Stine Lastein

Bio: Stine Lastein is an academic researcher from University of Oslo. The author has contributed to research in topics: Crucian carp & Olfaction. The author has an hindex of 5, co-authored 6 publications receiving 154 citations.

Seasonal variations in olfactory sensory neurons--fish sensitivity to sex pheromones explained?

Abstract: Olfactory sensory neurons of vertebrates regenerate throughout the life of the animal. In fishes, crypt cells are a type of olfactory sensory neurons thought to respond to sex pheromones. Here, we demonstrate that the number of crypt cells in the olfactory epithelium of the crucian carp varies dramatically throughout the year. During winter, few crypt cells are observed at any location within the sensory epithelium. In spring, the majority of crypt cells are located deep in the epithelium not yet exposed to the environment. However, during the summer spawning season, crypt cells are positioned at the epithelial surface. These findings may explain previous studies demonstrating a relationship between circulating androgen and olfactory sensitivity to sex pheromones.

Gender Distinction in Neural Discrimination of Sex Pheromones in the Olfactory Bulb of Crucian Carp, Carassius carassius

Abstract: Studies on projection of the sensory neurons onto the olfactory bulb in fish have revealed a clear subdivision into spatially different areas that each responded specifically to different classes of odorants. Amino acids induce activity in the lateral part, bile salts induce activity in the medial part, and alarm substances induce activity in the posterior part of the medial olfactory bulb. In the present study, we demonstrate a new feature of the bulbar chemotopy showing that neurons specifically sensitive to sex pheromones are located in a central part of the ventral olfactory bulb in crucian carp. Extensive single-unit recordings were made from these neurons, stimulating with four sex pheromones, 17,20beta-dihydroxy-4-pregnen-3-one, 17,20beta-dihydroxy-4-pregnen-3-one-20-sulfate, androstenedione, and prostaglandin F(2alpha), known to induce specific reproductive behaviors in males of carp fish. All substances were applied separately to the sensory epithelium at a concentration of 10(-9) M. Of the 297 neurons recorded in males, the majority (236 or 79.5%) responded exclusively to one of the four sex pheromones and thus showed a high specificity. Of the 96 neurons recorded from the olfactory bulb in females, only 1 unit showed such a specific activation. These findings reflect remarkable differences between males and females in the discriminatory power of the olfactory neurons toward these sex pheromones. The gender differences are discussed in relation to behavior studies, expression of olfactory receptors, and the convergence of sensory neurons onto the secondary neurons in the olfactory bulb.

Female crucian carp, Carassius carassius, lose predator avoidance behavior when getting ready to mate.

Abstract: In predator-prey interactions, the prey often have to compromise fitness-related behaviors such as feeding, courting, and territorial defense in order to avoid predators. In these trade-off situations, some behaviors have priority over others. These priorities are not rigid, and may be context-dependent; for instance, many animals show increased risk-taking during courtship behavior by paying less attention to potential predators. We investigated whether the fright reaction, a stereotypical avoidance response to olfactory cues from injured conspecifics, may be affected by reproductive status in a teleost fish, the crucian carp. We demonstrate that among individuals not responding to alarm substances with a fright reaction, the majority were ovulated or spermiated. In females, mean plasma concentrations of 17beta-estradiol and testosterone, gonadal steroids known to decrease during the later stages of sexual maturation, were lower in the individuals not responding with a fright reaction compared to those responding. In males, there were no differences between responsive and non-responsive individuals in mean plasma levels of androgens (testosterone and 11-ketotestosterone) involved in spermatogenesis and male sexual behavior. As the fright reaction in crucian carp consists of behavior incompatible with spawning behavior, we hypothesize that this short-term suppression of the alarm response has evolved so that spawning can occur uninterrupted.

Single unit responses to skin odorants from conspecifics and heterospecifics in the olfactory bulb of crucian carp Carassius carassius.

