99
Neuroscience Letters, 123 (1991) 99-101
© 1991 ElsevierScientificPublishers Ireland Ltd. 0304-3940/91/$ 03.50 ADONIS 0304394091000978 NSL 07540
Glucocorticoids promote localized activity of rat hippocampal CA1 pyramidal neurons in brain slices N . D o i 1~, S. M i y a h a r a 2 a n d N. H o r i 2 t Department of Biology, Faculty of Science and 2Department of Pharmacology, Faculty of Dentistry, Kyushu University, Fukuoka (Japan)
(Received 21 March 1990; Revisedversion received2 November 1990; Accepted 7 November 1990) Key words: Glucocorticoid;Corticosterone; Hippocampus; CAI pyramidal neuron; Slice; Rat
The effects of giucocorticoids on rat hippocampal CAI pyramidal neurons were studied using brain slice preparations. At 10 days after bilateral adrenalectomy, a localized region of CA 1 showed a drastic reduction of excitabilityinduced by CA3 stimulation as compared to control. The region of CA1 most effectedwas 1.4-2.0 mm from the most rostral side of the hippocampus. Upon perfusion of corticosterone, the response to synaptic activation was reduced in this region in slices from adrenalatomized animals increased rapidly toward control values, volatile responses in other regions were unaffected. These results suggest that glucocorticoid receptors are concentrated in restricted regions of hippocampus and that these receptors have important roles in regulation of synaptic excitability.
Glucocorticoid, an adrenocortical stress hormone, has been reported to make the hippocampus more vulnerable to ischemia [4, 11] and to be directly neurotoxic [710] in morphological studies. However, the reported electrophysiological effects of glucocorticoids on hippocampal neurons have been inconsistent [1-3, 5, 6, 12]. These inconsistencies have led to the present experiments. It is known that some parts of hippocampus (i.e. CA1) are more sensitive to ischemia than others and, therefore, we considered the possibility that if the effects of glucocorticoids are related to ischemic damage, there might also be a regional difference in the glucocorticoid effects. In this report we show regional differences in the effects of adenectomy and application of glucocorticoid on the synaptic response in hippocampal neurons. Adult, male Wistar rats (200-250 g) were subjected to bilateral adrenalectomy or sham surgery under pentobarbital anesthesia more than 10 days prior to preparation of brain slices. The animals were killed by cervical dislocation under light ether anesthesia and the brain quickly removed and placed in cold K r e b s - R i n g e r solution. The brain was trimmed along the lateral olfactory tract and placed on the stage of a chamber with the cut surface down. The brain was then cut with a simple vibratome at 450 p m thickness. Slices (about eight) were made almost perpendicular to the long axis of the hippoCorrespondence: N. Hori, Wadsworth Center for Laboratories and Research, New York State Department of Health and School of Public Health, Albany, NY 12201-0509, U.S.A.
campus (Fig. 1A), and individual slices were identified as R1 to R8 as indicated in the diagram in Fig. 1. The slices were preincubated for 2 h in oxygenated Krebs-Ringer (95% 02, 5% CO2) at 35°C and then transferred to the recording chamber. Oxygenated Krebs-Ringer solution was perfused through the chamber throughout the experiment at 3-5 ml/min over the submerged slice at 35°C. Field potentials were recorded from the CA 1 pyramidal layer with glass electrodes (about 5/~m tip diameter) filled with saline, and 10 consecutive postsynaptic population spikes (PS) were averaged with a microcomputer. Stimulation designed for maximal response in CA1 was applied to CA3 with a m o n o p o l a r electrode (50 /ts, 10-15 V) as indicated in Fig. 1A. Synaptic activation of CA3 and dentate gyrus (DG) neurons was accomplished by stimuli delivered at D G and the perforant pathway (PP), respectively. Corticosterone (CORT), which is the principal glucocorticoid in rats, was used as a representative glucocorticoid. C O R T was dissolved in ethanol and diluted with Krebs-Ringer to the desired concentration. Slices prepared from nine animals subjected to adrenalectomy were examined at 10-60 days after surgery. In all adrenalectomized animals there were no differences in synaptic responses recorded in CA3 or D G as compared to sham-operated control animals. There were, however, significant differences recorded in CA1, but only in a restricted region. The PS was smaller in one or two slices from every animal, and the slices were consistently R3, R4, or R5. The variability presumably reflects slight dif-
100 A
/
Rt
cot/~
s5
4.1m
/
R 4 (anti)
.•lmV 20rnsec
Fig. 1. A: schematic diagram of recording and stimulating sites on hippocampal slice (above) and schematic diagram of dorsal hippocampus showing cutting sites (below). f, fimbria (detailed in text). B: averaged CA1 field potentials recorded in slices from an animal 14 days after adrenalectomy. Stimulus was delivered orthodromically (CA3) or antidromically (anti.). At about the middle of the hippocampus along the axis (R4 in this case), the response to orthodromic stimulus was obviously smaller than that in other regions. CA1 response in R4 to antidromic stimulus was also small.
