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Regulation of hippocampal corticosterone receptors by a vasopressin analogue
Peptides. Vol. 5, pp. 1225-1227, 1984. ~ Ankho International inc. Printed in the U.S.A.
0196-9781/84 $3.00 + .00
BRIEF COMMUNICATION
Regulation of Hippocampal Corticosterone Receptors by a Vasopressin Analogue B A R B A R A T. F E L T , R O B E R T
M. S A P O L S K Y 1 A N D B R U C E S. M c E W E N
Laboratory of Neuroendocrinology, The Rockefeller University, 1230 York Avenue, New York, N Y 10021 R e c e i v e d 7 M a y 1984 FELT, B. T., R. M. SAPOLSKY AND B. S. McEWEN. Regulation of hippocampal corticosterone receptors by a vasopressin analogue. PEPTIDES 5(6) 1225-1227, 1984.--Vasopressin can alter hippoeampal corticosterone receptor number, as a congenital absence of a peptide in the Brattleboro rat results in decreased concentrations of the receptor; this deficit can be reversed with des-glycinimide arginine vasopressin (dGVP), a centrally-acting VP analogue. We examined whether vasopressin might regulate less dramatic fluctuations of hippocampal corticosterone receptor number in the normal rat. Administration of dGVP failed to alter the rate of or extent of down- or up-regulation of hippocampal eorticosterone receptors by circulating corticosterone, suggesting that alteration of neural VP content is not a mediating step in such regulation. Corticosterone Corticosterone receptors Vasopressin Hippocampus Des-glycinimide arginine vasopressin Autoregulation Brattleboro rat
VASOPRESSIN (VP), 'in addition to its regulation of diuresis and pituitary ACTH-release [5,6], is found in the brain and is presumed to have a neuromodulatory or neurotransmitter role [12]. Neural V P appears capable of regulating the concentration of receptors in the hippocampus for the adrenal steroid, corticosterone. The Brattleboro rat congenitally lacks V P and has a selective depletion of hippocampal corticosterone receptors (HippCr) [I I]. N o other area of the brain has a receptor depletion. Administration of a centrally-acting V P analogue with no peripheral diuretic or ACTH-releasing effects normalizes the receptor loss [I l]. Decreased circulating titers of corticosterone produce elevated hypothalamic V P content [10] and elevated HippCr number [4]. whereas elevated corticosterone titers produce the opposite results [7,10]. These observations suggest that corticosterone might similarly regulate hippocarnpal VP, and that changes in such V P might mediate corticosterone regulation of HippCr. In the present paper, we examine whether a V P analgoue can alter corticosterone-induced up- or down-regulation of HippCr number, or can alter normal concentrations of the receptors. METHOD F o r the Brattleboro studies, subjects were either homozygotic diabetes-insipidus Brattleboro rats or LongEvans strain controls (male subjects of 5 months of age), obtained from Blue Spruce Farms, Altamont, NY. Remaining subjects were Sprague-Dawley males, 4--8 months of age,
from Charles River Breeding Laboratories. Subjects were given assess to food and water ad lib, and were maintained on a 14:10 L : D cycle (lights on: 0700). Des-giycinimide-arginine vasopressin (dGVP) was dissolved in a slow-release zinc phosphate solution [3]. Subjects were injected SC with 2/~g of the peptide in 0.1 ml. Control subjects were injected with zinc phosphate alone. In experiments with Brattleboro subjects, Brattleboro rats were injected with dGVP or vehicle daily for seven days, and HippCr concentrations were compared with LongEvans controls. An additional group of Long-Evans rats was treated for a week with dGVP, to determine whether HippCr concentrations could be altered in the normal rat. In additional experiments, Sprague-Dawley rats were treated for a week with 10 mg/day of corticosterone in sesame oil along with d G V P or vehicle. Such steroid treatment leads t o progressive down-regulation of HippCr number [7]. A final group o f Sprague-Dawley rats were adrenaiectomized and administered dGVP or vehicle for 7 days. Adrenalectomy leads to progressive increases in HippCr number [4]. Cytosolic corticosterone receptor concentrations in the hippocampus (dorsal, ventral, subiculum) were measured as previously described [7]. Steroid treatment was suspended 24 hours before assay, and all intact subjects were adrenalectomized 12 hours prior to assay. Bmax (fmol/mg cytosol protein) and Kd (dissociation constant, mol/liter x 109) were derived by Scatchard analysis.
