A comparison of the contribution of the major histocompatibility complex (MHC) and Y chromosomes to the discriminability of individual urine odors of mice by Long-Evans rats

Rats rely on airflow cues for self-motion perception

Self-motion perception is a vital skill for all species. It is an inherently multisensory process that combines inertial (body-based) and relative (with respect to the environment) motion cues. Although extensively studied in human and non-human primates, there is currently no paradigm to test self-motion perception in rodents using both inertial and relative self-motion cues. We developed a novel rodent motion simulator using two synchronized robotic arms to generate inertial, relative, or combined (inertial and relative) cues of self-motion. Eight rats were trained to perform a task of heading discrimination, similar to the popular primate paradigm. Strikingly, the rats relied heavily on airflow for relative self-motion perception, with little contribution from the (limited) optic flow cues provided-performance in the dark was almost as good. Relative self-motion (airflow) was perceived with greater reliability vs. inertial. Disrupting airflow, using a fan or windshield, damaged relative, but not inertial, self-motion perception. However, whiskers were not needed for this function. Lastly, the rats integrated relative and inertial self-motion cues in a reliability-based (Bayesian-like) manner. These results implicate airflow as an important cue for self-motion perception in rats and provide a new domain to investigate the neural bases of self-motion perception and multisensory processing in awake behaving rodents.

Sex-limited chromosomes and non-reproductive traits

Sex chromosomes are typically viewed as having originated from a pair of autosomes, and differentiated as the sex-limited chromosome (e.g. Y) has degenerated by losing most genes through cessation of recombination. While often thought that degenerated sex-limited chromosomes primarily affect traits involved in sex determination and sex cell production, accumulating evidence suggests they also influence traits not sex-limited or directly involved in reproduction. Here, we provide an overview of the effects of sex-limited chromosomes on non-reproductive traits in XY, ZW or UV sex determination systems, and discuss evolutionary processes maintaining variation at sex-limited chromosomes and molecular mechanisms affecting non-reproductive traits.

How can the MHC mediate social odor via the microbiota community? A deep dive into mechanisms

Genes of the major histocompatibility complex (MHC) have long been linked to odor signaling and recently researchers’ attention has focused on MHC structuring of microbial communities and how this may in turn impact odor. However, understanding of the mechanisms through which the MHC could affect the microbiota to produce a chemical signal that is both reliable and strong enough to ensure unambiguous transmission of behaviorally important information remains poor. This is largely because empirical studies are rare, predictions are unclear, and the underlying immunological mechanisms governing MHC–microbiota interactions are often neglected. Here, we review the immunological processes involving MHC class II (MHC-II) that could affect the commensal community. Focusing on immunological and medical research, we provide background knowledge for nonimmunologists by describing key players within the vertebrate immune system relating to MHC-II molecules (which present extracellular-derived peptides, and thus interact with extracellular commensal microbes). We then systematically review the literature investigating MHC–odor–microbiota interactions in animals and identify areas for future research. These insights will help to design studies that are able to explore the role of MHC-II and the microbiota in the behavior of wild populations in their natural environment and consequently propel this research area forward.

Odortypes and MHC peptides: Complementary chemosignals of MHC haplotype?

The olfactory and immune systems must perform optimally in the task of recognizing thousands of molecules to ensure survival. A particularly intriguing link between these systems is that animals can smell differences in the major histocompatibility complex (MHC), a cluster of highly polymorphic genes found on human chromosome 6 and mouse chromosome 17. Two different sets of compounds found in urine have been postulated to convey information on MHC haplotype: volatile compounds (odortypes) and MHC peptides. Here we argue for complementary roles for these chemosignals.

