Brain Research, 545 (1991) 351-354 ADONIS 0006899391246060
351
BRES 24606
Cocaine-induced behavioral sensitization is not associated with loss of GABA-immunoreactive neurons in the amygdala Michael A. Lee, Joseph M. Paris and Kathryn A. Cunningham Department of Pharmacology, University of Texas Medical Branch, Galveston, TX 77550 (U.S.A.)
(Accepted 8 January 1991) Key words: Cocaine; y-Aminobutyric acid; Amygdala, Sensitization; Rat
We investigated whether cocaine-induced behavioral sensitization (15 mg/kg, twice daily for 7 days) is associated with changes in y-aminobutyrie acid (GABA) neurons in the lateral-basolateral amygdala of male Sprague-Dawley rats. The number of GABAimmunoreactive neurons in the amygdala did not differ between cocaine- and saline-treated rats. Although some aspects of this behavioral phenomenon parallel the kindling model of epilepsy, limbic alterations in GABA neurons do not appear to be associated with behavioral sensitization to cocaine. Cocaine is well-characterized as a psychostimulant in humans 14 and produces locomotor stimulation and stereotyped behaviors in laboratory animals 6. Repeated exposure to cocaine at low doses results in a progressive enhancement of its behavioral effects 15. Intermittent, subconvulsive doses of cocaine also elicit limbic responses virtually identical to those seen with progressive electrical stimulation of limbic structures ('kindling') which is proposed as a model for epilepsy 4'~4'24'25. Although the relationship between behavioral sensitization and kindling phenomena is unclear, the similar temporal and behavioral patterns seen in cocaine sensitization and electrical kindling 15 as well as the noted ability of cocaine to 'kindle' limbic neurons 25 suggest that neural mechanisms underlying behavioral sensitization and kindling phenomena may overlap. Modifications in y-aminobutyric acid ( G A B A ) inhibitory systems are strongly implicated in the progressive establishment of kindling. Decreases in GABA-immunoreactive (-IR) neurons t'5 and loss of GABAergic inhibitory postsynaptic potentials 3'19 have been observed in limbic areas of kindled rats. The purpose of the present experiment was to determine whether rats behaviorally sensitized to cocaine exhibit altered numbers of G A B A IR neurons in the basolateral/lateral amygdala nuclei similar to that seen in electrical kindling 1. Male Sprague-Dawley rats (SASCO, 160-230 g) were housed in groups of 4 with food and water freely available. The rats were handled one day prior to the start of the experiment. Each rat was injected intraper-
itoneally (i.p.) with either cocaine hydrochloride (15 mg/kg) or physiological saline twice a day (09.00 and 16.00 h) for 7 days. Fifteen minutes following the first and last injection, their behavior was observed and rated for stimulant-induced stereotypic behaviors 6. The animals were assigned a score of 1-9 based upon the following behavioral characteristics: 1 - - asleep, lying down, eyes closed; 2 - - inactive, lying down, eyes open; 3 - - in place activities, normal grooming, chewing cage litter, eating, or drinking; 4 - - normal, alert, active, moving about cage, sniffing, rearing; 5 - - hyperactive with rapid changes in position; 6 - - slow-patterned, repetitive exploration of the cage at normal levels of activity; 7 - - fast-patterned, repetitive exploration of the cage with hyperactivity; 8 - - restricted, remaining in same place in cage with fast, repetitive head and/or forelimb movement (includes licking, chewing, and gnawing stereotypies); and 9 - - dyskinetic-reactive with backing up, jumping, seizures and abnormally-maintained postures. The experimenter was blind to the treatment during injections and observational ratings. Scores were expressed as median ratings and treatment groups were compared with the Wilcoxon rank sum procedure (SAS Institute, Cary, NC). Each rat was anesthetized with sodium pentobarbital (90 mg/kg, i.p.) 18-24 h after the last injection. A solution of Ca2÷-free tyrodes was perfused transcardially for 20 min (200-300 ml) followed by 300-500 ml of 4% paraformaldehyde fixative plus 0.5% glutaraldehyde. The brain was removed and submerged in the glutaral-
Correspondence: K.A. Cunningham, Department of Pharmacology (J-31), University of Texas Medical Branch, Galveston, TX 77550, U.S.A.
