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Biomedical subjects

A H Cohen

Publications and source records attributed to A H Cohen.

At least 19 recordsLinked to original sources
PubMed1992

Glutamate-like immunoreactivity in the leech central nervous system.

Using a monoclonal antibody for glutamate the distribution was determined of glutamate-like immunoreactive neurons in the leech central nervous system (CNS). Glutamate-like immunoreactive neurons (GINs) were found to be localized to the anterior portion of the leech CNS: in the first segmental ganglion and in the subesophageal ganglion. Exactly five pairs of GINs consistently reacted with the glutamate antibody. Two medial pairs of GINs were located in the subesophageal ganglion and shared several morphological characteristics with two medial pairs of GINs in the first segmental ganglion. An additional lateral pair of GINs was also located in segmental ganglion 1. A pair of glutamate-like immunoreactive neurons, which are potential homologs of the lateral pair of GINs in segmental ganglion 1, were occasionally observed in more posterior segmental ganglia along with a selective group of neuronal processes. Thus only a small, localized population of neurons in the leech CNS appears to use glutamate as their neurotransmitter.

Animals↗
PubMed1992

Modelling of intersegmental coordination in the lamprey central pattern generator for locomotion.

Rhythmic motor activity requires coordination of different muscles or muscle groups so that they are all active with the same cycle duration and appropriate phase relationships. The neural mechanisms for such phase coupling in vertebrate locomotion are not known. Swimming in the lamprey is accomplished by the generation of a travelling wave of body curvature in which the phase coupling between segments is so controlled as to give approximately one full wavelength on the body at any swimming speed. This article reviews work that has combined mathematical analysis, biological experimentation and computer simulation to provide a conceptual framework within which intersegmental coordination can be investigated. Evidence is provided to suggest that in the lamprey, ascending coupling is dominant over descending coupling and controls the intersegmental phase lag during locomotion. The significance of long-range intersegmental coupling is also discussed.

Animals↗
PubMed1992

Experimental model of lead nephropathy. I. Continuous high-dose lead administration.

This study followed the progression of lead nephropathy in male Sprague-Dawley rats (E) administered lead acetate (0.5%) continuously in drinking water for periods ranging from 1 to 12 months. Control animals (C) were pair-fed. Observations included renal pathology by light and electron microscopy, wet and dry kidney weights, and glomerular filtration rate (GFR) to assess renal function. Urinary excretion of lead, the enzymes N-acetyl-beta-D-glucosaminidase (NAG) and glutathione-S-transferase (GST), and brush border antigens (BB50, CG9, and HF5) were utilized to explore possible markers of kidney injury. GFR was increased significantly after three months of lead exposure, but was decreased significantly after 12 months. Kidney wet weights were significantly greater in E than C from three months on. Kidney dry weight/wet weight ratio was constant up to three months, but decreased in E at 12 months. Glomerular diameters were normal at all time periods; the nephromegaly was related primarily to hypertrophy of proximal tubules. Lead inclusion bodies were found in nuclei of proximal convoluted tubules and pars recta at all times. Tubular atrophy and interstitial fibrosis first appeared at six months, and increased in severity thereafter. Brush borders of proximal tubules were disrupted at one and three months, but recovered thereafter. Focal and segmental glomerulosclerosis was observed in 2 of 10 rats at 12 months. Arteries and arterioles remained normal at all time periods. Urinary NAG was elevated in E above C after three months of lead exposure. However, urinary NAG in C also increased with age, obscuring changes in the 12 month E rats. GST was elevated after three months of lead administration in E, not without an attendant age-related increase in C rats. In three-month E rats, urinary brush border antigens were increased above C, but were decreased at six and 12 months, correlating with the morphologic changes in brush border. We conclude that a high dose of lead in rats may initially stimulate both renal cortical hypertrophy and an increase in GFR. Later, the adverse effects of lead on the tubulointerstitium predominate, and GFR falls. The urinary marker, NAG, was abnormal in the early stages of the disease, but age-related changes obscured its utility at later stages; urinary GST appeared to be a more consistent marker of injury.

Acetylglucosaminidase↗
PubMed1992

The role of heterarchical control in the evolution of central pattern generators.

