Methylmercury Differentially Affects GABAA Receptor-Mediated Spontaneous IPSCs in Purkinje and Granule Cells of Rat Cerebellar Slices

Using whole-cell recording techniques we compared effects of the environmental cerebellar neurotoxicant methylmercury (MeHg) on spontaneous IPSCs (sIPSCs) of both Purkinje and granule cells in cerebellar slices of the rat. In Purkinje cells, bath application of 10, 20 or 100 μM MeHg initially increased then suppressed the frequency of sIPSCs to zero. In granule cells, the initial increase in frequency was not observed in ≈50 % of cells examined, but suppression of sIPSCs by MeHg occurred in every cell tested. For both cells, time to onset of effects of MeHg was inversely related to the concentration; moreover, the pattern of changes in mIPSCs induced by MeHg in the presence of tetrodotoxin was similar to that in sIPSCs. For each concentration of MeHg, it took 2–3 times longer to block sIPSCs in Purkinje cells than it did in granule cells. MeHg also initially increased then decreased amplitudes of sIPSCs to block in both cells; again the response was more variable in granule cells. In most Purkinje and some granule cells, MeHg induced a giant, slow inward current during the late stages of exposure. Appearance of this current appeared to be MeHg concentration dependent, and the direction of current flow was reversed by changing the holding potentials. Reduction of the [Cl⁻] in the internal solution caused inwardly directed, but not outwardly directed giant currents to disappear, suggesting that this current is a Cl⁻-mediated response. However, bicuculline and picrotoxin failed to block it. MeHg apparently acts at both presynaptic and postsynaptic sites to alter GABA_A receptor-mediated inhibitory synaptic transmission. GABA_A receptors in granule cells appear to be more sensitive to block by MeHg than are those in Purkinje cells, although the general patterns of effects on the two cells are similar.     

降钙素基因相关肽抑制大鼠主动脉平滑肌细胞增殖

本工作用培养的大鼠主动脉平滑肌细胞，以细胞计数和＾３Ｈ－胸腺嘧啶掺入为指标，观察到降钙素基因相关肽呈剂量依赖地抑制ＶＳＭＣ增殖，１０＾－８和１０＾－７ｍｏｌ／ＬＣＧＲＰ可使＾３Ｈ－ＴｄＲ掺入量较对照组减少２６％（Ｐ＜０．０５）和３６％（Ｐ＜０．０１）并使细胞计数分别较对照组下降１７％（Ｐ＜０．０５）和３５％（Ｐ＜０．０１）。提示ＣＧＲＰ参与ＶＳＭＣ增殖的调节。     

Antiserum to Surface Antigens as a Marker for Cultured Rat Lung Endothelial Cells (1)

Antibodies were developed in rabbits against an established line of endo-thelial cells from normal adult rat lung. Pre- and postimmunization sera were tested for antibody activity by the indirect immunofluorescence technique. Preimmunization serum failed to react with the endothelial cells, whereas the antibody titer of postimunization serum from two rabbits was 1:512. Organ specificity and species specificity were assessed by absorbing the serum with packed dissociated cells from different organs of the rat and lung cells of other species. Only cells obtained from rat lung absorbed the antibodies completely. The antiserum showed some crossreactivity with the other cultured cells but the pattern of fluorescence was different. In the presence of complement the antiserum was found to be cytotoxic to cultured rat lung endothelial' cells but not to the other crossreacting cells.     

Differences in Mitogenic Responses of Murine T Cells to Two Distinct Phytohemagglutinin (Pha) Subcomponents

Two distinct mitogenic subcomponents of phytohemagglutinin (PHA) — leucoagglutinin (LA) and “purified” PHA — apparently stimulated different subpopulations of murine T cells. In the DBA/2J strain, the mitogenic responses of splenic lymphocytes to LA reached maximal levels after 24 to 36 hr exposure and almost completely disappeared by 48 hr, whereas maximal responses to PHA were maintained after 48 hr incubation. The levels of LA-responding T cells were highest in DBA/2J spleens at 5 weeks of age but markedly declined by 9 weeks of age, whereas thymic levels of LA-responding T cells reached a maximum at 9 weeks of age and remained maximal past 15 weeks of age. PHA-responding cells, in contrast, reached maximal levels in both the spleen and thymus of DBA/2J mice at 9 weeks of age. In C57BL/6J mice, splenic and thymic lymphocytes responded similarly to both components, except that the response of splenic lymphocytes to PHA reached a maximum after shorter incubation time and declined sooner than their response to LA. The mitogenic responses of C57BL/6J thymocytes to both components were already at their peak by 5 weeks of age and almost totally disappeared by 9 week, whereas the responses of splenic lymphocytes were maximal at 9-15 weeks of age. The responses of DBA/2J splenocytes to LA was significantly augmented by PHA, but LA markedly suppressed the proliferative responses to PHA.     

