A Novel Neural Substrate for the Transformation of Olfactory Inputs into Motor Output

Anatomical and physiological experiments in the lamprey reveal the neural circuit involved in transforming olfactory inputs into motor outputs, which was previously unknown in a vertebrate

The sense of smell, its signalling pathways, and the dichotomy of cilia and microvilli in olfactory sensory cells

Smell is often regarded as an ancillary perception in primates, who seem so dominated by their sense of vision. In this paper, we will portray some aspects of the significance of olfaction to human life and speculate on what evolutionary factors contribute to keeping it alive. We then outline the functional architecture of olfactory sensory neurons and their signal transduction pathways, which are the primary detectors that render olfactory perception possible. Throughout the phylogenetic tree, olfactory neurons, at their apical tip, are either decorated with cilia or with microvilli. The significance of this dichotomy is unknown. It is generally assumed that mammalian olfactory neurons are of the ciliary type only. The existance of so-called olfactory microvillar cells in mammals, however, is well documented, but their nature remains unclear and their function orphaned. This paper discusses the possibility, that in the main olfactory epithelium of mammals ciliated and microvillar sensory cells exist concurrently. We review evidence related to this hypothesis and ask, what function olfactory microvillar cells might have and what signalling mechanisms they use

Processing of Body Odor Signals by the Human Brain

Brain development in mammals has been proposed to be promoted by successful adaptations to the social complexity as well as to the social and non-social chemical environment. Therefore, the communication via chemosensory signals might have been and might still be a phylogenetically ancient communication channel transmitting evolutionary significant information. In humans, the neuronal underpinnings of the processing of social chemosignals have been investigated in relation to kin recognition, mate choice, the reproductive state and emotional contagion. These studies reveal that human chemosignals are probably not processed within olfactory brain areas but through neuronal relays responsible for the processing of social information. It is concluded that the processing of human social chemosignals resembles the processing of social signals originating from other modalities, except that human social chemosignals are usually communicated without the allocation of attentional resources, that is below the threshold of consciousness. Deviances in the processing of human social chemosignals might be related to the development and maintenance of mental disorders

Chemical cues and pheromones in the sea lamprey (Petromyzon marinus)

Chemical cues and pheromones guide decisions in organisms throughout the animal kingdom. The neurobiology, function, and evolution of olfaction are particularly well described in insects, and resulting concepts have driven novel approaches to pest control. However, aside from several exceptions, the olfactory biology of vertebrates remains poorly understood. One exception is the sea lamprey (Petromyzon marinus), which relies heavily upon olfaction during reproduction. Here, we provide a broad review of the chemical cues and pheromones used by the sea lamprey during reproduction, including overviews of the sea lamprey olfactory system, chemical cues and pheromones, and potential applications to population management. The critical role of olfaction in mediating the sea lamprey life cycle is evident by a well-developed olfactory system. Sea lamprey use chemical cues and pheromones to identify productive spawning habitat, coordinate spawning behaviors, and avoid risk. Manipulation of olfactory biology offers opportunities for management of populations in the Laurentian Great Lakes, where the sea lamprey is a destructive invader. We suggest that the sea lamprey is a broadly useful organism with which to study vertebrate olfaction because of its simple but well-developed olfactory organ, the dominant role of olfaction in guiding behaviors during reproduction, and the direct implications for vertebrate pest management

Presence of the vomeronasal system in aquatic salamanders.

Previous reports have indicated that members of the proteid family of salamanders lack a vomeronasal system, and this absence has been interpreted as representing the ancestral condition for aquatic amphibians. I examined the anatomy of the nasal cavities, nasal epithelia, and forebrains of members of the proteid family, mudpuppies (Necturus maculosus), as well as members of the amphiumid and sirenid families (Amphiuma tridactylum and Siren intermedia). Using a combination of light and transmission electron microscopy, I found no evidence that mudpuppies possess a vomeronasal system, but found that amphiuma and sirens possess both vomeronasal and olfactory systems. Amphiumids and sirenids are considered to be outgroups relative to proteids; therefore, these data indicate that the vomeronasal system is generally present in salamanders and has been lost in mudpuppies. Given that the vomeronasal system is generally present in aquatic amphibians, and that the last common ancestor of amphibians and amniotes is believed to have been fully aquatic, I conclude that the vomeronasal system arose in aquatic tetrapods and did not originate as an adaptation to terrestrial life. This conclusion has important implications for the hypothesis that the vomeronasal organ is specialized for detection of non-volatile compounds

Evolution of Vertebrate Olfactory Subsystems

Abstract: In this article, we describe the basic aspects of the structure and function of the olfactory system in the major groups of vertebrates. For each group, we discuss the behavioral significance of olfactory cues, as well as the means by which odorants are drawn across the sensory epithelium. We also describe the morphology of the receptor cell types that are present, and summarize the state of knowledge concerning the odorant receptor gene repertoire. The cell types and organization of the olfactory bulbs are described, as are the major central projections from the olfactory bulbs. In addition, the olfactory system proper and vomeronasal system are compared in taxa that possess both systems. Finally, the structure of the terminal nerve is described, and information concerning its function is summarized. Patterns of evolutionary change in each of these features are then analyzed