Gradient of extrajunctional acetylcholine receptors early after denervation of mammalian muscle

After denervation, the number of acetylcholine receptors (AChR) found within the endplate band of skeletal muscle increases transiently by about twofold. In this study, we used EM autoradiography to show that this increased endplate band label is not due to an elevated site density of receptors at the junctional folds. Rather, AChR site density within 500 microns of the endplate was found to be 4 X higher than in non-endplate areas defined as greater than 2 mm from the endplate. This nonuniform distribution of extrajunctional AChR early after denervation could represent a transient gradient, similar to that reported shortly after innervation during development.     

Videodensitometric ejection fractions from intravenous digital subtraction left ventriculograms: correlation with conventional direct contrast and radionuclide ventriculography

Forty-three patients who had undergone direct-contrast ventriculography were submitted to intravenous digital subtraction ventriculography and first-pass radionuclide ventriculography to compare the left ventricular ejection fractions obtained by each method. Ejection fractions were calculated by the area-length method from the direct contrast ventriculograms, by both area-length and videodensitometric methods from the digital subtraction ventriculograms, and by count densitometry from the radionuclide ventriculograms. Satisfactory correlations were found between values obtained by the late mask resubtracted videodensitometric method and the radionuclide method (r = 0.85) and by the digital ventriculographic area length method and direct-contrast method (r = 0.88). Videodensitometric methods may be an alternative way to estimate left ventricular ejection fractions accurately without reliance on geometric assumptions about the shape of the left ventricular cavity.     

The association between preterm newborn hypotension and hypoxemia and outcome during the first year

Ninety-eight newborn infants, less than 34 weeks at birth, were studied to examine the relationship between newborn hypotension and hypoxemia and brain damage. Heart rate, blood pressure and oxygen tension were recorded continuously during the 96 h following delivery. Outcome measures included neuropathology in children who died, and motor and cognitive development at one year corrected age in children who survived. There were 22 children with a minor and 27 with a major abnormal outcome. There was a relationship between newborn hypotension, newborn hypoxemia and low birth weight, and a major abnormal outcome. The probability of a major abnormal outcome increased from 8% in newborns with no hypotension or hypoxemia, to 53% in children with both hypotension and hypoxemia. These findings support the contention that combinations of sustained newborn hypotension and hypoxemia are important factors in the development of brain damage, accounting for a major abnormal outcome.     

Denervation increases turnover rate of junctional acetylcholine receptors.

The turnover rates of junctional acetylcholine receptors were measured in innervated and denervated mouse sternomastoid neuromuscular junctions by 125I-labeled alpha-bungarotoxin binding. First, we determined that the density of labeled toxin initially bound to the neuromuscular junction was essentially unchanged up to 16 days after denervation. Innervated muscles and muscles that had been denervated 8 days previously were then saturated with labeled toxin, and the specific label at the endplate regions was compared by gamma counting 7 days later. At that time, the residual junctional label seen in innervated muscle was 3.2 times greater than in denervated muscle. Electron microscope autoradiography further showed that, after saturation with unlabeled toxin, new binding sites appeared rapidly at the specialized receptive region of the postsynaptic membrane with an apparent half-time of turnover of 2-3 days. At innervated junctions, the half-time of turnover was about 10 days. These data show that the mechanisms that control receptor turnover rates are different from those that control high-density receptor clustering. The slow turnover rate of junctional receptors appears to be more directly dependent on the presence of the nerve than is the clustering of junctional receptors.     

Nerve extract induces increase and redistribution of acetylcholine receptors on cloned muscle cells

The effect of rat spinal cord explants and cell-free nerve extract on acetylcholine receptor site density and distribution was studied using (125)I- and rhodamine-labeled alpha-bungarotoxin on L(6), a cloned rat muscle cell line. Control L(6) myotubes have a low and uniform distribution of acetylcholine receptors (20 +/- 3 sites per mum(2) in the present study). The addition of spinal cord explants caused an increase in average receptor site density of about 6 times on myotubes within 2 mm of the explant, while a smaller increase of 3 times was observed at distances greater than 5 mm. The formation of high-density patches of receptors was also stimulated. These observations suggested that a diffusible substance originating from the explant was responsible for these changes. Cell-free homogenates of the central nervous system were prepared and found to produce the same effects. The effect of the homogenate was not strongly dependent on the age of the fetus from which the tissue was isolated, and fetal liver had little or no effect. The active component(s) appears to be a protein(s) with a molecular weight of about 100,000. Because the nerve homogenates make the L(6) cells resemble primary muscle cultures, we suggest that a common factor is responsible for regulating the acetylcholine receptor in the two types of muscle culture. The normally acetylcholine receptor-poor L(6) cells may provide a more sensitive assay for these factors than do primary muscle cultures.     

Antidiarrhoeal Activity of an Ethanol Extract of the Stem Bark of Piliostigma Reticulatum (Caesalpiniaceae) in Rats

Piliostigma reticulatum (Caesalpiniaceae) is used in Africa as a traditional medicine for the treatment of many diseases, such as malaria, tuberculosis and diarrhoea. We investigated the antidiarrhoeal properties of a crude ethanol extract from the stem bark of Piliostigma reticulatum (EEPR) in Wistar albino rats to substantiate its traditional use and to determine its phytochemical constituents. The antidiarrhoeal activity of the plant extract was evaluated in a castor oil-induced diarrhoea model in rats and compared with loperamide. The effect of the extract on gastrointestinal motility was also determined by the oral administration of charcoal meal and castor oil-induced intestinal fluid accumulation (enteropooling). EEPR showed remarkable dose-dependent antidiarrhoeal activity evidenced by a reduction of defecation frequency and change in consistency. Extracts at 250, 500 and 1000 mg/kg body weight significantly reduced diarrhoeal faeces. EEPR also significantly inhibited gastrointestinal motility and castor oil-induced enteropooling at 500 and 1000 mg/kg, similar to the inhibition obtained in control rats treated by atropine. Phytochemical screening revealed the presence of tannins, flavonoids, polyphenols and reducing sugars in the stem bark of P. reticulatum. No mortality or visible signs of general weakness were observed in the rats following administration of the crude extract in doses up to 6000 mg/kg body weight in an acute toxicity study. Our results show that the stem bark of P. reticulatum possesses antidiarrhoeal activity and strongly suggest that its use in traditional medicine practice could be justified.