Suppression of amygdala-kindled seizure in cats by enhanced GABAergic transmission in the substantia innominata

EXPERIMENTAL

NEUROLOGY

89,225-236

(1985)

Suppression of Amygdala-Kindled Seizure in Cats by Enhanced GABAergic Transmission in the Substantia Innominata’ K. MORITA, M. ORAMOTO,

K. SEKI,’ AND J. A. WADA

Department of Neuropsychiatry, Okayama University, Okayama, Japan, and Divisions of Neuroscience and Neurology, University of British Columbia, Vancouver, British Columbia V6T I W5, Canada Received December 6. 1984 The chronological effect of intracerebral injection of GABAergic drugs, either muscimol or gabaculine, into the substantia innominata, was examined in amygdalakindled cats. Results obtained indicate: (i) that the substantia innominata may play a significant role in ictal linkage between a nonmotor system such as the amygdala and the motor mechanism responsible for amygdala-kindled convulsion, and (ii) that the GABA terminals in the substantia innominata exert a suppressive action toward COnWdSiVC SeiZUre gC?WakatiOII of amygdala Origin. 8 1985 Academic Press, 1~.

INTRODUCTION The importance of the motor cortex in the expression of motor manifestations of amygdala (AM)-kindled seizure has been suggested in rats (3), rabbits (22), and subhuman primates (25, 26). In particular, our previous studies in subhuman primates suggest that the development of AM-kindled convulsive seizure is the consequence of the propagation of epileptic activity to the prerolandic cortex (25, 26). However, a direct projection from the AM to the cortex is not known. In this context, the substantia innominata (SI) appears to occupy a strategic position as it has reciprocal connections with the AM (5, 6, 13, 19, 30, 32) and its cholinergic neurons project to widespread areas of the cerebral cortex (4, 9-l 1, 14, 16). Abbreviations: AM-amygdala; SI-substantia innominata; ADT, GST-afterdischarge-, generalized seizure-triggering threshold; G-gabaculine; M-muscimol. ’ This work was supported in part by a Medical Research Council of Canada grant. 2 Present address: Department of Neuropsychiatry, Juntendo University, Tokyo, Japan. 225 0014-4886185 $3.00 CopyrigJ~t Q 1985 by Academic Press. Inc. All rights of reproduction in any form reserved

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AL.

A line of evidence indicates the important role of the cholinergic system in AM-kindled generalized seizures (1, 2, 8, 12, 23, 28, 29). Kimura et al. showed that the SI, among various cerebral cholinergic systems, when electrolytically injured, showed a marked reduction of electroclinical intensity of AM-kindled seizure (12). Based on those observations, they postulated that the cholinergic neurons in the SI might play an important role in AMkindled seizure generalization. However, it has been difficult to test this hypothesis adequately because electrolytic injury of the SI sufficient to abolish AM-kindled convulsion has not been compatible with the survival of the animal so treated. On the other hand, high glutamic acid decarboxylase activity in the SI (7, 27) suggests that the SI is richly supplied by gamma-aminobutyric acid (GABA) neurons or their terminals. As the important role of GABA as an inhibitory neurotransmitter of AM-kindled seizures has been suggested (15, 17, 18), we postulated that GABA terminals in the SI may exert an inhibitory action on the generalization of AM-kindled seizure. In this study, we investigated the role of the SI and its GABA terminals in the generalization of AM-kindled seizure in cats. Results obtained indicate: (i) that the SI plays a significant role in ictal linkage between a nonmotor system such as the AM and the motor mechanism responsible for AM-kindled convulsion, and (ii) that the GABA terminals in the SI exert a suppressive action on convulsive seizure generalization of AM origin. MATERIALS

AND

METHODS

Six female cats weighing more than 2.5 kg were used. Bi- or tripolar electrodes insulated except for 0.5 mm at the tip and with a tip separation of 1 mm, were implanted into the AM, the ventral hippocampus, the SI, or the frontal cortex. Five cats were implanted bilaterally with a combined cannula (21 gauge)-electrode into the SI, and the other (cat 800) had the same type of cannula electrode implanted in both the SI and the AM. One week after surgery, the animals were subjected to daily left AM stimulation according to a well established procedure (24). Briefly, AM stimulation was delivered bipolarly in a l/s train of constant current, 60-Hz sine wave at the afterdischarge threshold (ADT). The pattern of clinical seizure development was classified into six stages (24). All animals were kindled to a stable stage 6 generalized convulsion which was elicited every day for five successive days. Subsequently, a generalized seizure-triggering threshold (GST) was established by gradual reduction of stimulus intensity until the minimal intensity to elicit stage 6 seizure having an “all-or-none” property was found.

