Glayde Whitney

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.

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.

Ultrasonic vocalizing by adult female mice (Mus musculus).

Though an extensive body of literature exists concerning the emission of 70-kHz ultrasonic vocalizations by adult male mice (Mus musculus), almost nothing is known about the ultrasonic vocalizing of adult females. A series of five experiments was conducted to examine adult female mouse ultrasound emission. Results indicated female ultrasonic vocalizing to be typically displayed among female mouse dyads and comparable to the ultrasonic vocalizing levels obtained among male-female pairs. Genotypically based variations in the production of ultrasounds by females were also noted. Like male mice, socially naive females readily ultrasonically vocalized to anesthetized female conspecifics and rarely vocalized to anesthetized males. Unlike males, socially experienced females emitted few ultrasounds to either female urine or female-soiled cage shavings. Although social experience served to increase the ultrasound emission of male mice to female sex cues, the production of ultrasounds by females to these cues was decreased by social experience. Implications with regard to the existence of a behavioral/functional sexual dimorphism in adult mouse ultrasonic vocalizing are discussed.

Female odors evoke ultrasounds from male mice

Four experiments investigated the stimulus properties of female mice that influence ultrasound production by adult males. Female urine alone was less effective in evoking ultrasounds than was the female in male-female pairs. Visual cues were not necessary, since there was no difference in the incidence or latency of ultrasounds from male-female pairs when tested in light and dark conditions. A presently unspecified chemical cue produced by females, whose effectiveness is mediated by olfaction, was sufficient to evoke ultrasounds from male mice. The role of this chemical cue in a multimodal sequential communicative chain is discussed.

Generation of inositol phosphates in bitter taste transduction

It is probable that there is a diversity of mechanisms involved in the transduction of bitter taste. One of these mechanisms uses the second messengers, inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). Partial membrane preparations from circumvallate and foliate taste regions of mice tongues responded to the addition of known bitter taste stimuli by increasing the amount of inositol phosphates produced after 30 s incubation. Addition of both the bitter stimulus, sucrose octaacetate and the G-protein stimulant, GTP gamma S, led to an enhanced production of inositol phosphates compared with either alone. Pretreatment of the tissue samples with pertussis toxin eliminated all response to sucrose octaacetate plus GTP gamma S, whereas pretreatment with cholera toxin was without effect. Western blots of solubilized tissue from circumvallate and foliate regions probed with antibodies to the alpha-subunit of several types of G-proteins revealed bands reactive to antibodies against G alpha i1-2 and G alpha o, with no apparent activity to antibodies against G alpha i3. Given the results from the immunoblots and those of the toxin experiments, it is proposed that the transduction of the bitter taste of sucrose octaacetate in mice involves a receptor-mediated activation of a Gi-type protein which activates a phospholipase C to produce the two second messengers, IP3 and DAG.

Morphine ingestion: genetic control in mice.

C57BL/6J mice will drink large amounts of, and display a highly positive preference for, morphine sulfate when it is dissolved in an aqueous solution of sodium saccharin. In identical test situations DBA/2J mice will drink very little of, and display a strong avoidance toward, the morphine-saccharin solution. This clear separation between morphine-accepting and morphine-rejecting animals within a single species combined with a quick and simple method of inducing high levels of morphine ingestion could facilitate the discovery of causal factors in opiate addiction.

A method for isolating and patch-clamping single mammalian taste receptor cells.

Individual taste receptor cells were isolated from the tongue of the mouse by enzymatic treatment followed by mechanical dissociation. The cells were morphologically identical with taste cells from amphibians. Whole-cell voltage-clamp recordings indicated that the murine taste cells possess a variety of voltage-dependent inward and outward currents. Delayed rectifier currents were blocked by denatonium benzoate, one of the most bitter compounds known. This preparation should permit a detailed electrophysiologcal investigation of taste transduction in mammals at the level of taste receptor cells.

Chromosome mapping ofSoa, a gene influencing gustatory sensitivity to sucrose octaacetate in mice

Strain distribution patterns among recombinant inbred strains suggested that a locus influencing taste sensitivity to sucrose octaacetate was on chromosome 6. A location forSoa was established by linkage analysis of behavioral and electrophoretic data from outbred and congenic strains and from test-cross progeny. Haplotyping of 41 outbred CFW-Cr animals with a cDNA probe showed perfect cosegregation ofSoa andPrp, a gene for salivary proline-rich proteins. Five of twelve B6. SW-Soaa strains were found to retainLdr-1, lactate dehydrogenase regulator-1, on chromosome 6 as an allelic passenger from the SWR/J donor strain (source of theSoaa Taster allele). Centimorgan distance was estimated using the ABP/Le linkage-testing strain (non-Taster,Soab) and the SWR/J strain (Taster,Soaa) in a testcross breeding system. The data are consistent with a position for theSoa locus on mouse chromosome 6, 62 cM from the centromere.