John Nyby

Testosterone rapidly reduces anxiety in male house mice (Mus musculus)

Eight experiments supported the hypotheses that reflexive testosterone release by male mice during sexual encounters reduces male anxiety (operationally defined in terms of behavior on an elevated plus-maze) and that this anxiolysis is mediated by the conversion of testosterone to neurosteroids that interact with GABA(A) receptors. In Experiment 1, a 10-min exposure to opposite-sex conspecifics significantly reduced both male and female anxiety 20 min later (as indexed by increased open-arm time on an elevated plus-maze) compared to control mice not receiving this exposure. In contrast, locomotor activity (as indexed by enclosed-arm entries on the elevated plus-maze) was not significantly affected. The remaining experiments examined only male behavior. In Experiment 2, exposure to female urine alone was anxiolytic while locomotor activity was not significantly affected. Thus, urinary pheromones of female mice likely initiated the events leading to the male anxiolysis. In phase 1 of Experiment 3, sc injections of 500 microg of testosterone significantly reduced anxiety 30 min later while locomotor activity was not significantly affected. Thus, testosterone elevations were associated with reduced male anxiety and the time course consistent with a nongenomic, or very rapid genomic, mechanism of testosterone action. In phase 2 of Experiment 3, the anxiolytic effect of testosterone was dose dependent with a 250 microg sc injection required. Thus, testosterone levels likely must be well above baseline levels (i.e., in the range induced by pulsatile release) in order to induce anxiolysis. In Experiment 4, a high dosage of 5alpha-dihydrotestosterone was more anxiolytic than a high dosage of estradiol benzoate, suggesting that testosterone action may require 5alpha-reduction. In Experiments 5 and 6, 3alpha,5alpha-reduced neurosteroid metabolites of testosterone (androsterone and 3alpha-androstandione) were both anxiolytic at a lower dosage (100 microg/sc injection) than testosterone, supporting the notion that testosterone is converted into neurosteroid metabolites for anxiolytic activity. Experiments 7 and 8 found that either picrotoxin or bicucculine, noncompetitive and competitive antagonists of the GABA(A) receptor, respectively, blocked the anxiolytic effects of testosterone. However, conclusions from these 2 experiments must be tempered by the reduction in locomotor activity that was also seen. The possible brain locations of testosterone action as well as the possible adaptive significance of this anxiolytic response are discussed.

Ultrasonic communication of adult myomorph rodents

Abstract Many species of myomorph rodents produce ultrasounds. While the physical characteristics of rodent ultrasounds vary among species, the auditory system appears to be specially attuned for hearing conspecific ultrasounds. High frequency communication by rodents may have evolved because it provides a highly directional signal over a short distance without alerting distant predators. Ultrasounds from adults have been observed during courtship and sex behavior. In these situations, it is usually the male that emits ultrasounds although females of some species also emit ultrasounds. Such ultrasounds may serve as courtship signals prior to copulation and to maintain auditory contact during interejaculation intervals. Research to date has concentrated mainly on the house mouse, Norway rat, golden hamster, and collared lemming. Males of several species, notably excluding house mice, also emit ultrasounds during aggressive behavior. In rats, different types of ultrasound are emitted by dominant and subordinate animals. Although active ultrasonic echolocation would appear to be adaptive for many rodent species, it has not as yet been demonstrated.

The vomeronasal organ: primary role in mouse chemosensory gender recognition.

