Participation of estradiol and progesterone in the retrograde labeling of pubococcygeus motoneurons of the female rat

Reflex activity of the pubococcygeus muscle is modified throughout the estrous cycle in Wistar rats

Pubococcygeus muscle reflex activity has been reported to be driven by specialized neuronal circuitry, including the participation of spinal cord interneurons. Both the reflex and elements of the circuit are known to be sensitive to gonadal hormones, but studies using female rats have not considered the potential effects of estrous phase. Hence, in the present study we used mechanical stimulation of the clitoris to produce reflex activity, and recorded across the different phases of the estrous cycle, including the dark and light periods during each phase. Afterdischarge activity was observed only during the light and dark periods of proestrus, and during the light period of estrus coincident with the receptivity period in the rat́s reproductive behavior. Moreover, this reflex activity comprises at least five different motor unit groups with different firing patterns that are dependent on gonadal hormones variation.

Estrogens influence differentially on the pelvic floor muscles activation at somatovisceral reflexes involved in micturition of rabbits

OBJECTIVE

To determine the estrogen-dependency of the bladder and urethral function and the coordinated activation of pelvic floor muscles (PFM) during micturition.

METHODS

We allocated age-matched female rabbits to control, 1-month ovariectomized (OVX), and OVX plus 2-week estradiol benzoate (EB) groups to record cystometry, urethral pressure, and electromyograms of bulbospongiosus (Bsm), and pubococcygeus muscles (Pcm) simultaneously. We also measured serum estradiol levels and myofiber cross-sectional area. We assessed urodynamic and urethral variables, categorized the Bsm-Pcm activation patterns at storage and voiding phases, and obtained the power spectrum density of muscle activation around the voiding phase. We investigated the influence of ovarian hormones, in general, and the contribution of estrogen, particularly on the functions of the bladder, urethra, and PFM. Statistical significance was set at P < 0.05.

RESULTS

Ovarian hormones influence the bladder, urethral, and PFM functions. The urodynamics analyses indicated estrogens contribute to voiding duration and, to a lesser extent, to the time between bladder contractions. Urethral pressure at closure (maximal pressure-to-maximal urethral pressure ratio) improved partially (8%, P < 0.05) in the OVX plus 2-week estradiol benzoate compared with OVX, but urethral resistance increased (∼1.9-fold, P < 0.05) compared with control rabbits. Our findings support that Pcm activity at voiding is estrogen-sensitive, albeit EB administration reduced it at storage resume, which relates to high urethral resistance.

CONCLUSIONS

Ovariectomy impairs bladder and urethral pressures and Bsm and Pcm activation at micturition in anesthetized rabbits. Estrogen administration partially reverts some of these effects and influences Pcm activation.

The Expression of Hormone Receptors as a Gateway toward Understanding Endocrine Actions in Female Pelvic Floor Muscles

OBJECTIVE

To provide an overview of the hormone actions and receptors expressed in the female pelvic floor muscles, relevant for understanding the pelvic floor disorders.

METHODS

We performed a literature review focused on the expression of hormone receptors mainly in the pelvic floor muscles of women and female rats and rabbits.

RESULTS

The impairment of the pelvic floor muscles can lead to the onset of pelvic floor dysfunctions, including stress urinary incontinence in women. Hormone milieu is associated with the structure and function alterations of pelvic floor muscles, a notion supported by the fact that these muscles express different hormone receptors. Nuclear receptors, such as steroid receptors, are up till now the most investigated. The present review accounts for the limited studies conducted to elucidate the expression of hormone receptors in pelvic floor muscles in females.

CONCLUSION

Hormone receptor expression is the cornerstone in some hormone-based therapies, which require further detailed studies on the distribution of receptors in particular pelvic floor muscles, as well as their association with muscle effectors, involved in the alterations relevant for understanding pelvic floor disorders.

High Estradiol Differentially Affects the Expression of the Glucose Transporter Type 4 in Pelvic Floor Muscles of Rats

PURPOSE

To characterize the relationship between serum estradiol levels and the expression of glucose transporter type 4 (Glut4) in the pubococcygeus and iliococcygeus muscles in female rats.

