Abstract: Olfactory discrimination ofDrosophila melanogaster WT Berlin was determined in a learning paradigm.

Abstract: The secondary olfactory connections in the shark Scyliorhinus canicula and the ray Raja clavata have been studied with reduced silver techniques. After transections through the pedunculus olfactorius in Scyliorhinus degenerating fibers could be traced to the telencephalic hemisphere. On entering the hemisphere these fibers subdivide into a small medial and a larger lateral olfactory tract. The medial tract distributes fibers to the lateral part of the ipsilateral pallium dorsale, pars superficialis and area periventricularis pallialis, but the majority of its fibers terminate in the submeningeal zone of the pallium. The medial olfactory tract also projects contralaterally to the submeningeal pallial zone via the commissura olfactoria inferior and to the stratum granulare bulbi olfactorii by way of the commissura olfactoria superior. The lateral olfactory tract distributes mainly to the pallium laterale and to the region superficial to the lateral part of the area superficialis basalis, though the striatum also receives some fibers. In Raja the secondary olfactory tract could not be subdivided into medial and lateral components and its projections seem to be restricted to the ipsilateral pallium laterale. A striking difference between Scyliorhinus and Raja is that in the latter no contralateral projections could be recognized nor a projection to the area superficialis basalis. When these results are compared with those reported in the literature for other cartilaginous fishes, it appears that the secondary olfactory connections of Scyliorhinus are more extensive than in other chondrichthians studied experimentally. In some cases of peduncle transection in Scyliorhinus the lateral part of the striatum was also involved in the lesion. In addition to the pattern of degeneration seen after olfactory peduncle lesions, degenerating fibers could be distinguished both in the stria medullaris and basal forebrain bundle. The former projects to habenular nucleus, whereas the latter distributes to the hypothalamus, ventral thalamus, and brainstem tegmentum.

Abstract: Mouth gaping by rattlesnakes has been observed primarily during feeding sequences and interpreted as functioning to stretch the jaw in preparation for swallowing prey. However, exposure of prairie rattlesnakes to conspecific sociochemical signals elicited increased mouth-gaping actions, and the latter were sequentially followed by tongue flicks at significant levels. Mouth gaping may function to facilitate vomeronasal olfaction independent of jaw-stretching effects.

Abstract: Details of neuronal reorganization were investigated in golden hamster pups 10 days after neonatal olfactory lesions. Pups sustained unilateral olfactory tract section (ULOT) or unilateral olfactory bulbectomy (UOB) on postnatal day 5 (P5) and were then behaviorally tested through P15. UOBs were sacrificed after P15 to assess the extent of lesions. ULOTs were processed with degeneration techniques to demonstrate the terminal distribution of bulb fibers whose path had been either deflected or severed by the early tract section. Ten days after complete tract section, extensive sprouting of bulb fibers had occurred rostral to the cut in olfactory as well as adjacent nonolfactory (e.g., neocortical) regions. The pattern of rostral sprouting was similar to, and in some cases exceeded, that described in adults subjected to neonatal tract sections (Devor, 76b). Fibers grew caudally past the cut following aberrant paths to reinnervate limited regions of the olfactory tubercle and less frequently, the piriform cortex. Unlike the continuous band of terminals soon in the caudal field of adults given neonatal tract sections, at this early stage of regrowth, fibers were organized in small discontinuous fascicles that tended to cluster at the islands of Calleja of the tubercle. Although these fibers innervated a relatively restricted region in comparison with normal innervation, their connections were apparently functional, as measured by a thermotaxis behavioral assay for the effects of UOB. The ther-motaxis behavior of most pups showing tubercle reinnervation returned to normal, while the behavior of pups without tubercle reinnervation remained similar to UOBs (Small and Leonard, ′82). Excessive rostral sprouting and invasion of neocortex were seen in all tract-sectioned pups and were, therefore, apparently not sufficient to sustain normal behavior on this assay. Regrowth of sensory olfactory fibers and extensive formation of glo-meruli in the anterior olfactory nucleus and, occasionally, in prefrontal neocortex were found following olfactory bulbectomy. There was no correlation between the extent of glomerulization and the behavioral performance, however. The olfactory system provides an appropriate system for investigating the parameters governing age-dependent axonal sprouting and functional recovery following early brain damage.

Abstract: Olfaction has many facets — membrane excitability, cellular neurophysiology, ethology, orientation physiology, ecology, evolution, psychophysics etc. To combine several of these aspects with the aim of understanding an animal’s activities in its natural environment — this we could learn from men like K.D. Roeder, who made clear that one must understand an animal’s biology, and behaviour, and its nervous system in order to be able to ask reasonable questions about any one of these aspects. He with others awoke our interest in the neurobiological basis of behaviour. E.S. Hodgson, a collaborator of Roeder, with the help of one of Y. Lettwin’s good experimental ideas, successfully tackled such a problem in the area of chemoreception (Hodgson et al. 1955). He and his co-authors studied reactions of individually identifiable receptor cells in an insect taste hair. This method opened new access to the neural coding of olfactory stimuli at the receptor cell level amongst other problems. In the years after this pioneering work, a vast amount of data was collected on reactions of insect olfactory receptor cells (Kaissling 1971). Today we can say that the advantageous conditions which insect provide for such investigations led to results which are important for the understanding of chemoreceptors in general. This, of course, provided a good background for a study of the central olfactory pathway in insects, and one hope is that this might be a way to understand the role of the central networks which control reactions of animals to odours.