1Requestsforrepfintsshouldbeaddressed to R.M. Sapolsky, c/oPeptide Biology Laboratory, Salklnstitu~, P.O. Box 85800, San Diego, CA 92138.
1225
1226
F E L T . SAPOLSKY AND McEWEN TABLE 1 EFFECTSOF ONE WEEKADMINISTRATIONOF DEX-GLYCINIMIDEARGININEVASOPRESSINON 3H-DEXAMETHASONEBINDINGIN THE HIPPOCAMPUS Bmax
Kd
r
% Control
.97 .88 .93
100 76 96
.96 .92
100 104
A. Effects of dGVP on Binding in the Brattleboro Rat
Controls (n=8) Brattleboro + vehicle (8) Brattleboro + dGVP(8)
125 ~- 8 95 - 12" 120 ± 6
1.3 -+ 0.2 1.2 - 0.2 1.1 - 0.1
B. Effects of dGVP on Binding in the Spragne-Dawley Rat Vehicle-treated (18) dGVP-treated (16)
166 _ 16 173 ± 30
1.2 - 0.2 1.0 - 0.3
C. Effects of dGVP on Binding Following Corticosterone Treatment Controls (10) Corticosterone + vehicle (10) Corticosterone + dGVP ( 16
201 - 30 144 _ 8* 113 - 10t
1.1 - 0.1 1.0 ± 0.1
.95 .90
0.9 ± 0.1
.92
100 71 56
.95 .84 .91 NA .86
100 148 137 209 195
D. Effects of dGVP on Binding Following Adrenalectomy Controls (10) 3 days post-ADX 3 days post-ADX 7 days post-ADX 7 days post-ADX
+ + + +
vehicle (8) dGVP (8) vehicle (8) dGVP (9)
201 299 277 422 392
± ± ... ... --
30 3 19 36t 52t
1.1 - 0.2 !. 1 ± 0.1 1.1 - 0.1 NA 1.6 ± 0.3
Bmax (fmol/mg cytosol protein) and Kd (dissociation constant, mol/liter x 10~) were derived by Scatchard analysis. Mean ± S.E. Correlation coefficients (r) were derived from linear regression analysis of reciprocal plots, n=Number of rats per experiment. *, *Indicate significantly different levels of binding as compared with contrQls, at 0.05 and 0.01 levels, respectively (Scheffe test following one-way ANOVA). No other paired comparisons were statistically significant. NA=not available; full Scatchard analyses were not conducted on these tissues, and single point saturation assays at 60 nM were instead conducted. ADX=adrenalectomy. Data from part A have been previously published [12].
RESULTS
DISCUSSION
As previously reported [11], the Brattleboro rat had a depletion of cytosolic HippCr's without a change in receptor affinity (Table IA). One week of daily dGVP normalized HippCr number without changing receptor affinity. Such normalization was transient, as concentrations declined to pre-treatment levels six weeks after the end of dGVP treatment (unpublished data). Treatment of normal control subjects failed t o alter HippCr concentrations or affinity (Table IB). Administration of 10 mg of corticosterone in oil produces high physiological circulating titers of the steroid for up to 20 hours [7]; daily treatment with corticosterone for one week produced significant depletions of HippCr's without altering receptor affinity (Table IC). Such "down-regulation" also occurs in the amygdala, but in no other area of the brain or pituitary [7]. Administration of dGVP with the corticosterone failed to prevent such down-regulation. Finally, adrenalectomy was followed by a gradual increase of HippCr number (Table I D). Such up-regulation appears to reach a plateau at around one week [4]. Administration of dGVP following adrenalectomy failed to either accelerate the rate of or to increase the maximal extent of up-regulation seven days after adrenalectomy (Table 1D).
