The Pineal Gland and Stress: Effect of Pineal Stalk Section on the Plasma Corticosteroid Response to Cold in Rabbits

Abstract

To investigate the role of the pineal gland on plasma corticosteroid elevation during stress, a pineal stalk section was performed in rabbits implanted with a carotid cannula, while a comparable sham operation was carried out in a control group ( n = 8) similarly implanted. Six days after the surgery, the rabbits were exposed to a cold environment for 2 hr. Blood was withdrawn periodically throughout the 2 hr. of cold stress and for an additional 2 hr. after the rabbits were returned to their cages. Results show that plasma corticosteroids (cortisol + corticosterone) concentration in both groups rose during the cold exposure and gradually declined towards resting values after removal from the cold. The lesioned rabbits, however, exhibited an earlier and higher elevation in plasma corticosteroid levels in reaction to the cold. These observations suggest that the pineal stalk in normal animals influences the corticosteroid response to a stress in such a way as to increase the latency of its onset and decrease its amplitude. This effect is interpreted in the context of the general adaptation syndrome.