Plasticity of lumbosacral monosynaptic reflexes after a ventral root transection injury in the adult cat

Injuries to spinal ventral roots may induce plastic changes in adjacent segmental reflex pathways. Earlier studies in the cat have demonstrated that a partial loss of target motoneurons, following a ventral root avulsion injury, induces a compensatory enhancement of monosynaptic reflexes in adjacent segments. Here, we studied electrophysiologically the effects of a primarily non-lethal motoneuron injury of lumbosacral ventral roots on monosynaptic reflexes in adjacent intact motoneurons in the adult cat. A unilateral L7 or a combined L7 and S1 ventral root transection was first performed. We next recorded bilaterally monosynaptic reflexes from the L6 and S1 ventral roots while stimulating the bilateral L6, L7 and S1 dorsal roots at 6 and 12 weeks postoperatively. We demonstrated a prominent strengthening of monosynaptic reflexes in the immediately adjacent spinal cord segments. The reflexes had almost doubled in size at 6 and 12 weeks postoperatively. Possible mechanisms and factors contributing to the reflex enhancement are discussed.     

Effects of noxious skin heating on spontaneous cell activity in the magnocellular red nucleus of the cat

Neurones were extracellularly recorded in the magnocellular red nucleus (RNm) of decerebrated cats and identified by their monosynaptic responses to stimulation of the contralateral brachium conjunctivum (BC), and by their antidromic responses after stimulation of the rubrospinal tract in the cord. After each cell was isolated, noxious stimulation was applied to the skin, by touch-free radiant heat. The large majority of the cells (91.5%) responded to noxious stimulation of the skin, even after the RNm was deprived of cerebellar input by sectioning the contralateral BC. About half of this cell group was activated by noxious stimulation and the other half was inhibited. To obtain responses in RNm cells, the stimulus had to be above the thermal pain threshold, and the stimulation area had to be inside the somatic receptive field of the cell for low-threshold afferents. Thus, the receptive fields for nociceptive and low-threshold afferents are similarly organized somatotopically. Noxious stimulation sometimes induced a rhythmic pattern of spike bursts in RNm cells, which could be a reflection of the locomotor-like activity generated in the spinal cord. The results indicate that nociceptive information participates in sensorimotor control via the spinorubrospinal loop, which may also transmit low-threshold cutaneous input and corollary discharge of the activity in spinal motor centres to the RNm.     

右心室快速起搏致心力衰竭犬的心室电生理特性

目的: 研究右心室快速起搏致充血性心力衰竭(CHF)犬心室电生理特性。方法： 16只犬随机分为正常对照组（n=7）和CHF组（n=9），应用右心室快速起搏（240 pulse·min^-1）4-5周制作CHF犬模型，应用心脏电刺激和单相动作电位（MAP）记录技术测定心室生理指标。结果： （1）CHF组心室有效不应期、心室MAP时程、复极后期及传导时间均延长，分别延长26%（P<0.01）、43%（P<0.01）、318%（P<0.05）和19%（P<0.01）；（2）CHF组心室有效不应期与MAP时程的比值减小13%（P<0.05）；（3）CHF组兴奋恢复时间离散性增加185%（P<0.01）；（4）CHF组室颤阈值降低48%（P<0.01）。结论： CHF异常的心室电生理特性可能是导致恶性心律失常及心脏性猝死发生的基础。     

生理学教学实验用微机数据采集系统的研制

基于ＰＣ机的通用生物医学信号数据采集及处理系统研制成功产应用于生理学及电生理学的教学实验。该系统具有多通道数据采集，曲线刷新显示、参数测算、信号处理、存储和及打印输出等功能。实现了多道生理信号的无笔描枋。作者介绍该系统的硬件组成和软件设计方法，并给出部分实验内容和结果。     

THE EARLY HISTORY OF ELECTRODERMAL RESEARCH

The historical origins and early development of electrodermal research are reviewed in the light of a substantial number of previously unexamined sources. Relevant literature in electrophysiology, neurology, electrodiagnosis, and electrotherapy is examined with regard to the technology and the context of ideas in science and medicine. The first reports of basal skin resistance (BSR) and stimulated skin resistance (GSR) change by Vigouroux and Féré, respectively, are related to their other research and that of other workers. Hermann's early work on the sudomotor system is seen as much more advanced than has been realized, providing a sound basis for theory which the French apparently never noticed. Several additional sources suggest that Tarchanoff's work was performed with awareness of Féré's and was probably not an independent discovery. The growth of the field following “rediscovery” of the GSR by Mueller and Veraguth is seen as a product of interest in indexing “mental events.” The earlier work is seen as conceptually closer to current interest in the phenomena as aspects of the arousal system.     

Recording of the human electro-olfactogram

Electro-olfactograms (EOG) are electrical potentials of the olfactory epithelium that occur in response to olfactory stimulation. The EOG represents the sum of generator potentials of olfactory receptor neurons. While this response has been used extensively in animal research, there are only a handful of papers describing the properties of the human EOG. In addition to a discussion of methodological issues related to the EOG, this review summarizes the characteristics and uses of these recordings. Among other results, EOGs have been used to provide evidence for the dominant role of the central nervous system in olfactory desensitization, for the functional characterization of the olfactory epithelium, the specific topographical distribution of olfactory receptors, or the expression of olfactory receptor neurons in response to exposure to odorants, and the characterization of certain odorants as olfactory receptor antagonists. In conclusion, in combination with nasal endoscopy and air-dilution olfactometry, the EOG is a unique part of a large array of techniques used to provide a complete picture of the processing of olfactory information in humans.     