Differences in Mitogenic Responses of Murine T Cells to Two Distinct Phytohemagglutinin (Pha) Subcomponents

Two distinct mitogenic subcomponents of phytohemagglutinin (PHA) — leucoagglutinin (LA) and “purified” PHA — apparently stimulated different subpopulations of murine T cells. In the DBA/2J strain, the mitogenic responses of splenic lymphocytes to LA reached maximal levels after 24 to 36 hr exposure and almost completely disappeared by 48 hr, whereas maximal responses to PHA were maintained after 48 hr incubation. The levels of LA-responding T cells were highest in DBA/2J spleens at 5 weeks of age but markedly declined by 9 weeks of age, whereas thymic levels of LA-responding T cells reached a maximum at 9 weeks of age and remained maximal past 15 weeks of age. PHA-responding cells, in contrast, reached maximal levels in both the spleen and thymus of DBA/2J mice at 9 weeks of age. In C57BL/6J mice, splenic and thymic lymphocytes responded similarly to both components, except that the response of splenic lymphocytes to PHA reached a maximum after shorter incubation time and declined sooner than their response to LA. The mitogenic responses of C57BL/6J thymocytes to both components were already at their peak by 5 weeks of age and almost totally disappeared by 9 week, whereas the responses of splenic lymphocytes were maximal at 9-15 weeks of age. The responses of DBA/2J splenocytes to LA was significantly augmented by PHA, but LA markedly suppressed the proliferative responses to PHA.     

Lymphoproliferative Responses of Spleen Cells of Inbred Rat Strains to Mycoplasma arthritidis Mitogen

A potent mitogen for T lymphocytes of various species has recently been isolated from the supernatant of cultured Mycoplasma arthritidis organisms (MAS). In the mouse, reactivity to this mitogen has been observed to be controlled by the I-E subregion of the major histocompatibility complex. We have analysed the responses of spleen cells from several inbred rat strains covering practically all known haplotypes of the major histocompatibility complex of the rat (RT1). Unlike in the mouse, all of these responded well to MAS, except for the BN rat strain, which is a low responder to all T-cell mitogens, including phytohaemagglutinin and concanavalin A. This unresponsiveness, however, appeared to be unrelated to the RT1 haplotype, since LEW.1N rats carrying the same RT1n haplotype as BN animals responded well. Mice of the strain C57BL/6 are non-responders to MAS, but--as previously shown--their spleen cell responses can be reconstituted by the addition of 2-mercaptoethanol. No such reconstitution was observed for the low responsiveness of BN rat spleen cells. Stimulation with MAS induced high titres of interferon (presumably gamma interferon) in spleen cells from all rat strains tested. Spleen cells from BN rats produced lower interferon activities than those from other strains.     

Distinct GABA and glutamate receptors may share a common channel in Aplysia neurons

Using a microperfusion technique for rapid application of agonists to single identified voltage-clamped neurons of the marine mollusc Aplysia, chloride conductances elicited by gamma-aminobutyric acid (GABA) and L-glutamate were found to differ in rates of activation and desensitization, voltage dependence and dose-response relations. In spite of these marked differences, the two responses showed strong interaction: previous application of GABA could completely block the responses to glutamate while previous application of glutamate decreased the response to GABA. This interaction was not due to transmembrane chloride redistribution, and is probably not cross receptor blockade. Cross-desensitization of GABA and glutamate responses suggest that distinct receptors activate a common ion channel.     

钙调节激素对培养的纹状体细胞Ca^2＋转运的影响

本文观察了钙调节激素——甲状旁腺素(PTH)和降钙素(CT)对培养成活的脑纹状体神经细胞~(45)Ca转运的影响。结果表明,PTH(10-~7M)明显促进静息状态和去极化状态下细胞对~(45)Ca的摄取,并抑制去极化状态下的~(45)Ca释放,使胞内~(45)Ca净摄取量明显增加。CT(1u/ml)对细胞在静息状态下的~(45)Ca摄取无影响,但抑制去极化细胞的~(45)Ca摄取与释放,使胞内~(45)Ca净摄取最明显减少。结果提示,这两种钙调节激素可能通过影响神经细胞内的Ca~(2+)水平,参与某些中枢性的生理功能的调节。