Detection of G-protein heterotrimers on large dense core and small synaptic vesicles of neuroendocrine and neuronal cells

Heterotrimeric G proteins, initially believed to be exclusively present in the plasma membrane, have also been found to be associated with intracellular membrane compartments. There they are involved in various membrane trafficking processes including regulated secretion (reviewed in Bomsel, M., K. Mostov, Mol. Biol. Cell 3, 1317-1328 (1992)). Vesicles of two distinct types enter the regulated secretory pathway, i.e. large dense core vesicles and small synaptic vesicles, which differ in their membrane composition and content. Little is known about an association of heterotrimeric G proteins with regulated secretory vesicles, that would explain some aspects of the role heterotrimeric G proteins have during secretion. By immunofluorescence microscopy and immunoreplica analysis, we provide the first demonstration of the presence of complete sets of heterotrimeric G proteins, consisting of alpha-, beta-, and gamma-subunits, on large dense core vesicles from bovine adrenal medulla (chromaffin granules) and small synaptic vesicles from rodent and bovine brain. Each of the two types of secretory vesicles contains beta-subunits (at least beta 1 and beta 2), as well as gamma-subunits (at least gamma 2 or gamma 3). Interestingly, they differ in their composition of alpha-subunits. On small synaptic vesicles, we found two G(o) alpha-subunits (alpha o1 and alpha o2) and two Gi alpha-subunits (alpha i1 and alpha i2). In contrast, on chromaffin granules so far only one alpha o-subunit but no alpha i-subunits could be detected. Functional properties such as transmitter storage and/or exocytotic membrane fusion may be modulated by the various G-protein subunits associated with chromaffin granules and small synaptic vesicles.

In chromaffin cells, the mammalian Sec1p homologue is a syntaxin 1A-binding protein associated with chromaffin granules

Membrane proteins of the synaptic vesicle and the presynaptic plasma membrane together with soluble proteins form a secretory fusion complex conserved from yeast to neurons (Söllner, T., Whiteheart, S. W., Brunner, M., Erdjument-Bromage, H., Geromanos, S., Tempst, P., and Rothman, J. E. (1993) Nature 362, 318-324). Two of the membrane proteins have been localized in chromaffin cells, which secrete catecholamines stored in chromaffin granules. Syntaxin 1A and 1B are found in a plasma membrane-enriched fraction, whereas synaptobrevin is concentrated on the granules. Recombinant syntaxin 1A has been used in an affinity chromatography assay to isolate syntaxin receptor proteins of the chromaffin granules. Solubilized granule membranes contain a single protein with high affinity for syntaxin 1A. Sequencing revealed partial homology with Sec1p, a hydrophilic yeast protein acting late in the secretory process. Genetic suppressor analyses predicted the interaction of Sec1p with Sso1p, a yeast homologue of syntaxin 1A, and with Sec4p, a homologue of rab3A (Aalto, M., Ronne, H., and Keränen, S. (1993) EMBO J. 12, 4095-4104). Although rab3A is present on chromaffin granules, we did not detect it bound to syntaxin 1A together with the mammalian Sec1p homologue (mSec1). The mSec1 peptide sequences are almost identical with respective sequences of a soluble protein, termed Munc-18, reported to be the only brain protein with affinity for recombinant syntaxin 1A (Hata, Y., Slaughter, C. A., and Südhof, T. C. (1993) Nature 366, 347-351). The mSec1/Munc-18 may be a receptor protein for syntaxin 1A on the transmitter vesicles mediating their interaction with the plasma membrane in docking and fusion.

IL-2 promoter-driven lacZ expression as a monitoring tool for IL-2 expression in primary T cells of transgenic mice

