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Neonatal corticosterone treatment increases submissiveness in adulthood in mice
Physiology & Behavior, Vol. 19, pp. 163-165. Pergamon Press and Bram Research Publ., 1977. Printed m the U.S.A.
BRIEF COMMUNICATION Neonatal Corticosterone Treatment Increases Submissiveness in Adulthood in Mice l A L A N I. L E S H N E R A N D S U S A N M. S C H W A R T Z
Department o f Psychology, Bucknell University, Lewisburg, PA 17837 (Received 8 D e c e m b e r 1976) LESHNER, A. I. AND S.M. SCHWARTZ. Neonatal corttcosterone treatment increases submtssiveness tn adulthood in mice. PHYSIOL. BEHAV. 19(1) 163-165, 1977. - - Mice were treated with either a placebo, 100 or 300 mcg/day corticosterone during postnatal Days 3 - 5 and tested for submissiveness in adulthood. Neonatal corticosterone treatment, regardless of dosage level, resulted in increased adult levels of submissiveness. This effect cannot be ascribed to differences in adult resting corticosterone levels, since neonatal corticosterone- and placebo-treated mice did not differ in the levels of this hormone. Some alternative explanations of this effect of neonatal corticosterone treatment on adult social behavior are discussed. Neonatal corticosterone treatment
Submissiveness
Social behavior
• HE H O R M O N A L e n v i r o n m e n t during early stages o f d e v e l o p m e n t appears critical to b o t h the form and Intensity of m a n y behaviors e x h i b i t e d m a d u l t h o o d , since changing the early h o r m o n a l state can p r o d u c e p r o f o u n d and long-lasting changes m adult behavior patterns. A l t h o u g h m o s t studies have focused on the role of the gonadal h o r m o n e s in determining adult sexual and aggressive responses [2, 5, 9, 11], some recent studies [6,13] suggest that manipulating the level of the pltuitary-adrenocortical h o r m o n e s during early d e v e l o p m e n t a l periods can have marked effects on adult e m o t i o n a l responses. We report here the results of a study showing that increasing c o r t i c o s t e r o n e levels during postnatal Days 3 - 5 in mice also affects at least one socml behavior in a d u l t h o o d , submissiveness
p.m. The male pups were separated from their mothers and female littermates at 32 days of age. The males were housed in groups of 3 - 7 llttermates/cage for 8 - 1 0 days, after which t h e y were indwidually housed for two additional weeks prior to testing. In order to m i n i m i z e potential litter effects, each of the final three groups consisted of mice f r o m at least four different litters. The mice were given free access to f o o d and water t h r o u g h o u t The breeding and colony r o o m s were maintained on a 12 hr h g h t / d a r k cycle ( 6 : 0 0 a.m. - 6 : 0 0 p.m., hght), and the r o o m t e m p e r a t u r e was controlled at 24 + I°C. Submissiveness was assessed during an e n c o u n t e r b e t w e e n an e x p e r i m e n t a l anxmal and an o p p o n e n t m a neutral arena. The arena was a w o o d e n box measuring 30.5 × 30 5 × 45.7 cm. The o p p o n e n t s were untreated, adult male CD-1 mice that had been housed in isolation for eaght weeks in order to enhance aggressiveness [15, 16, 18]. For the e n c o u n t e r , the e x p e r i m e n t a l and o p p o n e n t ammals were placed t o g e t h e r into the arena and allowed to interact until the e x p e r i m e n t a l a m m a l submxtted. The test animal was considered to have submitted when it displayed the upright submissive posture, e m i t t e d high-pitched squeaks, and failed to fight back when subsequently attacked by the o p p o n e n t [3, 12, 14]. Three measures were recorded during the e n c o u n t e r . (a) the time from the start of the e n c o u n t e r until the o p p o n e n t attacked the test a m m a l (latency to attack), (b) the time f r o m the start of the
