Penile Flips Research Articles

Anatomy of the cavernous muscles of the kangaroo penis highlights marsupial-placental dichotomy.

The mammalian penis is a complex hydraulic organ of cavernous (spongy) tissue supported by both smooth and skeletal muscle structures. In placental mammals, the paired ‎Musculus ischiocavernosi anchor the corpora cavernosa to the pelvis (at the ischium), and the paired M.bulbospongiosi converge as they envelop the base of the corpus spongiosum. Male marsupials have a dramatically different anatomy, however, in which both sets of paired muscles remain separate, have a bulbous, globular shape and do not have any direct connection to the pelvis. Here we provide the first detailed anatomical investigation of the muscles of the penis in the western grey kangaroo (Macropus fuliginosus) incorporating dissection, histology, vascular casting and computed tomography. The M.ischiocavernosus and M.bulbospongiosus form massive, multipennate bodies of skeletal muscle surrounding the paired roots of the corpus cavernosum and corpus spongiosum, respectively. Bilateral vascular supply is via both the artery of the penis and the ventral perineal artery. Histological examination reveals cavernous tissues with substantial smooth muscle supported by fibroelastic trabeculae, surrounded by the thick collagenous tunica albuginea. The M.ischiocavernosus and M.bulbospongiosus are known to function during erection of the penis and ejaculation via muscular contraction increasing blood pressure within cavernous vascular tissues. The thick muscular anatomy of the kangaroo would be well suited to this function. The absence of any connection to the bony pelvis in marsupials suggests the possibility of different mechanisms of action of these muscles with regard to reduction of venous return, eversion from the cloaca, or movements such as penile flips, which have been described in some placental mammals. This highlights a greater diversity in form and function in the evolution of the mammalian penis than has been previously considered.

Anisomycin does not disrupt the activation of penile reflexes by testosterone in rats

A possible role of protein synthetic processes in the testosterone-activation of penile reflexes in rats was examined in these experiments. In Experiment 1, long-term castrated male rats were injected with 250 micrograms testosterone propionate (TP) and tested for penile reflexes 24 hr later. Fifteen minutes prior to TP these males received a systemic injection of the protein synthesis inhibitor anisomycin (ANI) or the saline vehicle. ANI had no disruptive effect on the activation of penile reflexes by TP; in fact, ANI facilitated erection frequency. In Experiments 2 and 3, a series of three ANI or saline injections were given at 2 hr intervals beginning with the injection of 250 micrograms TP, with no significant effect on any reflex parameters tested 12 or 24 hr after TP. In Experiment 4, the penile reflexes of male rats were stimulated by implanting a Silastic capsule containing testosterone subcutaneously for 2 weeks. A series of ANI or saline injections were spaced 3 hr apart, with penile reflexes tested 6 and 12 hr after the first injection. There were no significant differences between ANI and saline-treated males at 6 hr, whereas at 12 hr ANI-treated males had significantly shorter reflex latencies and significantly more penile flips than did males injected with saline. In a final experiment (Experiment 5), the Silastic capsules were removed from the males in the previous experiment. Three injections of ANI or saline were given at 4 hr intervals beginning with the removal of the Silastic capsule.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of perinatal androgen treatment on sexually dimorphic characteristics in rats

Rats were treated with testosterone propionate (TP) or oil (O) beginning in midgestation (group TTT), late gestation (group OTT), neonatally (group OOT), or were left untreated until adulthood (group OOO). At 40 days of age all animals were gonadectomized, received implants of TP in silastic capsules, and were tested in subsequent weeks for masculine copulatory behavior and ex copula phallic responses. Postmortem measures were taken of genital structures and of sexually dimorphic spinal nuclei. Males treated perinatally with androgen were unaffected or exhibited reduced masculinization except on two measures, i. e., number of penile flips and number of cells in the dorsolateral motor nucleus of the lumbar spinal cord, which reflected virilization greater than in normal males. All perinatally androgenized females showed virilization on almost every measure taken of their morphology and behavior. Relative to OOO females, the greatest increases in masculinization were evident in OOT and OTT females. No additional masculinization was detected in TTT females. Only among the TTT rats were males not reliably more masculine than females, but that usually was due to the reduced masculinization of TTT males. Four broad classes of influence characterized the effects of perinatal androgen treatment; these classes may reflect differences in the developmental courses of the variables measured.

Penile mechanisms and the role of the striated penile muscles in penile reflexes

Gross and subgross anatomical observations of the penis pointed to a mechanical arrangement whereby contraction of the bulbocavernosus (BC) muscles would enhance erections of the glans penis and contraction of the ischiocavernosus (IC) muscles would enhance or produce penile flips. These functions for the muscles were confirmed by electromyographic recordings taken during tests of penile erections and flips in spinal male rats. Surgical removal of the BC muscles did not reduce the total number of erections during penile reflex tests, but did eliminate the flared-cup type of erections. Surgical removal of the IC muscles reduced the occurrence of penile flips and virtually eliminated the long or extended flips. It is hypothesized that contractions of the BC and IC muscles, in producing penile cups and long flips, play a role in dislodgement of previously deposited seminal plugs and deposition of new plugs during mating. Contraction of the BC muscles, in forcefully emptying contents of the urethral diverticulum, would appear to play a role in the ejaculatory process by which the sperm-dense fraction of semen is first delivered to the vagina followed by delivery of a rapidly coagulating seminal plug.