GABA AND AMYGDALA

KINDLING

221

To examine the possible functional change of the SI induced by AM kindling, the transfer effect at the SI was examined by stimulating at 400 or 800 PA. When AD could not be induced, the intensity was increased to 1200 PA. After examination of the transfer phenomenon, the stability of the GST-induced AM-kindled convulsion was conhrmed by three daily stimulations. Four animals were then injected with 800 ng/5 1.c1muscimol (3-hydroxy-5-aminomethylisoxazole), a potent GABA agonist, into the SI bilaterally. Muscimol (M) was dissolved in physiologic saline with a concentration of 160 ng/rl, pH 6.8. Its effect on AM-kindled convulsion induced by GST stimulation was tested at 5, 30, 60, and 120 min after the injection, each test separated by at least l-week intervals. Several weeks after examination of the M effect, the left AM was again stimulated at the GST for 3 consecutive days to ascertain the stability of stage 6 kindled convulsion. Subsequently, 13.8 @3 ~1 gabaculine (G), a GABA-transaminase inhibitor, was injected into the left SI. The GST stimulation was applied at the kindled left AM during 10 days at 8- to 24h intervals. Gabaculine-HCl was dissolved in distilled water and buffered to pH 6.9 with sodium bicarbonate. Finally, to compare the effect of intra-SI and intra-AM injection of G, 30 &3 ~1 was injected into the SI ipsilateral to the kindled AM of cat 800; 3 weeks later, the same injection was made directly into the kindled AM after ensuring the stability of the kindled seizure by three daily GST stimulations. In this experiment, the kindled AM was stimulated at the GST at 6- to 24-h intervals during the 10 to 20 days following G injection. When AD failed to occur the stimulus intensity was increased until AD was elicited. Upon completion of the experiment, the animals were deeply anesthetized and their brains were perfused, serially sectioned, and stained with cresyl violet. Histological examination showed that all electrode tips were in the intended structures. The loci of the tips of the AM electrodes and the SI cannula electrodes is shown in Fig. 1. Except for a mild gliosis along the electrode or cannula-electrode tracks, no histologic changes were detected under light microscopic examination. RESULTS

Examination of the Transfer Eflect at the Substantia Innominata followin, Completion of Ipsilateral Amygdala Kindling (Table 1). Epileptic respona to SI stimulation showed an “all-or-none” property; that is, only when AD was induced was generalized convulsive seizure strikingly similar to an AMkindled stage 6 seizure elicited. The AD duration was very prolonged, apparently due to the delay of generalized convulsive seizure onset, as seen

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ET AL.

F 15.2

FI 1.5 \

I

FIG. 1. The loci of the tips of the substantia innominata (SI) and amygdala (AM) electrodes (solid circles). The numbers in the figure represent the cats’ numbers.

from the control data in Table 2. However, this interpretation needs to be verified because generalized convulsion was induced only once at the SI. Eflect on Amygdala-Kindled Convulsion of Bilateral Injection of Muscimol into the Substantia Innominata. The chronologic effect of M injection is summarized in Table 2. The anticonvulsive effect of the drug was most prominent at 30 min after intra-SI injection. In cat 1, no AD was induced, whereas cat 3 showed a low-frequency spike discharge localized to the left AM and ventral hippocampus lasting 4 s. In cat 5, generalized convulsive seizure became markedly asymmetrical at 30 min. In cats 1 and 3, generalized convulsive seizure was elicited when the AM was restimulated at 50 PA above the GST 35 min after M injections. The AD duration and latency to the onset of generalized convulsive seizure were compared between a mean of the last five generalized convulsions during AM kindling and generalized convulsion 30 or 35 min after M injection. As seen in TABLE 1 Effect of Substantia lnnominata Stimulation on Completion of Primary Site Amygdafa Kindling Cat

ADT”

ss

ADD

L

1 3 4 5 6

>1200 >1200 800 800 800

0 0 6 6 6

0 0 193 123 131

80 74 18

’ Abbreviations: ADT-afterdischarge threshold (FA), SS-clinical afterdischarge duration (s), L-latency to convulsive seizure (s).