METHODS

The muscles were excised from virgin rats during the metestrus and proestrus stages of the estrous cycle, and from sham and ovariectomized rats implanted with empty or estradiol benzoate-filled capsules. The expression of estrogen receptors (ERs) was inspected in the muscles at metestrus and proestrus. Relative Glut4 expression, glycogen content, and serum glucose levels were measured. Appropriate statistical tests were done to identify significant differences (P≤0.05).

RESULTS

The pubococcygeus and iliococcygeus muscles expressed ERα and ERβ. Glut4 expression and glycogen content in the pubococcygeus muscle were higher at proestrus than at metestrus. No significant changes were observed in the iliococcygeus muscle. In ovariectomized rats, the administration of estradiol benzoate increased Glut4 expression and glycogen content in the pubococcygeus muscle alone.

CONCLUSION

High serum estradiol levels increased Glut4 expression and glycogen content in the pubococcygeus muscle, but not in the iliococcygeus muscle.

Spinal cord neuronal components involved in the reflex activity of female rat pubococcygeus motoneurons

Evoked EMG reflex activity from the pubococcygeus muscle of female Wistar rats has been reported, but has not been carefully analyzed. Here, we studied this reflex activity through mechanical stimulation of the clitoris, perigenital skin, caudal vagina and foot, all of which produced bilateral reflex multiunit electromyographic (MEMG) tonic "on" activity and displayed a rapid adaptation. However, deep vagina and cervical stimulation did not modify MEMG baseline activity even if it was combined with clitoris, perigenital skin and foot stimulation. Electrical stimulation of the dorsal nerve of the clitoris produced bilateral MEMG activity that when recorded at fast sweep speed, it was possible to observe that the ipsilateral response had an 8 ms latency, while the contralateral response had a 10 ms latency. These data suggest that bilateral reflex activation of pubococcygeus muscle motoneurons is produced by several sensory sources in which a specialized neural circuitry of afferent and efferent components and several spinal cord interneurons are involved. This is in accordance with the multi functionality of this muscle in reproductive and behavioral processes.

Hormonal Treatment Effects on the Cross-sectional Area of Pubococcygeus Muscle Fibers After Denervation and Castration in Male Rats

We explore the interaction of muscle innervation and gonadal hormone action in the pubococcygeus muscle (Pcm) after castration and hormone replacement. Male Wistar rats were castrated and the Pcm was unilaterally denervated; after 2 or 6 weeks, the cross-sectional area (CSA) of Pcm fibers was assessed. Additional groups of castrated rats were used to examine the effects of hormone replacement. At 2 weeks post surgeries, rats were implanted with Silastic capsules containing either dihydrotestosterone (DHT), estradiol benzoate (EB) or both hormones, and the CSA of Pcm fibers was assessed after 4 weeks of hormone treatment. At 2 weeks post surgeries, gonadectomy without hormone replacement resulted in reductions in the CSA of Pcm fibers, and denervation combined with castration increased the magnitude of this effect; further reductions in CSA were present at 6 weeks post surgeries, but again denervation combined with castration increased the magnitude of this effect. Hormone replacement with DHT resulted in hypertrophy in the CSA of nondenervated muscles compared to those of intact normal males, but this effect was attenuated in denervated muscles. Hormone replacement with EB treatment prevented further castration-induced reductions in CSA of nondenervated muscles, but denervation prevented this effect. Similar to that seen with treatment with EB alone, combined treatment with both DHT and EB prevented further reductions in CSA of Pcm fibers in nondenervated muscles, but again denervation attenuated this effect. Thus, while hormone replacement can reverse or prevent further castration-induced atrophy of Pcm fibers, these effects are dependent on muscle innervation. Anat Rec, 300:1327-1335, 2017. © 2017 Wiley Periodicals, Inc.

