Ligand-induced internalization of cholecystokinin receptors. Demonstration of the importance of the carboxyl terminus for ligand-induced internalization of the rat cholecystokinin type B receptor but not the type A receptor

Internalization of a variety of different heptahelical G protein-coupled receptors has been shown to be influenced by a number of different structural determinants of the receptors, including the carboxyl terminus. To investigate the role of the carboxyl terminus of cholecystokinin (CCK) receptors in receptor internalization, the rat wild type (WT) CCK-A receptor (WT CCKAR) and the rat WT CCK-B receptor (WT CCKBR) were truncated after amino acid residue 399 (CCKAR Tr399) and 408 (CCKBR Tr408), thereby deleting the carboxyl-terminal 45 and 44 residues, respectively. All WT and mutant CCK receptors were stably expressed in NIH/3T3 cells. Internalization of the CCKAR Tr399 was not significantly different from the WT CCKAR. In contrast, internalization of the CCKBR Tr408 was decreased to 26% compared with the WT CCKBR internalization of 92%. The mutation of all 10 serine and threonine residues (as potential phosphorylation sites) in the carboxyl terminus of the CCKBR to alanines (mutant CCKBR DeltaS/T) could account for the majority of this effect (39% internalization). All mutant receptors displayed similar ligand binding characteristics, G protein coupling, and signal transduction as their respective WT receptors, indicating that the carboxyl termini are not necessary for these processes. Thus, internalization of the CCKBR, unlike that of the CCKAR, depends on the carboxyl terminus of the receptor. These results suggest that, despite the high degree of homology between CCKAR and CCKBR, the structural determinants that mediate the interaction with the endocytic pathway reside in different regions of the receptors.

Fluorescent recovery after photobleaching (FRAP) of a fluorescent transferrin internalized in the late transferrin endocytic compartment of living A431 cells: theory

In previous works, other authors characterized a compartment (LCT) of A431 carcinoma cells in which markers of transferrin endocytose had accumulated during a long chase period. This compartment, was essentially formed by large stationary vacuoles. A few small vesicles budded from these vacuoles, rapidly saltated along microtubules and eventually fused with other vacuoles, causing an intracellular transport of the marker bound to the limiting membrane (M. De Brabander, R. Nuygens, H. Geerts, C.R. Hopkins, Cell. Mot. Cytoskel. 9 (1988) 30). In the present paper, we derived the fluorescence recovery after photobleaching (FRAP) of a fluorescent marker of LCT. We assumed that the rate of the intracellular transport of the marker was controlled by the fission-fusion process between vesicles and vacuoles. We showed that the concentration of a bleached fluorescent marker was a decreasing exponential function of the time elapsed from the beginning of the recovery phase. The rate constant of this exponential was equal to the product of the vesicle surface by the number of vesicles which fused with a unit of vacuole surface during one second. If a fraction of the marker spontaneously reactivated itself with a much higher rate constant of reaction than the rate constant of the transport process, the fractional FRAP of the marker was the sum of the fractional FRAP of both processes occurring separately. In a companion paper (F. Azizi, P. Wahl, Biochim. Biophys. Acta 1327 (1997) 75-88), our FRAP experiments will be described and analysed with the mathematical expressions derived in the present paper.

Fluorescence recovery after photobleaching (FRAP) of a fluorescent transferrin internalized in the late transferrin endocytic compartment of living A431 cells: experiments

In this work, we verified that transferrin fluorescently labelled with lissamine rhodamine sulfochloride (Tf-LRSC) is internalized in epidermoid A431 carcinoma cells through the specific endocytic pathway of transferrin. The FRAP of this fluorescent marker internalized in the late compartment of transferrin endocytosis (LCT) was measured in living A431 cells. These experiments showed the presence of an active intracellular transport of Tf-LRSC which can be interpreted by a mechanism involving carrier vesicles budding from stationary vacuoles, saltating along microtubules and fusing with other stationary vacuoles, according to previous video-microscopy observations of a membranous traffic dynamics in these cells, revealed by a gold complex of an Anti-Transferrin Receptor (ATR) (M. De Brabander, R. Nuygens, H. Geerst, C.R. Hopkins, Cell. Motil. Cystoskel. 9 (1988) 30). When the A431 cells were treated with nocodazole or metabolic inhibitors, there remained a residual FRAP which was ascribed to the spontaneous reactivation of the bleached molecules. According to a theoretical result obtained in the companion paper (P. Wahl, F. Azizi, Biochim. Biophys. Acta 1327 (1997) 69-74), we derived the fractional FRAP characterizing the transport process of Tf-LRSC by subtracting the fractional FRAP of the nocodazole-treated cells from the fractional FRAP of the non-treated cells. This FRAP of transport was fitted to a formula derived in that companion paper and based on the mechanism outlined above. From the time constant value determined by this fit, the number of vesicles which fused with a unit of vacuole surface was calculated to be 0.15 microm(-2) s(-1). The rate value of the fusion of vesicles with vacuoles was divided by two in cells treated by AlF4-, and increased to 20% in cells treated with Brefeldin A. These results correspond to an homotypic fusion process regulated by an heterotrimeric G-protein. Our work suggests that FRAP can be used to bring information on the transport of membrane components in living eukaryotic cells.

