[Modification by wheat germ agglutinin delays the ocular elimination of liposome]

The purpose of this study is to explore the feasibility of wheat germ agglutinin (WGA) modified liposome as a vehicle for ophthalmic administration. Liposome loaded with 5-carboxyfluorescein (FAM) was prepared by lipid film hydration method. WGA was thiolated and then conjugated to the surface of the liposome via polyethylene glycol linker to constitute the WGA-modified and FAM-loaded liposome (WGA-LS/FAM). The amount of thiol groups on each WGA molecule was determined, and the bioactivity of WGA was estimated after it was modified to the surface of liposome. The physical and chemical features of the WGA-modified liposome were characterized and the ocular bioadhesive performance was evaluated in rats. The result showed that each thiolated WGA molecule was conjugated with 1.32 thiol groups. WGA-LS/FAM had a mean size of (97.40 +/- 1.39) nm, with a polydispersity index of 0.23 +/- 0.01. The entrapment efficacy of FAM was about (2.95 +/- 0.21)%, and only 4% of FAM leaked out of the liposome in 24 h. Erythrocyte agglutination test indicated that after modification WGA preserved the binding activity to glycoprotein. The in vivo ocular elimination of WGA-LS/FAM fitted first-order kinetics, and the elimination rate was significantly slower than that of the unmodified liposome, demonstrating WGA-modified liposome is bioadhesive and suitable for ophthalmic administration.

Sources of calretinin inputs to motoneurons of extraocular muscles involved in upgaze

Recent monkey studies showed that motoneurons of the oculomotor nucleus involved in upward eye movements receive a selective input from afferents containing calretinin (CR). Here, we investigated the sources of these CR-positive afferents. After injections of tract-tracers into the oculomotor nucleus (nIII) of two monkeys, the retrograde labeling was combined with CR-immunofluorescence in frozen brainstem sections. Three sources of CR inputs to nIII were found: the rostral interstitial nucleus of the medial longitudinal fascicle (RIMLF), the interstitial nucleus of Cajal, and the y-group. CR is not present in all premotor upward-moving pathways. The excitatory secondary vestibulo-ocular neurons in the magnocellular part of the medial vestibular nuclei contained nonphosphorylated neurofilaments, but no CR, and they received a strong supply of large CR-positive boutons. In conclusion, the present study presents evidence that only specific premotor pathways for upward eye movements--excitatory upgaze pathways--contain CR, but not the up vestibulo-ocular reflex pathways. This property may help to differentiate between premotor up- and downgaze pathways in correlative clinico-anatomical studies in humans.

Wheat germ agglutinin enhanced cerebral uptake of anti-Aβ antibody after intranasal administration in 5XFAD mice

Alzheimer's disease (AD) is the 6th leading cause of death in United States afflicting >5 million Americans. This number is estimated to triple by the middle of the century if effective treatments are not discovered. Current therapy for AD is mainly symptomatic. Effective disease-modifying treatments are needed that would eliminate the cause rather than the symptoms of the disease. Polymerization of monomeric beta-amyloid peptide (Aβ) into dimers, soluble oligomers and insoluble fibrils is considered the prime causative factor in triggering AD pathogenesis. Based on these facts, removal/reduction of Aβ has gained importance as a primary therapeutic target in treating the cause of the disease. In that regard, passive immunotherapy with direct delivery of anti-Aβ antibodies to the brain has shown great promise, but awaits the challenge of overcoming greater influx of anti-Aβ antibody into the brain. This investigation was undertaken to maximize direct delivery of immunotherapeutics to the brain by using wheat germ agglutinin (WGA) as a novel axonal transporter-carrier to be conjugated with anti-Aβ antibody (6E10) raised against EFRHDS 3-8 amino acid (aa) epitopes of Aβ known to react with 1-16 aa residues of mono-/di-/oligomeric Aβ. This is the first report showing the use of WGA as an efficient axonal transporter carrier that not only enhanced the influx of anti-Aβ antibody directly into the brain but also resulted in greater reduction of cerebral Aβ compared to the unconjugated anti-Aβ antibody delivered intranasally in Alzheimer's 5XFAD model.

Tri-partite complex for axonal transport drug delivery achieves pharmacological effect

BACKGROUND

Targeted delivery of pharmaceutical agents into selected populations of CNS (Central Nervous System) neurons is an extremely compelling goal. Currently, systemic methods are generally used for delivery of pain medications, anti-virals for treatment of dermatomal infections, anti-spasmodics, and neuroprotectants. Systemic side effects or undesirable effects on parts of the CNS that are not involved in the pathology limit efficacy and limit clinical utility for many classes of pharmaceuticals. Axonal transport from the periphery offers a possible selective route, but there has been little progress towards design of agents that can accomplish targeted delivery via this intraneural route. To achieve this goal, we developed a tripartite molecular construction concept involving an axonal transport facilitator molecule, a polymer linker, and a large number of drug molecules conjugated to the linker, then sought to evaluate its neurobiology and pharmacological behavior.

RESULTS

We developed chemical synthesis methodologies for assembling these tripartite complexes using a variety of axonal transport facilitators including nerve growth factor, wheat germ agglutinin, and synthetic facilitators derived from phage display work. Loading of up to 100 drug molecules per complex was achieved. Conjugation methods were used that allowed the drugs to be released in active form inside the cell body after transport. Intramuscular and intradermal injection proved effective for introducing pharmacologically effective doses into selected populations of CNS neurons. Pharmacological efficacy with gabapentin in a paw withdrawal latency model revealed a ten fold increase in half life and a 300 fold decrease in necessary dose relative to systemic administration for gabapentin when the drug was delivered by axonal transport using the tripartite vehicle.

CONCLUSION

Specific targeting of selected subpopulations of CNS neurons for drug delivery by axonal transport holds great promise. The data shown here provide a basic framework for the intraneural pharmacology of this tripartite complex. The pharmacologically efficacious drug delivery demonstrated here verify the fundamental feasibility of using axonal transport for targeted drug delivery.

Lectin-conjugated PLGA nanoparticles loaded with thymopentin: Ex vivo bioadhesion and in vivo biodistribution

The conjugation of lectins onto PLGA nanoparticles has been demonstrated to effectively improve the intestinal absorption of thymopentin. In this study, thymopentin-loaded nanoparticles made from fluorescein isothiocyanate labeled PLGA were modified with wheat germ agglutinin (WGA). The specific bioadhesion of nanoparticles on rat intestinal mucosa was studied ex vivo. An important increase of interaction between WGA-conjugated nanoparticles and the intestinal segments was observed compared with that of the unconjugated one (p<0.05). Fluorescence photomicrographs confirmed the bioadhesion of WGA-conjugated nanoparticles on intestinal villous epithelium as well as Peyer's patches. Biodistribution of nanoparticles was evaluated using tissues obtained from rats, to which nanoparticles were orally administered. The highest amount of WGA-conjugated nanoparticles was detected in small intestine, suggesting an increase of intestinal bioadhesion and endocytosis. The systemic uptake was as high as 6.48-13.4% of dose at 1 day and 7.32-15.26% at 7 days, which representing an increase of almost 1.4-3.1 fold across the intestine compared to <4.9% of the unconjugated one. The enhanced uptake was related to the increasing of WGA density on nanoparticles. These results further revealed the promising potential of lectin-conjugated nanoparticles on the improvement of intestinal bioadhesion and absorption for oral drug delivery.