Olfactory regulation of maternal behavior in mammals

In mammals, olfactory cues are extensively used in many aspects of maternal care to ensure the coordination of mother-infant interactions and consequently the normal development of the offspring. Outside the period of parturition and lactation, when the young are not a behavioral priority, olfactory cues play an inhibitory role on maternal responsiveness since in most mammalian species studied so far, nonpregnant females find the odor of young aversive. On the contrary at the time of parturition, a shift in the hedonic value of infantile odors occurs so that the young now become a very potent stimulus and this sensorial processing constitutes an important part of the maternal motivational system. Moreover, infants' odors provide a basis for individual recognition by their mothers and some species (ungulates) have developed highly specialized mechanisms for processing of the infant signals. Perception of the smell of the young also regulates various aspects of maternal behavior. Dodecyl propionate, a compound released by of pup's preputial glands, has been shown to influence anogenital licking behavior, a fundamental pattern of maternal behavior in rodents. While there is no functional specificity of either the main or the accessory olfactory systems in the development of maternal behavior amongst species, it appears that only the main olfactory system is implicated when individual odor discrimination of the young is required. Neural structures, such as the main olfactory bulb, undergo profound changes when exposed to offspring odors at parturition. These changes in synaptic circuitry contribute both to maternal responsiveness to these odors, to their memorization, and to effects of long-term maternal experience.

MHC-congenic mice (C57BL/6J and B6-H-2K) show differences in speed but not accuracy in learning the Hebb-Williams Maze

We compared spatial learning and memory in male and female mice of two MHC-congenic strains (C57BL/6J and B6-H-2K) in two versions of the Hebb-Williams Maze. In the food-reward paradigm, males required fewer sessions to learn than females, but there were no strain differences in acquisition. There were no strain or sex differences in the number of errors during the test phase, but the B6-H-2K mice reached the goal box faster than the C57BL/6J mice. In the water-escape paradigm, the C57BL/6J mice required more sessions than the B6-H-2K mice during acquisition. There were no strain or sex differences in the number of errors or in the latency to swim to the goal box in the test phase of the water-escape task. There were no significant correlations between the number of sessions to learn the two mazes; the number of errors made or the latencies to reach the goal box in each maze. These results indicate that these two strains show differences in performance in the Hebb-Williams Maze, but do not differ in cognitive ability.

Marked differences in olfactory sensitivity and apparent speed of forebrain neuroblast migration in three inbred strains of mice

In the adult forebrain, new neuroblasts constantly migrate from the subventricular zone along the rostral migratory stream to the olfactory bulb, where many become neurons. It is unclear whether this process is different in commonly used mouse strains and whether it is related to olfactory function. Adult male BALB/c, C57BL/6, and 129/S1 (formerly 129SV) mice were tested for olfactory sensitivity plus discrimination, using male mouse urine from the two other strains. BALB/c mice had the greatest olfactory sensitivity, followed by 129/S1, and C57BL/6 mice, by an order of magnitude each. Newly formed cells were pulse-labeled for 3 h with i.p. 5-bromo-2'-deoxyuridine (BrdU) injections and the animals analyzed 24 h later. In 129/S1 mice, a greater proportion of neuroblasts were present closer to the olfactory bulb than in BALB/c mice, followed by C57BL/6 mice. The total number of BrdU-labeled cells did not differ, suggesting differences in migration and not proliferation. The impaired olfactory function in C57BL/6 mice might be caused by the reduced number of neuroblasts that reach the olfactory bulbs. However, olfactory function in BALB/c and 129/S1 mice did not correlate with their putative migration speed, suggesting a more complex nature of cellular processes that contribute to olfactory function. These results caution against comparing studies of olfactory function or neural precursors that use different strains of mice, and question the use of C57BL/6 mice as a "normal" strain or as transgenic background. Perhaps more importantly, the results point to an opportunity to identify genes that regulate olfactory function and neuroblast behavior.

Social and individual recognition in rodents: Methodological aspects and neurobiological bases

What animals know about each other, and how they construct and use knowledge of their social world involves at least an ability to recognise different social categories. Although much evidence has accumulated that animals are able to identify and classify other individuals into different categories, few studies have definitively demonstrated true individual recognition, i.e. discrimination between individuals on the basis of their idiosyncratic characteristics. Furthermore, the neural structures and pathways involved in social and, a fortiori, individual recognition have as yet been poorly investigated. This paper discusses various methods and measures currently used to assess different forms of social categorisations in animals, with special reference to rodents. Recent progress concerning the neurobiological bases involved in social recognition is also discussed. Finally, integrative perspectives for studying individual recognition in the context of social cognition is underlined in relation to different approaches investigating rodents' ability to use learned olfactory information.

