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Fos oncoprotein expression in the rat forebrain following muscimol-induced absence seizures
ELSEVIER
Neuroscience Letters 210 (1996) 169-172
NIUROSCIEHCt IHTflIS
Fos oncoprotein expression in the rat forebrain following muscimol-induced absence seizures X i a Z h a n g a,b,c, G i l d a s L e G a l L a S a l l e b, V a l e r i e R i d o u x b, P e t e r H. Y u c, G o n g J u a,* aDepartment of Neurobiology, Institute of Neurosciences, 17 Chang Le Xi Road, Xian, 710032, People's Republic of China blnstitut Alfred Fessard, Central National de la Recherche Scientifique (CNRS), 91198 Gif sur Yvette, France CNeuropsychiatry Research Unit, Department of Psychiatry, University of Saskatchewan, S7N 5E4, Canada
Received 14 October 1995; revised version received25 April 1996; accepted26 April 1996
Abstract
Fos oncoprotein expression is a marker of neuronal activation following seizures. Here, using this method we examined the anatomical locations of muscimol-induced absence seizures in the rat forebrain. Six hours after a systemic injection of muscimol a massive Fos immunoreactivity appeared in the olfactory system, retrosplenial cortex and paraventricular thalamic nucleus, whereas other cortical areas contained low level of Fos expression. These results provide the first functional morphological evidence suggesting that these forebrain structures with Fos expression may play an important role in the pathophysiology of muscimol-induced absence seizures. Keywords: Absence seizure; Muscimol; c-fos oncogene; Fos oncoprotein; Rat; Forebrain; Immunohistochemistry
Absence seizures are characterized by the abrupt onset and cessation of bilaterally synchronous, 3 c/s spike-andwave discharges emerging from a normal cortical electroencephalograph (EEG) [4,6,7,14-16]. Among the various animal models of absence seizures [4], the muscimol model is so special that after 2 mg/kg muscimol injection spikes appear and intermingle with waves which are the only EEG sign of absence seizures following 1 mg/kg muscimol injection [14]. In 1969, Scotti de Carolis et al. [14] provided EEG data showing that muscimol-induced absence seizures might develop in the posterior sensorimotor-optic cortex. Because the EEG method is useful specifically to display the pathophysiological changes in relatively large cortical areas, the exact anatomical location of muscimol-induced absence seizures in the rat brain remains to be elucidated with a more accurate method. Recently, Fos oncoprotein expression has been extensively used as a marker for functionally activated neurons following a variety of brain insults, including various types of seizures [3,7-10,13,17]. The general utility, sensitivity, and resolution power of Fos expression as a marker for functionally activated cells have been extensively discussed elsewhere [9,10,13,17] and need not be * Corresponding author. Fa~: +86 29 3246270.
reiterated here. Using this method this work aimed to study the exact forebrain localization of wave and spikeand-wave discharges during muscimol-induced absence seizures in the rat. Adult male Sprague-Dawley rats were given a single i.p. injection of vehicle or freshly prepared muscimol at the dose of 1 or 2 mg/kg (four rats for each group). Since our preliminary experiment showed that Fos expression peaked at 6 h after muscimol injection, all the animals were perfused, at 6 h after muscimol, first with saline and then with 700 ml of 4% paraformaldehyde for 2 h. The brains were immersed in 15% sucrose overnight. Two adjacent series of coronal sections (50/~m) through the forebrain were cut on a freezing microtome. All the sections were processed for Fos immunohistochemistry as described before [18]. Briefly, the sections were first incubated in sheep antiserum against 55 kDa Fos oncoproteins (1:3000, CRB) for 3 days at 4°C, and then they were sequentially incubated in biotinylated anti-sheep IgG (1:200, Vector) and streptavidin-biotinylated HRP (1:100, Sigma) for 2 h each. The peroxidase activity was revealed using DAB. Control sections were incubated without Fos antiserum or with a serum that had been preabsorbed with Fos peptide in a concentration of 10 -9 M (CRB). One series of sections were counterstained with cresyl violet.