Brain delivery of vasoactive intestinal peptide enhanced with the nanoparticles conjugated with wheat germ agglutinin following intranasal administration

The development of biotech drugs such as peptides and proteins that act in the central nervous system has been significantly impeded by the difficulty of delivering them across the blood-brain barrier. The surface engineering of nanoparticles with lectins opened a novel pathway to the absorption of drugs loaded by biodegradable poly (ethylene glycol)-poly (lactic acid) nanoparticles in the brain following intranasal administration. In the present study, vasoactive intestinal peptide, a neuroprotective peptide, was efficiently incorporated into the poly (ethylene glycol)-poly (lactic acid) nanoparticles modified with wheat germ agglutinin and the biodistribution, brain uptake and neuroprotective effect of the formulation were assessed. The area under the concentration-time curve of intact 125I-vasoactive intestinal peptide in brain of mice following the intranasal administration of 125I-vasoactive intestinal peptide carried by nanoparticles and wheat germ agglutinin-conjugated ones was significantly enlarged by 3.5 approximately 4.7 folds and 5.6 approximately 7.7 folds, respectively, compared with that after intranasal application of 125I-vasoactive intestinal peptide solution. The same improvements in spatial memory in ethylcholine aziridium-treated rats were observed following intranasal administration of 25 microg/kg and 12.5 microg/kg of vasoactive intestinal peptide loaded by unmodified nanoparticles and wheat germ agglutinin-modified nanoparticles, respectively. Distribution profiles of wheat germ agglutinin-conjugated nanoparticles in the nasal cavity presented their higher affinity to the olfactory mucosa than to the respiratory one. Inhibition experiment with specific sugars suggested that the interaction between the nasal mucosa and the wheat germ agglutinin-functionalized nanoparticles were due to the immobilization of carbohydrate-binding pockets on the surface of the nanoparticles. The results clearly indicated wheat germ agglutinin-modified nanoparticles might serve as promising carriers especially for biotech drugs such as peptides and proteins.

Lectin-conjugated PEG–PLA nanoparticles: Preparation and brain delivery after intranasal administration

In order to improve the absorption of nanoparticles in the brain following nasal administration, a novel protocol to conjugate biorecognitive ligands-lectins to the surface of poly (ethylene glycol)-poly (lactic acid) (PEG-PLA) nanoparticles was established in the study. Wheat germ agglutinin (WGA), specifically binding to N-acetyl-D-glucosamine and sialic acid, both of which were abundantly observed in the nasal cavity, was selected as a model lectin. The WGA-conjugated nanoparticles were prepared by incorporating maleimide in the PLA-PEG molecular and taking advantage of its thiol group binding reactivity to conjugate with 2-iminothialane thiolated WGA. Coupling of WGA with the PEG-PLA nanoparticles was confirmed by the existence of gold-labeled WGA-NP under TEM. The retention of biorecognitive activity of WGA after the covalent coupling procedure was confirmed by haemagglutination test. The resulting nanoparticles presented negligible nasal ciliatoxicity and the brain uptake of a fluorescent marker-coumarin carried by WGA functionized nanoparticles was about 2 folds in different brain tissues compared with that of coumarin incorporated in the unmodified ones. Thus, the technique offered a novel effective noninvasive system for brain drug delivery, especially for brain protein and gene delivery.

Differential uptake of molecules from the circulation and CSF reveals regional and cellular specialisation in CNS detection of homeostatic signals

The uptake of hydroxystilbamidine (OHSt, FluoroGold equivalent) and wheat germ agglutinin (WGA), into the hypothalamus, two hours after injections into either the circulation or the cerebrospinal fluid, were compared in adult rats. Following intravenous injection, OHSt was found in astrocytes of the median eminence and medial part of the arcuate nucleus whereas WGA intensely labelled the blood vessels and ependymal cells throughout the hypothalamus. In complete contrast, intracerebroventricular (icv) injection into the lateral ventricle resulted in OHSt uptake by ependymocytes and astrocytes in the area adjacent to the third ventricle, with virtually no uptake in regions taking up this dye following systematic injections, i.e., the median eminence and medial arcuate. Following icv injection WGA labelling was intense in all parts of the ependymal layer of the third ventricle, including the alpha- and beta-tanycytes. Injections into the cisterna magna gave a different pattern of uptake with OHSt being found only in astrocytes in the ventral part of the hypothalamus lateral to the arcuate nucleus whilst WGA uptake was virtually absent. This highlights the regional and cellular specialisation for uptake of molecules from the circulation and CSF. The median eminence and medial arcuate take up molecules from the circulation, with different cell types taking up different molecules. As the CSF flows through the ventricular system, different cells lining the ventricular and subarachnoid spaces take up molecules differentially. Molecules in the CSF appear to be excluded from the median eminence and medial arcuate region.

Apical endocytosis in outer hair cells of the mammalian cochlea

Outer hair cells (OHCs), the sensory-motor cells of the mammalian cochlea, contain an endocytic tubulovesicular compartment below their apical stereocilia. We have used two-photon imaging of FM1-43 in the intact epithelium to show that these cells take up membrane in a Ca(2+)-dependent manner from a distinct apical site. The uptake rate was 0.8 microm(2)/s and internalized membrane was trafficked rapidly to a compartment along the lateral wall and distinct intracellular compartments. Double labelling with FM1-43 and DiOC(6), an endoplasmic reticulum (ER) marker, showed that these compartments are part of the tubulovesicular endoplasmic reticulum of OHCs. Labelling with a lysosomal marker showed that OHC lysosomes are restricted to the apex. Using the protein marker wheat germ agglutinin (WGA-FITC) we demonstrate that apical protein internalization and trafficking is about eight times slower than membrane internalization. Using double labelling with FM1-43 and WGA-FITC, we show that membrane and protein internalization are apically colocalized but that patterns of protein and membrane traffic differ. Protein was targeted only to the most apical third of the lateral wall. In control conditions, OHCs displayed only weak WGA-FITC surface labelling at the site of endocytosis. Lowering the rate of apical endocytosis increased this surface signal. The results suggest that OHCs endocytose membrane and membrane proteins with a high turnover rate and that these cells may use apical endocytosis to sort proteins via an indirect pathway to the lateral membrane.

Preparation, characterization and application of artificial Caco-2 cell surfaces in the silver nanoparticle enhanced fluorescence technique

To approach in vivo conditions during real time monitoring of biorecognitive interactions, biomimetic surfaces were prepared by fusion of purified plasma membrane fractions from Caco-2 cells with self-assembled monolayers attached to silver colloid coated standard microplates. Proper orientation and integrity of the membrane coating was confirmed by binding of fluorescein-labelled wheat germ agglutinin (F-WGA) which interacts with certain carbohydrates of the glycocalyx. Additionally, the competition with the complementary carbohydrate decreased the F-WGA binding to 15%. The assay setup offers information about the real time binding kinetics and the affinity of the interaction with the cell membrane excluding interfering events such as internalization and metabolism. As exemplified by F-WGA-binding, the mean velocity of the interaction is 627.07 mFU/s and the working range is 40-240 nM with a detection limit of 1.6 pmol F-WGA. The storage stability of the ready-to-use plates exceeded at least 1 month. The real time monitoring of lectin-prodrug binding to the biomimetic membranes revealed that high conjugation numbers reduces the affinity. The assays are simple and fast one-step reactions without any washing steps as this new technique discriminates between membrane bound and bulk fluorescence. Thus, biomimetic membranes on silver colloid layers represent a versatile tool for high throughput screening at early stages of drug discovery and development.

