Surgical removal of presumptive bursal tissue at 72 hr in ovo results in high mortality before hatching and low survival in the first week thereafter. The viable chicks are underweight and usually remain so. Both the spleen and thymus of the bursectomized (Bx) chicks are reduced in size and lymphoid population. The effect on the thymus may be related to stress and subsequent adrenal cortical activity or may reflect some endocrine function of the bursa necessary for the maturation of thymic lymphoid tissue. The effect on the spleen seems to be more direct. In the absence of the primary level organ which induces maturation of the stem cells, the number of germinal centres in the secondary level organ is reduced. Some of the remaining germinal centres may be of T-cell origin, although these cells are more commonly found in diffuse lymphoid areas. The bulk of the germinal centres found in the Bx spleen must be of B-cell origin. Repeated stimulation of the humoral immune system with antigens and mitogens elicits a response in some Bx birds. The response is generally not found in the primary stimulation and is rarely of the magnitude of a normal response even after several stimulations. Antibody production may be limited to IgM type immunoglobulin; further studies are necessary to verify this. Autopsy and histological examination of the tissues of the responsive birds failed to show any evidence of residual bursal tissue. Whether these findings constitute proof of the role of the bursa in the humoral immune response or whether they reflect the broader consequences of bursectomy in the development of the bird requires further study. The inductive capacities of the bursa and the source and autonomous capacity of the stem cells thought to be induced in the bursa should also be investigated. The effects of early hormonal and late surgical bursectomy are similar to those found in this study, where an early embryonic surgical technique was used to avoid the possible complications of these other methods. / Land and Food Systems, Faculty of / Graduate

Chicken pectoralis muscle was inoculated with Pseudomonas fragi and incubated at room temperature. Alterations in the nonprotein nitrogen, water-soluble protein nitrogen, and salt-soluble protein nitrogen fractions were studied and attempts were made to relate these changes to structural changes observed by scanning and transmission electron microscopy. A significant decrease in myofibrillar protein solubility was found in the inoculated muscle during the protein extract-ability study. Results of the gel filtration study indicated that proteolysis of the sarcoplasmic proteins occurred and that the nonprotein nitrogen fraction increased due to growth of P. fragi. Alterations were observed in the disc gel electrophoretic patterns of the sarcoplasmic and myofibrillar protein fractions. Arginine, threonine, serine, proline and tyrosine were selectively utilized by P. fragi. Scanning electron micrographs indicated that proteolysis of the endomysium occurred after 2 days of incubation at 25°C. Proteolysis of the endomysium became more extensive as incubation time increased. After 4 days of incubation the myofibrils showed evidence of disruption as a result of bacterial growth. Disruption of the muscle fiber was limited to a depth of 2 to 4 micrometers after 9 days of incubation. Bacteria were observed growing between the muscle fibers. Proteolysis was not as extensive in samples incubated at 5°C. Electron micrographs prepared from thin sections of myofibrils inoculated with P. fragi showed marked disruption of the myofibrils due to bacterial growth. A clear zone, devoid of structural detail, surrounded the bacterial cell. A region of disrupted tissue exists between the clear zone and intact myofibrils. Cellular protrusions were observed on the surface of the bacteria. / Land and Food Systems, Faculty of / Graduate

Evaluation of several methods of fixing chicken skin for scanning electron microscopy (SEM) indicated standard chemical fixation using glutaraldehyde and osmium tetroxide followed by chemical dehydration with 2,2-dimethoxypropane to be the method of choice. SEM revealed that chicken skin has a convoluted surface. Two types of chicken skin, distinguishable on the basis of chemical composition and appearance were observed. Type I has a filamentous surface with 55% moisture and 25% fat, whereas Type II skin has a globular appearance, 52% fat and 33% moisture. The fatty acid profiles of Types I and II skin are the same. Bacteria have greater affinity for Type II than Type I skin. Attachment studies indicated that Salmonella typhimurium quickly attach to the skin surface and cannot be removed easily by washing with water or with water containing a surfactant. / Land and Food Systems, Faculty of / Graduate

In 1971 Schally and co-workers (Schally et al., 1971) isolated gonadotropin-releasing hormone (now called luteinizing hormone-releasing hormone (LH-RH)) from sheep hypothalami and established that the hormone was a decapeptide with the amino acid sequence: pGlu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-Gly-NH₂. The peptide was subsequently synthesised (Matsuo et al., 1971b) and shown to stimulate the release of gonadotropins (luteinizing hormone and follicle-stimulating hormone) in a wide range of mammalian species (Schally et al., 1973, 1976). With the exception of amphibians, nonmammalian vertebrates have a poor gonadotropin response to synthetic mammalian LH-RH (for reviews, see Ball, 1981; Jackson, 1981; King and Millar, 1981a). Since there is considerable molecular heterogeneity in the related neurohypophysial nonapeptide hormones (oxytocin-vasopressin) amongst vertebrates (Acher et al., 1972), we postulated that differences might exist in the structure of hypothalamic LH-RH in different vertebrate classes, Utilising a combination of regionspecific antisera and chromatographic techniques, we established that amphibian hypothalamic LH-RH is identical to the mammalian peptide while avian, reptilian, and piscine hypothalamic LH-RHs differ structurally in the region Gly⁶-Leu⁷-Arg⁸ (King and Millar, 1979a, 1980), We have now conducted further studies on avian hypothalamic LH-RH, which indicate that the arginine residue in position eight of mammalian LH-RH is substituted by glutamine in this vertebrate class. Purification of LH-RH from chicken hypothalami and determination of the amino acid composition have confirmed that the structure of avian LH-RH is: pGlu-His-Trp-Ser-Tyr-Gly-Leu-Gln-Pro-Gly-NH₂.

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