James W. Hinds

Early ganglion cell differentiation in the mouse retina: An electron microscopic analysis utilizing serial sections☆

Abstract The retina of a mouse embryo on day 13 of gestation, the first day when ganglion cells with axons are detectable, has been studied both qualitatively and quantitatively by reconstructing a large number of cells (more than 100) from an electron microscopic serial section series. Direct evidence has been obtained for migration of prophase nuclei of ventricular cells to the ventricle within an intact process which spans the thickness of the retinal wall. At metaphase most of the vitreal process appears to be pinched off, and the cell completely rounds up. After cytokinesis, cells take one two courses: (1) regrowth of their vitreal process to the vitreal surface while keeping their ventricular process attached at the ventricular surface by a junctional complex; these cells will undergo another round of DNA synthesis and division; (2) regrowth of their vitreal process only so far as the marginal layer with detachment of their ventricular process from the junctional complex and beginning migration of their centrioles and cilium away from the ventricle. These changes represent the earliest detectable quantitative or qualitative changes undergone by cells that will subsequently differentiate into ganglion cells. The sequence of events for the formation of unipolar ganglion cells from these early bipolar cells involves transformation of the simple vitreal process ending in the marginal layer into an axonal growth cone insinuating itself between the tangential axons of the marginal layer and growing toward the optic stalk; at the same time the Golgi complex and centrioles migrate to the perikaryon, and the ventricular process completely withdraws. Usually, but not always, both daughter cells of a mitotic division appear to have the same fate, either both remain ventricular cells or both become ganglion cells. This result is used to construct a simple hypothesis explaining some of the apparently contradictory results of neuronal development, both in the retina and in the rest of the central nervous system.

Cell proliferation in the neural tube: An electron microscopic and Golgi analysis in the mouse cerebral vesicle

SummaryThe shape and fine structure of ventricular (primitive ependymal) cells during their generation cycle was studied. Interphase cells are radially oriented bipolar elements with processes spanning the thickness of the brain wall. Zonular junctional complexes joining internal processes at the ventricle consist of gap junctions and wider intermediate junctions. The external limiting layer consists of expanded end-feet in simple apposition; they resemble axonal growth cones and contain a feltwork of 60 Å microfilaments, elements of smooth endoplasmic reticulum but no microtubules. During prophase, nuclei of ventricular cells move to a juxtaventricular position, while their external processes remain fully extended. The internal processes of such cells contain numerous longitudinally arranged microtubules and microfilaments. Subsequent to nuclear migration, in prometaphase or metaphase, the cell withdraws or pinches off its external process and becomes nearly spherical. During telophase an asymmetrical furrow formation results in a thin connector (midbody) between daughter cells which is adjacent to the ventricle and attached there by the junctional complex. Either before or after complete separation, an external process starts regrowing towards the external limiting layer, eventually resulting in a bipolar interphase cell again. Microfilaments are present in telophase cells before outgrowth of external processes and in growing tips of external processes.

Reconstruction of dendritic growth cones in neonatal mouse olfactory bulb

SummaryAn improved and simplified method of serial sectioning for electron microscopy was used to prepare material from which were reconstructed dendritic growth cones of mitral cells in neonatal mouse olfactory glomerulus. Growth cones are characterized by: (1) one or more filopodia, each approximately 0.2 μm in diameter, projecting from an expanded dendritic terminal or pre-terminal region; (2) a polygonal array of microfilaments approximately 50 Å in diameter, filling the enlarged terminal and filopodia; (3) an absence of microtubules and a paucity of mitochondria; (4) a few profiles of smooth endoplasmic reticulum or vesicles; (5) occasional axodendritic synapses. These characteristics are compared with those of other growing processes in the nervous system and a consistent picture of the appearance of growing neuronal processes obtained, suitable to use as a guide in a search for additional growing processes in developing and mature brains.

Stability of synaptic density and spine volume in dentate gyrus of aged rats.

The number of synapses per unit volume and per granule cell and the size of dendritic spines were studied in the dentate gyrus of Sprague-Dawley rats 6, 24, and 30 months of age. Neither synaptic density nor mean spine volume showed any age-related trends. An increase in granule cell packing density at 24 months and concomitant stability of the height of the granule cell layer is consistent with the idea that postnatal generation of granule cells may continue late into life. Possible explanations for the discrepancies in the literature regarding synaptic loss in this area include differences in morphometric techniques, age of animals used, regional differences within dentate gyrus, and sampling variability. Generalized synapse loss in the senescent rodent brain remains to be established.

Capillaries in aging rat olfactory bulb: A quantitative light and electron microscopic analysis

Olfactory bulbs from Charles River (Crl) rats from 3 to 36 months have been examined with light and electron microscopy. Total capillary length, surface, and volume, as well as number of endothelial cells, increases during the twofold increase in olfactory bulb volume from 3 to 18 months, but the relative density of these parameters shows no change during this time; from 18 to 36 months when neuronal cell body and dendrites are decreasing markedly in size, the relative density of capillaries shows only a modest decrease. Capillary lumen size and capillary wall thickness remain the same throughout life, but basal lamina thickness doubles from 3 to 24 months and then remains constant from 24 to 36 months. The incidence of several unusual ultrastructural features of the outer capillary basal lamina has been shown to increase with age.

