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I always said, since I wrote in Portuguese "My Real Sex", that
homosexuality was not a being question, but a taste question,a love question.
Bonobos primates (Pan paniscus), the most related primates with humans, have
bisexual tastes, systematically... surely not all of them
have problems with their brains, as a hole species...so, sexual orientation
was not a question of brain differentiation, but a QUESTION OF TASTE.We do not
understand how pheromones work in our noses... how pheromones atract women and
men... but today we know they are important to define our tastes and sexual
orientation. Obviously, homosexuality has something to do, as heterosexuality,
with pheromones. One day, I hope soon, we will understand better how it works...
and modulate our sexual tastes. The important now, is to understand how our
noses work with pheromones, why some noses feel atracted by men, others by
women, others by both...others by noone. Our noses pheromone sensors are
related to our brains...surely thru our hypothalamus...
Effects of putative male pheromones on female ratings of male attractiveness: influence of oral contraceptives and the menstrual cycle.
Thorne F, Neave N, Scholey A, Moss M, Fink B.
Human Cognitive Neuroscience Unit, Division of Psychology, Northumbria University, Newcastle upon Tyne, UK.
Previous research has revealed that natural and synthetic pheromones can enhance ratings of opposite sex attractiveness. The present study investigated the effects of exposure to male axillary secretions on female ratings of the sexual attractiveness of male stimuli. Thirty-two female undergraduates, half of whom were contraceptive pill users, rated male vignette characters and photographs of male faces on aspects of attractiveness. On two separate study days, corresponding to different phases of their menstrual cycle, stimuli were presented while exposed to male axillary pheromones and under a control condition (no pheromone). The order of testing was balanced with respect to pheromone/control condition and menstrual cycle phase. Pheromone exposure resulted in significantly higher attractiveness ratings of vignette characters and faces. Use of the contraceptive pill or menstrual cycle phase had equivocal effects on some vignette items and neither had any influence on female ratings of male facial attractiveness. The results of this study suggest that exposure to natural male axillary pheromones can significantly enhance female perceptions of various aspects of male attractiveness.
PMID: 12195229 [PubMed - indexed for MEDLINE]
1: Ann Biol Clin (Paris). 2003 May-Jun;61(3):275-8.
[Pheromones: an underestimated communication signal in humans]
[Article in French]
The pheromones are molecules, mainly aliphatic acids, with or without perceptible odor, recognized by specific receptors, the stimulation of which induces neuroendocrine reactions and affects the individual behavior. Olfactory receptors are underexpressed in human, 70 % of genes have become nonfunctional pseudogenes. But the remaining function was tested and is able to induce emotional reactions corresponding to a non-verbal signal of social interactions. In the present study, we review the actual knowledge on the olfactory receptors. They belong to the G-protein-coupled-receptors. Their signal is transduced to the hypothalamic-pituitary-gonadal axis. Some HLA-based olfactory cues are shown with reference to recent experiments. The pathophysiological hypotheses are considered with respect to studies in anorexia nervosa and Alzheimer' disease.
PMID: 12805004 [PubMed - indexed for MEDLINE]
1: Biol Reprod. 2003 Jun;68(6):2107-13. Epub 2003 Jan 22.
Monell Chemical Senses Center, Philadelphia, Pennsylvania 19104.
Human underarm secretions, when applied to women recipients, alter the length and timing of the menstrual cycle. These effects are thought to arise from exposure to primer pheromones that are produced in the underarm. Pheromones can affect endocrine (primer) or behavioral (releaser) responses, provide information (signaler), or perhaps even modify emotion or mood (modulator). In this study, we extracted underarm secretions from pads worn by men and placed the extract under the nose of women volunteers while monitoring serum LH and emotion/mood. Pulses of LH are excellent indicators of the release of GnRH from the brain's hypothalamus. In women, the positive influence of GnRH on LH affects the length and timing of the menstrual cycle, which, in turn, affects fertility. Here we show that extracts of male axillary secretions have a direct effect upon LH-pulsing and mood of women. In our subjects, the putative male pheromone(s) advanced the onset of the next peak of LH after its application, reduced tension, and increased relaxation. These results demonstrate that male axillary secretions contain one or more constituents that act as primer and modulator pheromones.
