Abstract
Abstract
The timing of functional hypothalamic responsiveness during embryogenesis remains incompletely defined. We examined hypothalamic activation in chicken embryos from embryonic day (ED) 12–17 following experimental stimulation consisting of a localized foot injection of paraformaldehyde (PFA) together with the associated handling procedures required for its administration. Hypothalamic activation was quantified as the proportion of c-Fos-positive cells within the paraventricular nucleus (PVN). Generalized linear modelling revealed significant effects of both embryonic age and stimulation condition on c-Fos expression, with no evidence of an Age × Stimulation interaction. Across development, stimulated embryos exhibited higher proportions of c-Fos-positive cells than age-matched controls. Independent of stimulation, the only significant difference between adjacent developmental stages occurred between ED14 and ED15, suggesting a candidate transition in hypothalamic maturation. Exploratory analysis indicated that these findings are consistent with an early (ED12–ED14) and a late (ED15–ED17) developmental phase and suggest that ED14–ED15 may represent a candidate phase boundary in hypothalamic maturation.