Physiology & Behavior, Vol. 17, pp. 153-154. Pergamon Press and Brain Research Publ., 1976. Printed in the U.S.A.

BRIEF COMMUNICATION Exteroceptive Olfactory Stimuli: Their Influence on Plasma Corticosterone in Rats 1SAIAS L O Y B E R , N O R M A I. P E R A S S I A N D F R A N C I S C O A. L E C U O N A

hlstituto de FisiologT"a "Prof. Dr. Oscar Orias", Facultad de Ciencias Mddicas Universidad Nacional de COrdoba, COrdoba, Argentina ( R e c e i v e d 17 M a r c h 1975) LOYBER, I., N. I. PERASSI AND F. A. LECUONA. Exteroceptive olfactory stimuli. their influence on plasma corticosterone in rats. PHYSIOL. BEHAV. 17(1) 153-154, 1976. - The present study was carried out with a view to ascertaining the importance of exteroceptive olfactory stimuli during the decrease of plasma corticosterone produced in bulbectomized rats. For this purpose, normal rats, with sectioned olfactory nerves and extirpated olfactory bulbs were used; the plasma corticosterone levels in bulbectomized rats were significantly lower than in the other 2 groups under study. On the other hand, in rats with sectioned olfactory nerves, there were no significant changes of corticosterone when compared with normal animals. These results would indicate that the decrease of plasma corticosterone in bulbectomized rats might be due to a disruption in the nonolfactory function of olfactory bulbs. Olfactory bulbs

Plasma corticosterone

Olfactory stimuli

Olfactory nerves

groups: (a) u n o p e r a t e d c o n t r o l s (n = 16): (b) w i t h s e c t i o n e d o l f a c t o r y nerves (n = 17); (c) with bilateral removal of t h e o l f a c t o r y b u l b s (n = 9). All surgery was p e r f o r m e d u n d e r e t h e r anaesthesia. Sectioning of t h e o l f a c t o r y nerves and b u l b e c t o m y was a c c o m p l i s h e d b y r e m o v a l of a 3 × 4 m m p o r t i o n of skull over t h e o l f a c t o r y bulbs, using a d e n t a l drill. S e c t i o n of the o l f a c t o r y nerves was e f f e c t e d by passing a specially designed c u t t i n g tool a r o u n d the a n t e r i o r tip and v e n t r a l surface of the bulbs. In b u l b e c t o m y the o l f a c t o r y bulbs were severed f r o m t h e rest of the brain with a scalpel and t h e n removed. T h e t r a n s e c t i o n was m a d e a n t e r i o r to the f r o n t a l lobes, care being t a k e n to avoid injury to the f r o n t a l poles. All animals were m a i n t a i n e d u n d e r the same c o n d i t i o n s , being h o u s e d 10 per cage. To avoid the possibility of stress i n f l u e n c i n g c o r t i c o s t e r o n e m e a s u r e m e n t s , the rats were h a n d l e d twice a day during the interval of t i m e b e t w e e n o p e r a t i o n and plasma c o r t i c o s t e r o n e d e t e r m i n a t i o n . The rats were d e c a p i t a t e d in t h e r o o m in w h i c h t h e y were h o u s e d w i t h a small a n i m a l guillotine: less t h a n 5 sec elapsed b e t w e e n the r e m o v a l of the a n i m a l f r o m its h o m e cage and its d e c a p i t a t i o n . All rats were d e c a p i t a t e d b e t w e e n 9 : 0 0 a n d 1 1 : 0 0 a.m., 35 days a f t e r o p e r a t i o n . T r u n k b l o o d was collected, c e n t r i f u g e d and plasma collected. Individual plasma samples were f r o z e n and stored for s u b s e q u e n t d e t e r m i n a t i o n of plasma c o r t i c o s t e r o n e c o n c e n t r a t i o n according to the m e t h o d of R e r u p and H e d n e r [5 ]. Results were evaluated b y S t u d e n t ' s t test.

