Description): Traumatic labor and vaginal delivery during childbirth can produce permanent dysfunction of the pelvic musculature, in many cases leading to urinary and fecal incontinence. Damage to the pelvic nerves and failure to achieve complete reinnervation account for much of the deficit. Factors that modulate regrowth of damaged axons therefore may influence functional recovery. The investigators have shown recently that smooth muscle of the reproductive tract, which shares many similarities with urethral and anal sphincter smooth muscle, undergoes dramatic changes in innervation as a consequence of hormonal fluctuations. Elevated plasma estrogen results in marked reductions in numbers of sympathetic nerves, while other neuronal populations are unaffected. Preliminary data suggest that these changes are related to decreased nerve growth factor (NGF) synthesis. The investigators hypothesize that the high levels of estrogen in periparous females result in depressed neurotrophin synthesis in pelvic smooth muscle. Accordingly, sympathetic nerves, whose presence is essential for normal sphincter contractile tone, fail to regenerate to their full potential after nerve injury.
In Specific Aim 1, the investigators will determine the effects of estrogen and pregnancy on protein and mRNA levels of NGF and the related neurotrophin, NT3, in urethral and anal sphincter smooth muscle using in situ hybridization, quantitative competitive polymerase chain reaction, immunohistochemistry and enzyme-linked immunoassays. In the second aim, they will use quantitative in situ hybridization and immunohistochemistry to determine the extent to which estrogen and pregnancy influence expression of the neurotrophin receptors trkA and p75NTR, which mediate the sympathetic nerve response to NGF and NT3.
In aim 3, they will use immunohistochemistry to examine the effects of estrogen and pregnancy on the normal innervation of the urethral and anal sphincter smooth muscles.
Aim 4 will employ immunohistochemistry and physiological and pharmacological measurements of urethral and anal smooth muscle contractile function to assess the effects of estrogen on sphincter reinnervation following a noradrenergic neurotoxin lesion with 6-hydroxydopamine, or pelvic distension to simulate childbirth trauma, and these will be compared with injury of normal delivery. The fifth aim uses collagen gel co-cultures of sphincter smooth muscle and sympathetic ganglia in the presence of selective neutralizing antibodies to ascertain the roles of neurotrophins in modulating sympathetic neurite sprouting toward smooth muscle of estrogen-treated or pregnant rats. These studies should provide important new information on how hormones may affect neurotrophin synthesis by smooth muscle of the organs of continence, and how this in turn may alter sympathetic reinnervation of sphincters after axonal damage due to traumatic vaginal delivery, thus leading to urinary and fecal incontinence.