Influence of MHC on sibling discrimination in Arctic char, Salvelinus alpinus (L.)

The preference of juvenile Arctic char [Salvelinus alpinus (L.)] for odors from siblings and nonsiblings with different major histocompability complex class II (MHC) genotypes was studied in two-choice fluviarium tests. In the first part of the study, test fish demonstrated no preference for water scented by a sibling with a MHC genotype different from its own versus water scented by a MHC identical nonsibling. When both donors were siblings with different MHC genotypes, however, the test fish chose the water scented by the fish with the same MHC type as the test fish. The results suggest that odors with information about kinship are dependent on MHC but also on other, unknown factors. In the second part of the study, we observed that fish isolated since fertilization did not show any behavioral discrimination towards siblings, based on MHC genotype. One reasonable explanation for this result is that Arctic char learn to discriminate between odors from individuals of different MHC types.

Unravelling the chemical basis of competitive scent marking in house mice

Major urinary proteins (MUPs) in the urine of male house mice, Mus domesticus, bind the male signalling volatiles 2- sec -butyl-4,5-dihydrothiazole (thiazole) and 3,4-dehydro- exo -brevicomin (brevicomin) and slowly release these volatiles from urinary scent marks. To examine the role of urinary proteins and volatiles, either attached or unattached to the proteins, in competitive scent marking, we fractionated urine from isolated male BALB/c laboratory mice, Mus musculus, by size-exclusion chromatography into three pools. Pool I contained all of the urinary proteins and their bound ligands while pools II and III contained lower molecular weight components including unbound signalling volatiles. In experiment 1, pools I-III were streaked out on to absorbent paper (Benchkote) and introduced into enclosures housing single wild-caught male mice, together with a clean control surface. Each male was tested with fresh stimuli and with aged stimuli deposited 24 h previously. Only pool I stimulated significantly more countermarking and investigation than the control, attracting mice to investigate from a distance even when the rate of ligand release was considerably reduced after 24 h. Experiment 2 examined responses to pool I when this was fresh, aged by 7 days, or had been mixed with menadione to displace ligands from the proteins. Although all three protein stimuli were investigated and countermarked more than a clean control, the aged and menadione-treated pool I stimulated the strongest responses, despite containing the lowest levels of thiazole and brevicomin. Thus competitive countermarking is stimulated by proteins or by nonvolatile protein-ligand complexes in male urine, while release of volatile ligands attracts attention to a competitor's scent marks. Copyright 1999 The Association for the Study of Animal Behaviour.

MHC and kin discrimination in juvenile Arctic charr, Salvelinus alpinus (L.)

Kin recognition and discrimination are thought to occur in several species of various taxonomic groups. In salmonid fish, juveniles can discriminate between odours of siblings and nonsiblings from the same population even if the odour donors and the test fish have been reared separately since fertilization. This indicates that some genetic factor is important in the recognition process. The mechanisms behind kin recognition and discrimination have not yet been described. In the present study, we performed fluviarium tests to examine whether kin recognition and discrimination in juvenile Arctic charr are influenced by the major histocompatibility complex (MHC). Prior to the fluviarium tests, exon 2 of an MHC class II B gene in charr was analysed with denaturing gradient gel electrophoresis (DGGE) and individual genotypes were determined. In the fluviarium, when fish had the choice between water scented by an MHC identical sibling and a sibling with a different MHC genotype they preferred water from identical siblings. Moreover, water scented by an MHC different sibling was preferred to water from an MHC different nonsibling. However, we observed no discrimination when the test fish shared one allele with the nonsibling donor but no alleles with the sibling donor. Our results indicate that the MHC has a significant influence on the odours used for kin recognition and discrimination in juvenile Arctic charr.Copyright 1998 The Association for the Study of Animal Behaviour

