Physiology & Behavior, Vol. 19, pp. 485--487. Pergamon Press and Brain Research Publ., 1977. Printed in the U.S.A.
Effects of Olfactory Bulbectomy and Domicile on Stress-Induced Corticosterone Release in the Rat K. D. C A I R N C R O S S, A. WREN, B. COX AND H. SCHNIEDEN
Department o f Pharmacology, Materia Medica and Therapeutics, University o f Manchester Manchester M13 9PT, England (Received 10 May, 1977) K. D. CAIRNCROSS, A. WREN, B. COX AND H. SCHNIEDEN. Effects of olfactory bulbectomy and domicile on stress induced corticosterone release in the rat. PHYSIOL. BEHAV. 19(4) 485-487, 1977. -- Following bilateral olfactory bulbectomy or sham surgery, rats were housed either in groups of 5 or individually. After 10 days the animals were sacrificed and plasma corticosterone levels were measured. Half the animals in each group received predictable stress in the form of footshock immediately prior to exsanguination. Two levels of corticosterone elevation were noted, an intermediate level (circa 40 /ug/100 ml plasma), in bulbectomised animals without stress and in sham operated animals with stress. Extreme corticosterone elevation (circa 80 #g/100 ml plasma) occurred in bulbectomised rats with stress. The type of housing had no effect on corticosterone elevation. The results are discussed in terms of a non olfactory function for the olfactory bulb, and the role of corticosterone and ACTH in acquisition learning. Stress
Bulbectomy
Corticosterone
Housing
RATS subjected to bilateral olfactory bulbectomy (BOL) exhibit a performance deficit in a one way avoidance task, accompanied by a reduction in telencephalic noradrenaline concentration [4, 5, 8]. The behavioural changes associated with bulbectomy in the rat include hypermotitity, aggression to cage mates, irritability to the experimenter and a performance deficit in passive avoidance tasks [12,14], which can be modulated by treatment with different types of psychotropic drugs [ 13,16]. It was decided to investigate whether circulating corticosterone levels could provide a physiological correlate to behavioural testing. Bassett, Cairncross and King [1] have established that plasma corticosterone elevation can be quantitated in the rat at two levels, an intermediate elevation ( 4 5 - 5 5 t~g/100 ml of blood plasma) and an extreme elevation ( 8 0 - 9 0 ~g/100 ml blood plasma). The degree of corticosterone elevation was dependent on the type of stressor to which the animal was exposed. Predictable footshock resulted in intermediate steroid elevation, whereas unpredictable footshock (even with the possibility of escape) induced extreme steroid elevation. It was concluded that extreme corticosterone elevation occurred when a psychological stressor (unpredictability) was superimposed on a physical stressor (footshock). Thus, it was decided to examine the effect of bulbectomy as a stressor, and to expose bulbectomised rats and sham operated (SO) rats to a predictable stress in the form of footshock. Plasma corticosterone levels to be measured after the stress session. Furthermore, due to the particular behavioural syndrome
including aggression associated with BOL and the effect this might have on plasma corticosterone levels, it was necessary to examine glucocorticoid concentrations in both group housed and individually housed rats. METHOD Male Sprague-Dawley rats (Manchester strain, 8 7 - 9 3 days old) were used in all experiments. The animals were housed in groups of 5 in Experiment 1, and individually in Experiment 2, under conditions of constant temperature and humidity (21 -+ 0.5°C, 45% humidity). The animals were subjected to a 14 hr day schedule (light 6 a.m. - 8 p.m.). Food and water were provided ad lib. Both control and BOL rats were handled daily during a 4 day preoperative and a 10 day postoperative recovery period.
Procedure Rats were anaesthetised with Equithesin (0.33 ml/100 g body weight IP). The head was shaved and placed in a stereotaxic frame and the skull exposed by a mid-line incision. Two holes were drilled on either side of the mid-line at a point 5 mm anterior to bregma. The olfactory bulbs were sectioned and removed by aspiration. The wound was closed and a 10 day postoperative recovery period allowed. SO rats underwent the same surgical procedure, but the olfactory lobes were not touched. Deafferentation consisted of placing a curved probe through the burr hole and severing the olfactory nerves above the cribiform plate of the ethmoid bone.
