Morphological structures for potential sperm storage in poeciliid fishes. Does superfetation matter?

Sperm storage within the female reproductive tract has been reported as a reproductive strategy in several species of vertebrates and invertebrates. However, the morphological structures that allow for sperm to be stored and kept viable for long periods are relatively unknown in osteichthyes. We use histological and stereological tools to identify and quantify sperm storage structures (spermathecae) in 12 species of viviparous Poeciliidae. We found spermathecae in nine species, six of which exhibit superfetation (the ability of females to simultaneously carry within the ovary two or more broods of embryos at different stages of development). These spermathecae are folds of ovarian tissue that close around spermatozoa. We compared the number and size (volume) of spermathecae between species with and without superfetation. Species that exhibit superfetation had a significantly higher number of spermathecae than species that do not exhibit this reproductive strategy. In addition, we found that the mean volume of spermathecae and total volume of spermathecae present in the ovary are marginally higher in species with superfetation. Our results contribute to the understanding of the morphological structures that allow for sperm storage in viviparous osteichthyes and suggest a positive relationship between superfetation and the capacity of females to store sperm.

Retrograde axonal transport obstruction of brain-derived neurotrophic factor (BDNF) and its TrkB receptor in the retina and optic nerve of American Cocker Spaniel dogs with spontaneous glaucoma.

OBJECTIVE: To determine the degree of retrograde optic nerve axonal transport obstruction at the scleral lamina cribosa level by examining levels of brain-derived neurotrophic factor (BDNF) and its tyrosine kinase receptor type B (TrkB) in dogs presenting with high intraocular pressure. ANIMALS STUDIED: A total of 10 eyes, four normal and six glaucomatous eyes, from normal and affected American Cocker Spaniels with primary glaucoma were studied. All eyes were assessed by neuro-ophthalmic examination, tonometry, gonioscopy, slit-lamp biomicroscopy, and indirect ophthalmoscopy prior to enucleation. METHODS: Immunocytochemistry analysis was performed to evaluate BDNF and TrkB receptor expression in retina and optic nerve in normal and glaucomatous dogs. RESULTS: In all normal eyes BDNF immunostaining was detected in the cytoplasm of retinal ganglion cells (RGC), inner plexiform layer (IPL), inner nuclear layer (INL), nerve fiber layer (NFL), optic nerve head cells, and lamina cribosa cells. In all glaucomatous eyes BDNF was more evident in RGC, NFL and lamina cribosa cells. TrkB receptor was detected in the cytoplasm of RGC, NFL and ONH bundles in all normal eyes, and in a more intense pattern in all glaucomatous eyes. CONCLUSIONS: BDNF retrograde axonal transport is substantially inhibited by intraocular pressure elevation. TrkB accumulation at the ONH in glaucoma suggests a role for neurotrophin deprivation in the pathogenesis of RGC death in canine glaucoma, as well as a possible paracrine and/or autocrine signaling within the lamina cribosa. Neurotrophin signaling may regulate more than neuronal development, survival and differentiation. BDNF neurotrophin and its TrkB receptor expression by lamina cribosa cells and ONH astrocytes in glaucomatous eyes may help to determine the role of these cells as a paracrine source in terms of retinal ganglion cell survival, during episodes of elevated intraocular pressure.

Measurement of retinal nerve fiber layer thickness in normal and glaucomatous Cocker Spaniels by scanning laser polarimetry.

OBJECTIVE: To measure changes in the thickness of the retinal nerve fiber layer in normal and early glaucomatous dogs with scanning laser polarimetry. ANIMALS STUDIED: A total of 45 eyes, 32 normal and 13 glaucomatous eyes, of American Cocker Spaniels with primary glaucoma were used. All eyes were evaluated through a complete neuro-ophthalmic examination, tonometry, gonioscopy, slit-lamp biomicroscopy, and indirect ophthalmoscopy prior to enucleation. METHODS: The retinal nerve fiber layer thickness was measured in anesthetized animals with scanning laser polarimetry (Nerve fiber analyzer, GDx; Laser Diagnostic Technologies, LTD, San Diego, CA, USA). Glaucomatous eyes retained some vision at the time of this study. RESULTS: The mean +/- SD of the retinal nerve fiber layer thickness was 141.69 +/- 18 microm for normal dogs and 105.08 +/- 23.86 microm for visual glaucomatous dogs. The average retinal nerve fiber layer thickness in the superior and inferior retinal quadrants was 148.03 +/- 8.5 and 141.06 +/- 8.73 microm, respectively, for normal dogs, and 106.61 +/- 25.77 and 107.08 +/- 24.99 microm in the superior and inferior retinal quadrants, respectively, for glaucomatous dogs. The superior to nasal retinal nerve fiber layer thickness ratio was 1.45 for normal dogs and 1.26 for visual glaucomatous dogs. CONCLUSIONS: Using scanning laser polarimetry it was possible to detect changes in retinal nerve fiber layer thickness in glaucomatous dogs at early stages of the disease. Therefore, this instrument has the potential to improve the clinical management of canine glaucoma by detecting progressive changes to the retinal nerve fiber layer.