slices f r o m a d r e n a l e c t o m i z e d animals, a n d has this effect w i t h o u t c h a n g i n g responses f r o m o t h e r p a r t s o f CA1. Fig. 2 shows recordings f r o m slices f r o m an a n i m a l adren a l e c t o m i z e d 60 d a y s p r i o r to experiment. The responses in slices R 2 a n d R6 were large a n d totally unaffected by a 30 min perfusion o f C O R T . The PS in R5 was consid e r a b l y smaller, a n d was slightly increased in a m p l i t u d e a n d d e v e l o p e d some later oscillations after 30 min o f C O R T . R e s p o n s e s in R4 are shown in Fig. 2B, with the effect o f C O R T perfusion for 30, 40 a n d 60 min. In this p r e p a r a t i o n there was a l m o s t no response to synaptic a c t i v a t i o n in the control. A f t e r 30 min o f C O R T perfusion, there was a clear response which grew in a m p l i t u d e so as to a p p r o a c h a n o r m a l a m p l i t u d e after 60 min perfusion o f C O R T . Even m o r e d r a m a t i c results are shown in Fig. 2C f r o m a slice f r o m a n i m a l s a d r e n a l e c t o m i z e d 30 d a y s p r i o r to the experiment. O n l y the effect o f C O R T perfusion on the response in R 4 is s h o w n (the p a t t e r n o f A,
CONT
CORT 30
L/
CONT
C O R T . , 10
ferences in slice p r e p a r a t i o n f r o m a n i m a l to animal. F i g u r e 1B illustrates r e c o r d s t a k e n f r o m an a n i m a l 14 d a y s after a d r e n a l e c t o m y . In this e x p e r i m e n t the PS e v o k e d by C A 3 s t i m u l a t i o n was d r a m a t i c a l l y smaller in R 4 as c o m p a r e d to t h a t in slices R3 a n d R6, while the PS in slice R5 was reduced. N o t e the a n t i d r o m i c response in slice R 4 is also very small. This o b s e r v a t i o n suggests t h a t the small s y n a p t i c response is n o t a result o f a p r o b l e m with synaptic t r a n s m i s s i o n b u t r a t h e r reflects a general loss o f n e u r o n a l excitability. These o b s e r v a t i o n s suggest a very localized r e d u c t i o n o f excitability in CA1 after a d r e n a l e c t o m y . W h i l e there was some v a r i a t i o n in PS a m p l i t u d e in different animals, such a small response in a restricted a r e a was never seen in a n y o f the c o n t r o l o r s h a m - o p e r a e d p r e p a r a t i o n s studied. F u r t h e r m o r e , the responses r e c o r d e d in C A 3 a n d D G f r o m the a d r e n a l e c t o m i z e d a n i m a l s d i d n o t differ significantly f r o m those o f c o n t r o l o r s h a m - o p e r a t e d animals. There was an i n d i c a t i o n t h a t the d e p r e s s i o n o f response in this very localized a r e a p r o g r e s s e d with time ( a l m o s t no response in Fig. 2B, o b t a i n e d 60 d a y s after a d r e n a l e c t o m y , a n d very small in Fig. 2C, after 30 days), b u t the n u m b e r o f p r e p a r a t i o n s is t o o small to be certain o f this conclusion. Perfusion o f C O R T (10 - 6 M ) d i d n o t have a consistent effect o n the a m p l i t u d e o f PS e v o k e d in C A 3 , D G o r a n y p a r t o f CA1 in slices f r o m c o n t r o l o r s h a m o p e r ated animals. H o w e v e r , C O R T d i d alter the r e d u c e d response o b t a i n e d f r o m the localized region o f CA1 in
20
g.
CONT.