Human olfactory contrast changes during the menstrual cycle.
Watanabe K, Umezu K, Kurahashi T.
Department of Biophysical Engineering, Osaka University, Toyonaka, 560-8531 Japan.
Several lines of studies have reported that olfactory perception is influenced by physical and hormonal conditions. In the present study, we investigated changes of olfactory perception during the menstrual cycle of the human. Cyclopentadecanolide vapor was used and its perception intensity was measured by 6-point category scale methods. We especially focused on a novel concept termed "olfactory contrast" that has been just very recently derived from the patch clamp experiment that uses the solitary olfactory receptor cell. The results obtained from 18 trials (15 subjects) showed that olfactory contrast was significantly enhanced at the ovulatory and/or menstrual phases. It is suggested that olfactory contrast, which we defined as a new parameter, provides a useful tool in many kinds of studies exploring the olfactory perceived ability.
Institut fur Zoophysiologie der Universitat Bonn, Entwicklungsbiologie, Germany. firstname.lastname@example.org
Classically hormones are defined as molecules that are secreted by endocrine glandular or neurosecretory cells into the blood stream and transported to their target tissue where they induce physiological processes at very low concentrations. Studies on the potential origin and the evolution of cell-to-cell communication systems suggest that exocrine pheromones (food signals and toxins) might have been the primitive bioregulatory molecules of unicellular organisms for chemical communication with each other and with the biosphere. The broad distribution and the structural diversity of pheromones suggests that these molecules and their receptors were predecessor modules of cell communication systems in metazoa. Neurosecretory cells, as we find them in Cnidarians, possibly served as basic modules for the evolution of neurohormonal systems of higher animals. Studies on genetic model organisms, such as Drosophila or the mouse, have demonstrated that chemical communication between neighbouring or more distant cells does not just involve endocrine and neurosecretory cells, but also unexpectedly tissues and organs such as the heart or the adipose tissue (e. g. the leptin signalling pathway). Comparative endocrinology could show that molecular components of hormonal systems represent signalling networks that are generally used during cellular communication processes and the differentiation of cell types during ontogenesis. Some of their functions are evolutionarily conserved, others not, as disscussion on steroid hormones and the prolactin signalling pathway will demonstrate.
[Human and animal vomeronasal systems in health and disease]
[Article in Russian]
Institute of Human Morphology, 117418, Moscow.
The vomeronasal organ (VO) or the second olfactory organ has the form of paired epithelial pockets at the base of the nasal septum. In animals it has various functions including reception of pheromones mediating sexual, parental and social behavior. Human VO was considered to be rudimental until the last decade of the XXth century. Since then it was found to be present almost in every adult individual and was proved to be functional. The paper provides new facts on the occurrence of VO in man and animals, analyzes possible consequences of plastic surgery of the nose and considers some vomeronasal abnormalities, their diagnosis and treatment.
The vomeronasal system in mammals plays an important role in social and reproductive behaviour. Pheromones are airborne chemical signals that are released by an individual into the environment and affects another member of the same species. The human vomeronasal system was commonly regarded as vestigial, but recently new interest is focussed on this chemoreceptor organ, located at the base of the human nasal cavity. Although vomeronasal systems have long been known to exist in all fetal humans, little is known of the growth of this system in adults. We give a summary of the publications to the features, the frequency of occurrence, the ultrastructure, the developmental aspects and the functional significance of the Jacobson's organ in human.
Pheromone detection by mammalian vomeronasal neurons.
Zufall F, Kelliher KR, Leinders-Zufall T.
Department of Anatomy and Neurobiology and Program in Neuroscience, University of Maryland, Baltimore, Maryland 21201-1509, USA.
