Immunolocalization of smooth muscle-like cells in the quail ovary.

We localized alpha-smooth muscle actin (alpha-SMA) in the quail ovary, using the peroxidase-anti-peroxidase technique. Special attention was paid to the influence of fixation on the immunoreactivity of the antigen. The immunostaining of alpha-SMA largely depended on the nature of the fixative. The antigen could most successfully be localized in ovaries fixed in Carnoy's fluid. We also localized alpha-SMA and desmin in semi-thin glycol methacrylate sections of the pre-ovulatory follicle, using the immunogold-silver staining method. The sections were pretreated with Lugol's iodine or sodium metaperiodate to enhance the immunoreactivity. alpha-SMA was demonstrated in the cells of the chordae, the tunica albuginea, and the theca externa of each follicle. These structures were inter-connected, forming an ovarian suspensory apparatus. The thecal cells of prelampbrush follicles also expressed alpha-SMA. In the wall of the pre-ovulatory follicle, desmin was found in the cells of the chordae and the tunica albuginea, and in a few cells of the theca externa. In the theca interna, desmin, and sometimes alpha-SMA, was observed in cells adjacent to the endothelium of sinusoids, which are probably pericytes. Our results support the hypothesis that in birds the ovarian follicles possess a thecal contractile system, that is presumably involved in the ovulatory process.