Colocalization of androgen receptors and mating-induced FOS immunoreactivity in neurons that project to the central tegmental field in male rats.

ABSTRACT

Bilateral lesions of the central tegmental field (CTF) in male rats virtually eliminate mating behavior. This study examined if mating-induced Fos expression (a measure of neuronal activation) and androgen receptors (AR) are colocalized in brain and spinal cord neurons which project to the CTF. Animals received unilateral injections of the retrograde tracer Fluorogold (FG) in the lateral part of the CTF (CTFl), and 10 days later were killed after ejaculating with females. Brains and spinal cords were examined for FG transport, AR-immunoreactivity (AR-ir), and Fos-immunoreactivity (Fos-ir). AR-ir and Fos-ir were visualized with fluorescence microscopy using cyanine-conjugated and fluorescein-conjugated secondary antibodies. The CTFl received projections from AR-containing neurons in forebrain structures (bed nucleus of stria terminalis, medial preoptic area, lateral and ventromedial hypothalamus), in the central amygdala and various mid- and hindbrain structures (dorsolateral tegmentum, superior and inferior colliculi, pedunculopontine nucleus), and in the lumbosacral spinal cord (lamina X). Some of the AR-containing neurons in bed nucleus of stria terminalis and in the dorsal part of the medial preoptic area with projections to the CTFl were activated by mating. Most AR-containing neurons in spinal lamina X with projections to the CTFl were also activated by mating. Information from spinal cord and pontine nuclei and from outputs descending from the forebrain may be relayed in the CTFl. Thus, as part of a network of hormone-sensitive neurons linking brain and spinal cord mechanisms for mating, the CTFl could participate in the integration of visceral and somatic information relevant for sexual behavior.