Effect of multiparity on morphometry and oestrogen receptor expression of pelvic and perineal striated muscles in rabbits: is serum oestradiol relevant?

OBJECTIVE

To determine changes in morphometry and expression of oestrogen receptors (OR) in the pubococcygeus and bulbospongiosus muscles, and the concentration of serum oestradiol associated with multiparity.

STUDY DESIGN

Twelve chinchilla-breed female rabbits were divided into multiparas who had undergone four consecutive deliveries and age-matched virgin nulliparas. Pubococcygeus and bulbospongiosus muscles were surgically removed from each rabbit and processed histologically. Fibre cross-sectional area, number of peripheral nuclei, and expression of ORα and ORβ were measured for each muscle. Serum samples were obtained and the concentration of serum oestradiol was quantified.

RESULTS

Multiparity increased (p ≤ 0.05) fibre cross-sectional area and the number of peripheral nuclei per fibre in pubococcygeus muscle, but not in bulbospongiosus muscle. Expression of both ORα and ORβ was high (p ≤ 0.05) in both muscles from multiparous rabbits. A rise in serum oestradiol was measured at the end of the second pregnancy, which was absent (p ≤ 0.05) at the end of the fourth pregnancy. The concentration of serum oestradiol was similar (p > 0.05) in nulliparous and multiparous rabbits.

CONCLUSIONS

Multiparity caused morphometric changes in pubococcygeus muscle but not in bulbospongiosus muscle. As OR expression was high for both muscles, some properties related to fibre composition or muscle physiology could be affected. The finding that serum oestradiol was not elevated at the end of the fourth pregnancy could be related to changes in pelvic and perineal muscles associated with multiparity.

Multiparity causes uncoordinated activity of pelvic- and perineal-striated muscles and urodynamic changes in rabbits

Temporal and coordinated activation of pelvic- (pubococcygeous) and perineal- (bulbospongiosus and ischiocavernosus) striated muscles occurs during micturition in female rabbits. We have hypothesized that the coordinated activation of pelvic and perineal muscles is modified during the micturition of young multiparous rabbits. Young virgin and multiparous female chinchilla rabbits were used to simultaneously record cystometrograms and electromyograms of the pubococcygeous, ischocavernosus, and bulbospongiosus muscles. Bladder function was assessed using standard urodynamic variables. The temporal coordination of pelvic- and perineal-striated muscle activity was changed in multiparous rabbits. The cystometrogram recordings were different than those obtained from virgin rabbits, as seen in alterations of the threshold volume, the residual volume, the voiding duration, and the maximum pressure. In rabbits, we find that multiparity causes uncoordinated activity of pubococcygeous, ischiocavernosus, and bulbospongiosus muscles and modifies the urodynamics.

Neural control of the female urethral and anal rhabdosphincters and pelvic floor muscles

The urethral rhabdosphincter and pelvic floor muscles are important in maintenance of urinary continence and in preventing descent of pelvic organs [i.e., pelvic organ prolapse (POP)]. Despite its clinical importance and complexity, a comprehensive review of neural control of the rhabdosphincter and pelvic floor muscles is lacking. The present review places historical and recent basic science findings on neural control into the context of functional anatomy of the pelvic muscles and their coordination with visceral function and correlates basic science findings with clinical findings when possible. This review briefly describes the striated muscles of the pelvis and then provides details on the peripheral innervation and, in particular, the contributions of the pudendal and levator ani nerves to the function of the various pelvic muscles. The locations and unique phenotypic characteristics of rhabdosphincter motor neurons located in Onuf's nucleus, and levator ani motor neurons located diffusely in the sacral ventral horn, are provided along with the locations and phenotypes of primary afferent neurons that convey sensory information from these muscles. Spinal and supraspinal pathways mediating excitatory and inhibitory inputs to the motor neurons are described; the relative contributions of the nerves to urethral function and their involvement in POP and incontinence are discussed. Finally, a detailed summary of the neurochemical anatomy of Onuf's nucleus and the pharmacological control of the rhabdosphincter are provided.