In situ hybridization for leptin. Rats injected with saline solution, lactic acid or LS were euthanized 48 hr after injections and their brains were fixed in formalin immediately after euthanasia. Leptin mRNA was visualized using in situ hybridization in sections of the brains of rats injected with saline solution (A, C), and LS extract (C, D). Leptin expression is observed in the cytoplasm of neurons in the hypothalamus (A, B; arrows) and hippocampus (C, D; arrows). Stronger expression is noted in LS-injected animals. Light counterstain with hematoxylin. Magnification × 200.