Hippocampai VP appears capable of regulating HippCr number, as demonstrated by the HippCr depletion of the Brattleboro rat and its correction with dGVP. Circulating corticosterone titers also regulate HippCr number [4,7]. Furthermore, the steroid induces parallel changes in hypothalamic VP content [I0]. Although similar regulation of hippocampal VP by circulating corticosterone has not yet been demonstrated, and such VP may not have the same cells of origin as hypothalamic VP [i,2], we speculated that alterations in hippocampai VP might mediate corticosteroneinduced alterations in HippCr number. We have tested this hypothesis and failed to find supporting evidence. VP does not mediate HippCr up- or down-regulation in the normal rat, and administration of dGVP did not alter normal HippCr number. Administration of high physiological levels of corticosterone down-regulated HippCr, as previously reported [7], and simultaneous administration of dGVP (at a dose which raised receptor number in the Brattleboro rat) failed to attenuate the down-regulation. This demonstrates that corticosterone-induced reduction in VP content in the hippocampus, were it occurring, is not a mediating step in down-regulation of HippCr number. Finally, as previously reported [4], long-term adrenalectomy
CORTICOSTERONE RECEPTORS AND A VP A N A L O G U E results in a gradual rise in HippCr number, and administration of dGVP following adrenalectomy did not accelerate or increase this up-regulation. This suggests that disinhibition of hippocampal VP following adrenalectomy is not the mediating step in up-regulation of HippCr number. These data and the Brattleboro data can be reconciled in a number of ways: Homozygous Brattleboro rats and all other subjects employed in this study may differ markedly in the number of affinity of hippocampal VP receptors and thus may differ in the sensitivity to the dGVP administration. There are no data presently available to evaluate this possibility. The presence of VP might be essential for full expression of HippCr number, but the peptide might play only a small permissive role in such regulation. Once minimal critical presence of the peptide is established in the hippocampus, normal receptor concentrations are induced, and further increases in peptide levels will not alter receptor number. Thus, in the present data, high corticosterone titers do not reduce hippocampai VP levels sufficiently to alter HippCr's via this route. If this were the case, a variety of doses of dGVP (including a dose of less than 2 p.g/day) would all be
1227 equally efficacious in normalizing HippCr number in the Brattleboro rat. In addition, complete destruction of the vasopressinergic input into the hippocampus should result in decreased HippCr. This has not yet been tested. Alternatively to this, it is possible that the subset of HippCr's which are sensitive to the presence of VP is a different one than is subject to corticosterone-induced up- or down-regulation. If such were the case, the relatively few HippCr's demonstrable in the Brattleboro rat would be subject to down- and up-regulation to the same extent as control rats. In addition, quantitative autoradiographic methods [9] would demonstrate different subsets of HippCr's in the Brattleboro rat sensitive to dGVP treatment and autoregulation. We have found evidence for such distinct pools of HippCr's ([8], unpublished data).
ACKNOWLEDGEMENTS dGVP was generously supplied by Dr. Maurice Manning, Medical College of Ohio at Toledo. Funding was supplied by a predoctoral grant from the National Institute on Aging to RMS.