R E C E N T studies f r o m these l a b o r a t o r i e s regarding the f u n c t i o n o f t h e o l f a c t o r y b u l b in the rat have led us to t h e suggestion t h a t these s t r u c t u r e s along w i t h o t h e r extrah y p o t h a l a m i c c e n t r e s have a r e g u l a t o r y effect o n corticost e r o n e secretion a n d / o r release [ 2 , 4 ] . Previous empirical studies [3] have b e e n c o m p l e t e d w h i c h e x a m i n e d the i n f l u e n c e of t h e o l f a c t o r y b u l b s o n s e r u m p r o t e i n levels in the rat. T h e results o b t a i n e d i n d i c a t e d t h a t lesion or r e s e c t i o n of the bulbs ( b u l b e c t o m y ) reduces the c o n c e n t r a t i o n of s e r u m p r o t e i n , and t h a t this decrease is n o t observed in rats with cut o l f a c t o r y nerves ( d e a f f e r e n t a t i o n ) . The fact t h a t s e r u m p r o t e i n s decrease in b u l b e c t o m i z e d rats, b u t n o t following d e a f f e r e n t a t i o n w o u l d seem to i n d i c a t e t h a t t h e decrease is i n d e p e n d e n t of the e x t e r o c e p tive o l f a c t o r y stimulus. In o r d e r to test this possibility t h e following s t u d y was u n d e r t a k e n to d e t e r m i n e plasma c o r t i c o s t e r o n e levels in rats s u b j e c t e d to d e a f f e r e n t a t i o n and b u l b e c t o m y . If a decrease of plasma c o r t i c o s t e r o n e was o b t a i n e d o n l y following b u l b e c t o m y and n o t with d e a f f e r e n t a t i o n , it would a p p e a r t h a t it is n o t loss of the o l f a c t o r y sense b u t d i s r u p t i o n of some n o n o l f a c t o r y f u n c t i o n of t h e o l f a c t o r y bulbs, w h i c h i n d u c e s this effect. METHOD A t o t a l of 42 w h i t e female virgin rats, b r e d in o u r I n s t i t u t e , weighing f r o m 1 5 0 - 1 8 0 g were used. F o o d and w a t e r were given ad lib. The animals were divided i n t o 3 153

154

L O Y B E R , PERASS1 AND L E C U O N A RESULTS AND DISCUSSION

TABLE 1

Thirty-five days was allowed to elapse following surgery before plasma c o r t i c o s t e r o n e levels were determined. This relates to previous studies [4] in which it was d e m o n s t r a t e d that following b u l b e c t o m y , plasma c o r t i c o s t e r o n e levels were lowest b e t w e e n 30 and 45 days. As may be seen f r o m Table 1, deafferented animals show lower values of c o r t i c o s t e r o n e than u n o p e r a t e d controls, but the difference is not significant. The possibility that the lowered plasma c o r t i c o s t e r o n e values observed could be caused by some change in the bulbs secondary to the section of the olfactory nerves appears unlikely. Such a conclusion is supported by the work of Albert and Galef [ 1 ], and of Spector and Hull [6] who found no histological alteration of the olfactory bulbs in rats following destruction of the olfactory mucosa and d e a f f e r e n t a t i o n respectively. Table 1 d e m o n s t r a t e s also that in b u l b e c t o m i z e d animals the c o r t i c o s t e r o n e levels were significantly lower than in u n o p e r a t e d controls ( p < 0 . 0 0 1 ) or following deafferentation ( p < 0 . 0 2 ) . Since the d e a f f e r e n t a t i o n alone did not induce a significant decrease in plasma corticosterone, it would appear that it is not loss of the olfactory sense, but rather the alteration of some n o n o l f a c t o r y f u n c t i o n of the

PLASMA CORTICOSTERONE LEVELS FOLLOWING SECTION OF THE OLFACTORY NERVES AND EXCISION OF THE OLFACTORY BULBS IN RATS Group

Normal Deafferented Bulbectomized

Days after operation

Numbe~ ~of animals

Corticosterone ~ g/100 mt

I~" 35 35

i;

[5.7 1,48 ~ !2.4 ~ 170 7,7 ~- 0,77-~

,,

*Mean *_ S E +p

Exteroceptive olfactory stimuli: their influence on plasma corticosterone in rats.

Physiology & Behavior, Vol. 17, pp. 153-154. Pergamon Press and Brain Research Publ., 1976. Printed in the U.S.A. BRIEF COMMUNICATION Exteroceptive O...
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