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Biomedical subjects

G C Johnson

Publications and source records attributed to G C Johnson.

At least 37 records · Page 2Linked to original sources
PubMed1998

Effect of 4-aminopyridine and single-dose methylprednisolone on functional recovery after a chronic spinal cord injury.

The demyelination process is an important factor contributing to long term sensory and motor impairments after spinal cord injury (SCI). Exposure of axonal K+ channels after demyelination may contribute to blockage of action potentials across the injury site. A K+ channel blocker, 4-aminopyridine (4-AP), has been effective in restoring some sensory and motor impairment in incomplete SCI patients. The long-term effect of this compound in chronic model of SCI is not known. In this study, after a compression injury of 50 grams in rats, a randomized treatment was initiated 3 weeks after the initial injury which was followed by daily administration of 4-AP at 2 mg/kg (n = 8), 4 mg/kg (n = 8), and 6 mg/kg (n = 8) for 4 weeks. A group of methylprednisolone (MP)-treated (30 mg/kg, n = 8) and non-treated animals (n = 8) were included for comparison. The functional motor outcome was measured in each animal at regular time points up to 4 weeks post-treatment. All animals receiving 6 mg/kg developed generalized seizure and were excluded from the study. In the other animal groups, analysis of the behavioral outcome and neuro-pathological changes were essentially similar and did not show any significant effect of treatment. Our data indicate that daily administration of 4-AP, over 4 weeks of treatment period, lacks any significant effect on axonal function in chronically injured rats. This could be due to (a) lack of significant numbers of demyelinated axons which could improve the functional outcome and (b) a treatment regimen that was not adequate to contribute to a better functional outcome. One time bolus-administration of MP at 30 mg/kg also did not ensure a better functional outcome.

4-Aminopyridine↗
PubMed1996

Epidemiologic evaluation of encephalitic listeriosis in goats.

OBJECTIVE: To evaluate host and environmental factors associated with the development of encephalitic listeriosis in goats. DESIGN: Retrospective analysis of diagnostic laboratory records and survey of veterinarians and goat producers. SAMPLE POPULATION: 355 goat herds accessible through laboratory records; 38 veterinarians who treated goats and 76 goat producers. PROCEDURE: Data regarding breed and use for goats affected with encephalitic listeriosis were obtained from surveys and case follow-up information. Listeria monocytogenes isolates from the brains of 7 affected goats were serotyped and subjected to DNA restriction analysis. RESULTS: Odds ratio for the development of encephalitis listeriosis in Angora (mohair-producing) goats was 22.9 by use of diagnostic laboratory records. Survey also revealed a high prevalence in herds of Angora and other breeds that subsisted on woody browse, although Angora goats feeding predominantly on hay or pasture were not affected. Listeria monocytogenes isolates from 4 Angora goats in 3 herds differed in DNA restriction patterns, although the pattern was identical in 3 other goats from another herd. CLINICAL IMPLICATIONS: Encephalitic listeriosis can be observed in all goat breeds, but a lifestyle of heavy browse consumption seems important to the development of disease in some herds.

Animal Feed↗
PubMed1996

Pretreatment with NMDA receptor antagonist MK801 improves neurophysiological outcome after an acute spinal cord injury.

The post-traumatic release of excitatory amino acids (EAA) and their actions on N-methyl-D-aspartate (NMDA) receptors plays a major role in the spinal cord secondary injury process. The neuronal damage caused by the release of EAA may be reduced by NMDA-receptor channel blockers. To investigate the involvement of NMDA receptors in spinal cord injury (SCI), we pretreated animals with the noncompetitive NMDA antagonist MK801 (1.0 mg kg-1) before a compressive acute SCI. Pretreated animals with MK801 significantly (p = 0.038) improved the recovery of function as measured by evoked potential activities. Morphologically, specimens from rats treated with MK801 were characterized by milder and more localized hemorrhage in the gray matter. Immunohistochemical staining for glial fibrillary acidic protein (GFAP) and neurofilament (NF) histochemistry showed leakage of these antigens in traumatized cord while characteristic staining of astrocytes and neurons and their processes was observed in morphologically preserved tissue. The loss of NF immunoreactivity was reduced by MK801 treatment.