REFERENCES I. Buijs, R. lntra- and extrahypothalamic vasopressin and oxytocin pathways in the rat. Cell Tissue Res 192: 423--429, 1978. 2. De Vries, G. and R. Buijs. The origin of the vasopressinergic and oxytocinergic innervation of the rat brain with special reference to the lateral septum. Brain Res 273: 307-317, 1983. 3. De Wied, D. Inhibitory effects of ACTh and related peptides on extinction of conditioned avoidance behavior in rats. Proc Soc Exp Biol Med 122: 28-35, 1966. 4. McEwen, B., B. Stephenson and L. Krey. Radioimmunoassay of brain tissue and cell nuclear corticosterone. J Neurosci Methods 3: 57-65, 1980. 5. Reid. 1. A. Salt and water regulation. In: Brain Peptides, edited by D. T. Krieger, M. J. Brownstein and J. B. Martin. New York: John Wiley and Sons, 1983, pp. 333--348. 6. Rivier, C. and W. Vale. Modulation of stress-induced ACTH release by corticotropin-releasing factor, catecholamines and vasopressin. Nature 305: 325-327, 1983. 7. Sapolsky, R. M.. L. C. Krey and B. S. McEwen. Stress downregulates corticosterone receptors in a site-specific manner in the brain. Endocrinology 114: 287-292, 1984.
8. Sapolsky, R. M., L. C. Krey, B. S. McEwen and T. C. Rainbow. Do vasopressin-related peptides induce hippocampal corticosterone receptors.'? Implications for aging. J Neurosci 4: 1479-1485, 1984. 9. Sapolsky, R. M., B. S. McEwen and T. C. Rainbow. Quantitative autoradiography of 3H corticosterone receptors in rat brain. Brain Res 271: 331-337, 1983. 10. Silverman, A. J., D. Hoffman, C. A. Gadde, L. C. Krey and E. A. Zimmerman. Adrenal steroid inhibition of the vasopressinneurophysin neurosecretory system to the median eminence of the rat. Neuroendocrinology 32: 129--133, 1981. ! 1. Veldhuis, H. and E. R. DeKioet. Vasopressin-related peptides increase the hippocampal corticosterone receptor capacity of diabetes insipidus (Brattleboro) rats. Endocrinology 110: 153157, 1982. 12. Zimmerman, E. A. Oxytocin, vasopressin, and neurophysins. In: Brain Peptides, edited by D. T. Kreiger, M. J. Brownstein and J. B. Martin. New York: John Wiley and Sons, 1983, pp. 597-612.
0196-9781/84 $3.00 + .00
BRIEF COMMUNICATION
Regulation of Hippocampal Corticosterone Receptors by a Vasopressin Analogue B A R B A R A T. F E L T , R O B E R T
M. S A P O L S K Y 1 A N D B R U C E S. M c E W E N
Laboratory of Neuroendocrinology, The Rockefeller University, 1230 York Avenue, New York, N Y 10021 R e c e i v e d 7 M a y 1984 FELT, B. T., R. M. SAPOLSKY AND B. S. McEWEN. Regulation of hippocampal corticosterone receptors by a vasopressin analogue. PEPTIDES 5(6) 1225-1227, 1984.--Vasopressin can alter hippoeampal corticosterone receptor number, as a congenital absence of a peptide in the Brattleboro rat results in decreased concentrations of the receptor; this deficit can be reversed with des-glycinimide arginine vasopressin (dGVP), a centrally-acting VP analogue. We examined whether vasopressin might regulate less dramatic fluctuations of hippocampal corticosterone receptor number in the normal rat. Administration of dGVP failed to alter the rate of or extent of down- or up-regulation of hippocampal eorticosterone receptors by circulating corticosterone, suggesting that alteration of neural VP content is not a mediating step in such regulation. Corticosterone Corticosterone receptors Vasopressin Hippocampus Des-glycinimide arginine vasopressin Autoregulation Brattleboro rat
VASOPRESSIN (VP), 'in addition to its regulation of diuresis and pituitary ACTH-release [5,6], is found in the brain and is presumed to have a neuromodulatory or neurotransmitter role [12]. Neural V P appears capable of regulating the concentration of receptors in the hippocampus for the adrenal steroid, corticosterone. The Brattleboro rat congenitally lacks V P and has a selective depletion of hippocampal corticosterone receptors (HippCr) [I I]. N o other area of the brain has a receptor depletion. Administration of a centrally-acting V P analogue with no peripheral diuretic or ACTH-releasing effects normalizes the receptor loss [I l]. Decreased circulating titers of corticosterone produce elevated hypothalamic V P