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R L Snyder

Publications and source records attributed to R L Snyder.

At least 55 records · Page 3Linked to original sources
PubMed1986

Identification and localization of pre-s-encoded polypeptides from woodchuck and ground squirrel hepatitis viruses.

A segment from the pre-s region of the woodchuck hepatitis virus (WHV) was inserted into an open reading frame vector allowing for the expression in Escherichia coli of viral determinants as part of a fusion protein. The bacterially synthesized fusion molecule contained eight amino acids from beta-galactosidase (beta-gal) at the N terminus, followed by 89 pre-s-encoded amino acids and 219 amino acids of chloramphenicol acetyltransferase (CAT) at the C terminus (beta-gal:pre-s:CAT). This tribrid protein was used to generate antiserum which had a significant titer to the viral portion of the fusion polypeptide. Anti-beta-gal:pre-s:CAT was used in Western blot analysis to identify viral proteins containing pre-s-encoded determinants. Antiserum to the tribrid molecule recognized four WHV polypeptides with molecular masses of 33, 36, 45, and 47 kilodaltons, each of which was also recognized by a monoclonal antibody to WHV surface antigen. Using the same anti-tribrid serum, we also identified analogous polypeptides from ground squirrel hepatitis virus. The antiserum was also used to immunoprecipitate virus particles containing endogenous DNA polymerase activity, indicating that pre-s determinants are found on the surface of mature virions. Based on previous computer studies and the location of pre-s-encoded molecules on the surface of virus particles, a role in hepadnavirus host cell entry is suggested for these polypeptides.

Animals↗
PubMed1986

Experimental infection of the woodchuck (Marmota monax monax) with woodchuck hepatitis virus.

Six woodchucks, 10 1/2 months of age, injected intramuscularly with 0.02 ml of woodchuck hepatitis virus (WHV)-positive serum and two woodchucks of similar age and origin injected with phosphate buffered saline were studied by serial blood samples and liver biopsy sections over an 18 week period. Serum samples were assayed for WHV surface antigen (WHsAg), its corresponding antibody (anti-WHs) and antibody to WHV core antigen (anti-WHc). WHV core antigen (WHcAg) was detected in liver biopsy sections by fluorescent labeled anti-WHc, and WHsAg was detected by the Victoria blue stain. All six experimentally infected woodchucks eventually developed anti-WHs and four developed serologic and histologic signs of acute hepatitis. Hepatic lesions resembled lesions described in the livers of chimpanzees and humans with acute hepatitis B viral infections. The first histologic signs of liver change coincided with the appearance of WHsAg within the serum and WHcAg within the cytoplasm of hepatocytes. After WHcAg was no longer detected in the serum, WHsAg appeared in the cytoplasm of hepatocytes. Microfocal areas of hepatic necrosis were associated with aggregates of lymphocytes, macrophages, and a few neutrophils and plasma cells. The periportal exudate became increasingly abundant during the 18-week study period in the four animals with acute hepatitis. The results from this study indicate that acute hepatitis may be induced in the woodchuck by experimental infection with WHV. Furthermore, the woodchuck might serve as an excellent model for the study of the pathogenesis of acute viral hepatitis in man.

Acute Disease↗
PubMed1986

Atrial fibrillation.

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Anti-Arrhythmia Agents↗
PubMed1985

Forward masking of the auditory nerve neurophonic (ANN) and the frequency following response (FFR).

The forward masking behavior of two averaged neurophonic responses was examined in cats. The auditory nerve neurophonic (ANN) was recorded with bipolar electrodes placed on the auditory nerve as it exits the internal meatus. The frequency following response (FFR) was recorded using scalp electrodes placed at the vertex and below the stimulated ear. Masking functions (response amplitude vs masker level) for frequencies both above and below the probe frequency were recorded. From these masking functions, 30% iso-depression contours (forward masking tuning curves, FMTCs) were constructed. The time course of the recovery from forward masking was also examined. It was found that the forward masking behavior of these neurophonics have many similarities to the behavior of other responses recorded using psychophysical and physiological methods. However, forward masking of the ANN and FFR has a number of unusual features. First, the best masking frequency (BMF), which in most forward masking studies is equal to the probe frequency, can be off-set from the probe frequency by as much as an octave. Second, the masker level at BMF can be as much as 30 dB below the probe level. Third, the magnitude of both of these off-sets is a function of the probe level. Fourth, low level neurophonic response could be enhanced by some forward 'maskers'. The features of neurophonic forward masking are discussed and a model of the neurophonics is suggested. This model is based on the spatial distribution of phase and amplitude in the phase-locked activity in the auditory nerve and it can qualitatively account for many of the properties of the neurophonics.

Animals↗
PubMed1984

The auditory neurophonic: basic properties.