Y chromosome, urinary chemosignals, and an agonistic behavior (offense) of mice

In mice, offense is one type of agonistic behavior associated with attacks. Offense of male mice was measured in a panel of testers design. The mice were DBA1 (D1) and DBA1.C57BL10-Y (D1.B10-Y). These are congenic for the male-specific, nonrecombining part of the Y chromosome. For the behavioral experiments, urine from D1 or D1.B10-Y mice was daubed on gonadectomized opponents. The opponents were of two genotypes, D1 or D1.B10-Y. The experimental subjects were of the same two genotypes. There were main effects for strain of experimental subject and strain of urine donor as well as interactions for strain of experimental subject x strain of gonadectomized opponent, strain of gonadectomized opponent x strain of urine donor, and strain of experimental subject x strain of gonadectomized opponent x strain of urine donor. These findings are consistent with a model in which this part of the Y chromosome affects testosterone-dependent pheromones and non-testosterone-dependent odor types acting as motivating stimuli, the olfactory perception of motivating stimuli for offense, and the motivational mechanism for offense.

Searching for candidate genes with effects on an agonistic behavior, offense, in mice

It is well established that the agonistic behavior of offense in mice is heritable. However, few genes have been identified or mapped for offense. For segments of chromosomes with effects on offense, a positional candidate strategy can be used to find such genes. This approach is illustrated for the effect of the male specific part (nonpseudoautosomal region; NPAR) of the mouse Y chromosome on offense. It is proposed that a positional candidate for this effect is Sry. The Sry protein is a transcription factor. Its mRNA is expressed in fetal and adult brain. Its protein binds to response elements in the 5' end of the aromatase and the Fra1 genes. Each of these genes has potential effects on several brain neurotransmitter systems involved in offense. The NPAR Y chromosomes of several pairs of inbred strains have differential effects on offense. This hypothesis would be tested by sequencing Sry for some of these pairs of strains.

Aggression in wild house mice: current state of affairs

This paper reviews our present state of knowledge of genetic variation in (offensive) aggression in wild house mice. The basic tools in this research were lines bidirectionally selected for attack latency (fast attacking SAL and slow attacking LAL males), descended from a feral population. Using congenic lines for the nonpseudoautosomal region of the Y chromosome (YNPAR), reciprocal crosses between (parental) SAL and LAL, and crosses between parentals and congenics, an autosomally dependent Y chromosomal effect on aggression has been found. Both the pseudoautosomal (YPAK) region and the YNPAR play a role. As for environmental sources of variation, prenatal and postnatal maternal effects are of minor importance for the development of aggression differences. One of the physiological factors by which genetic effects may be mediated is testosterone (T). Besides quantitative aspects, the timing of T release seems crucial. Two important time frames are discussed: the perinatal and pubertal time periods. Finally, neurochemical and neuroanatomical correlates are considered. Differences in neostriatal dopaminergic activity, and sizes of the intra- and infrapyramidal mossy fiber terminal fields, as well as Y chromosomal effects on the latter two, are discussed.

Autosomal and Y chromosomal effects on the stereotyped response to apomorphine in wild house mice

The behavioral response to apomorphine, a dopamine agonist, was shown to be different between a selection line characterized by Short Attack Latencies (SAL) and a selection line having Long Attack Latencies (LAL) (4). Aggressive SAL mice were more sensitive to apomorphine than nonaggressive LAL males. The aim of this research was to determine whether the stereotyped response to apomorphine is affected by the Y chromosome in the same way as it influences attack latency. For this purpose, F1 reciprocal hybrids as well as congenic lines (SAL.LY and LAL.SY) were used. The major difference between the congenic and parental lines is the nonpairing part of the Y chromosome (non-PAR). Apomorphine was injected subcutaneously at a preselected dose level of 5.0 mg/kg to induce stereotyped behavior manifested in compulsive sniffing, gnawing, and licking. Both the autosomes and the non-PAR Y chromosome affected the response to apomorphine. The effect of the autosomes was in accordance with the aggression data, whereas the effect of the non-PAR Y chromosome was different, and suggests a specific relation between dopamine systems and the non-PAR Y chromosome.

What is the role of the immune system in determining individually distinct body odours?

