The Nucleus Interstitialis Striae Terminalis and the Nucleus Amygdaloideus Medialis: Prime Targets for Androgen in the Rat Forebrain*

The following autoradiographic study was done to examine the patterns of aromatization within the limbic system itself. It has been established that during the aromatization of testosterone (T) to estradiol the C-lβ and the C-2β hydrogens are lost, while those at C-lα and C-2α are retained. Thus, by comparing animals injected with testosterone labeled in either the lα,2α or the 1α,2beta; positions, one can determine whether aromatization has taken place in a given region of the limbic system. Twenty-four-day-old female rats, which had been ovariectomized and adrenalectomized 24 h before the experiment, were injected with either 1 μg/100 g BW 1β, 2β-3H(N)T (40 Ci/mmol) or lα, 2α-3H (N) T (59 Ci/mmol). In addition, a few animals that received the β-labeled T were treated with 100 μg/100 g BW unlabeled T. The animals were killed 1.5 h later and the brains were removed, sliced, and mounted on tissue holders. The ounted tissue was then frozen in liquified propane and stored in liquid nitrogen until processing. Four-micrometer frozen sections were cut in a cryostat and mounted for autoradiography on emulsion-coated slides according to the dry mount procedure. The slides were then exposed at –15 C for up to 14 months and photographically processed and stained with methyl green-pyronin. In autoradiograms from the animals injected with the α-labeled T, a specific topographical pattern of concentrations of radioactivity was found in nuclei of neurons in the limbic system, similar to what has been reported in the past. In autoradiograms from those animals injected with β-labeled T, the quantity of radioactivity was drastically reduced and absent in many nuclei. The two nuclei which were consistently labeled in the autoradiograms from the animals injected with β-labeled T are the nucleus interstitialis striae terminalis and the medial nucleus of the amygdala. Unlabeled T inhibited all localization. The data sggest that the nucleus interstitialis striae terminalis and the medial nucleus of the amygdala may be key sites for the action of androgen in the rat brain.