0304-3940/96/$12.00 © 1996 Elsevier Science IrelandLtd. All rights reserved PII: S0304-3940(96) 12697-3
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x. Zhang et al. / Neuroscience Letters 210 (1996) 169-172
The designation and terminology used in this work were adopted from an atlas of the rat brain [12]. Consistent with Scotti de Carolis et al.'s observation [14], after 1 mg/kg m u s c i m o l injection the rats rapidly showed a succession of behavioral arrest and motor mani-
festations consisting of slight ataxia, c h e w i n g and diffuse tremors within 2 h post-injection. A d m i n i s t r a t i o n of 2 m g / kg m u s c i m o l produced a longer duration (4--6 h) of the drug effect. There was no cellular i m m u n o r e a c t i v i t y in vehicle-
Fig. 1. Muscimol-induced Fos expression in the rat brain. In comparison with control rat which exhibited no specific Fos immunoreactivity in the piriform cortex (A) and other brain structures, 1 mg/kg muscimol injection (B-E) induced Fos expression only in the main olfactory bulb (B), anterior olfactory nucleus (C) and piriform cortex (D), whereas other structures, including the retrosplenial cortex (E), displayed no Fos immunolabeling. Increasing the muscimol dose to 2 mg/kg (F-H) resulted in further induction of Fos oncoprotein in other regions, i.e. the retrosplenial and occipital cortices (F), thalamus (G) and hippocampus (H). AOD (L, M, V), dorsal (lateral, medial, ventral) part of the anterior olfactory nucleus; CAI-3, CAI-3 fields; EPI, external plexiform layer of the main olfactory bulb; IGr, internal granular layer of the main olfactory bulb; Mi, mitral cell layer of the main olfactory bulb; Oc, occipital nucleus; Pir, piriform cortex; RSA, retrosplenial agranular cortex; RSG, retrosplenial granular cortex. Bar scales: 15 ,um in (A,D,H), l0/.tm in (B), 24/.*m in (C,E,F), and 18/am in (G).
x. Zhang et al./Neuroscience Letters 210 (1996) 169-172
injected rats (Fig. I A). After 1 mg/kg muscimol injection Fos expression was found only in the following olfactory structures. Cell nuclei in the mitral cell external plexiform layers of the main olfactory bulb showed intensive Fos immunostaining (Fig. IB), whereas the anterior olfactory nucleus (Fig. I C) and piriform cortex (Fig. 1D) displayed low to moderate density of Fos-positive cells. No Fos immunoreactivity could be identified in other brain regions including the retrosplenial cortex (Fig. IE). Similar patterns of Fos expression in these three olfactory regions also appeared in rats receiving 2mg/kg muscimol. In addition, 2 mg/kg muscimol evoked Fos expression in other brain regions as well. A massive Fos expression occurred in the retrosplenial cortex (Fig. IF), and a low level of Fos induction was present in layer V of the parietal, temporal, occipital (Fig. IF) and perirhinal cortices. The paraventri~cular thalamic nucleus contained moderate Fos expression (Fig. IG). A few Fos-positive cells were found in the hippocampal CAI and CA3 fields (Fig. I H) as well as in the paraventricular hypothalamic nucleus and medial preoptic area (results not shown). Since it has recently been shown that stress can induce Fos expression in a varic~'tyof brain regions [2], the previously reported low level of Fos expression in several brain regions induced by vehicle injection [3] may be evoked by stress effect. In this study, however, we observed no specific immunostaining throughout the brain following a systemic vehicle injection. This suggests that Fos expression demonstrated in this study was not evoked by the stress effect of the animal treatment procedure. Muscimol injection has been shown to produce hypotension in the rats [I], and so Fos expression in the hypothalamus may be stimulated by hypotensive effects of muscimol because the hypothalamus is well known to be tightly associated with the blood pressure regulation [11]. Together with our previous observation that absence seizures are capable of inducing Fos expression [18], all the evidence suggests that Fos expression in the rat forebrain except the hypothalamus is very probably stimulated by muscimol-induced absence seizures. Using an EEG recording method, Scotti de Carolis et al. [14] found, in the rat, that I mg/kg muscimol induced waves in all cortical regions, whereas 2 mg/kg muscimol produced spikes prominent in the posterior sensorimotoroptic cortex. It is well known that spike and wave represent, respectively, excitation and inhibition in certain neuronal networks [7]. Accordingly, when EEG displays only waves the cortical neurons may be in a state of inhibition, whereas when spikes appear and intermingle with the waves the cortical neurons may be activated. The retrosplenial cortex recognized in this study is actually in the territory of posterior sensorimotor-optic cortex referred to by Scotti de Carolis et al. [14]. Therefore, our results of cortical Fos expression may be explained as follows: after 2 mg/kg muscimol injection the cortical neurons, espe-