The vomeronasal organ (VNO) of mammals plays an essential role in the perception of chemical stimuli of social nature including pheromone-like signals but direct evidence for the transduction of pheromones by vomeronasal sensory neurons has been lacking. The recent development of electrophysiological and optical imaging methods using confocal microscopy has enabled researchers to systematically analyze sensory responses in large populations of mouse vomeronasal neurons. These experiments revealed that vomeronasal neurons are surprisingly sensitive and highly discriminative detectors of volatile, urinary metabolites that have pheromonal activity in recipient mice. Functional mapping studies of pheromone receptor activation have uncovered the basic principles of sensory processing by vomeronasal neurons and revealed striking differences in the neural mechanisms by which chemosensory information is detected by receptor neurons in the VNO and the main olfactory epithelium. These advances offer the opportunity to decipher the logic of mammalian pheromonal communication. Copyright 2002 Wiley-Liss, Inc.
Recent progress in the neurobiology of the vomeronasal organ.
Department of Anatomy, School of Health Sciences, Kyorin University, Hachioji, Tokyo 192-8508, Japan. email@example.com
In many terrestrial tetrapodes, a pair of vomeronasal organs (VNOs), which are chemosensory apparatuses, are situated at the base of the nasal septum in the anterior nasal cavity. The purposes of this review are to summarize comparative neuroanatomy and to introduce recent progress in neurobiological studies of the VNO. Five types of VNOs can be identifiable in terms of anatomical organization; snakes possess the most complex one. Sensory cells in the VNO, vomeronasal receptor neurons (VRNs), are located in its neuroepithelium, vomeronassal sensory epithelium. The VRNs retain the characteristic of epithelial cells in that they are born continuously from progenitor cells. They contain two prominent subcellular structures: microvilli and extraordinarily large amounts of smooth endoplasmic reticulum and a few unique glycoconjugates. The VRNs express two types of G-protein -subunits: Gi(alpha2) and Go(alpha) and each of them is coupled with putative pheromone receptors, V1Rs and V2Rs, respectively. Recent physiological and biochemical studies have demonstrated that pheromones depolarize the V1R-Gi(alpha2) and V2R-Go(alpha) VRNs via IP(3)-mediated mechanisms. The VRNs do not show adaptation and are ultrasensitive to putative pheromones. Other than being a chemosensory organ, the VNO and its primordium might play important roles for brain development; hypothalamic neurons that produce gonadotropin-releasing hormone are born in the VNO primordium and a few other neuron-like cells may be born in the VNO primordium and VNO. In human fetuses, anatomical findings strongly suggest that their VNOs contain a neuroepithelium. By contrast, it is unlikely that adult human VNO serves as a chemosensory organ. Copyright 2002 Wiley-Liss, Inc.
Sexual differentiation of the neuroendocrine mechanisms regulating mate recognition in mammals.
Centre for Cellular and Molecular Neurobiology, Research Group in Behavioural Neuroendocrinology, University of Liege, B-4020 Liege, Belgium. firstname.lastname@example.org
When in breeding condition, male and female mammals seek out and mate with opposite-sex conspecifics. The neural mechanisms controlling mate recognition and heterosexual partner preference are sexually differentiated by the perinatal actions of sex steroid hormones. Many mammalian species use odours to identify potential mates. Thus, sex differences in partner preference may actually reflect sex differences in how male and female mammals perceive socially relevant odours. Two olfactory systems have evolved in vertebrates that differ considerably in their anatomy and function. It is generally believed that the main olfactory system is used to detect a wide variety of volatile odours derived from food prey among many sources, whereas the accessory olfactory system has evolved to detect and process primarily nonvolatile odours shown to influence reproductive behaviours and neuroendocrine functions. Some recent results obtained in oestradiol-deficient aromatase knockout (ArKO) mice that provide evidence for a developmental role of oestradiol in olfactory investigation of volatile body odours are discussed, suggesting that: (i) oestrogens contribute to the development of the main olfactory system and (ii) mate recognition is mediated by the main as opposed to the accessory olfactory system. Thus, sex differences in mate recognition and sexual partner preference may reflect sex differences in the perception of odours by the main olfactory system.
Mating types in yeast, vomeronasal organ in rodents, homosexuality in humans: does a guiding thread exist?