A transgenic mouse system has been established to follow the pattern of IL-2 expression at the level of single T cells. This was achieved by introducing a human IL-2 promoter-driven reporter gene (Escherichia coli lacZ) into the germline of mice and monitoring its product, beta-galactosidase (beta-gal), by FACS analysis. Ex vivo experiments confirmed that the regulated expression of the transgene is comparable with that of the endogenous IL-2 gene. Transgene expression is inducible by mitogens, restricted to T cells, and diminished by immunosuppressive agents, such as cyclosporin A, at concentrations known to suppress IL-2 transcription. Depending on the mitogens used, 30-50% of peripheral T cells produced IL-2 with an asynchronous induction pattern, as measured by transgenic beta-gal activity. Both helper (CD4+CD8-) and cytotoxic T cells (CD4-CD8+) respond with comparable heterogenous expression levels but they show different frequencies of beta-gal production. Transgenic beta-gal-producing T cells were detectable as early as 2 h after mitogen stimulation. These cells represent a transitional IL-2 secreting, IL-2 receptor alpha-chain negative T cell population, which occurs in the autocrine process of T cell activation. Administration of staphylococcal enterotoxin A (SEA), a bacterial superantigen, resulted in a T cell specific (Thy-1.2) increase (2.5-fold) of reporter gene expression in vivo. In summary, we could demonstrate that IL-2 promoter-driven reporter gene expression in transgenic mice is a sensitive tool to characterize IL-2 expressing cells phenotypically.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain stem chemosensitivity: its implication in central respiratory regulation

Central brain stem chemosensitivity plays an essential role in acid-base regulation. The site of the chemosensitive neuronal elements has not yet been clearly established. To address this question, we used an in vitro adult guinea pig isolated brain stem preparation, maintained in survival conditions by intrabasilar and bath perfusions of Krebs solution saturated with 95% O2 and 5% CO2. Hypercapnic stimulation, produced by modifying the CO2 concentration of the medium perfusing brain stem structures via the basilar perfusion system, increased the respiratory burst frequency recorded from the hypoglossal nerve. Hypercapnia evoked by ventral surface superfusion increased the respiratory burst amplitude. These data suggest that chemosensitive neuronal elements could be located at the ventral surface as well as in the deeper brainstem structures. However, their characteristics may be different.

Oxygen supply and respiratory-like activity in the isolated perfused brainstem of the adult guinea pig

In isolated brainstem preparations of mature guinea pigs the respiratory network remains functional only if perfused internally via the basilar artery with Krebs solution equilibrated with 95% O2/5% CO2. In order to determine the oxygen availability in this preparation, we measured tissue partial oxygen pressures at the level of respiratory-related neurons using oxygen-sensitive microelectrodes. To estimate oxygen consumption we studied the effects of ischemia and cyanide-induced blockade of oxidative metabolism in relation to the respiratory-like rhythmic activity recorded from the hypoglossal nerve. The pO2 profiles obtained from 9 stepwise measurements from the ventral to the dorsal surface decreased from 423 +/- 32 (SE) mmHg on the ventral surface to 219 +/- 64 mmHg at 1900 microns and stabilized near this value up to a depth of 5000 microns. In the superfused preparation without internal perfusion pO2 was 0 mmHg within the first 500 microns. An interruption of perfusion resulted in a rapid (less than 2 min) decrease of tissue pO2 to 0 mmHg. During the ischemic period, respiratory-like neural activity exhibited first an increase in frequency and tonic discharge, followed by a marked decrease in both parameters. Cyanide added to the perfusate caused an immediate increase of tissue pO2 and the drop of tissue pO2 associated with ischemia was abolished. We conclude that there is a considerable oxygen consumption but no hypoxic or anoxic core in the isolated perfused brainstem at the level of the respiratory-related neurons.

[D-dimer and plasminogen activator of the urokinase type: personal experiences with breast cancer]

Plasma values of d-dimer, a stable end product of plasmin-induced fibrinolysis, were ascertained in 128 female patients with mammary carcinoma. These patients demonstrated significantly increased d-dimers in comparison with the control group with benign mammary disease (p < 0.01). The sensitivity and specificity of d-dimer were slightly higher than those of the established tumour marker CA 15-3 and CEA. There was no correlation between d-dimers in the plasma and increased expression of urokinase plasminogen activator (UPA) in the tissue. Increased d-dimers in the plasma of female patients with mammary carcinoma reflect multi-factoral interactions between carcinoma growth and the haemostatic-fibrinolytic system, and may be used as tumour markers.