The preglomerular nucleus of gymnotiform fish: relay station for conveying information between telencephalon and diencephalon

The preglomerular nucleus of teleost fishes, believed to be a lateral part of the posterior tuberculum in the diencephalon, receives input from several sensory areas. By employing an in vitro technique, the pattern of connectivity between this cell group and the telencephalon has been explored through retrograde and anterograde tracing in the gymnotiform fish Apteronotus leptorhynchus. Neurons of the preglomerular nucleus project to the following telencephalic areas: central division of dorsal forebrain, dorsal subdivision of dorsolateral telencephalon, posterior subdivision of dorsolateral telencephalon, dorsal posterior telencephalon, and probably, also subdivision 2 of dorsomedial telencephalon. Experiments in which tracer application was restricted to the lateral subdivision of the preglomerular nucleus, or in which tracer substance was placed into various regions of the telencephalon revealed a differential projection pattern of cells in the lateral and the medial subdivision of the preglomerular nucleus. Neurons in the central division of the dorsal forebrain, the dorsal posterior telencephalon, and likely, also in the subdivision 2 of the dorsomedial telencephalon and the ventricular zone of the intermediate subdivision of the ventral telencephalon project back to the preglomerular nucleus. Thus, a major function of the preglomerular nucleus appears to be to act as a relay station for conveying information between diencephalon and telencephalon.

Interaction of rabbit C-reactive protein with phospholipid monolayers studied by microfluorescence film balance with an externally applied electric field

C-reactive protein (CRP) is one of the most characteristic acute-phase proteins in humans and many other animals. It binds to phosphorylcholine in a calcium-dependent manner. In addition, CRP activates the complement systems via the classical pathway. The interaction between rabbit CRP (rCRP) and model biological membrane is studied using dimyristoylphosphatidylethanolamine and dipalmitoylphosphatidylcholine monolayers. Observations with fluorescence microscopy indicate that rCRP is more likely to be incorporated in the liquid phase of monolayers. Such incorporation does not depend on the presence of calcium and is not inhibited by phosphocholine. The area occupied by the protein when incorporated into the monolayer was estimated. The dipole moment density of the protein crossing the air/water interface was measured by applying an external electric field. Our results indicate that calcium binding leads to a conformational change in CPR, which might modify the orientation of CRP in the monolayer. In addition, a negative charge or negative difference in dipole moment density facilitates the incorporation of CPR into the monolayer.

Persistent neuronal labeling by retrograde fluorescent tracers: a comparison between Fast Blue, Fluoro-Gold and various dextran conjugates

The permanence of retrograde neuronal labeling by the fluorescent tracers Fast Blue, Fluoro-Gold, Mini-Ruby, Fluoro-Ruby and Fluoro-Emerald was investigated in adult rat spinal motorneurons at 1, 4, 12 and 24 weeks after tracer application to a transected muscle nerve. After 1 week, the largest number of retrogradely labeled motoneurons was found with Mini-Ruby, Fluoro-Gold and Fluoro-Ruby, while Fluoro-Emerald yielded a smaller number of labeled cells. With increasing survival time, all of these tracers exhibited a marked decrease in the number of labeled neurons. Fast Blue also produced very efficient staining after 1 week and, in addition, the number of Fast Blue-labeled cells remained constant over the entire time period studied. Also in embryonic spinal cord tissue exposed to Fast Blue. the label persisted for at least 6 months after transplantation into adult spinal cord. Double-labeling experiments combining Fast Blue with Fluoro-Gold, Mini-Ruby, Fluoro-Ruby or Fluoro-Emerald showed that all these substances were non-toxic and that the time-related decrease in the number of neurons labeled by the latter tracers was due to degradation or leakage of the dyes. Thus, Fast Blue would be the tracer of choice for motoneuronal labeling in long-term experiments, whereas the usage of the other tracers should be restricted to experiments of limited duration.