352 d e h y d e fixative plus 20% sucrose for one hour and then stored overnight in a solution of sodium azide, bacitracin and sucrose in 0.1 M p h o s p h a t e buffer (PB) at 4 °C. The next day, the brain was rapidly frozen on dry ice and sliced into 40/~m slices in a cryostat at - 1 5 °C; tissue was
collected in 0.1 M PB and 0.1% sodium azide and stored overnight at 4 °C. Standard immunocytochemical p r o c e d u r e s were employed 23. Tissue sections were incubated in n o r m a l goat serum for 20 min, then in p r i m a r y a n t i b o d y (rabbit
A Fig. 1. A: cross-hatched area represents the area of the lateral and basolateral amygdala in which GABA-IR neurons were counted in each brain. Numbers represent distance in mm posterior to bregma ~3. B: low-power (50x) photomicrograph of a coronal section through the basolateral amygdala processed for GABA immunohistochemistry. Area within box is enlarged in C. Bar = 100 ~tm. C: high-power magnification (100x) of the ventral aspect of the basolateral amygdala. Arrowheads indicate examples of GABA-IR cells. Bar = 20/~m.
353 anti-GABA, Incstar, Stillwater, MN) at a concentration of 1:5000 for 24 h at 4 °C. Sections then were incubated in biotinylated secondary antibody (goat anti-rabbit) for 30 rain and then in an avidin-horseradish peroxidase complex (Vector Laboratories, Burlingame, CA) for 60 min with 30 min rinses in PB (3 changes) following each incubation. Control procedures involved substitution of normal serum for the primary antibody and preadsorption of the anti-GABA serum (1:5000) with G A B A (Sigma; 500 ~g/ml). Sections were then reacted with 3,3"-diaminobenzidine (DAB), rinsed, mounted on slides, and air-dried overnight. After being dehydrated and intensified in 0.1% osmium tetroxide, coverslips were applied using Permount. Neurons stained for G A B A were counted in 4 coronal planes through the amygdala: 2.12, 2.56, 3.14, and 3.60 mm posterior from bregma 13 as shown in Fig. 1A. G A B A - I R neurons were counted manually by an experimenter blind to treatment using a 40x objective of a light microscope. The number of cells found in each of the 4 coronal planes were analyzed by analysis of variance (ANOVA; SAS Institute, Cary, NC). On the first injection, rats administered saline exhibited a median score of 3 (range: 2-4) which did not differ from the median score of 4 (range: 3-6) of rats injected with cocaine. Furthermore, the median scores of salinetreated rats on the first and last injection did not differ. However, a significant increase in the median behavioral score for cocaine-treated rats was observed between the first (4; range: 3-6) and last injection (8; range: 6-8; P < 0.05) indicating that behavioral sensitization had developed 6. The G A B A immunohistochemical procedures resulted in excellent staining of G A B A neurons and varicosities in the amygdala nuclei. The numbers and distribution of G A B A - I R correlate very well with previous reports in which antibodies directed against G A B A 1°'11 and glutamate decarboxylase ( G A D ) 12 were used. An example of basolaterai amygdaloid neurons stained for G A B A is shown in Fig. 1C. Preadsorption of the primary antiserum with G A B A or substitution with normal serum eliminated all G A B A - I R . The number of G A B A - I R neurons counted at each coronal plane and the total numbers of cells counted in both cocaine- and salinetreated rats are shown in Fig. 2. There were no significant effects of cocaine treatment on the number of G A B A - I R neurons found in the lateral-basolateral amygdala (F3.18 = 1.15; P > 0.05). The present results suggest that cocaine-induced behavioral sensitization is not associated with a loss of G A B A - I R cells in the lateral-basolateral amygdala as is seen in electrically kindled rats ~. There is evidence, however, to suggest that cocaine interferes with G A B A metabolism 2. Benzodiazepines, which enhance G A B A
200
Tar~mm
-
r--"1 S a l i n e Cocaine
o
== z >=
1~o
~
100-
E _E
50-
O-
-
-
2.12 2.56 3.14 3.60 Posterior Distance from Bregma (ram)
Fig. 2. The number of GABA-IR neurons (mean + S.E.M.) in each of the 4 coronal planes in saline- (n = 4) and cocaine- (15 mg/kg, b.i.d., i.p.; n = 4) treated rats. Inset depicts the means (_+ S.E.M.) for the total number of GABA-IR neurons in both groups of rats.