Manifestation of atopy is not related to patient's month of birth

The first months of life may be an important period for allergic sensitization. Several studies suggest a relationship between the month of birth (MB) and the development of skin sensitivity to aeroallergens or the manifestation of an atopic disease. In 1988 and 1989 we investigated a population of 1066 Bavarian preschool children aged 5-6 years. Skin prick tests were performed with common aeroallergens (grass pollen, birch pollen, house-dust mite, cat epithelia). The personal history of atopic disease (atopic eczema, allergic rhinitis, bronchial asthma) was recorded by a questionnaire, and the presence of overt atopic disease was documented by a personal examination. Positive prick test reactions to the above-mentioned aeroallergens were found in 15.4%, 9.2%, 12.2%, and 10.4% of the subjects, respectively; lifetime prevalence of manifest atopic disease was 22.2% for atopic eczema, 11.7% for allergic rhinitis, and 4.5% for asthma. The MB distributions of children reacting to aeroallergens or of those with atopic diseases were compared with those of subjects with corresponding negative findings. Chi-square tests were performed for each aeroallergen and each of the atopic diseases separately. No significant differences among the MB distributions were found (P > 0.3). Thus, in this coherent group, MB correlated neither to allergic sensitization nor to manifest atopic disease.

[Estimating the denominator of a sentinel practice using accounting data of the federal physicians association]

In order to interpret the regional and temporal variation in the number of cases reported for sentinel topics, rates have to be calculated which relate these figures to a common denominator. For this denominator different definitions are possible, where this paper focuses on the contact denominator, counting all contacts between the patient and the doctor in a specified period of time and a specified population (i.e. children between 2 and 3 years of age by sex for the first MORBUS topic). One patient may produce different contacts. Due to work load considerations contact denominators could not be directly recorded in sentinel practices in the MORBUS-project. A method was developed which combined minimal denominator information obtained from sentinel practices with routine (accounting) data from the doctor's associations, in order to estimate denominators with a high degree of precision. Data elements in the accounting data base include number of personal patient-doctor-contacts by type of treatment (screening/cure/emergency/referral) and insurance status (ordinary member, family member, retired) itemized list of actions that were reimbursed through the insurance company structural data about the doctor/practice (specialty, accreditation date) etc. For a first assessment of the degree of accuracy with which denominators can be estimated by such data, a pilot test was scheduled for April 1991. Doctors recorded the number of contacts with children between two and three years of age (by sex) for one week on a simple checklist. A linear model which included specialty, region, number of vouchers per quarter, number of infant health assessments and date of accreditation as predictors, was fitted to the data.(ABSTRACT TRUNCATED AT 250 WORDS)

Breathing, transcutaneous blood gases, and CO2 response in SIDS siblings and control infants during sleep

Age-related changes of 20 variables describing breathing patterns, transcutaneous blood gases, and estimated CO2 response during sleep were examined in a cross-sectional study of 30 healthy control infants and 150 healthy siblings of sudden infant death syndrome victims within the first 18 mo of life. Whole-night measurements were performed using noninvasive respiratory induction plethysmography and transcutaneous blood gas electrodes. Each candidate for the study was extensively screened and found to be healthy. Mean transcutaneous PCO2 (PtcCO2, median 40.3 Torr) and maximum PtcCO2 (median 44.8 Torr), as well as the estimated ventilatory response to inhalation of 2% CO2 in air during regular breathing, causing a 20-36% increase of ventilation per Torr PtcCO2, were not related to postnatal age. In contrast, paradoxical breathing decreased from 49.5 to 0% of total sleep time (TST), periodic breathing from 5.5 to 0% TST, and respiratory rate during regular breathing from 40 to 22 breaths/min; the portion of regular breathing increased from 32 to 55% TST and mean and minimum transcutaneous PO2 from 65.4 and 47 to 69.7 and 52 Torr with increasing stability. The largest changes occurred in the first 6 mo of life. Maximum apnea duration (9.5 s, maximum 16 s), mean apnea duration (3.74 s, breathing pauses > or = 2 s), and time spent apneic per hour of irregular breathing (199 s/h) were not related to age. The comparison of data from siblings and controls showed similarities in the above-mentioned variables. No significant differences were found among the groups. Also a comparison of 30 pairs of siblings and controls, matched for age, gender, birth, and actual body weight, did not show significant differences. The present study extends the knowledge of development of breathing control beyond the first 6 mo of life.

