerts its local neurotoxicity through some cooperative interaction with endogenously released glutamate. On this hypothesis, agents which inhibit the release of glutamate might decrease the toxic effects of kainic acid, whereas agents which enhance the activity of glutamate systems might have the opposite effect. Michaelis et al. (10) suggested that both pharmacologic and binding data indicate “a probable Abbreviations:
GAD-glutamic
acid decarboxylase. CAT-choline
acetyltransferase
359 0014-4886/80/080359-06$02.00/O Copyright All rights
0 1980 by Academic Press. Inc. of reproduction in any form reserved
360
MCGEER,
JAKUBOVIC,
AND
SINGH
hyperactivity of the glutamate excitatory system in the central nervous system during chronic ethanol intoxication.” Acute treatment with baclofen (parachlorophenyl GABA), on the other hand, has been said to inhibit the synaptic release of glutamate (4, 12). It seemed possible therefore that such treatments might alter kainic acid neurotoxicity. Because intrastriatal injections of kainic acid destroy local cholinergic and GABA neurons, measurements of glutamic acid decarboxylase (GAD) and choline acetyltransferase (CAT) in injected compared with control striata were found useful indices of the extent of neuronal damage (7). We therefore studied striatal GAD and CAT activities after local injections of kainic acid in animals pretreated with ethanol or baclofen and compared them with those of controls. METHODS Male Wistar rats weighing about 250 g at the time of injection were housed singly in a room with a 12-h light:dark cycle during both pre- and post-injection periods. The ethanol group was given free access for 16 days to a 6% solution of ethanol in Metrecal liquid, chocolate flavor (manufactured by Mead-Johnson, Canada); controls for this group were similarly offered Metrecal with an isocaloric amount of sucrose added. The daily average ethanol intake was 3.5 to 4.3 ml/rat. Rats injected with baclofen (5 mg/kg, i.p., 30 min before the kainic acid injection) and controls for this group were given standard laboratory chow. All kainic acid injections were done stereotaxically under Nembutal anesthesia, as previously described (7), with the total injection volume of 1 ~1 being injected into the striatum during a IO-min period. The contralateral striatum in each rat served as control. The rats were killed 8 to 10 days after injection, and striata were dissected, homogenized, and assayed for protein, CAT, GAD, and tyrosine hydroxylase by previously reported procedures (7). Injections and assays were always done in parallel on control and drug-treated groups. In a separate series of experiments, rats were similarly offered ethanolMetrecal or sucrose-Metrecal for 16 days and killed at the time corresponding to the kainic acid injections. The striata were dissected, then homogenized in 0.32 M sucrose, and portions of the homogenates were used to assay high-affinity glutamate accumulation and kainic acid binding by previously reported methods (9, 14). RESULTS There were no significant differences between any of the groups in the enzyme or protein values in the noninjected striatum, suggesting that the drug treatments per se did not have a significant effect on the enzyme activities measured.
ETHANOL,
BACLOFEN,
AND KAINIC
TABLE
361
ACID
I
Protein Values and Enzyme Activities in Kainic Acid-Injected Striatum as Percentage of Values in the Contralateral Striatum (Mean t SD) Group and treatment”
N
GAD”
CAT’
Protein
1. Ethanol 2. Controls
282 8 61 2 l3**”
33-+ 8 64 + 13***
942 962
15 IO
3. Baclofen 4. Controls
79 2 20 32 2 7**
73 2 20 25 + lo**
lO7* 952
5 7
5. Baclofen 6. Controls
52 -t 14 35 i- 6*
60 k 24 34 2 9*
98t 962
6 7
7. Baclofen 8. Controls
87 2 21 63 t I2
81 2 22 62 t 11
102+ 98C
3 4
’ Groups 1,2,7. and 8 were injected with 2.5 nmoles and groups 3 through 6 with 5 nmoles kainic acid. Control values in pmol, h-i, 100 mg-’ protein averaged 15.8 ? 1.3 for GAD and 34.8 i 2.9 for CAT. b Glutamic acid decarboxylase. ” Choline acetyltransferase. * P < 0.05. ** P < 0.01. *** P < 0.001.
