Autoradiographic localization of sex steroid-concentrating cells in the brain of the teleost Macropodus opercularis (Osteichthyes: Belontiidae).

Tritiakd estradiol or testosterone was administered to gonadectomized male paradise fish, Macropodus opercularis, to investigate the neuroanatomical location of sex steroidretaining cells. Each male was sacrificed 2 hr following intraperitoneal injection of the labeled hormone. Autoradiograms were prepared, and sections were taken from the entire brain, the anterior spinal cord, and the pituitary. Following 4 to 12 months of exposure, the distribution of labeled cells was seen to be the same for males which had received the estradiol as those which received testosterone, but estradiol resulted in a greater number of labeled cells. Steroid-concentrating cells were located in the ventral telencephalon, preoptic area, lateral tuberal nucleus, nucleus of the lateral recess of the third ventricle, and caudal portion of the posterior periventricular nucleus. In addition, the caudal pars distalis of the pituitary contained many labeled cells. No steroid-retaining cells were seen in the mesencephalon, rhombencephalon, or anterior spinal cord.