Pheromones and their receptors are the molecules used by very different organisms in order to join two haploid cells. It happens evidently in yeast, since the two blending haploid cells are also the two mating organisms, whereas in rodents pheromone receptors are the triggers of the vomeronasal system which, supervising sexual behaviors, is responsible for copulation and therefore for fertilization. The debate is still open about the real significance of pheromones in humans but a working vomeronasal organ, able to recognize pheromones of the same sex, could be the simplest biological explanation of homosexuality. This hypothesis is discussed and connected with some well known experimental data.
Mecanismes de communication, Unite de Recherche Associee-CNRS 1491, Batiment 446, Universite Paris-Sud, 91405, Orsay-Cedex, France. email@example.com
Pheromones are intraspecific chemical signals important for mate attraction and discrimination. In the fruit fly Drosophila melanogaster, hydrocarbons on the cuticular surface of the animal are sexually dimorphic in both their occurrence and their effects: Female-specific molecules stimulate male sexual excitation, whereas the predominant male-specific molecule tends to inhibit male excitation. Complete feminization of the pheromone mixture produced by males was induced by targeted expression of the transformer gene in adult oenocytes (subcuticular abdominal cells) or by ubiquitous expression during early imaginal life. The resulting flies generally exhibited male heterosexual orientation but elicited homosexual courtship from other males.
PMID: 9171057 [PubMed - indexed for MEDLINE]
1: Mol Biol Evol. 2003 Jun 27 [Epub ahead of print].
Positive Selection During the Diversification of Class I Vomeronasal Receptor-Like (V1RL) Genes, Putative Pheromone Receptor Genes, in Human and Primate Evolution.
Mundy NI, Cook S.
Institute of Biological Anthropology, University of Oxford, Oxford, England.
Vomeronasal receptors are the major receptors for pheromones in vertebrates and five putative type 1 vomeronasal receptors (V1RL) have been identified in humans. The evolution of the V1RL1 gene in non-human primates, and patterns of selection on V1RL genes, were investigated. The presumed orthologue of V1RL1 was sequenced from thirteen species of non-human primate, and in eight of these species V1RL1 was a pseudogene. Phylogenetic reconstructions reveal that V1RL1 pseudogene formation occurred independently in multiple primate lineages. Using maximum likelihood estimates of dN/dS ratios in PAML we show that V1RL genes have evolved under neutral evolution in lineages in which they became a pseudogene. In contrast, among lineages in which V1RL genes contain an open reading frame, the majority of sites are under purifying selection and a minority of sites are under significant positive selection. These results provide an interesting case where all three categories of selection can be teased apart in the same dataset using maximum likelihood methods. The finding of positive selection on V1RL genes during primate evolution provides indirect support for the hypothesis that V1RL genes have a function in species-specific pheromone detection in primates.
PMID: 12832635 [PubMed - as supplied by publisher]
1: Proc Natl Acad Sci U S A. 2003 Jul 8;100(14):8337-41. Epub 2003 Jun 25.
Evolutionary deterioration of the vomeronasal pheromone transduction pathway in catarrhine primates.
Zhang J, Webb DM.
Department of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI 48109, USA. firstname.lastname@example.org
Pheromones are water-soluble chemicals released and sensed by individuals of the same species to elicit social and reproductive behaviors or physiological changes; they are perceived primarily by the vomeronasal organ (VNO) in terrestrial vertebrates. Humans and some related primates possess only vestigial VNOs and have no or significantly reduced ability to detect pheromones, a phenomenon not well understood at the molecular level. Here we show that genes encoding the TRP2 ion channel and V1R pheromone receptors, two components of the vomeronasal pheromone signal transduction pathway, have been impaired and removed from functional constraints since shortly before the separation of hominoids and Old World monkeys approximately 23 million years ago, and that the random inactivation of pheromone receptor genes is an ongoing process even in present-day humans. The phylogenetic distribution of vomeronasal pheromone insensitivity is concordant with those of conspicuous female sexual swelling and male trichromatic color vision, suggesting that a vision-based signaling-sensory mechanism may have in part replaced the VNO-mediated chemical-based system in the social/reproductive activities of hominoids and Old World monkeys (catarrhines).
