Localization of the inositol 1,4,5-trisphosphate receptor in synaptic terminals in the vertebrate retina.

Inositol 1,4,5-trisphosphate (InsP3) mobilizes internal Ca2+ in cells by binding to a receptor protein, which has recently been purified and molecularly cloned. To clarify those neuronal functions that are regulated by InsP3, we have localized this InsP3 receptor protein immunocytochemically in the retina, a neural tissue of well-defined structure and function. Positive staining in neurons is confined almost exclusively to the synaptic layers. Using dissociated retinal neurons, we have further localized the receptor to presynaptic terminals of photoreceptors and bipolar cells, as well as the synaptic processes of amacrine cells. The specific association of InsP3 receptors with synaptic terminals suggests a role for InsP3 in synaptic modulation, especially with respect to transmitter release.     

Growth and elimination of nerve terminals at synaptic sites during polyneuronal innervation of muscle cells: a trophic hypothesis

This paper examines the possibility that the elimination of synapses from cells arises from a competition between the nerve terminals for trophic molecules made available by the cells. This idea is applied to the elimination of synapses that occurs during the polyneuronal innervation of muscle cells which accompanies both the development and reinnervation of muscles. In the proposed model, each motorneuron makes the same amount of receptor in its soma for a trophic molecule provided in limited quantities by each muscle cell; this receptor is then distributed to the collateral terminals of the motorneuron in concentrations proportional to the amount of receptor made in the soma by the motorneuron; the more collateral terminals initially possessed by a motorneuron the less will be their concentration of receptor. The receptors in the several collateral terminals on a muscle cell then compete for the trophic molecule provided by the muscle, and terminal growth is proportional to the number of receptor-trophic-molecule bonds formed. An autocatalytic effect has been introduced whereby the increase in size of a terminal accelerates the rate by which the trophic molecule is made available to that terminal for bonding with its receptors. In addition, the affinity between nerve terminal receptors and muscle molecules can be varied in the model. Finally, motorneuron cell death has been analysed as the elimination of neurons that have insufficient terminal area to take up a growth factor in amounts that will allow for the survival of the neuron.     

用荧光标记钠钾ATP酶显示气道感受器结构

由于普通光学和荧光显微镜功能上的限制以及缺乏良好的染色方法,我们对于呼吸道感受器形态方面的认识进展缓慢,缺乏对感受器结构的认识,阻碍了对其基本生理活动的探讨,随着共聚焦显微镜的产生与图像处理技术的进展,不但提高了对荧光结构的分辨率,还可通过三维重组而展现微小物体的整体结构。本文阐述了一种新颖方法,利用上述技术并结合免疫组织化学方法,采用Na^ /K^ -ATPase作为标记,对家兔呼吸道感受器进行了观察。本文中经过处理的气道组织结构,背景清晰,感受器部位着色强,观察到的整个感受器,结构复杂,呈树枝状,感受器末梢膨大,形成叶片状,本文首次以高清晰度展示了呼吸气道中单个感受器的整体结构,改变了需要以手绘来刻画感受器的现状,无疑,这种新方法能促进了解感受器的结构及其生理活动的机理。     

Kainate receptor activation enhances both tonic and phasic GABA-ergic inhibition in CA1 hippocampal interneurons

Kainate receptor agonists are powerful convulsants and excitotoxins. It has been a lot of controversy around functions of these receptors in the brain. It is shown in this article that kainate enhances evoked GABAergic IPSC (phasic currents) in CA1 interneurons in concentration-dependent manner. The phenomenon is likely to be due to kainate-mediated lowering of the threshold for action potential generation in interneuron axons and increased number of terminals responding to the same stimulus strength. Kainate application also induced an enhancement in tonic GABAergic conductance. This phenomenon can be attributed to massive extracellular GABA accumulation caused by interneuron firing in the presence of kainate. Extracellular GABA also shunts synaptic currents by activating tonic conductance as well as desensitizing synaptic GABAA receptors. Thus, the enhancement of the evoked IPSCs by 1 microM kainate was complicated by early and transient decrease. The kainate receptor-mediated enhancement of GABAergic tonic and phasic signalling to interneurons can contribute to the depression of GABAergic transmission to pyramidal neurons. The consequence of this phenomenon may play a major role in the epileptogenic action of this agent.     