CORT
3O
3O
40
60
,~JlmV 20reset
.~J0 5(R61 20reset
Fig. 2. A,B: averaged CA1 field potentials recorded in slices from an animal 60 days after adrenalectomy. Stimulus was delivered at CA3. Response in R4 (B) was obviously smaller than that in the other slices (A). Some oscillatory responses were observed in R5, which may reflect some abnormality in this region. In 30 min after onset of 10-6 M CORT (CORT., 30), CAI response in R2 and R6 were not affected, that in R5 slightly increased and that in R4 obviously increased. The response in R4 continuously increased with time after onset of CORT (40, 60 min). C: averaged CA1 field potentials recorded in R4 from an animal 30 days after adrenalectomy. Stimulus was delivered to CA3. In this animal, also, CA1 response in R4 was obviously smaller than that in other slices. The depressed CA1 response was increased by CORT application (10 6 M) with time (minutes) after onset of CORT.
101 other responses was similar to that in Figs. 1 and 2A). There was little response in the control, but u p o n C O R T perfusion the response grew with time to be very robust after a 30 min perfusion. These observations suggest that glucocorticoids regulate the excitability o f neurons in some specific areas o f hippocampus, but have few or no effects elsewhere. The fact that excitabiltity is restored after glucocorticoid perfusion is evidence that the small localized response on CA1 is not secondary to excitotoxic injury or neuronal cell death. The inconsistencies in the results o f previous studies are p r o b a b l y secondary to the fact that, as these studies demonstrate, there are regional differences in glucocorticoid sensitivity and receptor distribution in the hippocampus. While the mechanisms underlying these effects are not known, the effects might be secondary to glucocorticoid regulation o f cell metabolism. Glucocorticoids have been reported to exert extensive catabolic effects on target neurons [10]. I f glucocorticoids alter energy m e t a b o lism in h i p p o c a m p u s in a regional fashion this effect m a y be correlated with differences in sensitivity to ischemic injury. It is i m p o r t a n t to emphasize that our observations do not indicate a toxic role for glucocorticoids, but rather a role in m o d u l a t i n g neuronal excitability. 1 Barak, Y.B., Gutnick, M.J. and Feldman, S., Iontophoretically applied corticosteroids do not affect the firing of hippocampal neurons, Neuroendocrinology, 23 (1977) 248-256.
2 Dafny, N., Phillips, M.I., Taylor, A.N. and Gilman, S., Dose effects of cortisol on single unit activity in hypothalamus, reticular formation and hippocampus of freely behaving rats correlated with plasma steroid levels, Brain Res., 59 (1973) 257-272. 3 Joels, M. and Ronald de Kloet, E., Effects of glucocorticoids and norepinephrine on the excitability in the hippocampus, Science, 245 (1989) 1502-1505. 4 Koide, T., Wieloch, T.W. and Siesjo, B.K., Chronic dexamethasone pretreatment aggravates ischemic neuronal necrosis, J. Cereb. Blood Flow Metab., 6 (1986) 395-404. 5 Pfaff, D.W., Silva, M.T.A. and Weiss, J.M., Telemetered recording of hormone effects on hippocampal neurons, Science, 172 (1971) 394-395. 6 Rey, M., Carlier, E. and Soumireu-Mourat, B., Effects of corticosterone in hippocampal slice electrophysioloy in normal and adrenalectomized BALB/c mice, Neuroendocrinology 46 (1987) 424429. 7 Sapolsky, R.M., Glucocorticoid toxicity in the hippocampus: Temporal aspects of neuronal vulnerability, Brain Res., 359 (1985) 300305. 8 Sapolsky, R.M., A mechanism for glucocorticoid toxicity in the hippocampus: increased neuronal vulnerability to metabolic insuits, J. Neurosci., 5 (1985) 1228-1232. 9 Sapolsky, R.M., Glucocorticoid toxicity in the hippocampus, Neuroendocrinology, 43 (1986) 440 444. 10 Sapolsky, R.M., Packan, D.R. and Vale, W.W., Glucocorticoid toxicity in the hippocampus: in vitro demonstration, Brain Res., 453 (1988) 367-371. 11 Sapolsky, R.M. and Pulsinelli, W.A., Glucocorticoids potentiate ischemic brain injury: therapeutic implications, Science, 229 (1985) 1397-1400. 12 Vidal, C., Jordon, W. and Zieglgansberger, W., Cortisterone reduces the excitability of hippocampal pyramidal cells in vitro, Brain Res., 383 (1986) 54-59.
