Citations

To determine the effect of diabetes on the development of axonal degeneration after acute nerve compression, the mobilized peroneal nerves of rats with streptozotocin-induced diabetes and of control rats were compressed at 150 mmHg (1 mmHg = 133 Pa) for 30 min by using specially devised cuffs. At three intervals after compression--3 days, rats diabetic for 31 wk; 14 days, diabetic for 6 wk; and 24 days, diabetic for 31 wk--groups of nerves were studied to assess numbers and sizes of fibers above, at, and below the cuff and to assess frequency of fiber degeneration in teased fibers from nerve distal to the cuff. Teased fibers with pathologic abnormalities were more frequent in nerves from controls than in nerves from diabetic rats in all three groups but the difference was statistically significant only at 3 and 14 days after compression. The lack of significant difference at 24 days may be explained by higher rates of disappearance of degenerating products and of fiber regeneration at 24 than at 3 and 14 days. This study provides evidence that in addition to delaying the reported functional deficit of vibratory detection threshold and conduction block during nerve compression, diabetes also may partially prevent axonal injury. Low nerve myo-inositol concentration did not predispose diabetic nerve to acute compression injury. If these results also apply to human diabetes and if repeated acute compression is involved in the genesis of fiber degeneration in entrapment, then a higher frequency of entrapment neuropathy among diabetics might be due to mechanisms other than increased susceptibility of fibers to acute compression--e.g., possibly to greater constriction of nerve due to pathologic alterations of the carpal ligament.

The potential of nonterminal cellular differentiation to stably repress the expression of the neoplastic phenotype of transformed cells is established. Nonterminal differentiation induces spontaneously transformed 3T3 T cells to revert to a nontransformed state and induces the revertant cell clones to become resistant to retransformation by UV irradiation or 4-nitroquinoline oxide treatment. Nonterminal differentiation also induces simian virus 40-transformed 3T3 T cells to repress expression of the large tumor antigen and to revert to a nontransformed state. Although the molecular mechanisms that mediate these and other forms of anticancer activity have not been definitively established, data are presented which suggest that differentiation-induced repression of large tumor antigen expression can be regulated at the level of transcription and/or RNA processing.

The sex steroids, androgens and estrogens, are major regulators of bone metabolism. However, whether these hormones act on bone cells through direct or indirect mechanisms has remained unclear. A nuclear binding assay recently used to demonstrate estrogen receptors in bone [Eriksen, E.F., Colvard, D.S., Berg, N.J., Graham, M.L., Mann, K.G., Spelsberg, T.C. & Riggs, B.L. (1988) Science 241, 84-86] was used to identify specific nuclear binding of a tritiated synthetic androgen, [3H]R1881 (methyltrienolone), in 21 of 25 (84%) human osteoblast-like cell strains and a concentration of bound steroid receptors of 821 +/- 140 (mean +/- SEM) molecules per cell nucleus. Binding was saturable and steroid-specific. Androgen receptor gene expression in osteoblasts was confirmed by RNA blot analysis. Relative concentrations of androgen and estrogen receptors were compared by measuring specific nuclear estrogen binding. Nuclear binding of [3H]estradiol was observed in 27 of 30 (90%) cell strains; the concentration of bound estradiol receptor was 1537 +/- 221 molecules per cell nucleus. The concentrations of nuclear binding sites were similar in males and females for both [3H]R1881 and [3H]estradiol. We conclude that both androgens and estrogens act directly on human bone cells through their respective receptor-mediated mechanisms.

The mRNA levels of genes known to be regulated by sex steroids are not altered until 1 hr or longer after steroid treatment, although the steroid receptor complexes are bound to nuclear acceptor sites within 5 min. In a search for early regulation of gene transcription, total chick oviduct RNA was isolated at various times after injection (i.p.) of progesterone and analyzed for c-myc expression. Levels of c-myc mRNA began to decrease in response to progesterone by 10 min after injection. The mRNA levels continued to decrease, reached a 70% reduction at 30 min, and returned to control values by 8 hr after steroid injection. Changes in alpha-tubulin mRNA levels were markedly less in these same RNA preparations. The effect was dependent on the dose of the steroid and was target-tissue specific. These changes occurred much more rapidly than changes in egg-white protein mRNA levels. Vehicle alone did not alter c-myc mRNA levels. Early regulated genes such as c-myc may represent the initial site of action of steroid receptors in the genome.