Arm autotomy in brittlestars (Echinodermata: Ophiuroidea)

Although ophiuroid arm shedding has long been accepted as an example of autotomy, there has been little investigation of the phenomenon to substantiate this. This paper describes the outwardly visible aspects of autotomy and the function of the internal components of the arm during detachment. Observations are focussed on Ophiocomina nigra, some comparisons being made with eight other species.
Ophiuroid autotomy is characterized by its occurrence close to the point of stimulation, its rapidity, and by the pattern of intervertebral muscle separation at the insertions which is constant for a given species. Evidence is presented showing the important role played by the intervertebral ligament. Both this and the muscle insertions are collagenous, and it is suggested that they and the other intersegmental connective tissues facilitate autotomy by undergoing a drastic, nervously mediated loss in tensile strength which enables the animal to part from its arm with a minimum of effort. Comparable properties have been ascribed to other echinoderm connective tissues, and their role in asteroid and holothurian autotomy has been acknowledged, but such a mechanism has not previously been suggested for ophiuroid arm autotomy.     

The role of G-protein coupled receptors and associated proteins in receptor tyrosine kinase signal transduction

It is well established that stimulation of G-protein coupled receptors (GPCRs) can activate signalling from receptor tyrosine kinases by a process termed transactivation. Indeed, in recent years, it has become apparent that transactivation is a general phenomenon that has been demonstrated for many unrelated GPCRs and receptor tyrosine kinases. In this case the GPCR/G-protein participation is up-stream of the receptor tyrosine kinase. Substantial research has addressed these findings but meanwhile another mechanism of cross talk has been slowly emerging. For over a decade, a growing body of evidence has demonstrated that numerous growth factors use G-proteins and attendant signalling molecules such as beta-arrestins that participate down-stream of the receptor tyrosine kinase to signal to effectors, such as p42/p44 MAPK. This review highlights this novel mechanism of cross talk between receptor tyrosine kinases and GPCRs, which is distinct from growth factor receptor transactivation by GPCRs.     

Stress detection at the autotomy plane in the decapod crustacea

Summary The preformed autotomy plane of most reptantian decapods circumnavigates the basi-ischiopodite of the pereiopods. Associated with discrete areas of soft or thin cuticle in the proximity of the breakage plane are two connective chordotonal organs. These organs are sensitive to cuticular stress and are referred to as Cuticular Stress Detectors (CSD).The CSD organs respond to pressure applied to the basi-ischiopodite and upon deformation of the discrete areas of soft cuticle onto which the connective tissue strands of the receptors insert. The CSDs exhibit a wide range of unit activity and both receptors have a similar population of unit types. Some units are active only on application or removal of a force applied to the soft cuticle but a large number of phaso-tonic and tonic units respond to a constant pressure applied to the soft cuticle. The majority of the units respond during application of the stimulus (ON units) but a small proportion of the units increase activity on removal of the stimulus (OFF units).Passively produced tension in the anterior levator (autotomiser) muscle and depressor muscle tendons of the C-B joint is a potent stimulus to both receptors.Both receptors respond to movement of the B-I joint of the Nephropsidean walking leg and to movement of the I-M joint in the pereiopods of other reptantian decapods where the basipodite and ischiopodite have fused. The degree of activity is not directly related to the joint position or direction of movement.During autotomy both receptors respond strongly, particularly CSD 1. CSD 2 also shows increased activity but as the receptor is located distal to the breakage plane the receptor nerve is severed when breakage occurs.After autotomy CSD 1 responds normally to deformation of the soft cuticle but manipulation of the breakage plane membrane or of the regenerating limb bud produces low levels of activity even though the stimulus is gross.The possible functional roles of the receptors are discussed.This work was supported in part by European Science Exchange Programme study visit grants awarded to F. Clarac and W. Wales.     