Neuroscience Letters, 123 (1991) 99-101
© 1991 ElsevierScientificPublishers Ireland Ltd. 0304-3940/91/$ 03.50 ADONIS 0304394091000978 NSL 07540
Glucocorticoids promote localized activity of rat hippocampal CA1 pyramidal neurons in brain slices N . D o i 1~, S. M i y a h a r a 2 a n d N. H o r i 2 t Department of Biology, Faculty of Science and 2Department of Pharmacology, Faculty of Dentistry, Kyushu University, Fukuoka (Japan)
(Received 21 March 1990; Revisedversion received2 November 1990; Accepted 7 November 1990) Key words: Glucocorticoid;Corticosterone; Hippocampus; CAI pyramidal neuron; Slice; Rat
The effects of giucocorticoids on rat hippocampal CAI pyramidal neurons were studied using brain slice preparations. At 10 days after bilateral adrenalectomy, a localized region of CA 1 showed a drastic reduction of excitabilityinduced by CA3 stimulation as compared to control. The region of CA1 most effectedwas 1.4-2.0 mm from the most rostral side of the hippocampus. Upon perfusion of corticosterone, the response to synaptic activation was reduced in this region in slices from adrenalatomized animals increased rapidly toward control values, volatile responses in other regions were unaffected. These results suggest that glucocorticoid receptors are concentrated in restricted regions of hippocampus and that these receptors have important roles in regulation of synaptic excitability.
Glucocorticoid, an adrenocortical stress hormone, has been reported to make the hippocampus more vulnerable to ischemia [4, 11] and to be directly neurotoxic [710] in morphological studies. However, the reported electrophysiological effects of glucocorticoids on hippocampal neurons have been inconsistent [1-3, 5, 6, 12]. These inconsistencies have led to the present experiments. It is known that some parts of hippocampus (i.e. CA1) are more sensitive to ischemia than others and, therefore, we considered the possibility that if the effects of glucocorticoids are related to ischemic damage, there might also be a regional difference in the glucocorticoid effects. In this report we show regional differences in the effects of adenectomy and application of glucocorticoid on the synaptic response in hippocampal neurons. Adult, male Wistar rats (200-250 g) were subjected to bilateral adrenalectomy or sham surgery under pentobarbital anesthesia more than 10 days prior to preparation of brain slices. The animals were killed by cervical dislocation under light ether anesthesia and the brain quickly removed and placed in cold K r e b s - R i n g e r solution. The brain was trimmed along the lateral olfactory tract and placed on the stage of a chamber with the cut surface down. The brain was then cut with a simple vibratome at 450 p m thickness. Slices (about eight) were made almost perpendicular to the long axis of the hippoCorrespondence: N. Hori, Wadsworth Center for Laboratories and Research, New York State Department of Health and School of Public Health, Albany, NY 12201-0509, U.S.A.
campus (Fig. 1A), and individual slices were identified as R1 to R8 as indicated in the diagram in Fig. 1. The slices were preincubated for 2 h in oxygenated Krebs-Ringer (95% 02, 5% CO2) at 35°C and then transferred to the recording chamber. Oxygenated Krebs-Ringer solution was perfused through the chamber throughout the experiment at 3-5 ml/min over the submerged slice at 35°C. Field potentials were recorded from the CA 1 pyramidal layer with glass electrodes (about 5/~m tip diameter) filled with saline, and 10 consecutive postsynaptic population spikes (PS) were averaged with a microcomputer. Stimulation designed for maximal response in CA1 was applied to CA3 with a m o n o p o l a r electrode (50 /ts, 10-15 V) as indicated in Fig. 1A. Synaptic activation of CA3 and dentate gyrus (DG) neurons was accomplished by stimuli delivered at D G and the perforant pathway (PP), respectively. Corticosterone (CORT), which is the principal glucocorticoid in rats, was used as a representative glucocorticoid. C O R T was dissolved in ethanol and diluted with Krebs-Ringer to the desired concentration. Slices prepared from nine animals subjected to adrenalectomy were examined at 10-60 days after surgery. In all adrenalectomized animals there were no differences in synaptic responses recorded in CA3 or D G as compared to sham-operated control animals. There were, however, significant differences recorded in CA1, but only in a restricted region. The PS was smaller in one or two slices from every animal, and the slices were consistently R3, R4, or R5. The variability presumably reflects slight dif-
100 A
/
Rt
cot/~
s5
4.1m
/
R 4 (anti)
.•lmV 20rnsec
Fig. 1. A: schematic diagram of recording and stimulating sites on hippocampal slice (above) and schematic diagram of dorsal hippocampus showing cutting sites (below). f, fimbria (detailed in text). B: averaged CA1 field potentials recorded in slices from an animal 14 days after adrenalectomy. Stimulus was delivered orthodromically (CA3) or antidromically (anti.). At about the middle of the hippocampus along the axis (R4 in this case), the response to orthodromic stimulus was obviously smaller than that in other regions. CA1 response in R4 to antidromic stimulus was also small.