neurotransmission, have been reported to block the sensitizing effect of cocaine in rats 17 yet enhance its locomotor stimulating properties in mice 26. Few attempts to assess the role of G A B A function in cocaine sensitization or its pharmacological kindling properties have been made. Cocaine/s a potent local anesthetic 21, but its stimulant properties are broadly attributed to its potentiation of catecholamine action by inhibition of the reuptake of dopamine and norepinephrine 8. The fact that repeated injections of amphetamine, which lacks local anesthetic actions, result in sensitization but fail to induce limbic kindling 9 supports a dissociation between stimulant-induced behavioral sensitization and limbic electrical kindling TM, although there is not a consensus 7. The importance of local anesthetic actions in pharmacologic kindling is further supported by the finding that repeated administration of lidocaine which has minimal monoamine stimulant effects2°'27 induces seizures, which differ from cocaine seizures in lethality 16'22. Thus, it is likely that cocaine-induced kindling is related to the local anesthetic actions of cocaine while sensitization is dependent upon its monoaminergic stimulant properties. Moreover, cocaine-induced behavioral sensitization and electrical kindling may not share a similar GABA-mediated mechanism (present results). Notwithstanding, we cannot rule out the possibility that cocaine might induce more subtle alterations in G A B A sytems, perhaps at the receptor or metabolic levels, which could not be detected in the present experiment.
The authors would like to acknowledge Patrick M. Callahan for his advice on quantification of GABA immunohistochemistry. This study was supported by DA05708 (K.A.C.), DA05381 (J.M.P.), the National Alliance for Research on Schizophrenia and Affective Disorders (K.A.C.) and NIH-UTMB Medical Student Research Training Program (M.J.L.).
354
1 Callahan, P.M., Paris, J.M., Cunningham, K.A. and ShinnickGallagher, P., Decrease in amygdaloid GABA-immunoreactive neurons after kindling, Soc. Neurosci. Abstr., 16 (1990) 1106. 2 Gale, K., Catecholamine-independent behavior and neurochemical effects of cocaine in rats. In C.W. Sharp (Ed.), NIDA Research Monograph Series 54: Mechanisms of Tolerance and Dependence, U.S. Govt. Printing Office, Washington, D.C., 1984, pp. 323-332. 3 Gean, P.W., Shinnick-Gallagher, P. and Anderson, A.C., Spontaneous epileptiform activity and alteration of GABA, and NMDA-mediated neurotransmission in amygdala neurons kindled in vivo, Brain Research, 494 (1984) 177-181. 4 Goddard, G.V., McIntyre, D.C. and Leech, C.K., A permanent change in brain function resulting from daily electrical stimulation, Exp. Neurol., 25 (1969) 294-330. 5 Kamphuis, W. and Lopes da Silva, EH., The kindling model of epilepsy: the role of GABAergic inhibition, Neurosci. Res. Commun., 6 (1990) 1-10. 6 Kilbey, M.M. and Ellinwood, E.H., Chronic administration of stimulant drugs: response modification. In E.H. Ellinwood and M.M. Kilbey (Eds.), Cocaine and Other Stimulants, New York, Plenum, 1976, pp. 409-429. 7 Kirkby, R.D. and Kokkinidis, L., Evidence for a relationship between amphetamine sensitization and electrical kindling of the amygdala, Exp. Neurol., 97 (1987) 270-279. 8 Koe, B.K., Molecular geometry of inhibitors of the uptake of catecholamines and serotonin in synaptosomal preparations of rat brain, J. Pharmacol. Exp. Ther., 199 (1976) 549-661. 