Male sexual behavior comprises a complex pattern of genital and somatomotor responses. Hormones act via receptors in brain, spinal, and peripheral sites to bias sensory inputs and motor outputs to favor sexual responsiveness. Copulation includes mounts, intromissions, and ejaculations, followed by sexual quiescence. After 6–12 ejaculations, male rats become sexually satiated. Neural controls include chemosensory inputs via the main and accessory olfactory systems to the medial amygdala, which transmits information directly and indirectly to the medial preoptic area (mPOA), which integrates sensory and hormonal information and elicits genital reflexes and copulatory patterns and contributes to sexual motivation. Genital sensory input arrives via the central tegmental field/dorsolateral tegmentum (including the subparafasicular nucleus) directly or indirectly into the mPOA. Output from the mPOA is via the paraventricular nucleus and midbrain and brainstem sites. The mesocorticolimbic dopamine pathway contributes motivational fervor, and neural programs for erection and ejaculation reside in the lumbosacral spinal cord. Dopamine facilitates male sexual behavior, whereas serotonin (5HT) is largely inhibitory, although stimulation of 5-HT1A receptors facilitates ejaculation. Norepinephrine has both stimulatory and inhibitory effects on copulation, via α1- and α2-adrenoceptors, respectively. Endogenous opioids play a complex modulatory role in all aspects of copulation. The brain areas that regulate male sexual behavior also influence other social behaviors.

Male Sexual Behavior

This article considers causes of variability in male sexual performance and identifies management techniques that can be used to improve the reproductive success and efficacy of our captive animal populations.

Male sexual behavior.

Sperm-induced leukocytosis in the equine uterus.

Slow-cooled stallion spermatozoa, with and without seminal plasma removed by centrifugation, were diluted in Kenney's extender (KE) containing nonfat dry skim milk with glucose and antibiotics or in KE supplemented by adding a modified high-potassium Tyrode's medium (KMT). Four ejaculates from each of four stallions were collected and divided factorially across these four treatments. Percentage of motile sperm, path velocity, and linearity immediately after treatment (0 h) and after storage at 4 degrees C for 24, 48, and 72 h were evaluated objectively by use of a HTM-2030 sperm motility analyzer. Stallions were a significant source of variation (P less than .01) throughout. After sperm had cooled, effects of stallion, extender, centrifugation, and their interactions were all found to be significant (P less than .01). The motility at 0, 24, 48, and 72 h for centrifuged KE was 74, 47, 39, and 24%; for uncentrifuged KE was 76, 56, 50, and 37%; for centrifuged KMT was 76, 75, 72, and 64%; and for uncentrifuged KMT was 80, 50, 26, and 13%, respectively. The extender x centrifugation interaction, after 24, 48, and 72 h of storage, accounted for half or more of the variation. Whereas centrifugation of semen extended in KE seemed to be harmful to sperm, motility of sperm extended in KMT after centrifugation was remarkably conserved for 72 h and was superior to all other treatments (P less than .05). This extender is promising for preserving liquid stallion semen when it must be transported before use in artificial insemination.

Extender and centrifugation effects on the motility patterns of slow-cooled stallion spermatozoa.

Endometritis in the mare: A diagnostic study comparing cultures from swab and biopsy

Effects of semen fractionation and dilution ratio on equine spermatozoal motility parameters.

The semen of 26 stallions, 2-20 years of age, was collected once a day for 7 consecutive days to determine daily sperm output (DSO). After the last collection, 17 stallions were castrated. Testicular volume was estimated using two methods. Length, width, height, of each testis were measured by caliper. Length, width, height, cross-sectional area and circumference at the widest point of the testis were measured by ultrasonography. Both caliper and ultrasound measurements were first made in the live animal, and again in vitro. There were no differences in these measurements because of method or condition of the animal, i.e., whether the measures were taken in the live animal or after castration. The volume of an ellipsoid (4/3 pi abc, a = height/2, b = width/2, c = length/2) is introduced as a method of accurately estimating testicular volume (r = 0.99) as well as predicting DSO (r = 0.92) in the stallion. The authors of this report suggest that this estimation can be performed by substituting values derived by ultrasonography or calipers.

Evaluation of measures taken by ultrasonography and caliper to estimate testicular volume and predict daily sperm output in the stallion.

Imipramine hydrochloride was administered to five male horses (400-500 kg b.wt.): one experienced young stallion, two mature normal breeding stallions, one 5-year-old stallion with erection and ejaculatory dysfunction, and one long-term castrated male horse. Oral imipramine treatment (100 to 600 mg, twice daily) led to frequent erection and masturbation while at rest in the stall in a nonsexual context. Intravenous imipramine treatment over a range of doses (50 to 1000 mg) similarly induced erection and masturbation in all animals. Erection typically occurred within 10 minutes after injection, and the erection and masturbation continued intermittently for 1 to 2 hours. These erections proceeded as during sexual excitement to a normal firmness and eventual engorgement of the glans penis. Two stallions ejaculated while masturbating. Mild ataxia and drowsiness appeared at the higher doses, but the animals remained responsive to auditory, visual, and tactile stimuli. Erection and masturbation were often interrupted by activities about the barn or the approach of the handler, suggesting cortical inhibitory control of the erection. When tested in a sexual context immediately following IV treatment (500 mg), the two mature breeding stallions bred normally. The 5-year-old stallion, which had not ejaculated over several months of breeding attempts, spontaneously ejaculated following IV imipramine treatment. Subsequently, this stallion has ejaculated during copulation while on low dose oral (100 mg. twice daily) imipramine treatment. Plasma total androgens increased during treatment in these stallions. The long-term castrate showed erection and masturbation following IV imipramine treatment, suggesting that the effect of imipramine is not testosterone dependent.

M.C. Garcia

Papers

Effects of semen fractionation and dilution ratio on equine spermatozoal motility parameters.

Evaluation of measures taken by ultrasonography and caliper to estimate testicular volume and predict daily sperm output in the stallion.

Imipramine-induced erection, masturbation, and ejaculation in male horses

Comparison of two techniques for obtaining endometrial bacteriologic cultures in the mare.

Conditioned suppression of sexual behavior in stallions and reversal with diazepam.