Abstract: Injured fish skin leaks alarm substances that induce the fright reaction upon olfactory detection. The skin also contains a multitude of other odorants traditionally related to other behaviors, but to what extent they are detected upon injury is unknown. We have performed single unit recordings in the olfactory bulb (OB) of crucian carp while exposing the olfactory epithelium to skin extracts from conspecifics and three other species of the carp family, common carp, tench and bream. The aims were to investigate whether neural activity may be induced by different types of skin odorants and how well the odorants from injured conspecifics are distinguished from other species. The OB of crucian carp shows a clear chemotopy as units located in different regions respond to either food-related odorants, to pheromones or to alarm odorants respectively. Units in all regions responded to skin extracts, which indicate the detection of odorants usually involved in reproduction and feeding, in addition to the alarm substances. Among OB units responding to only one of the skin extracts, most were sensitive to conspecific skin extract. Furthermore, pair-wise comparisons showed that the discrimination between conspecific skin extract and skin extract from another species was in general better than the discrimination between skin extracts from two heterospecifics. The findings suggest that identification of injured fishes may be based on different groups of odorants and that the crucian carp olfactory system discriminates well between odorants from conspecifics and those from other fish species.

Effects of antalarmin, a CRF receptor 1 antagonist, on fright reaction and endocrine stress response in crucian carp (Carassius carassius)

Abstract: The corticotrophin-releasing factor (CRF) receptors show striking homogeneity throughout the vertebrate subphylum. In mammals, the CRF1 receptor (CRFR1) plays an important role in mediating behavioral and endocrine responses to fear and stress. The specific roles of this receptor subtype in fear and stress reactions in non-mammalian vertebrates are largely unknown. Crucian carp displays the olfactory-mediated fright reaction, a stereotypic behavioral response to waterborne cues from damaged skin of conspecifics. This reaction shows several similarities to basic components of avoidance behavior in mammals. In the present study, we applied the non-peptide CRFR1 antagonist, antalarmin, to crucian carp 1 h before exposure to conspecific skin extract. This treatment resulted in a suppression of the fright reaction. After skin extract exposure, antalarmin treatment also lead to lower plasma cortisol values, as compared to vehicle treatment. This suppression of the behavioral fright reaction and the stress induced rise in plasma cortisol in crucian carp suggests that the functions of the CRFR1 are conserved by evolution.

Chemical ecology of predator–prey interactions in aquatic ecosystems: a review and prospectusThe present review is one in the special series of reviews on animal–plant interactions.

Abstract: The interaction between predator and prey is an evolutionary arms race, for which early detection by either party is often the key to success. In aquatic ecosystems, olfaction is an essential sourc...

Olfactory neural circuitry for attraction to amino acids revealed by transposon-mediated gene trap approach in zebrafish

Abstract: In fish, amino acids are food-related important olfactory cues to elicit an attractive response. However, the neural circuit underlying this olfactory behavior is not fully elucidated. In the present study, we applied the Tol2 transposon-mediated gene trap method to dissect the zebrafish olfactory system genetically. Four zebrafish lines (SAGFF27A, SAGFF91B, SAGFF179A, and SAGFF228C) were established in which the modified transcription activator Gal4FF was expressed in distinct subsets of olfactory sensory neurons (OSNs). The OSNs in individual lines projected axons to partially overlapping but mostly different glomeruli in the olfactory bulb (OB). In SAGFF27A, Gal4FF was expressed predominantly in microvillous OSNs innervating the lateral glomerular cluster that corresponded to the amino acid-responsive region in the OB. To clarify the olfactory neural pathway mediating the feeding behavior, we genetically expressed tetanus neurotoxin in the Gal4FF lines to block synaptic transmission in distinct populations of glomeruli and examined their behavioral response to amino acids. The attractive response to amino acids was abolished only in SAGFF27A fish carrying the tetanus neurotoxin transgene. These findings clearly demonstrate the functional significance of the microvillous OSNs innervating the lateral glomerular cluster in the amino acid-mediated feeding behavior of zebrafish. Thus, the integrated approach combining genetic, neuroanatomical, and behavioral methods enables us to elucidate the neural circuit mechanism underlying various olfactory behaviors in adult zebrafish.

Neural circuits mediating olfactory-driven behavior in fish

Abstract: The fish olfactory system processes odor signals and mediates behaviors that are crucial for survival such as foraging, courtship and alarm response. Although the upstream olfactory brain areas (olfactory epithelium and olfactory bulb) are well studied, less is known about their target brain areas and the role they play in generating odor-driven behaviors. Here we review a broad range of literature on the anatomy, physiology and behavioral output of the olfactory system and its target areas in a wide range of teleost fish. Additionally, we discuss how applying recent technological advancements to the zebrafish (Danio rerio) could help in understanding the function of these target areas. We hope to provide a framework for elucidating the neural circuit computations underlying the odor-driven behaviors in this small, transparent and genetically amenable vertebrate.