content [10] and elevated HippCr number [4]. whereas elevated corticosterone titers produce the opposite results [7,10]. These observations suggest that corticosterone might similarly regulate hippocarnpal VP, and that changes in such V P might mediate corticosterone regulation of HippCr. In the present paper, we examine whether a V P analgoue can alter corticosterone-induced up- or down-regulation of HippCr number, or can alter normal concentrations of the receptors. METHOD F o r the Brattleboro studies, subjects were either homozygotic diabetes-insipidus Brattleboro rats or LongEvans strain controls (male subjects of 5 months of age), obtained from Blue Spruce Farms, Altamont, NY. Remaining subjects were Sprague-Dawley males, 4--8 months of age,
from Charles River Breeding Laboratories. Subjects were given assess to food and water ad lib, and were maintained on a 14:10 L : D cycle (lights on: 0700). Des-giycinimide-arginine vasopressin (dGVP) was dissolved in a slow-release zinc phosphate solution [3]. Subjects were injected SC with 2/~g of the peptide in 0.1 ml. Control subjects were injected with zinc phosphate alone. In experiments with Brattleboro subjects, Brattleboro rats were injected with dGVP or vehicle daily for seven days, and HippCr concentrations were compared with LongEvans controls. An additional group of Long-Evans rats was treated for a week with dGVP, to determine whether HippCr concentrations could be altered in the normal rat. In additional experiments, Sprague-Dawley rats were treated for a week with 10 mg/day of corticosterone in sesame oil along with d G V P or vehicle. Such steroid treatment leads t o progressive down-regulation of HippCr number [7]. A final group o f Sprague-Dawley rats were adrenaiectomized and administered dGVP or vehicle for 7 days. Adrenalectomy leads to progressive increases in HippCr number [4]. Cytosolic corticosterone receptor concentrations in the hippocampus (dorsal, ventral, subiculum) were measured as previously described [7]. Steroid treatment was suspended 24 hours before assay, and all intact subjects were adrenalectomized 12 hours prior to assay. Bmax (fmol/mg cytosol protein) and Kd (dissociation constant, mol/liter x 109) were derived by Scatchard analysis.
1Requestsforrepfintsshouldbeaddressed to R.M. Sapolsky, c/oPeptide Biology Laboratory, Salklnstitu~, P.O. Box 85800, San Diego, CA 92138.
1225
1226
F E L T . SAPOLSKY AND McEWEN TABLE 1 EFFECTSOF ONE WEEKADMINISTRATIONOF DEX-GLYCINIMIDEARGININEVASOPRESSINON 3H-DEXAMETHASONEBINDINGIN THE HIPPOCAMPUS Bmax
Kd
r
% Control
.97 .88 .93
100 76 96
.96 .92
100 104
A. Effects of dGVP on Binding in the Brattleboro Rat
Controls (n=8) Brattleboro + vehicle (8) Brattleboro + dGVP(8)
125 ~- 8 95 - 12" 120 ± 6
1.3 -+ 0.2 1.2 - 0.2 1.1 - 0.1
B. Effects of dGVP on Binding in the Spragne-Dawley Rat Vehicle-treated (18) dGVP-treated (16)
166 _ 16 173 ± 30
1.2 - 0.2 1.0 - 0.3
C. Effects of dGVP on Binding Following Corticosterone Treatment Controls (10) Corticosterone + vehicle (10) Corticosterone + dGVP ( 16
201 - 30 144 _ 8* 113 - 10t
1.1 - 0.1 1.0 ± 0.1
.95 .90
0.9 ± 0.1
.92
100 71 56
.95 .84 .91 NA .86
100 148 137 209 195
D. Effects of dGVP on Binding Following Adrenalectomy Controls (10) 3 days post-ADX 3 days post-ADX 7 days post-ADX 7 days post-ADX
+ + + +
vehicle (8) dGVP (8) vehicle (8) dGVP (9)
201 299 277 422 392
± ± ... ... --
30 3 19 36t 52t
1.1 - 0.2 !. 1 ± 0.1 1.1 - 0.1 NA 1.6 ± 0.3
Bmax (fmol/mg cytosol protein) and Kd (dissociation constant, mol/liter x 10~) were derived by Scatchard analysis. Mean ± S.E. Correlation coefficients (r) were derived from linear regression analysis of reciprocal plots, n=Number of rats per experiment. *, *Indicate significantly different levels of binding as compared with contrQls, at 0.05 and 0.01 levels, respectively (Scheffe test following one-way ANOVA). No other paired comparisons were statistically significant. NA=not available; full Scatchard analyses were not conducted on these tissues, and single point saturation assays at 60 nM were instead conducted. ADX=adrenalectomy. Data from part A have been previously published [12].
