J.L. Contreras

Sensory control of the male rat's copulatory thrusting patterns

The effects of reduced somatosensory feedback from the penis and/or the preputial region upon the male rats copulatory thrusting patterns and sexual behavior were analyzed. Copulatory thrusting was recorded with an accelerometric technique allowing for the determination of duration and frequency of the thrusting trains. Section of the dorsal penile nerves (denervation) or lidocaine applied to the distal part of the penis reduced the number of intromissions and the intromission ratio. These treatments had no effect on copulatory thrusting patterns. Lidocaine injected into the preputial region also reduced the number of intromissions and the intromission ratio. Moreover, the number of disorganized mounts, as revealed by the accelerometric record, was much increased by this treatment. In addition, the duration of the thrusting trains associated with mount and intromission was increased. No effect was found on thrusting frequency. These data suggest that somatosensory feedback from the penis is critical for the achievement of intromission, whereas feedback from the preputial region is important for the execution of copulatory thrusting. Furthermore, it is possible that the strong sensory stimulation of the prepuce associated with penile insertion participates in the termination of thrusting and penile withdrawal.

Androgen regulation of the motor copulatory pattern in the male New Zealand White rabbit.

Abstract The effect of castration and testosterone propionate (TP) treatment on the motor copulatory pattern was studied by an accelerometric technique in five sexually experienced New Zealand white male rabbits. This technique permits the oscillographic recording of thrusting frequency, rhythmicity, and amplitude of the pelvic movements occurring during copulation. Castration resulted in a marked decrease in sexual activity in all rabbits. Mounting, including occasional intromissions, was retained by four of the rabbits for periods ranging from 2 to 15 weeks. Castration did not affect mount duration, but decreased strength and frequency of pelvic thrusting. Diminution in the frequency of pelvic thrusting was mainly due to intercalation of pauses within the mounting trains. The change in the rhythm of pelvic thrusting was related to the failure of most mounts performed by castrated rabbits to stimulate lordosis in the female. Testosterone propionate (TP, 10 mg daily for 15 days) restored mounting activity and increased strength and frequency of pelvic thrusting in all rabbits. It is concluded that TP, besides stimulating sexual motivation, regulates the vigor and rhythm of pelvic movements during copulation in the rabbit.

Dopamine and sexual behavior in the male rabbit

Male rabbits were treated with the dopamine releasing drug amphetamine or the dopamine D1/D2 receptor antagonist cis(Z)-flupenthixol. Amphetamine, 1 to 4 mg/kg, had no effect on sexual behavior. Flupenthixol, 2 mg/kg, reduced the proportion of rabbits that ejaculated and the number of ejaculations per test. Lower doses were ineffective. Castrated males were treated with both drugs at two intervals after castration, 19-21 and 27-29 days postcastration, respectively. Amphetamine was without effect while flupenthixol, 1 mg/kg, reduced sexual behavior at the test 19-21 days postcastration. At the second test, sexual behavior was almost completely absent in control animals. Therefore, no further reduction could be observed after treatment with flupenthixol. Another group of animals was castrated and given androgen replacement. Testosterone decanoate was injected once weekly at a dose of 3 mg/kg. This treatment maintained a stable, low sexual activity. In these animals, amphetamine was again ineffective whereas flupenthixol, 1 mg/kg, inhibited sexual behavior. Gross motor function was evaluated in a water escape test. Amphetamine was inactive, and the effective dose of flupenthixol was 10 mg/kg. This dose is far above the dose required for inhibiting sexual behavior. In sum, facilitated dopaminergic transmission does not seem to affect on sexual behavior in the male rabbit, whereas reduced dopaminergic activity disrupts this behavior.

Testosterone, androstenedione, and 5α-dihydrotestosterone on male sexual behavior and penile spines in the hamster