In anesthetized cats an AC signal or neurophonic can be recorded from the auditory nerve and from the scalp when the cochlea is stimulated with low frequency tones. This study examines some of the basic properties of the auditory neurophonics. The auditory nerve signal, termed the auditory nerve neurophonic (ANN), was differentially recorded with a pair of platinum-iridium ball electrodes placed on either side of the auditory nerve as it exits the internal meatus. The signal recorded from the scalp, termed the frequency following response (FFR), was recorded with silver wire. For purposes of comparison the round window-recorded cochlear microphonic was also examined under identical stimulus conditions. Several measures of the response to acoustic stimulation were taken for each recording configuration. Among these were total response amplitude as a function of stimulus level, spectral component amplitude and phase as a function of stimulus level, fundamental component amplitude as a function of stimulus frequency, response amplitude as a function of time after stimulus onset, response amplitude as a function of forward masker intensity. By all these measures the neurophonic responses are signals that are distinct from the CM and share many of the properties of single units in the auditory nerve. In addition, micro-injections of kainic acid into the cochlear nucleus leave these responses largely unaffected, while tetrodotoxin injections into the cochlea greatly diminish both neurophonic responses, while leaving the CM largely intact. From these results, we conclude that at stimulus levels below 90 dB SPL the ANN is almost entirely neural in origin, while the FFR is certainly largely neural, that is, that both responses are quite distinct from the CM. We also conclude that they represent a spatial summation of neural activity in the auditory nerve, probably arising from the phase-locked response of single units to low frequency stimuli. In addition to demonstrating that the neurophonics are neural responses, we have begun the process of relating their properties to the distributed phase-locked activity in the auditory nerve.

Acoustic Stimulation↗
PubMed1984

The effect of light intensity, temperature, and diet on growth in red-legged partridge.

Three hundred Red-legged partridge chicks ( Alectoris graeca) were divided into two groups and fed starter diets calculated to contain 24.5 and 24.9% crude protein and 2646 and 2662 kcal/kg metabolizable energy, respectively. One diet consisted of 5% fish meal while the other contained all vegetable protein. One-half of the birds on each diet were grown under fluorescent light intensity of 300 lx; the remainder received 5 lx. The results indicated that neither the source of protein nor intensity of light had an effect on the rate of growth to 8 weeks of age. At 8 weeks of age, the birds were randomly divided among three climatic chambers and kept under a constant temperature of either 18.3, 23.9, or 29.5 C. At 12 weeks of age, one-half of the birds in each chamber were fed a 20% turkey grower diet; the remainder received equal parts by weight of the turkey grower diet and whole milo . Individual body weights and feed consumption were measured biweekly. Best growth was obtained in birds kept at 29.5 C and fed equal parts of turkey grower and milo from 12 to 30 weeks of age.

Animals↗
PubMed1983

The effect of ambient temperature and energy level on reproduction in Red-Legged partridges.

The effects of temperature and dietary energy on various reproductive parameters were studied in Red-Legged partridges (Alectoris graeca) reared in three environmental chambers at either 18.3, 23.9, or 29.5 C. These birds were then cycled through two consecutive production periods. In Period 1, at 38 weeks of age, the birds in each chamber, 118 pair total, were divided into four subgroups and fed a diet containing either 2600, 2800, 3000, or 3200 kcal/kg of metabolizable energy. The energy to protein ratio was held constant at 186. In Period 2, at 63 weeks of age, chambers with the lowest and highest temperatures were changed from 18.3 to 15.6 C and 29.5 to 32.2 C, respectively. Only the lowest and highest energy diets were used. In both periods, the birds kept at higher temperatures and fed the high energy diets consumed significantly less feed (P less than .05) than the other comparable groups. Hatchability was significantly higher (P less than .05) in groups fed the 3000 and 3200 kcal/kg diets as compared to the 2600 kcal/kg diet group. In Period 2, egg production increased in all groups, but birds kept at 32.2 C laid significantly fewer (P less than .05) eggs per bird than those kept at 15.6 and 23.9 C, respectively. The best performance, as measured by salable chicks produced per hen, was obtained in the group kept under a constant temperature of 23.9 C and fed the high energy diet (3200 kcal/kg).

Animals↗
PubMed1982

Light and electron microscopic autoradiographic study of the dorsal root projections to the cat dorsal horn.