Four experiments were conducted to determine the chemosensory modality that supports ultrasonic courtship vocalizations by male mice to females and to chemosignals from females. Both removal of the olfactory bulbs (Experiment 1) and removal of the vomeronasal organ (Experiments 2-4) produced similar deficits in the pattern of ultrasonic vocalizations elicited by conspecifics or their odors. Removal of the vomeronasal organ did not impair the ability to locate food buried under cage shavings. These results are consistent with the notion that the analysis of food related odors is subserved by olfaction and that vocalizations to sex chemosignals are elicited primarily by stimulation of the vomeronasal organ/accessory olfactory bulb. Removal of the vomeronasal organ did not induce seminal vesicle regression or lower plasma immunoreactive testosterone levels (Experiment 2) nor was an attempt to restore vocalizations with exogenous testosterone successful (Experiment 4). Thus the altered vocalization pattern following removal of the vomeronasal organ does not appear to arise as a motivational deficit mediated by androgens. Experiments 2 and 3 demonstrated that, in the absence of the vomeronasal organ, stimulation of other sensory systems can, to some extent, maintain the males tendency to vocalize more to females or their odors than to males or their odors. However, this responsiveness to females may rely upon additional behavioral cues. Previous experience also plays a considerable role in the response to chemosensory gender cues by males who lack their vomeronasal organs. Removal of the vomeronasal organ prior to adult heterosexual encounters (Experiment 3) virtually eliminated the males responsiveness to either anesthetized females or their chemosignals. Hence males require adult heterosexual experience with a functioning vomeronasal organ before other chemosensory systems acquire the ability to mediate gender recognition as measured by ultrasonic vocalizations.

Ultrasonic vocalizations by male mice (Mus musculus) to female sex pheromone: Experiential determinants.

Adult male mice (Mus musculus), separated from females at weaning, did not emit 70-kHz courtship ultrasounds to female urine. Other adult males that in addition were given 3-min exposures per day to stimulus females and males for 8 consecutive days later emitted many ultrasounds to female urine. However, even those males that initially responded to female urine typically ceased responding during the course of repeated presentations of female urine. This loss of responsiveness to urine did not generalize to female stimuli. Thus, both the acquisition and maintenance of the male ultrasonic response to female urine are affected by experiential factors.

Ultrasonic vocalizations during sex behavior of male house mice (Mus musculus): A description

After placing a female house mouse into the home cage of a male, the occurrences of four behaviors were recorded on separate channels of an event recorder: (1) male sniffing female, (2) male mounting female, (3) male intromitting female, and (4) 70-kHz vocalizations. The amount of vocalizing was greatest shortly after pairing and was associated with the male sniffing the female. After the male began mounting, vocalizations also were associated with mounting. Vocalizations were recorded during intromissions and occasionally occurred coincident with pelvic thrusts. Very few vocalizations were detected when the male was not sniffing or mounting the female. Vocalizations ceased following ejaculation but typically resumed several minutes before the resumption of another mounting sequence. Thus 70-kHz vocalizations appear to be closely linked to male sexual arousal.

Postpubertal experience establishes signal value of mammalian sex odor.

After encountering adult female mice (Mus musculus) odorized with perfume, adult male mice emitted 70-kHz courtship vocalizations in response to the perfume itself. Living with perfumed mothers odorized from birth to weaning, however, was without effect. This evidence supports the notion that some “sex pheromones” acquire their saliency as a result of adult experience.

40- and 70-kHz vocalizations of mice (Mus musculus) during copulation.

Ultrasonic vocalizations were tape recorded from five pairs of copulating mice and subjected to spectrographic analysis. As expected, the mice emitted numerous 70-kHz vocalizations. At the beginning of the test, before copulation began, 70-kHz calls were emitted almost continuously, while calls with lower spectrographic frequencies were not observed. Subsequently, bursts of 70-kHz calling generally began shortly before mounts and intromissions and persisted until dismount. Intermixed with these 70-kHz calls were additional vocalizations of about 40 kHz. Calling rates were highest just prior to intromission. Once intromissions began, 70-kHz calls continued at a lower rate until dismount; however, 40-kHz calls occurred infrequently. In a second experiment, the male was found to emit the majority of the 70-kHz calls and all of the 40-kHz calls. When the male was devocalized, few calls were detected, regardless of whether the female was able to call. If the male was not devocalized, high rates of calling were detected, even if the female was devocalized.

