An anatomicosurgical study of the temporal branch of the facial nerve

The surgical anatomy of the temporal branch of the facial nerve was studied bilaterally in 10 embalmed cadaveric heads. Particular attention was paid to the relationships between the temporal branch, the galeal-fascial layers, and the fat pads of the temporal-zygomatic region. The temporal branch of the facial nerve pierces the parotidomasseteric fascia below the zygomatic arch. This branch travels first in the subcutaneous tissue and then, above the zygomatic arch, in the subgaleal space. The temporal branch divides into an anterior, a middle (frontal), and a posterior ramus soon after it pierces the parotid fascia. The course of the terminal twigs of the temporal branch of the facial nerve in the subgaleal space is extremely variable, with their location being at times posterior to the anterior one-fourth of the temporalis muscle. Occasionally, a twig for the frontalis muscle may run in between the two layers of the superficial temporal fascia. Because of these findings (anteroposterior variability of temporal branch twigs and recurrent intrafascial twig), Yasargil's interfascial dissection may at times fail. A combined frontotemporal scalp/superficial temporal fascia dissection is anatomically suited to preserve the temporal branch of the facial nerve.

The agrin receptor. Localization in the postsynaptic membrane, interaction with agrin, and relationship to the acetylcholine receptor

Agrin is a component of the synaptic basal lamina that induces the aggregation of acetylcholine receptors (AChRs) and other elements of the postsynaptic membrane. We have determined the localization, binding characteristics, and biochemical profile of the agrin receptor in Torpedo electric organ membranes and defined domains of agrin that bind this receptor. Postsynaptic membranes from Torpedo electric organ bind agrin as judged by depletion of AChR clustering activity from solution. A ligand-based radioimmunoassay shows that agrin binding to postsynaptic membranes is saturable and calcium-dependent. Half-maximal binding is observed at agrin concentrations < or = 10(-10) M. Identification of the bound agrin polypeptides shows that at least one membrane binding domain of agrin is located in a 70-kDa proteolytic fragment. Immunofluorescent visualization and radioimmunoassay of agrin binding demonstrates that the agrin receptor is selectively concentrated in postsynaptic membranes, with little binding detected on nonsynaptic or liver membranes. Agrin binding is greatly reduced if the membranes are pretreated with trypsin, but is unaffected by phosphatidylinositol-specific phospholipase C. Membranes stripped of peripheral proteins by alkaline treatment retain full ligand binding capacity. alpha-Bungarotoxin affinity columns bind AChRs but not agrin receptors. The ratio of agrin receptors to AChRs in postsynaptic membranes is approximately 1:200. We conclude that the agrin receptor is an integral membrane glycoprotein that is selectively concentrated in postsynaptic membranes, but that is not tightly complexed with the AChR. The results also indicate that the biological activity of agrin is mediated through intracellular signal transduction events triggered by ligand binding to the agrin receptor.

Monoclonal anti-CD44 antibody acts in synergy with anti-CD2 but inhibits anti-CD3 or T cell receptor-mediated signaling in murine T cell hybridomas

We investigated the effects of anti-murine CD44 monoclonal antibodies on the activation of antigen-specific T cell hybridomas. Anti-murine CD44 antibodies by themselves did not induce the production of IL-2 by antigen-specific T cell hybridomas. However, anti-murine CD44 monoclonal antibodies were able to either inhibit or enhance the production of IL-2, depending on the other monoclonal antibodies used as comitogenic stimuli. When a T cell hybridoma was activated by antigen and antigen-presenting cells or anti-CD3 antibodies, addition of anti-CD44 antibodies inhibited IL-2 production. In contrast, monoclonal anti-CD44 antibodies acted in synergy with anti-human CD2 antibodies in stimulating a murine T cell hybridoma stably transfected with the human CD2 gene to produce IL-2. Therefore, cross-linking of surface CD44 is able to deliver either a positive or a negative signal in murine antigen-specific T cell hybridomas. One of the ligands for CD44 is hyaluronic acid. Hyaluronic acid in vitro significantly increased the activation of murine T cell hybridomas. Hyaluronic acid itself was mitogenic for T cell hybridomas. Therefore, in addition to being an adhesion molecule, CD44 functions as a signal-transducing molecule on murine T cell hybridomas.