A cDNA library, prepared from poly(A)+ RNA isolated from quiescent AKR-2B cells 4 hr after stimulation with epidermal growth factor in the presence of cycloheximide, was screened to identify RNA transcripts whose abundance is specifically increased as a primary response to growth stimulation. Approximately 40% of the inducible clones detected by this procedure corresponded to either cytoskeletal beta- or gamma-actin genes. One nonactin clone, designated c99, was found to be derived from an 8.5-kilobase RNA whose abundance began to increase as early as 30 min after stimulation. DNA sequencing established the identity of this RNA as fibronectin. Several additional mitogens were then tested and found to efficiently induce fibronectin mRNA. These included fetal calf serum, platelet-derived growth factor, and transforming growth factor type beta. For at least one inducer, fetal calf serum, the increase in mRNA was preceded by an increase in fibronectin gene transcription. This increase was rapid, reaching maximal levels within 10 min, and was accompanied by near-coordinate increases in both c-fos and beta-actin transcription. These results indicate that fibronectin is a member of a class of "early-response" genes, typified by c-fos and including beta-actin, whose rapid expression may be important in mediating cellular responses to peptide growth factors.

The albumin (Alb), IgG, and IgM concentrations in the endoneurium of fascicular sural nerve biopsy samples were evaluated in controls (n = 9 or 10), diabetic patients without neuropathy (n = 6), and diabetic patients with polyneuropathy (n = 17 or 18). These values were significantly increased in diabetic patients with and without neuropathy when expressed both per endoneurial dry weight or endoneurial total protein compared to biopsy samples from healthy controls. When these concentrations, expressed per endoneurial total protein, were related to plasma concentrations similarly expressed, the resulting blood-nerve barrier (BNB) indices were significantly increased for Alb (6.1 times; P less than 0.00001), IgG (4.9 times; P = 0.00037), and IgM (2.7 times; P = 0.015). The diabetic patients without neuropathy (defined as having an index of pathology of greater than 0.65; a measure of the severity of the pathological abnormality based on morphological criteria) also had significant increases in two of these BNB indices that were intermediate between the diabetic neuropathy patients and controls (Alb, 3.9 times controls; P = 0.00002: IgG, 4.6 times controls; P = 0.00016: IgM, 1.8 times controls; not significant). No correlations were observed between the endoneurial concentrations of these plasma proteins or the BNB indices and the index of pathology, suggesting that these increases in endoneurial plasma proteins precede the pathologic alterations. The increased values for the diabetics in the absence of pathological abnormalities may prove useful in predicting neuropathic complications. The ratio of the IgG-BNB index to the Alb-BNB index was decreased 19%, and the ratio of the IgM-BNB index to the Alb-BNB index was decreased 56% in diabetic neuropathy patients compared to controls. Although the IgG and IgM concentrations are increased in the diabetic endoneurium, the Alb increase is greater and a mechanism other than size indiscriminate extravasation of plasma proteins, therefore, is suggested. Morphometric assessment of the endoneurial compartments, which would be expected to contain these plasma proteins, suggests that they are not altered in diabetic neuropathy; hence, it is hypothesized that the observed increase in endoneurial concentration of these plasma proteins results from altered transport through the endothelial or perineurial barrier, which supports an underlying vascular mechanism in the development of diabetic polyneuropathy.

Antibodies specific for the neuronal ganglionic nicotinic acetylcholine receptor (nAChR) are found in high titer in serum of patients with subacute autonomic failure. This clinical disorder is known as autoimmune autonomic neuropathy (AAN). Rabbits immunized with a neuronal nAChR α3 subunit fusion protein produce ganglionic nAChR antibodies and develop autonomic failure (experimental AAN, or EAAN). We used quantitative measures of autonomic function to demonstrate that this animal model of neuronal nAChR autoimmunity recapitulates the cardinal autonomic features of AAN in humans. The severity of dysautonomia in the rabbit ranges from isolated cardiovagal impairment to severe panautonomic failure with fixed mydriasis, gastroparesis, dry eyes, impaired heart rate variability, hypotension, and low plasma catecholamines. The severity of autonomic failure correlates with serum antibody levels. Immunohistochemical staining of superior cervical ganglia and myenteric plexus neurons demonstrates intact presynaptic nerve terminals and intact postsynaptic neurons containing cytoplasmic nAChR, but lacking surface nAChR. These findings define the autonomic physiology and histopathology of this novel animal model and support the concept that AAN in humans is a disorder of ganglionic cholinergic synaptic transmission caused by ganglionic nAChR antibodies.