seizure stage, ADD-

GABA AND AMYGDALA

229

KINDLING

TABLE 2 Bilateral Injection of Muscimol (800 ngf5 ~1) into the Substantia Innominata

Chronology (min) Cat 1 3 4 5

5

30

60

l c

0

0 0

0 0

0

0

A

A

120

0

Latency to convulsive generalization” (s)

Ad duration’ (4 CONTROL* 66.8 71.6 106.4 88.0

+ + + +

3.3 2.2 5.6 4.5

MUSCIMOL 82d 87d 123 95

CONTROL” 32.0 39.8 62.8 41.4

f + + f

0.6 3.8 2.8 1.7

MUSCIMOL 52d 49d 74 47

’ Primary site AM stimulation at generalized seizure threshold (GST) 30 min aBer Muscimol. Prolongation means: AD duration, 13.6 + 2.1 s, p < 0.01; latency, 11.5 + 3.1 s, p < 0.05. * Control: mean of five amygdala (AM)-kindled convulsions. ’ O-Generalized convulsion, O-no afterdischarge (AD), A-asymmetrical generalized convulsion, every brief localized spike discharge only. dGeneralized convulsion induced 35 min after Muscimol when stimulated at 50 PA above GST.

Table 2, both AD duration and latency to convulsive generalization were significantly increased after M injection. Thus, bilateral intra-SI injection of M exerted a suppressive effect on AM-kindled convulsion with maximal effect at 30 min due to the ADT elevation, but even when generalized convulsion was induced, there was a significant delay in the generalization of convulsive seizure. Efect of Intra-substantia Innominata Injection of Gabaculine on Ipsifateral Kindled Amygdala Seizure. Results are summarized in Table 3 and Fig. 2, in which control data represent a mean of three AM-kindled seizures. As seen in Fig. 2, AM-kindled seizure was completely blocked between 12 and 96 h in cat 3 and between 48 and 168 h in cat 4. There was a very brief low-frequency AD, localized to the AM and @lateral SI and ventral hippocampus, without any overtly apparent clinical correlates. Although cats 1 and 5 did not show any suppression of kindled seizure, there was a transient prolongation of AD duration coincident with delay in generalization of convulsive seizure. None of the animals showed an overtly apparent electroclinical change following G injection. Cats 1 and 4 were found dead on the 10th and 9th day, respectively, but autopsy failed to disclose gross or histologic pathology. The effect of intra-SI injection of G was somewhat similar to that of M, showing either complete suppression of AM-kindled convulsion or a significant prolongation of convulsive seizure generalization. Comparison of Efects of Intra-amygdala and Intra-substantia Innominata

MORITA

230

ET AL.

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hD durotlon Latrncy to c~~~ts~vo Saixurr stopa Oooth controt I mwn 1

30 clays gwmrahxohon

FIG. 2. The anticonvulsive effects of intra-SI injection of gabaculine on AM-kindled convulsions of cats. Gabaculine (13.8 #g/3 pl) was injected into the SI ipsilateral to the stimulated amygdala. In cats 3 and 4, convulsive manifestations of AM-kindled seizure were completely suppressed from 12 h to 4 or 7 days after the injection. In two other cats, transient prolongation of the latency for the onset of generalized convulsion was observed, whereas convulsive manifestations were not suppressed.

Injeclion duration of five kindled recurred

of Gabaculine. Results are summarized in Fig. 3, where AD and latency to convulsive generalization at 0 h represents a mean kindled seizures. In&a-S1 injection of G produced regression of seizure between the Ist and 6th days but kindled stage 6 seizure on day 7. There was a transient prolongation of AD duration

s ADD LAT

s ADD LAT

s ADD LAT

3

4

5

6 63.5 + 3.1 36.0 f 3.9

6 88.5 f 6.6 55.8 & 3.3

6 70.6 f 6.7 49.8 f 4.6

6 71.8 f 7.9 36.3 f 3.3

6 74 38

6 69 37

6 87 50

6 155 84

-

0 6

6 118 42

24

6 98 58

0 24 -

-

0 5

6 122 57

2

duration (s), LAT-latency

0 7 0

-

0 4

6 91 34

12

Hours

6 91 53

6 79 51

6 81 39

4

a Mean of three kindled seizures. b S-seizure stage, ADD--afterdischarge ’ Death.