Two-year double-blind trial of a monomethoxy polyethylene glycol (mPEG) modified grass pollen extract at different dose levels

The aim of this study was to compare the efficacy and safety of a monomethoxypolyethylene glycol (mPEG) modified grass pollen mix allergen preparation (mPEG-gm) and a partly purified grass pollen mix allergen preparation (gm) in hyposensitization (HS), evaluating both products at two dose levels. Thirty adult patients with allergic rhinoconjunctivitis were allocated into two treatment groups based on their sensitivity to conjunctival provocation tests (CPT). Treatment was given in a double-blind manner. The starting dose was 20 BU and was approximately doubled weekly up to 20,000 BU the first year and 120,000 BU the second year. Skin testing and CPT were performed before treatment and at each dose level. All patients reached 20,000 BU the first year. Twenty-five patients continued the second year. Twenty-one of those reached 120,000 BU (9/12 on mPEG-gm and 12/13 on gm). The frequency of general side effects was reduced by about 50% with the mPEG grass mix compared with native grass mix. A significant improvement in the conjunctival sensitivity was found in both treatment groups the second year (120,000 BU) but not the first year (20,000 BU). Seventy-eight percent of the patients in the gm group and 50% in the mPEG-gm group improved by CPT (not statistically significant). The skin sensitivity was reduced after 1 year at low dose in 69% of the gm-treated patients and 33% of the mPEG treated patients. After the second year at high dose levels, the skin sensitivity decreased in all patients.(ABSTRACT TRUNCATED AT 250 WORDS)

The calcium-binding protein MRP-8 is produced by human pulmonary tumor cells

A calcium-binding protein was isolated from serum-free culture medium of human squamous carcinoma cells (HS 24). N-Terminal sequencing of the protein yielded 30 amino acids which were identical to the N-terminus of cystic fibrosis antigen. Northern blot analysis with an oligonucleotide derived from the N-terminus resulted in the detection of a transcript of approximately 600 bases. Screening of a HS 24-cDNA library with the same oligonucleotide led to the isolation of a 381-bp-cDNA encoding a protein of 93 amino acids. The corresponding protein has been identified as the calcium-binding protein MRP-8 usually found in Macrophages.

[Animal experiment model of the effect of ultraviolet irradiation on hexachlorobenzene-induced porphyria]

The Effect of UV-Irradiation on the Hexachlorobenzene-induced Porphyria in an Experimental Animal Model Hexachlorobenzene is able to induce in humans and different animal species a hepatic porphyria, which is comparable to porphyria cutanea tarda. We studied whether hexachlorobenzene feeding could induce this porphyria also in hairless rats (Rowett-Nude), as these are suitable for photobiologic studies. After development of hepatic porphyria the rats were irradiated either with UV-A or UV-B light. Biochemical effects on the porphyrin metabolism and clinical as well as histologic skin changes were examined. In the liver of the porphyric rats, UV-A and UV-B irradiation induced increased aminolevulinic acid synthase activity accompanied with augmentation of hepatic porphyrin content. UV-A or UV-B irradiation also lead to increased total porphyrin contents in the skin of porphyric compared to non-irradiated animals. Clinically and histologically, however, only UV-A irradiation induced lesions, which were comparable to skin manifestations of porphyria cutanea tarda.

Fusion of neurotransmitter vesicles with target membrane is calcium independent in a cell-free system

In adrenal chromaffin cells, stimulation of Ca2+ influx leads to the secretion of neurotransmitters. The intracellular Ca2+ target involved in the fusion of secretory vesicles with the plasma membrane (PM) is still not known. We have reconstituted this fusion in vitro by using chromaffin granules (CGs) and target membrane vesicles and a Ca2(+)-dependent phospholipase A2 (PLA2). Vesicle fusion is measured by a fluorescence dequenching assay with octadecyl rhodamine B used as the marker. CGs fuse with PM vesicles only in the presence of active PLA2. The kinetics of this fusion process depend on the amount of target PM added. Once fusion competence of PM vesicles is achieved by exposure to PLA2 (primed PM vesicles), it is conserved after removal of the PLA2 even in Ca2(+)-free buffer. The kinetics of fusion between these primed PM vesicles and CGs depend on the amount of PM and on the temperature. Further incubation of the PLA2-treated PM vesicles at 30 degrees C in the absence of calcium results in an enhanced fusion competence. During this incubation, the amount of free arachidonic acid liberated by PLA2 decreases, suggesting that during a second process arachidonic acid may be processed to the terminal fusogen. The final steps of secretion can thus be subdivided into a Ca2(+)-dependent and -independent process: first, a Ca2(+)-dependent activation of PLA2 liberating fatty acids from phospholipids and second, a Ca2(+)-independent processing to the terminal fusogen and subsequent Ca2(+)-independent fusion of the CGs with the PM.