Kinetic analysis of pairing and strand exchange catalyzed by RecA. Detection by fluorescence energy transfer

RecA is a 38-kDa protein from Escherichia coli that polymerizes on single-stranded DNA, forming a nucleoprotein filament that pairs with homologous duplex DNA and carries out strand exchange in vitro. In this study, we measured RecA-catalyzed pairing and strand exchange in solution by energy transfer between fluorescent dyes on the ends of deoxyribo-oligonucleotides. By varying the position of the dyes in separate assays, we were able to detect the pairing of single-stranded RecA filament with duplex DNA as an increase in energy transfer, and strand displacement as a decrease in energy transfer. With these assays, the kinetics of pairing and strand displacement were studied by stopped-flow spectrofluorometry. The data revealed a rapid, second order, reversible pairing step that was followed by a slower, reversible, first order strand exchange step. These data indicate that an initial unstable intermediate exists which can readily return to reactants, and that a further, rate-limiting step (or steps) is required to effect or complete strand exchange.

Simultaneous anterograde labeling of axonal layers from lateral superior olive and dorsal cochlear nucleus in the inferior colliculus of cat

The laminar organization of the central nucleus of inferior colliculus includes layers of axons that may be important in shaping the responses of neurons. Depending on their source, some layered axons are afferents that are superimposed and terminate on the same postsynaptic neurons, while other layered afferents, such as those from the ipsilateral and contralateral lateral superior olive, terminate side-by-side. The specific pattern of convergence may dictate which populations of axons are presynaptic to layered disc-shaped neurons in the central nucleus. We compared the distribution of afferent axons from the dorsal cochlear nucleus and the lateral superior olive to the contralateral inferior colliculus in the cat. Injection sites in cochlear nucleus and superior olive were physiologically characterized by extracellular recordings of single and multiple units in response to monaural and binaural acoustic stimulation. Two separate injections were made in each case, and both injection sites contained units with overlapping best frequencies. Biotinylated dextran, fluorescent dextran, 3H-leucine, and wheat germ agglutinin conjugated to horseradish peroxidase were used as anterograde tracers. The present results show that layered axons from the dorsal cochlear nucleus and lateral superior olive are superimposed in part of the contralateral central nucleus. Both projections were arranged in rostro-caudally oriented axonal layers that converged in the ventral part of the central nucleus. However, in the dorsal part of the central nucleus, the same layer of axons from the dorsal cochlear nucleus did not terminate with afferents from the lateral superior olive. Within the overlapping layers in the ventral central nucleus, the overlap of axons from the dorsal cochlear nucleus and the lateral superior olive was uniform except for small patches that were usually smaller than the dendritic fields of disc-shaped neurons. These data suggest that the layers may create specific functional zones in the central nucleus of the inferior colliculus. One zone may contain neurons with binaural responses that combine the properties of the inputs from the contralateral lateral superior olive and the dorsal cochlear nucleus. A second zone may contain inputs from the cochlear nucleus but lack those of the lateral superior olive.

Local changes in vascular architecture following partial spinal cord lesion in the rat

Lesions of the CNS induce a complex cascade of tissue reactions. The purpose of this study was to determine the response of the vasculature to partial spinal cord transection. Adult rat spinal cords were lesioned and then examined during acute, subacute, and chronic periods for the presence of endothelial cells and blood vessels at the lesion site. The association of endothelial cells and astrocytes was examined immunohistochemically (RECA-1 and glial fibrillary associated protein, respectively). During the first 48 h following an incision lesion of the dorsal spinal cord, the vasculature was significantly decreased, concurrently with the tissue loss due to primary and secondary degeneration. Subsequently, at 4 days postlesion, vasculature repair processes were evidenced by a significant increase in the number of vessels present at the lesion center. Blood vessels even formed in areas densely packed with macrophages and tissue debris. After 1 week, the number of blood vessels declined in the lesion center and at the place of the forming caverns. These results show significant initial attempts at repair of the vasculature which do not, however, lead to the restoration of a compact tissue and cannot prevent the subsequent formation of caverns.