Sb ADD” LATb

1

Cat

Control” (mean +- SD)

0 9

0 3 6 162 96

-

-

2 8

6 154 99

4

6 174 80

-

0 2

6 92 59

6 231 136

5

to convulsive seizure (s).

6 117 80

-

-

0 4

6 126 66

3

6 110 47

-

0 4

6 93 57

6 193 83

6

Days

6 107 60

-

0 5

6 113 72

6 191 77

7

6 87 51

6 139 64

6 108 70

6 128 60

8

e

6 89 59

-

6 113 64

6 125 56

9

Effects of Gabaculine (13.8 c(g/3 ~1) Injection into the Substantia Innominata Ipsilateral to the Kindled Amygdala

TABLE 3

6 90 56

-

6 112 64

’ -

10

6 68 36

-

6 74 48

-

30

232

*

MORITA

ET AL.

6 t 5

GST

stage

Seizure

-------f---

I

,

r

0

6

12

A:

Gobaculmr

3Op9/3pl

6:

Gobocullnr

3Op9/

3~1

r

,

,

,

2436466072A”

5

6

into

I0 sate

SI

nrs 0-O

into

1. site

AM.

M

Lotrncy

--e-w

GST

AD

7”

9”

6

IODayr

duration

Abortivr

to 9wuroliztd

stage

convulsion

4

FIG. 3. Comparative effect of injection of gabaculine (30 &3 ~1) into the substantia innominata (A) or amygdala (B) in AM-kindled cat 800. Inserts show the positions of the cannulae.

coincident with a delay in generalization of convulsive seizure. When the same quantity of G was injected into the kindled AM, no AD could be elicited between 36 and 62 h. However, with increasing stimulus intensity, stage6 seizure was restored without a significant delay in convulsive seizure generalization. DISCUSSION Results of this experiment indicate that GABAergic drugs such as M and G, although having different mechanismsof action, suppressthe generaliza-

GABA AND AMYGDALA

KINDLING

233

tion of AM-kindled convulsion when injected into the SI. Bilateral SI injection of M induced an elevation of both GST and ADT, the suppression of AM-kindled convulsion, or the delay of convulsive seizure generalization. These results indicate that enhanced GABAergic transmission in the SI suppresses the convulsive generalization of AM seizure. The result of intra-SI injection of G in cats is comparable to that in rats similarly treated (20), i.e., it suppressed kindled convulsion without changing the AD threshold followed by the recurrence of AM-kindled convulsion, although a marked delay in generalization of convulsive seizure was evident. This is in contrast with the result of intra-AM injection, which resulted in the complete abolition of AD generation, although kindled convulsion could be re-activated by increasing the stimulus intensity. This finding supports our conclusion that enhanced GABAergic transmission interferes with the role of the SI in mediating ictal linkage between the AM and the motor system responsible for AM-kindled convulsion. The results of intraSI injection of M and the evidence that G increases the synaptosomal GABA concentration (31) indicate that this effect may be mediated by a postsynaptic GABA receptor. Intra-SI injection of M suppressed AD generation in the stimulated AM in cat 1 but when the stimulus intensity was increased, generalized convulsion was reactivated. This is comparable to our finding with intra-AM injection of G which completely suppressed AD generation at the GST, but when the stimulus intensity was increased, generalized kindled convulsion was reactivated (Fig. 3). These findings suggest that the M effect may be due to drug diffusion into the AM because intra-SI injection of G caused no change in the ADT. In fact, the quantity of M injected was 5 ~1 vs. 3 ~1 of G. Therefore, the possibility of diffusion of the intra-SI-injected M into the AM cannot be excluded. Furthermore, the intra-SI injection of M suppressed AM-kindled convulsion in cat 3, but when the stimulus intensity was increased, generalized convulsion was reactivated. Whether or not the anticonvulsant effect of injecting G into the SI is also due to its diffusion into the AM, and if so, would generalized convulsion be induced by increasing the stimulus intensity, remains to be clarified. However, the quality of AM-kindled convulsion was different according to the site of injection; that is, the latency for the generalization of convulsive seizure was extremely prolonged in the case of SI injection, but not with AM injection. Therefore, it seems reasonable to assume that the effect of intraSI injection of G or M is different from the intra-AM injection of either drug, although when the quantity of the drug injected is relatively high, drug diffusion into the adjacent structures could modify the anticonvulsive effect to some extent. Comparative results obtained in cat 800 between intra-AM and intra-SI injection of G support this assumption. Results of a