The acceptance of the concept of central pattern generators (CPGs) led to the perception that descending inputs initiate stereotyped movements, such as locomotion, but play relatively minor roles after the movement begins. Sensory input could entrain the CPG, and the CPG was responsive to the proper inputs for switching, etc. Evidence is here presented that the influences of both descending and sensory inputs are two-way. Descending inputs are shown to be involved in an ongoing manner during locomotion, as it has been found that CPGs are phasically driving the same descending systems that themselves activate the CPGs. Similarly, sensory inputs are being actively processed by the CPG and, here again, produce a two-way interaction between sensory input and CPGs. Finally, mechanical factors are shown to be major contributors to the form of the movement. Thus, overall the CPG can only be considered as one of several contributors to any movement; all concurrently process the flow of information. Control is viewed as distributed, that is, as heterarchical as opposed to hierarchical. Because of the complexity of interaction between the levels of the system, it is argued that any change in the body will propagate through the system and effect the final output regardless of where the change originates. Thus, ontogenetic and phylogenetic changes must have influences felt throughout the entire system. Examples are presented to demonstrate that this is, indeed, the case. The effect of these changes will primarily be manifest in the interface between the layers, that is, in the interface between the descending and sensory inputs and the CPG, so that the changes can be adaptively accommodated on a moment by moment basis when necessary.

Animals↗
PubMed1992

Acquired cystic disease in chronically rejected renal transplants.

Acquired cystic disease has been documented to complicate most forms of chronic renal damage; it has only infrequently been described in transplanted kidneys. Five patients with noncystic ESRD and chronically rejected transplants in which acquired cystic disease arose are reported. The diagnosis of acquired cystic disease was established in examination of transplant nephrectomies from four patients and a core biopsy from the fifth. The allografts were in place from 44 to 80 months; three patients were treated with hemodialysis before the diagnosis of acquired cystic disease, whereas two received peritoneal dialysis. Three of the four patients evaluated had cysts in the native kidneys. Although papillary hyperplasia of lining epithelium was evident in four specimens, only one kidney was the site of neoplasms in the form of multiple small tubular adenomas. No malignant neoplasms were noted in this study or in the few similar previous ones; however, it is possible that chronically rejected transplanted kidneys may harbor neoplasms with the same malignant potential as those in acquired cystic disease in native kidneys.

Adult↗
PubMed1992

The effect of head trauma on the visual system: the doctor of optometry as a member of the rehabilitation team.

Brain injury results from either head trauma or strokes and causes many visual and visually related disturbances. Rehabilitation is aimed at developing skills that allow the patient to optimally function as a viable and independent member of society. Often the resultant visual deficits remain undiagnosed and untreated, which hinder the patient's total rehabilitation. Optometric evaluation of brain injured patients should routinely be performed as part of the transdisciplinary team approach to rehabilitation. Optometrists are uniquely qualified to diagnose and treat visual and functional deficits of the visual system in the brain injured population. The purpose of this paper is to present a rationale for optometric participation in the rehabilitation of head trauma and stroke patients.

Brain Injuries↗
PubMed1992

Optometric management of binocular dysfunctions secondary to head trauma: case reports.

Extropia, esotropia, hyper elements, visual sequencing problems, accommodative dysfunctions and inefficient Motor Planning are common consequences of head trauma. Optometric visual therapy is an effective treatment modality for these dysfunctions. Two case reports are presented in order to illustrate optometric management of patients exhibiting these problems secondary to head trauma.

Adult↗
PubMed1992

Focal segmental glomerulosclerosis in desquamative interstitial pneumonia.

Renal involvement in desquamative interstitial pneumonitis (DIP) manifesting as chronic renal failure has been reported only once. An uncommon disorder in children, DIP has been associated with a variety of systemic disorders and has an immune-mediated pathogenesis. A 16-year-old Black male was diagnosed to have DIP on lung biopsy at the age of 10 months. He was first noted to have proteinuria at age 5 which progressed to nephrotic syndrome by age 13 when the laboratory tests showed elevated IgG, normal serum complement, increased circulating immune complexes and absent anti-GBM antibodies. A percutaneous renal biopsy specimen performed at age 13 revealed focal segmental glomerulosclerosis. Despite prednisone treatment of 2 mg/kg/day for 12 weeks, renal failure progressed requiring hemodialysis. Pulmonary functions, although reduced, remained stable.