Comparison between Sulphorhodamine-B dye staining and 51Cr-release method in cytotoxicity assay of endodontic sealers

The aim of this study was to evaluate Sulphorhodamine-B (SRB) staining against 51Cr-release in cytotoxicity tests of six endodontic sealers, namely, MU sealer (Mahidol University) ROCANAL 2, ROCANAL 3, Apexit, Endomethasone, and AH-26. Monolayers (5 x 10(5) cells/ml) of the mouse cell line Mu-mu-1 were used as test cells. Following incubation at 37 degrees C in 5% CO2 for 24 h in the presence of each sealer, cells were stained with 0.4% SRB and the absorbance at 540 nm determined as measure of cell viability. For 51Cr-release assay, cells were labelled with 51Cr before testing with sealers, and radioactivity in the supernatant was measured in a liquid scintillation counter. Both techniques indicated that Apexit was the least toxic sealer. In view of the ease of conducting SRB staining for tests of cell viability, this may be the method of choice over 51Cr-release assay in the evaluation of endodontic sealer cytotoxicity.

The responses of mammalian spinal axons to an applied DC voltage gradient

We have imposed a steady, rostrally negative, weak (ca 0.4 mV/mm) voltage gradient across transections of ascending white matter tracts in the adult guinea pig using an implanted stimulator and electrodes for about 1 month. We have evaluated the projections of these axons relative to the transection approximately 2 months postinjury by anterograde transport of injected tetramethylrhodamine-conjugated dextran and the use of an indwelling marker device which locates the plane of the original transection. Tract tracing was accomplished with conventional epifluorescence microscopy and confocal laser microscopy. Sham-treated control spinal cords contained well-filled lateral and dorsal column ascending tracts terminating caudal to the lesion which formed at the level of the hemisection. Electric field-treated spinal cords contained similarly labeled columns of axons that penetrated the lesion within the caudal segment of the spinal cord, branched within it, and in some cases such branches projected across the plane of transection. Ascending axons also passed around the lesion through undamaged parenchyma, branched repeatedly at the plane of the hemisection, and passed into the rostral segment of the spinal cord. Spear-shaped endings typical of growth cones were found at the terminals of these processes which often branched again within the rostral segment. Centrally projecting fibers, their processes, and the overall level of branching in these projections was not observed in our previous studies using high molecular weight horseradish peroxidase tracers.

Cholecystokinin-induced desensitization, receptor phosphorylation, and internalization in the CHP212 neuroblastoma cell line

Agonist stimulation of cells often results in desensitization of the response, to protect the cell from overstimulation. We have previously shown that the type A cholecystokinin (CCK) receptor on the pancreatic acinar cell and on the model CHO-CCKR cell line undergoes desensitization in response to CCK, with receptor phosphorylation and internalization playing key roles. Although these mechanisms contribute in a cell-specific manner, no analogous information exists for the CCK receptor expressed on neuronal cells, where in vivo data demonstrate a particularly sensitive response to CCK. The present study was designed to explore CCK receptor desensitization in the CHP212 neuroblastoma cell line, focusing on inositol 1,4,5-trisphosphate (IP3) responses to CCK and on recognized molecular and cellular mechanisms of desensitization. CCK promptly stimulated IP3 responses in these cells, with hormonal responsiveness rapidly and completely desensitized. Both receptor phosphorylation and internalization were observed to occur, with the former occurring most rapidly and likely being responsible for the earliest desensitization observed. Although the time course of receptor phosphorylation and dephosphorylation, and the groups of kinases involved in the neuroblastoma cell line, were most similar to those in the pancreatic cell, the movement of the agonist-bound receptor in these cells was quite different from that in the pancreatic cell and most similar to that in the CHO-CCKR cell line. This hybrid response supports the cell-specific nature of CCK receptor regulation and provides an important system to explore the molecular determinants of these processes.

Laser fragmentation of pancreatic duct stones using a rhodamine laser with an automatic stone-tissue detection system. Basic in-vitro studies

OBJECTIVES

The aim of our study was to examine the suitability of a rhodamine 6G laser with an integrated stone-tissue detection system (STDS) for fragmenting pancreatic stones.

METHODS

A total of 64 pancreatic duct stones were measured for weight, diameter, main chemical components and in some cases for their computerized tomography density. Recognition of all stones was checked with the standard STDS or a prototype version. Number of fragmentation pulses, total fragmentation energies and correlation with the individual stone parameters were determined. The quality of the tissue-detection mode was evaluated in postmortem pancreata.