Animals↗
PubMed1996

Histologic and immunohistochemical characterization of hemangiomas in the skin of seven young horses.

The histologic and immunochemical characteristics of benign vascular tumors excised from the skin of seven young horses were evaluated. The patients were male horses of various breeds and were 16 months of age or younger at the time of presentation. Six tumors occurred on the extremities, and one was removed from the lip. Histologically, most tumors consisted of cellular nodules of varying compactness with few to many blood-filled lumina. Nodular growth separated preexisting adnexa and subcutaneous collagen. Some tumors contained or consisted predominantly of loosely packed arrays of ramifying, veins, and capillaries separated by collagen within the dermis and subcutis. Within areas of nodular growth, multilayered vascular walls were encircled by reticulin strands that surrounded the endothelium and adjacent pericytes and also separated nonperivascular cells in the mass. Immunohistochemical staining of factor-VIII-related antigen and labeling by Ulex europeus-1 lectin was restricted to an innermost layer of cells surrounding vascular spaces, confirming their vascular endothelial origin. The plump fusiform cells arranged concentrically around the endothelium and some of those unassociated with vascular lumina stained with antibody to alpha-smooth muscle actin, as did the muscularis of larger vessels inside and outside of tumor nodules. These findings demonstrate an orderly arrangement between endothelium and supportive cells in these benign vascular neoplasms of young horses, similar to that observed during vascular development.

Actins↗
PubMed1995

Comparison of argyrophilic nucleolar organizer regions (AgNORs) and mitotic index in distinguishing benign from malignant canine smooth muscle tumors and in separating inflammatory hyperplasia from neoplastic lesions of the urinary bladder mucosa.

Staining for argyrophilic nucleolar organizer regions (AgNORs) has proven useful in differentiating recurrent or malignant neoplasms from less aggressive or benign ones. We applied this stain to benign and malignant smooth muscle tumors and to hyperplastic and carcinomatous lesions in the urinary bladder of dogs in an effort to determine its utility in diagnostic situations. The stain was simply performed, and the results were repeatable for different staining intervals and between staining batches. For smooth muscle tumors, enumeration of AgNORs in 100 nuclei was about as efficient as mitotic index in correctly categorizing histologically benign and malignant neoplasms. The mean number of AgNORs/100 nuclei for leiomyomas was significantly less than that obtained for leiomyosarcomas and significantly greater than that obtained for normal smooth muscle. Counts for smooth muscle tumors correlated with the mitotic indexes. Counts by an individual observer were repeated without introducing significant variation, but there was variability between observers, particularly in AgNOR counts for leiomyosarcomas. AgNORs were not useful in separating hyperplastic or polypoid cystitis from transitional cell carcinoma, misclassifying both. Mean AgNOR counts for these 2 conditions did not differ at the 5% level of significance; mitotic index was more efficient at separating the 2 conditions. There was no correlation between mitotic index and AgNOR in urinary tract mucosal specimens. This easily prepared stain may be useful in separating benign and malignant smooth muscle tumors, although AgNORs were less contributory to diagnosing mucosal lesions of the urinary bladder of dogs.

Analysis of Variance↗
PubMed1995

Evaluation of laboratory tests for confirming the diagnosis of encephalitic listeriosis in ruminants.

Retrospective analysis of 93 bovine, ovine, and caprine cases diagnosed as listerial encephalitis revealed positive bacterial isolations in only 63% of 59 cases in which bacterial culture was attempted. Only 42% of 41 attempted bovine brain cultures were successful, compared with 67% from 6 sheep brains and 92% from 12 goat brains. Gram stains and Listeria-specific immunohistochemistry were evaluated as tools for verifying the presence of bacteria or listerial antigens in 38 animals. Sixteen of 17 animals in this group with positive bacterial isolations were immunochemically positive for listerial antigens (including 5/6 cattle), but Gram stains detected only 9/17 positive animals (including 1/6 cattle). Antigen was also detected in 15 of 21 animals (including 5/9 cattle) with unsuccessful or unattempted bacterial isolations. Of all 38 animals, the histologic diagnosis could be verified in 82% by immunohistochemistry, compared to 47% verified by Gram stains. Immunohistochemical testing was especially beneficial in locating antigen in lesions with few bacteria or bacterial antigens and is a rapid method of confirming the diagnosis of encephalitic listeriosis where inappropriate material is submitted for bacterial isolation or in culture-negative cases.