Innervation of the receptors present at the various joints of the pereiopods and third maxilliped of Homarus gammarus (L.) and other macruran decapods (crustacea)

Summary This paper gives a full account of the number and structure of the chordotonal organs present at all joints between the coxopodite and dactylopodite of the pereiopods and 3rd maxilliped of the macruran Homarus gammarus L. (H. vulgaris M. Ed.). Some comparative data is supplied for other macruran decapods. As the form of the receptors depends to some degree upon the structure of the joint we have included details of musculature, planes of movement and degrees of freedom at each of the joints.The third maxilliped has a smaller number of chordotonal organs than the pereiopod, in particular at the mero-carpopodite and carpopodite-propodite joints where only one organ is present. In some species the propodite-dactylopodite organ is absent from this limb.The electrical activity recordable from the receptors in the 3rd maxilliped shows considerable differences from the corresponding receptors in the pereiopod.The structure of the carpopodite-propodite joint of both limbs is discussed in detail as this joint differs greatly from that of the Brachyura. In the 3rd maxilliped and 2nd pereiopod three muscles are present. In the latter the joint is capable of rotation about the longitudinal axis but the third muscle does not appear to produce this rotation. A small number of units in the CP₂ receptor respond to rotation.A receptor is described in the basipodite of the pereiopod and 3rd maxilliped situated just proximal to the plane through which the limb breaks at autotomy or autospasy. This receptor does not monitor joint movement and may detect cuticular strain, thus preventing accidental autotomy of limbs. A similar receptor has been observed in Carcinus.Cuticular receptor structures (CAP organs) are described as present at the M-C and C-P joints in both limbs, and at the I-M joint of the pereiopod.     

Orexin-A (Hypocretin-1) and leptin enhance LTP in the dentate gyrus of rats in vivo

Orexin-A (Hypocretin-1) has been localized in the posterior and lateral hypothalamic perifornical region. Orexin containing axon terminals have been found in hypothalamic nuclei and many other parts of the brain; for example, the hippocampus. Two types of orexin receptors have been discovered. Orexin 1 type of receptors have been described and been shown to be widely distributed in the rat brain including the hippocampus. Subsequently Orexin-A was found to impair both water maze performance and hippocampal long term potentiation (LTP). Leptin is expressed in adipose tissue and released into the blood where it affects food intake and can also produce widespread physiological changes mediated via autonomic preganglionic neurons, pituitary gland, and cerebral cortex. Immunoreactivity for leptin receptors has been found in various hypothalamic nuclei including the lateral hypothalamic area as well as the hippocampus especially in the dentate gyrus and CA1. Leptin receptor deficient rats and mice also show impaired LTP in CA1 and poor performance in the water maze. The present study was conducted to determine the effects of 0.0, 30, 60, 90, and 100 nM, orexin-A, and leptin, 0.0, 1.0, 100 nM, 1, and 10 microM, in 1.0 microl of ACSF, applied directly into the dentate gyrus, on LTP in medial perforant path dentate granule cell synapses in urethane anesthetized rats. Orexin-A specifically enhanced LTP at the 90 nM dose; and it was possible to block the enhancement by pretreating the animals with SB-334867, a specific orexin 1 receptor antagonist. Leptin enhanced normal LTP at 1.0 microM but inhibited LTP at lower and higher doses. These results and previous data indicate that the same peptide could possibly have different modulatory post synaptic effects in different hippocampal synapses dependent upon different types of post synaptic receptors.     

Reactive motility of dendrites

The neurohistological data on the nonspecific reactive phenomenon the dendrite neuroplasm excrescences were compared with intravital data on reactive mobility of the processes of the surviving neurons and nerve cells in tissue cultures. It was demonstrated that static pictures on histological preparations correspond to the stages of reactive reconstruction of live dendrites, such as retraction, extrusion and autotomy. The neuroplasmic excrescences reflect the reverse displacement of the neuroplasm associated with the process retraction rather than enhancement of its proximodistal flow.     