Lectin-mediated drug delivery: discrimination between cytoadhesion and cytoinvasion and evidence for lysosomal accumulation of wheat germ agglutinin in the Caco-2 model

Lectin-mediated drug delivery may become a promising strategy to improve the efficacy of poorly permeable drugs by utilising active high-capacity transport pathways of epithelial tissues. This requires the elucidation of the basic mechanisms of lectin uptake prior to their practical use. We studied the interaction between the dietary lectin wheat germ agglutinin (WGA) and Caco-2 cells (single cells and monolayers) by a newly established assay design that is able to discriminate between cellular binding and uptake as well as by confocal microscopy: (i) All binding sites available for WGA at the cell membrane were occupied within 10 min of incubation. (ii) Cytoadhesion was followed by immediate uptake. After 20 min, 60% (single cells) or 30% (monolayers) of the membrane bound lectin were internalised. However, regardless of cell arrangement, 80% of the surface bound lectin was taken up into the cells during the course of the experiment. (iii) About 50% of the internalised lectin accumulated within the lysosomes after 1 h. This was confirmed by assays in the presence of monensin, an inhibitor of endosomal acidification, and by colocalisation with lysosomal cathepsin followed by semiquantitative image analysis. Further analysis by immunocytochemistry suggested that the trans-Golgi complex and the caveoli were not involved. Due to cytoadhesion, cytoinvasion and partial lysosomal accumulation, WGA-mediated drug delivery may provide for improved intracellular availability of conjugated drugs or colloidal carrier systems.

Lectin-mediated drug delivery: influence of mucin on cytoadhesion of plant lectins in vitro

As the mucous layer represents the first barrier to peroral lectin-mediated drug delivery, the influence of mucin on the cytoadhesive properties of lectins was studied in vitro by establishing a rapid and simple microplate format assay using pig gastric mucin (PGM) for coating the wells. The lectin-binding capacity of mucin followed the order WGA>>UEA-I>>LCA=STL>PNA>DBA. The PGM-binding of wheat germ agglutinin (WGA) was strongly dependent on pH being highest at pH 5.0. In comparison, PGM-binding of WGA was about 15% at gastric pH and 60-70% at intestinal pH. This points to unimpeded gastric transit of WGA-grafted formulations and favorable conditions within the intestine for binding to mucus coated enterocytes. Moreover the WGA-PGM interaction was concentration-dependent, specific and fully reversible. According to a competitive assay in the presence of Caco-2 monolayers, the PGM-binding of WGA was saturated and influenced by the lectin-concentration yielding 28% Caco-2 bound WGA (125 ng WGA/0.29 cm(2) monolayer) and 68% Caco-2 bound WGA (4 microg WGA/0.29 cm(2) monolayer), respectively. Following on from these results, lectins are expected to suffer at least partially from premature inactivation by shed off mucus like bioadhesives of the first generation, however initial but reversible mucus-binding of lectins offers partititioning to the cell membrane followed by uptake into the enterocyte.

Medullary neurones regulate hypothalamic corticotropin-releasing factor cell responses to an emotional stressor

Hypothalamic-pituitary-adrenal axis activation is a hallmark of the stress response. In the case of physical stressors, there is considerable evidence that medullary catecholamine neurones are critical to the activation of the paraventricular nucleus corticotropin-releasing factor cells that constitute the apex of the hypothalamic-pituitary-adrenal axis. In contrast, it has been thought that hypothalamic-pituitary-adrenal axis responses to emotional stressors do not involve brainstem neurones. To investigate this issue we have mapped patterns of restraint-induced neuronal c-fos expression in intact animals and in animals prepared with either paraventricular nucleus-directed injections of a retrograde tracer, lesions of paraventricular nucleus catecholamine terminals, or lesions of the medulla corresponding to the A1 or A2 noradrenergic cell groups. Restraint-induced patterns of neuronal activation within the medulla of intact animals were very similar to those previously reported in response to physical stressors, including the fact that most stressor-responsive, paraventricular nucleus-projecting cells were certainly catecholaminergic and probably noradrenergic. Despite this, the destruction of paraventricular nucleus catecholamine terminals with 6-hydroxydopamine did not alter corticotropin-releasing factor cell responses to restraint. However, animals with ibotenic acid lesions encompassing either the A1 or A2 noradrenergic cell groups displayed significantly suppressed corticotropin-releasing factor cell responses to restraint. Notably, these medullary lesions also suppressed neuronal responses in the medial amygdala, an area that is now considered critical to hypothalamic-pituitary-adrenal axis responses to emotional stressors and that is also known to display a significant increase in noradrenaline turnover during restraint. We conclude that medullary neurones influence corticotropin-releasing factor cell responses to emotional stressors via a multisynaptic pathway that may involve a noradrenergic input to the medial amygdala. These results overturn the idea that hypothalamic-pituitary-adrenal axis response to emotional stressors can occur independently of the brainstem.

Motoneurons of twitch and nontwitch extraocular muscle fibers in the abducens, trochlear, and oculomotor nuclei of monkeys

Eye muscle fibers can be divided into two categories: nontwitch, multiply innervated muscle fibers (MIFs), and twitch, singly innervated muscle fibers (SIFs). We investigated the location of motoneurons supplying SIFs and MIFs in the six extraocular muscles of monkeys. Injections of retrograde tracers into eye muscles were placed either centrally, within the central SIF endplate zone; in an intermediate zone, outside the SIF endplate zone, targeting MIF endplates along the length of muscle fiber; or distally, into the myotendinous junction containing palisade endings. Central injections labeled large motoneurons within the abducens, trochlear or oculomotor nucleus, and smaller motoneurons lying mainly around the periphery of the motor nuclei. Intermediate injections labeled some large motoneurons within the motor nuclei but also labeled many peripheral motoneurons. Distal injections labeled small and medium-large peripheral neurons strongly and almost exclusively. The peripheral neurons labeled from the lateral rectus muscle surround the medial half of the abducens nucleus: from superior oblique, they form a cap over the dorsal trochlear nucleus; from inferior oblique and superior rectus, they are scattered bilaterally around the midline, between the oculomotor nucleus; from both medial and inferior rectus, they lie mainly in the C-group, on the dorsomedial border of oculomotor nucleus. In the medial rectus distal injections, a "C-group extension" extended up to the Edinger-Westphal nucleus and labeled dendrites within the supraoculomotor area. We conclude that large motoneurons within the motor nuclei innervate twitch fibers, whereas smaller motoneurons around the periphery innervate nontwitch, MIF fibers. The peripheral subgroups also contain medium-large neurons which may be associated with the palisade endings of global MIFs. The role of MIFs in eye movements is unclear, but the concept of a final common pathway must now be reconsidered.

Cholesterol depletion by methyl-beta-cyclodextrin blocks cholera toxin transport from endosomes to the Golgi apparatus in hippocampal neurons

We recently demonstrated that although cholera toxin (CT) is found in detergent-insoluble domains/rafts at the cell surface of cultured hippocampal neurons, it is internalized via a raft-independent mechanism. Thus, cholesterol depletion by methyl-beta-cyclodextrin (MbetaCD) did not affect the rate of CT internalization from the plasma membrane, but did affect the rate of CT degradation, which occurs in lysosomes. In the current study, we analyze which step of CT intracellular transport is inhibited by MbetaCD. Whereas pre-incubation with MbetaCD completely blocked CT degradation, it had no effect on the degradation of wheat germ agglutinin (WGA) or bovine serum albumin (BSA), which are internalized by receptor-mediated and fluid phase endocytosis, respectively. Brefeldin A also completely blocked CT degradation but had no effect on WGA or BSA degradation. In contrast, MbetaCD did not affect CT degradation, or CT-mediated cAMP generation, when added to neurons after CT had been transported to the Golgi apparatus. We conclude that CT transport from endosomes to the Golgi apparatus is cholesterol-dependent, whereas CT transport from the Golgi apparatus to lysosomes is cholesterol-independent.