Adolescent↗
PubMed1991

A case report of Drash syndrome in a 46,XX female.

Progressive renal insufficiency, male pseudohermaphrotidism, and Wilms tumor are known as the triad of Drash syndrome. The renal involvement has been reported in association with Wilms tumor with or without pseudohermaphroditism. The nephropathy progresses rapidly, is unresponsive to steroids, and eventually requires dialysis. The case we report is a 46,XX phenotypic female child who had diffuse mesangial sclerosis (DMS) and developed Wilms tumor 3 years after initiating dialysis for end-stage renal disease (ESRD). Any child presenting with DMS should be considered at risk for development of Wilms tumor and should be investigated for the presence of XY gonadal dysgenesis. Once ESRD develops in such a child, prophylactic nephrectomy and possibly gonadectomy should be undertaken.

Child, Preschool↗
PubMed1991

Long-term cyclosporine A treatment of steroid-resistant and steroid-dependent nephrotic syndrome.

Eighteen patients with steroid-resistant nephrotic syndrome (SRNS) and steroid-dependent nephrotic syndrome (SDNS) were treated with cyclosporine A (CyA) (6 mg/kg/d) for 2 to 29 months. CyA levels were monitored monthly and plasma levels by Abbott TDX (Therapeutic Drug Analyzer System) fluorescence polarization immunoassay were maintained at 100 to 150 ng/mL. The corticosteroid dosage administered at the time CyA therapy was initiated was variable and was continued following CyA therapy. Six of these patients (all with SDNS and minimal change nephrotic syndrome [MCNS]) had been treated with one or more courses of cytotoxic drug therapy, and all had clinical evidence of corticosteroid toxicity after receiving corticosteroid therapy for 26 to 120 months. The corticosteroid dosage was reduced by slow tapering and was ultimately discontinued in six patients. These patients were maintained on CyA monotherapy for 7 to 21 months at a dose of 3.2 to 6.7 mg/kg/d. Following 11 to 29 months of CyA therapy, seven patients underwent an elective renal biopsy, which showed nephrotoxicity in all seven. This led to discontinuation of CyA in four patients. Following discontinuation of CyA monotherapy, all four patients relapsed within 2 to 4 months. CyA therapy did not achieve a remission in 10 patients with SRNS regardless of the presence of focal segmental glomerulosclerosis (FSGS) or MCNS on renal biopsy. In conclusion, CyA has limited effectiveness in patients with SDNS who manifest corticosteroid toxicity; however, CyA should be used cautiously because of the potential for CyA nephrotoxicity and the failure to obtain a sustained remission following discontinuation of CyA monotherapy. CyA dependence is substituted for corticosteroid dependence.

Biopsy↗
PubMed1991

Vitamin B-6 deficiency and renal function and structure in chronically uremic rats.

In preliminary studies, rats with chronic renal failure (CRF) demonstrated worsening renal function, as measured by urea clearance, when fed vitamin B-6-deficient diets. However, urea clearance is not a precise measure of glomerular filtration rate (GFR) and these studies did not indicate the mechanism for the reduced GFR. To measure renal function more precisely and to assess whether B-6 deficiency augments renal injury, we examined [14C]inulin clearance, urine oxalate excretion, and renal histopathology in rats with CRF pair fed to receive a pyridoxine-replete or -deficient diet for 3 or 6 wk. After 3 or 6 wk, pyridoxine-deficient rats had significantly lower [14C]inulin clearances and increased urine oxalate excretion. Histological evaluation indicated increased renal damage in kidneys from pyridoxine-deficient rats as compared with tissue from pyridoxine-replete rats. These findings suggest that in rats with CRF, vitamin B-6 deficiency reduces the GFR and increases renal scarring.

Animals↗
PubMed1991

Dimethyl sulfoxide enhances hexose monophosphate shunt activity in cultured glomerular mesangial cells, leukocytes and erythrocytes.

