Fred E. Hossler

The gill arch of the striped bass (Morone saxatilis). IV. Alterations in the ultrastructure of chloride cell apical crypts and chloride efflux following exposure to seawater

Osmotically induced alterations in the ultrastructure of the apical crypts of chloride cells and changes in chloride efflux were studied in striped bass (Morone saxatilis). Striped bass were divided into three groups: fish adapted to freshwater, fish transferred directly from freshwater to 100% seawater (3% salt, w/v) for 24 hr or less, and fish adapted to 100% seawater for 7 days or more. Transmission electron microscopy studies revealed multicellular complexes of cells in both freshwater‐ and seawater‐adapted fish. Cytoplasmic indigitations between cells in the complex were more numerous in seawateradapted bass. Scanning electron microscopy studies showed that the apical extensions in freshwater fish were uniform in size. Changes in ultrastructure and chloride efflux were observed within 3 hr after transfer to seawater. Initially the apical extensions of chloride cells become longer, more prominent, and branched. After 7 days in seawater some of the apical crypts develop into a deeper “pit” structure, while others remain like those of freshwater fish. An increase in the number of apical crypts is measured by 14 days after transfer. Chloride efflux increases to five times freshwater values after 24 hr and 17 times freshwater values after 7 days in seawater. Mitochondrial density is not significantly different between freshwater and seawater fish (7 or more days). The response of chloride cell apical crypts is not an all‐or‐none phenomenon as observed in other species. Striped bass are able to increase chloride efflux when osmotically stressed with little ultrastructural alteration.

Surface morphology of fetal neural transplants into the lateral ventricles after hippocampal lesions

The surface morphology of transplants of rat fetal hippocampal tissue, and of cavities formed by aspiration lesion of the adult rat hippocampus and overlying neocortex into which the transplants were placed, was studied by scanning electron microscopy. The surface of lesion cavities was covered by a scar upon which occasional cellular profiles were found. The surface cells resembled supraependymal macrophages. Lesion cavities with a transplant showed similar scarring although the number of supraependymal structures was increased. Polymorphic cells and numerous fiber processes were observed both on the surface and embedded in the scar. Ependymal structures were seen on the non-damaged ventricular surfaces adjacent to the lesion site. These regions, however, also displayed increases in the number and types of supraependymal structures. Scanning electron microscopy demonstrated considerable variability in surface morphology of different transplants and over the surface of individual transplants. A transplant could show regions of scarring, areas covered by cells resembling ependymal cells, and regions covered by a dense matrix of fibers. In many regions the fibers coalesced to form a branching, web-like network over the transplant surface. Transmission electron microscopy indicated that the surface could be covered by ependymal cells or by the scar seen in scanning specimens. Some surface fibers were identified as axons. Cells on the surface of the transplants could be identified as neuronal, glial-like, and phagocytic. The cells and the possible effects of surface morphology on transplant function is discussed.

Vasoconstrictor and dilator responses to neurokinin A in isolated guinea pig heart

Effects of neurokinin A (NKA) and substance P (SP) on coronary resistance vessels were studied in isolated guinea pig hearts perfused with isotonic buffer containing 20 mM KCl. Injections of NKA and SP caused dose-dependent reductions in perfusion pressure with ED50 values of 14.0 and 0.326 pmol, respectively. Blockade of nitric oxide synthesis or removal of the endothelium inhibited vasodilator responses to neurokinins. Infusions of NKA or SP caused tachyphylaxis and cross-desensitization to the other neurokinin but not to acetylcholine. Injections of 2.5 nmol NKA increased perfusion pressure by 31 +/- 8% when given after tachyphylaxis developed to infused SP (2.5 nmol/100 microliters/min). It was concluded that 1) neurokinins cause an endothelium-dependent relaxation of coronary resistance vessels by stimulating NK-1 receptors on endothelial cells, and 2) desensitization of the receptor mediating vasodilation unmasks a vasoconstrictor response to NKA.

Microvasculature of the Urinary Bladder of the Dog: A Study Using Vascular Corrosion Casting

The urinary bladder is an unusual organ in that its normal function includes filling and emptying with alternating changes in internal pressure. Although fluctuations in blood flow to the bladder wall are known to accompany these changes, detailed descriptions of the bladder microvasculature are sparse. The present study uses vascular corrosion casting and scanning electron microscopy to describe the three-dimensional anatomy of the microvasculature of the urinary bladder of the dog. Specialized features of that microvasculature, including collateral circulation, vessel folding, vessel orientation, the presence of valves and sphincters, and mucosal capillary density, that may enhance and control blood flow during normal bladder function, are described and discussed.

Comparative study of dentition among species of Poecilia (Pisces)

Many studies in the genus Poecilia have focused on reproductive and genetic characteristics of Poecilia formosa, the Amazon molly, and its sympatric species P. latipinna and P. mexicana. The research literature of Poecilia dentition has been limited to general tooth morphology. Essentially absent are comparative analyses of dentition patterns and total numbers of teeth. The current study uses dentition analysis as a method to compare species in the genus Poecilia and to address some taxonomic issues related to these fish. The study focused on fish from the areas of southern Texas and northeastern Mexico. Through the use of scanning electron microscopy, the lower jaws of Poecilia spp were examined to determine total numbers of outer and inner teeth. In addition, the differences in distribution patterns of the inner teeth were recorded and compared. Statistical analyses were performed to determine which comparisons were significant. This study reveals several observations: 1) variations in the numbers of outer and inner teeth exist in some of these fish with respect to site of collection; 2) differences in total teeth numbers and dentition patterns were found both interspecifically and intraspecifically; and 3) in addition, dentition analysis provided evidence regarding the origin of P. formosa. This study supports the current notion that P. latipinna, the proported paternal component, and P. mexicana limantouri, the purported maternal component, are the progenitor species of P. formosa. Two unresolved taxonomic questions were addressed through dentition analysis. First, the present study supports the exclusion of the triploid associate of P. formosa as a separate species from P. formosa. Second, this study shows a significant difference in the number of inner teeth and in dentition patterns between P. mexicana limantouri and P. mexicana mexicana. Such differences, in addition to previously known distinguishing characteristics, should prompt careful consideration of whether or not these taxa deserve specific status or retention of their current subspecific status. J. Morphol. 239:271–282, 1999.