Fluid phase and receptor-mediated endocytosis in Paramecium primaurelia by fluorescence confocal laser scanning microscopy

In ciliated protozoa, most nutrients are internalized via phagocytosis by food vacuole formation at the posterior end of the buccal cavity. The uptake of small-sized molecules and external fluid through the plasma membrane is a localized process. That is because most of the cell surface is internally covered by an alveolar system and a fibrous epiplasm, so that only defined areas of the cell surface are potential substance uptake sites. The purpose of this study is to analyze, by fluorescence confocal laser scanning microscopy, the relationship between WGA (Triticum vulgaris agglutinin) and dextran internalization in Paramecium primaurelia cells blocked in the phagocytic process, so that markers could not be internalized via food vacuole formation. WGA, which binds to surface constituents of fixed and living cells, was used as a marker for membrane transport and dextran as a marker for fluid phase endocytosis. After 3 min incubation, WGA-FITC is found on plasma membrane and cilia, and successively within small cytoplasmic vesicles. After a 10-15 min chase in unlabeled medium, the marked vesicles decrease in number, increase in size and fuse with food vacuoles. This fusion was evidenced by labeling food vacuoles with BSA-Texas red. Dextran enters the cell via endocytic vesicles which first localize in the cortical region, under the plasma membrane, and then migrate in the cytoplasm and fuse with other endocytic vesicles and food vacuoles. When cells are fed with WGA-FITC and dextran-Texas red at the same time, two differently labeled vesicle populations are found. Cytosol acidification and incubation in sucrose medium or in chlorpromazine showed that WGA is internalized via clathrin vesicles, whereas fluid phase endocytosis is a clathrin-independent process.

TrkB dimerization during development of the prefrontal cortex of the macaque

To date, two subtypes of TrkB, a BDNF receptor, have been described. One is full-length TrkB (TK+), which has a tyrosine kinase-containing intracellular domain. The other is truncated TrkB (TK-), which has a short intracellular domain lacking the tyrosine kinase. In this study, we investigated the dimerization of TrkB subtypes in the developing monkey prefrontal cortex by means of cross-linking. At embryonic day 120, the TK+/TK+ and the 100 kDa/100 kDa homodimers were observed with BDNF stimulation. At the newborn stage, the TK+/TK+ and the TK-/TK- homodimers were observed with BDNF stimulation. At the adult stage, the TK-/TK- homodimer and the TK+/TK- heterodimer were formed by BDNF stimulation. The levels of all dimers increased in proportion to the concentration of BDNF. Moreover, the dimers were clearly formed within 5 min of treatment with BDNF. BDNF and NT-4/5 induced the dimers, whereas NT-3 formed slight dimers but NGF did not. Furthermore, anti-BDNF antibody inhibited the TrkB dimerization. Moreover, the intercellular binding proteins of TrkB were not cross-linked by BS3. Therefore, these results suggest that the change in dimerization among TrkB subtypes occurs during development of the monkey prefrontal cortex.

The interaction between wheat germ agglutinin and other plant lectins with prostate cancer cells Du-145

The bioadhesive properties of fluorescein-labeled plant lectins with different carbohydrate specificities were investigated by flow cytometry at 4 and 37 degrees C using Du-145 prostate cancer cells. At both temperatures the lectin association rate increased following the order: Dolichos biflorus agglutinin (DBA)<peanut agglutinin<Ulex europaeus isoagglutinin I<Lens culinaris agglutinin<Solanum tuberosum lectin << wheat germ agglutinin (WGA), reflecting the glycosylation pattern of Du-145 cells. Both, the BSA-binding capacity of the cells referring to nonspecific binding and inhibition studies using the complementary carbohydrate, assured specificity of the lectin-cell interactions except for DBA. The WGA-association rate of Du-145 cells was dependent on temperature indicative for cellular uptake of membrane-bound WGA. Intracellular enrichment of WGA was confirmed by confocal microscopy. As resulted from experiments in presence of ouabain active transport mechanisms were involved in cellular uptake of WGA. Equilibration of the intracellular pH with monensin pointed to accumulation of intracellular located WGA within acidic compartments of Du-145 cells such as the lysosomes or the trans-Golgi complex. Consequently the interaction of WGA with Du-145 cells at 37 degrees C is a one way process due to immediate active transport of membrane-bound lectin into acidic compartments of prostate cancer cells.

The influence of a colonic microbiota on HPMA copolymer lectin conjugates binding in rodent intestine

Germ-free (GF) animals lack a colonic microflora like that seen in conventional (CV) animals. Bacterial presence plays a role in the development of glycoproteins in the gastrointestinal (GI) tract; the absence of a microbiota has been seen to suppress the production of certain glycoproteins and glycolipids. Binding patterns of lectins are modified when glycoprotein structures are altered (e.g., during development or disease). Little information on lectin binding patterns in mature GF animals is available. We examined the binding of free and N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-conjugated fluorescein isothiocyanate (FITC)-labeled wheat germ agglutinin (WGA) [P(HPMA)-(WGA-FITC)] and FITC-labeled peanut agglutinin (PNA) [P(HPMA)-(PNA-FITC)] in CV and GF mouse colon with and without neuraminidase pretreatment. Anti-Thomsen-Friedenreich (TF) antigen (a development and disease-related glycoprotein) antibody binding was also examined in these tissues. Subtle differences were seen in the binding patterns between CV and GF animals. CV animals showed strong P(HPMA)-(WGA-FITC) binding in goblet cells, but minimal P(HPMA)-(PNA-FITC) binding was visible. In GF animals, luminal surface binding of P(HPMA)-(WGA-FITC) was visible, and goblet cell binding of P(HPMA)-(PNA-FITC) was seen. These subtle changes suggest that altered glycoprotein expression occurred under GF conditions.

Lectin-mediated bioadhesion: preparation, stability and caco-2 binding of wheat germ agglutinin-functionalized Poly(D,L-lactic-co-glycolic acid)-microspheres

To take advantage of the cytoadhesive characteristics of Wheat germ agglutinin (WGA) for improved particulate drug delivery, the interaction between WGA-grafted poly(D,L-lactic-co-glycolic acid)-microspheres and Caco-2 monolayers was investigated using bovine serum albumin (BSA) or glycine coated microspheres as a control. Covalent immobilization of WGA by the carbodiimide/N-hydroxysuccinimide-method on 4 microm microspheres yielded a surface density of 9.67+/-1.21x10(6) molecules/particle, whereas 0.22+/-0.04x10(6) WGA-molecules were bound by physical adsorption. After storage for 21 days in HEPES-buffer and treatment of the particles with 5 M urea, 86% of covalently linked lectin was still attached to the particles. At 4 degrees C the Caco-2 binding rate of both, WGA- and BSA-modified particles increased with addition of increasing numbers of particles until saturation was reached at 38150+/-1740 (WGA) or 12066+/-1195 (BSA) microspheres bound/mm(2) Caco-2 monolayer. Inhibition of Caco-2 binding of WGA-functionalized microspheres by chitotriose indicated for specificity of the interaction. As observed by confocal laser scanning microscopy, the fluorescein-loading of the particles was accumulated intracellularly after incubation of Caco-2 monolayers with WGA-modified microspheres contrary to glycine-grafted microspheres. Additionally, in case of WGA-functionalized microspheres the amount of cell associated fluorescein was 200-fold higher than that of the free solution. In conclusion, WGA-modified microspheres are expected to enhance intestinal transport of incorporated drugs due to cytoadhesion provided by the lectin coating.