As indicated in Table 1, both the CAT and the GAD results suggest that the kainic acid injections caused a significantly higher neurotoxicity in the ethanol-treated group than in the controls. Baclofen, on the other hand, seemed to afford a slight protective action, although the greater variability in the baclofen-treated groups rendered the results less significant.Tyrosine hydroxylase values were not significantly affected in any group. Measurements of kainic acid binding showed no significant difference between the ethanol-treated and the control groups, but the sodium-dependent, net accumulation of labeled glutamate at 1O-6 M was significantly greater in synaptosomes from ethanol-treated animals than in those from controls (Table 2). DISCUSSION Chronic ethanol usage would appear to potentiate the neurotoxicity of small doses of kainic acid. This is consistent with the hypothesis that kainic acid is dependent on an interaction with glutamate systems if, as reported by Michaelis et al. (lo), exposure of rats to ethanol under conditions such as used here leads to hyperactive glutamate systems. The results with bac-
362
MCGEER,
JAKUBOVIC,
AND SINGH
TABLE 2 Glutamate Accumulation and Kainic Acid Binding in the Striatum of Rats After Various Drug Treatments (Mean * SD) Treatment
N
Glutamate accumulation (pmol, 5 min-‘, g-l protein)
Kainic acid binding (fmol, mg-1 protein)
Ethanol Controls
10 10
3.03 ?I 0.34 2.58.2 0.22*
196 2 24 193 c 21
Baclofen Controls
10 10
2.34 -t- 0.19 2.62 + 0.37
-
n Accumulation of radioactive glutamate (IO-& M) was measured after a S-min incubation at 37°C of synaptosomal fractions in Krebs-Ringer phosphate with sodium-free incubations used as blanks (9). Specific kainic acid binding to striatal membranes was measured as the difference in binding of labeled kainate (400 mM) observed in the absence and presence of 10m3M unlabeled kainic acid (14). *P < 0.01.
lofen are less convincing but are at least in the direction predicted on the basis of the prior reports that baclofen inhibits the release of glutamate (4, 12). It must be said, however, that the effects of both ethanol and baclofen on glutamate systems are still not proven and would undoubtedly be only part of the effects of these drugs on various neurotransmitter systems. The increased accumulation of labeled glutamate in the ethanol-treated animals was somewhat surprising in view of prior literature, Michaelis et al. (lo), using concentrations of radioactive glutamate similar to those used here, found an increase in glutamate binding with synaptosomal membranes, but they were studying the sodium-independent binding sites and the amount of binding they found was approximately 1/50th of the sodiumdependent accumulation found in the present study. Roach ef al. (13) found about 16% less sodium-dependent accumulation of radioactive glutamate in whole brain tissue from alcohol-treated compared with control rats. However, they used the supernate of a IOOOg centrifugation and calculation indicates that, if the endogenous glutamate was released into this supernate, the concentration at which Roach et al. were working would have been of the order of 10m4 M. Under those conditions, considerably more low-affinity uptake would be expected than in our studies where we used the synaptosomal fraction. Under our conditions, the increased accumulation in the ethanol-treated animals may not reflect an increase in net uptake as such but rather may be due to an increase in homo exchange consequent to an increased release. Further experiments will be needed to determine whether or not this is the case. Although the binding data of Michaelis et al. (10) might indicate supersensitive postsynaptic receptors (and thus lead one to expect decreased presynaptic release), the field of glutamate
ETHANOL.