9 Lesse, H. and Harper, R.K., Frequency-related, bidirectional limbic responses to cocaine: comparisons with amphetamine and lidocaine, Brain Research, 335 (1985) 21-31. l0 McDonald, A.J., Immunohistochemical identification of gamma-aminobutyric acid-containing neurons in the rat basolateral amygdala, Neurosci. Lett., 53 (1985) 203-207. 11 McDonald, A.J. and Pearson, J.C., Coexistence of GABA and peptide immunoreactivity in non-pyramidal neurons of the basolateral amygdala, Neurosci. Lett., 100 (1989) 53-58. 12 Mugnaini, E. and Oertel, W., An atlas of the distribution of GABAergic neurons and terminals in the rat CNS as revealed by GAD immunohistochemistry. In A. Bj6rklund and T. Hfkfelt (Eds.), Handbook of Chemical Neuroanatomy: GABA and Neuropeptides in the CNS, Part I, Elsevier Science Publishers, Amsterdam, 1985, pp. 436-608. 13 Paxinos, G. and Watson, C., The Rat Brain in Stereotaxic Coordinates (2nd edn.), Academic, Orlando, 1986. 14 Post, R.M., Clinical implications of a cocaine-kindling model of
psychosis, Clin. Neuropharmacol., 2 (1977) 25-42. 15 Post, R.M. and Contel, N.R., Human and animal studies of cocaine: implications for development of behavioral pathology. In I. Creese (Ed.), Stimulants: Neurochemical, Behavioral and Clinical Perspective, Raven, New York, 1983, pp. 169-203. 16 Post, R.M., Kennedy, C., Shinohara, M., SquiUace, K., Miyaoka, M., Suda, S., Ingvar, D.H. and Sokoloff, L., Metabolic and behavioral consequences of lidocaine-kindled seizures, Brain Research, 324 (1984) 295-304. 17 Post, R.M., Weiss, S.R.B., Pert, A. and Uhde, T.W., Chronic cocaine administration: sensitization and kindling effects. In S. Fisher, A. Raskin and E.H. Uhlenhuth (Eds.), Cocaine: Clinical and Biobehavioral Aspects, Oxford Univ. Press, New York, 1987, pp. 109-173. 18 Rackham, A. and Wise, R.A., Independence of cocaine sensitization and amygdaloid kindling in the rat, Physiol. Behav., 22 (1979) 631-633. 19 Ribak, C.E., Harris, A.B., Vaughn, J.E. and Roberts, E., Inhibitory GABAergic nerve terminals decrease at sites of focal epilepsy, Science, 205 (1979) 211-214. 20 Riker, D.K., Zito, Jr., R.A. and Roth, R.H., Lidocaine selectively diminishes medullary serotonin metabolism in the rat, Neuropharmacology, 20 (1981) 1233-1236. 21 Ritchie, J.M. and Greene, N.M., Local anesthetics. In A.G. Gilman, L.S. Goodman, T.W. Rail and E Murad (Eds.), The Pharmacological Basis of Therapeutics, MacMillan, New York, 1985, pp. 302-321. 22 Squillace, K.M., Post, R.M. and Pert, A., Effect of lidocaine pretreatment on cocaine-induced behavior in normal and amygdala-lesioned rats, Neuropsychology, 8 (1982) 113-122. 23 Sternberger, L.A., Immunocytochemistry, Wiley, New York, 1979. 24 Stripling, J.S., Cocaine and 'pharmacological kindling; in the rat, Exp. Neurol., 82 (1983) 499-503. 25 Stripling, J.S. and Ellinwood, Jr., E.H., Cocaine: physiological and behavioral effects of acute and chronic administration. In S.J. Mule (Ed.), Cocaine: Chemical, Biological, Clinical, Social, and Treatment Aspects, CRC Press, Cleveland, 1976, pp. 167-185. 26 Thiebot, M.H., Kloszko, J., Chermat, R., Peuch, A.J., Soubrie, P. and Simon, P., Enhancement of cocaine-induced hyperactivity in mice by benzodiazepines: evidence for an interaction of GABAergic processes with catecholaminergic neurons? Eur. J. Pharmacol., 76 (1981) 335-343. 27 Wagman, I.H., de Jong, R.H. and Prince, D.A., Effects of lidocaine on the central nervous system, Anesthesiology, 28 (1967) 155-172.