Renal dopamine receptors and hypertension

Dopamine has been recognized as an important modulator of central as well as peripheral physiologic functions in both humans and animals. Dopamine receptors have been identified in a number of organs and tissues, which include several regions within the central nervous system, sympathetic ganglia and postganglionic nerve terminals, various vascular beds, the heart, the gastrointestinal tract, and the kidney. The peripheral dopamine receptors influence cardiovascular and renal function by decreasing afterload and vascular resistance and promoting sodium excretion. Within the kidney, dopamine receptors are present along the nephron, with highest density on proximal tubule epithelial cells. It has been reported that there is a defective dopamine receptor, especially D(1) receptor function, in the proximal tubule of various animal models of hypertension as well as in humans with essential hypertension. Recent reports have revealed the site of and the molecular mechanisms responsible for the defect in D(1) receptors in hypertension. Moreover, recent studies have also demonstrated that the disruption of various dopamine receptor subtypes and their function produces hypertension in rodents. In this review, we present evidence that dopamine and dopamine receptors play an important role in regulating renal sodium excretion and that defective renal dopamine production and/or dopamine receptor function may contribute to the development of various forms of hypertension.     

Endogenous adenosine inhibits CNS terminal Ca(2+) currents and exocytosis

Bursts of action potentials (APs) are crucial for the release of neurotransmitters from dense core granules. This has been most definitively shown for neuropeptide release in the hypothalamic neurohypophysial system (HNS). Why such bursts are necessary, however, is not well understood. Thus far, biophysical characterization of channels involved in depolarization-secretion coupling cannot completely explain this phenomenon at HNS terminals, so purinergic feedback mechanisms have been proposed. We have previously shown that ATP, acting via P2X receptors, potentiates release from HNS terminals, but that its metabolite adenosine, via A(1) receptors acting on transient Ca(2+) currents, inhibit neuropeptide secretion. We now show that endogenous adenosine levels are sufficient to cause tonic inhibition of transient Ca(2+) currents and of stimulated exocytosis in HNS terminals. Initial non-detectable adenosine levels in the static bath increased to 2.9 microM after 40 min. These terminals exhibit an inhibition (39%) of their transient inward Ca(2+) current in a static bath when compared to a constant perfusion stream. CPT, an A(1) adenosine receptor antagonist, greatly reduced this tonic inhibition. An ecto-ATPase antagonist, ARL-67156, similarly reduced tonic inhibition, but CPT had no further effect, suggesting that endogenous adenosine is due to breakdown of released ATP. Finally, stimulated capacitance changes were greatly enhanced (600%) by adding CPT to the static bath. Thus, endogenous adenosine functions at terminals in a negative-feedback mechanism and, therefore, could help terminate peptide release by bursts of APs initiated in HNS cell bodies. This could be a general mechanism for controlling transmitter release in these and other CNS terminals.     

The m. caudifemoralis longus and its relationship to caudal autotomy and locomotion in lizards (Reptilia: Sauna)

Although the phenomenon of tail autotomy has traditionally been viewed in a purely adaptive light, functional constraints imposed by the locomotor system appear to have influenced the presence and extent of autotomy in lizards. Them. caudifemoralis longus is an unsegmented hind limb retractor that originates from the caudal vertebrae. It does not participate in autotomy and thus limits the proximal position of autotomic septa. Variation in the extent of the m. caudifemoralis is correlated with locomotor type. The muscle is large and originates from a long series of caudal vertebrae in fast moving lizards with powerful limb retraction, as exemplified by taxa capable of bipedal running. In slower lizards with sprawling postures, such as geckos, the m. caudifemoralis is small and restricted to the first few postsacral vertebrae. Autotomy is typically restricted or absent in the former lizards, while in the latter only the most proximal vertebrae are incapable of autotomy. In the evolution of existing patterns of caudal autotomy, functional demands intrinsic to the tail may be subservient to locomotor constraints imposed on the tail base by the m. caudifemoralis longus .     

Analgesia in phasic and tonic pain tests in a pharmacological model of autotomy

Self-mutilation or self-injurious behaviour is a well known behavioural disorder in humans. The proposition that this behaviour in animals is a response to chronic pain of peripheral nerve injury has been met with controversy. In the present study a pharmacological model, which produces no sensory or motor loss was used to study how autotomy is related to pain. In a group of rats autotomy was induced by amphetamine in phenoxybenzamine and reserpine treated animals. The pain tests, both phasic and tonic were then performed. The results of this study showed that a total analgesia was produced in both phasic and tonic pain tests, in animals that exhibited autotomy. Injection of naloxone in these animals prevented autotomy. A correlation between autotomy and no pain is suggested in this pharmacological model of autotomy.     

