三叉神经中脑核神经元膜的电学特性

用大鼠脑干脑片,给三叉神经中脑核79个神经元作了细胞内记录,测算了20个神经元膜的电学特性:静息电位-60.3±5.6mV;输入阻抗为10.5±5.4MΩ;时间常数1.3±0.5ms。电刺激可诱发动作电位,测算32个神经元的有关参数:阈电位-50—-55mV;波幅69.5±6.1mV;超射11.9±3.6mV;波宽0.8±0.2ms。TTX(0.3μmol/L)或无钠使之消失。通以长时程矩形波电流可引起200—250Hz的2—15个重复放电,但在通电停止前终止,TEA或4-AP可延长放电。膜电位-60—-55mV时在动作电位之后可看到阈下电位波动,它不受TTX的影响,无钙时消失,TEA或4-AP使波幅增大。静息电位去极化可使45个神经元中的40个发生外向整流作用,并被TEA,4-AP或无钙抑制,超极化则发生内向整流作用,Cs或无钠抑制之。灌流液中加入各种钾通道阻断药时神经元的稳态I-V曲线发生相应变化,提示I_(DR),l_A,I_(K(Ca))及I_Q可能都与静息时的膜电导有关。     

Mechanisms of Injury-Induced Calcium Entry into Peripheral Nerve Myelinated Axons: Role of Reverse Sodium-Calcium Exchange

Abstract: To investigate the route of axonal Ca²⁺ entry during anoxia, electron probe x-ray microanalysis was used to measure elemental composition of anoxic tibial nerve myelinated axons after in vitro experimental procedures that modify transaxolemmal Na⁺ and Ca²⁺ movements. Perfusion of nerve segments with zero-Na⁺/Li⁺-substituted medium and Na⁺ channel blockade by tetrodotoxin (1 µM) prevented anoxia-induced increases in Na and Ca concentrations of axoplasm and mitochondria. Incubation with a zero-Ca²⁺/EGTA perfusate impeded axonal and mitochondrial Ca accumulation during anoxia but did not affect characteristic Na and K responses. Inhibition of Na⁺-Ca²⁺ exchange with bepridil (50 µM) reduced significantly the Ca content of anoxic axons although mitochondrial Ca remained at anoxic levels. Nifedipine (10 µM), an L-type Ca²⁺ channel blocker, did not alter anoxia-induced changes in axonal Na, Ca, and K. Exposure of normoxic control nerves to tetrodotoxin, bepridil, or nifedipine did not affect axonal elemental composition, whereas both zero-Ca²⁺ and zero-Na⁺ solutions altered normal elemental content characteristically and significantly. The findings of this study suggest that during anoxia, Na⁺ enters axons via voltage-gated Na⁺ channels and that subsequent increases in axoplasmic Na⁺ are coupled functionally to extraaxonal Ca²⁺ import. Intracellular Na⁺-dependent, extraaxonal Ca²⁺ entry is consistent with reverse operation of the axolemmal Na⁺-Ca²⁺ exchanger, and we suggest that this mode of Ca²⁺ influx plays a general role in peripheral nerve axon injury.     

Neurotrophin-4: The odd one out in the neurotrophin family

Neurotrophin-4 (NT-4) is a member of a family of neurotrophic factors, the neurotrophins, that control survival and differentiation of vertebrate neurons (2–4). Besides being the most recently discovered neurotrophin in mammals, and the least well understood, several aspects distinguish NT-4 from other members of the neurotrophin family. It is the most divergent member and, in contrast to the other neurotrophins, its expression is ubiquitous and appears to be less influenced by environmental signals. NT-4 seems to have the unique requirement of binding to the lowaffinity neurotrophin receptor (p75^LNGFR) for efficient signalling and retrograde transport in neurons. Moreover, while all other neurotrophin knock-outs have proven lethal during early postnatal development, mice deficient in NT-4 have so far only shown minor cellular deficits and develop normally to adulthood. Is NT-4 a recent addition to the neurotrophic factor repertoire in search of a crucial function, or is it an evolutionary relic, a kind of wisdom tooth of the neurotrophin family?     

神经敏感性的降低是棉铃虫对拟除虫菊酯抗药性的重要机制

用扫描电子显微镜和光学显微镜的染色观察,研究了棉铃虫Helicoverpa armigeraHubner 3龄幼虫腹部神经一肌肉的分布,表明其腹纵肌细胞适合于作电生理细胞内记录。用电生理细胞内微电极记录法研究了棉铃虫三个品系：对照品系、功夫菊酯抗性品系(Cy-R,抗性指数13.4)和氰戊菊酯抗性品系(Fn-R,抗性指数37.9)的3龄幼虫神经一肌肉材料对相应杀虫剂的神经敏感性。结果表明：用10^-6mol/L的功夫菊酯处理Cy-R,在30min内有40%的个体对药剂无反应,另外60%的个体产生反应所需的时间是对照品系的3.5倍。用10^-6mol/L的氰戊菊酯处理Fn-R,在30min内有47%的个体对药剂无反应,另外53%的个体产生反应所需的时间是对照品系的4.2倍。这些结果说明神经敏感性降低是棉铃虫对拟除虫菊酯抗药性的重要机制。     

