Early Cellular Events Research Articles

Force-induced rapid changes in cell fate at midpalatal suture cartilage of growing rats.

The application of expansional force induces replacement of the cartilaginous tissue with bone at the midpalatal suture of growing rats. We examined the early cellular events evoked by force by analyzing the expression of proliferating cell nuclear antigen (PCNA), an operational marker of cell proliferation, and of several bone matrix proteins. A rectangular orthodontic appliance was set between the right and left upper molars of four-week-old rats, with 50 g of initial expansional force. Two days after application of the force, the pre-existing cartilage was separated laterally. Mesenchymal cells with stretched shapes were arranged parallel to the expansional force and filled the center of the suture. Only a few of these stretched cells exhibited nuclear accumulation of PCNA. In contrast, many polygonal mesenchymal cells distributed along the inner lateral side of the cartilaginous tissue exhibited strong immunoreactivity for PCNA. Localization of alkaline phosphatase activity overlapped into this proliferating cell zone. Nascent extracellular matrix under the proliferating cells was positive for osteocalcin, indicating commencement of active bone formation. These findings indicated that, among mesenchymal cells subjected to expansional forces, only cells located on the inner side of the cartilaginous tissue proliferate and differentiate into osteoblasts. In agreement with rapid bone growth progression, apoptosis was also observed in the zone of proliferating cells, as measured by TdT-mediated dUTP-biotin nick end labeling (TUNEL) assays.

Rapid downregulation of rat renal Na/P(i) cotransporter in response to parathyroid hormone involves microtubule rearrangement.

Renal proximal tubule cells express in their apical brush border membrane (BBM) a Na/P(i) cotransporter type IIa that is rapidly downregulated in response to parathyroid hormone (PTH). We used the rat renal Na/P(i) cotransporter type IIa (NaPi-2) as an in vivo model to assess early cellular events in the rapid downregulation of this transporter. When rats were treated with PTH for 15 minutes, NaPi-2 abundance in the BBM was decreased. In parallel, transporter accumulated in intracellular vesicles. Concomitantly, microtubules (MTs) were found to form dense bundles of apical-to-basal orientation. After 60 minutes of PTH action, the cells were vastly depleted of NaPi-2, whereas their microtubular cytoskeleton had returned to its normal appearance. Prevention of MT rearrangement by taxol resulted in accumulation of NaPi-2 in the subapical cell portion after 15 minutes and a strong delay in depletion of intracellular transporter after 60 minutes of PTH action. Furthermore, the subapical accumulation of NaPi-2 was associated with the expansion of dense apical tubules of the subapical endocytic apparatus (SEA). Depolymerization of MTs by colchicine likewise caused a retardation of intracellular NaPi-2 depletion. These results suggest that NaPi-2 is downregulated in response to PTH through a rapid endocytic process in 2 separate steps: (a) internalization of the transporter into the SEA, and (b) its delivery to degradative organelles by a trafficking mechanism whose efficiency depends on a taxol-sensitive rearrangement of MTs.

Cyclosporin and chronic pancreatitis: a supermodel?

See article on page 269 Most patients with acute pancreatitis develop their disease in association with either biliary tract stones or abuse of ethanol, whereas chronic pancreatitis is most commonly...

Successive formative stages of precartilaginous mesenchymal condensations in vitro: modulation of cell adhesion by Wnt-7A and BMP-2.