1The skilled technical assistance of Miss Christine Forster is gratefully acknowledged. 485
486
CAIRN(;ROSS 57 .ti,
Fo o tsh o ck
RESU L IS
Rats were placed in a clear perspex box 55 cm ~ with a stainless steel grid floor set at 1.5 cm centres. Footshock was delivered through the grid floor (as a 1.5 mA, 50 pulses/sec square wave) for 5 sec every 55 sec over a 30 rain period. This procedure ensured that corticosterone elevation was maximal [2]. Corticosterone Assay
In the control non-stress situation the SO and BOL rats were removed from their home-cage and sacrificed in a different room. They were exsanguinated within 2 rain of removal from the home cage, this prevented the parameter of novelty elevating the plasma corticosterone level [ 1 ]. In the stress situation SO and BOL rats were sacrificed immediately following the last stress episode. In all situations, the animals were sacrificed between 10 a.m. and noon.
Blood was collected in heparinised tubes, the samples were centrifuged to obtain cell free plasma which was stored at - 2 0 ° C . Corticosterone levels in plasma were determined subsequently by the fluorometric method of Mattingly [lO] which is specific for free l l - h y d r o x y c o r ticoids. Bulbectomy was confirmed as previously described [8]. A two tailed students t-test was used to analyse the results. J deafferentation E~
sham-operation
[~
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80.
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Unstressed
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Housing
Experiment 1
Group housed BOL rats exposed to no stressful procedure other than daily handling had a significantly higher (p< 0.00 I) circulating corticosterone level than similarly housed SO rats (Fig. 1). When the SO group housed animals were subjected to footshock a significant elevation of plasma corticosterone was observed compared with nonstressed SO controls (p
Effects of Olfactory Bulbectomy and Domicile on Stress-Induced Corticosterone Release in the Rat K. D. C A I R N C R O S S, A. WREN, B. COX AND H. SCHNIEDEN
Department o f Pharmacology, Materia Medica and Therapeutics, University o f Manchester Manchester M13 9PT, England (Received 10 May, 1977) K. D. CAIRNCROSS, A. WREN, B. COX AND H. SCHNIEDEN. Effects of olfactory bulbectomy and domicile on stress induced corticosterone release in the rat. PHYSIOL. BEHAV. 19(4) 485-487, 1977. -- Following bilateral olfactory bulbectomy or sham surgery, rats were housed either in groups of 5 or individually. After 10 days the animals were sacrificed and plasma corticosterone levels were measured. Half the animals in each group received predictable stress in the form of footshock immediately prior to exsanguination. Two levels of corticosterone elevation were noted, an intermediate level (circa 40 /ug/100 ml plasma), in bulbectomised animals without stress and in sham operated animals with stress. Extreme corticosterone elevation (circa 80 #g/100 ml plasma) occurred in bulbectomised rats with stress. The type of housing had no effect on corticosterone elevation. The results are discussed in terms of a non olfactory function for the olfactory bulb, and the role of corticosterone and ACTH in acquisition learning. Stress
Bulbectomy
Corticosterone
Housing
RATS subjected to bilateral olfactory bulbectomy (BOL) exhibit a performance deficit in a one way avoidance task, accompanied by a reduction in telencephalic noradrenaline concentration [4, 5, 8]. The behavioural changes associated with bulbectomy in the rat include hypermotitity, aggression to cage mates, irritability to the experimenter and a performance deficit in passive avoidance tasks [12,14], which can be modulated by treatment with different types of psychotropic drugs [ 13,16]. It was decided to investigate whether circulating corticosterone levels could provide a physiological correlate to behavioural testing. Bassett, Cairncross and King [1] have established that plasma corticosterone elevation can be quantitated in the rat at two levels, an intermediate elevation ( 4 5 - 5 5 t~g/100 ml of blood plasma) and an extreme elevation ( 8 0 - 9 0 ~g/100 ml blood plasma). The degree of