Effects of perchlorate on the molecules of excitation-contraction coupling of skeletal and cardiac muscle

To understand the nature of the transmission process of excitation-contraction (EC) coupling, the effects of the anion perchlorate were investigated on the voltage sensor (dihydropyridine receptor, DHPR) and the Ca release channel (ryanodine receptor, RyR) of the sarcoplasmic reticulum (SR). The molecules, from rabbit skeletal muscle, were either separated in membrane vesicular fractions or biochemically purified so that the normal EC coupling interaction was prevented. Additionally, the effect of ClO4- was investigated on L-type Ca2+ channel gating currents of guinea pig ventricular myocytes, as a native DHPR not in the physiological interaction of skeletal muscle. At 20 mM, ClO4- had minor effects on the activation of ionic currents through Ca channels from skeletal muscle transverse tubular (T) membranes fused with planar bilayers: a +7-mV shift in the midpoint voltage, V, with no change in kinetics of activation or deactivation. This is in contrast with the larger, negative shift that ClO4- causes on the distribution of intramembrane charge movement of skeletal muscle. At up to 100 mM it did not affect the binding of the DHP [3H]PN200-110 to triad-enriched membrane fractions (TR). At 8 mM it did not affect the kinetics or the voltage distribution of gating currents of Ca channels in heart myocytes. These negative results were in contrast to the effects of ClO4- on the release channel. At 20 mM it increased several-fold the open probability of channels from purified RyR incorporated in planar bilayers and conducting Ba2+, an effect seen on channels first closed by chelation of Ca2+ or by the presence of Mg2+. It significantly increased the initial rate of efflux of 45Ca2+ from TR vesicles (by a factor of 1.75 at 20 mM and 4.5 at 100 mM). ClO4- also increased the binding of [3H]ryanodine to TR fractions. The relative increase in binding was 50-fold at the lowest [Ca2+] used (1 microM) and then decayed to much lower values as [Ca2+] was increased. The increase was due entirely to an increase in the association rate constant of ryanodine binding. The chaotropic ions SCN- and I- increased the association rate constant to a similar extent. The binding of ryanodine to purified RyR protein reconstituted into liposomes had a greater affinity than to TR fractions but was similarly enhanced by ClO4-. The reducing agent dithiothreitol (5 mM) did not reduce the effect of ClO4-, and 5% polyethylene glycol, with an osmolarity equivalent to 20 mM ClO4-, did not change ryanodine binding.(ABSTRACT TRUNCATED AT 400 WORDS)

Gastric vagus mediates immobilization-induced hypocalcemia in rats

The involvement of the parasympathetic nervous system in the etiology of stress-induced hypocalcemia was investigated in the rat. Atropine methyl bromide (0.1 and 0.6 mg/kg ip) given 20 min before immobilization (IMB) was observed to suppress the induction of hypocalcemia in a dose-dependent manner. A vagotomy of the bilateral cervical trunks also abolished the IMB-induced hypocalcemia. A vagotomy on either the thyroid/parathyroid branches or the celiac branches had no effect on the IMB-induced hypocalcemia, but a vagotomy on the gastric branches completely abolished it. Pretreatment with either secretin (2 and 6 micrograms/kg ip), an inhibitor of gastrin release, or cimetidine (5 and 10 mg/kg ip), a histamine H2-receptor antagonist, diminished the IMB-induced hypocalcemia. The concentration of serum gastrin increased significantly during IMB. It is thus concluded that the decreased levels of plasma calcium caused by IMB are due to the activation of the vagus innervating the stomach. Gastrin and histamine are also involved as a consequence of the activation of the vagus.

Antibody penetration of viable human cells. II. Anti-RNP antibodies binding to RNP antigen expressed on cell surface, which may mediate the antibody internalization