Lectin-mediated transport of nanoparticles across Caco-2 and OK cells

Recent experiments by a number of workers have suggested that it may be possible to use various targeting molecules, which bind to the intestinal epithelium, to promote the uptake and transport of nanoparticles from the intestine to the circulation. We have used commercial nanoparticles to examine the effect of size, density and inhibitors on uptake of lectin-coated nanoparticles by epithelial cells. The degree of uptake was most influenced by the density of lectin on the particle, with size and type of lectin being less important. Uptake could be inhibited by the presence of specific sugars or free lectin. These studies should provide a good basis for the design of targetable biodegradable drug-loadable particles suitable for oral delivery.

Morphological evidence of the inhibitory effect of taxol on the fast axonal transport

The short term effects of taxol, a stabilizing drug of microtubules, on the peripheral nerves in the rat was investigated using a new chamber system which can be applied to incubate a sciatic nerve with various solutions in vivo. A functional analysis of retrograde axonal transport using rhodamine-labeled wheat germ agglutinin (WGA-rhodamine) showed the inhibitory effect of the drug. An electron microscopic study also revealed that a variety of vesicles were observed to accumulate on both the proximal and the distal sides of the chamber, however, no significant increase in the number of microtubules in the axons, based on the pharmacological effect of the drug, was observed even though one had been expected. These findings support the inhibitory effect of taxol on the fast axonal transport of the neurons. Furthermore, the accumulated vesicles were morphologically different from those accumulated by ligation. These results suggest that a special component of the fast axonal transport was thus selectively blocked by the drug.

Reciprocal connections between the red nucleus and the trigeminal nuclei: a retrograde and anterograde tracing study

An anterograde biocytin and a retrograde WGA-colloidal gold study in the rat can provide information about reciprocal communication pathways between the red nucleus and the trigeminal sensory complex. No terminals were found within the trigeminal motor nucleus, in contrast with the facial motor nucleus. A dense terminal field was observed in the parvicellular reticular formation ventrally to the trigeminal motor nucleus. The parvicellular area may be important for the control of jaw movements by rubrotrigeminal inputs. On the other hand, the contralateral rostral parvicellular part of the red nucleus receives terminals from the same zone in the rostral part of the trigeminal sensory complex, where retrogradely labelled neurones were found after tracer injections into the red nucleus. Such relationships could be part of a control loop for somatosensory information from the orofacial area.

Wheatgerm agglutinin-mediated toxicity in pancreatic cancer cells

Lectin binding specificities for carbohydrate allow phenotypic and functional characterization of membrane-associated glycoproteins expressed on cancer cells. This analysis examined wheatgerm agglutinin binding to pancreatic cancer cells in vitro and the resulting toxicity. Membrane preparations of nine human pancreatic carcinoma cell lines were studied for lectin binding using wheatgerm agglutinin (WGA), concanavalin A (ConA) and phytohaemagglutinin-L (PHA-L) in a lectin blot analysis. Cell proliferation in vitro was measured by thymidine incorporation in the absence or presence of lectins at various concentrations. Sialic acid binding lectins or succinyl-WGA (succWGA) served as controls. WGA toxicity was tested after swainsonine or neuraminidase pretreatment. Binding and uptake of fluorescein-labelled lectins was studied under fluorescence microscopy. All pancreatic cell lines displayed high WGA membrane binding, primarily to sialic acid residues. Other lectins were bound with weak to moderate intensity only. Lectin toxicity corresponded to membrane binding intensity, and was profound in case of WGA (ID50 at 2.5-5 microg ml(-1)). WGA exposure induced chromatin condensation, nuclear fragmentation and DNA release consistent with apoptosis. Important steps for WGA toxicity included binding to sialic acid on swainsonine-sensitive carbohydrate and lectin internalization. There was rapid cellular uptake and subsequent nuclear relocalization of WGA. In contradistinction to the other lectins studied, WGA proved highly toxic to human pancreatic carcinoma cells in vitro. WGA binding to sialic acid residues of N-linked carbohydrate, cellular uptake and subsequent affinity to N-acetyl glucosamine appear to be necessary steps. Further analysis of this mechanism of profound toxicity may provide insight relevant to the treatment of pancreatic cancer.

MR imaging of neuronal transport in the guinea pig facial nerve: initial findings

Certain dextran coated iron oxides such as MION (monocrystalline iron oxide nanocompound) coupled to wheat germ agglutinin (MION-WGA) have been shown to exhibit i) neuronal uptake ii) axonal transport and iii) strong magnetic effects on tissues (superparamagnetism) in which they are localized. In the current study, we utilized such an agent to visualize axonal transport in the facial nerve in vivo by magnetic resonance (MR) imaging. Following injection of the compound into the facial nerves of guinea pigs, MR images were obtained at multiple time points (1, 3 and 5 days) and the imaged tissues were processed for subsequent histological examination. In nerves that had been injected with MION-WGA, the entire nerve appeared as a uniformly hypointense structure with a calculated transport rate of 5 mm/day. By 3 days, the agent within the facial nerve was traceable by MRI from a site of injection in the buccal branch to the stylomastoid foramen. Fluorescence and autoradiography studies confirmed axonal transport. These results show that MION-based magnetopharmaceuticals can be used to demonstrate slow axonal transport, and thereby visualize functional peripheral nerves in vivo by MR imaging. The method holds promise for developmental neuroscience research as well as a method to detect neural abnormalities by MR imaging.

Differences in the connectivity of rat pudendal motor nuclei as revealed by retrograde transneuronal transport of wheat germ agglutinin

Bilateral coordinated activation of pudendal motoneurons is an essential component of penile reflexes in male rats. However, little is known about the intraspinal organization of these reflexes. In the present study, retrograde transneuronal transport of wheat germ agglutinin (WGA) was used to examine the organization of spinal motoneurons and putative interneurons mediating penile reflexes in adult male rats. Injection of WGA into the ventral bulbospongiosus muscle resulted in direct retrograde labeling of motoneurons in the ipsilateral dorsomedial (DM) nucleus and transneuronal labeling of ipsilateral and contralateral DM motoneurons. Motoneurons in the ipsilateral and contralateral dorsolateral (DL) nuclei were not labeled. WGA-labeled putative interneurons were observed bilaterally, primarily in the ventromedial spinal gray matter extending dorsally to the central canal and the dorsal gray commissure. The number of transneuronally labeled putative interneurons increased with longer survival times. Injection of WGA into the ischiocavernosus muscle resulted in direct retrograde labeling of motoneurons in the medial subdivision of the ipsilateral DL nucleus. However, no WGA labeling was detected in motoneurons in the lateral subdivision of the ipsilateral DL nucleus, the contralateral DL nucleus, or the DM nuclei at any of the survival times studied (1-7 days). Only a small number of transneuronally labeled putative interneurons was observed in the ventrolateral gray matter at longer survival times (3-7 days). Thus, marked differences were observed between the DM and DL nuclei with respect to the transneuronal transport of WGA. These results are discussed with respect to the organization of the spinal circuits that mediate pudendal motor reflexes.

