Showing papers by "Government of Canada published in 1994"

Olfaction and gustation in fish: an overview

Abstract: Living in an aquatic environment, often devoid of light but rich in dissolved compounds, fish have highly developed chemosensory and chemical signalling systems. The olfactory and gustatory systems comprise the major chemosensory pathways. Despite considerable variations in structural organization of the peripheral olfactory organ throughout fish species, ultrastructural organization of the olfactory sensory epithelium is extremely consistent. The olfactory receptor cell is a bipolar neurone which is directly exposed to the external environment and sends information to the brain by its own axon (cranial nerve I). Four major classes of chemicals have been identified as specific olfactory stimuli and their stimulatory effectiveness characterized: amino acids, sex steroids, bile acids/salts and prostaglandins. Olfactory signals such as those involved in reproduction and feeding may be processed independently through two distinct subsystems: the lateral and medial olfactory systems. The taste buds constitute the structural basis of the gustatory organ. Taste buds may occur not only in the oropharyngeal cavity, but on the whole body surface. Chemical information detected by specialized epithelial cells, gustatory cells, is transmitted to the central nervous system by cranial nerve VII (facial), IX (glossopharyngeal), and X (vagal). Besides diverse sensitivities and specificities for amino acids, fish gustatory receptors detect various organic acids, nucleotides and bile salts. Putative receptors, molecular mechanisms of transduction and the role played by olfaction and gustation in feeding, reproduction, migration and other fish behaviours are discussed.

Optimum Currency Areas and Shock Asymmetry: A Comparison of Europe and the United States

Abstract: Les auteurs examinent l'optimalite de l'Union Monetaire Europeenne (UME) en partant d'une evaluation empirique du degre d'asymetrie des chocs d'offre et de demande auxquels sont soumis treize pays d'Europe et en comparant les resultats avec ceux qu'ils ont obtenus pour neuf regions des Etats-Unis. Dans un premier temps, ils identifient les chocs d'offre ainsi que les chocs de demande reels et nominaux a l'aide de restrictions imposees aux effets que ces chocs peuvent avoir a long terme sur le niveau de la production, des prix et des encaisses reelles.

Distribution patterns of palatal taste buds and their responses to amino acids in salmonids

Abstract: The distribution pattern of the palatal taste buds and their electrical response characteristics to amino acids were studied in five salmonid species: Arctic grayling (Thymallus arcticus), lake whitefish (Coregonus clupeaformis), Atlantic salmon (Salmo salar), brown trout (Salmo trutta), and kokanee (Oncorhynchus nerka). In these fish the most dense taste bud populations were found on ridges in tine area around the palatine teeth. With the exception of lake whitefish, the ridges adjacent to the teeth on the head and shaft of the prevomer were also dense in taste buds, which appear to be largely responsible for amino acid detection. All species, except for lake whitefish, responded well to l-proline (l-Pro) and l-α-amino-β-guanidinopropionic acid (l-AGPA), with thresholds at 10−8-10−7 and 10−5-10−4 M, respectively. These species also responded to varying degrees to hydroxy-l-proline (l-Hpr) and l-alanine (l-Ala), believed to be agonists for l-Pro receptors. In addition, kokanee detected l-phenylalanine, l-leucine and betaine. Of six lake whitefish examined, only one specimen responded to l-Pro, l-AGPA and l-arginine. We concluded that in these five salmonid species l-Pro and l-AGPA receptors play a major role in amino acid gustation, and further proposed a hypothesis that salmonids may have initially evolved these two gustatory receptors. With phylogenetic advancement, they gained greater response capabilities by (1) acquiring new receptor types, and (2) by losing the specificity of existing receptors.

Effects of dietary n−3 polyunsaturated fatty acids on lipid and fatty acid composition and haematology of juvenile Arctic charr Salvelinus alpinus (L.)

Abstract: The effect of dietary n−3 and n−6 polyunsaturated fatty acids (PUFAs) on juvenile Arctic charr Salvelinus alpinus (L.) were investigated with respect to essential fatty acid (EFA) deficiency and lipid metabolism using one commercial and 12 casein-based test diets. Arctic charr with mean weight of 1.6g were fed test diets for 12 weeks at 10°C. At the end of the feeding, blood, liver, muscle and whole fish were sampled to determine haematocrit, haemoglobin, water content, lipid and fatty acid composition. Charr fed diets containing 0–1.0% n−3 PUFAs showed typical EFA deficiency signs: fatty liver or elevated water content in whole body or substantial accumulation of 20:3n−9 in liver polar lipids. These signs were less apparent or disappeared when charr were fed diets containing ≥ 2.0% 18:3n−3. No correlation was found between dietary PUFAs and haematocrit or haemoglobin values. Significant changes in fatty acid composition of liver polar lipids in charr fed dietary PUFAs indicate that charr can convert 18:3n−3, 18:2n−6 and 20:5n−3 into long-chain PUFAs. While charr had a direct incorporation of dietary 22:6n−3 into liver and muscle there appears to be preferential utilization of n−3 PUFAs for elongation and desaturation. The conversion of 18:4n−3 was less in muscle than in livers. These findings, combined with data on growth and feed efficiency reported previously by Yang and Dick (1993), indicate that charr require 1−2% dietary 18:3n−3 (dry weight). Small amounts of dietary 18:2n−6 (up to 0.7%) did not have detrimental effects on charr.

THE CAUSES OF UNEMPLOYMENT IN CANADA: A Review of the Evidence

Abstract: L'auteur examine differentes theories du chomage structurel et la possibilite de s'en inspirer pour tenter d'expliquer les hausses du chomage que le Canada a connues au cours du dernier cycle economique. La principale conclusion de cette etude est qu'il faut tenir compte de plusieurs hypotheses de nature structurelle lorsqu'on forme des jugements au sujet du taux de chomage non accelerationniste (TCNA).