Animals↗
PubMed1995

Liver disease in cattle induced by consumption of moldy hay.

Normally innocuous forages are sporadically associated with hepatogenous photosensitization outbreaks at certain times of the year or when grown and harvested during unusual environmental conditions, such as periods of excessive rainfall. Allegations of livestock illness following consumption of such moldy hays are associated with clinical syndromes uncharacteristic of known forage-related diseases, suggesting that unidentified toxin(s) may be responsible. This study was instigated by field observations of hepatogenous photosensitization in cattle fed alfalfa-grass forage. To document the toxic nature of the hay, large bales of hay (450 kg) were fed, ad libitum, to 3 groups of 2 calves each. Elevated serum liver enzymes provided evidence of hepatobiliary disease. Gamma glutamyl transferase activities in serums of the calves sustained at least a 10-fold increase above baseline during the feeding trials. Histologic examination of liver biopsies and postmortem sections revealed mild periportal fibrosis and biliary hyperplasia. Culture material from 12 fungal isolates from the hay failed to induce liver disease in calves.

Animal Feed↗
PubMed1994

Disseminated peritoneal leiomyomatosis in a horse.

A 6-year-old female Quarter Horse became inappetent, lost weight, was febrile, and had abdominal enlargement and infrequent bouts of mild colic. Palpation per rectum detected a prominent, smooth-walled mass adjacent to the pelvic flexure of the colon. Analyses revealed the peritoneal fluid was apparently normal except for a high protein concentration. By the use of ultrasonography, the mass was observed adjacent to the body wall in many locations throughout the abdomen, appearing as an irregular, multiloculated structure composed of innumerable cysts of various sizes with interspersed, circular hyperechoic nodules. A celiotomy was performed, and the 34-kg mass was removed. On the basis of histologic examination, a diagnosis of disseminated peritoneal leiomyomatosis was made. The horse had an uncomplicated recovery and gained weight. Further problems have not been reported and the horse subsequently gave birth to a healthy foal. A complete examination of the horse 22 months after surgery did not reveal signs of redevelopment of the condition.

Animals↗
PubMed1994

Amaranthus retroflexus (redroot pigweed) poisoning in cattle.

Amaranthus retroflexus (redroot pigweed)-induced nephrotoxicity was diagnosed in 6 herds of cattle from 3 counties in southwest Missouri. Forty-eight cows and calves died and another 35 were clinically affected. Serum urea nitrogen concentration, determined in 4 affected calves, was between 55 and 284 mg/dl, and serum creatinine concentration was between 6.7 and 29.9 mg/dl. Postmortem examination of affected cows and calves revealed amber-colored fluid in peritoneal cavities and retroperitoneal perirenal edema. Histologic examination of kidney sections revealed widespread degeneration and necrosis of proximal and distal tubules. Compared with archived kidney sections from cattle with Quercus (oak) poisoning, distal renal tubules were more severely affected. Oak poisoning also was associated with a higher prevalence of interstitial fibrosis and renal tubular oxalosis. We concluded that ingestion of the aerial and leafy portions of pigweed by cattle in drought situations does not necessarily lead to nitrate-induced sudden death associated with consumption of the nitrate-containing stems.

Animals↗
PubMed1994

Hypodipsic hypernatremia in a dog with defective osmoregulation of antidiuretic hormone.

Hypernatremia was detected in a dog that was evaluated because of seizures. During hospitalization, the dog was fully conscious and remained hypernatremic when drinking voluntarily and when water was added to the food. Urine volume increased and urine osmolality decreased during an infusion of hypertonic saline (2.5% NaCl) solution, despite development of progressive hyperosmolality. There was no correlation between plasma antidiuretic hormone concentration and osmolality during the infusion study. The dog released antidiuretic hormone normally after nonosmotic stimulation (ie, apomorphine administration). These findings allowed a diagnosis of hypodipsic hypernatremia caused by destruction of hypothalamic osmoreceptors. At necropsy, there was hydrocephalus, atrophy of the septum pellucidum, and neuraxonal dystrophy of the cuneate nuclei. The underlying neurologic disease responsible for the CNS lesions could not be determined, but hydrocephalus may have led to pressure atrophy in the region of the hypothalamus that contains osmoreceptors.