Blood to brain and brain to blood passage of native horseradish peroxidase, wheat germ agglutinin, and albumin: pharmacokinetic and morphological assessments

Native horseradish peroxidase (HRP) and the lectin wheat germ agglutinin (WGA) conjugated to HRP are protein probes represented in the blood-brain barrier (BBB) literature for elucidating morphological routes of passage between blood and brain. We report the application of established pharmacokinetic methods, e.g., multiple-time regression analysis and capillary depletion technique, to measure and compare bidirectional rates of passage between blood and brain for radioactive iodine-labeled HRP (I-HRP), WGA-HRP (I-WGA-HRP), and the serum protein albumin (I-ALB) following administration of the probes intravenously (i.v.) or by intracerebroventricular (i.c.v.) injection in mice. The pharmacokinetic data are supplemented with light and electron microscopic analyses of HRP and WGA-HRP delivered i.v. or by i.c.v. injection. The rates of bidirectional movement between blood and brain are the same for coinjected I-HRP and I-ALB. Blood-borne HRP, unlike WGA-HRP, has unimpeded access to the CNS extracellularly through sites deficient in a BBB, such as the circumventricular organs and subarachnoid space/pial surface. Nevertheless, blood-borne I-WGA-HRP enters the brain approximately 10 times more rapidly than I-HRP and I-ALB. Separation of blood vessels from the neocortical parenchyma confirms the entry of blood-borne I-WGA-HRP to the brain and sequestration of I-WGA-HRP by cerebral endothelial cells. Nearly half the I-WGA-HRP radioactivity associated with cortical vessels is judged to be subcellular. Light microscopic results suggest the extracellular pathways into the brain available to blood-borne native HRP do not represent predominant routes of entry for blood-borne WGA-HRP. Ultrastructural analysis further suggests WGA-HRP is likely to undergo adsorptive transcytosis through cerebral endothelia from blood to brain via specific subcellular compartments within the endothelium. Entry of blood-borne I-WGA-HRP, but not of I-ALB, is stimulated with coinjected unlabeled WGA-HRP, suggesting the latter may enhance the adsorptive endocytosis of blood-borne I-WGA-HRP. With i.c.v. coinjection of I-WGA-HRP and I-ALB, I-WGA-HRP exists the brain more slowly than I-ALB. The brain to blood passage of I-WGA-HRP is nil with inclusion of unlabeled WGA-HRP, which does not alter the exist of I-ALB. Adsorptive endocytosis of i.c.v. injected WGA-HRP appears restricted largely to cells lining the ventricular cavities, e.g., ependymal and choroid plexus epithelia. In summary, the data suggest that the bidirectional rates of passage between brain and blood for native HRP are comparable to those for albumin.

Labelling of neurons in the rat superior cervical ganglion after injection of wheat-germ agglutinin-horseradish peroxidase into the contralateral ganglion: evidence of transneuronal labelling

Recent studies have shown that injection of the tracer wheat-germ agglutinin-horseradish peroxidase (WGA-HRP) into the superior cervical ganglion (SCG) of one side results in labelling of neurons in the contralateral SCG and the stellate ganglion. This study was designed to verify whether or not bilateral projections from the superior cervical ganglion to the midline structures, particularly to the pineal gland, play a role in the transport of WGA-HRP to the contralateral SCG. One group of rats received WGA-HRP injection into the right SCG (group I). Four groups of rats underwent the following operations prior to the injection of WGA-HRP into the right superior cervical ganglion: transection of the external carotid nerve (group II), transection of the internal carotid nerve (group III), transection of the external carotid nerve combined with pinealectomy (group IV), transection of both the internal and the external carotid nerves (group V). The mean number of labelled neurons in the left SCG of each group were found as follows: group I, 1516 +/- 221 (mean +/- S.D.); group II, 861 +/- 122; group III, 543 +/- 99; group IV, 562 +/- 144; group V, 220 +/- 52. The results of this study suggest that the contralateral labelling depends on the transneuronal transport of WGA-HRP through the terminal fields of innervation of the midline structures that receive bilateral projections from both SCGs.

Urinary bladder innervation in male rat: termination of primary afferents in the spinal cord as determined by transganglionic transport of WGA-HRP

The distribution of afferents innervating the urinary bladder in the spinal cord of male rats has been studied with the axonal tracer horseradish peroxidase conjugated to wheat germ agglutinin (WGA-HRP) injected into various portions of one side of the urinary bladder (dome, body, base, or neck) and other pelvic organs (prostate and rectum). Labeled neurons were found in dorsal root ganglia of the lumbosacral cord (L1-S3, peak in S1-S2). The strongest and most extensive transganglionic labeling of primary afferents resulted after injections in the body of the bladder. Primary afferents were observed bilaterally in Lissauer's tract and laminae I-II at the apex of the dorsal horn, from L6 to S3. The projection extended laterally up to the sacral parasympathetic nucleus and medially up to the gray matter dorsal to the central canal, where they formed a plexus of fibers and terminals. Deposits in the dome and base of the bladder labeled more heavily the medial projection, while the least intense projection was seen after injections in the bladder neck. Our results indicate a common pattern of termination of primary afferents from the bladder, although some topographical differences exist.

Morphological heterogeneity within the cingulate cortex in rat: a horseradish peroxidase transport study

We compared the connections of two areas within rat cingulate cortex, the Cg1/Cg2 area vs the Cg3 area, by iontophoresing small quantities of wheatgerm agglutinin-horseradish peroxidase (WGA-HRP) into either of these two divisions and identifying afferent and efferent connections. Cortical projections were more widespread for the cingulate cortex (Cg3) area than for the Cg1/Cg2 area and included the dysgranular and agranular insular cortex, and perirhinal cortex. The Cg3 area received input from the CA1 layer of the hippocampus while the Cg1/Cg2 area was interconnected primarily with retrosplenial cortex. In the brainstem, both received input from Barrington's nucleus however, many of the subcortical connections of the two areas differed and supported the hypothesis that the Cg3 area is part of the limbic and visceral motor system while the Cg1/Cg2 area is more closely allied with somatic motor control. The Cg3 area received input from the basolateral nucleus of the amygdala, the supramammillary hypothalamic nucleus, the laterodorsal tegmental nucleus, and the lateral parabrachial nucleus. The Cg1/Cg2 area received input from the substantia nigra and targeted deep layers of the superior colliculus. Thus, rat cingulate cortex is a heterogeneous area that can be further subdivided into separate limbic/autonomic (Cg3) and somatic motor areas (Cg1/Cg2).

Transneuronal transport of wheat germ agglutinin conjugated horseradish peroxidase into last order spinal interneurones projecting to acromio- and spinodeltoideus motoneurones in the cat. 1. Location of labelled interneurones and influence of synaptic activity on the transneuronal transport

Transneuronal transport of wheat germ agglutinin conjugated horseradish peroxidase (WGA-HRP) was used to define the location of last order spinal interneurones projecting to deltoideus motoneurones in C5-C8 of the cat. Labelled interneurones were found bilaterally from rostral C1 to caudal Th5 and from L3 to the L4/5 border. Ipsilaterally they were located in laminae V-IX, while contralaterally they were confined to lamina VIII except for a few cells in laminae VII and IX. To estimate the degree to which interneuronal activity facilitates the transneuronal transport from deltoideus motoneurones, the numbers of labelled interneurones were compared under different experimental conditions after WGA-HRP injection. The number of labelled last order interneurones was larger in one awake and active cat than in one awake but inactive cat and also larger in six anaesthetized animals in which spinal pathways were stimulated to evoke antidromic and synaptic activation of the interneurones, than in two anaesthetized animals without stimulation. It is concluded that the transneuronal transport of WGA-HRP is considerably facilitated by increased activity in the last order interneurones. An overall tendency was observed for a positive correlation between the number of labelled interneurones and the number of primarily stained deltoideus motoneurones. In order to reach a detectable concentration of WGA-HRP in the last order interneurones a certain number of motoneurones has to be labelled to the extent that they appear homogenously black.

