Origin of impulse initiation in the slowly adapting stretch receptor of the crayfish

Summary Characteristic for the crayfish stretch receptor is a gradual decrease in axon diameter up to a stretch of axon about 350 m away from the soma-axon border. In response to depolarizing currents applied at different positions along the axon this stretch of axon can be localized as the most excitable membrane region. When depolarizing current steps of 10–25 nA intensity are injected into the soma the first impulse is always triggered in the soma (due to sudden rise in the membrane potential) while the second impulse originates at the axon region of highest escitability. As the intensity of the stimulus is increased the site of impulse initiation along the axon shifts nearer to the receptor soma. At a stimulus intensity of 50 nA the second impulse is suppressed and only the membrane potential at the axon hillock increases slightly. An analysis of the conductances for sodium and potassium ions as well as of the leakage current suggests that the molecular basis for the observed variations in excitability resides in a gradual decrease of the sodium conductance between the cell soma and the small-diameter region of the axon. However, the resting potential in this most excitable axon region is only some 3 mV more positive as compared to the receptor soma. A mathematical formulation is presented for the encoder mechanism in a soma-axon region with varying diameter. Using a slightly modified form of the Hodgkin-Huxley equations the experimentally observed changes in membrane potential and in the time course of the ionic currents can be adequately described by applying a nonlinear cable equation to the inhomogeneous axon.     

Functional AMPA/kainate receptors in human embryonic and foetal central nervous system

Here, functional AMPA/kainate receptors in human embryonic (5.5–7.5 gestational weeks) and foetal (8–10 gestational weeks) central nervous system tissue, shown by the cobalt labeling method, are reported. Specific agonist-induced cobalt incorporation was detected in brainstem and spinal cord cells, even in the youngest embryo studied. T-AMPA or kainate, but also vegetal toxins such as L-BOAA or acromelate, induced accumulation of cobalt. In contrast, no labeling was observed after exposure to KCl or NMDA. Cobalt labeled cells were particularly prominent in motor regions of brainstem and spinal cord. Co-application of the diuretic agent cyclothiazide, a desensitization blocker at AMPA receptors, dramatically increased the number of stained cells, which was particularly obvious in sensory regions, suggesting different receptor properties in motor versus sensory regions. This is the first study providing evidence for functional AMPA/kainate receptors, permeable to divalent cations, in brainstem and spinal cord at an early stage of human central nervous system development. Since many developmental processes are influenced by the modulation of cytosolic calcium, exposure at critical stages of embryogenesis to food or drug substances modifying the activity of AMPA/kainate receptors may alter brain development.     

Captopril in Cushing's syndrome

Summary To analyse the role of the renin angiotensin system in the pathogenesis of hypertension in Cushing's syndrome ten patients with hypercorticism (five with pituitary hypothalamic dysfunction, three with adrenal adenomas and two with adrenal carcinomas) received a single oral dose of 25 mg captopril. Mean arterial pressure was then determined at short intervals over periods of up to 240 min. Plasma renin activity (PRA) was measured immediately before the administration of captopril. Eleven patients with severe essential hypertension, who showed a comparable distribution of basal PRA values, served as a control. Patients with elevated basal PRA values (>3 ng/ml·3 h) showed, both in the subgroup of cases with essential hypertension and in that with Cushing's syndrome, a statistically significant fall (P<0.05–P<0.001) in mean arterial pressure, the decrease being slightly more pronounced in essential hypertensives. On the other hand patients with normal PRA values (3 ng/ml·3 h) exhibited only a minor fall in mean arterial pressure reaching statistical significance (P<0.05) only after 60 min (essential hypertension) and 180 min (Cushing's syndrome), respectively. Our results document that in patients with Cushing's syndrome the effect of captopril seems to be determined by the activity of the renin angiotensin system. Thus, in a substantial number of patients with hypercorticism, the renin angiotensin system may be an important factor in the pathogenesis of hypertension, whereas in patients with low PRA values other factors like oversecretion of mineralocorticoids may be responsible for the observed blood pressure increases.     

音猬因子的功能受体斑片在培养神经干细胞中的表达

目的　观察在培养的神经干细胞内是否有发育调控分子———音猬因子 (sonichedgehog)功能受体———斑片 (patched)表达。　方法　神经干细胞克隆在体外培养传代后 ,用patched的特异性引物对培养的神经干细胞进行RT PCR分析 ,PCR产物经克隆测序后 ,用地高辛标记克隆的探针 ,对神经干细胞进行原位杂交分析。　结果　神经干细胞克隆内大量的细胞均可表达sonichedgehog的功能受体patched ,patched阳性细胞间未见明显差别 ,克隆边缘与中央的patched分布也未见明显差别。　结论　sonichedgehog信号传导路可能在神经干细胞的增殖与分化过程中起重要作用。     

Modulation of large conductance calcium-activated K+ channel by membrane-delimited protein kinase and phosphatase activities

Large conductance Ca²⁺-activated K⁺ channel was identified and studied in excised inside-out membrane patches of freshly dispersed smooth muscle cells from rabbit gastric antrum. The current-voltage relationship of the single channel was linear from -80 to +80 mV of pipette voltage in which single channel conductance was 249±17.8 pS (n=19) in symmetrical concentration of K⁺ (145mM) across the patch. Activity of the channel (NPo) depended not only on cytoplasmic calcium concentration but also on membrane potential. MgATP increased NPo in a dose-dependent manner and Mg²⁺ was prerequisite for the effect. Okadaic acid (l00nM), inhibitor of protein phosphatases, increased NPo further in the presence of MgATP. Therefore, it would be concluded that activity of the calcium-activated K⁺ channel in gastric smooth muscle cells was controlled by phosphorylation state of the channel protein and the state is further modulated by membrane-delimited protein kinase and protein phosphatase activities.     

周围神经干自然分束部位血管形态及临床意义

应用微血管灌注透明法观察研究5具成人周围神经干标本.重点观察神经自然分束部位微血管形态和分支分布规律.神经干内有非常完兽的血供系统.手术中循神经自然分束进行追踪分离,不会对神经血供产生明显影响.但在张力下牵拉缝合神经,将对神经干血供产生严重影响.神经束膜缝合比神经外膜缝合更强调在无张力下进行.