The expression of masculine sexual behavior (MSB) in male hamsters is optimally stimulated by aromatizable androgens like androstenedione (AD) and testosterone (T), while the non-aromatizable androgen, 5alpha-dihydrotestosterone (DHT), exerting potent androgenic peripheral effects, only in high doses maintains MSB after castration. No data exist on the ability of these androgens to restore long intromissions after castration. In this study, AD, T, and DHT were administered to four-week gonadectomized, sexually experienced male hamsters, for three weeks, in doses of 25 microg/day or up to 1000 microg/day to compare their potency in restoring MSB, penile size, and penile spines growth. Plasma levels of these steroids and the metabolites estrone and estradiol, were determined at the end of the treatment period. Gonadectomy completely suppressed MSB and induced a regression of penile spines. AD was more potent than T in restoring MSB, ejaculatory behavior being displayed by most castrated subjects with a lower dose of AD (50 microg/day) than of T (300 microg/day), and long intromissions being shown by all AD-treated castrated hamsters but only by 20% of T-treated ones, when doses of 1000 microg/day were given. DHT did not stimulate any copulatory response. The three androgens, even at the lowest dose, partially stimulated penis and penile epithelium growth, DHT showing the highest potency. Treatment of castrated hamsters with AD (50 microg/day), restored steroid levels to similar values as those of intact animals. These results show that AD and T restored MSB even with a partial stimulation of penile spines growth, AD being more potent than T. In contrast, DHT did not restore MSB in the hamster in spite of its peripheral androgenic potency.

Detailed analysis of the male copulatory motor pattern in mammals: Hormonal bases

Data obtained, using a polygraphic technique, on the characteristics of the motor and genital copulatory responses of male rabbits, rats, mice, hamsters, and guinea pigs are reviewed. This methodology provided detailed information, not accessible to other analyses, on the frequency and dynamic organization of copulatory pelvic thrusting trains of the species studied. This comparative analysis showed that: (1) The male rat may display two types of ejaculatory responses, differing in the dynamic organization of the pelvic thrusting train, and in the duration of the intravaginal thrusting period preceding ejaculation. (2) In the guinea pigs and small rodents, but not in rabbits, pelvic thrusting at ejaculatory responses persists during intromission, and a period of fast intravaginal thrusting is associated with ejaculation. (3) The motor copulatory pattern of the rabbit, but not of the rat, hamster, or guinea pig, is affected by castration and hormone treatment, suggesting that, in rabbits, androgen acts both on motivation and on the spinal neural systems related to copulation.

Serotonin and sexual behavior in the male rabbit

Summary. Sexual behavior was evaluated in sexually experienced male rabbits after the administration of different serotonergic drugs. The serotonin1A receptor agonist 8-OH-DPAT, 1 mg/kg, inhibited male rabbit sexual behavior when animals were tested 15 min after subcutaneous (SC) administration of this compound. Lower doses, 0.25 and 0.5 mg/kg, were ineffective at a test 30 min after drug injection. Furthermore, 8-OH-DPAT, 0.25 mg/kg, failed to revert the inhibitory effects upon sexual behavior produced by lidocaine application to the rabbit penis. Stimulation of 5-HT1B/2C receptors by TFMPP, at doses between 0.625 and 2.5 mg/kg, produced a drastic inhibition of sexual behavior when the drug was administered SC 30 min before behavioral observation. Doses below 5 mg/kg were ineffective when given intraperitoneally 15 min before test. When the 5-HT1D/2C receptors were stimulated by the agonist mCPP a reduced number of mounts and ejaculations was observed after the SC administration of 1.25 and 2.5 mg/kg. Similarly, the mixed 5-HT agonist/antagonist lisuride reduced the percentage of rabbits displaying mounting behavior at doses of 0.25 and 0.5 mg/kg SC. All compounds tested produced a clear inhibition of male rabbit sexual behavior independently of the receptor subtype activated. These results are at variance with previous observations in rats where 8-OH-DPAT and lisuride produced a drastic facilitation of masculine coital behavior. Moreover, while the inhibition of male sexual behavior in rats produced by TFMPP and mCPP is associated with a disruption of the execution of this behavior, in rabbits these compounds reduced sexual motivation. These results indicate that the effects of serotonergic drugs on sexual behavior are species specific.

Sexual behavior and copulatory thrusting patterns in male rabbits treated with GABA transaminase inhibitors

The effects of enhanced central nervous system GABA levels on sexual behavior and copulatory pelvic thrusting were evaluated in male New Zealand white rabbits. The GABA transaminase inhibitors sodium valproate and gamma-acetylen GABA (GAG), in doses of 100 and 200 mg/kg and 50 and 100 mg/kg, respectively, were intraperitoneally administered and sexual behavior recorded at several intervals after drug administration. At the same time, copulatory thrusting was registered using a polygraphic technique. Tests for gross motor functions were also performed. None of the drugs had any effect in these latter tests. Sodium valproate, in a dose of 100 mg/kg, had a slight inhibitory effect on sexual behavior at 280 min postinjection. A dose of 200 mg/kg inhibited sexual activity already 15 min postinjection, and the effect lasted for at least 280 min. GAG, 100 mg/k, inhibited mounting behavior at 8 h postinjection, and ejaculation was reduced from 2 to at least 8 h postinjection. Copulatory thrusting patterns were not affected by the drug treatments. These data suggest that increased GABAergic activity reduces sexual arousal in the rabbit. GABA does not seem to be critically involved in the regulation of the motor patterns underlying pelvic thrusting. There are important quantitative and qualitative differences between rats and rabbits with regard to the actions of GABA transaminase inhibitors upon sexual functions.