PMID: 12826614 [PubMed - indexed for MEDLINE]
1: Proc Natl Acad Sci U S A. 2003 Mar 18;100(6):3328-32. Epub 2003 Mar 11.
Relaxed selective pressure on an essential component of pheromone transduction in primate evolution.
Liman ER, Innan H.
Department of Biological Sciences and Program in Neurosciences, University of Southern California, Los Angeles, CA 90089, USA. Liman@USC.edu
The vomeronasal organ (VNO) detects pheromones in many vertebrate species but is likely to be vestigial in humans. TRPC2(TRP2), a gene that is essential for VNO function in the mouse, is a pseudogene in humans. Because TRPC2 is expressed only in the VNO, the loss of selective pressure on this gene can serve as a molecular marker for the time at which the VNO became vestigial. By analyzing sequence data from the TRPC2 gene of 15 extant primate species, we provide evidence that the VNO was most likely functional in the common ancestor of New World monkeys and Old World monkeys and apes, but then became vestigial in the common ancestor of Old World monkeys and apes. We propose that, at this point in evolution, other modalities, notably the development of color vision, may have largely replaced signaling by pheromones.
PIP: The role of olfactory sexual attractants in the sex behavior of primates is discussed. These olfactory cues can prompt mounting, masturbation, and ejaculation, increase grooming behavior, and reduce aggressive behavior. In rhesus monkeys, the addition of phenylpropanoic and parahydroxyphenylpropanoic acids to a synthetic acid mixture has been shown to enhance the effectiveness of the synthetic pheromone. However, the response produced was often varied, which demonstrates the complexity of defining an olfactory sexual response in higher primates. A possible mechanism by which pheromones elicit sexual behavior is discussed.
Identification of V1R-like putative pheromone receptor sequences in non-human primates. Characterization of V1R pseudogenes in marmoset, a primate species that possesses an intact vomeronasal organ.
Giorgi D, Rouquier S.
IGH, CNRS UPR 1142, Montpellier, France.
The vomeronasal organ (VNO) is responsible in terrestrial vertebrates for the sensory perception of some pheromones, chemicals that elicit characteristic behaviors among individuals of the same species. Two multigene families (V1R, V2R) that encode proteins with seven putative transmembrane domains that are expressed selectively in different neuron subsets of the VNO have been described in rodents. Pheromone-induced behaviors and a functional VNO have been described in a number of mammals, but this sensory organ seems absent in adult catarrhines and apes, including humans. Until now, only pseudogenes have been isolated in humans, except one putative V1R (hV1RL1) sequence expressed in the main olfactory epithelium. We sought to isolate V1R-like genes in a New World monkey species, the marmoset Callithrix jacchus, that possesses an intact VNO and for which pheromone-induced behavior has been well documented. Using library screening approaches, we have identified five different sequences that exhibit characteristic features of V1R sequences, but that are non-functional pseudogenes. In an attempt to sort out functional V1R genes, we next cloned by polymerase chain reaction (PCR) the primate orthologues of hV1RL1. This approach was successful for gorilla, chimpanzee and orangutan, but not for the other species, including marmoset, probably because these species are too divergent from humans. Chimpanzee and orangutan V1RL1 genes are pseudogenes, whereas the gorilla counterpart is potentially functional. These observations raise the possibility that the V1R family has evolved in such a manner in mammals that every species that relies on a VNO-mediated sensory function possesses its own set of functional vomeronasal genes.
Functional imaging of brain activity in conscious monkeys responding to sexually arousing cues.
Ferris CF, Snowdon CT, King JA, Duong TQ, Ziegler TE, Ugurbil K, Ludwig R, Schultz-Darken NJ, Wu Z, Olson DP, Sullivan Jr JM, Tannenbaum PL, Vaughan JT.
Department of Psychiatry, University of Massachusetts Medical School, 55 Lake Ave North, Worcester, MA 01655, USA.