RESULTS

The standard STDS detected only 45% of the pancreatic stones correctly. When using the prototype, the detection rate improved significantly up to 75% (P < 0.01). All laser pulses were cut off if tissue contact occurred. All the stones were completely disintegrated by the laser pulses. A slight correlation was found only between the required fragmentation energy and the stone weight (linear regression: R2 = 0.77); other factors had no significant impact.

CONCLUSION

The rhodamine 6G laser is suitable for the fragmentation of pancreatic stones in vitro. The integrated STDS is less effective for pancreatic stones than reported for biliary stones.

Potential and distribution of transplanted hematopoietic stem cells in a nonablated mouse model

Increasingly, allogeneic and even more often autologous bone marrow transplants are being done to correct a wide variety of diseases. In addition, autologous marrow transplants potentially provide an opportune means of delivering genes in transfected, engrafting stem cells. However, despite its widespread clinical use and promising gene therapy applications, relatively little is known about the mechanisms of engraftment in marrow transplant recipients. This is especially so in the nonablated recipient setting. Our data show that purified lineage negative rhodamine 123/Hoechst 33342 dull transplanted hematopoietic stem cells engraft into the marrow of nonablated syngeneic recipients. These cells have multilineage potential, and maintain a distinct subpopulation with "stem cell" characteristics. The data also suggests a spatial localization of stem cell "niches" to the endosteal surface, with all donor cells having a high spatial affinity to this area. However, the level of stem cell engraftment observed following a transplant of "stem cells" was significantly lower than that expected following a transplant of the same number of unseparated marrow cells from which the purified cells were derived, suggesting the existence of a "nonstem cell facilitator population," which is required in a nonablated syngeneic transplant setting.

Astrocytes and microglial cells incorporate degenerating fibers following entorhinal lesion: a light, confocal, and electron microscopical study using a phagocytosis-dependent labeling technique

Entorhinal lesion leads to anterograde degeneration of perforant path fibers in their main termination zone in the outer molecular layers of the dentate gyrus. Concomitantly, astrocytes become hypertrophic, and microglial cells alter their phenotype, suggesting participation in anterograde degeneration. This study analyzes the involvement of these lesion-induced activated glial cells in the process of phagocytosis of degenerated axonal debris. We established a phagocytosis-dependent labeling technique that allows for direct and simultaneous visualization of both labeled incorporated axonal debris and incorporating glial cells. Stereotaxic application of small crystals of the biotin- and rhodamine-conjugated dextran amine Mini Ruby (MR) into the entorhinal cortex led to strong and stable axonal staining of perforant path axons. Following entorhinal lesion, labeled terminals and fibers condensed and formed small granules. Incorporation of these rhodamine-fluorescent granules resulted in a phagocytosis-dependent cell labeling. During the first 3 days, we were able to identify these cells as microglia by using double-fluorescence and confocal microscopy. The first unequivocally double-labeled astrocytes were found 6 days post lesion (dpl). Whereas in all stages a subpopulation of microglial cells remained devoid of MR-labeled granules, all astrocytes in the middle molecular layer were double-labeled after long survival times (20 dpl). On the ultrastructural level, labeled granules appeared to be perforant path axons containing the tracer. Both terminals and myelinated fibers could be seen inside the cytoplasm of microglial cells and astrocytes. Thus, anterograde degeneration is a sufficient stimulus to induce axon incorporation by both astrocytes and a subpopulation of microglial cells.

Labeling of amoeboid microglial cells and intraventricular macrophages in fetal rats following a maternal injection of a fluorescent dye

Amoeboid microglial cells (AMC) in fetal brains were labeled by rhodamine B isothiocyanate (RhIc) when injected intravenously or intraperitoneally into mother rats at late state of pregnancy. The fluorescent cells were immunostained with antibodies OX-42 and OX-18 that recognize complement type 3 (CR3) receptors and major histocompatibility complex class I (MHC-I) surface antigen, respectively. RhIc-labeled AMC were first observed in the cavum septum pellucidum and subependymal cysts associated with the cerebral aqueduct as well as the fourth ventricle, and subsequently at other sites including the corpus callosum and other subcortical white matter. The fluorescence intensity increased with time after RhIc administration so that after 1 day the cells were brightly labeled. The majority of the labeled cells were round, with some elongated ones bearing two or three processes. Besides AMC, macrophages in the ventricular system were also labeled. All fluorescent cells were double labeled with OX-42 and OX-18 antibodies. Present results suggest that when introduced into the maternal circulation, RhIc could readily gain access into the fetal brain through the inefficient placental, blood-brain and blood-cerebrospinal-fluid (blood-CSF) barriers. The avid uptake of RhIc in circulation by brain macrophages indicates an active scavenging role of these cells in fetal brain. The labeling of cells by maternal route offers a rapid method for study of distribution of brain macrophages in fetuses.