slices f r o m a d r e n a l e c t o m i z e d animals, a n d has this effect w i t h o u t c h a n g i n g responses f r o m o t h e r p a r t s o f CA1. Fig. 2 shows recordings f r o m slices f r o m an a n i m a l adren a l e c t o m i z e d 60 d a y s p r i o r to experiment. The responses in slices R 2 a n d R6 were large a n d totally unaffected by a 30 min perfusion o f C O R T . The PS in R5 was consid e r a b l y smaller, a n d was slightly increased in a m p l i t u d e a n d d e v e l o p e d some later oscillations after 30 min o f C O R T . R e s p o n s e s in R4 are shown in Fig. 2B, with the effect o f C O R T perfusion for 30, 40 a n d 60 min. In this p r e p a r a t i o n there was a l m o s t no response to synaptic a c t i v a t i o n in the control. A f t e r 30 min o f C O R T perfusion, there was a clear response which grew in a m p l i t u d e so as to a p p r o a c h a n o r m a l a m p l i t u d e after 60 min perfusion o f C O R T . Even m o r e d r a m a t i c results are shown in Fig. 2C f r o m a slice f r o m a n i m a l s a d r e n a l e c t o m i z e d 30 d a y s p r i o r to the experiment. O n l y the effect o f C O R T perfusion on the response in R 4 is s h o w n (the p a t t e r n o f A,
CONT
CORT 30
L/
CONT
C O R T . , 10
ferences in slice p r e p a r a t i o n f r o m a n i m a l to animal. F i g u r e 1B illustrates r e c o r d s t a k e n f r o m an a n i m a l 14 d a y s after a d r e n a l e c t o m y . In this e x p e r i m e n t the PS e v o k e d by C A 3 s t i m u l a t i o n was d r a m a t i c a l l y smaller in R 4 as c o m p a r e d to t h a t in slices R3 a n d R6, while the PS in slice R5 was reduced. N o t e the a n t i d r o m i c response in slice R 4 is also very small. This o b s e r v a t i o n suggests t h a t the small s y n a p t i c response is n o t a result o f a p r o b l e m with synaptic t r a n s m i s s i o n b u t r a t h e r reflects a general loss o f n e u r o n a l excitability. These o b s e r v a t i o n s suggest a very localized r e d u c t i o n o f excitability in CA1 after a d r e n a l e c t o m y . W h i l e there was some v a r i a t i o n in PS a m p l i t u d e in different animals, such a small response in a restricted a r e a was never seen in a n y o f the c o n t r o l o r s h a m - o p e r a e d p r e p a r a t i o n s studied. F u r t h e r m o r e , the responses r e c o r d e d in C A 3 a n d D G f r o m the a d r e n a l e c t o m i z e d a n i m a l s d i d n o t differ significantly f r o m those o f c o n t r o l o r s h a m - o p e r a t e d animals. There was an i n d i c a t i o n t h a t the d e p r e s s i o n o f response in this very localized a r e a p r o g r e s s e d with time ( a l m o s t no response in Fig. 2B, o b t a i n e d 60 d a y s after a d r e n a l e c t o m y , a n d very small in Fig. 2C, after 30 days), b u t the n u m b e r o f p r e p a r a t i o n s is t o o small to be certain o f this conclusion. Perfusion o f C O R T (10 - 6 M ) d i d n o t have a consistent effect o n the a m p l i t u d e o f PS e v o k e d in C A 3 , D G o r a n y p a r t o f CA1 in slices f r o m c o n t r o l o r s h a m o p e r ated animals. H o w e v e r , C O R T d i d alter the r e d u c e d response o b t a i n e d f r o m the localized region o f CA1 in
20
g.
CONT.
