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ADRENOCORTICAL HORMONES AND AVOIDANCE BEHAVIOUR OF RATS B. BOHUSand K. LJSSAK Institute of Physiology, University Medical School, P&s, Hungary (Accepted
Summary-The effect of cortisone treatment as well as of adrenalectomy on conditioned avoidance and goal-directed intertrial behaviour was investigated. Cortisone treatment during acquisition resulted in a decrease in intertrial goal-directed activity without afkting the acquisition of the avoidance response. Adrenalectomy performed 1 day prior to conditioning brought about an enhancement of intertrial activity, whilst no changes in avoidance acquisition were observed when the rats were maintained on saline or DOCA treatment. A delay of extincExtinction of avoidance response was facilitated by cortisone treatment. tion was observed in adrenalectomized rats operated prior to the extinction procedure, INTRODUCTION OBSERVATJONS from
this laboratory suggest that pituitary-adrenal hormones affect conditioned behaviour of dogs, cats and rats in both avoidance and approach situations (LJSSAKand ENDR~~CZI,1964; BOHUSand ENDR~~CZJ,1965). However, recent evidence suggests that adrenocorticotropic hormone (ACTH) or ACTH-like peptides may influence fear-motivated behaviour through an extra-adrenal mechanism (MILLER and OGAWA, 1962; DE WJED, 1965, 1966; BOHUSand DE WJED, 1966). Furthermore, DE WIED (1966a), reported that administration of dexamethasone or corticosterone during the extinction of a conditioned avoidance response resulted in a facilitation of extinction, this effect being opposite to that obtained with ACTH or ACTH-like peptides. It is of interest, therefore, to study the acquisition and extinction of an avoidance response of cortisone-treated or adrenalectomized rats and, in particular, to ascertain whether behavioural changes following the administration of ACTH observed in previous studies (BOHUS and ENDR~CZJ, 1965) are due to the subsequent increase in adrenal corticosteroid secretion. METHODS
Adult male albino rats of an inbred strain were used. The rats were fed on rat purine chow and allowed to drink water ad libitum. Avoidance conditioning was performed in a one-compartment box (50 x 50 cm), the grid floor of which served for delivering the unconditioned stimulus (US) of shock (50 V, d.c.). The rats could avoid the shock by jumping onto a platform. A bell was used as the conditioned stimulus (CS). This was presented 10 set prior to the US. The CS-US combination was terminated as soon as the rats escaped onto the platform. If the animals had jumped onto the platform within 10 set, the CS was immediately terminated and the rats avoided the shock. Twelve or 20 conditioning trials were given in each daily session. Thirty set following the onset of CS the rats were removed from the platform. When intertrial goal-directed 301 B
B. BOWS and K.
responses occurred, i.e. when the rats jumped onto the platform during the intertrial interval, they were placed back onto the grid floor immediately. Conditioning trials were given with a fixed intertrial interval of 60 sec. Acquisition of the conditioned avoidance response (CAR) was studied by conditioning the rats for 10 days with 12 trials per day. When extinction of the CAR was investigated, 20 trials were given daily until the learning criterion was achieved-thirty-six or more avoidances during two consecutive days. Those rats which reached the criterion were put on a I4-day extinction procedure. The schedule for extinction was the same as that for conditioning except that the US of shock was never presented and the CS was tcrminated after IO set when avoidance response did not occur. The number of CAR’s and of intertrial responses (ITR’s) was recorded. The total number of CAR’s scored during conditioning or extinction served as the index of avoidance bchaviour for each rat. Cortisone acetate (Adreson, Organon, Holland) was used for treatment. The hormone was injected subcutaneously 2 hr prior to the session. Bilateral adrenalectomy was performed under ether anaesthesia through lumbar approach. Adrenalectomized rats were either allowed to drink a 1% solution of sodium chloride or maintained on deoxycorticostcrone acetate (DOCA) supplementary therapy. DOCA was given subcutaneously every other day in a dose of 500 pg/rat. The salt preference test was used to exclude accessory adrenals. A comparison was made of the uptake of 3% saline solution and of distilled water by adrcnalectomized rats and sham-operated controls during 3 consecutive days. Statistical evaluation of results was carried out by means of Student’s t-distribution test.
RESULTS As shown
in Table I, administration of 2.0 or I.0 mg of cortisone/l00 g body weight during conditioning did not affect the acquisition of the conditioned avoidance response. However, intertrial behaviour of those rats treated with cortisone was markedly influenced. Cortisone treatment at both dose-levels brought about a significant decrease in the number The difference between the two groups treated with of goal-directed intertrial responses. I.0 or 2.0 mg of cortisone was not significant. TABLE
Treatment Cortisone 2.0 mg/lOO g b.w./day Cortisone I.0 mg/lOO g b.w./day Saline
No. of rats 12 11 17
CA R’s 99.2&7*8* 98.0% 13.5 98.2f6.7
ITR’s 12.5,1:4*9t 21.2zk6.lt 56.819~1
*Mean i standard error of mean. fsignificant at O+Ol level.