351
BRES 24606
Cocaine-induced behavioral sensitization is not associated with loss of GABA-immunoreactive neurons in the amygdala Michael A. Lee, Joseph M. Paris and Kathryn A. Cunningham Department of Pharmacology, University of Texas Medical Branch, Galveston, TX 77550 (U.S.A.)
(Accepted 8 January 1991) Key words: Cocaine; y-Aminobutyric acid; Amygdala, Sensitization; Rat
We investigated whether cocaine-induced behavioral sensitization (15 mg/kg, twice daily for 7 days) is associated with changes in y-aminobutyrie acid (GABA) neurons in the lateral-basolateral amygdala of male Sprague-Dawley rats. The number of GABAimmunoreactive neurons in the amygdala did not differ between cocaine- and saline-treated rats. Although some aspects of this behavioral phenomenon parallel the kindling model of epilepsy, limbic alterations in GABA neurons do not appear to be associated with behavioral sensitization to cocaine. Cocaine is well-characterized as a psychostimulant in humans 14 and produces locomotor stimulation and stereotyped behaviors in laboratory animals 6. Repeated exposure to cocaine at low doses results in a progressive enhancement of its behavioral effects 15. Intermittent, subconvulsive doses of cocaine also elicit limbic responses virtually identical to those seen with progressive electrical stimulation of limbic structures ('kindling') which is proposed as a model for epilepsy 4'~4'24'25. Although the relationship between behavioral sensitization and kindling phenomena is unclear, the similar temporal and behavioral patterns seen in cocaine sensitization and electrical kindling 15 as well as the noted ability of cocaine to 'kindle' limbic neurons 25 suggest that neural mechanisms underlying behavioral sensitization and kindling phenomena may overlap. Modifications in y-aminobutyric acid ( G A B A ) inhibitory systems are strongly implicated in the progressive establishment of kindling. Decreases in GABA-immunoreactive (-IR) neurons t'5 and loss of GABAergic inhibitory postsynaptic potentials 3'19 have been observed in limbic areas of kindled rats. The purpose of the present experiment was to determine whether rats behaviorally sensitized to cocaine exhibit altered numbers of G A B A IR neurons in the basolateral/lateral amygdala nuclei similar to that seen in electrical kindling 1. Male Sprague-Dawley rats (SASCO, 160-230 g) were housed in groups of 4 with food and water freely available. The rats were handled one day prior to the start of the experiment. Each rat was injected intraper-
itoneally (i.p.) with either cocaine hydrochloride (15 mg/kg) or physiological saline twice a day (09.00 and 16.00 h) for 7 days. Fifteen minutes following the first and last injection, their behavior was observed and rated for stimulant-induced stereotypic behaviors 6. The animals were assigned a score of 1-9 based upon the following behavioral characteristics: 1 - - asleep, lying down, eyes closed; 2 - - inactive, lying down, eyes open; 3 - - in place activities, normal grooming, chewing cage litter, eating, or drinking; 4 - - normal, alert, active, moving about cage, sniffing, rearing; 5 - - hyperactive with rapid changes in position; 6 - - slow-patterned, repetitive exploration of the cage at normal levels of activity; 7 - - fast-patterned, repetitive exploration of the cage with hyperactivity; 8 - - restricted, remaining in same place in cage with fast, repetitive head and/or forelimb movement (includes licking, chewing, and gnawing stereotypies); and 9 - - dyskinetic-reactive with backing up, jumping, seizures and abnormally-maintained postures. The experimenter was blind to the treatment during injections and observational ratings. Scores were expressed as median ratings and treatment groups were compared with the Wilcoxon rank sum procedure (SAS Institute, Cary, NC). Each rat was anesthetized with sodium pentobarbital (90 mg/kg, i.p.) 18-24 h after the last injection. A solution of Ca2÷-free tyrodes was perfused transcardially for 20 min (200-300 ml) followed by 300-500 ml of 4% paraformaldehyde fixative plus 0.5% glutaraldehyde. The brain was removed and submerged in the glutaral-
Correspondence: K.A. Cunningham, Department of Pharmacology (J-31), University of Texas Medical Branch, Galveston, TX 77550, U.S.A.