As U1 small nuclear ribonucleoprotein (U1 snRNP2) has a crucial role in pre-mRNP splicing, the interaction of anti-RNP antibody with snRNP within viable lymphocytes may profoundly influence cell functions. We have shown that antibody can penetrate viable human lymphocytes, and anti-RNP antibodies enter more cells than other anti-nuclear antibodies or control IgG. In order to study the in vitro interaction of anti-RNP antibodies with viable cells, T lymphocytes were metabolically labelled with 35S-methionine, then incubated with the antibodies and washed. A set of 35S-labelled cell-associated snRNP polypeptides A, B'/B, C and D were found to bind to both monospecific human polyclonal anti-RNP IgG (human anti-RNP IgG) and a mouse monoclonal anti-RNP antibody (2.73), indicating that anti-RNP antibodies interacted with RNP antigen inside or/and on the surface of viable cells. To investigate antibody binding to RNP antigen on the cell surface, the cell surface proteins were either iodinated with 125I or the cells processed for immunoelectron microscopic studies after incubation with MoAb. At least seven 125I-labelled polypeptides on the cell surface were found to be immunoprecipitated by the anti-RNP MoAb which have similar molecular weights to U snRNP polypeptides 70K, A, B, D, E, F, and G. The immunoelectron microscopic studies showed that the gold particles formed clustered patches on the cell membrane. Further studies suggested that RNP antigen bound to the cell surface, and the RNP binding structure was probably a heterodimer receptor. This study provides evidence to suggest that anti-RNP antibody entry into viable cells may be mediated by interaction with RNP antigen expressed on the cell surface.

The influence of denervation on beta-amyloid protein precursor and alpha 1-antichymotrypsin in mouse skeletal muscle

A serpin, alpha 1-antichymotrypsin (alpha 1-ACT), and Kunitz inhibitor containing forms of the beta-amyloid precursor protein (beta APP) may be important components of the balance between serine proteases and inhibitors in the nervous system. In the current report we studied whether axotomy affected the localization of beta APP and alpha 1-ACT in adult mouse muscle. Immunocytochemical experiments indicated that beta APP was present in normal muscle both at neuromuscular junctions and within intramuscular nerves. alpha 1-ACT was also present at neuromuscular junctions, on the perineurium of nerves and endothelial cell surfaces. Following axotomy, both beta APP and alpha 1-ACT disappeared from intramuscular nerves simultaneously. However, at the neuromuscular junction alpha 1-ACT decreased more rapidly with beta APP lingering before disappearing.

An allosteric model of the molecular interactions of excitation-contraction coupling in skeletal muscle

A contact interaction is proposed to exist between the voltage sensor of the transverse tubular membrane of skeletal muscle and the calcium release channel of the sarcoplasmic reticulum. This interaction is given a quantitative formulation inspired in the Monod, Wyman, and Changeux model of allosteric transitions in hemoglobin (Monod, J., J. Wyman, and J.-P. Changeux. 1965. Journal of Molecular Biology. 12:88-118), and analogous to one proposed by Marks and Jones for voltage-dependent Ca channels (Marks, T. N., and S. W. Jones. 1992. Journal of General Physiology. 99:367-390). The allosteric protein is the calcium release channel, a homotetramer, with two accessible states, closed and open. The kinetics and equilibrium of this transition are modulated by voltage sensors (dihydropyridine receptors) pictured as four units per release channel, each undergoing independent voltage-driven transitions between two states (resting and activating). For each voltage sensor that moves to the activating state, the tendency of the channel to open increases by an equal (large) factor. The equilibrium and kinetic equations of the model are solved and shown to reproduce well a number of experimentally measured relationships including: charge movement (Q) vs. voltage, open probability of the release channel (Po) vs. voltage, the transfer function relationship Po vs. Q, and the kinetics of charge movement, release activation, and deactivation. The main consequence of the assumption of allosteric coupling is that primary effects on the release channel are transmitted backward to the voltage sensor and give secondary effects. Thus, the model reproduces well the effects of perchlorate, described in the two previous articles, under the assumption that the primary effect is to increase the intrinsic tendency of the release channel to open, with no direct effects on the voltage sensor. This modification of the open-closed equilibrium of the release channel causes a shift in the equilibrium dependency of charge movement with voltage. The paradoxical slowing of charge movement by perchlorate also results from reciprocal effects of the channel on the allosterically coupled voltage sensors. The observations of the previous articles plus the simulations in this article constitute functional evidence of allosteric transmission.

Hypothalamic involvement in stress-induced hypocalcemia in rats

Although hormonal regulation of blood calcium homeostasis has been intensively investigated in the peripheral organs, the involvement of the central nervous system in calcium regulation is still poorly understood. In the present study, we found that (1) bilateral lesions of the ventromedial nucleus of the hypothalamus (VMH), but not those of the paraventricular hypothalamic nucleus or the lateral hypothalamic area, eliminated immobilization (IMB)-induced hypocalcemia, and (2) electrical stimulation of the VMH decreased the blood calcium level. The results suggest that the VMH has a hypocalcemic function and plays a role in IMB-induced hypocalcemia.