CORT
3O
3O
40
60
,~JlmV 20reset
.~J0 5(R61 20reset
Fig. 2. A,B: averaged CA1 field potentials recorded in slices from an animal 60 days after adrenalectomy. Stimulus was delivered at CA3. Response in R4 (B) was obviously smaller than that in the other slices (A). Some oscillatory responses were observed in R5, which may reflect some abnormality in this region. In 30 min after onset of 10-6 M CORT (CORT., 30), CAI response in R2 and R6 were not affected, that in R5 slightly increased and that in R4 obviously increased. The response in R4 continuously increased with time after onset of CORT (40, 60 min). C: averaged CA1 field potentials recorded in R4 from an animal 30 days after adrenalectomy. Stimulus was delivered to CA3. In this animal, also, CA1 response in R4 was obviously smaller than that in other slices. The depressed CA1 response was increased by CORT application (10 6 M) with time (minutes) after onset of CORT.
101 other responses was similar to that in Figs. 1 and 2A). There was little response in the control, but u p o n C O R T perfusion the response grew with time to be very robust after a 30 min perfusion. These observations suggest that glucocorticoids regulate the excitability o f neurons in some specific areas o f hippocampus, but have few or no effects elsewhere. The fact that excitabiltity is restored after glucocorticoid perfusion is evidence that the small localized response on CA1 is not secondary to excitotoxic injury or neuronal cell death. The inconsistencies in the results o f previous studies are p r o b a b l y secondary to the fact that, as these studies demonstrate, there are regional differences in glucocorticoid sensitivity and receptor distribution in the hippocampus. While the mechanisms underlying these effects are not known, the effects might be secondary to glucocorticoid regulation o f cell metabolism. Glucocorticoids have been reported to exert extensive catabolic effects on target neurons [10]. I f glucocorticoids alter energy m e t a b o lism in h i p p o c a m p u s in a regional fashion this effect m a y be correlated with differences in sensitivity to ischemic injury. It is i m p o r t a n t to emphasize that our observations do not indicate a toxic role for glucocorticoids, but rather a role in m o d u l a t i n g neuronal excitability. 1 Barak, Y.B., Gutnick, M.J. and Feldman, S., Iontophoretically applied corticosteroids do not affect the firing of hippocampal neurons, Neuroendocrinology, 23 (1977) 248-256.
2 Dafny, N., Phillips, M.I., Taylor, A.N. and Gilman, S., Dose effects of cortisol on single unit activity in hypothalamus, reticular formation and hippocampus of freely behaving rats correlated with plasma steroid levels, Brain Res., 59 (1973) 257-272. 3 Joels, M. and Ronald de Kloet, E., Effects of glucocorticoids and norepinephrine on the excitability in the hippocampus, Science, 245 (1989) 1502-1505. 4 Koide, T., Wieloch, T.W. and Siesjo, B.K., Chronic dexamethasone pretreatment aggravates ischemic neuronal necrosis, J. Cereb. Blood Flow Metab., 6 (1986) 395-404. 5 Pfaff, D.W., Silva, M.T.A. and Weiss, J.M., Telemetered recording of hormone effects on hippocampal neurons, Science, 172 (1971) 394-395. 6 Rey, M., Carlier, E. and Soumireu-Mourat, B., Effects of corticosterone in hippocampal slice electrophysioloy in normal and adrenalectomized BALB/c mice, Neuroendocrinology 46 (1987) 424429. 7 Sapolsky, R.M., Glucocorticoid toxicity in the hippocampus: Temporal aspects of neuronal vulnerability, Brain Res., 359 (1985) 300305. 8 Sapolsky, R.M., A mechanism for glucocorticoid toxicity in the hippocampus: increased neuronal vulnerability to metabolic insuits, J. Neurosci., 5 (1985) 1228-1232. 9 Sapolsky, R.M., Glucocorticoid toxicity in the hippocampus, Neuroendocrinology, 43 (1986) 440 444. 10 Sapolsky, R.M., Packan, D.R. and Vale, W.W., Glucocorticoid toxicity in the hippocampus: in vitro demonstration, Brain Res., 453 (1988) 367-371. 11 Sapolsky, R.M. and Pulsinelli, W.A., Glucocorticoids potentiate ischemic brain injury: therapeutic implications, Science, 229 (1985) 1397-1400. 12 Vidal, C., Jordon, W. and Zieglgansberger, W., Cortisterone reduces the excitability of hippocampal pyramidal cells in vitro, Brain Res., 383 (1986) 54-59.