METHOD Thirty-six male, albino CD-1 mice bred in our l a b o r a t o r y were tested for submissiveness at 5 4 - 5 8 days of age. D t t e r s had been culled to eight pups at birth, and each litter was assigned as a whole to one of three conditions. On postnatal Days 3 - 5 , all pups in each h t t e r received injections of either 0 (Placebo), 100 or 300 m c g / d a y c o r t i c o s t e r o n e (Nutritional Biochemical Corp.) m 0.02 cc steroid suspending vehicle. All rejections were admimstered subcutaneously b e t w e e n the hours of 11:00 a.m. and 1:00
Supported in part by Research Grant No. BMS-75-08120 from NSF. During completion of this project, the first author was a Visiting Scientist at the Wisconsin Regional Primate Research Center and was supported by National Research Service Award No. HD-05394 from NICHD. The authors thank O. Floody for critical comments on an earlier version of the manuscript, and M. Breen, J. Politch and K. Roche for technical assistance. Steroid suspending vehicle was generously provided by Drug Research and Development Chemotherapy, N.C.I. 163
164
t [ : S H N t R A \ I ) hi Ilia \ l ( I /
TABLE
1
MEANS _+ S T A N D A R D ERRORS OF B E H A V I O R A L A N D P H Y S I O L O G I C A L MEASURES
Group
n
Latency to Attack (sec)
Placebo 100 mcg 300 mcg
9 14 13
1647_+616 165.4+-512 1381+_286
encounter until the experimental ammal submitted (latency to s u b m i t ) , a n d (c) t h e n u m b e r of a t t a c k s b y the o p p o n e n t n e e d e d to i n d u c e s u b m i s s i o n m t h e test a m m a l The i n t e r v a l b e t w e e n t h e first a t t a c k b y the o p p o n e n t a n d s u b m i s s i o n by t h e test a n i m a l was used as o n e m e a s u r e of submissiveness ( t h e s h o r t e r the interval, t h e m o r e submissive t h e a m m a l ) , and t h e n u m b e r of a t t a c k s n e e d e d to r e d u c e s u b m i s s i o n was used as the s e c o n d m e a s u r e of submlSslveness ( t h e fewer attacks reqmred, the m o r e submissive t h e test a n i m a l ) . All e n c o u n t e r s were c o n d u c t e d b e t w e e n t h e h o u r s of 9 0 0 a.m. and 12 0 0 n o o n RESULTS AND DISCUSSION
A c c o r d i n g to b o t h m e a s u r e s o f s u b m t s s w e n e s s used m th~s s t u d y , the t w o g r o u p s o f m~ce t r e a t e d n e o n a t a l l y w i t h c o r t t c o s t e r o n e were m o r e submissive t h a n the p l a c e b o t r e a t e d m~ce Further, the two cortlcosterone-treated groups did n o t d i f f e r s l g n i h c a n t l y f r o m each o t h e r o n any measure. As s h o w n m Table 1, a l t h o u g h all g r o u p s were a t t a c k e d equally readily by t h e o p p o n e n t s , F ( 2 , 3 3 ) = 0.10, p > 0 . 0 5 , t h e c o r t l c o s t e r o n e - t r e a t e d mice s u b m i t t e d m o r e rapidly t h a n t h e p l a c e b o - t r e a t e d mice, F ( 2 , 3 3 ) = 7.67, p<0.005 In a d d i t i o n , f e w e r a t t a c k s were r e q u i r e d to induce submission m the cortlcosterone-treated animals t h a n m the p l a c e b o - t r e a t e d ammals, F ( 2 , 3 3 ) = 4 8 5 , p < 0 025 T h e r e f o r e , t r e a t i n g mice w i t h c o r t l c o s t e r o n e at dosage levels of e i t h e r 100 or 300 m c g / d a y d u r i n g p o s t n a t a l Days 3 - 5 increases t h e i r s u b m i s s i v e n e s s in a d u l t h o o d In seeking an e x p l a n a t i o n for these findings we exa m i n e d a d u l t r e s t i n g c o r t l c o s t e r o n e levels Previous studies had s h o w n t h a t raising or l o w e r i n g c o r t l c o s t e r o n e levels in a d u l t h o o d has d r a m a t i c e f f e c t s o n b o t h t h e t e n d e n c y to avoid a t t a c k a n d s u b m i s s w e n e s s [10] T h e r e f o r e , we t h o u g h t t h a t t h e effects o b s e r v e d m th~s s t u d y m i g h t be due to d i f f e r e n c e s in a d u l t b a s e h n e c o r t l c o s t e r o n e levels r e d u c e d b y d i f f e r e n t i a l c o r t ~ c o s t e r o n e t r e a t m e n t d u r i n g the n e o n a t a l p e r i o d Seven days a f t e r t e s t i n g we collected t r u n k b l o o d samples b y d e c a p i t a t i o n d u r i n g the same m o r n i n g t i m e p e r i o d as w h e n t e s t i n g had b e e n c o n d u c t e d . Plasma c o r t l c o s t e r o n e levels were assayed using a m l c r o f l u o r o m e t r i c t e c h n i q u e [4] E x a m i n a t i o n o f a d u l t resting c o r t l c o s t e r o n e levels ( T a b l e 1) revealed n o significant d i f f e r e n c e s a m o n g the groups, F(2,33) = 084, p>005 T h e r e f o r e , the increased sub-