BACLOFEN,
AND KAINIC
ACID
363
binding sites is presently too complex to allow any firm interpretation of such data. The kainic acid binding experiments did not indicate any significant abnormality in the kainic acid binding sites after chronic ethanol treatment. As it is becoming increasingly clear, however, that these binding sites are not identical with the postsynaptic glutamate receptors, a supersensitivity of these postsynaptic receptors, such as implied by Michaelis ef cl/. (lo), is not ruled out. It is interesting to speculate on the possible meaning of these results in relation to human disease. The histologic and biochemical patterns seen after injection of kainic acid into the striatum, hippocampus, or cerebellum of rats have been compared with those seen in various human degenerative disorders (2,5, 1 I). Because of this, and because glutamate is itself neurotoxic, it was hypothesized that neuronal death in degenerating disorders such as Huntington’s disease, senile dementia, or some of the ataxias may depend on some pre- or postsynaptic abnormality in glutamatergic systems which results in prolonged, excessive stimulation of the postsynaptic neurons. If there is any validity to this hypothesis, the present data and those of Michaelis et al. (10) might provide a rationale as to why the chronic use of ethyl alcohol would be contraindicated in persons at risk for those diseases. Similarly, ethanol might be expected to have a deleterious effect in epilepsy because glutamate and its analogs have convulsive properties. On the other hand, on the same hypothesis, chronic treatment with an agent which inhibits glutamate release might slow the rate of cell loss in a condition such as Huntington’s disease. Short-term clinical trials of baclofen in Huntington’s disease have been negative (1). but even a potent inhibitor of glutamate release could not be expected, on this hypothesis of its action, to improve established symptomatology. In any case, the present data suggest that any such agent would have to be far more potent than baclofen on glutamate systems. REFERENCES 1. BARBEAU. A. 1973. GABA and Huntington‘s chorea. Li~ncrt 2: 1499-1500. 2. BIZIERE, K.. AND J. T. COYLE. 1978. Infiuence of corticostriatal afferents on striatal kainic acid neurotoxicity. Neurosci. Left. 8: 303-310. 3. COYLE, J. T., E. G. MCGEER, AND P. L. MCGEER. 1978. Neostriatal injections: a model for Huntington’s chorea. Pages 139-161 in E. G. MCGEER, J. W. OLNEY. AND P. L. MCGEER, Eds. Kainic Acid 0.~ a Tool in Neurobiology. Raven Press. New York. 4. Fox, S.. K. KRNJEVIC, M. E. MORRIS, E. PUIL, AND R. WERMAN. 1978. Action of baclofen on mammalian synaptic transmission. Neuroscience 3: 495-5 15. 5. HERNDON, R.M.. AND J. T. COYLE. 1978. Glutamatergic innervation, kainic acid, and selective vulnerability in the cerebellum. Pages 189-200 in E. G. MCGEER, J. W. OLNEY, AND P. L. MCGEER, Eds.. Kainic Acid as cl Tool in Neurobiology. Raven Press. New York.
364
MCGEER,
JAKUBOVIC,
AND
SINGH
6. K~HLER, C., R. SCHWARCZ, AND K. FUXE. 1978. Perforant path transections protect hippocampal granule cells from kainate lesions. Neurosci. Letr. 10: 241-246. 7. MCGEER, E. G., AND P. L. MCGEER. 1978. Some factors influencing the neurotoxicity of intrastriatal injections of kainic acid. Neurochem. Res. 3: 501-517. 8. MCGEER, E. G., P. L. MCGEER, AND K. SINGH. 1978. Kainic acid-induced degeneration of neostriatal neurons: dependency upon cortico-striatal tract. Bruin Res. 139: 381-383.
9. MCGEER, P. L., E. G. MCGEER, U. SCHERER, AND K. SINGH. 1977. A glutamatergic corticostriatal path? Brain Res. 128: 369-373. 10. MICHAELIS, E. K., M. J. MULVANEY, AND W. J. FREED. 1978. Effects of acute and chronic ethanol intake on synaptosomal glutamate binding activity. Biochem. Pharmacol.
27: 1685-1691.
11. NADLER, J. V., B. W. PERRY, AND C. W. COTMAN. 1978. Preferential vulnerability of hippocampus to intraventricular kainic acid. Pages 219-237 in E. G. MCGEER, J. W. OLNEY, AND P. L. MCGEER , Eds., Kainic Acid as a Tool In Neurobiology. Raven Press, New York. 12. POTASHNER, S. J. 1979. Baclofen: effects on amino acid release and metabolism in slices of guinea pig cerebral cortex. J. Neurochem. 32: 103-109. 13. ROACH, M. K., M. M. KHAN, R. COFFMAN, W. PENNINGTON, AND D. L. DAVIS. 1973. Brain (Na+ + K+)-activated adenosine triphosphatase activity and neurotransmitter uptake in alcohol-dependent rats. Brain Res. 63: 323-329. 14. VINCENT, S. R., AND E. G. MCGEER. 1978. Kainic acid binding to membranes of striatal neurons. Life Sci. 24: 265-270.