RESULTS
DISCUSSION
As previously reported [11], the Brattleboro rat had a depletion of cytosolic HippCr's without a change in receptor affinity (Table IA). One week of daily dGVP normalized HippCr number without changing receptor affinity. Such normalization was transient, as concentrations declined to pre-treatment levels six weeks after the end of dGVP treatment (unpublished data). Treatment of normal control subjects failed t o alter HippCr concentrations or affinity (Table IB). Administration of 10 mg of corticosterone in oil produces high physiological circulating titers of the steroid for up to 20 hours [7]; daily treatment with corticosterone for one week produced significant depletions of HippCr's without altering receptor affinity (Table IC). Such "down-regulation" also occurs in the amygdala, but in no other area of the brain or pituitary [7]. Administration of dGVP with the corticosterone failed to prevent such down-regulation. Finally, adrenalectomy was followed by a gradual increase of HippCr number (Table I D). Such up-regulation appears to reach a plateau at around one week [4]. Administration of dGVP following adrenalectomy failed to either accelerate the rate of or to increase the maximal extent of up-regulation seven days after adrenalectomy (Table 1D).
Hippocampai VP appears capable of regulating HippCr number, as demonstrated by the HippCr depletion of the Brattleboro rat and its correction with dGVP. Circulating corticosterone titers also regulate HippCr number [4,7]. Furthermore, the steroid induces parallel changes in hypothalamic VP content [I0]. Although similar regulation of hippocampal VP by circulating corticosterone has not yet been demonstrated, and such VP may not have the same cells of origin as hypothalamic VP [i,2], we speculated that alterations in hippocampai VP might mediate corticosteroneinduced alterations in HippCr number. We have tested this hypothesis and failed to find supporting evidence. VP does not mediate HippCr up- or down-regulation in the normal rat, and administration of dGVP did not alter normal HippCr number. Administration of high physiological levels of corticosterone down-regulated HippCr, as previously reported [7], and simultaneous administration of dGVP (at a dose which raised receptor number in the Brattleboro rat) failed to attenuate the down-regulation. This demonstrates that corticosterone-induced reduction in VP content in the hippocampus, were it occurring, is not a mediating step in down-regulation of HippCr number. Finally, as previously reported [4], long-term adrenalectomy
CORTICOSTERONE RECEPTORS AND A VP A N A L O G U E results in a gradual rise in HippCr number, and administration of dGVP following adrenalectomy did not accelerate or increase this up-regulation. This suggests that disinhibition of hippocampal VP following adrenalectomy is not the mediating step in up-regulation of HippCr number. These data and the Brattleboro data can be reconciled in a number of ways: Homozygous Brattleboro rats and all other subjects employed in this study may differ markedly in the number of affinity of hippocampal VP receptors and thus may differ in the sensitivity to the dGVP administration. There are no data presently available to evaluate this possibility. The presence of VP might be essential for full expression of HippCr number, but the peptide might play only a small permissive role in such regulation. Once minimal critical presence of the peptide is established in the hippocampus, normal receptor concentrations are induced, and further increases in peptide levels will not alter receptor number. Thus, in the present data, high corticosterone titers do not reduce hippocampai VP levels sufficiently to alter HippCr's via this route. If this were the case, a variety of doses of dGVP (including a dose of less than 2 p.g/day) would all be
1227 equally efficacious in normalizing HippCr number in the Brattleboro rat. In addition, complete destruction of the vasopressinergic input into the hippocampus should result in decreased HippCr. This has not yet been tested. Alternatively to this, it is possible that the subset of HippCr's which are sensitive to the presence of VP is a different one than is subject to corticosterone-induced up- or down-regulation. If such were the case, the relatively few HippCr's demonstrable in the Brattleboro rat would be subject to down- and up-regulation to the same extent as control rats. In addition, quantitative autoradiographic methods [9] would demonstrate different subsets of HippCr's in the Brattleboro rat sensitive to dGVP treatment and autoregulation. We have found evidence for such distinct pools of HippCr's ([8], unpublished data).