The process and results of revolution in dental caries treatment

The traditional system devised by G.V. Black for dental caries treatment has been fundamentally changed by the development of new knowledge about dental caries pathology and chemically adhesive resin composite. The scientific background is first discussed, together with the process of the development of new materials, following which the essence of the latest clinical techniques are described and illustrated. The system of minimal tissue reduction is extremely simple and painless, not requiring anaesthesia and is able to secure maximal longevity of restored teeth. The author describes his personal record in the development of acid etched dentine and composite restoration systems.

Peroxynitrite and oxidative damage in experimental autoimmune uveitis

PURPOSE

Results of a previous study demonstrated the presence of superoxide and nitric oxide in experimental autoimmune uveitis (EAU). These two chemical entities have recently been shown to combine rapidly to form one of the most potent known biologic oxidants, peroxynitrite. As an extension of the previous study, the current study was proposed to determine whether peroxynitrite is generated in EAU and the site and extent of any oxidative damage thereby inflicted.

METHODS

Experimental uveitis was induced in Lewis rats with retinal S-antigen. The localization of peroxynitrite was carried out by immunohistochemical detection of its nitration product, nitrotyrosine, using polyclonal rabbit antinitrotyrosine antibody. The lipid peroxides in the membrane were detected by fluorescent labeling of their secondary carbonyl products with 3-hydroxy-2-naphthoic acid hydrazide. This fluorescent product was also visualized by coupling with Fast Blue B. A confocal laser scanning microscope was used for detection.

RESULTS

In EAU, the peroxynitrite plaques were observed to concentrate in the photoreceptors but were also visible in some inner retinal areas, including ganglion cell layers, nerve fiber layers, and retinal blood vessels. The lipid peroxides were localized exclusively in the photoreceptors, concentrating in the vicinity of the infiltrating phagocytes but not localized on the phagocytic cells themselves. Similar peroxide lesions in the photoreceptors were also generated by aerobically exposing the naive, open eyecups to a radical generator, 2,2'azobis(2-amidinopropane) hydrochloride.

CONCLUSIONS

In EAU, there was a substantial concentration of peroxynitrite in the photoreceptors. The presence of this oxidant appears to correlate with the pathologic oxidation demonstrated in this area. The photoreceptors are especially prone to radical-induced lipid peroxidation caused by the high concentration of docasahexaenoic acid that is contained in these structures.

Axial rotation of sliding actin filaments revealed by single-fluorophore imaging

In the actomyosin motor, myosin slides along an actin filament that has a helical structure with a pitch of approximately 72 nm. Whether myosin precisely follows this helical track is an unanswered question bearing directly on the motor mechanism. Here, axial rotation of actin filaments sliding over myosin molecules fixed on a glass surface was visualized through fluorescence polarization imaging of individual tetramethylrhodamine fluorophores sparsely bound to the filaments. The filaments underwent one revolution per sliding distance of approximately 1 microm, which is much greater than the 72 nm pitch. Thus, myosin does not "walk" on the helical array of actin protomers; rather it "runs," skipping many protomers. Possible mechanisms involving sequential interaction of myosin with successive actin protomers are ruled out at least for the preparation described here in which the actin filaments ran rather slowly compared with other in vitro systems. The result also indicates that each "kick" of myosin is primarily along the axis of the actin filament. The successful, real-time observation of the changes in the orientation of a single fluorophore opens the possibility of detecting a conformational change(s) of a single protein molecule at the moment it functions.

