Cytoplasmic CD3+ surface CD8+ lymphocytes develop as a thymus-independent lineage in chick-quail chimeras

We have analyzed the embryonic development of a population of lymphoid cells that express a CD3 antigenic determinant in the cytoplasm but not on the cell surface. Since these cells lack T cell receptor (TcR) molecules, we have provisionally named them TCRO cells. Their development, expansion and distribution was investigated following transplantation of splenic and bursal fragments from chicken embryos into quail embryos. Since quail cells are not recognized by our panel of monoclonal antibodies against chicken TcR1, TcR2, TcR3, CD3, CD4 and CD8 molecules, these antibodies provided reliable markers for donor chick lymphocytes in the tissues of the quail recipients. Transplanted spleen and bursa both generated CD3+ cells, the number of which increased as a function of age. Notably, approximately half of these CD3+ cells expressed surface CD8, but none acquired TcR1 (gamma/delta), TcR2 (alpha/beta) or TcR3 expression. Since TCRO cells normally appear first in the spleen of 8-day chick embryos (E8), their generation in E6 splenic transplants indicated an extrathymic origin. The TCRO cells of chick splenic origin migrated to the spleen, bursa and thymus of the quail recipients. In six of seven chimeras acquiring CT3+ cells in the recipient thymus, these cells were restricted to the medulla and displayed the typical TCRO phenotype: CD3+CD8+TcR1-TcR2-TcR3-. These intrathymic TCRO cells also lacked the CT1 thymocyte antigen. We conclude that the TCRO cells represent a thymus-independent lineage of lymphoid cells that can migrate into a receptive thymus by rarely, if ever, differentiate into conventional T cells.     

四倍体胚胎发育阶段对胚胎干细胞嵌合体小鼠制备的影响

目的 探讨四倍体胚胎发育阶段对胚胎干细胞(ES)嵌合体小鼠制备的影响.方法 通过2-细胞胚胎电融合法制备四倍体胚胎,采用显微注射方法将ES细胞分别注入1-细胞、4-细胞、囊胚3个发育阶段的四倍体胚胎中.所用ES细胞分别为杂交系B6D2F1×129/Sv和近交系C57BL/6J,经胚胎移植和剖腹产以获得ES小鼠.结果 实...     

Avian photogenic epilepsy and embryonic brain chimeras: neuronal activity of the adult prosencephalon and mesencephalon

Photogenic genetic epilepsy was studied in an avian model, using either the Fayoumi epileptic chicken (Fepi) or neural chimeras obtained by replacement of em bryonic brain vesicles in normal chickens with those of Fepi embryos. In these two kinds of animals motor seizures accompanied by electroencephalographic (EEG) desynchronization and flattening (DF) were evoked by intermittent light stimulation (ILS). In chimeras with on ly the prosencephalon grafted, motor seizures were less severe but DF remained. ILS-induced DF persisted un der paralysis by gallamine triethiodide (Flaxedil). Extra cellular recordings were made in the prosencephalon (wulst) and in the mesencephalon (optic tectum) of paralysed animals. Units recorded in the prosencephalon of Fepi and chimeras showed abnormal interictal burst ing activity, distinctly different from the non-epileptic Fayoumi heterozygotes (Fhtz) and normal chickens. The mesencephalic units of Fepi and chimeras having both prosencephalon and mesencephalon grafted showed two types of abnormal activities during ILS-induced DF, which were distinct from the non-epileptic chickens: type I neurons displaying early, high sensitivity to ILS fol lowed by a prolonged suppression of activity; type II neurons displaying an early and prolonged suppression of activity. The results are discussed with respect to the brain structures generating ictal and interictal EEG ac tivities and motor seizures.     

Immune responses of thymus/lymphocyte embryonic chimeras: studies on tolerance and major histocompatibility complex restriction in Xenopus

A new model has been developed to address the question of whether T cells that traverse an allogeneic thymus during early and late life become restricted to interact, in vivo, with other leukocytes and target cells that display the major histocompatibility complex (MHC) antigens of the thymus haplotype. Chimeras were made microsurgically with pairs of 24-h-old Xenopus embryos such that the anterior region of an embryonic chimera contained the thymus anlagen and was of one MHC genotype, whereas the posterior region contained the anlagen of all hemopoietic cells and was of another genotype. Assays to determine the MHC haplotype restriction specificity of T cells in chimeras that had been reared through metamorphosis involved: specific antibody responses (IgM and IgG) to dinitrophenylated keyhole limpet hemocyanin; rejection of minor H locus disparate skin grafts that expressed the MHC antigens of either the thymus donor or the lymphocyte donor; and mixed leukocyte culture. MHC-mismatched chimeras displayed split tolerance since they accepted skin grafts of the thymus haplotype but had lymphocytes that proliferated in response to MHC antigens of the thymus donor strain as well as to MHC antigens of third-party donors. IgM responses of MHC-matched and MHC-mismatched chimeras and of nonchimeric controls did not differ. However, the IgG responses of MHC-mismatched thymus/lymphocyte chimeras peaked later than those of MHC-matched chimeras and normal controls. Data from skin grafting protocols were consistent with the proposition that there may be in vivo selection of T cells reactive to minor H antigens presented in association with the MHC antigens of the thymus rather than the MHC antigens of the lymphocytes themselves. These data suggest that although it is not absolute, there is thymic selection of the T cell repertoire in Xenopus.     