High-density chick limb bud cell culture is a useful model to study mesenchymal condensatifons and chondrogenesis. Most previous studies have focused on the effects of soluble reagents on terminal chondrogenic differentiation and have not defined the early cellular processes and signaling events. In this study, we defined five successive stages in the differentiation process: 1) dissociated cells, 2) small aggregates, 3) formation of cell clusters, 4) precartilaginous condensations, and 5) cartilage nodule. We used RCAS retrovirus-mediated Wnt-7a gene transduction to test the effect of Wnt-7a on the differentiation process. We found that Wnt-7a suppressed chondrogenic differentiation. Wnt-7a did not inhibit the initiation of condensation formation but blocked the progression of precartilaginous condensations to cartilage nodules. The Wnt-7a-transduced cultures showed characteristics of a less mature culture with persistent expression of NCAM, N-cadherin, wider distribution of integrin beta1 and fibronectin, and suppression of tenascin-C. BMP-2 is known to enhance chondrogenic differentiation in these cultures by promoting cell clusters to form continuous sheet-like precartilaginous condensations. However, cultures exposed to both BMP-2 and Wnt-7a showed inhibition of chondrogenic differentiation. Different signaling molecules such as Wnt-7a and BMP-2 may have antagonistic effects on cartilage differentiation and the gradient of the two molecules may be involved in defining the boundaries of the initial precartilaginous condensation. We propose that the shape of the precartilaginous condensations may be modulated by local concentrations of signaling molecules, such as Wnt-7a and BMP-2, which act to alter cell-substrate and cell-cell adhesions.

Cellular changes in denervated tissue during wound healing in a rat model.

There is increasing evidence that innervation, possibly mediated via neuropeptides, promotes wound healing. This study presents data on the early cellular events during healing in denervated tissue. Free oblique groin flaps were raised on 25 adult Sprague-Dawley rats. Excisional wounds were placed within the flap and in two control sites, the contralateral inguinal region and the thorax. The absence of innervation in the free flap wounds was confirmed 10 days after surgery by indirect immunofluorescence with a pan-neuronal marker. The cellular infiltrate of the wounds was analysed immunohistochemically with a panel of antibodies to rat macrophages and monocytes (ED1), rat B lymphocytes (CD45R) and T lymphocytes (CD2). The immunostained cellular infiltrate was quantified at 2, 4, 7 and 10 days postoperatively. Our results show that denervated wounds have a significantly lower macrophage and T-lymphocyte count at day 4 of wound healing (P < 0.05). Inflammatory cells, particularly macrophages, are known to play an important part in wound healing and their reduced chemotaxis in denervated tissue may be related to the observed delay in wound closure.

Immunity to Chlamydia trachomatis mouse pneumonitis induced by vaccination with live organisms correlates with early granulocyte-macrophage colony-stimulating factor and interleukin-12 production and with dendritic cell-like maturation.

As is true for other intracellular pathogens, immunization with live Chlamydia trachomatis generally induces stronger protective immunity than does immunization with inactivated organism. To investigate the basis for such a difference, we studied immune responses in BALB/c mice immunized with viable or UV-killed C. trachomatis mouse pneumonitis (MoPn). Strong, acquired resistance to C. trachomatis infection was elicited by immunization with viable but not dead organisms. Immunization with viable organisms induced high levels of antigen-specific delayed-type hypersensitivity (DTH), gamma interferon production, and immunoglobulin A (IgA) responses. Immunization with inactivated MoPn mainly induced interleukin-10 (IL-10) production and IgG1 antibody without IgA or DTH responses. Analysis of local early cytokine and cellular events at days 3, 5, and 7 after peritoneal cavity immunization showed that high levels of granulocyte-macrophage colony-stimulating factor and IL-12 were detected with viable but not inactivated organisms. Furthermore, enrichment of a dendritic cell (DC)-like population was detected in the peritoneal cavity only among mice immunized with viable organisms. The results suggest that early differences in inducing proinflammatory cytokines and activation and differentiation of DCs may be the key mechanism underlying the difference between viable and inactivated organisms in inducing active immunity to C. trachomatis infection.

Reinitiation of cell division and polyamine and aromatic monoamine levels in alfalfa explants during the induction of somatic embryogenesis

The early cellular events in leaf explants of Medicago sativa L. cultured on somatic embryogenesis‐ and callogenesis‐inducing media (EIM and CIM, respectively) were correlated with the endogenous contents of polyamines (PAs) and aromatic monoamines (AMs). On the second day of culture, replication of DNA occurred in epidermal and subepidermal cells on the edges of explants on EIM and was a prerequisite for proembryonal mass and, later, globular proembryo formation. In explants cultured on CIM, replication occurred at least one day later and in fewer cells, which were randomly spread all over the explant. Transition of leaf explant cells to rapidly dividing meristematic‐like cells on EIM or to enlarged, highly vacuolated cells on CIM was observed. The increase in total PA levels in cultured explants was primarily a consequence of increases in putrescine (Put) and spermidine (Spd) contents and was much more pronounced on EIM than on CIM. High Spd levels were characteristic of meristematic cells and might be essential for the development of globular structures. The higher amount of insoluble PA conjugates was determined in explant cells on EIM, as compared with CIM. Proembryogenic cell mass formation was positively correlated with free tyramine and negatively correlated with free phenylethylamine contents.