171
cially those in the retrosplenial cortex, were activated and subsequently expressed Fos. Our observation that muscimol constantly evoked Fos expression in the olfactory bulb, anterior olfactory nucleus and piriform cortex strongly suggests that neurons in these olfactory structures may be activated after muscimol injection. This suggestion is also supported by other evidence: (1) electric stimulation of the lateral olfactory tract, which projects from the mitral and plexiform neurons in the main olfactory bulb to layer I! of the piriform cortex, induced typical absence seizures and none or all spike-and-wave discharges in these three olfactory regions in the rat [5]; (2) after ~-hydroxybutyrate (GHB)induced generalized absence seizures we found a massive Fos expression in the main olfactory bulb and piriform cortex [18]. After 2 mg/kg muscimol injection we observed a moderate Fos expression in the paraventricular thalamus nucleus. This is compatible with our previous finding that GHB-induced generalized absence seizures provoked a dramatic Fos expression in the same nucleus [18]. The significance of the paraventricular thalamic nucleus in the genesis of absence seizures has been well discussed in our previous study [18]. However, different patterns of Fos expression between these two animal models occurred in other forebrain structures, such as the intralaminar thalamic nuclei where Fos expression was intensive in the GHB model [18] but absent in the muscimol model, or the retrosplenial cortex where Fos expression was high after muscimol injection but absent following GHB administration [18]. These differences may be caused by different pathophysiological mechanisms of muscimoland GHB-induced absence seizures. It has been generally considered that the hippocampus plays little part in absence seizures but is mainly involved in grand mal seizures and complex partial seizures [7]. Scotti de Carolis et al. also observed similar results [14]. In this study, only a few Fos-immunoreactive cells were detected in CA3 and CA1 fields following muscimol administration. These results imply that the hippocampus makes little contributions to muscimol-induced absence seizure development. The original research in this study was supported by a grant from the National Natural Science Foundation for the Youth of China (No. 39100043, to X. Zhang). In the later stages of this research, Dr. X. Zhang was a postdoctoral fellow first in Institut Alfred Fessard, CNRS, France, and then in Neuropsychiatry Research Unit, University of Saskatchewan, Canada. [I] Baum, T. and Becker, F.T., Hypotensiveand postural effects of the 7-aminobutyric acid agonist muscimol and of clonidine, J. Cardiovasc. Pharmacol.,4 (1982) 165-169. [2] Cullinan, W.E., Herman, J.P., Battaglia, D.F., Akil, H. and Watson, S.J., Pattern and time course of immediate early gene ex-
172
[3]
[4] [5]
[6]
[7]
[8]
[9] [10]
X. Zhang et al. / Neuroscience Letters 210 (1996) 169-172
pression in rat forebrain following acute stress, Neuroscience, 64 (1995) 477-505. Dragunow, M. and Faull, R., The use of c-fos as a metabolic marker in neuronal pathway tracing, J. Neurosci. Methods, 29 (1989) 261-265. Fisher, R.S., Animal models of the epilepsies, Brain Res. Rev., 14 (1989) 245-278. Freeman, W.J., Petit mal seizure spikes in olfactory bulb and cortex caused by runaway inhibition after exhaustion of excitation, Brain Res. Rev., I1 (1986) 259-284. Gloor, P., Neurophysiological mechanisms of generalized spikeand-wave discharge and its implication for understanding absence seizures. In M.S. Myslobodsky and A.F. Mirsky (Eds.), Elements of Petit Mal Epilepsy, Peter Lang, New York, 1988, pp. 159-209. Gloor, P., Avoli, M. and Kostopoulos, G., Thalamocortical relationships in generalized epilepsy with bilaterally synchronous spike-and-wave discharge. In M. Avoli., P. Gloor, G. Kostopolous and R. Naquet (Eds.), Generalized Epilepsy: Neurobiological Approaches, Birkhauser, Boston, 1990, pp. 190-212. Le Gal La Salle, G., Long-lasting and sequential increase of c-fos oncoprotein expression in kainic acid-induced status epilepticus, Neurosci. Lett., 88 (1988) 127-130. Morgan, J.l. and Curran, T., Proto-oncogene transcription factors and epilepsy, TIPS, 12 (1991) 343-349. Morgan, J.l. and Curran, T., Stimulus-transcription coupling in the nervous system: involvement of the inducible proto-oncogenes fos and jun, Annu. Rev. Neurosci., 14 (1991) 421-451.
