Testosterone-induced alterations in the reactivity pattern of the neurons in the arcuate nucleus of male mice

The effects of testosterone administration on the hypothalamic arcuate nucleus were studied in adult male mice by means of karyometry. Four animals per group were sacrificed 1, 2, and 3 h after intramuscular injection of 100 micrograms testosterone propionate/100 g body weight. The nuclear diameter of neurons was measured in serial coronal sections. Testosterone induced an increase in the nuclear diameter of neurons located in the dorsal and medial periventricular zones of the arcuate nucleus. The neurons exhibiting the greatest changes in nuclear diameter were situated in the rostral portion of the nuclear area examined. In the central portion of the arcuate nucleus no response to testosterone was found. The present data support previous observations showing mosaically arranged nerve-cell groups in this hypothalamic nucleus.