Adrenalectomy performed 1 day prior to the first session of conditioning did not also affect the acquisition of the avoidance response when operated rats were maintained on saline (Table 2). On the other hand, the number of ITR’s was significantly higher in adrenalectomized rats. Significant disturbance in the acquisition of CAR was observed in adrenalectomized
Adrenocortical TABLE 2.
hormones and avoidance behaviour of rats
EFFECTOF ADRENALECTOMY ON ACQUISITION OF AVOIDANCEHESPONWAND ON INTERTRIAL BEHAVIOUR OF RATS MAINTAINEDON SALINE
No. of rats
1 day prior to conditioning
97*3110*0* Y5-6zk Il.9
102.6119.2t 40.3 119-5
*Mean & standard error of mean. tsignificant at O+lOl level.
therapy (Fig. 1). Since the escape response had longer latency in adrenalectomized rats, the CS-US interval was increased to I5 set to acquisition. As shown in Fig. 1, avoidance acquisition did not vary in rats with or without supplementary therapy.
of performance study avoidance adrenalcctomized
Adrex on Deco /cs-us: IO set/ Adrex on Saline KS-US: 15 set/ Adrex KS-US:15 se0
'Y. Adrex .' KS -us: 10 set
I 3 Days
FIG. 1. Avoidance
acquisition of adrenalectomized rats maintained tap water in two conditioning schedules.
on saline, DOCA or
Forty-five rats were conditioned to achieve the learning criterion and then divided randomly into three groups. In the two groups treated with 2.0 or I.0 mg of cortisone throughout, extinction of the CAR took place at a faster rate (Fig. 2). The total number of CAR’s scored during extinction was 87.0&12.0 in rats treated with 2.0 mg of cortisone daily, and 125*5&l 1.7 in those treated with 1.0 mg of the hormone. Avoidance performance in cortisone-treated rats was significantly lower at the OGll level compared to the saline-treated controls (190*5&14+). The difference between the two cortisonetreated groups was also significant at the 0.01 level. Of a further twenty-eight rats conditioned to achieve the learning criterion, sixteen were adrenalectomized and twelve sham-operated after the last session of conditioning. An extinction run of 14 days was made without a recovery period after the operation. Eight of the adrenalectomized rats were maintained on saline while the others were on DOCA treatment. A delay in the extinction of CAR was observed in both groups of adrenalectomized rats (Fig. 3). The total number of CAR’s in those maintained on saline
B. BOHUSand K. L&K
mg Cortisone Treatment
FIG. 2. Effect of cortisone treatment on avoidance extinction
\ \,Shom \
FIG. 3. Avoidance extinction of adrenalectomized
rats maintained on saline or DOCA.
was 197.651 I.2 compared to 1924h9.7 in the group maintained on DOCA treatment. Avoidance performance of these animals was significantly (p
The experiments described above demonstrate clearly that excess or absence of adrenocortical hormones affects the acquisition and extinction of a conditioned avoidance response in different ways. Treatment with cortisone did not influence the acquisition of the avoidance habit. Adrenalectomized rats maintained on either saline or DOCA treatment acquired the avoidance response similarly to the controls. MOYER (1958) and MOYER et al (1959), have demonstrated an unimpaired learning function of adrenalectomized rats. Although an
Adrenocorticalhormones and avoidancebehaviour of rats
important role of corticosteroids in maintaining the appropriate physical conditions for performance of the motor pattern of avoidance response at normal speed, the present experiments suggest that the role of corticosteroids is to maintain a normal and/or sensory function, since, using a longer CS-US interval, adrenalectomized rats acquired the avoidance habit as successfully as controls. Extinction of the one-way conditioned avoidance response was more markedly affected by adrenocortical function. Removal of the adrenals prior to extinction resulted in its delay. Cortisone treatment during the extinction led to its dose-dependent facilitation. Similar observations were made by DE WIED (1966a), using rats treated with dexamethasone or corticosterone in a shuttle-box avoidance situation. These observations clearly demonstrated that corticosteroids play a substantial role in the extinction of a fear-motivated response. There is ample evidence to suggest that ACTH or ACTH-like peptides delay the extinction of fear-motivated responses through extra-adrenal mechanisms (MILLER and OGAWA, 1962; DE WIED, 1965, 1966; BOHUSand DE WIED, 1966). Adrenalectomy is known to increase the release of pituitary ACTH (GEMZELLet al., 1951; BARRETTet al., 1957). On the other hand, suppression of ACTH release occurs following treatment with corticosteroids (GEMZELLet al., 1951). Thus, changes in the rate of extinction of the conditioned avoidance response in adrenalectomized or cortisone-treated rats may be due to the increase or suppression of pituitary ACTH release. However, it is known that some days after adrenalectomy, an increase of pituitary