Intracranial androgenic and estrogenic stimulation of male-typical behaviors in house mice (Mus domesticus)

Two experiments in house mice (Mus domesticus) examined the neural sites at which steroid hormones activate the following male-typical behaviors: 70 kHz ultrasonic mating vocalizations in response to stimulus females or their urine, urinary marking in response to stimulus males or stimulus females, mounting of estrous females, and intermale aggression. In the first experiment, four groups of castrated males received bilateral intracranial implants of testosterone (T) into either the septum (SEPTUM), medial preoptic area (MPO), anterior hypothalamus (AHA), or ventromedial hypothalamus (VMH). Two control groups received subcutaneous silastic capsules of T (TSIL) or empty silastic capsules (BSIL). The TSIL males performed all behaviors at male-typical levels while the BSIL males were unresponsive. MPO males emitted ultrasonic mating vocalizations at high levels while few vocalizations were seen in males of the other brain implant groups. The VMH, AHA, and MPO males urine marked at higher levels than the BSIL males but did not exhibit the high levels of the TSIL males. Mounting was observed only in MPO and TSIL males. Aggression was rare in males from any of the brain implant groups. In the second experiment, the hormone activity of the implants was increased by using testosterone propionate (TP) or a 50% mixture of estradiol (E2) and cholesterol. The six groups were SEPTUMTP, SEPTUME2, MPOTP, MPOE2, TPSIL, and BSIL. The TPSIL males performed all behaviors at male-typical levels while the BSIL males were unresponsive. TP was effective at restoring vocalizations and urine marking only when placed in the MPO; however, E2 was effective at both sites. Again aggression and mounting were less evident in the brain implanted males. In conclusion, implants of T or TP were effective in restoring ultrasonic mating vocalization when placed into the MPO. MPO implants of T and TP were also effective in stimulating urine marking, although VMH and AHA implants also showed some effectiveness. The restorative effects of E2 were not localized which is probably related to the greater hormonal activity of this treatment. Comparisons of the properties of the various brain implants to restore more than one behavior were discussed.

Male mouse (Mus musculus) utrasonic vocalizations to female urine: Why is heterosexual experience necessary?

Previous research was consistent with the hypothesis that urinary chemosignals from female mice (Mus musculus) serve as a conditioned stimulus (CS) for the elicitation of male ultrasonic courtship vocalizations while some other unknown aspect of the female serves as an unconditioned stimulus (US). According to this hypothesis adult heterosexual experience is necessary for males to pair the urinary CS with the US. Three experiments further examined this hypothesis. Experiment 1 demonstrated that the hypothesized US was not female behavior. Experience with anesthesized males and females was just as effective as experience with awake conspecifics. Experiments 2 and 3, however, question the primacy of the Classical Conditioning hypothesis. In both experiments sexually naive males were allowed contact with either normal females or female surrogates. The female surrogates were neonatally castrated males (Experiment 2) or hypophysectomized females (Experiment 3), both of which appeared to possess the hypothesized US but not the urinary CS on the basis of previous research. While exposure to normal females caused the highest level of vocalization to urine from normal females, exposure to the two classes of female surrogates also resulted in vocalizations to the urine of normal females. Thus under some circumstances, males do not require experience with a normal female to emit ultrasounds to urine from normal females. Factors in addition to Classical Conditioning must be operating to account fully for the role of adult heterosexual experience in causing female urine to come to elicit male courtship vocalization.

Reflexive testosterone release: a model system for studying the nongenomic effects of testosterone upon male behavior.

Male mammals of many species exhibit reflexive testosterone release in mating situations. In house mice (Mus musculus), the dramatic robustness of such release, occurring primarily in response to a novel female, suggests some function. The resulting testosterone elevations typically peak during copulatory behavior and may serve to activate transitory motivational and physiological responses that facilitate reproduction. However, such a function requires that testosterone be working through either nongenomic, or very quick genomic, mechanisms. The first part of the review describes reflexive sex hormone release in house mice. The second part summarizes research implicating testosterones fast actions in affecting anxiety, reward, learning, analgesia, and penile reflexes in rodents, all of which could optimize male mating success. The review concludes with a speculative model of how spontaneous and reflexive hormone release might interact to regulate reproductive behavior and why mice appear to be an ideal species for examining testosterones quick effects.