[11] Palkovits, M., Neuronal circuits in central baroreceptor mechanism, Prog. Hypertension, 1 (1988) 387-409. [12] Paxinos, G. and Watson ,C., The Rat Brain in Stereotaxic Coordinates, Academic Press, Sydney, 1986. [13] Sagar, S.M., Sharp, F.R. and Curran, T., Expression of c-fos protein in brain: metabolic mapping at the cellular level, Science, 240 (1988) 1328-1331. [14] Scotti de Carolis, A., Lipparini, F. and Longo, V.G., Neuropharmacological investigations on muscimol, a psychotropic drug extracted from Amanita muscaria, Psychopharmacology, 15 (1969) 186-195. [15] Snead, O.C., Gamma-hydroxybutyric acid, gamma-aminobutyric acid, and petit mal epilepsy. In A. Fariello (Ed.), Neurotransmitters, Seizures and Epilepsy II, Raven Press, New York, 1984, pp. 37-46. [16] Snead, O.C., ~,-Hydroxybutyrate model of generalized absence seizures: further characterization and comparison with other absence models, Epilepsia, 29 ( 1988) 361-368. [17] Zhang, X. and Ju, G., Induction and visualization of c-fos oncogene: a new method reflecting the functional neural pathways, Sheng Li Ko Hsueh Chin. Chan., 22 (1991) 299-303. [18] Zhang, X., Ju, G. and Le Gal La Salle, G., Fos expression in GHB-induced generalized absence epilepsy in the thalamus of the rat, NeuroReport, 2 (1991) 469-472.
Neuroscience Letters 210 (1996) 169-172
NIUROSCIEHCt IHTflIS
Fos oncoprotein expression in the rat forebrain following muscimol-induced absence seizures X i a Z h a n g a,b,c, G i l d a s L e G a l L a S a l l e b, V a l e r i e R i d o u x b, P e t e r H. Y u c, G o n g J u a,* aDepartment of Neurobiology, Institute of Neurosciences, 17 Chang Le Xi Road, Xian, 710032, People's Republic of China blnstitut Alfred Fessard, Central National de la Recherche Scientifique (CNRS), 91198 Gif sur Yvette, France CNeuropsychiatry Research Unit, Department of Psychiatry, University of Saskatchewan, S7N 5E4, Canada
Received 14 October 1995; revised version received25 April 1996; accepted26 April 1996
Abstract
Fos oncoprotein expression is a marker of neuronal activation following seizures. Here, using this method we examined the anatomical locations of muscimol-induced absence seizures in the rat forebrain. Six hours after a systemic injection of muscimol a massive Fos immunoreactivity appeared in the olfactory system, retrosplenial cortex and paraventricular thalamic nucleus, whereas other cortical areas contained low level of Fos expression. These results provide the first functional morphological evidence suggesting that these forebrain structures with Fos expression may play an important role in the pathophysiology of muscimol-induced absence seizures. Keywords: Absence seizure; Muscimol; c-fos oncogene; Fos oncoprotein; Rat; Forebrain; Immunohistochemistry
Absence seizures are characterized by the abrupt onset and cessation of bilaterally synchronous, 3 c/s spike-andwave discharges emerging from a normal cortical electroencephalograph (EEG) [4,6,7,14-16]. Among the various animal models of absence seizures [4], the muscimol model is so special that after 2 mg/kg muscimol injection spikes appear and intermingle with waves which are the only EEG sign of absence seizures following 1 mg/kg muscimol injection [14]. In 1969, Scotti de Carolis et al. [14] provided EEG data showing that muscimol-induced absence seizures might develop in the posterior sensorimotor-optic cortex. Because the EEG method is useful specifically to display the pathophysiological changes in relatively large cortical areas, the exact anatomical location of muscimol-induced absence seizures in the rat brain remains to be elucidated with a more accurate method. Recently, Fos oncoprotein expression has been extensively used as a marker for functionally activated neurons following a variety of brain insults, including various types of seizures [3,7-10,13,17]. The general utility, sensitivity, and resolution power of Fos expression as a marker for functionally activated cells have been extensively discussed elsewhere [9,10,13,17] and need not be * Corresponding author. Fa~: +86 29 3246270.