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comparable study in AM-kindled rats confirm the differential G effect of intra-AM and intra-SI injection (M. Sato et al., in preparation). It is interesting that the SI electrode site, where the positive transfer effect was observed after ipsilateral AM kindling, does not necessarily correspond to those sites where G and M produced an anticonvulsive effect. Theoretically, the site of the cannula and that of the electrodes which are attached to the cannula are the same. However, it is possible that the extent of the neuronal aggregates involved in AD generation by electrical stimulation may be smaller than the region of drug diffusion. Similarly, the effect of the drug injected and the extent of diffusion could be different between M and G. Furthermore, the SI may not be cytoarchitectonically homogenous (21), and may have a certain synaptic organization with respect to GABA neurons and those cholinergic neurons involved in a functional connection with the cerebral system. Therefore, a lack of complete correspondence between the results of electrical stimulation and those of drug injection does not necessarily contradict our assumption that the SI plays an important role in the generalization of AM-kindled seizure. Finally, verification as to how appropriate our interpretation is of the results presented here must await results of chronological biochemical assessment of both the extent of drug diffusion and regional GABA concentrations. Such a study is now in progress. REFERENCES 1. ARNOLD, P. S., R. J. RACINE, AND R. A. WISE. 1973. Effect of atropine, reserpine,6-

hydroxydopamine and handling on seizuredevelopment in the rat. Exp. Neural. 40: 457-470. 2. CAIN, D. P. 1983. Bidirectional transferof electrical and carbachol kindling. Brain Rex 260: 135-138. 3. CORCORAN,M. E., H. URSTAD, J. A. MCCAUGHRAN, JR., AND J. A. WADA. 1976. Pages 2 1S-228 in J. A. WADA Ed., Kindling Raven Press, New York. 4. DIVAC, I. 1975. Magnocellular nuclei of the basal forebrain project to neocortex, brain stem and olfactory bulb. Review of some functional correlates. Brain Res. 93: 385-398. 5. EMSON, P. C., G. PAXINOS, G. LE GAL LA SALLE, Y. BEN-AIR, AND A. SILVER. 1979. Choline acetyltransferase and acetylcholinesterase containing projections from the basal forebrain to the amygdaloid complex of the rat. Brain Res. 165(2): 271-282. 6. FEMANO, P. A., H. M. EDINGER, AND A. SIEGEL. 1983. The effects of stimulation of the substantia innominata and the sensory receiving areas of the forebrain upon the activity of neurons within the amygdala of the anesthetized cat. Brain Res. 269: 119- 132. 7. FONNUM, F., I. WALAAS, AND E. IVERSEN. 1977. Localization of GABAergic, choline& and aminergic structures in the mesolimbic systems.X Neurochem. 29: 2 19-230. 8. GIRGIS, M. 198 1. Electrical vs. choline& kindling. Elecfroenceph. C/in. Neurophysiol. 51: 417-425. 9. JOHNSTON, M. V., M. MCKINNERY, AND J. T. COYLE. 1979. Evidence for a cholinergic projection to the neocortex from neurons in the basal forebrain. Proc. Natl. Acad. Sci. U.S.A.

76: 5392-5396.

