Androgen influence on lateral hypothalamus in the male rat: possible behavioral significance.

The lateral hypothalamus and other structures in the forebrain were explored with microelectrodes in the male rat under urethane anesthesia before and after IV injections of testosterone. In the lateral hypothalamus, significant proportion of neurons responded after a few minutes to the hormonal increases by changes in firing rate. These responses could be attributed neither to a solvent effect nor to generalized changes in cerebral activity as indicated by EEG monitoring. The rapid onset implies that the steroid molecule exerted a non-genomic effect on target cells. The brain cells detected here were either such testosterone target cells or other neurons transsynaptically connected to them. All units tested with estradiol and testosterone reacted in the same way to both steroids, suggesting that testosterone acts after being aromatized into estradiol. This supports a possible role of these neurons in the regulation of male sexual behavior. Their involvement in the modulation of motivation during the appetitive component of sexual behavior, according to the hormonal state of the subject, is discussed.