Contrasting behavioural effects of 8-OH DPAT in the dorsal raphé nucleus and ventral hippocampus.

Administration of the 5-HT1A receptor agonist (+-)-8-Hydroxy-dipropylaminotetralin (8-OH DPAT, 50 ng) into the dorsal raphé nucleus (DRN) increased social interaction but did not change the motor activity of rats tested in high light, thus indicating an anxiolytic response. This effect was blocked by coadministration of the 5-HT1A antagonist, tertatolol (3 micrograms). In contrast, 8-OH DPAT (50 and 100 ng) was without effect on social interaction when administered to the DRN projection area in the ventral hippocampus, but did change locomotor activity. The effects depended on the light level and dose: thus when the rats were tested in low light, 50 ng increased locomotor activity, but in high light a decrease was found with 100 ng and also an induction of wet dog-shakes. Thus, our results support the importance of the somatodendritic autoreceptors in the DRN in alleviating anxiety, whereas the post-synaptic receptors in the ventral hippocampus play no role. They do, however, mediate changes in activity and the 5-HT syndrome.