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10. KIEVIT, J., AND H. G. J. M. KUYPERS. 1975. Subcortical a&rents to the frontal lobe in the rhesus monkey studied by means of retrograde horseradish peroxidase transport. Bruin Res. 85: 261-266. 1 I. KItmu, H., P. L. MCGEER, F. PENG, AND E. G. MCGEER. 1980. Choline acetyltransfemsecontaining neurons in the rodent brain demonstrated by immunohistochemistry. Science u18: 1057-1059. 12. K~MURA, H., Y. KANEKO, AND J. A. WADA. 1981. Catecholamine and choline& systems and amygdaloid kindling. Pages 265-287 in Kindling 2. J. A. WADA, Ed., Raven Press, New York. 13. Kt~uru, H., A. KASHIBA, T. MAEDA, Y. UNEKO, AND J. A. WADA. 1982. Choline& systems in the substantia innominata and amygdaloid kindling. Pages 509-512 in H. AKIMOTO, M. KAzA~~rauur, M. SEINO,AND J. A. WADA, Eds., Advances in Epileptology. Raven Press, New York. 14. K~MURA, H., P. L. MCGEER, J. H. PENG, AND E. G. MCGEER. 1981. The central cholinergic system: choline acetyltransferase immunohistochemical study in the cat brain. J. Camp. Neural. 2OOz 151-201. 15. LE GAL LA SALLE, G. 1980. Inhibition of kindling-induced generalized seizures by aminooxyacetyc acid. Can. J. Physiol. Pharmacol. 58: 7-l 1. 16. MESULAM, M. M., AND G. W. VAN HOESEN. 1976. Acetyltransferase-rich projection from the basal forebrain of the rhesus monkey to the neocortex. Bruin Res. 109: I52- 157. 17. MYSLOBODSKY, M. S., R. F. ACKERMANN, AND J. ENGEL, JR. 1979. Effects of gammaacetylenic GABA and gamma-vinyl GABA on metrazol-activated and kindled seizures. Pharmacol. Biochem. Behav. 11: 265-27 1. 18. MYSLOBODSKY, M. S., AND E. S. VALENSTEIN. 1980. Amygdaloid kindling and the GABA system. Epilepsia 21: 163-175. 19. NAGAI, T., H. KIMURA, T. MEDA, P. L. MCGEER, F. PENG, AND E. G. MCGEER. 1982. Cholinergic projections from the basal forebrain of the rat to the amygdala. J. Neurosci. 2: 5 13-520. 20. OKAMOTO, M., AND J. A. WADA. 1984. Reversible suppression of amygdaloid kindled convulsion following unilateral gabaculine injection into the substantia innominata Brain Res. 305: 389-392. 2 I. PRICE, J. L., AND R. STEIN. 1983. Individual cells in the nucleus basalis-diagonal band complex have restricted axonal projections to the cerebral cortex in the rat. Bruin Res. 260: 352-356. 22. TANAKA, A. 1972. Pmgmssive changes of behavioural and electroencephalographic responses to daily amygdaloid stimulation in rabbits. Fukuoka Acta Med. 63: 152-164. 23. Vosu, H., AND R. A. WISE. 1975. Cholinergic seizure kindling in the rat: comparison of caudate, amygdala and hippocampus. Behav. Biol. 13: 491-495. 24. WADA, J. A., AND M. SATO. 1974. Generalized convulsive seizures induced by daily electrical stimulation of the amygdala in cats. Neurology 24: 565-574. 25. WADA, J. A. 1980. Amygdaloid and frontal cortical kindling in subhuman primates. Pages 133-146 in M. GIRGIS AND L. G. KILOH, Eds., Limbic Epilepsy and the Dyscontrol Syndrome. Elsevier, Amsterdam. 26. WADA, J. A., T. MIZOGUCHI, AND S. KOMAI. 1981. Cortical motor activation in amygdaloid kindling: observations in nonepileptic rhesus monkeys with anterior 3 callosal bisection. Pages 235-248 in J. A. WADA, Ed., Kindling 2. Raven Press, New York. 27. WALAAS, I., AND F. FONNUM. 1979. The distribution of putative monoamine, GABA, acetylcholine and glutamate fibers in the mesolimbic system. Pages 60-73 in P. KROCSGAAD, Ed., GABA-Neurotransmitters. Munksgaad, Copenhagen.

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ET AL.

28. WASTERLAIN, C. G., AND V. JONEC. 1980. Transsynaptic generation of a chronic seizure focus. Life Sci. 26: 387-391. 29. WASTERLAIN, C. G., AND V. JONEC. 1983. Chemical kindling by muscarinic amygdaloid stimulation in the rat. Bruin Res. 271: 31 l-322. 30. WATSON, R. E., AND A. SIEGEL. 1981. A “‘C-2-deoxyglucose analysis of the functional pathways mediating the propagation of seizure activity from the rat amygdala. Pages 453-464 in Y. BEN-AR], Ed., The Amygdaloid Complex, INSERM Symposium No. 20. Elsevier/North-Holland, Amsterdam. 3 I. WOOD, J. A., AND E. KLJRYLO. 1984. Amino acid content of nerve endings (synaptosomes) in different regions of the brain: effects of gabacuhne and isonicotonic acid hydrazide. .I. Neruchem.

42: 420-425.

32. YIM, C. Y., AND G. J. MOGENSON. 1983. Responses of ventral pallidal neurons to amygdala stimulation and its modulation by dopamine projections to the nucleus accumbens. J. Neurophysiol. 50: 148- 161.