ACKNOWLEDGEMENTS dGVP was generously supplied by Dr. Maurice Manning, Medical College of Ohio at Toledo. Funding was supplied by a predoctoral grant from the National Institute on Aging to RMS.
REFERENCES I. Buijs, R. lntra- and extrahypothalamic vasopressin and oxytocin pathways in the rat. Cell Tissue Res 192: 423--429, 1978. 2. De Vries, G. and R. Buijs. The origin of the vasopressinergic and oxytocinergic innervation of the rat brain with special reference to the lateral septum. Brain Res 273: 307-317, 1983. 3. De Wied, D. Inhibitory effects of ACTh and related peptides on extinction of conditioned avoidance behavior in rats. Proc Soc Exp Biol Med 122: 28-35, 1966. 4. McEwen, B., B. Stephenson and L. Krey. Radioimmunoassay of brain tissue and cell nuclear corticosterone. J Neurosci Methods 3: 57-65, 1980. 5. Reid. 1. A. Salt and water regulation. In: Brain Peptides, edited by D. T. Krieger, M. J. Brownstein and J. B. Martin. New York: John Wiley and Sons, 1983, pp. 333--348. 6. Rivier, C. and W. Vale. Modulation of stress-induced ACTH release by corticotropin-releasing factor, catecholamines and vasopressin. Nature 305: 325-327, 1983. 7. Sapolsky, R. M.. L. C. Krey and B. S. McEwen. Stress downregulates corticosterone receptors in a site-specific manner in the brain. Endocrinology 114: 287-292, 1984.
8. Sapolsky, R. M., L. C. Krey, B. S. McEwen and T. C. Rainbow. Do vasopressin-related peptides induce hippocampal corticosterone receptors.'? Implications for aging. J Neurosci 4: 1479-1485, 1984. 9. Sapolsky, R. M., B. S. McEwen and T. C. Rainbow. Quantitative autoradiography of 3H corticosterone receptors in rat brain. Brain Res 271: 331-337, 1983. 10. Silverman, A. J., D. Hoffman, C. A. Gadde, L. C. Krey and E. A. Zimmerman. Adrenal steroid inhibition of the vasopressinneurophysin neurosecretory system to the median eminence of the rat. Neuroendocrinology 32: 129--133, 1981. ! 1. Veldhuis, H. and E. R. DeKioet. Vasopressin-related peptides increase the hippocampal corticosterone receptor capacity of diabetes insipidus (Brattleboro) rats. Endocrinology 110: 153157, 1982. 12. Zimmerman, E. A. Oxytocin, vasopressin, and neurophysins. In: Brain Peptides, edited by D. T. Kreiger, M. J. Brownstein and J. B. Martin. New York: John Wiley and Sons, 1983, pp. 597-612.