The distribution of terminals arising from dorsal root primary afferents was examined in the lumbar spinal cord of cats using light- and electron-microscopic autoradiography. Tritiated proline or leucine was injected into either the L6 or L7 dorsal root ganglion. The light-microscopic spinal cord distribution of radioactivity in the ganglia was independent of the type of amino acid used. Likewise, the length of the survival time after injection had no effect. The projections to the substantia gelatinosa and the marginal zone were consistently densest. However, the topography of the dorsal horn distribution, relative to the segment of entry, varied significantly especially in the gelatinosa, depending upon the ganglia injected. Those to the substantia gelatinosa were largely limited to the segment of entry; those to the marginal zone and nucleus proprius extended many segments beyond the level of entry. At all levels the projection was exclusively ipsilateral to the side of injection. At the electron-microscopic level the distribution of radioactivity was determined in each of the three easily recognizable areas of the dorsal horn: the marginal zone, the substantia gelatinosa and the nucleus proprius. In each dorsal horn area the total terminal population was divided into four basic categories. Each of these areas was found to contain a characteristic distribution of these four terminal categories. The difference between areas arose, primarily, as a consequence of the dorsal to ventral decreasing frequency gradient of two types of terminal: those containing large, dense-cored vesicles and the increasing gradient of those containing flattened vesicles. The terminals with small pleomorphic vesicles and those with large round vesicles were frequently encountered in all three areas without a detectable frequency gradient. Similarly the primary afferent terminal population that is the subset of the total terminal population labelled after dorsal root ganglion injection, was also characteristic of the area, and each area was dominated by a different terminal-type. In the marginal zone the terminals containing large dense-cored vesicles dominated. In the substantia gelatinosa the terminals with pleomorphic vesicles (which included the so-called 'C' type terminals) dominated. And the terminals containing large round vesicles dominated the primary afferent population in the nucleus proprius. The terminals containing flattened vesicles were never found to be specifically labeled in any of the areas examined.

Afferent Pathways↗
PubMed1982

Uptake and transport of horseradish peroxidase by cochlear spiral ganglion neurons.

Cochlear spiral ganglion neurons in the cat have been classified as type I and type II. The type II neurons are of special interest since they are reported to provide the afferent innervation to three-quarters of the cochlear hair cells, and also because of a recent assertion that they do not project to the brain. In the present study the neuronal marker horseradish peroxidase (HRP) was utilized to re-examine these issues. HRP was injected into the intranuclear cochlear nerve root of adult cats. 18 to 48 h post-injection HRP reaction product was observed in both type I and type II neurons. The majority of labeled cells were characterized by granular reaction product, while a smaller number of cells were also diffusely filled with HRP, resulting in intense staining of the cell soma and its processes. These data indicate that the central axons of type II neurons are constituents of the cochlear nerve root at the level of the brainstem and thus do project centrally. In the organ of Corti HRP-filled fibers to both inner and outer hair cells were observed and demonstrated in electron microscopy to be afferent neurons. This intra-axonal accumulation of the HRP by outer hair cell afferents constitutes direct evidence of the functional projection of these neurons to the cochlear nucleus.

Animals↗
PubMed1980

The topographic organization of corticocollicular projections from physiologically identified loci in the AI, AII, and anterior auditory cortical fields of the cat.

The connections of the three auditory fields AI, AII, and the anterior auditory field (AAF) with the inferior colliculus (IC) were studied using anterograde tracing techniques. Microinjections of tracers were placed at physiologically identified loci after these fields had been functionally mapped using microelectrode recording techniques. This methodology ensured that the injections were well within the borders of each cortical field that was studied and enabled the elucidation of the topographies of the projections of AI and AAF onto the IC with respect to their cochleotopic organizations. The projection of loci in AI to the caudal aspect of the IC was in the form of sheets of terminals in the dorsomedial division of the central nucleus bilaterally and the pericentral nucleus ipsilaterally. The topography of projection with respect to the cochleotopic organizaton of AI appeared to be in register with the described cochleotopic organization of the central nucleus and the pericentral nucleus. The sheets of labeled terminals in the dorsemedial division of the central nucleus that resulted from the projection of single loci in AI were of the proper orientation to be continuous with the morphological laminae described in the ventrolateral division of the central nucleus. These sheets of corticocollicular terminals also paralleled the dorsomedial aspect of the physiolocally defined "isofrequency contours" of the central nucleus. Single injections placed in AAF produced autoradiographic label in the IC that was of the same basic pattern and systematic topography as the labeling recorded with AI injections; however, it was much weaker. The projection from AII was to the lateral (ipsilateral) and medial (bilateral) aspects of the pericentral nucleus.

Animals↗
PubMed1980

Isolation, characterization, and comparison of recombinant DNAs derived from genomes of human hepatitis B virus and woodchuck hepatitis virus.

The human hepatitis B virus (HBV) and the woodchuck hepatitis virus (WHV) are closely related by several criteria and belong to the same class of DNA viruses. The DNA genomes from these viruses are difficult to obtain in quantities required for biochemical analysis. We have, therefore, cloned these two DNAs in the vector lambda gtWES and subcloned into the kanamycin resistance plasmid pA01. Comparison of the recombinant DNAs with authentic viral DNAs by specific hybridization, size, and restriction enzyme analysis suggests that the recombinants contain the complete genome of each virus. The nominal size of the cloned HBV genome was 3150 base pairs, compared to 3200 base pairs for the cloned WHV genome. The small amount of nucleic acid homology previously reported between the HBV and WHV DNAs could be demonstrated between the cloned viral DNAs.