Transneuronal transport of wheat germ agglutinin conjugated horseradish peroxidase into last order spinal interneurones projecting to acromio- and spinodeltoideus motoneurones in the cat. 2. Differential labelling of interneurones depending on movement type

Transneuronal transport of wheat germ agglutinin conjugated horseradish peroxidase was used to define the location of last order spinal interneurones projecting to deltoideus motoneurones during voluntary target-reaching and/or in unrestricted walking on the ground. Labelled interneurones were found bilaterally from C2 to Th1 in target-reaching cats and almost exclusively in the C5-Th1 segments in walking cats, although the total number of labelled interneurones in these cats was considerably higher than in the target-reaching cats. These results confirm the previous finding that propriospinal neurones in the C3-C4 segments can mediate the descending command for target-reaching movements with the forelimb. In both groups of cats labelled interneurones were found ipsilaterally in laminae V-IX, while contralaterally they were mainly restricted to lamina VIII. In the forelimb segments there was a larger number of labelled interneurones in the walking cats in the lateral part of laminae V-VII and in laminae VIII and IX. There was a positive, almost linear correlation between the total number of labelled interneurones and motoneurones in all cats. The results suggest that both excitatory and inhibitory last order interneurones can be transneuronally labelled. It is concluded that this method can be used for functional identification of last order interneurones active during the preparation and/or execution of different movements.

Synchronized endocytosis studied in the oocyte of a temperature-sensitive mutant of Drosophila melanogaster

This study demonstrates that endocytosis in the oocyte of Drosophila melanogaster is reversibly blocked at the stage of pit formation by the temperature-sensitive, single-gene mutant, shibirts1. Uptake of horeradish peroxidase conjugated with wheat-germ agglutinin was observed to be normal in mutant oocytes at 19 degrees C, but was blocked at 29 degrees C. After 10 min at 29 degrees C, there was a build-up of coated pits along invaginations of the plasma membrane. Also, the endosomal compartment consisting of tubules, bulbs, and small yolk spheres, disappeared. Lowering the temperature to 19 degrees C after 10 min at 29 degrees C released a synchronized wave of endocytosis into a cytoplasm cleared of uptake-related organelles. By observing this synchronized wave after exposure to 19 degrees C for varying durations, we determined that endocytosis proceeds as follows: coated pits/vesicles----tubules----small yolk spheres----mature yolk spheres. The observations suggest that these organelles transform one into another within this sequence.

Protein-gold complexes as neuronal markers for long-term tracing studies

In this study, we have tested the possible use of protein-gold complexes as neuronal markers for long-term tracing studies in rat. The tracer we have used consisted of colloidal gold particles coupled to wheat-germ agglutinin apohorseradish peroxidase conjugate (WGA-apoHRP). The neuronal labeling was studied for survival periods of up to nineteen months following injection in the central nervous system. Maximal visualization of the gold particles was achieved through gold silver intensification. The tracer could be detected throughout the entire range of periods considered. The injection site consisted of a dense black core and retrogradely labeled cells were characterized by round black granules over the cell body. The retrogradely labeled cells were cytochemically characterized by demonstrating their transmitter content. Thus protein-gold complexes may be used as long-term neuronal markers compatible with the persistance of the vital functions of the labeled cells.

Enucleation-induced transsynaptic labeling with WGA-HRP in the developing rat visual system

Wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) is a neuroanatomical tracer which is transported transneuronally. In order to investigate whether transport of WGA-HRP is across synapses, labeling was studied in the developing retinotectal pathway where it is known that enucleation results in increased ipsilateral synaptic connections from the remaining eye. While little or no transneuronal labeling was evident in controls, after enucleation transneuronal labeling was consistently observed. Furthermore, the critical period for enucleation-induced transneuronal labeling coincides with the known critical period for enucleation-induced neuronal survival and synaptic formation. The results suggest that transneuronal exchange of WGA-HRP depends on the presence of synapses, and is therefore transsynaptic.

Transcytosis of macromolecules through the blood-brain barrier: a cell biological perspective and critical appraisal

A critical appraisal is presented of nearly two decades of research publications and review articles advocating the bidirectional transcytosis of fluid-phase molecules, most notably native horseradish peroxidase (HRP), through the normal and experimentally modified blood-brain barrier (BBB). Extracellular routes circumventing the BBB in normal and pathological states and artifact introduced in histological preparation of CNS tissue exposed to blood-borne peroxidase are emphasized. The potential for transcytosis of macromolecules entering the nonfenestrated cerebral endothelium by the processes of non-specific fluid phase endocytosis (e.g., HRP), adsorptive endocytosis (e.g., lectins) and receptor-mediated endocytosis (e.g., ligands) is analyzed in the context of the cellular secretory process and the complimentary events of endocytosis and exocytosis at the luminal and abluminal plasma membranes. Available data suggest that the cerebral endothelium is polarized with regard to endocytosis and the internalization of cell surface membrane; hence, the transcytosis of specific macromolecules through the BBB may be vectorial. If these data are correct, the blood-brain barrier is not absolute, whereas its counterpart, the brain-blood barrier, may be.

The plasma membrane of Xenopus laevis spermatozoon

Xenopus laevis sperm plasma membrane ultrastructure has been studied by means of freeze-fracture, deep-etching, and lectin-gold binding. Xenopus spermatozoa differ from those of other species in that their plasma membrane does not exhibit topographical domains. In fact, no geometric arrangement or characteristic array of particles is present on fractured plasma membrane. Fractures rarely occur in acrosomal or nuclear membranes. Wheat germ agglutinin receptors are distributed homogeneously on the plasma membrane of the sperm head and tail.

A hypothesis for the superior sensitivity of wheat germ agglutinin as a neuroanatomical probe

We have shown that a conjugate of wheat germ agglutinin (WGA), with horseradish peroxidase (HRP), is more sensitive than native HRP as a probe of neuroanatomic connections involving the retrograde transport of the lectin. It has also been shown in our laboratory that WGA-HRP remains at the site of injection twice as long as HRP. The purpose of the present morphometric study was to investigate the basis for the higher sensitivity of WGA-HRP over HRP as a retrogradely transported tracer molecule. To do this, we modified the experiment of Heuser and Reese which utilized the tracing of HRP in the frog neuromuscular junction (Heuser, J.E. and Reese, T.S., J. Cell Biol., 57 (1973) 315-344). Instead of using HRP alone, we examined, in double labeling experiments, fluid and adsorptive endocytosis with free HRP and WGA coupled to ferritin (WGA-ferritin) respectively. Immediately after nerve stimulation, both markers are taken up simultaneously into cisternae, and in tubular structures strikingly similar to the described compartment of uncoupling of receptor from ligand (CURL). Frequently, cisternae were connected with putative CURL. This early double labeling of cisternae and putative CURL was followed by the appearance of synaptic vesicles labeled with WGA-ferritin only (72-79%), HRP only (6-11%), and both labels (13-16%). In contrast to the labeling pattern of synaptic vesicles, the majority of cisternae and putative CURL had both labels throughout the duration of the experiments (77-80%). The results of this study indicate that most of WGA-ferritin and HRP are co-localized in cisternae and putative CURL, compartments involved in endocytosis and surface receptor recycling.(ABSTRACT TRUNCATED AT 250 WORDS)

Satellite cells as blood-ganglion cell barrier in autonomic ganglia

In a preliminary study a difference in the uptake and transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) between the trigeminal ganglion and the superior cervical ganglion was observed. After injection of WGA-HRP and HRP into the trigeminal ganglion, peroxidase was found in the space between the satellite cell processes and the ganglion cells. The ganglion cells showed pinocytosis and uptake of WGA-HRP and HRP. In the superior cervical ganglion WGA-HRP and HRP were found alongside the satellite cells but were absent in the space between satellite cells and ganglion cells. Intravenous injection revealed the presence of HRP in the space between sensory ganglion cells and their satellite cells of the trigeminal and nodose ganglion whereas HRP was absent in the space between autonomic ganglion cells and their satellite cells of the superior cervical, medial cervical and pterygopalatine ganglion although HRP lined the satellite cell membranes. By means of electron microscopy, satellite cell processes in the superior cervical ganglion were found to enwrap ganglion cells very tightly with a marginal space between both cell types. Satellite cells and their processes were mutually anchored by numerous tight junctions. In the trigeminal ganglion the extracellular space between ganglion cells and satellite cells was larger and satellite cells were found to be more loosely arranged around the ganglion cells. Satellite cell processes were only occasionally linked by tight junctions. It is concluded that satellite cells in autonomic ganglia comprise an effective barrier for WGA-HRP and HRP and probably large molecules in general. This barrier is absent in sensory ganglia.