Latency to Submit-Latency to Attack (sec) 298.9_+1089 448_+ 200 63.5+_ 210
Plasma Attacks to Cort~costerone Submission (#) (mcg/100 ml) 119_+4~ 36_+05 55_+07
140_+21 116+_20 104+_18
mlsslveness o f mice t r e a t e d n e o n a t a l l y w i t h c o r t l c o s t e r o n e m u s t be due to some f a c t o r o t h e r t h a n changes in a d u l t resting c o r t l c o s t e r o n e levels One a l t e r n a t i v e e x p l a n a t i o n of the effects of n e o n a t a l c o r t i c o s t e r o n e t r e a t m e n t o n a d u l t submissiveness m i g h t be t h a t a l t h o u g h this t r e a t m e n t does n o t a f f e c t resting c o r t l c o s t e r o n e levels m a d u l t mice, this t r e a t m e n t m i g h t affect e i t h e r t h e p a t t e r n o f a d r e n o c o r t i c a l s e c r e t i o n or the r e s p o n s l v l t y of t h e a d r e n a l c o r t e x t o stressful s t i m u h ( s u c h as a t t a c k ) . However, studies of the rat [7, 8, 17] have s h o w n n e o n a t a l c o r t l c o s t e r o n e t r e a t m e n t t o be w i t h o u t effect o n e i t h e r t h e c~rcadlan perlod~clty o f c o r t l c o s t e r o n e s e c r e t i o n or t h e r e s p o n s i v e n e s s o f the a d r e n a l c o r t e x to A C T H or stress e x p o s u r e m a d u l t h o o d T h e r e f o r e , it w o u l d seem u n h k e l y t h a t changes in e i t h e r p i t u i t a r y - a d r e n a l r h y t h m s or r e a c t w l t y to stress c o u l d a c c o u n t for the b e h a v i o r a l effects o f n e o n a t a l c o r t l c o s t e r o n e t r e a t m e n t o b s e r v e d m this s t u d y o f the m o u s e . A s e c o n d possible e x p l a n a t i o n o f the findings of this s t u d y is t h a t n e o n a t a l c o r t l c o s t e r o n e t r e a t m e n t m~ght p r o d u c e some long-lasting general m e t a b o h c a b n o r m a l i t y t h a t c o u l d result in increased b e h a v i o r a l r e s p o n d i n g to social stress. However, m a n o t h e r s t u d y ( L e s h n e r and S c h w a r t z , u n p u b h s h e d ) we f o u n d n o e f f e c t o f s i m d a r n e o n a t a l c o r t l c o s t e r o n e t r e a t m e n t s o n a d u l t b o d y weight levels, a measure o f t e n used as an i n d e x ot the general h e a l t h of an a m m a l T h e r e f o r e , we b e h e v e it u n h k e l y t h a t mice t r e a t e d n e o n a t a l l y w i t h cort~costerone are m o r e s u b m l s s w e m a d u l t h o o d because t h e y suffer f r o m some general m e t a b o h c & s t u r b a n c e O f course, this p o s s l b d l t y has n o t b e e n studied directly, and an e v a l u a t i o n of its a d e q u a c y as an e x p l a n a t i o n for the effects o f n e o n a t a l cort~costerone t r e a t m e n t on adult s u b m i s s w e n e s s will have to awatt f u r t h e r studies A final p o s s l b l h t y is t h a t n e o n a t a l c o r t l c o s t e r o n e treatm e n t m a y increase submlss~veness b y p r o d u c i n g p e r m a n e n t changes in the states o f t h e n e u r a l c~rcu~ts t h a t will be involved m the c o n t r o l of submissive r e s p o n d i n g m adulth o o d . P o s t n a t a l t r e a t m e n t w~th thas steroid has b e e n s h o w n to m o d i f y p e r m a n e n t l y b o t h n e u r a l s t r u c t u r e s a n d n e u r a l o r g a m z a t l o n [1,7] These c h a n g e s in b r a i n f u n c t i o n m a y include c h a n g e s m the states of the n e u r a l circuits t h a t c o n t r o l the d e v e l o p m e n t and e x p r e s s i o n of submissiveness
REFERENCES
1. CotterreU, M., R. Balazs and A L. Johnson Effects of cortleosterolds on the biochemical maturation of rat brain postnatal cell formation. J. Neurochem 19: 2151-2167, 1972.
