Evaluation of changes in testosterone concentration of the rat central nervous system following progesterone administration



Neurosteroids are steroids that are produced in the central nervous system (CNS). While progesterone and dehydroepiandostendione (the precursors of testosterone) are among the identified neurosteroids, it is not clear that testosterone could be considered as a neurosteroid. The testosterone synthesis has been demonstrated in the brain of castrated frog, but not in the rat brain. In the present work, we tried to demonstrate testosterone synthesis in the rat brain and spinal cord by administration of progesterone. Endogenous level of testosterone was measured in the whole brain, spinal cord, and plasma of mature male, female and castrated Sprague-Dawely rats. Progesterone (5 mg/kg) was injected subcutaneously and testosterone was measured after 3 hours. Testosterone was significantly (P<0.001) lower in the CNS and plasma of female and castrated male rats in comparison with male rats. Administration of progesterone failed to alter testosterone concentrations in all groups. The results of this study could not support testosterone synthesis in the rat CNS. This may show that unlike the frog brain, testosterone synthesis in the rat brain has a minor importance.