Olfactory cues can elicit intense emotional responses. This study used fMRI in male common marmoset monkeys to identify brain areas associated with sexual arousal in response to odors of ovulating female monkeys. Under light anesthesia, monkeys were secured in a specially designed restrainer and positioned in a 9.4 T magnetic resonance spectrometer. When fully conscious, they were presented with the scents of both ovariectomized and ovulating monkeys. The sexually arousing odors of the ovulating monkeys enhanced signal intensity in the preoptic area and anterior hypothalamus compared to the odors of ovariectomized monkeys. These data corroborate previous findings in monkeys based on invasive electrical lesion and stimulation techniques and demonstrate the feasibility of using non-invasive functional imaging on fully conscious common marmosets to study cue-elicited emotional responses.
Female marmoset monkeys (Callithrix jacchus) can be identified from the chemical composition of their scent marks.
Smith TE, Tomlinson AJ, Mlotkiewicz JA, Abbott DH.
School of Biology and Biochemistry, Queen's University of Belfast, Medical Biology Centre, Belfast, UK. email@example.com
The present study analyzed 42 organic solvent extracts of scent mark pools from five dominant female common marmosets by gas chromatography (GC) and combined GC and mass spectrometry. We determined whether there were qualitative or quantitative differences between the chemical composition of scent marks from individual females. Gas chromatography and mass spectral analysis detected the same 162 chemicals in 86% (36/42) of scent mark pools from five dominant females. This near identical chemical composition of scent marks suggested there were few, if any, qualitative differences between the chemical composition of scent marks from individual females. Instead, quantitative differences in scent may provide the key factor distinguishing individual females. Using the relative concentration of highly volatile chemicals detected by GC in scent marks, linear discriminant analysis classified scent mark pools to their correct donor approximately 91% of the time. Such highly reliable statistical matching of scent to donor suggested that each individual female common marmoset has a unique ratio of highly volatile chemicals in their scent marks which may permit individual identification of females from odors in their scent alone.
Comparative morphology and histochemistry of glands associated with the vomeronasal organ in humans, mouse lemurs, and voles.
Roslinski DL, Bhatnagar KP, Burrows AM, Smith TD.
School of Physical Therapy, Slippery Rock University, Slippery Rock, Pennsylvania 16057, USA.
The vomeronasal organ (VNO) is a chemosensory structure of the vertebrate nasal septum that has been recently shown to exist in nearly all adult humans. Although its link to reproductive behaviors has been shown in some primates, its functionality in humans is still debated. Some authors have suggested that the human VNO has the capacity to detect pheromones, while others described it as little more than a glandular pit. However, no studies have utilized histochemical techniques that would reveal whether the human VNO functions as a generalized gland duct or a specialized chemosensory organ. Nasal septal tissue from 13 humans (2-86 years old) were compared to that of two adult lemurs (Microcebus murinus) and eight adult voles (four Microtus pennsylvanicus and four Microtus ochrogaster). Sections at selected intervals of the VNO were stained with periodic acid-Schiff (PAS), alcian blue (AB), AB-PAS, and PAS-hematoxylin procedures. Results revealed typical well-developed VNOs with tubuloacinar glands in Microtus and Microcebus. VNO glands were AB-negative and PAS-positive in voles and mouse lemurs. Homo differed from Microtus and Microcebus in having more branched, AB and PAS-positive glands that emptied into the VNO lumen. Furthermore, the human VNO epithelium had unicellular mucous glands (AB and PAS-positive) and cilia, similar to respiratory epithelia. These results demonstrate unique characteristics of the human VNO which at once differs from glandular ducts (e.g., cilia) and also from the VNOs of mammals possessing demonstrably functional VNO. Copyright 2000 Wiley-Liss, Inc.
Effect of vomeronasal organ removal on male socio-sexual responses to female in a prosimian primate (Microcebus murinus).
CNRS URA 1183, Laboratoire d'Ecologie Generale, MNHN, Brunoy, France.