Origins of Spiral Wave Meander and Breakup in a Two-Dimensional Cardiac Tissue Model

We studied the stability of spiral waves in homogeneous two-dimensional cardiac tissue using phase I of the Luo–Rudy ventricular action potential model. By changing the conductance and the relaxation time constants of the ion channels, various spiral wave phenotypes, including stable, quasiperiodically meandering, chaotically meandering, and breakup were observed. Stable and quasiperiodically meandering spiral waves occurred when the slope of action potential duration (APD) restitution was <1 over all diastolic intervals visited during reentry; chaotic meander and spiral wave breakup occurred when the slope of APD restitution exceeded 1. Curvature of the wave changes both conduction velocity and APD, and their restitution properties, thereby modulating local stability in a spiral wave, resulting in distinct spiral wave phenotypes. In the LR1 model, quasiperiodic meander is most sensitive to the Na⁺ current, whereas chaotic meander and breakup are more dependent on the Ca²⁺ and K⁺ currents. © 2000 Biomedical Engineering Society. PAC00: 8719Hh, 8717Nn, 8717Aa, 8716Uv     

Effects of dinitrophenol on active-transport processes and cell membranes in the Malpighian tubule of Formica

In Formica Malpighian tubules KCl secretion is driven by a V-type H⁺ ATPase in the luminal membrane in parallel with a H⁺/K⁺ antiporter. The effect of the protonophore dinitrophenol (DNP) was investigated on the isolated, symmetrically perfused tubule. DNP was applied in two different concentrations: 0.2 mmol/l and 1 mmol/l. The effects were fast and rapidly reversible. The equivalent short-circuit current (I _sc) was reduced significantly to respectively 25±3% Cn=4) and –3±7% (n=11) of the control value when 0.2 mmol/ l or 1 mmol/l was added to the bath. When 1 mmol/l DNP was applied the transepithelial resistance (R _te) decreased significantly to 74±11% of the control value (n=11), and the luminal over basolateral voltage divider ratio (VDR), providing an estimate of luminal over basolateral membrane resistance, decreased to 37±12% of the control (n=6). A concentration of 1 mmol/l DNP was also applied from the lumen. The decrease in I _sc was significant, but much less pronounced (74±5% of control; n=6) and no significant changes in R _te and VDR were observed. It is argued that, when the concentration in the bath is high enough, DNP may cross the cell and have a protonophoric effect not only on the mitochondria but also across the luminal cell membrane explaining the drop in transepithelial and in relative luminal membrane resistance. The diminished effectiveness of DNP, when applied from the luminal side, suggests that the luminal membrane is somehow less permeable to toxic substances, but that DNP very rapidly enters the cell via the basolateral membrane and may bring about an initial protonophoric effect across this membrane.     

Divalent cations and the action potential of leech Retzius cells

Summary The effects of Sr, Ba, Mn, La and Co on the action potential of the leech Retzius cell were examined using intracellular recording techniques. A previous paper showed that these cells could fire Ca-dependent action potentials in Na-free solution provided TEA was present (Kleinhaus and Prichard, 1975). Under the same conditions Sr 1.5-20 mM was capable of substituting as a current carrier. Ba 2–25 mM added to normal Ringer prolonged the duration and increased the amplitude of the action potential of the Retzius cell, and supported action potentials without requiring TEA in Na-free solutions. The overshoots of the Sr- and Ba-dependent action potentials varied with a slope of 40 mM and 75 mV, respectively per 10-fold change in divalent cation concentration. Mn and La selectively blocked that portion of the action potential resulting from an inward movement of Ca, Sr or Ba without affecting the Na-dependent depolarization. The actions of Ca 1 mM on Sr-dependent action potentials were compatible with reversible competitive antagonism. In conclusion the findings: 1. support the proposition that outward K current must be blocked in order for divalent cations to dominate the Retzius cell's behavior during excitation. 2. characterize the divalent cation conductance channel as pharmacologically distinct from the Na conductance channel in the Retzius cell and similar to those described in several other excitable membranes. 3. suggest that the current carrying divalent cations probably flow through the same channel.     

Taurocholate depolarizes rat hepatocytes in primary culture by increasing cell membrane Na+ conductance

Rat hepatocytes in primary culture were impaled with conventional microelectrodes. Addition of 5–100 mol/l taurocholate led to a slowly developing depolarization that was maximal at 50 mol/l (10.5±1.5 mV, n=15) and not reversible. The effect was Na⁺ dependent and decreased in cells preincubated with 1 mol/l taurocholate. Increasing external K⁺ tenfold depolarized the cells by 12.3±2.3 mV under control conditions and by 6.3±1.2 mV with 50 mol/l taurocholate present (n=7). Depolarization by 1 mmol/l Ba²⁺ was 7.6±0.8 mV and 6.0±0.7 mV (n=9) before and after addition of taurocholate, respectively. Cable analysis and Na⁺ substitution experiments reveal that this apparent decrease in K⁺ conductance reflects an actual increase in Na⁺ conductance: in the presence of taurocholate, specific cell membrane resistance decreased from 2.8 to 2.3 k · cm² · Na⁺ substitution by 95% depolarized cell membranes by 8.9±2.9 mV (n=9), probably due to indirect effects on K⁺ conductance via changes in cell pH. With taurocholate present, the same manoeuvre changed membrane voltages by –0.8±2.6 mV. When Na⁺ concentration was restored to 100% from solutions containing 5% Na⁺, cells hyperpolarized by 3.5±3.6 mV (n=7) under control conditions and depolarized by 4.4±2.9 mV in the presence of taurocholate, respectively. In Cl^– substitution experiments, there was no evidence for changes in Cl^– conductance by taurocholate. These results show that taurocholate-induced membrane depolarization is due to an increase in Na⁺ conductance probably via uptake of the bile acid.