Vasopressin released within the septal brain area during swim stress modulates the behavioural stress response in rats

The aim of the present study was to investigate the physiological significa nce of the neuropeptide arginine vasopressin (AVP) released within the sept um, in the behavioural response of rats to stress. In the first experiment, rats were chronically implanted with a microdialysis probe aimed at the me diolateral or ventral septum to monitor the local release of AVP in respons e to 10 min of forced swimming in 20 degrees C warm water. Exposure to this stressor caused a significant increase in AVP release in both the mediolat eral (174 +/- 21%, P < 0.01) and ventral septum (220 +/- 33%, P < 0.01). In contrast, microdialysates collected outside the mediolateral septum or in the lateral ventricle remained at prestress levels throughout the dialysis period. Furthermore, unstressed control animals failed to show significant alterations in vasopressin release in the mediolateral septum. In a second experiment, the introduction of the V1 receptor antagonist d(CH2)(5)Tyr(Me) AVP into the mediolateral septum via inverse microdialysis concomitant with stressor exposure caused the rats to spend an increased time floating and a reduced time swimming compared to vehicle-treated rats. This effect was a cute and also detected 24 h after antagonist administration. Taken together , these findings demonstrate a significant activation of the septal vasopre ssinergic system in response to swim stress. Furthermore, our data support the view that AVP released within this brain area is involved in the genera tion of active behavioural strategies aimed at coping with new and challeng ing situations.