Feeding and 8-OH-DPAT-related release of serotonin in the rat lateral hypothalamus

Based on the different effects of somatodendritic 5-HT1A agonist 8-OH-DPAT on food intake whether given to food-deprived rats or freely feeding rats, we hypothesized that the effects of 8-OH-DPAT on extracellular serotonin (5-HT) in the lateral hypothalamus (LH) will interfere with different feeding states, eventually resulting in different patterns of 5-HT release. In a microdialysis study we measured extracellular 5-HT in the LH after 8-OH-DPAT under four experimental conditions, i.e., in freely feeding rats with no food available, freely feeding rats with access to food, in food-deprived rats with no food available, and in food-deprived rats with good available after treatment. The results show a significant decrease of 5-HT release after 300 microg/kg 8-OH-DPAT (i.p.) in freely feeding rats. This effect is not seen when food is provided after drug treatment. In contrast, the same dose of 8-OH-DPAT has no effect on 5-HT release in food-deprived rats. In addition, providing food after drug treatment does not change the release pattern significantly in food-deprived rats, suggesting more complexity in the underlying mechanisms. The present study describes the effects of 8-OH-DPAT on 5-HT release in the LH, depending on feeding conditions and feeding-related behavioral states.