Abstract: By application of a differential saturation EAG technique, the olfactory receptor system for compounds active as sex pheromones in the American cockroach was elucidated. The interaction of sex pheromone mimics with receptors responsive to a sex pheromone (periplanone-B) was revealed. As suggested by the single cell recording studies, the presence of sex pheromone receptors responsive specifically to sex pheromones (periplanone-A and-B) was shown, as well as the presence of general odor receptors which are functionally different from the sex pheromone receptors.

Abstract: The present investigation is concerned with chemoreceptivity in the male three-spined stickleback (Gasterosteus aculeatus L.) during reproductive behaviour. The functions of cranial nerves were studied with regard to nest building (N), the increase in the zigzag dance (a measure of the sexual tendency (S)) between N and the day of fertilization (F) of the eggs, the zigzag dance between F and the day of hatching (H), suppression of the zigzag dance (if still present) at H, and fanning activity (P) during these days of a reproductive cycle (F-H). The methods of quantifying S and P, as well as the methods of sectioning the olfactory nerves and the branches of cranial nerves possibly involved in the conduction of chemical stimuli are described. The behavioural changes observed after sectioning the olfactory nerves, branches of cranial nerves or combinations of these nerves are compared with behavioural data of unoperated fish. Special attention is given to behavioural changes following regeneration of transected nerves. Nest building is still possible after sectioning of the olfactory nerves, but occurs only in a few fish. The functioning of the olfactory nerves might influence the development of nest building behaviour by inducing hormonal changes, necessary to start such reproductive activities. During the period between N and F (the latter determined by the observer), the number of zigzags (S) increases from zero up to 100 or more per 5 minutes. The olfactory nerves are indispensable for the promotion of sexual behaviour during this period. It seems likely that these nerves are necessary to induce hormonal changes in such a way that the reproductive cycle can proceed from nest building to courtship stage. In the exceptional case that a nest was built by a fish in which the olfactory nerves had been sectioned, the zigzag score remaining low, all other reproductive activities still occurred, including fertilization. Fanning activity in such fish appeared to be quantitatively normal. When the olfactory nerves were sectioned between N and F, at a stage when the zigzag scores had reached an essential level ( 100 per 5 min), both sexual and fanning activity between F and H were normal. This is explained by the supplementary functioning of both the ramus posttrematicus IX and the ramus pretrematicus X1. Both eggs and embryos stimulate sexual behaviour between F and H. The olfactory nerves exert an exciting function with regard to sexual behaviour during the first days of the cycle (F-H). The area in the roof of the pharynx, situated between the first and second gill arches appeared to perceive stimuli from eggs and embryos, exciting sexual behaviour (referred to as sex-excitation area). The sensory fibres from this area run in a dorsal direction, some joining the rami pharyngei X1, others one of the rami pharyngei IX (referred to as the S-anastomosis), their excitation increasing during the course of the cycle. The S-anastomosis which joins the ramus posttrematicus IX near or just dorsal of the second arteria branchialis dorsalis, exites sexual behaviour during most days of the cycle (F-H). Similarly, the rami pharyngei X1 which join the ramus pretrematicus X1 at a point dorsal of the second arteria branchialis dorsalis, excite sexual behaviour during the last days of the cycle. The presence of young following hatching suppresses sexual behaviour, if still present, at H. Such stimuli are perceived by the rami pharyngei IX, which join the ramus posttrematicus IX near or dorsal to the first arteria branchialis dorsalis. Perceiving such stimuli results in an immediate suppression of sexual behaviour. Both eggs and embryos also stimulate fanning behaviour between F and H. Our experiments have shown that the following three nerves are involved in the conduction of such stimuli: nervus olfactorius, ramus posstrematicus IX (including its anastomosis with the ramus pretrematicus X1, referred to as the F-anastomosis), and the ramus pretrematicus X1. The involvement of the cranial nerves I, IX and X in the reproductive activities of the male three-spined stickleback is illustrated in a schematic way in Fig. 27.

Abstract: Histomorphological and histochemical data show that the primary function of the nasal chambers in the lungless Hydromantes italicus is olfaction in a subaerial environment. Having a well shaped Jacobson's organ, an independent vomero-nasal nerve and a big accessory olfactory bulb, the animal can test and choose the food introduced into its mouth. The outward migration of the prepyriform cells towards a cortical differentiation of the dorso-lateral pallium is the neural basis for the animal's ability to detect and distinguish food in total darkness by smell alone.

Abstract: The olfactory hypothesis for salmon homing, first presented by Hasler and Wisby in 1951, has three basic tenets: (1) because of local differences in soil and vegetation of the drainage basin, each stream has a unique chemical composition and, thus, a distinctive odor; (2) before juvenile salmon migrate to the sea they become imprinted to the distinctive odor of their home stream; and (3) adult salmon use this information as a cue for homing when they migrate through the home-stream network to the home tributary. This chapter reviews the evidence for olfactory imprinting in salmon. Two central themes are intertwined throughout this section: (1) the results of experimental replications performed by different investigators are remarkably consistent, and (2) many experiments were conducted in the field instead of the laboratory and thereby provide direct evidence that salmon use olfactory cues for homing.