352 d e h y d e fixative plus 20% sucrose for one hour and then stored overnight in a solution of sodium azide, bacitracin and sucrose in 0.1 M p h o s p h a t e buffer (PB) at 4 °C. The next day, the brain was rapidly frozen on dry ice and sliced into 40/~m slices in a cryostat at - 1 5 °C; tissue was
collected in 0.1 M PB and 0.1% sodium azide and stored overnight at 4 °C. Standard immunocytochemical p r o c e d u r e s were employed 23. Tissue sections were incubated in n o r m a l goat serum for 20 min, then in p r i m a r y a n t i b o d y (rabbit
A Fig. 1. A: cross-hatched area represents the area of the lateral and basolateral amygdala in which GABA-IR neurons were counted in each brain. Numbers represent distance in mm posterior to bregma ~3. B: low-power (50x) photomicrograph of a coronal section through the basolateral amygdala processed for GABA immunohistochemistry. Area within box is enlarged in C. Bar = 100 ~tm. C: high-power magnification (100x) of the ventral aspect of the basolateral amygdala. Arrowheads indicate examples of GABA-IR cells. Bar = 20/~m.
353 anti-GABA, Incstar, Stillwater, MN) at a concentration of 1:5000 for 24 h at 4 °C. Sections then were incubated in biotinylated secondary antibody (goat anti-rabbit) for 30 rain and then in an avidin-horseradish peroxidase complex (Vector Laboratories, Burlingame, CA) for 60 min with 30 min rinses in PB (3 changes) following each incubation. Control procedures involved substitution of normal serum for the primary antibody and preadsorption of the anti-GABA serum (1:5000) with G A B A (Sigma; 500 ~g/ml). Sections were then reacted with 3,3"-diaminobenzidine (DAB), rinsed, mounted on slides, and air-dried overnight. After being dehydrated and intensified in 0.1% osmium tetroxide, coverslips were applied using Permount. Neurons stained for G A B A were counted in 4 coronal planes through the amygdala: 2.12, 2.56, 3.14, and 3.60 mm posterior from bregma 13 as shown in Fig. 1A. G A B A - I R neurons were counted manually by an experimenter blind to treatment using a 40x objective of a light microscope. The number of cells found in each of the 4 coronal planes were analyzed by analysis of variance (ANOVA; SAS Institute, Cary, NC). On the first injection, rats administered saline exhibited a median score of 3 (range: 2-4) which did not differ from the median score of 4 (range: 3-6) of rats injected with cocaine. Furthermore, the median scores of salinetreated rats on the first and last injection did not differ. However, a significant increase in the median behavioral score for cocaine-treated rats was observed between the first (4; range: 3-6) and last injection (8; range: 6-8; P < 0.05) indicating that behavioral sensitization had developed 6. The G A B A immunohistochemical procedures resulted in excellent staining of G A B A neurons and varicosities in the amygdala nuclei. The numbers and distribution of G A B A - I R correlate very well with previous reports in which antibodies directed against G A B A 1°'11 and glutamate decarboxylase ( G A D ) 12 were used. An example of basolaterai amygdaloid neurons stained for G A B A is shown in Fig. 1C. Preadsorption of the primary antiserum with G A B A or substitution with normal serum eliminated all G A B A - I R . The number of G A B A - I R neurons counted at each coronal plane and the total numbers of cells counted in both cocaine- and salinetreated rats are shown in Fig. 2. There were no significant effects of cocaine treatment on the number of G A B A - I R neurons found in the lateral-basolateral amygdala (F3.18 = 1.15; P > 0.05). The present results suggest that cocaine-induced behavioral sensitization is not associated with a loss of G A B A - I R cells in the lateral-basolateral amygdala as is seen in electrically kindled rats ~. There is evidence, however, to suggest that cocaine interferes with G A B A metabolism 2. Benzodiazepines, which enhance G A B A
200
Tar~mm
-
r--"1 S a l i n e Cocaine
o
== z >=
1~o
~
100-
E _E
50-
O-
-
-
2.12 2.56 3.14 3.60 Posterior Distance from Bregma (ram)
Fig. 2. The number of GABA-IR neurons (mean + S.E.M.) in each of the 4 coronal planes in saline- (n = 4) and cocaine- (15 mg/kg, b.i.d., i.p.; n = 4) treated rats. Inset depicts the means (_+ S.E.M.) for the total number of GABA-IR neurons in both groups of rats.
