Sex difference of LiCl-induced feeding suppression and, autonomic and HPA axis responses in crows

Visceral sensation is crucial for feeding, emotion, and decision making in humans and non-human animals. Visceral discomforting stimulation activates stress-coping systems, such as the autonomic nervous system (ANS) and hypothalamus-pituitary-adrenal (HPA) axis, with varied responses and thresholds between sexes. Despite these systems working together during visceral discomfort, ANS and HPA have been separately investigated with few studies examining the co-occurrence of the ANS and HPA responses to visceral stimulations. The basic profiles of the ANS and HPA responses to visceral discomfort and sex differences in birds are poorly elucidated. This study investigated the effects of visceral stimulation via intraperitoneal injection of lithium chloride (LiCl) on feeding behavior, ANS and HPA activities, and sex differences in crows. We identified the LiCl dose that suppressed the intake of a preferred food and compared the LiCl-induced feeding suppression between sexes. Changes in heart rate variability (HRV), as a proxy of sympathetic and parasympathetic activities, and serum corticosterone (CORT) levels by LiCl injection were compared. Feeding suppression occurred at higher LiCl doses in males than in females. HRV analysis revealed that LiCl injection reduced HR and increased parasympathetic activity; however, it did not change sympathetic activity, with no sex differences in any variables. In contrast, LiCl injections at lower doses increased serum CORT levels more in males than in females. Our findings provide the first evidence of sex-specific response profiles to feeding suppression and ANS and HPA activities associated with LiCl-induced visceral discomfort in birds.