Genetic fusion of subunits I, II, and III of the cytochrome bo ubiquinol oxidase from Escherichia coli results in a fully assembled and active enzyme

The cytochrome bo ubiquinol oxidase from Escherichia coli is a five-subunit enzyme which is a member of the superfamily of heme-copper respiratory oxidases. Three of the subunits (I, II, and III) are homologous to the three mitochondrial encoded subunits of the eukaryotic aa3-type cytochrome c oxidase. Subunits, I, II, and III of the eukaryotic oxidase contain 12, 2, and 7 putative transmembrane spans, respectively. The hydropathy profiles of the subunits of most other members of this oxidase superfamily are consistent with these structures. However, subunit I from the E. coli oxidase contains 15 transmembrane spans, with one additional span at the N-terminus and two additional spans at the C-terminus in comparison to the eukaryotic oxidase. The additional transmembrane helix at the N-terminus predicts that the amino terminal residue should be on the periplasmic side of the membrane. By deleting the intergenic region between the cyoA and cyoB genes, an in-frame fusion between subunit II (cyoA) and subunit I (cyoB) was generated. This links the C-terminus of subunit II, known to be on the periplasmic side of the membrane, to the N-terminus of subunit I. The resulting oxidase is fully active, and supports the toplogical folding pattern previously suggested for subunit I with the N-terminus in the periplasm. Whereas subunit I of the E. coli oxidase has two additional membrane-spanning helices at the C-terminus, subunit III has two fewer helices than does the corresponding subunit III of the eukaryotic oxidase.(ABSTRACT TRUNCATED AT 250 WORDS)

TSF1 to TSF6, required for silencing the Saccharomyces cerevisiae GAL genes, are global regulatory genes

The Saccharomyces cerevisiae GAL1 and GAL10 genes are controlled in response to the availability of galactose and glucose by multiple activating and repressing proteins bound at adjacent or overlapping sites in UASG. Negative control elements in UASG, designated GAL operators GALO1 to GALO6, are required to silence basal level transcription of GAL1 and GAL10 when galactose is absent. We isolated and characterized recessive mutations in six nuclear genes, TSF1 to TSF6, that impair silencing of GAL1 and GAL10 gene expression. Surprisingly, the results of several experiments suggest that the TSF genes encode global regulatory factors. tsf1 to tsf6 mutations derepressed expression from yeast CYC-GAL hybrid promoters (fused to lacZ) that harbor a variety of operator sequences, and caused pleiotropic defects in cell growth, mating, and sporulation. S1 mapping and Northern blot results for tsf3 suggest that the molecular defect is at the transcriptional level. Mutant phenotypes were additive in certain combinations of tsf double mutants, implying that more than one silencing pathway is involved in TSF1 to TSF6 function. Most significantly, mutations in all six TSF1 to TSF6 genes activated expression from GAL1 and CYC1 promoters (fused to lacZ) lacking upstream activating sequences. Combined, the simplest interpretation of these results is that TSF1 to TSF6 encode factors that control the function of the basic RNA polymerase II transcriptional machinery.

The mandibular swing-transcervical approach to the skull base: anatomical study. Technical note

This report describes in a stepwise fashion the surgical anatomy of an approach to the midline and lateral compartments of the skull base (clivus, infralabyrinthine/infratemporal regions). The salient features of this procedure are represented by a mandibulotomy and by detachment of the pharynx from the skull base through a combined oral and cervical approach. There is full neurovascular control of the internal carotid artery and lower cranial nerves with the possibility of complete exposure of the intrapetrous and intracavernous segments of the internal carotid artery on the side of the exposure. This approach, which may be regarded as an expansion of the original work of Krespi, should be considered when dealing aggressively with extensive skull-base lesions invading the midline and lateral compartments of the skull base.

