factor that prevents SNB motor neurons from dying FIGURE 1222 Forger et al 1997

Factor that prevents snb motor neurons from dying

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factor, that prevents SNB motor neurons from dying FIGURE 12.22) (Forger et al, 1997). The developmental rescue of SNB motor neurons is accomplished indirectly as a consequence of actions on muscle, but androgens can also directly affect the neurons themselves. SNB neurons contain androgen receptors and retain androgen sensitivity throughout life. In adulthood, androgen acts directly on the neurons to cause them to frow (Watson et al., 2001) and start producing substances to aid in the formation of j ...and a ! second rise ! at puberty. ! The male SDN-POA is large. [ ...and her SDN- POA is small. ...develops a large SDN-POA. .. .have no effect on the size of a female's SDN-POA. Conception Birth Sensitive period Adult 12.21 SEXUALLY DIMORPHIC NUCLEUS OF THE PREOPTIC AREA (SDN-POA) Testosterone can permanently enlarge the SDN-POA in rats, but only if given during a "sensitive period" early in life. spinal nucleus of the bulbocavernosus (SNB) A group of motor neurons in the spinal cord of rats that innervate striated muscles controlling the penis. SEX 393 fl
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Male rat Spinal cord Motor neuron Neuromuscular junction Bulbocavernosus muscle In both sexes, spinal motor neurons make connections with the bulbocavernosus muscle early in development. The muscle expresses androgen receptors in both sexes. Androgen receptor Male 1 S' \ {] ' ^ / Testosterone ~~^^~r*^-. | In males, circulating testosterone binds to the androgen receptors. In females, the receptors remain unoccupied. u ' ,-Trophic factors In males, the activated receptors promote the survival of the muscle and cause it to secrete trophic factors, which are picked up by the motor neurons. In females, the lack of receptor activation causes the muscle to die, and no trophic factors are produced. | In males, the trophic factors picked up by the motor neurons promote their survival. In females, the lack of trophic factors causes the motor neurons to die. Female tt SNB Female rat 12.22 SEXUAL DIFFERENTIATION OF THE SPINAL NUCLEUS OF THE BULBOCAVERNOSUS (SNE Onuf's nucleus The human homolog of the spinal nucleus of the bulbocaverno- sus (SNB) in rats. new connections. For example, androgens directly stimulate SNB neurons to produce N-cadherin, a cell adhesion molecule that mediates the formation of new contacts be- tween cells (D. A. Monks and Watson, 2001). These are examples of activational ef f e c - - of androgens. All male mammals have BC muscles, but in nonrodents the BC motor neurons are found in a slightly different spinal location and are known as Onuf's nucleus. Sur- prisingly, most female mammals retain a BC muscle into adulthood; in women, far example, the BC (also known as constrictor vestibule) helps constrict the vaginal ope ing. But, as in rodents, the system is profoundly sexually dimorphic. Men have largo- EC muscles and more numerous Onuf's motor neurons, most likely determined by androgen exposure during fetal development (Forger and Breedlove, 1986,1987).
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