Preservation of retinal structure in aged pigmented mice

The effects on the retina of advancing age were studied in pigmented mouse strain (C57BL/6J). The mice range in age from 65 days to 1000 days, an age well beyond the mean life span of the population (850 days). The thickness of the neuronal and plexiform layers and the planimetric density and size of the component neurons were assessed in both central (200-500 micrometers from the optic disc) and peripheral (within 200 micrometers of the retinal margin) areas. In addition, the overall size of the retina was determined by measuring its length along the horizontal meridian. Although retinas of albino rodents degenerate extensively during aging [10, 18, 31, 32, 40], in the retinas of pigmented mice neither the central nor the peripheral locus showed either marked thinning of the retinal layers or neuronal loss with advancing age. We suggest that previous findings of severe retinal degeneration in albino rodents during aging can be attributed to their lack of pigment and that pigmented animals offer a more suitable animal model for normal retinal aging.

Rehabilitation following early malnutrition in the rat: Body weight, brain size, and cerebral cortex development

Sprague-Dawley rats were malnourished by giving their mothers an 8% casein diet starting at day 10 of gestation, while controls were fed a 24% casein diet. Starting at postnatal day 20 (P20), rehabilitation of the malnourished animals was attempted by: (1) feeding both mother and young a 24% casein diet, (2) leaving the pups with their mothers until they were 40 days old, and (3) reducing the litter size from 8 to 4 pups. Observations were made on aldehyde-perfused tissue from animals 20, 40 and 70 days old. The somatosensory cortex from one hemisphere was embedded in Araldite, and that from the other side was processed fro Golgi staining. At 20 days of age the body weight of the malnourished animals was 21% that of the controls, but at 70 days it was no longer different. The anterior-posterior length, the width, and the height of the cerebral hemispheres were also significantly reduced at P20, but the differences had disappeared by P70. The thickness of area 3 of the cerebral cortex was measured in 1 micron sections. It was significantly reduced in the malnourished animals at P20, but at P40, following rehabilitation, the difference was no longer statistically significant. In tangential 1 micron sections the fraction of the volume of tissue occupied by neuropil was measured in layers II through IV. At P20 it was significantly reduced only in the upper half of layers II/III of the malnourished animals; at P40 this difference was no longer present. The mean volume of upper layer II/III cell bodies was estimated and found to be significantly reduced in the experimental animals at P20 but not at P40. In the Golgi preparations, pyramidal cells in upper layer II/III were studied. Their estimated volume, as well as the thickness of their basal dendrites, was significantly reduced in the 20 day malnourished animals, but not in the rehabilitated animals. These results show that animals severely malnourished until 20 days of age can reach normal body weight and attain cerebral hemispheres of normal size when proper nutrition is provided. The effects of malnutrition on the cerebral cortex of these animals are most apparent in upper layer II/III which, during the time of nutritional restriction, is the least developed of the cortical layers. However, when proper nutrition is provided, the cerebral cortex may attain normal morphology.

Variation in longevity of rats: Evidence for a systematic increase in lifespan over time

Male-Sprague-Dawley rats (CrL:CD(SD)BR) were maintained under barrier conditions at Charles River Breeding Laboratories (Wilmington MA) from August, 1975, to July, 1983. Animals were provided food and water ad libitum. Survival data from 8 completed cohorts of 100 animals each and one continuing cohort reveal a highly significant linear increase in median lifespan, yielding a 26% increase in this parameter for cohorts born over a period of less than six years. The biological factors responsible for this increase are not clear at present. Nevertheless, these results in outbred rats, taken in conjunction with previous observations of a trend towards increased longevity in inbred mice, indicate that the assumption of cohort equivalence underlying many cross-sectional studies of biological aging may not be valid.

One Hundred New Provincial, National, and Continental Lichen and Allied Fungi Records from Parc National de la Gaspésie, Québec, Canada

Abstract We report 100 lichen and allied fungi species for the first time from Québec, Canada. Six of these species are new to North America: Arthonia subastroidea, Biatora mendax, Cornutispora pyramidalis, Gyalecta hypoleuca, Taeniolella pertusariicola, and Varicellaria lactea. Six additional species are new to Canada: Cecidonia xenophana, Lecidea commaculans, L. herteliana, Polycoccum sporastatiae, Scoliciosporum intrusum, and Stereocaulon leucophaeopsis. All collections are from parc national de la Gaspésie on the Gaspé Peninsula in eastern Québec. Our collections were made between 2012 and 2017, primarily during Crum and Tuckerman Workshops. We provide diagnostic descriptions of all species that are new continental or national records. Our results demonstrate the parks rich and unexplored biodiversity and conservation importance, and contribute to a better understanding of the lichen and allied fungus biota of Canada and North America.