Insight into the active-site structure and function of cytochrome oxidase by analysis of site-directed mutants of bacterial cytochrome aa3 and cytochrome bo

Cytochrome aa3 of Rhodobacter sphaeroides and cytochrome bo of E. coli are useful models of the more complex cytochrome c oxidase of eukaryotes, as demonstrated by the genetic, spectroscopic, and functional studies reviewed here. A summary of site-directed mutants of conserved residues in these two enzymes is presented and discussed in terms of a current model of the structure of the metal centers and evidence for regions of the protein likely to be involved in proton transfer. The model of ligation of the heme a3 (or o)-CuB center, in which both hemes are bound to helix X of subunit I, has important implications for the pathways and control of electron transfer.

Drilling the posterior wall of the petrous pyramid: a microneurosurgical anatomical study

Posterior approaches to the petroclival area requiring extensive drilling of the posterior pyramidal wall have been described in the last 10 years. If hearing is to be preserved, damage to the inner-ear structures must be avoided; however, the fine points of this pyramidal drilling technique have never been reported in detail. A microneurosurgical anatomical study was undertaken in 15 cadavers to determine the relationships between bone landmarks and labyrinthine structures that could be used to give some practical drilling guidelines. Drilling of the posterior pyramidal wall is facilitated on identification of the intersection of the petrous ridge with the most anterior portion of the bone ledge covering the sigmoid sinus (petrosigmoid intersection), the bony operculum of the endolymphatic sac, and the petrous ridge. Drilling may proceed rather safely at a minimum depth of 2.5 mm in an area 0.9 cm anterior and 1 cm inferior to the petrosigmoid intersection and petrous ridge, respectively. From there, identification of the vestibular aqueduct, genu, and horizontal portion is necessary to safely open the posterior wall of the internal auditory canal. The vestibular aqueduct represents the lateral and superior limits of drilling. The bone between these areas may then be safely drilled to a depth of at least 2.5 mm. A microneurosurgical dissection of the posterior pyramidal wall conducted in cadaveric material according to these guidelines did not violate any inner-ear structures.

TSF3, a global regulatory protein that silences transcription of yeast GAL genes, also mediates repression by alpha 2 repressor and is identical to SIN4

TSF3 encodes one of six (TSF1 to TSF6) recently identified global negative regulators of transcription in Saccharomyces cerevisiae. Mutant tsf3 strains exhibit defects in transcriptional silencing of the GAL1 promoter, allow expression from upstream activation sequence-less promoters, and exhibit pleiotropic defects in cell growth and development. Here we show that TSF3 is involved in transcriptional silencing mediated by the alpha 2 repressor and demonstrate that specific systems of transcriptional silencing may depend on the more global role of TSF3. Cloning and sequencing of TSF3 allowed us to predict a 974-amino-acid gene product identical to SIN4, a negative regulator of transcription of the HO (homothallism) mating type switching endonuclease. TSF3 disruptions are not lethal but result in phenotypes similar to those of the originally isolated alleles. Our results, together with those of Y. W. Jiang and D. J. Stillman (Mol. Cell. Biol. 12:4503-4514, 1992), suggest that TSF3 (SIN4) affects the function of the basal transcription apparatus, and this effect in turn alters the manner in which the latter responds to upstream regulatory proteins.

Cardiovascular deconditioning effects of long-term simulated weightlessness in rats

The aim of our serial work was to investigate the cardiovascular deconditioning effect of long-term simulated weightlessness and to elucidate its mechanisms. Our research goal was established in view of the following three reasons. Firstly, even after several decades of extensive research, there still exist significant gaps in our knowledge concerning microgravity induced cardiovascular effect. Secondly, to guarantee the health and safety of astronauts in the future prolonged missions, it is important to understand the cardiovascular adaptation to long-term weightlessness. Thirdly, the reported ultrastructural degenerative changes in myocardium of rats flown on the Cosmos 1887 biosatellite has raised concerns about the question whether long-term spaceflight may lead to myocardial degeneration. To achieve this, we considered an appropriate animal model to simulate cardiovascular and other effects of long-term microgravity was of first importance. By making some modifications to the Morey-Holton's model, a method of long-term tail-suspension with less stressful influence and no injurious effects on the tail skin was developed. Up to now, the longest period of suspension in our laboratory has been of 120-day long. In this paper, we will focus primarily on the findings from our recent works on the cardiovascular deconditioning effect of 90-/120-day tail-suspension and changes in baroreflex responsiveness and in contractility and ultrastructure of the heart in rats.