Differences in responsiveness to testosterone of penile reflexes and copulatory behavior of male rats

The display of penile reflexes and copulatory behavior appears to reflect the activity of two different underlying neuronal systems, both of which are modulated by systemic testosterone (T) concentration. To indirectly compare the two systems, the responsiveness to T of penile reflexes and copulatory behavior was examined. In the first experiment castrated spinal male rats were given penile reflex tests while receiving replacement T through Silastic capsule implants filled with T (50 mm T). After capsule removal the number of penile erections and flips declined within 24 hr and gradually decreased for 12 days. Subjects were then reimplanted with new 50-mm T capsules. The number of penile flips and erections increased within 6 and 12 hr, respectively. This is a much more rapid response rate to T than has been established for copulatory behavior. In the second experiment castrated spinal male rats were tested for penile reflexes with a 50-mm T capsule, which was then replaced with a 10-, 5-, or 2-mm T or an empty capsule. The number of penile reflexes declined in a dose-response fashion. In the third experiment, castrated sexually experienced male rats were tested for copulatory behavior with two 25-mm T capsules which were then replaced with a 10 or 2-mm T or an empty capsule. Only males with empty capsules had decrements in copulatory behavior, revealing that a low level of T can maintain virtually normal sexual behavior despite a marked decline in penile reflex activity. The neuronal system underlying penile reflexes (spinal neurons) is apparently much more responsive to changes in T concentrations than the neuronal system underlying motivational and appetitive aspects of copulatory behavior (brain neurons).

Copulatory behavior and sexual reflexes of male rats treated with naloxone

Two experiments explored a potential role for endogenous opiates in the regulation of sexual behavior of male rats. Specifically, we questioned whether such opiates regulated the refractory period following ejaculation during copulation, or the latency period for the evocation of penile reflexes (erections, cups, and flips) from supine males. Animals were injected IP with 15–45 mg/kg naloxone hydrochloride 30 min prior to the start of reflex testing, and with 7.5–45 mg/kg naloxone hydrochloride 30 min before testing for copulation. Naloxone resulted in a small but reliable decrease in the number of penile flips. Reflex latency and other measures of penile reflexes were unaffected. At all doses used, naloxone significantly prolonged the postejaculatory refractory period, and there were no other effects on copulation.

Sexual reflexes of spinal male house mice

The question motivating this study was whether species differences in the sexual behavior of rodents may be reflected in species differences in spinally mediated penile reflexes. Sexually mature male house mice (B6D2F1/J) were tested for penile reflexes after the manner used for Norway rats. Intact mice (n=7) displayed no reflexes in two 30–45 min tests. However, penile erections and cups could be induced and maintained by pressing on the abdomen. Apparently in mice, unlike rats, abdominal pressure can simulate the hydraulic action of the muscles that normally induce erection. A second group of mice (n=10) was spinally transected at the T-9 vertebra and tested for penile reflexes 1, 2, 5 and 7 days after transection. Transected mice displayed clusters of penile erections, cups, and flips similar in form to those of rats. The responses occurred with the brief latencies characteristic of spinal rats, but the mice had many more reflexes per cluster than do spinal rats, and penile flips were especially elevated. The greater number of flips and other reflexes per cluster shown by mice relative to rats may reflect the fact that house mice thrust repeatedly during copulatory intromissions, whereas Norway rats thrust only once during their brief insertions. Data from other species will be needed to test and extend the tentative parallels drawn here between species-typical copulatory patterns and spinally-mediated penile reflexes.

Supraspinal influences on the penile reflexes of the male rat: A comparison of the effects of copulation, spinal transection, and cortical spreading depression

The penile reflexes of the rat were observed on interruption of the copulatory behavior sequence after intromission and ejaculation in the initial ejaculatory series, after the penultimate series, during sexual exhaustion, and during recovery from sexual exhaustion 24 and 72 hr later. These were compared to the reflexes of the normal rat in control conditions, to those of the male rat after spinal transection, and to those of the sexually rested and sexually exhausted male rat under cortical spreading depression (CSD). It was concluded that (1) the stimuli associated with copulation evoke disinhibition of the penile reflexes, these showing the short reflex latencies observed in the spinal animal. The release of the spinal mechanisms is lost within 30 min of the last copulatory event. CSD further inhibits reflex responsivity. (2) Stimuli associated with intromission provoke acceleration of the normal rhythmic presentation of reflexes seen in the normal and spinal rat, resulting in a decrease in the duration of intervals between reflex clusters and an increase in reflex number. This excitation decays within about 15 min after intromission. (3) The increase in degree of penile extension and percentage of penile flips after spinal transection suggests tonic inhibition of reflex intensity in the normal rat. The decrease in capacity to attain full erection with the approach of sexual exhaustion suggests an increase in this inhibition. This does not recover during a rest period but instead intensifies. CSD effects did not mimic the effects of spinal transection but instead depressed reflex excitability. The relationship of these changes to the copulatory behavior pattern is discussed.

Relationship of sexual behavior and castration to tumescence in the male rat

Previous research has established that the occurrence of erection in the rat is facilitated by spinal transection, and by exogenous androgen treatment after castration. No data have been reported showing the decline in the occurrence of erection in the castrated, spinally intact rat in the absence of exogenous androgen replacement. In this investigation males initially without mating experience were provided from 3–7 mating trials prior to treatment. Castration was carried out on some of the animals and subsequent tests performed on mating and (or) the occurrence of erection. The frequency of erection had not significantly declined in castrated males in comparison to intact males by two months following castration. However, the duration that erection was maintained showed significant decreases by two months following castration. If castrated males were tested until the frequency of behavioral intromissions reached zero, then subsequent tests showed significant reductions in the frequency of erection as well as in the duration that erection was maintained. There was no apparent relationship between intromission frequency and ejaculation observed in the 3–7 mating trials, and erection frequency and penile flips during the later erection trials. It was concluded that the duration that erection is maintained is more sensitive to androgen withdrawal than is the frequency of erection.