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Biomedical subjects

M J Hunter

Publications and source records attributed to M J Hunter.

At least 19 recordsLinked to original sources
PubMed2006

The role of corticosterone in supporting migratory lipogenesis in the dark-eyed Junco, Junco hyemalis: a model for central and peripheral regulation.

The functional role of corticosterone (CORT) in regulating migratory hyperphagia and lipogenesis was investigated in an annual migrant, the dark-eyed junco (Junco hyemalis). Intraperitoneal injections of either dexamethasone (9 microg DXM/500 microL of 5% EtOH in saline, n=10) to inhibit an increase in baseline CORT or saline (5% EtOH, n=9) were given every 48 h for 15 d after transfer from short (10.5L:13.5D) to long (15.5L:8.5D) days. Food intake, body mass, furcular fat deposition scores, and nocturnal migratory activity were recorded for 29 d after photostimulation. Both groups showed the same increase in daily food intake over the study period (DXM=52%, control=41%). Controls began to increase baseline CORT and mass about 2 wk after photostimulation. DXM-treated birds maintained low CORT and did not increase mass or CORT until injections ceased, at which time they gained mass at the same rate shown earlier by controls. DXM-treated birds did not show greater levels of migratory activity despite experiencing an increase in energy intake during the CORT-inhibited period. Collectively, the results support the migration modulation hypothesis, illustrating how an increase in baseline CORT is needed to support the development of migratory condition. We address the apparent conflict with earlier studies on CORT and migratory food intake and propose a model in which migratory hyperphagia is supported by changes in centrally regulated responses to CORT that can occur even if CORT remains low and lipogenesis is regulated predominantly by peripheral mechanisms that require an increase in baseline CORT.

Animal Migration↗
PubMed2001

Eagle's syndrome: a report of 4 patients treated using a modified extraoral approach.

PURPOSE: This study evaluated a slightly modified extraoral approach to removing the symptomatic elongated styloid process. A brief description of this surgical technique and its comparison to the intraoral approach is provided. PATIENTS AND METHODS: Four patients in whom an extraoral approach was used to expose and remove the elongated calcified stylohyoid complex were evaluated. Five sides were treated and reviewed individually. All patients were interviewed preoperatively and postoperatively, and their records were thoroughly examined. Patients were objectively evaluated for pain, function, sensory and motor nerve deficits, and aesthetics. RESULTS: Follow-up time ranged from 6 to 39 months with an average of 21 months. Improvement in the original symptoms was reported for 4 of the 5 operated sides. Three of 5 procedures resulted in more than an 80% reduction in pain and improvement in function. All patients had a satisfactory cosmetic result and no paresthesia. CONCLUSIONS: The advantages of the extraoral approach are reflected in this small retrospective study by the absence of perioperative complications and the minimal blood loss, surgical morbidity, and hospital stay.

Adult↗
PubMed2000

Zinc-reversible antimicrobial activity of recombinant calprotectin (migration inhibitory factor-related proteins 8 and 14).

Recombinant calprotectin, consisting of 2 individual peptide chains also called migration inhibitory factor-related protein (MRP)-8 and MRP14, was tested for antimicrobial activity in a Candida albicans growth inhibition assay. Both chains contain HEXXH zinc-binding sites and might be expected to manifest zinc-reversible, antimicrobial activity similar to that of native calprotectin. When tested alone, neither MRP8 nor MRP14 showed activity in the Candida growth assay. A synthetic 20-amino acid peptide containing the HEXXH sequence of MRP14, along with a nearby HHH sequence, was also inactive in this assay. However, equimolar concentrations of MRP8 and MRP14 demonstrated a potent growth inhibitory effect that was reversible by 30 microM zinc. Truncated MRP14 (missing the C-terminal GHHHKPGLGEGTP tail) used in combination with MRP8 demonstrated zinc-reversible activity that was somewhat less than that with complete MRP14. These results suggest that intact calprotectin, consisting of a heterodimer of MRP8 and MRP14, is necessary to form a zinc-binding site capable of inhibiting microbial growth.

Amino Acid Sequence↗
PubMed1998

High level expression and dimer characterization of the S100 EF-hand proteins, migration inhibitory factor-related proteins 8 and 14.