Early cellular events in the penumbra of human spontaneous intracerebral hemorrhage

Spontaneous intracerebral hemorrhage causes high morbidity and mortality rates, and yet its treatment remains controversial, partly because of a poor understanding of the pathogenesis and timescale of injury in the surrounding brain. This study was undertaken to clarify the cellular reactions around human spontaneous intracerebral hematomas and relate these to hematoma duration and volume, in order to provide further data that might aid the development of therapeutic strategies. Brain tissue from the margin of the hematoma in 33 fatal cases of spontaneous intracerebral hemorrhage and corresponding tissue from 13 normal controls was studied using immunohistochemistry for heat-shock proteins, metallothionein, and various neuronal, glial, macrophage, and endothelial markers. Hematoma volumes were calculated from computed tomographic (CT) scans and autopsy measurements, whereas hematoma age was estimated from clinical records. The results showed that cellular events are time dependent, but not related to hematoma volume, and are identifiable in neurons, glia, and endothelium as early as 5 hours after hemorrhage. Peripheral macrophage infiltration begins at 5 days. The results suggest that the therapeutic window in humans for reperfusion of the ischemic penumbra of a hematoma is less than 5 hours, although progression of the infarcted core to the penumbral periphery within 1 to 3 days suggests a wider cytoprotective window. Edema, caused by blood-brain barrier breakdown, was also identified at 5 hours, and prompt treatment of this may reduce the space-occupying effects of the hematoma and, possibly, the morbidity and mortality.

Subcutaneous infection of mice with Paracoccidiodes brasiliensis induces a peculiar pattern of inflammatory and immune responses.

It is well established that resistance or susceptibility to Paracoccidioidis brasiliensis infection in mice is under strict host's genetic control. Mice from A/Sn strain inoculated by the ip route are resistant to fungal infection while infection induced in mice from B10.A strain results in a fatal disease. The early cellular events of infection in both strains are characterized by a marked neutrophilic infiltration that is more prominent in B10.A mice. A peculiar characteristic of the Paracoccidioides brasiliensis-mouse model is that the subcutaneous (sc) inoculations of the fungus either in resistant (A/Sn) or susceptible (B10.A) mice is self-curing and tums mice from the B10.A strain able to express typical DTH reaction to fungal antigens, as observed in A/Sn mice. Here we report the investigation on the early events of the inflammatory response induced by the inoculation of live fungus into the hind footpad of A/Sn (resistant) and B10.A (susceptible) mice. The influence of neutrophils on the inflammatory response and antibody titers or DTH response to gp43, the major fungal antigen, was also evaluated. Results showed a different course of the inflammatory response induced by fungal inoculation in A/Sn and B10.A mice. Neutrophil depletion before infection differently influenced the kinetics of the inflammatory process in both mice strains but did not modify the fungal load in the lesions. In neutrophil depleted mice from both strains, a decrease in DTH response and an increase in total antibody titers to gp43 were observed. The significant increase in the fungal load in lesions seen in nude mice indicates that the self-limited infection evoked by fungal inoculation into the subcutaneous tissue is a T-cell dependent phenomenon. The implications of these observations in the pathogenesis of paracoccidioidomycosis are discussed.

