Aim: 

In mammals, the selective agonist of 5-HT_1A receptor 8-OH-DPAT increases the sleep while the antagonist of 5-HT_1A receptor WAY-100635 and para-chlorophenylalanine (PCPA) causes continuous wakefulness. This work aims to study the effects of these drugs on the activity-rest rhythm in birds.

Methods: 

Ring-doves (140-170 g, n=9) were individually housed into an activimetry chamber with 12/12 L/D cycle, and maintained in standard conditions throughout the experimental period. After habituation, activity was continuously measured by infrared activimetry. After recording in basal conditions, animals were submitted to: saline administration, two PCPA injections (300 mg/kg i.p.) in consecutive days, 8-OH-DPAT (0.5 and 1 mg/kg i.p.), WAY-100635 (0.5 mg/kg i.p.). Then, the effect of 8-OH-DPAT was analysed after pre-treatment with WAY-100635 (0.5 mg/kg i.p.) and PCPA.

Results: 

Serotonin depletion by PCPA produced important decreases in locomotor activity (30% and 50% compared to saline). Locomotor activity increased after 8-OH-DPAT (60%, p<0.01) while decreased after WAY-100635 (43%, p<0.01). Pre-treatment with WAY-100635 blocked the stimulatory effect of 8-OH-DPAT on locomotor activity indicating an effect mediated by 5-HT_1A receptors.

After PCPA treatment, 8-OH-DPAT (0.5 mg/kg) effect on locomotor activity was further increased compared to the same 8-OH-DPAT dose without PCPA, suggesting 5-HT1A receptors supersensitivity as a consequence of the serotonin depletion by PCPA.

Conclusion: 

Contrary to mammals, serotonin seems to play a tonic stimulatory control on activity-rest rhythm mediated by 5HT_1A receptors in birds.

Research supported by grant BFI2002-04583-C02-029. S.T. was supported by a FPI grant (Govern Balear, Spain).