In situ molecular association of dystrophin with actin revealed by sensitized emission immuno-resonance energy transfer

A novel method was developed to detect molecular associations of dystrophin with actin in cryostat muscle tissue sections by combining resonance energy transfer technology with immunohistochemical techniques. This method takes advantage of the long phosphorescent lifetime of terbium chelates, a property that enables the accurate determination of energy transfer in biological tissues by lifetime measurements of sensitized emission. After a brief excitation pulse, terbium chelates emit for milliseconds after the intrinsically high autofluorescence of biological specimens has decayed to negligible levels. Rat skeletal muscle tissue sections were labeled with both anti-dystrophin monoclonal antibody conjugated to a terbium-based resonance energy transfer donor and anti-actin tetramethylrhodamine phalloidin as an acceptor. Resonance energy transfer between the two probes indicated that the distance separating the probes is within 10 nm (about the size of an IgG2b antibody molecule). The fraction of antibodies that participated in resonance energy transfer was estimated to be 80-90% because of the close agreement between the quenching of donor phosphorescence and the efficiency of resonance energy transfer revealed by lifetime measurements of sensitized emission by tetramethyl-rhodamine phalloidin. Sensitized emission was detectable only when both anti-dystrophin antibody and tetramethyl-rhodamine phalloidin were present. These results indicate that actin and dystrophin are closely associated within the cell. This method is potentially applicable to the investigation of many types of intracellular associations.

Corticospinal projection patterns following unilateral section of the cervical spinal cord in the newborn and juvenile macaque monkey

Immediately following a unilateral section of the midcervical spinal cord that interrupts the dorsolateral, lateral, and ventral columns, the macaque monkey has a severe flaccid paralysis on the side of the lesion. Recovery of hand function is rapid, and, although it is incomplete, within a few months, the monkey uses the initially disabled hand and fingers with considerable skill. We examined the accompanying changes in the pattern of projection of corticospinal neurons to the cervical spinal cord that occurred following such a lesion. Spinal section was done both in newborn and juvenile macaques, and the postlesion period was followed for up to 150 weeks. Corticospinal neuron populations were visualized by using both anterogradely and retrogradely transported labels, and their origins, spinal pathways, and terminations were examined at intervals during the period of recovery of hand function. Immediately following unilateral section of the spinal cord at C3, sampled counts of soma profiles of retrogradely labeled neurons indicated that there was a profound reduction in the corticospinal projection to the hemicord caudal to the lesion. The few labeled corticospinal axons spared by the lesion bypassed the spinal lesion by descending in the contralateral cord and then crossing the midline caudal to the lesion. A few corticospinal axons may also have bypassed the lesion in the ipsilateral ventromedial column when this was not fully interrupted by the lesion. In every monkey, we observed a similar, profound reduction in the corticospinal (and rubrospinal) projections to the hemicord caudal to the lesion: This pattern did not alter significantly over an extended recovery period. An unchanging corticospinal projection to the cervical spinal cord contralateral to the lesion was also visualized in each monkey and resembled that seen in the normal macaque. Although the resolution of the labeling and counting procedures used precluded the identification of small increases in the numbers of corticospinal neurons projecting to the hemicord caudal to the lesion, we concluded that there was no substantial reconstruction of this projection over a recovery period of more than 2 years.

Heterogeneity in the neuropeptide Y-containing neurons of the rat arcuate nucleus: GABAergic and non-GABAergic subpopulations

Neuropeptide Y, produced in the arcuate nucleus of the hypothalamus, plays a key role in the central regulation of anterior pituitary and appetitive functions. The pleiotropic nature of neuropeptide Y in these mechanisms indicates the existence of heterogeneity in the hypothalamic neuronal population producing neuropeptide Y. In this study, we report the coexistence of neuropeptide Y and the amino acid transmitter, gamma-aminobutyric acid (GABA), in neuronal perikarya of the arcuate nucleus. Fluorescent double immunolabeling for neuropeptide Y and glutamic acid decarboxylase was carried out on vibratome sections collected through the hypothalamic arcuate nuclei of animals that were pretreated with colchicine. It was found that about one third of the neuropeptide Y-producing arcuate nucleus perikarya co-expressed glutamic acid decarboxylase. This population of neuropeptide Y-containing GABAergic neurons were distributed longitudinally within the arcuate nucleus located predominantly in its dorsomedial aspects. These results show that there are at least two distinct populations of neuropeptide Y-producing neurons in the arcuate nucleus: a subset of neuropeptide Y and GABA-co-producing neurons located in the dorsomedial arcuate nucleus and a subset of non-GABAergic neuropeptide Y cells located in the ventral arcuate nucleus. This heterogeneity in the neuropeptide Y-producing perikarya of the hypothalamus may help explain adverse neuroendocrine and behavioral effects of arcuate nucleus neuropeptide Y.