Automated percutaneous lumbar discectomy with and without chymopapain pretreatment versus non-automated discoscopy-monitored percutaneous lumbar discectomy. An experimental study in human cadaver spines

Percutaneous lumbar discectomy has gained growing interest during recent years as an alternative to open surgery for protrusions and non-sequestrated subligamentous intervertebral disc herniations. As a less invasive method it competes with chemonucleolysis. At least two modifications are known to date: automated percutaneous lumbar discectomy (APLD) with a 2-mm suction probe and non-automated, discoscopy-monitored percutaneous lumbar discectomy with a suction rongeur and a motor-driven shaver (NAPLD). In this study these two methods are compared for the amount of material extracted, dependence upon the degree of degeneration of the disc and intrinsic technical problems, using 20 human cadaver lumbar specimens for experimental testing. Total nucleotomy was not possible with either method. APLD yielded significantly less material and proved to be less effective in severely degenerated intervertebral discs than the NAPLD procedure, as preexisting gaps within the degenerated nucleus pulposus allowed the tissue to shift away from the tip of the 2-mm probe and facilitated displacement of the probe within the anulus fibrosus. By contrast, the rongeur, which first cuts the material to be removed and then carries it away by suction, was much more effective. Further data to support the advantages of non-automated percutaneous nucleotomy are discussed. Pretreatment of the disc with chymopapain did not result in a higher yield of nucleus material when combined with APLD.

Inhibition of exocytosis by intracellularly applied antibodies against a chromaffin granule-binding protein

Exocytotic secretion requires the interaction and fusion of secretory vesicles with the plasma membrane. This process could be mediated by specific recognition molecules acting as intracellular, membrane-bound receptors and ligands. One possible component of such a recognition site on the plasma membrane is a protein of relative molecular mass (Mr) 51,000 (51K) that has been isolated from bovine adrenal chromaffin cells. This protein binds strongly to chromaffin granules, the secretory vesicles of these cells. To determine the function of this membrane-anchored chromaffin granule-binding protein in exocytosis, we tested the effect of intracellularly injected antibodies on secretion. Here we show, by two independent techniques in two different cell types, that antibodies against this protein inhibit exocytosis. In rat pheochromocytoma cell cultures, monospecific antibodies, applied by erythrocyte ghost fusion, impair the release of 3H-noradrenaline. The same antibodies, introduced into individual chromaffin cells through a patch pipette, block exocytosis, as revealed by the measurement of membrane capacitance. These results demonstrate the functional involvement in exocytosis of a plasma membrane protein with high affinity for secretory vesicles.

[Therapy of bone and joint changes in Albers-Schönberg osteopetrosis]

The history, genetic heterogenity, clinical appearance, radiologic morphology and specific pathology of Albers-Schönberg disease are described, with special reference to its orthopedic aspects, on the basis of 14 case histories. The orthopedic problems (osteomyelitis, delayed fracture and osteotomy healing, growth deviations of long bones, spinal pathology, arthrosis and fatigue fractures) are described in detail and documented. The disease is often recognized only by chance when routine X-ray examinations are performed. More serious manifestations of the disease, however, such as spontaneous osteomyelitis, fatigue fractures, coxarthrosis or gonarthrosis with or without growth aberrations, pose difficult problems of treatment. Delayed callus formation is routinely observed; this demands special osteosynthesis techniques must be constantly borne in mind during and after operative care.

