DIURNAL-VARIATIONS IN THE FEEDING RESPONSE TO 8-OH-DPAT INJECTED INTOTHE DORSAL OR MEDIAN RAPHE

To determine the impact on food intake of the 5-HT1A agonist, 8-OH-DPA T, administered at various times throughout the nocturnal cycle, rats were implanted with cannulae in either the dorsal or median raphe nucl ei and injected with saline or 8-OH-DPAT (0.4, 0.8 or 1.6 nmol) immedi ately following dark onset, or during the mid or late dark periods. 8- OH-DPAT potentiated feeding when administered in the mid or late dark phase, whereas treatment during the early dark actually suppressed foo d intake. These findings indicate that the feeding responses to dorsal and median raphe 8-OH-DPAT vary greatly depending on the time of admi nistration in the diurnal cycle and are consistent with recent reports of a biphasic action of this compound on ingestive behaviour.