The phenotypical and functional heterogeneity of different macrophage subpopulations are defined by discrete changes in the expression of two S100 calcium-binding proteins, migration inhibitory factor-related proteins (MRPs) 8 and 14. To further our understanding of MRP8 and MRP14 in the developmental stages of inflammatory responses, overexpression of the MRPs was obtained through a combination of a T7-based expression vector and the Escherichia coli BL21 (DE3) cell line. An efficient, two-step chromatographic protocol was then developed for rapid, facile purification. Extensive biophysical characterization and chemical cross-linking experiments show that MRP8 and MRP14 form oligomers with a strong preference to associate as a heterodimer. Heteronuclear NMR experiments indicate that a specific well packed dimer is formed only in equimolar mixtures of the two proteins. Our results suggest that there is a unique complementarity in the interface of the MRP8/MRP14 complex that cannot be fully reproduced in the MRP8 and MRP14 homodimers.

Amino Acid Sequence↗
PubMed1997

Structure of the fifth EGF-like domain of thrombomodulin: An EGF-like domain with a novel disulfide-bonding pattern.

The structure of the fifth EGF-like domain (residues Q387 to E426) of thrombomodulin (TMEGF5) has been determined by two-dimensional NMR. TMEGF5 binds to thrombin with a Ki of 1.9 microM and has been shown to have a novel disulfide bonding pattern in a fully active fragment of TM. In EGF, the disulfide bonding pattern is (1-3,2-4, 5-6), while TMEGF5 has an uncrossed (1-2,3-4,5-6) pattern. The structure of this novel domain, determined from 483 NOE-derived distance restraints, appears to have diverged from the common EGF-like structure. Superposition of the 14 lowest-energy structures of TMEGF5 gives an overall r.m.s.d. of 1.09 A for the backbone atoms. The central two-stranded beta-sheet common to all EGF-like domains is not present in TMEGF5. The A loop, residues C390 to C395, is twisted away from interacting with the B loop, residues C399 to C407, as in EGF, and is close to the C loop, residues C409 to C421. This twist causes the N and C termini to be closer together in TMEGF5 than in EGF. Most of the residues that are important for activity lie on one face of the molecule, which is likely to be the thrombin-binding surface of the domain. The structure of the C loop within the domain, which is a beta-hairpin similar to EGF, is similar to the structure of a synthetic version of the loop bound to thrombin as determined by transferred NOE experiments. Despite the similarity in the structures of the loops, the residues immediately following C421 are in different positions in the two structures suggesting that these "tail" residues may change conformation upon thrombin binding.

Amino Acid Sequence↗
PubMed1997

Morbidity and mortality with outpatient anesthesia: the experience of a residency training program.

PURPOSE: Previous studies regarding anesthetic-related morbidity and mortality rates in the oral surgery office have usually taken the form of a survey. This retrospective investigation of outpatient anesthetic morbidity and mortality was undertaken to compare the safety record of an oral and maxillofacial surgery training program with that of private practitioners. MATERIALS AND METHODS: Records from all outpatient general anesthesia cases performed in the Department of Oral and Maxillofacial Surgery at the Boston University Goldman School of Graduate Dentistry between August 13, 1990, and September 30, 1994, were reviewed for the incidence of nineteen separate categories of morbidity. RESULTS: There were 1,126 general anesthetics performed. There were 26 recorded incidents of morbidity (2.3%), none of which resulted in any postoperative sequelae. There were no deaths. The most common complication encountered was laryngospasm, with nine recorded incidents (0.8%). The second most common complication was cardiac dysrhythmia with eight recorded incidents (0.8%). CONCLUSIONS: The low incidence of anesthetic-related morbidity seen in this study can most likely be attributed to proper patient selection. A carefully reviewed medical history and physical examination are the two most useful methods to prevent anesthetic emergencies. Another factor considered when selecting the proper anesthetic method includes the length and difficulty of the surgical procedure, with outpatient general anesthesia being reserved for those procedures that are predicted to be relatively short (30 to 45 minutes), and with little potential for airway difficulties.

Ambulatory Surgical Procedures↗
PubMed1997

A split-shank prefabricated post system: a critical multidisciplinary review.

A multidisciplinary panel of senior academics and practitioners has evaluated a system of prefabricated threaded split-shank posts (Flexi-Post/Flexi-Flange) from published research and their own clinical use. These posts have been compared with requirements of an ideal post system in relation to clinical use, stress effects, stress distribution, retention, loosening and displacement, provision for cores, and biocompatibility. The purpose was to provide this critical review to allow interested clinicians to compare this novel design to other available post systems.

Dental Prosthesis Design↗
PubMed1996

The fifth epidermal growth factor-like domain of thrombomodulin does not have an epidermal growth factor-like disulfide bonding pattern.