2. Davldson, J.M. Hormones and reproductive behavior. In Hormones and Behavior. edited by S Levme New York" AcademlcPress, 1971, pp. 6 4 - 1 3 4
CORTICOSTERONE
AND SUBMISSIVENESS
3. Gmsburg, B. and W. C. Allee. Some effects of conditioning on social dominance and subordination in inbred strains of mice. Physiol. Zool. 15: 4 8 5 - 5 0 6 , 1942. 4. Glick, D., D. yon Redhch and S. Levine. Fluorometnc determination of corticosterone and cortlsol m 0.02-0.05 ml of plasma or submilligram samples of adrenal tissue. Endocrinology 74: 6 5 3 - 6 5 5 , 1964. 5. Goy, R.W. and D.A. Goldfoot. Experiential and hormonal factors influencing development of sexual behavior in the male rhesus monkey. In: The Neurosciences, Third Study Program, edited by F. O. Schmltt and F G. Worden. Cambridge MIT Press, 1974, pp. 5 7 1 - 5 8 1 . 6. Howard, E. Increased reactwity and impaired adaptability m operant behavior of adult mice given corticosterone in infancy. J. comp. physiol. Psychol. 8 5 : 2 1 1 - 2 2 0 , 1973. 7. Krieger, D.T. Circadian corticosterold periodicity, critical period for abolition by neonatal injection of cortlcosteroid. Science 178: 1205-1207, 1972. 8. Krieger, D.T. Effect of neonatal hydrocortisone on cortv costeroid circadian periodicity, responsiveness to ACTH and stress m prepuberal and adult rats. Neuroendocrinology 16: 3 5 5 - 3 6 3 , 1974. 9. Leshner, A.I. A model of hormones and agonlstlc behavior. Physiol. Behav. 15: 2 2 5 - 2 3 5 , 1975. 10. Moyer, J.A. and A.I. Leshner. Pituitary-adrenal effects on avoidance-of-attack in mice separation of the effects of ACTH and corticosterone. Physiol. Behav. 17: 2 9 5 - 3 0 1 , 1976.
165 11. Moyer, K. E. Sex differences in aggression. In. Sex Differences in Behavtor, edited by R. C. Friedman, R. M. Rlchart and R. L Vande Wiele. New York: John Wiley, 1974, pp. 335-372. 12. Nock, B.L. and A.I. Leshner. Hormonal mediation of the effects of defeat on agomsUc responding m mice. Physiol. Behav 17" 111-119, 1976. 13. Nyakas, C. and E. Endroczi. Effect of neonatal corticosterone admmlstratlon on behavioral and pitultary-adrenocortical responses in the rat. Acta phystol Acad. Sct. hung 42: 2 3 1 - 2 4 1 , 1972. 14. Scott, J.P. Incomplete adjustment caused by frustration of untrained fighter mice. J. comp. physiol. Psychol. 39: 3 7 9 - 3 9 0 , 1946. 15. Sigg, E. B. Relationship of aggressive behavlour to adrenal and gonadal function in mice. In. Aggresstve Behavtour, edited by S. Garattim and E. B. Slgg. New York: John Wiley, 1969, pp. 143-149. 16. Sigg, E B., C. Day and C. Colombo. Endocrine factors m isolation-reduced aggression in rodents. Endocrinology 78: 6 7 9 - 6 8 4 , 1966. 17. Turner, B.B. and A.N. Taylor. Perslstertt alteraUon of pituitary-adrenal function m the rat by prepuberal cortlcosterone treatment. Endocrinology 9 8 : 1 - 9 , 1976. 18. ValzeUi, L. Aggressive behaviour induced by isolation. In Aggres%zve Behavtour, edited by S Garattml and E. B Sigg. New York John Wiley, 1969, pp. 7 0 - 7 6
BRIEF COMMUNICATION Neonatal Corticosterone Treatment Increases Submissiveness in Adulthood in Mice l A L A N I. L E S H N E R A N D S U S A N M. S C H W A R T Z
Department o f Psychology, Bucknell University, Lewisburg, PA 17837 (Received 8 D e c e m b e r 1976) LESHNER, A. I. AND S.M. SCHWARTZ. Neonatal corttcosterone treatment increases submtssiveness tn adulthood in mice. PHYSIOL. BEHAV. 19(1) 163-165, 1977. - - Mice were treated with either a placebo, 100 or 300 mcg/day corticosterone during postnatal Days 3 - 5 and tested for submissiveness in adulthood. Neonatal corticosterone treatment, regardless of dosage level, resulted in increased adult levels of submissiveness. This effect cannot be ascribed to differences in adult resting corticosterone levels, since neonatal corticosterone- and placebo-treated mice did not differ in the levels of this hormone. Some alternative explanations of this effect of neonatal corticosterone treatment on adult social behavior are discussed. Neonatal corticosterone treatment