neurotransmission, have been reported to block the sensitizing effect of cocaine in rats 17 yet enhance its locomotor stimulating properties in mice 26. Few attempts to assess the role of G A B A function in cocaine sensitization or its pharmacological kindling properties have been made. Cocaine/s a potent local anesthetic 21, but its stimulant properties are broadly attributed to its potentiation of catecholamine action by inhibition of the reuptake of dopamine and norepinephrine 8. The fact that repeated injections of amphetamine, which lacks local anesthetic actions, result in sensitization but fail to induce limbic kindling 9 supports a dissociation between stimulant-induced behavioral sensitization and limbic electrical kindling TM, although there is not a consensus 7. The importance of local anesthetic actions in pharmacologic kindling is further supported by the finding that repeated administration of lidocaine which has minimal monoamine stimulant effects2°'27 induces seizures, which differ from cocaine seizures in lethality 16'22. Thus, it is likely that cocaine-induced kindling is related to the local anesthetic actions of cocaine while sensitization is dependent upon its monoaminergic stimulant properties. Moreover, cocaine-induced behavioral sensitization and electrical kindling may not share a similar GABA-mediated mechanism (present results). Notwithstanding, we cannot rule out the possibility that cocaine might induce more subtle alterations in G A B A sytems, perhaps at the receptor or metabolic levels, which could not be detected in the present experiment.
The authors would like to acknowledge Patrick M. Callahan for his advice on quantification of GABA immunohistochemistry. This study was supported by DA05708 (K.A.C.), DA05381 (J.M.P.), the National Alliance for Research on Schizophrenia and Affective Disorders (K.A.C.) and NIH-UTMB Medical Student Research Training Program (M.J.L.).
354
1 Callahan, P.M., Paris, J.M., Cunningham, K.A. and ShinnickGallagher, P., Decrease in amygdaloid GABA-immunoreactive neurons after kindling, Soc. Neurosci. Abstr., 16 (1990) 1106. 2 Gale, K., Catecholamine-independent behavior and neurochemical effects of cocaine in rats. In C.W. Sharp (Ed.), NIDA Research Monograph Series 54: Mechanisms of Tolerance and Dependence, U.S. Govt. Printing Office, Washington, D.C., 1984, pp. 323-332. 3 Gean, P.W., Shinnick-Gallagher, P. and Anderson, A.C., Spontaneous epileptiform activity and alteration of GABA, and NMDA-mediated neurotransmission in amygdala neurons kindled in vivo, Brain Research, 494 (1984) 177-181. 4 Goddard, G.V., McIntyre, D.C. and Leech, C.K., A permanent change in brain function resulting from daily electrical stimulation, Exp. Neurol., 25 (1969) 294-330. 5 Kamphuis, W. and Lopes da Silva, EH., The kindling model of epilepsy: the role of GABAergic inhibition, Neurosci. Res. Commun., 6 (1990) 1-10. 6 Kilbey, M.M. and Ellinwood, E.H., Chronic administration of stimulant drugs: response modification. In E.H. Ellinwood and M.M. Kilbey (Eds.), Cocaine and Other Stimulants, New York, Plenum, 1976, pp. 409-429. 7 Kirkby, R.D. and Kokkinidis, L., Evidence for a relationship between amphetamine sensitization and electrical kindling of the amygdala, Exp. Neurol., 97 (1987) 270-279. 8 Koe, B.K., Molecular geometry of inhibitors of the uptake of catecholamines and serotonin in synaptosomal preparations of rat brain, J. Pharmacol. Exp. Ther., 199 (1976) 549-661. 