Odor here, odor there: chemosensation and reproductive function.
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Biomedical subjects
Publications and source records attributed to Eric B Keverne.
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Much of the work on well-being and positive emotions has tended to focus on the adult, partly because this is when problems are manifest and well-being often becomes an issue by its absence. However, it is pertinent to ask if early life events might engender certain predispositions that have consequences for adult well-being. The human brain undergoes much of its growth and development postnatally until the age of seven and continues to extend its synaptic connections well into the second decade. Indeed, the prefrontal association cortex, areas of the brain concerned with forward planning and regulatory control of emotional behaviour, continue to develop until the age of 20. In this article, I consider the significance of this extended postnatal developmental period for brain maturation and how brain evolution has encompassed certain biological changes and predispositions that, with our modern lifestyle, represent risk factors for well-being. An awareness of these sensitive phases in brain development is important in understanding how we might facilitate secure relationships and high self-esteem in our children. This will provide the firm foundations on which to develop meaningful lifestyles and relationships that are crucial to well-being.
This study investigates how a targeted mutation of a paternally expressed imprinted gene regulates multiple aspects of foetal and post-natal development including placental size, foetal growth, suckling and post-natal growth, weaning age and puberty onset. This same mutation in a mother impairs maternal reproductive success with reduced maternal care, reduced maternal food intake during pregnancy, and impaired milk let-down, which in turn reduces infant growth and delays weaning and onset of puberty. The significance of these coadaptive traits being synchronized in mother and offspring by the same paternally expressed imprinted gene ensures that offspring that have extracted 'good' maternal nurturing will themselves be both well provisioned and genetically predisposed towards 'good' mothering.
Olfaction is the dominant sensory modality for most animals and chemosensory communication is particularly well developed in many mammals. Our understanding of this form of communication has grown rapidly over the last ten years since the identification of the first olfactory receptor genes. The subsequent cloning of genes for rodent vomeronasal receptors, which are important in pheromone detection, has revealed an unexpected diversity of around 250 receptors belonging to two structurally different classes. This review will focus on the chemical nature of mammalian pheromones and the complementary roles of the main olfactory system and vomeronasal system in mediating pheromonal responses. Recent studies using genetically modified mice and electrophysiological recordings have highlighted the complexities of chemosensory communication via the vomeronasal system and the role of this system in handling information about sex and genetic identity. Although the vomeronasal organ is often regarded as only a pheromone detector, evidence is emerging that suggests it might respond to a much broader variety of chemosignals.
Understanding the neurobiology of social behaviour in mammals has been considerably advanced by the findings from two species of vole, one of which is monogamous and pair bonds whereas the other species is promiscuous and fails to form any long-lasting social relationships. The combination of neurobehavioural studies and molecular genetics has determined behavioural differences between the two species linked to the neural distribution of vasopressin 1A receptor in the male brain. More importantly, vasopressin 1A receptor gene transfer including the upstream regulatory sequence has enhanced male social affiliation in a non-monogamous species. Male affiliative bonding depends upon release of both vasopressin and dopamine in the ventral striatum enhancing the reward value of odour cues that signal identity.
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Knocking-out selected genes for receptors of the vomeronasal organ has been found to impair specific aspects of pheromone-induced behaviour in the mouse. This is not unexpected; less predictable is the finding that deleting the gene for a vomeronasal-organ-specific ion channel causes gender blindness.
The expression of a subset of mammalian genes is subject to parent of origin effects (POE), most of which can be explained by genomic imprinting. Analysis of mutant animals has demonstrated that a number of imprinted genes influence brain development and behaviour. Here we provide evidence for POE on olfactory related behaviour and sensitivity to maternal odour cues. This was investigated by examining the odour preference behaviour of reciprocal cross F(1) mice made by embryo transfer to genetically unrelated foster parents. We determined that both adult males and females show an avoidance of female urinary odours of their genetic maternal but not paternal origin. This was found not to be due to any previous exposure to these odours or due to self-learning, but may be related to direct effects on the olfactory system, as reciprocal F(1) males show differential sensitivity to female odour cues. Currently the most robust theory to explain the evolution of imprinting is the conflict hypothesis that focuses on maternal resource allocation to the developing foetus. Kinship considerations are also likely to be important in the selection of imprinted genes and we discuss our findings within this context, suggesting that imprinted genes act directly on the olfactory system to promote post-weaning dispersal from the natal area.
The striking behavioral phenotypes of mice lacking the TRP2 ion channel have highlighted the importance of the vomeronasal organ in gender-specific sexual behavior.