Submissiveness
Social behavior
• HE H O R M O N A L e n v i r o n m e n t during early stages o f d e v e l o p m e n t appears critical to b o t h the form and Intensity of m a n y behaviors e x h i b i t e d m a d u l t h o o d , since changing the early h o r m o n a l state can p r o d u c e p r o f o u n d and long-lasting changes m adult behavior patterns. A l t h o u g h m o s t studies have focused on the role of the gonadal h o r m o n e s in determining adult sexual and aggressive responses [2, 5, 9, 11], some recent studies [6,13] suggest that manipulating the level of the pltuitary-adrenocortical h o r m o n e s during early d e v e l o p m e n t a l periods can have marked effects on adult e m o t i o n a l responses. We report here the results of a study showing that increasing c o r t i c o s t e r o n e levels during postnatal Days 3 - 5 in mice also affects at least one socml behavior in a d u l t h o o d , submissiveness
p.m. The male pups were separated from their mothers and female littermates at 32 days of age. The males were housed in groups of 3 - 7 llttermates/cage for 8 - 1 0 days, after which t h e y were indwidually housed for two additional weeks prior to testing. In order to m i n i m i z e potential litter effects, each of the final three groups consisted of mice f r o m at least four different litters. The mice were given free access to f o o d and water t h r o u g h o u t The breeding and colony r o o m s were maintained on a 12 hr h g h t / d a r k cycle ( 6 : 0 0 a.m. - 6 : 0 0 p.m., hght), and the r o o m t e m p e r a t u r e was controlled at 24 + I°C. Submissiveness was assessed during an e n c o u n t e r b e t w e e n an e x p e r i m e n t a l anxmal and an o p p o n e n t m a neutral arena. The arena was a w o o d e n box measuring 30.5 × 30 5 × 45.7 cm. The o p p o n e n t s were untreated, adult male CD-1 mice that had been housed in isolation for eaght weeks in order to enhance aggressiveness [15, 16, 18]. For the e n c o u n t e r , the e x p e r i m e n t a l and o p p o n e n t ammals were placed t o g e t h e r into the arena and allowed to interact until the e x p e r i m e n t a l a m m a l submxtted. The test animal was considered to have submitted when it displayed the upright submissive posture, e m i t t e d high-pitched squeaks, and failed to fight back when subsequently attacked by the o p p o n e n t [3, 12, 14]. Three measures were recorded during the e n c o u n t e r . (a) the time from the start of the e n c o u n t e r until the o p p o n e n t attacked the test a m m a l (latency to attack), (b) the time f r o m the start of the
METHOD Thirty-six male, albino CD-1 mice bred in our l a b o r a t o r y were tested for submissiveness at 5 4 - 5 8 days of age. D t t e r s had been culled to eight pups at birth, and each litter was assigned as a whole to one of three conditions. On postnatal Days 3 - 5 , all pups in each h t t e r received injections of either 0 (Placebo), 100 or 300 m c g / d a y c o r t i c o s t e r o n e (Nutritional Biochemical Corp.) m 0.02 cc steroid suspending vehicle. All rejections were admimstered subcutaneously b e t w e e n the hours of 11:00 a.m. and 1:00