9 Lesse, H. and Harper, R.K., Frequency-related, bidirectional limbic responses to cocaine: comparisons with amphetamine and lidocaine, Brain Research, 335 (1985) 21-31. l0 McDonald, A.J., Immunohistochemical identification of gamma-aminobutyric acid-containing neurons in the rat basolateral amygdala, Neurosci. Lett., 53 (1985) 203-207. 11 McDonald, A.J. and Pearson, J.C., Coexistence of GABA and peptide immunoreactivity in non-pyramidal neurons of the basolateral amygdala, Neurosci. Lett., 100 (1989) 53-58. 12 Mugnaini, E. and Oertel, W., An atlas of the distribution of GABAergic neurons and terminals in the rat CNS as revealed by GAD immunohistochemistry. In A. Bj6rklund and T. Hfkfelt (Eds.), Handbook of Chemical Neuroanatomy: GABA and Neuropeptides in the CNS, Part I, Elsevier Science Publishers, Amsterdam, 1985, pp. 436-608. 13 Paxinos, G. and Watson, C., The Rat Brain in Stereotaxic Coordinates (2nd edn.), Academic, Orlando, 1986. 14 Post, R.M., Clinical implications of a cocaine-kindling model of
psychosis, Clin. Neuropharmacol., 2 (1977) 25-42. 15 Post, R.M. and Contel, N.R., Human and animal studies of cocaine: implications for development of behavioral pathology. In I. Creese (Ed.), Stimulants: Neurochemical, Behavioral and Clinical Perspective, Raven, New York, 1983, pp. 169-203. 16 Post, R.M., Kennedy, C., Shinohara, M., SquiUace, K., Miyaoka, M., Suda, S., Ingvar, D.H. and Sokoloff, L., Metabolic and behavioral consequences of lidocaine-kindled seizures, Brain Research, 324 (1984) 295-304. 17 Post, R.M., Weiss, S.R.B., Pert, A. and Uhde, T.W., Chronic cocaine administration: sensitization and kindling effects. In S. Fisher, A. Raskin and E.H. Uhlenhuth (Eds.), Cocaine: Clinical and Biobehavioral Aspects, Oxford Univ. Press, New York, 1987, pp. 109-173. 18 Rackham, A. and Wise, R.A., Independence of cocaine sensitization and amygdaloid kindling in the rat, Physiol. Behav., 22 (1979) 631-633. 19 Ribak, C.E., Harris, A.B., Vaughn, J.E. and Roberts, E., Inhibitory GABAergic nerve terminals decrease at sites of focal epilepsy, Science, 205 (1979) 211-214. 20 Riker, D.K., Zito, Jr., R.A. and Roth, R.H., Lidocaine selectively diminishes medullary serotonin metabolism in the rat, Neuropharmacology, 20 (1981) 1233-1236. 21 Ritchie, J.M. and Greene, N.M., Local anesthetics. In A.G. Gilman, L.S. Goodman, T.W. Rail and E Murad (Eds.), The Pharmacological Basis of Therapeutics, MacMillan, New York, 1985, pp. 302-321. 22 Squillace, K.M., Post, R.M. and Pert, A., Effect of lidocaine pretreatment on cocaine-induced behavior in normal and amygdala-lesioned rats, Neuropsychology, 8 (1982) 113-122. 23 Sternberger, L.A., Immunocytochemistry, Wiley, New York, 1979. 24 Stripling, J.S., Cocaine and 'pharmacological kindling; in the rat, Exp. Neurol., 82 (1983) 499-503. 25 Stripling, J.S. and Ellinwood, Jr., E.H., Cocaine: physiological and behavioral effects of acute and chronic administration. In S.J. Mule (Ed.), Cocaine: Chemical, Biological, Clinical, Social, and Treatment Aspects, CRC Press, Cleveland, 1976, pp. 167-185. 26 Thiebot, M.H., Kloszko, J., Chermat, R., Peuch, A.J., Soubrie, P. and Simon, P., Enhancement of cocaine-induced hyperactivity in mice by benzodiazepines: evidence for an interaction of GABAergic processes with catecholaminergic neurons? Eur. J. Pharmacol., 76 (1981) 335-343. 27 Wagman, I.H., de Jong, R.H. and Prince, D.A., Effects of lidocaine on the central nervous system, Anesthesiology, 28 (1967) 155-172.
