Behavioral and metabolic effects of central injections of orexins/hypocretins in pigeons (Columba livia).

In the present study, the acute behavioral and ingestive effects of ICV injections of mammalian orexin-A (ORXA; vehicle, 0.2, 0.6 or 2 nmol) and of orexin-B (ORXB; vehicle, 0.2, 0.6 or 2 nmol), as well as possible long-term effects (through 24 h of continuous intake monitoring after 0.6 nmol of ORXA or ORXB) of these treatments in food/water intake and in blood levels of metabolic fuels (free fatty acids and glucose, after 0.2 or 0.6 nmol of ORXA) were examined in adult male pigeons. Both ORXA and ORXB treatments failed to produce acute (1-3 h) or long-term effects on feeding and drinking behaviors, and did not change blood free fatty acids and glucose 15 and 30 min after treatments, as compared to vehicle-treated animals. However, ORXA (but not ORXB) treatments evoked a dose-related, intense increase in exploratory behaviors, associated to reduced time spent in alert immobility and sleep-typical postures. These data substantiate the lack of orexigenic effects of ORXs in avian species, and suggest that an important role in vigilance control may represent a conserved functional attribute of orexinergic circuits in vertebrates.

Behavioural and electroencephalographic effects of systemic injections of 8-OH-DPAT in the pigeon (Columba livia).

The effects of systemic injections of the 5HT(1A) receptor agonist 8-OH-DPAT on the spontaneous ingestive, maintenance, locomotor and sleep-like behaviours, and the sleep/waking-related hippocampal electrographic activity were investigated in pigeons. 8-OH-DPAT (0.06, 0.2, 0.6 or 2.0mg/kg) was found to dose-dependently reduce food and water intake, acutely (in the first 3h) and 24h after treatment, during both low-activity morning hours (starting at 10:00 h) and high-activity evening hours (starting at 14:00 h). Automated 24h records of food and water intake indicated that hypophagic effects can last up to 18 h after injection. Duration and incidence of sleep-like postures increased at all doses, in both morning and afternoon. These effects were associated with decreases in exploratory and preening activities. The 8-OH-DPAT-induced hypnogenic, hypophagic and hypodipsic effects tended to be more intense in the morning than in the afternoon-trials. Pretreatment with WAY 100635 (a 5-HT(1A) antagonist; 0.6 mg/kg) eliminated all of these 8-OH-DPAT-induced effects. WAY 100635 failed to affect feeding when injected alone, but decreased frequency of sleep-like responses and increased the latency to the first sleep-like episode. Hippocampal EEG tracings after 8-OH-DPAT injections (0.6 or 2.0mg/kg) indicated that the hypnogenic effects are associated with a specific increase in the frequency and duration of slow wave sleep. Power density analysis of the hippocampal EEG failed to show differences between 8-OH-DPAT-induced sleep and the sleep occurring after vehicle injections, indicating that it may be electrographically similar to diurnal sleep episodes in the pigeon. These data suggest that while 5-HT(1a) receptor-mediated mechanisms play crucial roles in ingestive and sleep/waking behaviours in mammals and birds, their action upon these states shows substantial inter-taxon variance.