A simple mathematical model of cooperativity in receptor mosaics based on the "symmetry rule"

The phenomenon of receptor-receptor interactions was hypothesized about 20 years ago. It has been demonstrated by now that receptor-receptor interactions between G-protein coupled receptors (GPCRs) occur at plasma membrane level and result in the reciprocal modulation of their binding characteristics (i.e., cooperativity). One of the most important feature of this phenomenon is the concept of cluster of receptors, or receptor mosaic (RM). However, no proper mathematical approach has still been available to characterize RMs as far as their receptor composition, receptor topography and order of receptor activation inside the RM. This paper tries to fill the gap. A simple mathematical approach to the cooperativity in RMs formed by dimers of identical receptors and/or by iso-receptors is proposed. To this aim the so-called "symmetry rule" has been considered. This approach allows to describe by means of a simple energy function the effects of receptor composition (number of dimers), spatial organisation (respective location of the dimers) and order of activation (order according to which the single receptors are ligated) on the integrative cooperativity (index) of the RMs.     

High-affinity folate receptor in human ovary, serous ovarian adenocarcinoma, and ascites: radioligand binding mechanism, molecular size, ionic properties, hydrophobic domain, and immunoreactivity.

High-affinity folate receptors are expressed in normal ovaries and ovarian carcinomas. Binding of [3H]folate in human ovary, serous ovarian carcinoma tissue, and ascites is a complex process that has not been well characterized. This study shows changes in binding affinity and mechanism of binding with decreasing receptor concentration, inhibition by folate derivatives, and a slow radioligand dissociation at pH 7.4 becoming rapid and complete at pH 3.5. The receptor seems to be positively charged since it elutes in the front effluent of a DEAE-Sepharose CL-6B ion-exchange column at pH 6.3. The gel filtration profile of Triton X-100-solubilized tissue and ascites contained two peaks of radioligand-bound receptor (25 and 100 kDa). Exposure of ascites to cleavage by phosphatidylinositol-specific phospholipase C resulted in a partial conversion of the 100-kDa peak to a 25-kDa peak. This suggests that the receptor may be anchored to the membrane by a glycosylphosphatidyl residue that inserts into Triton X-100 micelles, resulting in a large molecular size on gel filtration. The receptor in ovarian carcinoma tissue immunoreacts with antibodies against purified human milk folate receptor protein as shown by enzyme-linked immunosorbent assay, immunoprecipitation, sodium dodecyl sulfate-polyacrylamide gel electrophoresis immunoblotting (a single band of 45 kDa), and immunohistochemistry. In only three of seven ovarian carcinomas did expression of radioligand-bound receptors exceed levels found in five normal ovaries. However, only receptors in ovarian carcinoma specimens showed a high degree of immunoreactivity. Hence, even without elevations of the total receptor level, a folate receptor isoform homologous to human milk folate receptor protein seemed to prevail in serous ovarian carcinomas.     

