Hormones--Target-Derived Neurotrophic Function:

• Ex. Spinal Nucleus of the Bulbocavernosus (SNB) (in rats)

• SNB is present in males and absent in females

• SNB neurons are motoneurons that innervate muscles attached to the penis (perineal muscles)

• early in development: androgens increase survival of muscles which leads to survival of motoneurons innervating the muscles

• later in development: androgens act subsequently to increase size of neurons (larger); ARs are expressed in SNB motoneurons at later time than ARs expressed in muscle

• administration of estrogen cannot masculinize SNB motoneurons (aromatization is not important); thus, androgens act directly at ARs to masculinize SNB system

SNB

Perineal

muscles

during

critical period

of development,

muscles can bind

androgens while the

motoneurons

cannot

secrete a

�retrograde factor�

that leads to survival

of neurons

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