reiterated here. Using this method this work aimed to study the exact forebrain localization of wave and spikeand-wave discharges during muscimol-induced absence seizures in the rat. Adult male Sprague-Dawley rats were given a single i.p. injection of vehicle or freshly prepared muscimol at the dose of 1 or 2 mg/kg (four rats for each group). Since our preliminary experiment showed that Fos expression peaked at 6 h after muscimol injection, all the animals were perfused, at 6 h after muscimol, first with saline and then with 700 ml of 4% paraformaldehyde for 2 h. The brains were immersed in 15% sucrose overnight. Two adjacent series of coronal sections (50/~m) through the forebrain were cut on a freezing microtome. All the sections were processed for Fos immunohistochemistry as described before [18]. Briefly, the sections were first incubated in sheep antiserum against 55 kDa Fos oncoproteins (1:3000, CRB) for 3 days at 4°C, and then they were sequentially incubated in biotinylated anti-sheep IgG (1:200, Vector) and streptavidin-biotinylated HRP (1:100, Sigma) for 2 h each. The peroxidase activity was revealed using DAB. Control sections were incubated without Fos antiserum or with a serum that had been preabsorbed with Fos peptide in a concentration of 10 -9 M (CRB). One series of sections were counterstained with cresyl violet.
0304-3940/96/$12.00 © 1996 Elsevier Science IrelandLtd. All rights reserved PII: S0304-3940(96) 12697-3
170
x. Zhang et al. / Neuroscience Letters 210 (1996) 169-172
The designation and terminology used in this work were adopted from an atlas of the rat brain [12]. Consistent with Scotti de Carolis et al.'s observation [14], after 1 mg/kg m u s c i m o l injection the rats rapidly showed a succession of behavioral arrest and motor mani-
festations consisting of slight ataxia, c h e w i n g and diffuse tremors within 2 h post-injection. A d m i n i s t r a t i o n of 2 m g / kg m u s c i m o l produced a longer duration (4--6 h) of the drug effect. There was no cellular i m m u n o r e a c t i v i t y in vehicle-
Fig. 1. Muscimol-induced Fos expression in the rat brain. In comparison with control rat which exhibited no specific Fos immunoreactivity in the piriform cortex (A) and other brain structures, 1 mg/kg muscimol injection (B-E) induced Fos expression only in the main olfactory bulb (B), anterior olfactory nucleus (C) and piriform cortex (D), whereas other structures, including the retrosplenial cortex (E), displayed no Fos immunolabeling. Increasing the muscimol dose to 2 mg/kg (F-H) resulted in further induction of Fos oncoprotein in other regions, i.e. the retrosplenial and occipital cortices (F), thalamus (G) and hippocampus (H). AOD (L, M, V), dorsal (lateral, medial, ventral) part of the anterior olfactory nucleus; CAI-3, CAI-3 fields; EPI, external plexiform layer of the main olfactory bulb; IGr, internal granular layer of the main olfactory bulb; Mi, mitral cell layer of the main olfactory bulb; Oc, occipital nucleus; Pir, piriform cortex; RSA, retrosplenial agranular cortex; RSG, retrosplenial granular cortex. Bar scales: 15 ,um in (A,D,H), l0/.tm in (B), 24/.*m in (C,E,F), and 18/am in (G).