corticosterone elevation was dependent on the type of stressor to which the animal was exposed. Predictable footshock resulted in intermediate steroid elevation, whereas unpredictable footshock (even with the possibility of escape) induced extreme steroid elevation. It was concluded that extreme corticosterone elevation occurred when a psychological stressor (unpredictability) was superimposed on a physical stressor (footshock). Thus, it was decided to examine the effect of bulbectomy as a stressor, and to expose bulbectomised rats and sham operated (SO) rats to a predictable stress in the form of footshock. Plasma corticosterone levels to be measured after the stress session. Furthermore, due to the particular behavioural syndrome
including aggression associated with BOL and the effect this might have on plasma corticosterone levels, it was necessary to examine glucocorticoid concentrations in both group housed and individually housed rats. METHOD Male Sprague-Dawley rats (Manchester strain, 8 7 - 9 3 days old) were used in all experiments. The animals were housed in groups of 5 in Experiment 1, and individually in Experiment 2, under conditions of constant temperature and humidity (21 -+ 0.5°C, 45% humidity). The animals were subjected to a 14 hr day schedule (light 6 a.m. - 8 p.m.). Food and water were provided ad lib. Both control and BOL rats were handled daily during a 4 day preoperative and a 10 day postoperative recovery period.
Procedure Rats were anaesthetised with Equithesin (0.33 ml/100 g body weight IP). The head was shaved and placed in a stereotaxic frame and the skull exposed by a mid-line incision. Two holes were drilled on either side of the mid-line at a point 5 mm anterior to bregma. The olfactory bulbs were sectioned and removed by aspiration. The wound was closed and a 10 day postoperative recovery period allowed. SO rats underwent the same surgical procedure, but the olfactory lobes were not touched. Deafferentation consisted of placing a curved probe through the burr hole and severing the olfactory nerves above the cribiform plate of the ethmoid bone.
1The skilled technical assistance of Miss Christine Forster is gratefully acknowledged. 485
486
CAIRN(;ROSS 57 .ti,
Fo o tsh o ck
RESU L IS
Rats were placed in a clear perspex box 55 cm ~ with a stainless steel grid floor set at 1.5 cm centres. Footshock was delivered through the grid floor (as a 1.5 mA, 50 pulses/sec square wave) for 5 sec every 55 sec over a 30 rain period. This procedure ensured that corticosterone elevation was maximal [2]. Corticosterone Assay
In the control non-stress situation the SO and BOL rats were removed from their home-cage and sacrificed in a different room. They were exsanguinated within 2 rain of removal from the home cage, this prevented the parameter of novelty elevating the plasma corticosterone level [ 1 ]. In the stress situation SO and BOL rats were sacrificed immediately following the last stress episode. In all situations, the animals were sacrificed between 10 a.m. and noon.
Blood was collected in heparinised tubes, the samples were centrifuged to obtain cell free plasma which was stored at - 2 0 ° C . Corticosterone levels in plasma were determined subsequently by the fluorometric method of Mattingly [lO] which is specific for free l l - h y d r o x y c o r ticoids. Bulbectomy was confirmed as previously described [8]. A two tailed students t-test was used to analyse the results. J deafferentation E~
sham-operation
[~
bulbectomy
80.
m
/ / / /
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,11
e-
.o_ "~ 40-
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=~ o
30-
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/
/1 /1
/
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20.
/ ii /
10-
0
/ OUnst~sed
Unstressed
Stressed
I
I Group
Housing
Experiment 1
Group housed BOL rats exposed to no stressful procedure other than daily handling had a significantly higher (p< 0.00 I) circulating corticosterone level than similarly housed SO rats (Fig. 1). When the SO group housed animals were subjected to footshock a significant elevation of plasma corticosterone was observed compared with nonstressed SO controls (p