Effects of Nerve Growth Factor and Phorbol Derivative on Reactivation of Herpes Simplex Virus Type 1 in Cultured Cells of Latently Infected Adult Mouse Trigeminal Ganglia

Reactivation of herpes simplex virus type 1 (HSV-1) occurred rapidly in cells of latently infected adult mouse trigeminal ganglia which were cultured in serum-free medium in the presence of sufficient nerve growth factor (NGF). However, HSV-1 reactivation was delayed significantly in ganglionic cultures in the absence of exogenous NGF or in cultures treated with 2-aminopurine in the presence of NGF. The delayed viral reactivation in ganglionic cultures without NGF was accelerated by treatment with phorbol myristate acetate or dibutyryl cyclic AMP. Culture conditions which affected HSV-1 reactivation did not affect replication of HSV-1 in normal ganglionic cultures.     

迷走神经背核的研究进展

迷走神经背核（ＤＭＶ）是一个重要的内脏运动核团和内脏感觉核团。ＤＭＶ与中枢及外周存在广泛的纤维联系。ＤＭＶ和孤束核、最后区一起构成了“迷走感觉运动中枢”。ＤＭＶ存在神经－体液回路,使ＤＭＶ神经元可以直接感受外周血及脑脊液中的信息。ＤＭＶ含乙酰胆碱、儿茶酚胺、神经肽类等多种递质及相应受体。ＤＭＶ参与中枢调节胃肠、心血管及内分泌等生理功能。     

Antioxidants in peripheral nerve

Oxidative stress and antioxidants have been related in a wide variety of ways with nervous tissue. This review attempts to gather the most relevant information related to a) the antioxidant status in non pathologic nervous tissue; b) the hypothesis and evidence for oxidative stress (considered as the disequilibrium between prooxidants and antioxidants in the cell) as the responsible mechanism of diverse neurological diseases; and c) the correlation between antioxidant alterations and neural function, in different experimental neuropathies. Decreased antioxidant availability has been observed in different neurological disorders in the central nervous system, for example, Parkinson's disease, Alzheimer's disease, epilepsy, amyotrophic lateral sclerosis, cerebral ischaemia, etc. Moreover, the experimental manipulation of the antioxidant defense has led in some cases to interesting experimental models in which electrophysiological alterations are associated with the metabolic modifications induced. In view of the electrophysiological and biochemical effects of some protein kinase C inhibitors on different neural experimental models, special attention is dedicated to the role of this kinase in peripheral nervous tissue. The nervous tissue, central as well as peripheral, has two main special features that are certainly related to its antioxidant metabolism: the lipid-enriched membrane and myelin sheaths, and cellular excitability. The former explains the importance of the glutathione (GSH)-conjugating activity towards 4-hydroxy-nonenal, a biologically active product of lipid peroxidation, present in nervous tissue and in charge of its inactivation. The impairment of the latter by oxidative damage or experimental manipulation of antioxidant metabolism is discussed. Work on different experimental neuropathies from author's laboratory has been primarily used to provide information about the involvement of free radical damage and antioxidants in peripheral nerve metabolic and functional impairment.     

Immunohistochemical demonstration of calbindin-containing nerve endings in the rat esophagus

Immunoreactivity for calbindin was found in nerve endings with irregular laminar shapes in the rat esophagus. In the myenteric ganglia, laminar endings of a range of sizes formed a complex network and appeared to lie at the surface of the ganglion. The myenteric ganglia that contained nerve endings were most abundant in the upper portion of the eosphagus, their number decreasing orally to anally. Calbindin-immunoreactive nerve cell bodies were scattered throughout the esophagus. Laminar terminals were found in the connective tissue of the lamina propria immediately beneath the epithelium and in the muscularis mucosae. Occasional nerve branches formed a network of aborizing endings that surrounded part of the submucosal arterioles. Immunoreactive nerve endings in the mucosa and submucosa were present only in the upper part of the cervical esophagus. Unilateral vagotomy caused a remarkable decrease in the number of the myenteric ganglia containing the calbindin-immunoreactive laminar endings after 15 days or survival; in some of ganglia, the laminar structures disappeared and nerve endings showing weak immunoreactivity had an indistinct appearance, so that the outline of the ganglia became obscure. In operated rats at 24 days, the number of innervated ganglia was about half that in normal rats. However, there was no change in the morphology and the occurrence of the immunoreactive laminar structures in the mucosa and submucosa after denervation. The results show that many of the laminar endings that are immunoreactive for calbindin in the myenteric ganglia are derived from the vagus nerve. Thus, the calbindin-immunoreactive nerve endings with laminar expansions that are found in the rat eosphageal wall could be sensory receptors.     

Rat brain Na channel mRNAs in non-excitable Schwann cells

The expression of rat brain voltage-sensitive Na⁺ channel mRNAs in Schwann cells was examined using in situ hybridization cytochemistry and RT-PCR. The mRNAs of rat brain Na⁺ channel subtype II and III, but not subtype I, were detected in cultured Schwann cells from sciatic nerve and in intact sciatic nerve, which contains Schwann cells but not neuronal cell bodies. These results indicate that rat brain Na⁺ channel mRNAs, which have been considered as mainly neuronal-type messages, are also expressed in glial cells in vitro and in vivo.