Animals↗
PubMed1994

Development toxicity of fumonisin in Syrian hamsters.

The effects of fumonisin on development of Syrian hamster fetuses were studied using fumonisin B1 and B2 extracted from Fusarium moniliforme corn-culture and purified fumonisin B1. A significant increase in litters with fetal deaths occurred with the high doses of purified (18 mg FB1/kg) and culture-extracted (18 mg FB1 plus 4.5 mg FB2) fumonisin. It is concluded that prenatal exposure to fumonisin on days 8 and 9 of gestation is detrimental to fetal hamster survivability but does not induce clinical maternal intoxication at these doses. Equivalent doses of fumonisin B1, whether from culture-extract or pure solution produced similar results.

Abnormalities, Drug-Induced↗
PubMed1994

Developmental toxicity in hamsters of an aqueous extract of Fusarium moniliforme culture material containing known quantities of fumonisin B1.

The purpose of this study was to investigate potential detrimental effects of fumonisin B1 on the developing hamster. In experiments 1 and 2, timed-bred hamsters were dosed with 0.0 to 12.0 mg fumonisin B1/kg from day 8 to day 10 or day 12 of gestation. Clinical signs of material toxicity were not observed. Pregnant animals had reduced weight gains and lower total bilirubin levels than nonpregnant females. Hamsters were euthanized on day 15 of gestation. Histologic evaluation revealed autolytic placental changes expected in terminal gestation, as well as more advanced placental necrosis in association with fetal resorptions. Mean fetal weights and crown-rump lengths of living term fetuses on a per-litter basis did not differ between untreated controls and treated animals given 6.0 mg fumonisin B1/kg or less. However, at higher doses of fumonisin B1, there was an increased incidence of prenatal losses (deaths and resorptions). A greater percentage of litters had 1 or more fetuses affected, and a greater percentage of total fetuses were lost/litter as the fumonisin dosage increased. At 12.0 mg/kg, all litters were affected and 100% of the fetuses were dead and resorbing. Fumonisin B1 appears a developmental toxicant in hamsters. Toxicity is manifest by increased numbers of prenatal deaths and resorptions at doses that do not induce clinicopathologic evidence of maternal toxicity.

Animal Feed↗
PubMed1994

Occipital condylar dysplasia in two Jacob sheep.

Two young Jacob sheep which presented with severe ataxia and torticollis had abnormally formed atlanto-occipital joints. Postmortem examination revealed marked dissimilarity in size between the left and right occipital condyles, with reduction in size of the foramen magnum. The atlantoaxial joint and dens were normally formed, and were not abnormally positioned in radiographs taken of one lamb. Histological evaluation of the cervicomedullary junction demonstrated extensive loss of axons and myelin, gliosis, and mild hydromyelia in one lamb.

Animals↗
PubMed1993

Therapeutic value of 21-aminosteroid U74389F in acute spinal cord injury.

The effect of bolus injections of 21-aminosteroid U74389F after an acute spinal cord compression trauma in rats was studied. Cortical somatosensory evoked potentials (CSEPs) were recorded before and after a weight-induced injury of 120 g and monitored up to five hours post-injury. All U74389F treatments were given as i.v. bolus injections of 15, 7.5, and 3.75 mg kg-1 at 1, 2, 3 h after the trauma, respectively. The CSEPs were abolished immediately after the injury in the control and treated animals. The majority of the treated animals (88.8%) demonstrated a return of the CSEPs within the second hour post-injury. In contrast, the animals in the control group showed only 44.4% recovery at this time period. At three hours post-injury, U74389F-treated animals (n = 18) showed a full recovery (100%) while the recovery rate remained at 44.4% for the control animals. We conclude that the bolus administration of U74389F one hour after injury facilitates the return of the spinal cord function as measured by the CSEPs in this compression model of acute spinal cord trauma.

Acute Disease↗