Supported in part by Research Grant No. BMS-75-08120 from NSF. During completion of this project, the first author was a Visiting Scientist at the Wisconsin Regional Primate Research Center and was supported by National Research Service Award No. HD-05394 from NICHD. The authors thank O. Floody for critical comments on an earlier version of the manuscript, and M. Breen, J. Politch and K. Roche for technical assistance. Steroid suspending vehicle was generously provided by Drug Research and Development Chemotherapy, N.C.I. 163
164
t [ : S H N t R A \ I ) hi Ilia \ l ( I /
TABLE
1
MEANS _+ S T A N D A R D ERRORS OF B E H A V I O R A L A N D P H Y S I O L O G I C A L MEASURES
Group
n
Latency to Attack (sec)
Placebo 100 mcg 300 mcg
9 14 13
1647_+616 165.4+-512 1381+_286
encounter until the experimental ammal submitted (latency to s u b m i t ) , a n d (c) t h e n u m b e r of a t t a c k s b y the o p p o n e n t n e e d e d to i n d u c e s u b m i s s i o n m t h e test a m m a l The i n t e r v a l b e t w e e n t h e first a t t a c k b y the o p p o n e n t a n d s u b m i s s i o n by t h e test a n i m a l was used as o n e m e a s u r e of submissiveness ( t h e s h o r t e r the interval, t h e m o r e submissive t h e a m m a l ) , and t h e n u m b e r of a t t a c k s n e e d e d to r e d u c e s u b m i s s i o n was used as the s e c o n d m e a s u r e of submlSslveness ( t h e fewer attacks reqmred, the m o r e submissive t h e test a n i m a l ) . All e n c o u n t e r s were c o n d u c t e d b e t w e e n t h e h o u r s of 9 0 0 a.m. and 12 0 0 n o o n RESULTS AND DISCUSSION
A c c o r d i n g to b o t h m e a s u r e s o f s u b m t s s w e n e s s used m th~s s t u d y , the t w o g r o u p s o f m~ce t r e a t e d n e o n a t a l l y w i t h c o r t t c o s t e r o n e were m o r e submissive t h a n the p l a c e b o t r e a t e d m~ce Further, the two cortlcosterone-treated groups did n o t d i f f e r s l g n i h c a n t l y f r o m each o t h e r o n any measure. As s h o w n m Table 1, a l t h o u g h all g r o u p s were a t t a c k e d equally readily by t h e o p p o n e n t s , F ( 2 , 3 3 ) = 0.10, p > 0 . 0 5 , t h e c o r t l c o s t e r o n e - t r e a t e d mice s u b m i t t e d m o r e rapidly t h a n t h e p l a c e b o - t r e a t e d mice, F ( 2 , 3 3 ) = 7.67, p<0.005 In a d d i t i o n , f e w e r a t t a c k s were r e q u i r e d to induce submission m the cortlcosterone-treated animals t h a n m the p l a c e b o - t r e a t e d ammals, F ( 2 , 3 3 ) = 4 8 5 , p < 0 025 T h e r e f o r e , t r e a t i n g mice w i t h c o r t l c o s t e r o n e at dosage levels of e i t h e r 100 or 300 m c g / d a y d u r i n g p o s t n a t a l Days 3 - 5 increases t h e i r s u b m i s s i v e n e s s in a d u l t h o o d In seeking an e x p l a n a t i o n for these findings we exa m i n e d a d u l t r e s t i n g c o r t l c o s t e r o n e levels Previous studies had s h o w n t h a t raising or l o w e r i n g c o r t l c o s t e r o n e levels in a d u l t h o o d has d r a m a t i c e f f e c t s o n b o t h t h e t e n d e n c y to avoid a t t a c k a n d s u b m i s s w e n e s s [10] T h e r e f o r e , we t h o u g h t t h a t t h e effects o b s e r v e d m th~s s t u d y m i g h t be due to d i f f e r e n c e s in a d u l t b a s e h n e c o r t l c o s t e r o n e levels r e d u c e d b y d i f f e r e n t i a l c o r t ~ c o s t e r o n e t r e a t m e n t d u r i n g the n e o n a t a l p e r i o d Seven days a f t e r t e s t i n g we collected t r u n k b l o o d samples b y d e c a p i t a t i o n d u r i n g the same m o r n i n g t i m e p e r i o d as w h e n t e s t i n g had b e e n c o n d u c t e d . Plasma c o r t l c o s t e r o n e levels were assayed using a m l c r o f l u o r o m e t r i c t e c h n i q u e [4] E x a m i n a t i o n o f a d u l t resting c o r t l c o s t e r o n e levels ( T a b l e 1) revealed n o significant d i f f e r e n c e s a m o n g the groups, F(2,33) = 084, p>005 T h e r e f o r e , the increased sub-