Human Renal Medullary Interstitial Cells and Analgesic Nephropathy

The aim of this study was to investigate the effects of known papillotoxins using cultures of human renal interstital medullary cells (hRMIC). The culture of hMIC was based on the primary culture of human renal medullary explants, selective detachment of interstitial cells and selective overgrowth of these cells in a serum-rich medium after dilution cloning. The homogenous population of cells obtained exhibited the characteristic morphological and functional characteristics of Type I interstitial cells, viz. stellate-shaped cells demonstrating numerous lipid droplets, abundant endoplasmic reticulum and mitochondria, fine filaments underlying the cell membrane and the production of extracellular matrix. Cytotoxicity studies using hMIC and known papillotoxins clearly demonstrated a reduction in cell viability that varied with bath exposure time and type of agent tested. While only phenylbutazone and mefenamic acid produced significant cytotoxicity after a 24 h incubation period, cell viability assessed using the MTT assay was only profoundly reduced by aspirin and paracetamol following sub-chronic exposure for 7 days. The rank order of cytotoxicity observed in hMIC was phenylbutazone > mefenamic acid > aspirin > paracetamol. The results demonstrate the potential of hMIC for investigating and defining the early cellular events in the pathogenesis of analgesic nephropathy.

Early Weaning Induces Jejunal Ornithine Decarboxylase and Cell Proliferation in Neonatal Rats

Increased ornithine decarboxylase (ODC) activity is associated with rapid cell proliferation in many cell types. The cellular effects of early weaning on intestinal development are not well established. To investigate whether ODC is involved in intestinal growth after early weaning, we precociously weaned suckling rats on postnatal d 15 and followed through d 21 (6 d after early weaning). Age-matched suckling pups served as controls. Rat pups were killed 1, 2, 3 and 6 d after early weaning and jejunal mucosa was assayed for ODC and sucrase activities, and protein and DNA contents. Jejunal cell proliferation was monitored by bromodeoxyuridine immunohistochemistry. Elevated jejunal ODC activity 1 d after early weaning was the earliest cellular event that was detected in the current study. ODC activity peaked at d 3 (about 15-fold greater than age-matched unweaned suckling controls). Sucrase activity was elevated at d 2 after weaning and peaked at d 3 (about 10-fold greater than controls). Greater bromodeoxyuridine immunostaining in early weaned rats occurred on d 3. Protein and DNA contents were greater in jejunal mucosa of early weaned rats at d 6. Serum corticosterone levels were elevated on d 1 and d 2 after early weaning compared to controls. To explore whether the intake of nonpurified diet played a role, we also compared the induction of jejunal ODC activity in early weaned pups and pups that were food-deprived for 1 d. ODC activity was not greater in the food-deprived group compared to suckling controls while the early weaned group had 6-fold greater activity 1 d after early weaning. Early weaning stimulates jejunal cell proliferation and differentiation. The temporal sequence of increased ODC activity followed by increases in other growth variables suggests that the induction of ODC activity may act as an early marker of intestinal growth during early weaning.

Radiation-induced instability and its relation to radiation carcinogenesis

Purpose: A model that identifies radiation-induced genetic instability as the earliest cellular event in the multi-step sequence leading to radiation-induced cancer was previously proposed. In this paper ongoing experiments are discussed which are designed to test this model and its predictions in mouse mammary epithelial cells. Results: Several lines of evidence are presented that appear to support this model: first, the development of delayed mutations in p53 following irradiation in altered growth variants; secondly, the high frequencies for the induction of both instability and transformation following irradiation in mammary epithelial cells; and finally, the demonstration that susceptibility to the induction of cytogenetic instability is a heritable trait that correlates with susceptibility to transformation and radiation-induced mammary cancer. Mice resistant to transformation and mammary cancer development are also resistant to the development of instability after irradiation. In contrast, mice sensitive to transformation and cancer are also sensitive to the development of cytogenetic instability. Conclusions: Data from this laboratory and from the studies cited above suggest a specific, and perhaps unique, role for radiation-induced instability as a critical early event associated with initiation of the carcinogenic process.

Orthotopic models are necessary to predict therapy of transplantable tumors in mice.