Genetically inbred mice and rats which are identical except for the genes of the major histocompatibility complex (MHC) produce unique urinary odours which can be discriminated by other animals. Congenic strains differing in both the Class I and Class II regions of the MHC produce distinct urinary odours. These urine odours can be used for mate selection and parental recognition, and it has been suggested that they provide a unique genetic mechanism for kin recognition. However, the non-MHC genes and the X and Y chromosomes also modulate the urinary odours of rodents, and rearing rats in a bacteria-free environment inhibits the production of unique MHC-related odours. We have found that dietary differences produce a greater effect on individual odours than differences at one MHC locus. These results suggest that the MHC, commensal bacteria, and dietary products interact to produce urinary odours which can be used for individual recognition in rodents. The problem is: what is the role of the immune system in determining individually distinct body odours? A model that suggests possible answers to this question is proposed.

Intermale aggression tested in two procedures, using four inbred strains of mice and their reciprocal congenics: Y chromosomal implications

Indications of a role for the nonpseudoautosomal region of the Y chromosome (YNPAR) in intermale attack behavior have been demonstrated by Maxson's group using C57BL/10 (B10) and DBA/1 (D1) inbred mouse strains and their reciprocal congenics. Carlier and Roubertoux' group, using CBA/H (H) and NZB/B1NJ (N) mice, did not find such a YNPAR effect. For the two research groups, however, not only were the parental strains different, but also the rearing conditions and testing methods. The divergent conclusions drawn may therefore have been due either to genetic variation or to environment-related variables. We carried out two experiments to investigate these alternatives. The N and H strains were raised and tested according to the experimental design used by Maxson's group (homogeneous set test) and the D1 and B10 strains were raised and tested according to the experimental design of Carlier and Roubertoux' group (standard opponent test). Considering all studies together, the YNPAR effect appeared in both sets of mice only when using the homogeneous set test. This raises the question of what environmentally related variables are involved in the YNPAR effect on intermale attack. One strong hypothesis is that the different types of opponents in each experimental design send differing olfactory signals, which, in turn, differentially affect the capacity to elicit intermale attack behavior.

Odors of individuality of germfree mice are not discriminated by rats in a habituation-dishabituation procedure

This study investigates whether differences in urinary odors of two major histocompatibility complex (MHC) congenic strains of mice reared in germfree conditions could be detected by male Sprague-Dawley rats in a habituation-dishabituation procedure. Rats were tested for their ability to discriminate between urine odors from one of the following pairs: (a) MHC congenic mice (B6 and B6-H-2k) housed in conventional conditions; (b) MHC congenic mice (B6 and B6-H-2k) raised in a germfree environment; (c) genetically identical mice maintained in conventional housing; or (d) genetically identical mice raised in a germfree environment. The urine odors of mice from the two MHC congenic strains raised in conventional housing were discriminable, but the urine odors of MHC congenic mice raised in a germfree environment were not discriminable. The odors of genetically identical mice, whether housed conventionally or under germfree conditions, were not discriminable. These results indicate that germfree rearing influences the urinary odors of individuality in MHC congenic mice. We discuss the possibility that the disparate findings from previous studies are a result of the methodologies employed.

Olfactory discrimination of urinary odortypes from congenic strains (DBA/1Bg and DBA1.C57BL10-YBg) of mice differing in their Y chromosomes

Differential effects of one or more genes in the nonpseudoautosomal region of the DBA1 and C57BL10 Y chromosomes on offensive attack may be mediated, at least in part, by differential effects of this Y chromosomal gene(s) on the sending and receiving of discriminable urinary odortypes. This hypothesis is based, in part, on the report that urine from a pair of Y chromosomal congenic strains (C57BL6.AKR-Y and C57BL6) of mice can be discriminated in a Y maze test. The AKR and C57BL6 Y chromosomes come from two distinct species of mouse (Mus domesticus and Mus musculus, respectively). Thus, this Y chromosomal variant exists between mouse species. The DBA1 and C57BL10 Y chromosomes come from a single species, Mus musculus. Here we show that in the Y maze system previously used, urine from mice with the DBA1 and with the C57BL10 Y chromosomes can also be discriminated. Thus, there are discriminable urinary odortypes for this pair of Y chromosomes from the same species, Mus musculus.