Background The triceps tendon has been described as a single unit with contribution from each of the 3 heads of the muscle. An observation at the time of surgical repair of a triceps tendon injury led to an anatomical study to further define the anatomy of this tendon as it inserts on the olecranon. Hypothesis The medial head of the triceps has a tendon that is distinct from, and deep to, the common tendon of the long and lateral heads. Study Design Descriptive laboratory study and case report. Methods Eight cadaveric elbows were dissected to examine the triceps tendon. None of the specimens had any evidence of prior injury or surgery to the elbow. All specimens were fresh-frozen and stored at–4°C until they were thawed for use. Skin and subcutaneous tissue were removed, and the tendon of each head of the triceps was explored from the muscle to its bony insertion. Results In all 8 specimens, on gross inspection, the medial head had a separate insertion deep to the common insertion of the lateral and long heads. The muscle of the medial head extended further distally than did the long and lateral heads. The medial head was muscular to its deep insertion, with a small amount of tendon blended with the muscle distally. Histologic analysis demonstrated that the tendon of the medial head and that of the other 2 heads are confluent distally at their olecranon insertion. Conclusion The medial head of the triceps has a tendon that is distinct from, and deep to, the common tendon of the long and lateral heads on gross inspection. Histologic studies show the insertion of these 2 tendons is confluent. Clinical Relevance This anatomy has important implications for surgical repair of these tendon injuries. Rupture of the deep triceps insertion alone can occur and lead to weakness of elbow extension with the elbow flexed beyond 90°. Triceps strength should be tested with the elbow fully flexed when injury to the tendinous insertion is suspected.

In a congenital myasthenic syndrome with a severe endplate myopathy, patch-clamp studies revealed markedly prolonged acetylcholine receptor (AChR) channel openings. Molecular genetic analysis of AChR subunit genes demonstrated a heterozygous adenosine-to-cytosine transversion at nucleotide 790 in exon 8 of the epsilon-subunit gene, predicting substitution of proline for threonine at codon 264 and no other mutations in the entire coding sequences of genes encoding the alpha, beta, delta, and epsilon subunits. Genetically engineered mutant AChR expressed in a human embryonic kidney fibroblast cell line also exhibited markedly prolonged openings in the presence of agonist and even opened in its absence. The Thr-264-->Pro mutation in the epsilon subunit involves a highly conserved residue in the M2 domain lining the channel pore and is likely to disrupt the putative M2 alpha-helix. Our findings indicate that a single mutation at a critical site can greatly alter AChR channel kinetics, leading to a congenital myasthenic syndrome. This observation raises the possibility that mutations involving subunits of other ligand-gated channels may also exist and be the basis of various other neurologic or psychiatric disorders.

Adenosine 3′:5′-cyclic monophosphate (cAMP) and guanosine 3′:5′-cyclic monophosphate (cGMP) were localized in cells of rat kidney cortex by an immunocytochemical technique before and after perfusion with parathyroid hormone (PTH). In control tissues the cAMP antiserum detected approximately the same intensity of fluorescence in cytoplasmic epithelial cell elements of cortical tubules and glomeruli (cells of Bowman's capsule and podocytes). PTH increased fluorescence in these glomerular cells and increased cAMP fluorescence in cytoplasmic granules in proximal tubular cells. These granules, whose structure has not been identified, were located predominantly on the luminal side of the tubular cells. In control rats, the renal cortical fluorescence detected with the cGMP antiserum was more pronounced in glomeruli (predominantly in the mesangial areas) and lesser amounts of fluorescence were observed in tubules. After PTH treatment, cGMP fluorescence increased in glomeruli and in renal tubular cells. A bright linear pattern of fluorescence was found in the area of the tubular luminal membrane. Perfusion with PTH caused relatively small increases in total tissue cAMP and no consistent increases in total tissue cGMP. Our observations suggest that both cAMP and cGMP are involved in the glomerular and tubular responses to PTH and point out the added dimension that this immunocytochemical technique brings to studies of cyclic nucleotide dynamics in heterogeneous tissues.