Digitonin-permeabilized cells are exocytosis competent

Release of norepinephrine from PC12 cells can be stimulated by free Ca2+ in micromolar concentrations after permeabilization with 10 micrograms/ml of digitonin. This release is time and temperature dependent, half-maximal at 0.3 microM Ca2+, and, after washing out of endogenous ATP, half-maximal at about 0.5 mM MgATP when exogenously added. Similar results were obtained with bovine adrenal chromaffin cells using the same protocol. Support for the idea that the mechanism of release from both permeabilized cell types is still exocytosis is demonstrated at the electron microscopic level by immunolabeling chromaffin granule membrane antigens that were introduced into the plasma membrane following stimulation. Electron micrographs furthermore demonstrate that chromaffin granules retain typical dense cores after permeabilization, indicating that leakiness of catecholamines from the granules was not a major factor. Pores, formed by digitonin in the plasma membranes, were utilized to introduce antibodies into such exocytosis-competent cells. Anti-actin and anti-chromaffin granule membrane antibodies show a staining pattern similar to conventionally fixed and stained preparations. Our results demonstrate that pores formed by digitonin do not impair the process of exocytosis although they are big enough to allow macromolecules to pass in both directions. The digitonin-permeabilized cell is therefore an ideal in vitro system with which to study the fusion process between chromaffin granules and the plasma membrane.

Docking of chromaffin granules--a necessary step in exocytosis?

Putative docking of secretory vesicles comprising recognition of and attachment to future fusion sites in the plasma membrane has been investigated in chromaffin cells of the bovine adrenal medulla and in rat phaeochromocytoma (PC 12) cells. Upon permeabilization with digitonin, secretion can be stimulated in both cell types by increasing the free Ca2+-concentration to microM levels. Secretory activity can be elicited up to 1 hr after starting permeabilization and despite the loss of soluble cytoplasmic components indicating a stable attachment of granules to the plasma membrane awaiting the trigger for fusion. Docked granules can be observed in the electron microscope in permeabilized PC 12 cells which contain a large proportion of their granules aligned underneath the plasma membrane. The population of putatively docked granules in chromaffin cells cannot be as readily discerned due to the dispersal of granules throughout the cytoplasm. Further experiments comparing PC 12 and chromaffin cells suggest that active docking but not transport of granules can still be performed by permeabilized cells in the presence of Ca2+: a short (2 min) pulse of Ca2+ in PC 12 cells leads to the secretion of almost all releasable hormone over a 15 min observation period whereas, in chromaffin cells, with only a small proportion of granules docked, withdrawal of Ca2+ leads to an immediate halt in secretion. Transport of chromaffin granules from the Golgi to the plasma membrane docking sites seems to depend on a mechanism sensitive to permeabilization. This is shown by the difference in the amount of hormone released from the two permeabilized cell types, reflecting the contrast in the proportion of granules docked to the plasma membrane in PC 12 or chromaffin cells. Neither docking nor the docked state are influenced by cytochalasin B or colchicine. The permeabilized cell system is a valuable technique for the in vitro study of interaction between secretory vesicles and their target membrane.

Expression, secretion and processing of hirudin in E. coli using the alkaline phosphatase signal sequence

A DNA fragment coding for the E. coli phoA signal peptide was synthesized and inserted into the expression vector pKK223-3. A single HindIII restriction site is located just at the end of the signal sequence. A gene coding for the proteinase inhibitor hirudin, which has previously been synthesized, was inserted into this HindIII site. The hybrid protein was expressed under control of the tac-promoter and secreted into the periplasm of E. coli. From the periplasmic fraction two processed proteins were isolated. One of these was identical with desulfatohirudin and also had similar biological properties.

Utilization of galactose in cultured brain cells of neonatal mice

Metabolism of galactose was examined in dissociated brain cells from neonatal mice after 10-13 days in culture. Consumption of galactose at levels up to 26 mM was much less than consumption of glucose at corresponding concentrations. Lactate was consumed from the media at all galactose levels, in contrast to experiments with glucose in which lactate was formed and released into the media. Generation of CO2 from 4 mM glucose was 9-fold greater than from an equimolar level of galactose. Relatively low concentrations of glucose could reduce uptake of galactose, whereas galactose at levels up to 11.6 mM failed to inhibit consumption of glucose or formation of lactate. In glucose-deficient states, galactose supplementation of the media led to a marked increase in sulfatide synthesis by oligodendrocytes in the culture with a maximum effect at 2.3 mM. Under these conditions, [1-14C]galactose was incorporated directly into the carbohydrate portion of sulfatide, although most of the label was found in phospholipids and in the nonlipid fraction of the cellular homogenate. These data suggest that galactose is poorly metabolized by brain cells, but does not exhibit toxic effects.