In most mammals, olfactory cues play an important role in regulating socio-sexual behaviors, but the relative contributions of the main olfactory system and the vomeronasal system remain unclear. The lesser mouse lemur, a nocturnal prosimian, possesses well-developed chemosensory structures, including a functional vomeronasal organ (VNO). In this primitive primate, social communication and competition between males for priority access to receptive females includes reliance on urinary chemical cues. To assess the role of the VNO in mediating males' behavioural responses to females, sexually-experienced intact males (C, n = 8) or males deprived of their VNO (VNX, n = 8) were put in pairs and their socio-sexual behaviors in response to a preoestrous female were monitored. Independent of social context (with or without female), VNX males exhibited less sniffing behaviors than C males, but their marking behaviors, although reduced, were not significantly different. Removal of the VNO dramatically reduced the frequency of both sexual behaviors (anogenital investigations, mounts) and intermale aggressive behaviors. However, VNO removal did not impair successful mating and had no effect on plasma testosterone levels. Lastly, VNX males always exhibited a significantly lower general activity level than C males. The decrease in sexual behaviors and the lack of aggressive intermale competition in responses to a preoestrous female possibly proceed from functional disturbances of central nervous areas connected to the vomeronasal system rather than from a chemosensory deficit per se.
Sexual responses to urinary chemosignals depend on photoperiod in a male primate.
Perret M, Schilling A.
CNRS URA 1183, Laboratoire d'Ecologie Generale, MNHN, Brunoy, France.
In male lesser mouse lemurs, testicular size and plasma testosterone levels are controlled by photoperiodic variations but can be modified by urinary cues from conspecifics. To test whether urinary cues may have differential effects on testicular size and testosterone levels depending on the photoperiodic state of the receiver, isolated males were exposed for 4 wk to urinary cues from oestrous females or dominant males:--at the beginning of the breeding season induced by long photoperiod (LD),--during refractoriness to LD leading to spontaneous sexual regression and during sexual quiescence exhibited by males kept in short photoperiod (SD). Urinary chemosignals from females were always stimulatory producing significant increases in testosterone levels. By contrast, urinary cues from dominant males produced significant differential effects on reproductive function. They depressed sexual function only at the beginning of the breeding season. During SD or during refractoriness to LD, chemosignals were stimulatory leading to increases in testosterone levels and full development of testes. These results demonstrate that the same chemosignal may have opposite effect on sexual function of the receiver depending on endocrine mechanisms set up by photoperiod.
Environmental and social determinants of sexual function in the male lesser mouse lemur (Microcebus murinus).
CNRS, URA 1183, MNHN, Brunoy, France.
Environmental factors that regulate the sexual activity of male lesser mouse lemurs have been studied experimentally with more than 60 captive animals over an 8-year period. In this nocturnal Malagasy prosimian, variation in day length is the primary factor controlling seasonal sexual activity. Plasma testosterone concentrations were low (= 9 ng/ml) during short days and reached 60 ng/ml during long days (> 12-hour day). This cyclic pattern persists unchanged when artificial photoperiodic rhythms are applied and is not altered by ageing. The timing of puberty is also regulated by photoperiodic changes. Nevertheless, the sexual activity of the male lesser mouse lemur can be dramatically modified by the social environment. In heterosexual groups, behavioural and physiological components of sexual activity are depressed in all males except the dominant one, whose aggressive interactions are always successful. Intermale sexual inhibition was shown to be mediated by chemical cues present in the urine of dominant or isolated males but not in urine of subordinate individuals. The inhibitory signals possess lipophilic properties and are not contingent on the gonadal activity of the urine donor but are linked to adrenocortical activity. By contrast, chemical signals stimulating the reproductive function of all males are found in the urine of females, the presence of which is required for the establishment of clear dominance among grouped males. Endocrine mechanisms underlying intermale sexual inhibition by chemical cues were analysed. Variations in prolactin strongly suggest that olfaction interacts with the photoperiodic regulation of reproductive function, leading to changes in the sensitivity of the negative feedback effect of testosterone on gonadotrophin secretion. Inhibitory or stimulatory effects of chemical signals are discussed in the context of their functional significance for wild populations.