The disulfide bonding pattern of the fourth and fifth epidermal growth factor (EGF)-like domains within the smallest active fragment of thrombomodulin have been determined. In previous work, this fragment was expressed and purified to homogeneity, and its cofactor activity, as measured by Kcat for thrombin activation of protein C, was the same as that for full-length thrombomodulin. CNBr cleavage at the single methionine in the connecting region between the domains and subsequent deglycosylation yielded the individual EGF-like domains. The disulfide bonds were mapped by partial reduction with tris(2-carboxyethyl)phosphine according to the method of Gray [Gray, W. R. (1993) Protein Sci. 2, 1732-1748], which provides unambiguous results. The disulfide bonding pattern of the fourth EGF-like domain was (1-3, 2-4, 5-6), which is the same as that found previously in EGF and in a synthetic version of the fourth EGF-like domain. Surprisingly, the disulfide bonding pattern of the fifth domain was (1-2, 3-4, 5-6), which is unlike that found in EGF or in any other EGF-like domain analyzed so far. This result is in line with an earlier observation that the (1-2, 3-4, 5-6) isomer bound to thrombin more tightly than the EGF-like (1-3, 2-4, 5-6) isomer. The observation that not all EGF-like domains have an EGF-like disulfide bonding pattern reveals an additional element of diversity in the structure of EGF-like domains.

Amino Acid Sequence↗
PubMed1996

Recognition of the scope of oral and maxillofacial surgery by the public and health care professionals.

PURPOSE: A recent British study has reported a lack of awareness among the general public as to the benefits provided by the specialty of oral and maxillofacial surgery (OMFS). Medical and dental practitioners surveyed had a greater awareness of OMFS than the general public, yet were deficient in knowledge of the wide range of services provided by them. Therefore, a similar survey was conducted in the Boston area to determine the awareness among the general public and health professionals of the proper providers of treatment for the maxillofacial region and the level of knowledge of the specialty of OMFS. MATERIALS AND METHODS: The study incorporated five groups of respondents: dental students, dental practitioners, medical students, medical practitioners, and the general public. The survey was mailed, or distributed, randomly to persons representing each group in the Boston area. Between 200 and 300 surveys were sent to each group, and data collection was stopped at 100 responses per group. Surveys from the general public were screened to eliminate responders involved in health professions. For each of 20 specific situations or treatments, respondents were asked to choose a source of treatment from among four categories of specialists: ear nose and throat surgery (ENT), plastic surgery, OMFS, and periodontology. A chi-square analysis was performed for each question to compare the pattern of responses among categories of respondents. RESULTS: The data showed that most of the health professionals, 90% of students, and 98% of practitioners had heard of OMFS, whereas only 62% of the public have heard of this specialty. Furthermore, only 22% of the lay responders had ever been treated by an OMFS. The results also suggested that many health professionals had a lack of understanding about the wide scope of surgical procedures that OMFSs offer. CONCLUSION: Despite all the progress that has occurred in OMFS, a large portion of the American population is still unaware of the specialty. If patients are to receive the best treatment available, it is essential to educate health care consumers and providers about the different specialties available and their role within the health profession.

Attitude of Health Personnel↗
PubMed1995

Synthesis, activity, and preliminary structure of the fourth EGF-like domain of thrombomodulin.

The fourth EGF-like domain of thrombomodulin (TM4), residues E346-F389 in the TM sequence, has been synthesized. Refolding of the synthetic product under redox conditions gave a single major product. The disulfide bonding pattern of the folded, oxidized domain was (1-3, 2-4, 5-6), which is the same as that found in EGF protein. TM4 was tested for TM anticoagulant activity because deletion and substitution mutagenesis experiments have shown that the fourth EGF-like domain of TM is essential for TM cofactor activity. TM4 showed no TM-like activity in two assay systems, both for inhibition of fibrin clot formation, and for cofactor activity in thrombin activation of protein C. A preliminary structure of TM4 was determined by 2D 1H NMR from 519 NOE-derived distance constraints. Distance geometry calculations yielded a single convergent structure. The structure resembles the structure of EGF and other known EGF-like domains but has some key differences. The central two-stranded beta-sheet is conserved despite the differences in the number of amino acids in the loops. The C-terminal loop formed by the disulfide bond between C372 and C386 in TM4 is five amino acids longer than the analogous loop between C33 and C42 of EGF protein. This loop appears to have a different fold in TM4 than in EGF protein. The loop forms the two outside strands of a broken, irregular tri-stranded beta-sheet, and amino acids H384-F389 lie between the two strands forming the middle strand of the sheet. Thus, although the C-terminus of EGF protein forms one of the outside strands of a tri-stranded antiparallel sheet, the C-terminus of TM4 forms the inside strand of an irregular tri-stranded parallel-anti-parallel sheet. The residues D349, E357, and E374, which were shown to be critical for cofactor activity by alanine scanning mutagenesis, all lie in a patch near the C-terminal loop, and are solvent accessible. The other critical residues, Y358 and F376, are largely buried and appear to play essential structural rather than functional roles.