Rapid evaluation of new cytotoxic agents and biological response modifiers for therapy of cancer and elucidation of their mechanisms of action require the use of relevant animal models. It is well established that the faithful reproduction of the tumor microenvironment that allows the emergence of subpopulations of tumor cells with the biological and metastatic properties observed in clinical cancer occurs with orthotopic tumor models (transplantable and transgenic). This review summarizes the evidence that phenotypic properties of metastatic cells are governed by the expression of genes that are regulated by interaction with the relevant organ environment. While ectopic models of cancer allow rapid screening of new compounds and transgenic models afford opportunities to study early cellular and molecular events in tumor progression and metastasis, orthotopic transplantation of tumor cells remains an affordable, reproducible and reliable methodology for the study of organ-specific determinants of the biology and therapy of cancer.

Neuroendocrine Systems and Avian Sexual Differentiation

SYNOPSIS. Sexual differentiation of the endocrine and behavioral components of the avian reproductive system occurs throughout embryonic development, initiating some of the early cellular events that form the central nervous system (CNS) and culminating in the organization of male or female neuroendocrine responses. Early cellular events have been studied intensively in recent years and these developmental processes appear to involve specific growth factors in the development of certain tissues. Subsequent to cellular differentiation, primordial germ cells migrate to the appropriate anatomical location and contribute to the development of the single ovary or testes; steroidogenesis begins soon thereafter. Other portions of the hypothalamo-pituitary-gonad (HPG) axis also appear during early embryonic development with migration of the gonadotropin-releasing hormone (GnRH) neurons from the olfactory region of the CNS to the midbrain and separate formation of the pituitary gland. The gonadal steroid hormones affect development of accessory sex structures as well as the later organization of neuroendocrine regulatory systems and secondary sex characteristics. Manipulation of steroids during embryonic and early posthatch periods results in altered endocrine and behavioral responses in adult birds. There are marked species differences in the timing of these events, especially when precocial and altricial species are compared. Altricial species hatch in a less developed state and as such are more dependent on parental care. Of necessity, the precocial species must be capable of feeding and other motor capabilities at hatch and coincidentally their other physiological systems also appear to be more mature at this time. Finally, there is the separate issue of song birds versus those avian species that do not have elaborate learned songs. It appears that most of the species with elaborate neural circuitry responsible for song are altricial. This may benefit them from the standpoint of gaining more time and contact with the parents to enable them to learn the appropriate song. There are also hormonal and neuroendocrine components critical in the process of song development. Finally, the effects of environmental factors, such as endocrine disrupting chemicals take on added significance when viewed in the context of exerting permanent organizational effects which are likely to alter endocrine and behavioral components of reproduction in the adult.

Prevention of late renal changes after initial ischemia/reperfusion injury by blocking early selectin binding.

Increasing clinical evidence suggests that delayed initial function secondary to ischemia/reperfusion injury alone, and particularly in combination with early episodes of acute rejection, reduces kidney allograft survival over time. We investigated changes developing over the long term following a standardized ischemia/reperfusion insult in a Lewis rat model. The left kidney was isolated in a uninephrectomized host and cooled, and the pedicle was clamped for 45 min. Animals were followed for 48 weeks after initial renal injury. Organs were removed serially (4, 8, 16, 24, 32, 40, and 48 weeks) for immunohistology and reverse transcriptase polymerase chain reaction. Progressive proteinuria developed after 8 weeks. By immunohistology, CD4+ leukocytes and ED-1+ macrophages infiltrated the ischemic organs in parallel with up-regulation of major histocompatibility complex class II antigen expression. Because macrophages have been shown to be critical in chronic changes in other models, they were examined primarily in these studies. By reverse transcriptase polymerase chain reaction, macrophage-derived, fibrosis-inducing factors (transforming growth factor-beta, interleukin 6, and tumor necrosis factor-alpha) remained highly and constantly expressed throughout the follow-up period. The long-term influence of initial treatment with the soluble form of P-selectin glycoprotein ligand-1, a soluble ligand for P- and E-selectin, was then examined. All functional and structural changes remained at relative baseline, similar to uninephrectomized controls. These data suggest that blocking the initial selectin-mediated step after ischemia/reperfusion injury, which triggers significant early cellular and molecular events, also reduces later renal dysfunction and tissue damage over time. In part, the findings may be explained by the sparing of functioning nephron units, which if destroyed or compromised by the original insult, may contribute to long-term graft failure. This approach may be important clinically in the transplantation of kidneys from non-heart-beating or marginal donors or organs experiencing prolonged ischemic times.

