Effects of intracerebroventricular administration of neuromedin U or neuromedin S in steers

Although neuromedin U (NMU) and neuromedin S (NMS) are reported to modulate stress responses mainly through corticotropin-releasing hormone system in rodents, the in vivo effects of centrally administered NMU or NMS on stress regulation have not been fully elucidated in cattle. We examined adrenocorticotropic hormone levels, body temperature, and behavioral responses to intracerebroventricularly (ICV) administered rat NMU or rat NMS in steers. ICV NMU and NMS (0.2, 2, and 20 nmol/200 μl) evoked a dose-related increase in plasma cortisol concentrations (CORT). There was a significant time–treatment interaction for the time course of CORT (p < 0.001). ICV NMU evoked a dose-related increase in rectal temperature (RT). There was a significant time–treatment interaction for the change in RT from pre-injection value (p < 0.05). There was a significant difference among treatments in the percentage of time spent lying (Friedman’s test, χ2 = 15.6, p < 0.01) and in the total number of head shaking (Friedman’s test, χ2 = 14.49, p < 0.01). A high dose of NMS tended to shorten the duration of lying and increase the number of head shaking. These findings indicate that both central NMU and NMS might participate in controlling the hypothalamo–pituitary–adrenal axis, that central NMU might participate in controlling body temperature, and that central NMS is likely to be involved in behavioral activation in cattle.