Stem cell autotomy and niche interaction in different systems

The best known cases of cell autotomy are the formation of erythrocytes and thrombocytes (platelets) from progenitor cells that reside in special niches. Recently, autotomy of stem cells and its enigmatic interaction with the niche has been reported from male germline stem cells (GSCs) in several insect species. First described in lepidopterans, the silkmoth, followed by the gipsy moth and consecutively in hemipterans, foremost the milkweed bug. In both, moths and the milkweed bug, GSCs form finger-like projections toward the niche, the apical cells (homologs of the hub cells in Drosophila). Whereas in the milkweed bug the projection terminals remain at the surface of the niche cells, in the gipsy moth they protrude deeply into the singular niche cell. In both cases, the projections undergo serial retrograde fragmentation with progressing signs of autophagy. In the gipsy moth, the autotomized vesicles are phagocytized and digested by the niche cell. In the milkweed bug the autotomized vesicles accumulate at the niche surface and disintegrate. Autotomy and sprouting of new projections appears to occur continuously. The significance of the GSC-niche interactions, however, remains enigmatic. Our concept on the signaling relationship between stem cell-niche in general and GSC and niche (hub cells and cyst stem cells) in particular has been greatly shaped by Drosophila melanogaster. In comparing the interactions of GSCs with their niche in Drosophila with those in species exhibiting GSC autotomy it is obvious that additional or alternative modes of stem cell-niche communication exist. Thus, essential signaling pathways, including niche-stem cell adhesion (E-cadherin) and the direction of asymmetrical GSC division - as they were found in Drosophila - can hardly be translated into the systems where GSC autotomy was reported. It is shown here that the serial autotomy of GSC projections shows remarkable similarities with Wallerian axonal destruction, developmental axon pruning and dying-back degeneration in neurodegenerative diseases. Especially the hypothesis of an existing evolutionary conserved “autodestruction program” in axons that might also be active in GSC projections appears attractive. Investigations on the underlying signaling pathways have to be carried out. There are two other well known cases of programmed cell autotomy: the enucleation of erythroblasts in the process of erythrocyte maturation and the segregation of thousands of thrombocytes (platelets) from one megakaryocyte. Both progenitor cell types - erythroblasts and megakaryocytes - are associated with a niche in the bone marrow, erythroblasts with a macrophage, which they surround, and the megakaryocytes with the endothelial cells of sinusoids and their extracellular matrix. Although the regulatory mechanisms may be specific in each case, there is one aspect that connects all described processes of programmed cell autotomy and neuronal autodestruction: apoptotic pathways play always a prominent role. Studies on the role of male GSC autotomy in stem cell-niche interaction have just started but are expected to reveal hitherto unknown ways of signal exchange. Spermatogenesis in mammals advance our understanding of insect spermatogenesis. Mammal and insect spermatogenesis share some broad principles, but a comparison of the signaling pathways is difficult. We have intimate knowledge from Drosophila, but of almost no other insect, and we have only limited knowledge from mammals. The discovery of stem cell autotomy as part of the interaction with the niche promises new general insights into the complicated stem cell-niche interdependence.     

Presynaptic receptor systems on cardiac sympathetic nerves.

The presence of a number of presynaptic receptor mechanisms on postganglionic sympathetic nerve terminals has been described by various investigators. In the present review evidence is presented which supports the concept that activation of these presynaptic receptors results in either the inhibition or facilitation of transmitter release from sympathetic nerve endings. The role of these mechanisms in controlling sympathetic function to the myocardium in physiological as well as pathophysiological condition is discussed. The possibility that pharmacological actions of several agents may have a presynaptic component is also discussed.     

Presynaptic kainate and NMDA receptors are implicated in the modulation of GABA release from cortical and hippocampal nerve terminals

One of the pathways implicated in a fine-tuning control of synaptic transmission is activation of the receptors located at the presynaptic terminal. Here we investigated the intracellular events in rat brain cortical and hippocampal nerve terminals occurring under the activation of presynaptic glutamate receptors by exogenous glutamate and specific agonists of ionotropic receptors, NMDA and kainate. Involvement of synaptic vesicles in exocytotic process was assessed using [³H]GABA and pH-sensitive fluorescent dye acridine orange (AO). Glutamate as well as NMDA and kainate were revealed to induce [³H]GABA release that was not blocked by NO-711, a selective blocker of GABA transporters. AO-loaded nerve terminals responded to glutamate application by the development of a two-phase process. The first phase, a fluorescence transient completed in ∼1 min, was similar to the response to high K⁺. It was highly sensitive to extracellular Ca²⁺ and was decreased in the presence of the NMDA receptor antagonist, MK-801. The second phase, a long-lasting process, was absolutely dependent on extracellular Na⁺ and attenuated in the presence of CNQX, the kainate receptor antagonist. NMDA as well as kainate per se caused a rapid and abrupt neurosecretory process confirming that both glutamate receptors, NMDA and kainate, are involved in the control of neurotransmitter release. It could be suggested that at least two types ionotropic receptor are attributed to glutamate-induced two-phase process, which appears to reflect a rapid synchronous and a more prolonged asynchronous vesicle fusion.