Anti-idiotype monoclonal antibodies specific for the MOPC167 anti-phosphocholine transgene-encoded antibody.

Four rat x mouse hybridomas secreting monoclonal anti-idiotypic (anti-Id) antibodies (MAb) specific for the transgene-encoded antibody of the 207-4 transgenic mouse line, which carries the VH1/V kappa 24 gene segments of the IgA, phosphocholine-(PC) specific MOPC167 myeloma, were developed from a fusion of Ag8-X63.653 mouse cells with spleen cells from a rat immunized with MOPC167 and HPCM27 anti-PC antibodies. The anti-Id MAb were shown by ELISA to be specific for PC-binding proteins of VH1/V kappa 24 H and L chains of various isotypes. They did not bind VH1/V kappa 22, VH1/V kappa 8, or VH1/V kappa 1 PC-binding proteins or other IgA or IgM myeloma proteins. Analysis by flow cytometry demonstrated that these MAb bind to the transgene-encoded membrane immunoglobulin (sIgM) as expressed on > 95% of the B220 positive 207-4 spleen cells. All four MAb were able to inhibit the binding of MOPC167 to PC conjugated to bovine serum albumin. Differences in fine specificity of binding were demonstrated by differential staining of spleen cells of the 216-7 mu kappa delta Mem MOPC167 transgenic mice. In these mice endogenous H chains associate with the transgene encoded L chain to form MOPC167 crossreactive idiotopes. Two of the MAb, 28-4-3 and 28-6-20, stained significant numbers of cells, while MAb 28-5-15 did not bind to 216-7 cells. Three of the MAb, 28-5-15, 28-6-20, and 28-4-3, when conjugated to Sepharose beads, were able to induce DNA synthesis in cultures of 207-4 transgenic spleen cells. None of the MAb were able to induce an antibody response in vivo. These MAb should prove useful in staining PC-transgenic B cells for flow cytometry studies and in defining early cellular events in the activation of idiotype positive B cells by anti-Id antibodies.

Inducible expression of Egr-1-dependent genes. A paradigm of transcriptional activation in vascular endothelium.

Throughout the vascular network, endothelium forms the continuous cellular interface between the circulating blood elements and the surrounding tissues. These cells provide a nonthrombogenic surface and a permeability barrier capable of modulating blood flow and vascular reactivity. As such, the integrity of the endothelium is a fundamental requirement for the maintenance of normal homeostasis. Injury to this lining and the subsequent inflammatory response are among the earliest cellular events in the pathogenesis of atherosclerosis.1 This can result in dramatic phenotypic changes that render otherwise quiescent endothelium adhesive and prothrombotic. Lesions of atherosclerosis and postangioplasty restenosis may develop under the influence of molecules inducibly expressed or simply released by activated or injured endothelium. Several lines of evidence over the last decade, based on ligand and receptor localization, overexpression, and infusion studies, have correlated PDGF with the development of vascular occlusive lesions. PDGF appears to play a regulatory role in the migratory, rather than proliferative, events associated with the response to arterial injury. PDGF expression is quite low in the quiescent vessel wall, but levels of the growth factor increase substantially after injury. This Mini Review will focus on the transcriptional mechanisms underlying inducible PDGF expression in vascular endothelium and smooth muscle cells, with particular emphasis on the role played by the early growth response gene product, Egr-1. The vessel wall responds to a changing local environment by modulating the expression of specific sets of genes. Transcriptional activation in response to these signals involves the regulated assembly of multiprotein complexes on promoters. The promoter regions of the PDGF-A and PDGF-B genes have been characterized, and some of the regulatory sequences and transcriptional activators have been defined. In endothelial cells, 5′ deletion analysis of both promoters has determined that the minimal promoters consist of ≈100 bp.2 3 The zinc-finger transcription factor, …

