The present study examined GABA immunoreactivity within the retinopetal nucleus isthmo-opticus (NIO) of the pigeon centrifugal visual system (CVS) using light- (immunohistofluorescence, peroxidase anti-peroxidase: PAP) and electron- (postembedding GABA immunogold) microscopic techniques. In some double-labeling experiments, the retrograde transport of the fluorescent dye rhodamine β−isothiocyanate (RITC) after its intraocular injection was combined with GABA immunohistofluorescence. GABA-immunoreactive (-ir) somata were demonstrated within the neuropilar zone of the NIO adjacent to the centrifugal cell laminae whereas the centrifugal neurons were always immunonegative. A quantitative ultrastructural analysis was performed which distinguished five categories of axon terminal profiles (P1–5) on the basis of various cytological criteria: type of synaptic contact (symmetrical or asymmetrical); shape, size, and density of synaptic vesicles as well as the immunolabeling (positive or negative), size of profile and appearance of hyaloplasm. Numerous GABA-ir afferents to centrifugal neurons via axon terminal types P2a, P2c, and P3 were observed which comprised 47.1% of the total input. Moreover, the data suggest that some of the P2a terminals, which make up 26.4% of the input, stem from the intrinsic GABA-ir interneurons, whereas the latter receive P1, P3, but also P2 terminal input, indicating that interneurons may contact other interneurons via type P2a axon terminals. The results also suggest that the GABA-ir P3 or the immunonegative P1b and P5 axon terminals are of extrinsic origin arising from cells in the optic tectum whereas the P2c and P4 axon terminals are associated with extra-tectal input to the NIO. The GABAergic innervation of centrifugal neurons within the NIO may be the basis for the demonstrated facilitatory effect of the centrifugal output upon ganglion cell responses. This is relevant to hypotheses regarding CVS involvement in attentional mechanisms through selective enhancement of retinal sensitivity depending on the location of meaningful or novel stimuli.

Extracellular matrices associated with conidia and germ tubes of Botrytis fabae (Sard.) sporelings grown on Vicia faba L. leaves were clearly visualized by epi-fluorescence microscopy following immunolabelling with the monoclonal antibodies, BC-KH4 and BC-FD7-G9. These antibodies were raised against surface washings of B. cinerea, are directed against B. cinerea and B. fabae, and are known to recognize carbohydrate epitopes on a glycoprotein. Both BC-KH4 and BC-FD7-G9 also labelled matrix material located at the surface of penetration and infection hyphae inside the leaf tissue by epi-fluorescence microscopy. Such matrix material was not visible by DIC microscopy.

Immunoelectron microscopy of B. fabae-infected leaf tissue, prepared by progressive low-temperature dehydration and embedding in acrylic resin, allowed further investigation of the spatial distribution of the antibody-binding sites. An abundance of BC-KH4 and BC-FD7-G9 antigenic sites were observed throughout the fibrillar-like matrix material surrounding the germ tubes on the leaf surface and the infection hyphae inside the host cells. However, close examination of the V. faba–B. fabae interface inside the host tissue showed that this fibrillar material extended some distance from the surface of the infection hyphae and through the swollen epidermal and mesophyll cell walls. Such fibrillar matrix material is thought to be of fungal origin. The possible role(s) of this matrix material in the infection process are discussed.

Double-immunolabelling studies using the BC-KH4 MAb and a polyclonal antiserum directed against oligosaccharides containing β-(1→3)-glucose were carried out in order to localize and distinguish between the fungal extracellular matrix material and translucent cell wall respectively. This technique allowed a closer examination of the interactions of the fungal matrix components with the host walls and degenerate host cytoplasm. Finally, inward curling of the leaf cuticle suggested that mechanical pressure is involved in the penetration process.

This review examines the avian heterophil leucocyte and provides a morphological and cytochemical profile drawn from light and electron microscopy studies of these cells and their characteristic cytoplasmic granules. Other aspects covered include relative and absolute heterophil counts in different avian species and the response of heterophils to stress and to acute inflammation. Heterophils are round cells and, with Romanowsky stains, their primary fusiform granules appear brick-red in colour. A secondary type of round granule, less dense in the electron microscope and smaller than the primary granule, can be seen in most avian species. The primary granules frequently display a ‘central body’ that may be proteinaceous in nature. Unlike mammalian neutrophils, avian heterophils are devoid of myeloperoxidase. However, their cytoplasmic granules contain several lysosomal and non-lysosomal enzymes including acid phosphatase, arylsulphatase, β-glucuronidase, phosphorylase, uridine diphosphate glucose-glucogen glycosyltrans-ferase, neutral and acid α-glucosidases, acid trimetaphosphatase and lysozyme. In the majority of birds heterophils are the second most numerous cell in circulation, the exceptions being several species of the Psittacine and Anseriformes orders, ostrich, ring-necked pheasant, pigeon and rosy flamingo. Heterophils generally outnumber lymphocytes in chicks between hatch and one week of age. Their numbers increase during mildly or moderately stressful conditions and consequently the heterophil/ymphocyte ratio can be used to detect the presence of physiological stress for most stressors. A heteropenia can occur, however, during severe stress. Heterophils respond to a stimulus (chemotactic agent) within about 30 minutes during the early inflammatory phase and they may also have sensitive and selective phagocytosing properties. By seven days heterophils become unrecognizable and, with macrophage recruitment, the characteristic heterophilic granuloma develops.