Simultaneous flow cytometric measurement of phagocytotic and oxidative burst activity of polymorphonuclear leukocytes in whole bovine blood

Polymorphonuclear neutrophils (PMN) are important in host defence against bacterial infection in the bovine mammary gland and techniques are needed to evaluate their functional activities. A rapid and sensitive two-color flow cytometric method for simultaneous measurement of phagocytosis rate and oxidative burst activity of bovine PMN in small blood samples is described. The method utilizes the oxidation of intracellular dihydrorhodamine 123 to green fluorescent rhodamine 123 by oxidative burst products that were generated by incubating the PMNs with red fluorescent propidium iodide labeled Staphylococcus aureus. Phagocytosis and oxidative burst both increased with time of incubation and with increasing bacteria concentration. A 20 min phagocytosis time and a ratio of 25 bacteria to one cell were considered optimal for assaying bovine blood PMN activity. To further evaluate the proposed two-color flow cytometric method, blood samples were treated with factors known to interfere with phagocytosis and oxidative burst metabolism of human neutrophils. Incubation of whole bovine blood with cytochalasin B at 10 micrograms ml-1 resulted in an approximate 70% decrease in the phagocytosis rate with a concommitant decrease in oxidative burst activity. Staurosporine (2 micrograms ml-1) inhibited bovine neutrophil oxidative burst formation for 95% while the phagocytosis was unaffected. PMNs in whole blood samples of ten cows differed significantly in their ability to phagocytose Staphylococcus aureus and to produce reactive oxygen products. However, only a weak correlation was detected between the burst activity:phagocytosis ratio of ten individual cows as indicated by the ROD/PI index.

Identification of phagocytic glial cells after lesion-induced anterograde degeneration using double-fluorescence labeling: combination of axonal tracing and lectin or immunostaining

Retrograde and anterograde degeneration have been reported to be sufficient stimuli to activate glial cells, which, in turn, are involved in phagocytosis of degenerating material. Here we describe a double-fluorescence technique which allows for direct and simultaneous visualization of both labeled incorporated axonal debris and incorporating glial cells in the course of anterograde degeneration. Stereotaxic application of small crystals of biotinylated and tetramethylrhodamine (TRITC)-conjugated dextran amine Mini Ruby into the medial entorhinal cortex resulted in a stable rhodamine fluorescence confined to fibers and terminals in the middle molecular layer of the dentate gyrus, the stratum lacunosum-moleculare, and the crossed temporo-hippocampal pathway. Subsequent stereotaxic lesion of the entorhinal cortex induced transformation of rhodamine-fluorescent fibers and terminals into small granules. Incorporation of these granules by microglial cells [labeled by fluorescein isothiocyanate (FITC)-coupled Bandeiraea simplicifolia isolectin B4] or astrocytes (labeled by FITC-coupled glial fibrillary acidic protein antibodies) resulted in phagocytosis-dependent labeling of these non-neuronal cells, which could be identified by double-fluorescence microscopy. Electron microscopical analysis revealed that, following lesion, the tracer remained confined to entorhinal axons which were found to be incorporated by glial cells. Our data show that TRITC- and biotin-conjugated dextran amines are versatile tracers leading to Phaseolus vulgaris leucoagglutinin-like axonal staining. Lesion-induced phagocytosis of anterogradely degenerating axons by immunocytochemically identified glial cells can be directly observed by this technique on the light and electron microscopical levels.

Topographic distribution and collateral projections of the two major populations of nigrothalamic neurons. A retrograde labeling study in the rat

The principal target nuclei of nigrothalamic projections in the rat are the mediodorsal (MD) and ventromedial (VM) nuclei. The present study examined the patterns of distribution and collateral projections of the two major groups of nigrothalamic neurons, i.e., nigro-MD and nigro-VM neurons. Retrograde fluorescent labeling with Fluoro-Gold was used to examine whether the distribution areas of nigro-MD and nigro-VM neurons might be overlapped with or segregated from each other in the substantia nigra pars reticulata. A clear tendency was observed that nigro-MD neurons were distributed more ventrally than nigro-VM neurons. It was further examined by retrograde fluorescent double labeling with Fluoro-Gold and Fluoro-Ruby whether or not these nigrothalamic neurons might provide axon collaterals to the superior colliculus or the pontine reticular formation. The nigro-MD neurons were found to send axon collaterals to the superior colliculus more frequently than the nigro-VM neurons. Additionally, a small number of nigrothalamic neurons were found to send axon collaterals to the pontine reticular formation. The functional significance of the two major populations of nigrothalamic neurons was discussed on the basis of their collateral projections to the superior colliculus or the pontine reticular formation.