Tissue Inhibitor of Metalloproteinases-1 (TIMP-1) Is Differentially Induced in Neurons and Astrocytes after Seizures: Evidence for Developmental, Immediate Early Gene, and Lesion Response

We investigated in vivo the expression of the tissue inhibitor of metalloproteinases-1 (TIMP-1) in the rat CNS after kainate (KA)-induced excitotoxic seizures. In situ hybridization revealed that TIMP-1 mRNA is induced rapidly and massively in most regions of the adult forebrain after KA treatment. Neuronal activity seems to be necessary but not sufficient to trigger TIMP-1 induction, because it is not observed in seizing 10-d-old pups, unlike what is observed in 21- and 35-d-old animals after seizures. The rapid induction of TIMP-1 is not prevented by the inhibitor of protein synthesis cycloheximide, suggesting that, after seizures, TIMP-1 is induced in neurons as an immediate early gene (IEG). The initial neuronal upregulation is followed by enhanced expression in astrocytes, as assessed by double-labeling experiments. In the hippocampus rapid increases in mRNA are followed by relatively delayed (8 hr after KA) increases in TIMP-1 immunoreactivity in the perisomatic and dendro-axonic areas, suggesting secretion of the protein. At 3 d after KA treatment, strong immunoreactivity is found in astrocytes and in the cell bodies and dendro-axonic projections of resistant neurons such as the dentate granule cells. Taken together, the results suggest that TIMP-1 may be instrumental for neurons and astrocytes in coupling early cellular events triggered by seizures with the regulation of long-lasting changes involved in tissue reorganization and/or neuroprotection.

Two peptides derived from the nerve growth factor precursor enhance cholinergic enzyme activities in vivo

LIP1, a 29-amino acid (aa) peptide, and LIP2, a 38aa peptide, corresponding to sequences within the nerve growth factor (NGF) precursor that are flanked by basic amino acid processing sites, were shown to be present in the rat intestine and to induce in PC12 cells several early cellular events, such as F-actin rearrangement and tyrosine phosphorylation of the Trk protein. In this report, we provide evidence that the two propeptides can affect cholinergic enzyme activities in vivo. Intracerebroventricular injections of LIP1 or LIP2 in neonatal hypothyroid rats significantly increased choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities in forebrain regions with an apparent regional specificity. Moreover, antibodies against LIP1 or LIP2 injected intracerebroventricularly in neonatal rats significantly decreased ChAT and AChE in the same regions of the brain. These data suggest a physiological role for the two propeptides derived from the proNGF in the development of forebrain cholinergic neurons. © 1997 Elsevier Science B.V. All rights reserved.

Interactions between Astrocytes and Oligodendroglia in Human and Experimental Creutzfeldt–Jakob Disease and Scrapie

We report here a rare interaction between reactive astrocytes and oligodendrocytes, first detected in a brain biopsy of human Creutzfeldt–Jakob disease (CJD) and then in experimental CJD in mice and in two models (263K and 22CH) of scrapie in hamsters. In human CJD brain biopsy, low-power electron microscopy revealed numerous examples of astrocytes and oligodendroglial cells in close apposition. At higher magnification, both types of cells were occasionally connected by adhesive plaque junctions (attenuated desmosomes). More complex structures were also seen. Astrocytic cytoplasm was penetrated by oligodendroglial processes or oligodendroglial cells were completely surrounded by astrocytic processes. An analogous phenomenon was identified in the brains of CJD-infected mice and in two models of scrapie-infected hamsters. In the CJD brain biopsy and in brain specimens from CJD-infected mice and scrapie-infected hamsters, GFAP-immunoreactive hypertrophic astrocytes were readily identified, particularly in those areas where the tissue damage was the most extensive. Oligodendrocytes frequently surrounded hypertrophic astrocytic processes or cell bodies and remained unstained in GFAP preparation. The significance of the interactions between astrocytes and oligodendrocytes is unclear at the present time. As in MS and other brain pathologies in which it has been studied, this interaction is not associated with a reaction toward any infectious pathogen but it may be an early cellular event that triggers further brain tissue destruction.