External urethral sphincter motor unit recruitment patterns during micturition in the spinally intact and transected adult rat.

In the rat, external urethral sphincter (EUS) activation during micturition consists of three sequential phases: 1) an increase in tonic EUS activity during passive filling and active contraction of the bladder (guarding reflex), 2) synchronized phasic activity (EUS bursting) associated with voiding, and 3) sustained tonic EUS activity that persists after bladder contraction. These phases are perturbed following spinal cord injury. The purpose of the present study was to characterize individual EUS motor unit (MU) patterns during micturition in the spinally intact and transected adult rat. EUS MU activity was recorded from either the L5 or L6 ventral root (intact) or EUS muscle (transected) during continuous flow cystometry in urethane-anesthetized adult female Sprague-Dawley rats. With the use of bladder pressure threshold and timing of activation, four distinct patterns of EUS MU activity were identified in the intact rat: low threshold sustained, medium/high threshold sustained, medium/high threshold not sustained, and burst only. In general, these MUs displayed little frequency modulation during active contraction, generated high-frequency bursts of action potentials during EUS bursting, and varied in terms of the duration of sustained tonic activity. In contrast, three general patterns of EUS MU activity were identified in the transected rat: low threshold, medium threshold, and high threshold. These MUs exhibited considerable frequency modulation during active contraction of the bladder, no bursting behavior and little to no sustained firing. The prominent frequency modulation of EUS MUs is likely due to the enhanced guarding reflex seen in EUS whole muscle electromyogram recordings in transected rats (D'Amico SC, Schuster IP, Collins WF 3rd. Exp Neurol 228: 59-68, 2011). In addition, EUS MU recruitment in transected rats more closely followed predictions by the size principle than in intact rats. This may reflect the influence of local synaptic circuits or intrinsic properties of EUS motoneurons that are active in intact rats but attenuated or absent in transected rats.

Partial agonist, but not pure antiestrogens stimulate doming, a marker of normal differentiation, in the MCF-7 breast cancer cell line.

UNLABELLED: Abstract Background: The mechanisms by which tamoxifen inhibits breast tumor growth are not completely understood. Partial agonist antiestrogens such as tamoxifen may cause the estrogen receptor (ER) to interact with genes different from those activated by ER bound to estradiol. Doming is a property often associated with, and considered a marker of, differentiation in mammary epithelial cells in culture. This study compared the ability of pure and partial agonist antiestrogens to stimulate doming. MATERIALS AND METHODS: MCF-7 cells grown in medium with 10% calf serum were treated with antiestrogens. Domes were counted in three rows (width of the 4× field) across the flask. RESULTS: Three partial agonist antiestrogens [4-hydroxytamoxifen (OHT), H1285 and RU 39,411] caused dome formation. None of the pure antiestrogens tested (ICI 164,384, ICI 182,780 and RU 58,668) caused doming. Doming was stimulated in a dose-dependent manner starting at 1 nM OHT with maximum stimulation at 10-100 nM. Estradiol did not stimulate doming, but blocked doming at 1%-10% of the OHT concentration. Trichostatin A (TSA) reduced the level of estrogen receptor alpha (ERα) and adding it 24 h before adding OHT prevented dome formation. CONCLUSIONS: OHT and the other partial agonist antiestrogens appear to act through the ER to stimulate doming. The ability of tamoxifen to induce a marker of differentiation may play a role in its inhibition of breast tumors. If so, then the fact that other partial agonist antiestrogens share this ability, but that pure antiestrogens lack it, may be an important consideration in developing new antiestrogens for breast cancer therapy.

Quantification of external urethral sphincter and bladder activity during micturition in the intact and spinally transected adult rat.

The goal of this study was to determine the effect of chronic mid-thoracic spinal cord transection on the time course of external urethral sphincter (EUS) and bladder activity associated with micturition events in the rat. Adult female Sprague-Dawley rats, either spinally intact or transected (T(9)-T(10)), were anesthetized with urethane and set up for continuous flow urodynamic recording of bladder intravesical pressure (BP) and EUS electromyography (EMG). Spinal transections were performed under isoflurane anesthesia 1-8 weeks prior to the terminal experiment. Four major differences between intact and transected rats were observed: 1) While the frequency of micturition events in the intact rat was dependent upon the rate of bladder filling, the bladder contraction and associated EUS activation in transected rats exhibited an intrinsic rhythm that was independent of the rate of bladder filling and post-transection survival time. 2) EUS activation was augmented at the beginning of active bladder contraction in the transected rat, indicating an amplified guarding reflex. 3) Phasic EUS activity at the peak of bladder contraction (EUS bursting) in the intact rat was markedly reduced or absent in the transected rat. 4) The sustained tonic EUS activity following bladder relaxation in the intact rat was absent in the transected rat. These data are discussed in the context of understanding the pathophysiology of spinal cord injury (SCI) induced destrusor-sphincter dyssynergia (DSD).