Acid natural clinoptilolite: structural properties against adsorption/separation of n-paraffins.

The employment of an acid natural clinoptilolite (AZH-1) in the adsorption and separation of n-paraffins has been evaluated. Natural clinoptilolite, NZ, was the raw material used to prepare the sodium-exchanged clinoptilolite (AZ) starting from which the AZH-1 sample was obtained by acid treatment. The structural stability of the samples after the applied treatments was demonstrated. The nitrogen adsorption experiments indicated that the acid sample has a homogeneous porous distribution and a considerable increase in the micropore volume with respect to NZ and AZ. The employment of the inverse gas chromatography at infinite dilution (IGCID) allowed studying the adsorption and separation of n-paraffin mixtures on AZH-1. It was also confirmed that the diffusion on AZH-1 took place in an unblocked structure through the A channel of ten members with minimal interactions. The IGCID results demonstrated the capacities of the acid Cuban natural zeolite in the adsorption and separation of n-paraffin mixtures.

Effect of tungsten on supported platinum catalysts

Addition of W to 0.3 wt % Pt/γ-Al 2 O 3 catalysts has been found to stabilize and even increase Pt dispersion after high temperature reduction (up to 1073 K). This effect appears to be caused by formation of Pt species bound to WO x during drying and calcination and by strong interaction between Pt crystallites and the mixed oxide surface after H 2 reduction. UV-vis spectra show the formation of WO x and PtO y species on the surface of alumina in the calcined state. Interaction between Pt 4+ - and W 6+ -bearing structures seems to enhance UV absorption with minor variations in the location of the band maxima. Pt/WO 3 -Al 2 O 3 * were in general more stable towards deactivation than monometallic Pt catalysts (reduced at 773 K) during hydrogenation of benzene. Reduction at 1073 K produced catalysts with lower initial activity but with increased resistance towards deactivation. Impregnation of Pt on WO x -(γ-Al 2 O 3 ) gave the best overall catalysts apparently because of an improved interaction of crystallites with the modified surface of Al 2 O 3 . This result is important in order to control deactivation and sintering of the metallic phase if high operation temperatures are involved.

Thermal Stability of Pt Nanoparticles Supported on WO x /Al 2 O 3 for n-Heptane Hydroconversion

The thermal stabilization of γ-Al 2 O 3 using W +6 ions has been found useful to the synthesis of Pt/Al 2 O 3 catalysts. The sequential impregnation method was used to study the effect of W 6+ upon Pt/ γ-Al 2 O 3 reducibility, Pt dispersion, Raman spectroscopy and n-heptane hydroconversion. The W/Pt atomic ratios varied from 3.28 to 75. We found that the W 6+ ions delayed reduction of a fraction of Pt +4 atoms beyond 773 K. At the same time, W 6+ inhibited sintering of the metallic crystallites once they were formed on the surface. For the sample with a W/Pt atomic ratio of 3.28, W 6+ did not inhibit the H 2 reduction of Pt oxides even below of 773 K, the Pt oxides were reduced completely, however, the Pt dispersion decreased for this sample with respect to the Pt/γ-Al 2 O 3 catalyst. After reduction at 1073 K, sequential samples impregnating Pt on WOx/γAl 2 O 3 were more active and stable during n-heptane hydroconversion than monometallic Pt/γAl 2 O 3 catalyst. Selectivities for dehydrocyclization, isomerization and Hydrocracking changed significantly when the W/Pt atomic ratio and reduction temperature increased. Initial and final reaction rates were more sensitive to reduction temperature. W 6+ ions promoted high thermal stability of Pt crystallites when sequential catalysts were reduced at 1073 K and deactivation of bimetallic catalysts reduced at 773 K and 1073 K was less than the deactivation of Pt/Al 2 O 3 catalyst.