ACTH release develops (GEMZELLet al., 1951; BARRETTet al., 1957; ULRICHand SLUSHER,1964). Furthermore, supplementary deoxycorticosterone suppresses the release of ACTH without affecting the rate of extinction. This data may suggest that adrenocortical hormones influence the extinction of avoidance response without involving the anterior pituitary. According to the present experiments, changes in the rate of avoidance extinction are elicited by the excess or absence of glucocorticosteroids. Intertrial goal-directed activity of the rats during conditioning was markedly affected by either cortisone treatment or adrenalectomy, being significantly diminished by cortisone. However, there were no significant differences between the effect of the two doses of cortisone. Furthermore, adrenalectomy performed one day prior to conditioning resulted in an increase of intertrial activity. This increased intertrial goal-directed activity of adrenalectomized rats was not affected by a mineralocorticosteroid (DOCA) treatment used for supplementary therapy. These observations suggest an effect of glucocorticosteroids on the goal-directed intertrial activity of the rats. ENDR~CZIand LISSAK(1962), suggested that goal-directed intertrial responses represent the somato-motoric manifestation drive motivating conditioned response. Avoidance responses are known to be motivated by fear. BRUSH (1962) assumed that intertrial responses represent the fear level of rats in the avoidance situation. These experiments suggest that the cortisone effect is manifest in suppression of fear in the avoidance situation, while a high number of intertrial responses in the absence of endogenous corticosteroids may represent a higher fear-level in adrenalectomized rats. This suggestion may also explain the marked effect of cortisone on the extinction of the conditioned avoidance response. Avoidance responses during conditioning are motivated by the electric shock and by the fear from shock (BARRY and MILLER, 1965). Avoidance performance during extinction is motivated only by fear in the absence of shock-reinforcement. The rapid extinction observed during cortisone treatment may be
B. BOHUS and K. LISSAK
due to the suppression of fear by glucocorticosteroid. If this hypothesis is correct, the present observations suggest that corticosteroids act in the avoidance situation by suppressing fear-motivated responses. Failure of cortisone to affect avoidance learning may be due to reinforcement by the shock itself. REFERENCES BARRETT, A. M., HODGES, J. R. and SAYERS, G. (1957). The influence of sex, adrenalectomy and stress on blood ACT’H levels in the rat. J. Endocr. 16: XIII. BAKRY, H. III and MILLER, N. E. (1965). Comparison of drug effects on approach, avoidance and escape motivation. J. camp. physiol. Psychol. 59: 18-24. BOHUS, B. and ENDRBCZI, E. (1965). The influence of pituitary-adrenocortical function on the avoiding conditioned reflex activity. Acta physiol. hung. 26: 183-l 89. Bouus, B. and DE WIED, D. (1966). Inhibitory and facilitatory effect of two related peptides on extinction of avoidance behavior. Science, N. Y. 153: 3 18-320. BRUSH, F. R. (1962). The effects of intertrial interval on avoidance learning in the rat. J. camp. physiol. Psychol. 55: 888-892. DE WIED, D. (1965). The influence of the posterior and intermediate lobe of the pituitary and pituitary peptides on the maintenance of a conditioned avoidance response in rats. Int. J. Neuropharmacol. 4: 157-167. DE WIED, D. (1966). Inhibitory effect of ACI’H and related peptides on extinction of conditioned avoidance behavior. Proc. Sot. exp. Biol. Med. 122: 28-32. DE WIED, D. (1966a). Antagonistic effect of ACTH and glucocorticoids on avoidance behavior of rats. 2nd Int. Congr. on Hormonal Steroids, Excpt. Med. Znt. Congr. Series 111: 89. ENDRBCZI, E. and LISSAK, K. (1962). Spontaneous goal-directed motor activity related to the alimentary conditioned reflex behaviour and its regulation by neural and humoral factors. Acta physiol. hrmE. 21: 265-283. GEMZELL, C. A., VAN DYKE, D. C., TOBIAS, C. A. and EVANS, H. M. (1951). Increase in formation and secretion of ACTH following adrenalectomy. Endocrinology 49: 325-336. LISSAK. K. and ENDR~CZI. E. (1964). Neuroendocrine interelationships and behavioural processes. In: M&or Problems in Nekoen>ocri~ology (BAJUSZ, E. and JASMIN, G., Eds.), pp. l-16. S. Karger, Basel, New York. MILLER, R. E. and OCAWA, N. (1962). The effect of adrenocorticotrophic hormone (ACTH) on avoidance conditioning in the adrenalectomized rat. J. camp. physiol. Psycho/. 55: 211-213. MOYER, K. E. (1958). Effect of adrenalectomy on anxiety motivated behavior. J. genet. Psychof. 92: 11-16. MOYER, K. E. and BUNNEL, B. N. (1959). Effect of adrenal demedullation on an avoidance response in the rat. J. camp. physiol. Psychol. 52: 215-216. ULRICH, R. and SLUSHER, M. A. (1964). Blood levels of ACTH in individual adrenalectomized rats. Endocrinology 75: 483-487.