x. Zhang et al./Neuroscience Letters 210 (1996) 169-172
injected rats (Fig. I A). After 1 mg/kg muscimol injection Fos expression was found only in the following olfactory structures. Cell nuclei in the mitral cell external plexiform layers of the main olfactory bulb showed intensive Fos immunostaining (Fig. IB), whereas the anterior olfactory nucleus (Fig. I C) and piriform cortex (Fig. 1D) displayed low to moderate density of Fos-positive cells. No Fos immunoreactivity could be identified in other brain regions including the retrosplenial cortex (Fig. IE). Similar patterns of Fos expression in these three olfactory regions also appeared in rats receiving 2mg/kg muscimol. In addition, 2 mg/kg muscimol evoked Fos expression in other brain regions as well. A massive Fos expression occurred in the retrosplenial cortex (Fig. IF), and a low level of Fos induction was present in layer V of the parietal, temporal, occipital (Fig. IF) and perirhinal cortices. The paraventri~cular thalamic nucleus contained moderate Fos expression (Fig. IG). A few Fos-positive cells were found in the hippocampal CAI and CA3 fields (Fig. I H) as well as in the paraventricular hypothalamic nucleus and medial preoptic area (results not shown). Since it has recently been shown that stress can induce Fos expression in a varic~'tyof brain regions [2], the previously reported low level of Fos expression in several brain regions induced by vehicle injection [3] may be evoked by stress effect. In this study, however, we observed no specific immunostaining throughout the brain following a systemic vehicle injection. This suggests that Fos expression demonstrated in this study was not evoked by the stress effect of the animal treatment procedure. Muscimol injection has been shown to produce hypotension in the rats [I], and so Fos expression in the hypothalamus may be stimulated by hypotensive effects of muscimol because the hypothalamus is well known to be tightly associated with the blood pressure regulation [11]. Together with our previous observation that absence seizures are capable of inducing Fos expression [18], all the evidence suggests that Fos expression in the rat forebrain except the hypothalamus is very probably stimulated by muscimol-induced absence seizures. Using an EEG recording method, Scotti de Carolis et al. [14] found, in the rat, that I mg/kg muscimol induced waves in all cortical regions, whereas 2 mg/kg muscimol produced spikes prominent in the posterior sensorimotoroptic cortex. It is well known that spike and wave represent, respectively, excitation and inhibition in certain neuronal networks [7]. Accordingly, when EEG displays only waves the cortical neurons may be in a state of inhibition, whereas when spikes appear and intermingle with the waves the cortical neurons may be activated. The retrosplenial cortex recognized in this study is actually in the territory of posterior sensorimotor-optic cortex referred to by Scotti de Carolis et al. [14]. Therefore, our results of cortical Fos expression may be explained as follows: after 2 mg/kg muscimol injection the cortical neurons, espe-
171
cially those in the retrosplenial cortex, were activated and subsequently expressed Fos. Our observation that muscimol constantly evoked Fos expression in the olfactory bulb, anterior olfactory nucleus and piriform cortex strongly suggests that neurons in these olfactory structures may be activated after muscimol injection. This suggestion is also supported by other evidence: (1) electric stimulation of the lateral olfactory tract, which projects from the mitral and plexiform neurons in the main olfactory bulb to layer I! of the piriform cortex, induced typical absence seizures and none or all spike-and-wave discharges in these three olfactory regions in the rat [5]; (2) after ~-hydroxybutyrate (GHB)induced generalized absence seizures we found a massive Fos expression in the main olfactory bulb and piriform cortex [18]. After 2 mg/kg muscimol injection we observed a moderate Fos expression in the paraventricular thalamus nucleus. This is compatible with our previous finding that GHB-induced generalized absence seizures provoked a dramatic Fos expression in the same nucleus [18]. The significance of the paraventricular thalamic nucleus in the genesis of absence seizures has been well discussed in our previous study [18]. However, different patterns of Fos expression between these