Amino Acid Sequence↗
PubMed1995

Thrombin-binding affinities of different disulfide-bonded isomers of the fifth EGF-like domain of thrombomodulin.

The fifth EGF-like domain of thrombomodulin (TM), both with and without the amino acids that connect the fifth domain to the sixth domain, has been synthesized and refolded to form several different disulfide-bonded isomers. The domain without the connecting region formed three disulfide-bonded isomers upon refolding under redox conditions. Of these three isomers, the (1-2,3-4,5-6) bonded isomer was the best inhibitor of fibrinogen clotting and also of the thrombin-TM interaction that results in protein C activation, but all the isomers were inhibitors in both assays. The isomer containing an EGF-like disulfide-bonding pattern (1-3,2-4,5-6) was not found among the oxidation products. The domain with the connecting region amino acids (DIDE) at the C-terminus formed two isolable products upon refolding in redox buffer. These products had the same two disulfide-bonding patterns as the earliest and latest eluting isomers of the domain without the DIDE. In order to compare the thrombin-binding affinities of these isomers to the isomer with the EGF-like disulfide bonds, acetamidomethyl protection of the second and fourth cysteines was used to force the disulfide bonds into the EGF-like pattern. Thrombin-binding affinity, measured as inhibition of fibrinogen clotting and as inhibition of protein C activation correlated inversely with the number of crossed disulfide bonds. As was found for the domain without the connecting region, the isomer that was the best inhibitor of fibrinogen clotting and of protein C activation was the isomer with no crossing disulfide bonds (1-2,3-4,5-6).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1995

Large-scale expression, purification and characterization of small fragments of thrombomodulin: the roles of the sixth domain and of methionine 388.

Fragments of human thrombomodulin (TM) have been expressed in large quantities in the Pichia pastoris yeast expression system and purified to homogeneity. Fermentation of P. pastoris resulted in yields of 170 mg/l TM. Purification to homogeneity resulted in an overall 10% yield, so that quantities of approximately 20 mg purified fragments can be readily obtained. Smaller fragments of TM, such as the individual fourth or fifth domains, were not active, nor were equimolar mixtures of the two domains. These results demonstrate that the fourth and fifth epidermal growth factor (EGF)-like domains together comprise the smallest active fragment of TM. The fragment containing the fourth and fifth EGF-like domains [TMEGF(4-5)] had 10% the specific activity of rabbit TM. Comparison of the M388L mutant TMEGF(4-5) fragment with the same mutant TMEGF(4-5-6) fragment showed that the fragment with the sixth domain had a 10-fold better Km value for thrombin than the fragment that did not contain the sixth domain; this factor completely accounts for the higher specific activity of the fragments containing the sixth domain. Comparison of the wild-type and M388L mutants showed that the M388L mutation resulted in a 2-fold increase in kcat for the activation of protein C by the thrombin-TM fragment complex, completely accounting for the 2-fold increase in specific activity of these mutant fragments.

Amino Acid Sequence↗
PubMed1992

Supplemental oxygen after outpatient oral and maxillofacial surgery.

Arterial oxygen saturation (SpO2) was monitored postoperatively with pulse oximetry in 72 dental patients. Intravenous general anesthesia was employed in 57 patients. All of these patients received supplemental oxygen intraoperatively, and of these, 29 received supplemental oxygen postoperatively. Fifteen patients received only local anesthesia without supplemental oxygen and served as the control group. Continuous pulse oximetry revealed 43 episodes of arterial oxygen desaturation (SpO2 decreases greater than 3% from baseline) in patients who did not receive postanesthesia supplemental oxygen and eight episodes of desaturation in patients who did receive postanesthesia oxygen. Patients with a smoking history had more episodes of desaturation than did nonsmokers in the group that received general anesthesia and breathed room air postoperatively. The total amount of methohexital administered had no significant effect on the number of patients with desaturation episodes. These observations emphasize the need for postoperative oxygen for patients who undergo general anesthesia for outpatient oral and maxillofacial surgery.

Adolescent↗
PubMed1985

The sagittal vestibulocollic reflex and its interaction with neck proprioceptive afferents in the decerebrate cat.

