A study of the increased sensitivity of denervated and re-innervated muscle to depolarizing drugs

1. The response of re-innervated muscles to depolarizing blocking drugs was studied.

2. During the early stages of re-innervation the `new' neuromuscular junctions are more sensitive to decamethonium and suxamethonium. The recovery from the block and the repolarization of the end-plate are markedly slowed.

3. This increased sensitivity does not appear to be characteristic of all newly formed neuromuscular junctions. It was found that in new-born kittens the muscles are very insensitive to neuromuscular blocking drugs.

4. It is concluded that the increased sensitivity of re-innervated muscles to depolarizing blocking drugs and the slow repolarization are due to a persistence of changes which developed during denervation.

     

Oriented astroglial cell growth on micropatterned polystyrene substrates

In an effort to develop a permissive environment for neural stem cell differentiation, directional growth of astrocytes has been achieved on polymer substrates in vitro. Manipulating a combination of physical and chemical cues, astrocyte adhesion and alignment in vitro were examined. To provide physical guidance, micropatterned polymer substrates of polystyrene (PS) were fabricated. Laminin was selectively adsorbed onto the grooves of the patterned surface. Rat type-1 astrocytes were seeded onto the micropatterned PS substrates, and the effects of substrate topography and the adsorption of laminin to the PS substrates on the behavior and morphology of the astrocytes were explored. The astrocytes were found to align parallel to the micropatterned grooves at initial seeding densities of approximately 7500, 13,000, and 20,000 cells/cm(2) due to the effects of the physical and chemical guidance mechanisms. Adsorbing laminin in the microgrooves of the micropatterned PS substrates improved cell adhesion and spreading of cytoskeletal filaments significantly. At these initial seeding densities, over 85% astrocyte alignment in the direction of the grooves was achieved on the micropatterned PS substrates with laminin adsorbed in the grooves. This combination of guidance cues has the potential to provide a permissive substrate for in vivo regeneration within the central nervous system.     

Psychosocial factors in medical and psychological treatment avoidance: the role of the doctor-patient relationship

A community sample of 1106 adults was examined to assess the impact of the doctor-patient relationship on participants' avoidance of treatment for a recognized medical or psychological problem. Of five aspects of participants' previous experience with their physicians, all but waiting time predicted participants' self-reported treatment avoidance. In two logistic regression models participants who felt their physicians listened more to their concerns were less likely to avoid treatment for both medical and psychological problems during the previous 12 months. These findings suggest that patients' perceptions of how they are treated by physicians may help explain why many people delay or avoid healthcare treatment, even when faced with a significant health problem.     

Loss of heterozygosity mutations of tumor suppressor genes in cytologically atypical areas in chronic lymphocytic thyroiditis

The relationship between chronic lymphocytic thyroiditis (CLT) and papillary thyroid carcinoma (PTC) is a subject of controversy. Some investigators suggest a causal relationship, whereas others regard the two as only a coincidental occurrence. An additional complicating factor is the presence of atypical nuclei frequently found within lymphoid infiltrates in CLT, which resemble those in PTC. The finding of the RET-PTC translocations in CLT has been reported by two independent groups of investigators, suggesting that the areas of nuclear atypia in CLT are neoplastic rather than reactive. In the present study, we report additional molecular findings that support the hypothesis that the atypical nuclear changes in CLT may be preneoplastic or neoplastic. We microdissected small areas with atypical nuclei in glands with CLT and observed loss-of-heterozygosity mutations of tumor suppressor genes. These genetic mutations are evidence of clonal preneoplastic or neoplastic changes in the follicular cells of CLT. The clinical malignant potential of these minute foci is likely to be very small but remains to be determined.     

Molecular alterations in atypical adenomatous hyperplasia occurring in benign and cancer-bearing lungs.

Atypical adenomatous hyperplasia (AAH) is considered to be a precursor lesion of the lung adenocarcinoma. Several genetic abnormalities have been reported in AAH associated with adenocarcinoma, but little is known about AAH associated with benign lung lesions. To address this we compared the molecular characteristics of AAH present in benign conditions to those coexisting with carcinoma. Seven cases of AAH from resected non-neoplastic lungs (AAH-B) and 12 cases from lungs resected for primary lung carcinoma (AAH-M) were analyzed for loss of heterozygosity (LOH) using 21 polymorphic microsatellite markers situated in proximity to known tumor suppressor genes on chromosomes 3p, 5q, 7p, 9p, 10q, and 17p. Direct DNA sequencing for K-ras mutation was also performed. There was a broad range of LOH in both groups. No LOH was identified in 3 cases (25%) of AAH-M, but all cases of AAH-B showed LOH (P=0.26). Six cases (50%) of AAH-M and 3 cases (43%) of AAH-B showed loss at 1 marker (P=0.99). LOH at 2 or more markers was identified in 3 (25%) cases of AAH-M and 4 (57%) cases of AAH-B (P=0.32). LOH was most frequently detected on chromosomes 3p and 10q in both groups. The difference in overall fractional allelic loss between the 2 groups did not reach statistical significance. K-ras mutations were not identified in either group. Our results showed a significant overlap in LOH patterns between AAH with or without coexistent lung malignancy. Therefore, AAH may represent a smoking induced low-grade neoplastic lesion that may be a precursor lesion of only a subset of invasive lung adenocarcinoma.     

Phorbol ester-induced inhibition of potassium currents in rat sensory neurons requires voltage-dependent entry of calcium

The whole cell patch-clamp technique was used to examine the effects of protein kinase C (PKC) activation (via the phorbol ester, phorbol 12,13 dibutyrate, PDBu) on the modulation of potassium currents (I(K)) in cultured capsaicin-sensitive neurons isolated from dorsal root ganglia from embryonic rat pups and grown in culture. PDBu, in a concentration- and time-dependent manner, reduced I(K) measured at +60 mV by approximately 30% if the holding potential (V(h)) was -20 or -47 mV but had no effect if V(h) was -80 mV. The PDBu-induced inhibition of I(K) was blocked by pretreatment with the PKC inhibitor bisindolylmaleimide I and I(K) was unaffected by 4-alpha phorbol, indicating that the suppression of I(K) was mediated by PKC. The inhibition of I(K) by 100 nM PDBu at a V(h) of -50 mV was reversed over several minutes if V(h) was changed to -80 mV. In addition, intracellular perfusion with 5 mM bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid (BAPTA) or pretreatment with omega-conotoxin GVIA or Cd(2+)-Ringer, but not nifedipine, prevented the PDBu-induced suppression of I(K) at -50 mV, suggesting that a voltage-dependent influx of calcium through N-type calcium channels was necessary for the activation of PKC. The potassium channel blockers tetraethylammonium (TEA, 10 mM) and 4-aminopyridine (4-AP, 3 mM and 30 microM) reduced I(K), but only TEA attenuated the ability of PDBu to further inhibit the current, suggesting that the I(K) modified by PDBu was sensitive to TEA. Interestingly, in the presence of 3 mM or 30 microM 4-AP, 100 nM PDBu inhibited I(K) when V(h) was -80 mV. Thus 4-AP promotes the capacity of PDBu to reduce I(K) at -80 mV. We find that activation of PKC inhibits I(K) in rat sensory neurons and that voltage-dependent calcium entry is necessary for the development and maintenance of this inhibition.