Latency to Submit-Latency to Attack (sec) 298.9_+1089 448_+ 200 63.5+_ 210
Plasma Attacks to Cort~costerone Submission (#) (mcg/100 ml) 119_+4~ 36_+05 55_+07
140_+21 116+_20 104+_18
mlsslveness o f mice t r e a t e d n e o n a t a l l y w i t h c o r t l c o s t e r o n e m u s t be due to some f a c t o r o t h e r t h a n changes in a d u l t resting c o r t l c o s t e r o n e levels One a l t e r n a t i v e e x p l a n a t i o n of the effects of n e o n a t a l c o r t i c o s t e r o n e t r e a t m e n t o n a d u l t submissiveness m i g h t be t h a t a l t h o u g h this t r e a t m e n t does n o t a f f e c t resting c o r t l c o s t e r o n e levels m a d u l t mice, this t r e a t m e n t m i g h t affect e i t h e r t h e p a t t e r n o f a d r e n o c o r t i c a l s e c r e t i o n or the r e s p o n s l v l t y of t h e a d r e n a l c o r t e x t o stressful s t i m u h ( s u c h as a t t a c k ) . However, studies of the rat [7, 8, 17] have s h o w n n e o n a t a l c o r t l c o s t e r o n e t r e a t m e n t t o be w i t h o u t effect o n e i t h e r t h e c~rcadlan perlod~clty o f c o r t l c o s t e r o n e s e c r e t i o n or t h e r e s p o n s i v e n e s s o f the a d r e n a l c o r t e x to A C T H or stress e x p o s u r e m a d u l t h o o d T h e r e f o r e , it w o u l d seem u n h k e l y t h a t changes in e i t h e r p i t u i t a r y - a d r e n a l r h y t h m s or r e a c t w l t y to stress c o u l d a c c o u n t for the b e h a v i o r a l effects o f n e o n a t a l c o r t l c o s t e r o n e t r e a t m e n t o b s e r v e d m this s t u d y o f the m o u s e . A s e c o n d possible e x p l a n a t i o n o f the findings of this s t u d y is t h a t n e o n a t a l c o r t l c o s t e r o n e t r e a t m e n t m~ght p r o d u c e some long-lasting general m e t a b o h c a b n o r m a l i t y t h a t c o u l d result in increased b e h a v i o r a l r e s p o n d i n g to social stress. However, m a n o t h e r s t u d y ( L e s h n e r and S c h w a r t z , u n p u b h s h e d ) we f o u n d n o e f f e c t o f s i m d a r n e o n a t a l c o r t l c o s t e r o n e t r e a t m e n t s o n a d u l t b o d y weight levels, a measure o f t e n used as an i n d e x ot the general h e a l t h of an a m m a l T h e r e f o r e , we b e h e v e it u n h k e l y t h a t mice t r e a t e d n e o n a t a l l y w i t h cort~costerone are m o r e s u b m l s s w e m a d u l t h o o d because t h e y suffer f r o m some general m e t a b o h c & s t u r b a n c e O f course, this p o s s l b d l t y has n o t b e e n studied directly, and an e v a l u a t i o n of its a d e q u a c y as an e x p l a n a t i o n for the effects o f n e o n a t a l cort~costerone t r e a t m e n t on adult s u b m i s s w e n e s s will have to awatt f u r t h e r studies A final p o s s l b l h t y is t h a t n e o n a t a l c o r t l c o s t e r o n e treatm e n t m a y increase submlss~veness b y p r o d u c i n g p e r m a n e n t changes in the states o f t h e n e u r a l c~rcu~ts t h a t will be involved m the c o n t r o l of submissive r e s p o n d i n g m adulth o o d . P o s t n a t a l t r e a t m e n t w~th thas steroid has b e e n s h o w n to m o d i f y p e r m a n e n t l y b o t h n e u r a l s t r u c t u r e s a n d n e u r a l o r g a m z a t l o n [1,7] These c h a n g e s in b r a i n f u n c t i o n m a y include c h a n g e s m the states of the n e u r a l circuits t h a t c o n t r o l the d e v e l o p m e n t and e x p r e s s i o n of submissiveness
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