The sagittal vestibulocollic reflex (v.c.r.) evoked by nose-up, nose-down movements of the head, has been studied in the neck extensor muscle biventer cervicis in the decerebrate cat. Nose-down movements of the head increased, and nose-up movements decreased, electromyographic (e.m.g.) activity in the biventer cervicis muscles of the left and right sides. At low frequencies of sinusoidal head movement (0.1-0.5 Hz), the gain of the sagittal v.c.r. was approximately constant, and e.m.g. modulation showed a phase lead of about 40 deg with respect to head position. At higher frequencies (2-5 Hz), v.c.r. gain increased at a rate close to 40 dB/decade, and phase lead increased to approach 150 deg. The relation between head movement and v.c.r. activity may be described by a transfer function containing two lead terms, with time constants of 0.07 and 0.23 s, and two lag terms, with time constants of 5.3 and 9.9 s. When movements of the head were accompanied by stretching of the biventer cervicis muscles, the gain of the sagittal v.c.r. was increased threefold, at all frequencies between 0.1 and 5 Hz, with no substantial change in phase. Sinusoidal stretching of the biventer cervicis muscles, with the head stationary, evoked a stretch reflex (cervicocollic reflex, c.c.r.) the behaviour of which was similar to that of a second-order system described by a transfer function containing two lead terms with time constants of 0.07 and 0.16 s. This difference in dynamics between the v.c.r. and the c.c.r. indicates that the lag terms in the v.c.r. transfer function reflect the frequency-response properties of the vestibular pathway to the biventer cervicis muscles, as they do not appear when the same muscles participate in the c.c.r. The vectorial differences between the frequency-response of the sagittal v.c.r. with and without concomitant stretching of the biventer cervicis muscles is quantitatively similar to the frequency-response of the c.c.r. evoked by sinusoidal stretching. The inputs from the vestibular and stretch receptors thus appear to sum linearly to produce the increase in v.c.r. gain, at least over the frequency range 0.1-1 Hz. Since most head movements, and all voluntary head movements, involve a rotation of the head in relation to the neck, the potentiation of the gain of the v.c.r. by afferents from stretch receptors (presumably muscle spindles) in the neck muscles is an important factor in the normal reflex stabilization of head position.

Animals↗
PubMed1984

Arsenazo III used as a calcium ion indicator in mouse oocytes.

The Ca2+-indicator dye Arsenazo III has been injected into mouse oocytes by intracellular ionophoresis, and the optical absorbance of the injected dye measured using a double-beam microspectrophotometer. The absorbance spectrum shows a broad peak between 565 and 580 nm, with a maximum of 0.020-0.095 in different oocytes. From these values, intracellular dye concentrations were estimated to be 0.1-0.5 mM, although estimated concentrations up to 1.0 mM have been used in later experiments where the dye absorbance was measured only at selected wave-lengths. The transport number for intracellular ionophoresis of the dye has been estimated. The mean value was 0.009 in experiments where the injection current was allowed to cross the cell membrane, but was only 0.0015 when the injection current was balanced by a current of opposite polarity through a second electrode barrel. In oocytes exposed to the mitochondrial uncoupler DNP (2,4-dinitrophenol), the shape of the Arsenazo III absorbance spectrum was found to change. The resulting difference spectra show the peaks at about 610 and 660 nm which are characteristic features of the Arsenazo III Ca2+-difference spectrum. These absorbance changes were not completely reversible on removal of DNP. Changes in the optical absorbance of Arsenazo III have been observed in oocytes injected with Ca2+ by intracellular ionophoresis. Estimated increases of intracellular free [Ca2+], which were of the order of 1 microM and decayed within 30 s, are discussed in relation to the Ca2+-buffering and Ca2+-elimination properties of the oocyte.

2,4-Dinitrophenol↗
PubMed1983

Interaction of alpha 2-macroglobulin with trypsin, chymotrypsin, plasmin, and papain.

The interaction alpha 2-macroglobulin with four proteinases has been investigated by binding assays and by gel electrophoresis. At pH 7.65 the binding ratios of the proteinase-alpha 2-macroglobulin complexes were found to be 2:1 (trypsin and papain), 1.4:1 (chymotrypsin), and 1:1 (plasmin). The progressive decrease in the stoichiometry of the three seryl proteinase complexes was paralleled by a concomitant decrease in the proteinase-dependent specific cleavage of the alpha 2-macroglobulin peptide chains. Rate studies have shown that the relative rates of reaction of the proteinases with alpha 2-macroglobulin also varied greatly: papain greater than trypsin greater than chymotrypsin greater than plasmin. The data suggest that the ability of a proteinase to saturate the second proteinase binding site is a reflection of its ability to bind to alpha 2-macroglobulin and cleave the second pair of scissile alpha 2-macroglobulin peptide bonds before the alpha 2-macroglobulin has undergone the conformational change initiated by the formation of the 1:1 proteinase alpha 2-macroglobulin complex.

Chymotrypsin↗