Effect of some serotoninergic agents on the rectal temperature of the domestic fowl ( gallus domesticus)

Abstract

The information currently available in the literature on the effects of serotonergic drugs on thermoregulation in the avian species is very scanty. Therefore, it was the objective in this project to study the influence of 5-hydroxytryptamine (5-HT), 5-hydroxytryptophan (5-HTP), benserazide, carbidopa (Mk 486), citalopram, cyproheptadine, methysergide, xylamidine, p-chlorophenylalanine (PCPA) and lysergic acid diethylamide (LSD-25) on the rectal temperature of young chicks. 5-hydroxytryptamine (0.8 mg/kg), produced significant dose-dependent hypothermia in young chicks. Similarly, 5-HTP (16 mg/kg) profoundly lowered the rectal temperature of young chicks. The hypothermie effect of 5-HTP was potentiated by benserazide (1.25–2.5 /kg). Pretreatment with carbidopa (50 mg/kg) potentiated 5-HTP induced hypothermia. Citalopram (5 mg/kg) significantly potentiated hypothermia induced by 5-HT. Pretreatment with PCPA (200 mg/kg, 24 hr previously) alone resulted in hyperthermia while the hypothermie effect of 5-HTP (16 mg/kg) was antagonised by pretreatment with PCPA. Cyproheptadine (1.25 mg/kg) antagonised the hypothermie effect of 5-HT (0.1 and 0.8 mg/kg). The antagonistic effect was weak when the chicks were pretreated with larger doses of cyproheptadine (i.e. 2.5–10 mg/kg). The hypothermia induced by 5-HT (0.8 mg/kg) was antagonised by smaller doses of methysergide (0.125–1.0 mg/kg) but potentiated by larger doses of methysergide (2.0 and 4.0 mg/kg). Xylamidine (1–2 mg/kg) alone induced hyperthermia and effectively antagonised hypothermia induced by 5-HT (0.8 mg/kg). d-Lysergic acid diethylamide (2.5–10 μg/kg) alone induced hypothermia. The interaction between LSD and 5-HT was dose-dependent and biphasic. Thus, small doses (2.5 μg/kg) potentiated while large doses (5 and 10 μg/kg) of LSD antagonised the 5-HT-induced hypothermia. Antagonism to hypothermia induced by 5-HTP (16 mg/kg) was also observed in chicks pretreated with LSD (5 μg/kg). In chicks pretreated with PCPA (200 mg/kg), LSD (5 μg/kg) reversed the hyperthermia. In conclusion, it appears that in the avian species, 5-HT acts as an excitatory transmitter in the heat loss effector pathways producing hypothermia, which is influenced by drugs acting on serotonergic mechanisms.