Animals↗
PubMed1980

Photorefractoriness and sexual response in aging partridge kept under constant long- and short-day photoperiods.

The duration of post-juvenile refractoriness was studied in Red-legged partridge kept under a long constant 16-hr photoperiod from hatch to 55 months of age. A second group of partridge was kept under a short constant 8-hr photoperiod from hatch to 38 months of age. Body weight was measured bimonthly, and daily egg production kept on birds reaching sexual maturity. Eighty one percent of all birds were alive at 36 months of age. Birds kept under a constant 16-hr photoperiod were generally heavier at all ages than comparable birds kept under 8-hr photoperiods. Refractoriness was terminated in 38% of the hens kept continuously under a 16-hr day. The first hen laid at 475 days of age. Median age at first egg for other sexually mature birds was 968 days. Forty percent of all birds kept under a constant 8-hr day laid at a median age of 339 days. It was concluded that post-juvenile refractoriness can be interrputed in some partridge without previous exposure to a short-day photoperiod. It is likely that uncontrolled resident temperature fluctuations and other seasonal effects may serve as preconditioners to lay.

Animals↗
PubMed1979

The effect of photoperiod and feed restriction on semen production in the turkey.

In Experiment 1, 72 yearling Broad Breasted White Turkey males were induced to molt under either stimulatory (16L:8D) or nonstimulatory (8L:16D) light used concurrently with a short period of feed and water deprivation, and followed by periods of daily feed restriction (50% of full feed). One-fourth of the males wer killed at intervals of 4, 8, 12, and 16 weeks and their testes weighed. In Experiment 2, 40 yearling Broad Breasted White males were killed at 2-week intervals during an 8-week period of 8 hr light per day followed by a 10-week period of 16 hr light per day. Testes were removed, weighed, and fixed in Bouin's solution for histological preparation. In Experiment 1, birds kept under 16 hr light and given different periods of feed and water deprivation, followed by 8 weeks of feed restriction, failed to terminate semen production, although their testes were reduced substantially in size and function. Other groups of males given 8 hr light per day with concurrent regimens of feed deprivation and daily feed restriction, terminated semen production within 4 weeks. When returned to 16 hr light, the testes were twice as heavy as those of males kept in production during the entire test. In Experiment 2, the testes of birds induced to molt under 8 hr light per day regressed by 73% and 89%, respectively, after 4 and 8 weeks of exposure. When given 16 hr light per day, some spermatogenic activity was noted at 4 weeks, and complete spermatogenesis, with maximum semen production, occurred after 6 weeks. There was evidence that a successful rejuvenation of the testes requires a period of complete quiescence.

Animals↗
PubMed1978

A comparative study of the neurons of origin of the spinocerebellar afferents in the rat, cat and squirrel monkey based on the retrograde transport of horseradish peroxidase.

The cell bodies of the neurons of the spinocerebellar pathways were examined using large injections of horseradish peroxidose into the cerebellum. Sections of each spinal segment were examined with both the DAB and the de Olmos O-dianisidine techniques. Results common to all three species were found. In Clarke's nucleus, the central cervical nucleus, and the spinal border cells there were many heavily labeled cells. Clarke's nucleus was found to project primarily ipsilaterally; the spinal border cells primarily contralaterally; and the central cervical nucleus bilaterally. In addition to these aggregates of spinocerebellar neurons there were numerous labeled neurons scattered throughout the spinal grey. Labeled neurons were found in all portions of the spinal grey except the substantia gelatinosa and lateral cervical nucleus and occurred in all spinal segments. They varied in morphology from large multipolar neurons, found predominantly in the ventral horn to small globular and fusiform neurons that were most abundant in the dorsal horn. These cells were found to project both ipsilaterally and contralaterally. Results common to only two of the species examined were also found. In the dquirrel monkey and the cat, but not the rat, the marginal layer of the dorsal horn in all segments of the spinal contained numerous labeled neurons. These marginal neurons were especially numerous in the squirrel monkey, where as many as 13 to 16 labeled neurons per section of the dorsal horn were found. In the rat and the squirrel monkey but not the cat, some intensely labeled large multipolar neurons were found in the sacral and caudal segments. These are the cells of Stilling's nucleus, a column of cells similar in position and orientation to that of Clarke's column but different in its projections and details of cytoarchitecture. Thus we have not only confirmed that Clarke's nucleus, the central cervical nucleus, and the spinal border cells project to the cerebellum but we have also found several new sources of spinocerebellar afferents.

Animals↗