GnRH activation and LH release following hormone priming. (A) Immunolabeling of GnRH (green) and FOS (red) in the region surrounding the OVLT following hormone priming (Experiment 1). Representative double labeled cells are indicated by the blue arrows and single labeled GnRH neurons are indicated by the white arrows. Double labeled cells were first visualized at low magnification and then verified at higher magnification (inset). (B) The percentage of double labeled neurons was significantly reduced by neonatal DPN administration but the magnitude of the effect was substantially greater in the EB treated group. (C) LH levels were below the limit of detection (indicated by the red line, 1 ng/ml) in all females neonatally exposed to EB, and three of the five animals in the HIGH DPN group. LH levels were significantly lower in the EB and HIGH DPN groups compared to the vehicle treated control group (OIL, P ≤ 0.05). A trend for lower LH levels in the MID DPN group was also observed (P ≤ 0.06). The overall pattern of serum LH levels was largely reflective of GnRH and FOS co-labeling. (3v = 3rd ventricle, Means ± S.E.M., *P ≤ 0.05, **P ≤ 0.001, † < 0.07).