two animal models occurred in other forebrain structures, such as the intralaminar thalamic nuclei where Fos expression was intensive in the GHB model [18] but absent in the muscimol model, or the retrosplenial cortex where Fos expression was high after muscimol injection but absent following GHB administration [18]. These differences may be caused by different pathophysiological mechanisms of muscimoland GHB-induced absence seizures. It has been generally considered that the hippocampus plays little part in absence seizures but is mainly involved in grand mal seizures and complex partial seizures [7]. Scotti de Carolis et al. also observed similar results [14]. In this study, only a few Fos-immunoreactive cells were detected in CA3 and CA1 fields following muscimol administration. These results imply that the hippocampus makes little contributions to muscimol-induced absence seizure development. The original research in this study was supported by a grant from the National Natural Science Foundation for the Youth of China (No. 39100043, to X. Zhang). In the later stages of this research, Dr. X. Zhang was a postdoctoral fellow first in Institut Alfred Fessard, CNRS, France, and then in Neuropsychiatry Research Unit, University of Saskatchewan, Canada. [I] Baum, T. and Becker, F.T., Hypotensiveand postural effects of the 7-aminobutyric acid agonist muscimol and of clonidine, J. Cardiovasc. Pharmacol.,4 (1982) 165-169. [2] Cullinan, W.E., Herman, J.P., Battaglia, D.F., Akil, H. and Watson, S.J., Pattern and time course of immediate early gene ex-
172
[3]
[4] [5]
[6]
[7]
[8]
[9] [10]
X. Zhang et al. / Neuroscience Letters 210 (1996) 169-172
pression in rat forebrain following acute stress, Neuroscience, 64 (1995) 477-505. Dragunow, M. and Faull, R., The use of c-fos as a metabolic marker in neuronal pathway tracing, J. Neurosci. Methods, 29 (1989) 261-265. Fisher, R.S., Animal models of the epilepsies, Brain Res. Rev., 14 (1989) 245-278. Freeman, W.J., Petit mal seizure spikes in olfactory bulb and cortex caused by runaway inhibition after exhaustion of excitation, Brain Res. Rev., I1 (1986) 259-284. Gloor, P., Neurophysiological mechanisms of generalized spikeand-wave discharge and its implication for understanding absence seizures. In M.S. Myslobodsky and A.F. Mirsky (Eds.), Elements of Petit Mal Epilepsy, Peter Lang, New York, 1988, pp. 159-209. Gloor, P., Avoli, M. and Kostopoulos, G., Thalamocortical relationships in generalized epilepsy with bilaterally synchronous spike-and-wave discharge. In M. Avoli., P. Gloor, G. Kostopolous and R. Naquet (Eds.), Generalized Epilepsy: Neurobiological Approaches, Birkhauser, Boston, 1990, pp. 190-212. Le Gal La Salle, G., Long-lasting and sequential increase of c-fos oncoprotein expression in kainic acid-induced status epilepticus, Neurosci. Lett., 88 (1988) 127-130. Morgan, J.l. and Curran, T., Proto-oncogene transcription factors and epilepsy, TIPS, 12 (1991) 343-349. Morgan, J.l. and Curran, T., Stimulus-transcription coupling in the nervous system: involvement of the inducible proto-oncogenes fos and jun, Annu. Rev. Neurosci., 14 (1991) 421-451.
[11] Palkovits, M., Neuronal circuits in central baroreceptor mechanism, Prog. Hypertension, 1 (1988) 387-409. [12] Paxinos, G. and Watson ,C., The Rat Brain in Stereotaxic Coordinates, Academic Press, Sydney, 1986. [13] Sagar, S.M., Sharp, F.R. and Curran, T., Expression of c-fos protein in brain: metabolic mapping at the cellular level, Science, 240 (1988) 1328-1331. [14] Scotti de Carolis, A., Lipparini, F. and Longo, V.G., Neuropharmacological investigations on muscimol, a psychotropic drug extracted from Amanita muscaria, Psychopharmacology, 15 (1969) 186-195. [15] Snead, O.C., Gamma-hydroxybutyric acid, gamma-aminobutyric acid, and petit mal epilepsy. In A. Fariello (Ed.), Neurotransmitters, Seizures and Epilepsy II, Raven Press, New York, 1984, pp. 37-46. [16] Snead, O.C., ~,-Hydroxybutyrate model of generalized absence seizures: further characterization and comparison with other absence models, Epilepsia, 29 ( 1988) 361-368. [17] Zhang, X. and Ju, G., Induction and visualization of c-fos oncogene: a new method reflecting the functional neural pathways, Sheng Li Ko Hsueh Chin. Chan., 22 (1991) 299-303. [18] Zhang, X., Ju, G. and Le Gal La Salle, G., Fos expression in GHB-induced generalized absence epilepsy in the thalamus of the rat, NeuroReport, 2 (1991) 469-472.