A visco-elastic theory of mechanoreceptor adaptation

1. Physical analysis of two visco-elastic models was performed, to afford a quantitative basis for examination of a theory of slip as applied to mechanoreceptor adaptation. In one model the coupling force between skin tissue and receptor was considered to be purely viscous; in another it was supposed to consist of parallel viscous and elastic forces, representing the properties of a gel.2. Predictions from the models were compared with experimental results from frog and rat skin receptors. Good fits with slope-latency and slope-amplitude curves were obtained, with the adjustment of two constants.3. The excitability changes during long subliminal stimuli showed dynamic and static phases, which developed at different rates as stimulus strength was increased. This behaviour could be explained qualitatively by the more complex model, but quantitative comparisons could not be achieved.4. Treatment of the skin with tissue-destroying enzymes caused changes in stimulus-response relationships consistent with predictions from the models. The effect of the enzymes seemed to be largely on the elastic coupling forces.5. The visco-elastic model offers a satisfactory but not exclusive explanation of certain time- and amplitude-dependent features of mechanoreceptor behaviour and also accounts for a specific delay in mechanical excitation.     

Cholecystokinin octapeptide and gastric mechanoreceptor activity in rat brain

Extracellular unitary recordings were made from neurons in the rat dorsal vagal nucleus, and the response of these neurons to iontophoretically applied cholecystokinin octapeptide (CCK-OP) and proglumide (a novel CCK antagonist) was studied. The effect of CCK-OP and proglumide on the response of the neurons to gastric distension was also studied. Seventy-four percent (n = 39) of the neurons studied were excited by CCK-OP. It was not possible to antagonize the response to CCK-OP with proglumide. CCK-OP was also found to be an effective modulator of the response to gastric distension; the effects were diverse ("on" responses were augmented; "off" and "transient" responses were diminished) but were always the same within each characteristic pattern of response to distension. These results provide supporting evidence for CCK-OP, a peptide common to both brain and gut, acting in the role of a neural modulator in the control of the gastrointestinal tract. It is possible to speculate that the potent effect of CCK-OP on neuronal excitability and on the central representation of gastric mechanoreceptor activity may well substantiate the role of CCK-OP as a central regulator of feeding behavior.     

Development of GABA responsiveness in embryonic turtle cortical neurons

The whole-cell patch-clamp method was used to study the development of functional GABA receptors in cortical neurons dissociated from embryonic turtles. GABA elicited an increase in membrane conductance, even from cells obtained from the earliest stages of corticogenesis. The GABA-mediated conductance had a mean value 7.4 times greater than membrane 'leak' conductance and increased with developmental age. In all stages studied, the response inverted polarity at a value approximating ECl- and was blocked by applications of bicuculline, suggesting that it was mediated by GABAA receptors. GABA receptors are thus present and functional very early in corticogenesis, preceding electrogenesis, synaptogenesis, and full neuronal differentiation.     

DEG/ENaC超家族-机械感受器的分子生物学基础

机械感觉(mechanosensation)是指将机械刺激转换为电信号(机械能转换为电能)而引起的对刺激模式、刺激空间和时间具有分辨能力的多种感觉功能，包括动物和人的触觉、本体觉、听觉、平衡觉以及细胞为了维持生命而对细胞体积随时调节的功能等。当前认为机械感觉功能感受器的分子结构基础高度保守，从无脊椎动物如软体类的线虫     

Effect of rectal mechanoreceptor stimulation on the striated musculature

Summary It was shown in acute experiments on cats (urethan anesthesia) that the threshold value and the character of the striated muscle reaction in response to interoceptive stimulation depends on the intensity of the receptor stimulation and the system of functional connection between the given muscle and the area stimulated.With a rise of the stimulation intensity of rectal mechanoceptors there primarily occurs a reaction of the anal sphincter, at first (in 50% of experiments) in the form of relaxation, with a somewhat greater stimulation intensity —in the form of contraction, followed by a relaxation, this time more complete. Abdominal muscles begin to react with a somewhat greater stimulation intensity (by relaxation with low stimulation values, and by contraction with higher ones).Muscles of the lower extremities also react in the same way; however, their relaxation occurs already with medium, and contraction — with higher stimulation values. Finally, with the greatest stimulation intensity reflex threshold is reached in the cervical muscles — they relax in response to all the effective stimulation intensities.(Presented by AMN SSSR Active Member V. V. Parin) Translated from Byullenten' Éksperimental'noi Biologii i Meditsiny, Vol. 53, No. 5, pp. 13–17, May, 1962     