Beta-bungarotoxin-induced cell-death of neurons in chick retina

The cytotoxicity of beta-bungarotoxin (beta-BTX), a snake venom neurotoxin with phospholipase A2 activity, for chick neurons was investigated using organ and monolayer cultures of retina. Beta-BTX led to a marked reduction in the total activities of choline acetyltransferase and glutamate decarboxylase of retina cultures at concentrations as low as 100 pM. The total activity of lactate dehydrogenase was, however, much less affected by beta-BTX. Also, the total activity of tyrosine hydroxylase of organ-cultured retina decreased only at 30-50 fold higher concentrations of the toxin. The total activity of the glial marker glutamine synthetase was not changed by beta-BTX. In contrast to this selectivity for neurons displayed by beta-BTX, non-neurotoxic phospholipases A2 from bee venom and porcine pancreas led to a simultaneous loss of both neuronal and glial marker enzymes. Light and electron microscopy of organ-cultured retina showed that only cells in the ganglion cell layer and the inner third of the amacrine cell layer degenerated after incubation with beta-BTX. In the toxin-sensitive cells, the Golgi apparatus and the endoplasmatic reticulum appeared the first subcellular structures to be affected. It is concluded that beta-BTX preferentially recognizes and/or destroys cholinergic and GABAergic cells in the amacrine and ganglion cell layers of the developing chick retina. This toxin may thus be a useful probe to investigate cell surface properties of cholinergic and GABAergic neurons in the chick central nervous system.

Internalization of nerve growth factor by pheochromocytoma PC12 cells: absence of transfer to the nucleus

The intracellular distribution of 125I-labeled nerve growth factor (NGF) in rat pheochromocytoma PC12 cells was studied by quantitative electron microscopic (EM) autoradiography and by subcellular fractionation. PC12 cells were grown as monolayer cultures in medium supplemented with serum in the presence of 125I-NGF. EM autoradiography showed that 125I-NGF was localized at the plasma membrane and cytoplasmic compartments but did not accumulate in the nuclear chromatin or in the nuclear membrane compartment of cells analyzed after 1 hr and 1, 2, and 8 d of incubation with 125I-NGF. 125I-NGF also was not detected in nuclear subcellular fractions prepared from cells grown in serum-supplemented medium either in suspension for 1 d or in monolayer cultures for 1 to 8 d. In contrast, and in confirmation of the results of Yankner and Shooter (Yankner, B. A., and E. M. Shooter (1979) Pro. Natl. Acad. Sci. U. S. A. 76: 1269-1273), about 60% of the cell-bound 125I-NGF was found in the nuclear pellet after cell fractionation if the cells had been kept previously in suspension for 1 d in phosphate-buffered saline supplemented with 0.2% glucose, 0.1% bovine serum albumin, and 125I-NGF. The ultrastructure of PC12 cells grown under such conditions, however, revealed signs of varying degrees of damage. Autoradiography of the nuclear pellet from these cells showed the grains to be located mainly over damaged nuclei or over cell debris between nuclei. It is concluded that NGF, after binding to specific receptors at the plasma membrane, is transferred to membrane-confined cytoplasmic compartments but does not have to be transferred further to the nuclear membrane or to the nuclear chromatin as a prerequisite for its physiological action.

Immunosympathectomy: lack of evidence for a complement-mediated cytotoxic mechanism

To determine whether the destruction of peripheral sympathetic neurons by anti-NGF-antibodies results from a complement-mediated cytotoxic action or from the deprivation of endogenous NGF or immunologically NGF-like cross-reacting molecules we investigated the time-course of the reversibility of the effect of NGF-antibodies by neutralizing doses of NGF, together with the effect of NGF-antibodies in complement-deficient mice. After administration of a single dose of 50 mg/kg of purified antibodies to newborn rats the TH level was reduced to 75% of controls after 12 h, to 48% after 24 h, 39% after 36, and 28% after 48 h. After this time no further reduction occurred and levels remained constant up to 14 days. The effect of the NGF-antibodies was reversible on addition of NGF up to 48 h after antibody administration. Although the reversibility was not complete (85% of controls) the extent of the reversibility was the same whether NGF was given 12 or 48 h after the antibodies. The incompleteness of the reversibility is reflected by the small number of degenerating neurons apparent as early as 12 h after antibody administration. Since these early degenerative effects were also seen in complement-deficient mice it is concluded that they involve a small population of neurons, sensitive to short-term NGF deprivation whereas the majority of the neurons can withstand deprivation for up to 48 h without sustaining irreversible damage.