False-positive artifacts of tracer strategies distort autonomic connectivity maps

The widespread use of new axonal transport tracing techniques in the ANS has resulted in substantially revised and amended descriptions of ANS organization. The present review suggests, however, that at least some of the results on which proposed revisions of ANS anatomy have been based have incorporated artifacts and therefore should be cautiously interpreted. The peripheral nervous system and viscera are composed in part of connective and endothelial tissues that are porous or 'leaky' to solutes with appropriate chemical characteristics, including the major tracer compounds. As a result, several extra-axonal routes for redistribution of label from the application site into other tissues are present. These include (1) diffusion through tissue membranes to enter directly adjacent tissues and (2) leakage into extracellular fluids within the body cavity, vasculature, lymphatics, exocrine ducts, or organ lumens to migrate to more distant tissues. As a consequence of the extreme sensitivity of the methods used, such redistribution of even minute amounts of label can produce false positives. Review of autonomic neuroanatomy suggests additional mechanisms, including tracer uptake by fibers of passage, can produce artifactual staining. Based on these surveys of tissue composition, tracer characteristics and sources of artifact, experimental controls and criteria for identifying and avoiding labeling artifacts are described. Since no single procedure is foolproof for ANS experimentation, the routine application of multiple controls, particularly ones which restrict or prevent tracer diffusion, are needed.

Transcytosis of protein through the mammalian cerebral epithelium and endothelium. I. Choroid plexus and the blood-cerebrospinal fluid barrier

The potential for transcytosis (endocytosis----intracellular transport----exocytosis) of protein and membrane events associated with fluid phase and adsorptive endocytic processes within epithelia of the choroid plexus [blood-cerebrospinal fluid (CSF) barrier] were investigated in mice injected intravenously or into the lateral cerebral ventricle with native horseradish peroxidase (HRP) or the lectin wheatgerm agglutinin (WGA) conjugated to HRP. WGA binds to specific cell surface oligosaccharides and enters cells by the process of adsorptive endocytosis; native HRP is taken into cells non-specifically by fluid phase endocytosis. The lysosomal system of organelles and the endoplasmic reticulum, identified by enzyme cytochemical markers applied to choroid epithelia, were analysed for possible participation in transcytosis and compared to epithelial organelles harbouring the exogenous tracer proteins. Blood-borne native HRP was endocytosed readily by choroid epithelia whereas WGA-HRP was not, perhaps because WGA-HRP does not escape fenestrated endothelia as easily as native HRP. The blood-borne proteins incorporated within endocytic vesicles by choroid epithelia were directed to endosomes (prelysosomes) and secondary lysosomes (e.g. tubules, multivesicular/dense bodies) for eventual degradation and did not reach the apical/microvillus surface. Both CSF-borne native HRP and WGA-HRP entered choroid epithelia within endocytic vesicles derived from the microvillus border. Native HRP, ultimately sequestered within endosomes and secondary lysosomes, failed to undergo transcytosis through the epithelia into the basolateral clefts. Conversely, CSF-borne WGA-HRP was transported through the epithelia and released into the basolateral clefts within 10 min post-injection. The lectin conjugate labelled epithelial vesicles, endosomes, secondary lysosomes and, at 30 min post-injection, the transmost saccule of the Golgi complex which exhibits acid hydrolase activity. Tubular profiles, related either to the endosome apparatus or to the lysosomal system, and the endoplasmic reticulum did not appear involved in the transcytotic pathway. The data suggest that CSF-borne protein entering the choroid epithelium by adsorptive endocytosis can undergo rapid transcytosis through the cell. The results provide insight to transcytotic pathways utilizing vesicles, the endosomal apparatus, and the Golgi complex within the choroid epithelium for circumventing the blood-CSF barrier. Hypothesized membrane events and morphological associations among constitutents of the endomembrane system within the choroid epithelium are summarized diagrammatically.

A quantitative study of anterograde and retrograde axonal transport of exogenous proteins in olfactory nerve C-fibers

The pike olfactory nerve which consists of a homogeneous population of C-fibers of 0.25 micron diameter or less was used to study quantitatively both anterograde and retrograde axoplasmic transport of wheat germ agglutinin and horseradish peroxidase. It was found that even in these extremely thin axons anterograde and retrograde transport takes place. Activity distribution profiles (transport profiles) for retrograde transport were established and found to be similar to the typical profiles of anterograde transport as they consisted of a small rapidly moving peak and a saddle region followed by the bulk of the material which moved more slowly. Horseradish peroxidase activity profiles were obtained both after injection into the synaptic region and after injection into the perikaryal region. From these transport profiles a maximal velocity of 25 mm/d (19 degrees C) for the leading peak and of about 7 mm/d for the slower component could be determined. There is no significant difference between the velocities for anterograde and retrograde transport. In the case of wheat germ agglutinin, only injection into the synaptic region resulted in typical transport profiles (retrograde transport) with a peak and saddle region. The maximum velocities of retrograde transport were about the same as for horseradish peroxidase [26 mm/d and 7 mm/d (19 degrees C)]. The electron microscopic analysis of horseradish peroxidase revealed that after injection into the olfactory bulb it was taken up into the neurons where it was found mainly in multivesicular bodies (0.5 micron diameter). In longitudinal sections of the nerve similar but slightly more elongated organelles (diameter 0.25 micron, length 0.4 micron) were found in those segments in which the slowly moving bulk of the peroxidase activity was located. The number of these organelles decreased with distance from the site of injection. The horseradish peroxidase transported within the leading peak could not be assigned to specific structures although several electron microscopic-histochemical methods were applied. It was concluded that anterograde and retrograde transport occur simultaneously in these axons, and that, therefore, even the large organelles, each of which almost fills the axon, must be able to pass each other. This would necessitate that the axons are able to transiently enlarge their diameter considerably.

Afferent connections and spinal projections of the pressor region in the rostral ventrolateral medulla of the cat

Following microinjection of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) into the pressor region of the rostral ventrolateral medulla of the cat, the medulla, pons and hypothalamus were examined for retrogradely labelled cell bodies, while the thoracolumbar segments of the spinal cord were examined for anterogradely labelled axons. Dense groups of labelled cells were found in the following areas: (1) the nucleus of the solitary tract, particularly the medial, ventrolateral and commissural subnuclei; (2) the ambiguous complex and immediately surrounding area; (3) the Kölliker-Fuse nucleus in the pons; (4) the paraventricular nucleus and lateral hypothalamic area. In the spinal cord, labelled axons formed a band extending throughout the dorsolateral and ventrolateral funiculi at thoracic segments, while terminal labelling was observed in the intermediolateral nucleus and to a lesser extent the central autonomic area, but not in other parts of the grey matter. The findings are discussed in relation to the role of the rostral ventrolateral medulla in cardiovascular regulation, particularly the baroreceptor reflex.