Two classes of slowly adapting mechanoreceptor fibres in reptile cutaneous nerve

1. The myelinated fibre spectrum of the plantar nerve of reptile consists of a unimodal distribution corresponding approximately to the delta elevation in mammalian nerve and contains a variety of receptor categories similar to those of mammals except for the obvious absence of structures related to hairs.2. The various receptor types of reptilian skin do not fall into discrete groups on the basis of conduction velocity.3. Only a few thermoreceptor fibres were identified but a large proportion of slowly adapting mechanoreceptors responded to rapid temperature transients.4. Two distinct categories of slowly adapting receptors whose discharge is related to the amplitude of skin displacement have been identified and studied in detail. These two receptors can be distinguished by their patterns of discharge, and display several distinctive features including differences in resting discharge, receptive field size, threshold, response to DC polarization, etc.5. The mathematical functions describing the response to stimuli of varying magnitude for one receptor type is markedly affected by the sequence of stimulus presentation.     

Intravascular mechanoreceptor modulation of renal sympathetic nerve activity in the cat

Experiments were performed in chloralose-anesthetized cats to characterize intravascular mechanoreceptro input to renal nerve activity in the intact and vagotomized sinoaortic-denervated states. High-pressure intravascular mechanoreceptors were stimulated by rises in arterial pressure caused by norepinephrine. Low-pressure intravascular mechanoreceptors were stimulated by progressive blood volume expansion (14-23%) at a rate of 4.4 or 17.6 ml/min. In addition, veratrine was used to stimulate directly both high- and low-pressure receptors. In the intact animal the administration of norepinephrine or blood volume expansion was associated with substantial decreases in renal nerve activity. Veratrine also caused a large dose-related decrease in renal nerve activity. However, in the vagotomized sinoaortic-denervated animal there was no change in renal nerve activity with norepinephrine, volume expansion, or veratrine administration. These experiments demonstrate that the major afferent pathways for renal sympathetic circulatory reflexes are confined to the carotid sinus and aortic and vagus nerves. No evidence was found for a significant contribution from sympathetic afferent nerves.     

Skin mechanoreceptor function in albino rats during transcranial electrical stimulation

Laboratory of Physiology of Reception, and Group for Physiological Mechanisms of Electroanesthesia, I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. (Presented by Academician of the Academy of Medical Sciences of the USSR S. N. Golikov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 110, No. 11, pp. 458–460, November, 1990.     

Development of the amygdalohypothalamic projection in the mouse embryonic forebrain

The amygdalohypothalamic projection, a major component of the stria terminalis, is involved in the conduction of emotional and olfactory information integrated in the amygdala to the hypothalamus to elicit emotional reactions. Despite the extensive studies on functional aspects of the amygdaloid complex, developmental mechanisms of the amygdala and related structures are still poorly understood. To investigate the development of the amygdalohypothalamic projection in the mouse embryonic brain, carbocyanine dye was applied to the amygdala to label the growing axons anterogradely and to the hypothalamus to label the amygdaloid neurons retrogradely. The initial outgrowth of the stria terminalis was found to be as early as E11.5. The pathway crossed in a saddle over the internal capsule, another prominent connection in the developing forebrain of the mammalian embryo. Bipolar immature neurons were distributed along the stria terminalis at the telencephalo-diencephalic boundary, and the internal capsule was also surrounded by these cells. These cells expressed immunoreactivities to calretinin and the lot-1 antigen which has been shown to be involved in guidance of the developing lateral olfactory tract. Ultrastructural analysis revealed an adherens-like junction between the stria terminalis and the apposed cells, implying contact-mediated guidance. These results suggest that, in the development of the stria terminalis, the axonal outgrowth is guided by a mechanism similar to that of the developing lateral olfactory tract, a major amygdalopetal connection.     

Development of muscle-specific features in cultured frog embryonic skeletal myocytes

To study the development of muscle-specific features during myogenesis, we analysed the ultrastructure and voltage-dependent currents of frog embryonic skeletal myocytes maintained in culture for 10 days. The cells were maintained under culture conditions that prevented cell division, fusion and cell contacts with neuroblasts. The cell surface was estimated morphometrically and from cell capacity and the values obtained were used to calculate ion current densities. It was shown that the expression of all main types of voltage dependent ionic currents occurs during the first 3–5 days. Na⁺ maximum specific conductance at days 1–2 was low but by day 7 it showed a 20-fold increase. The magnitude of Na⁺ current densities increased 16-fold from day 1 (3.6 A/cm) to the day 7 (58.1 A/cm). The maximum specific K⁺ conductance increased almost 3-fold during the first 5 days. In contrast to the other types of currents, I_K undergoes qualitative changes. Sodium action potentials, whose amplitude and time course depend on g_Na/g_K ratio, appeared from day 4 in culture, when myofibrils and the T-system also developed. The amplitude of DHP-sensitive slow I_Ca increased in parallel with the development of the T-membrane. I_Ca,S density per unit of T-membrane area reached an equilibrium of ca., 17 A/cm² on the day 4 and then remained stable until the end of the period of observation. These studies demonstrate that muscle-specific characteristics including morphology and excitatory properties begin to develop on the third day and resemble those of adult muscle cells by the sixth day in culture.