The effect of dimethyl sulfoxide (DMSO) on the rate of glucose oxidation by cultured rat glomerular mesangial cells, human erythrocytes and peritoneal exudate cells was studied. Mesangial cells, erythrocytes and peritoneal exudate cells incubated with DMSO showed enhancement of 14CO2 production from D-[1-14C] glucose but not from D-[6-14C] glucose. The concentration of DMSO required to stimulate respiratory burst activity was lowest for erythrocytes and highest for peritoneal exudate cells. Studies utilizing tritiated deoxyglucose revealed that the increased glucose oxidation associated with DMSO exposure was not due to increased transmembrane glucose movement at low concentrations of DMSO, and only partially responsible at high concentrations of DMSO. This study documents the ability of DMSO to specifically enhance the activity of the hexose monophosphate shunt pathway in all cells studied. The precise mechanism whereby DMSO stimulates shunt activity remains unknown.

Animals↗
PubMed1991

Frozen-section analysis of allograft renal biopsy specimens. Reliable histopathologic data for rapid decision making.

Rapid tissue diagnosis during acute events associated with renal transplantation is often necessary to permit immediate decisions regarding initiation or modification of therapy. To achieve this, we performed frozen section analyses with cryoprotected alcoholic Bouin's-fixed tissue, which permits evaluation within 2.5 hours. During a 30-month period, 200 allograft biopsies were performed; 68 frozen sections were obtained when deemed necessary by the clinical team. We compared frozen-section diagnoses with those following regular evaluation of the biopsy specimen. Agreement in diagnoses occurred in 61 (88.4%) of 69 specimens. Acute rejection was the dominant diagnosis (n = 39); others were acute tubular necrosis, cyclosporine toxicity, chronic rejection, and infection. Major misdiagnoses included acute vascular processes (three capillary and/or venous thromboses and one vascular inflammation); acute cellular rejection was missed in two cases, reflecting a sampling error. Secondary diagnoses not of immediate therapeutic importance were detected in seven frozen sections and missed in nine. These included chronic glomerulopathies, nephrosclerosis, and mild chronic rejection. Although acute vascular phenomena may be difficult to recognize in frozen sections, we conclude that allograft biopsy frozen-section analysis is a valuable part of the care of transplant recipients.

Biopsy↗
PubMed1990

Human immunodeficiency virus (HIV) infection and the kidney.

Since the first report on the acquired immunodeficiency syndrome (AIDS) in 1981, organ involvement of AIDS has increased. We discuss the effect of human immunodeficiency virus (HIV) infection, the causative agent of AIDS, on the field of nephrology. Hyponatremia, the commonest fluid and electrolyte abnormality, is caused by various pathophysiologic mechanisms, including adrenal insufficiency. The renal parenchymal complications are diverse, but a new entity, HIV-associated nephropathy, is becoming recognized because of its characteristic clinical and pathologic features, including the fact that it causes irreversible renal failure. HIV infection in patients with end-stage renal failure, both before and after initiation of maintenance dialysis, is a significant problem. The present methods of preventing spread of virus in dialysis units seem successful. Few patients who are infected with HIV or who have AIDS have had renal transplantation, although unsuspected viral infection of cadaveric organs remains a concern.

AIDS Serodiagnosis↗
PubMed1990

The development of the lamprey pattern generator for locomotion.

The life cycle of the lamprey includes a larval stage that can last for several years. The motor behavior of the larval lamprey, the ammocoete, has been only minimally studied and little is known of the neural correlates of that behavior. Comparison of known larval behavior to that of adults leaves unclear whether there are large or small changes in the spinal nervous system during transformation. The motor output of isolated larval and transforming spinal cords when stimulated to "swim" with D-glutamate has some differences from that of comparable adult preparations, but shares many important features with adults. Primarily, the fictive swimming is less well regulated and less stable than adults of the same species. We propose that a major difference in the structure and organization of the central pattern generator for locomotion between adults and ammocoetes is a relative lack or immaturity of some cell types that participate in the coordination of the segments and the generation of the rhythm of the periodic bursting.

Animals↗