5-HT1A RECEPTORS IN THE MEDIAN RAPHE NUCLEUS AND DORSAL HIPPOCAMPUS MAY MEDIATE ANXIOLYTIC AND ANXIOGENIC BEHAVIORS RESPECTIVELY

The behavioural response of rats in the high light unfamiliar condition of the social interaction test of anxiety was observed following direct administration of the 5-HT1A receptor agonist, (i)-8-hydroxy-dipropylaminotetralin (8-OH-DPAT, 50, 100 or 200 ng) or antagonist tertatolol (3 mu g) into the median raphe nucleus or dorsal hippocampus. In the median raphe nucleus, 8-OH-DPAT (200 ng) significantly increased social interaction without changing locomotor activity; lower doses were inactive. In the dorsal hippocampus, bilateral injection of 8-OH-DPAT (100 ng) significantly decreased social interaction, without effect on locomotor activity; both 50 and 100 ng significantly changed grooming. Tertatolol had no effect on social interaction following administration to the median raphe nucleus, but significantly increased locomotor activity. Bilateral injection of tertatolol into the dorsal hippocampus decreased social interaction and changed grooming. These effects are similar to those of 8-OH-DPAT suggesting tertatolol may have 5-HT1A receptor agonist properties. In conclusion, the findings of this study demonstrate that 5-HT1A somatodendritic autoreceptors and post-synaptic receptors mediate anxiolytic and anxiogenic effects, respectively, in the social interaction test.