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Biomedical subjects

J M Hilton

Publications and source records attributed to J M Hilton.

At least 19 recordsLinked to original sources
PubMed2001

Phosphorylation of a synaptic vesicle-associated protein by an inositol hexakisphosphate-regulated protein kinase.

Despite the fact that inositol hexakisphosphate (InsP(6)) is the most abundant inositol metabolite in cells, its cellular function has remained an enigma. In the present study, we present the first evidence of a protein kinase identified in rat cerebral cortex/hippocampus that is activated by InsP(6). The substrate for the InsP(6)-regulated protein kinase was found to be the synaptic vesicle-associated protein, pacsin/syndapin I. This brain-specific protein, which is highly enriched at nerve terminals, is proposed to act as a molecular link coupling components of the synaptic vesicle endocytic machinery to the cytoskeleton. We show here that the association between pacsin/syndapin I and dynamin I can be increased by InsP(6)-dependent phosphorylation of pacsin/syndapin I. These data provide a model by which InsP(6)-dependent phosphorylation regulates synaptic vesicle recycling by increasing the interaction between endocytic proteins at the synapse.

Amino Acid Sequence↗
PubMed2000

Phaeochromocytomas discovered during coronial autopsies in Sydney, Melbourne and Auckland.

BACKGROUND: The diagnosis of phaeochromocytoma can be difficult and previous autopsy studies have found that many of these tumours are not recognised during life. AIM: To determine the incidence of phaeochromocytoma during coronial autopsies and the characteristics of the individuals concerned. METHOD: Review of coronial autopsy records from Auckland (1981-97), Melbourne (1991-97) and Sydney (1991-97). RESULTS: Twenty-two patients were found giving an incidence of 0.05% (one tumour per 2031 autopsies) with similar figures in each centre. Thirteen of the patients were men, 12 were overweight (body mass index >25 kg/m2) and three of the seven Auckland patients were Maori. Fourteen of the tumours were left-sided, one was extra-adrenal and none had metastasised. The one patient with bilateral tumours had multiple endocrine neoplasia syndrome type 2 (MEN-2) which had not been recognised during life. The heart weight was increased in 95% of the patients. The tumour may have contributed to the patient's death in up to 50% of the cases, although the true significance of these lesions as a cause of death remains unclear. Three patients died soon after general anaesthetics had been given for unrelated reasons. CONCLUSIONS: Even though phaeochromocytomas are uncommon, we fail to diagnose a significant number of these tumours during life. Methods are needed to increase the detection of phaeochromocytoma and to distinguish functional and non-functional tumours.

Adrenal Gland Neoplasms↗
PubMed2000

Identification of key components in the irreversibility of salmon calcitonin binding to calcitonin receptors.

This study investigates the poor reversibility of salmon calcitonin (sCT) binding to rat and human calcitonin receptors. Efficacy of CT and analogue peptides in (125)I-sCT binding competition and cAMP assays was compared with the dissociation kinetics of (125)I-labelled peptides. Assessment was performed on cells stably expressing either rat or human calcitonin receptors. Dissociation kinetics of the antagonists, sCT(8-32) and AC512, revealed that binding was rapidly and completely reversible at the receptors, despite high affinity binding, suggesting that poor reversibility required the active conformation of the receptor. G protein coupling was not essential as the dissociation kinetics of (125)I-sCT binding to cell membranes did not significantly alter in the presence of GTP gamma S. Time course experiments established that the transition to irreversibility was slow, while the reversible component of binding appeared to involve a single population of either receptor states or binding sites. Pre-bound (125)I-human CT dissociated rapidly from the receptors, indicating that not all agonists bound irreversibly. To identify structural features of sCT that contribute to its poor reversibility, dissociation kinetics of sCT analogues with various structural modifications were examined. Increasing truncation of N-terminal residues of sCT analogues led to a corresponding increase in the rate of peptide dissociation. Salmon CT peptides which had been substituted at the N-terminus by 13-21 residues of human CT (hCT) were equipotent with sCT in binding competition and cAMP accumulation assays but exhibited a dissociation rate similar to hCT. In contrast, despite lower affinity and efficacy at the receptors, the chimeric analogue sCT(1-16)-hCT(17-32) displayed poorly reversible binding, similar to sCT. Analysis of the dissociation kinetics of sCT analogues with differing alpha-helix forming potential indicated that the ability to form alpha-helical secondary structure was an important factor in the rate of ligand dissociation. We hypothesise that poor reversibility results from a conformational change in the receptor and/or ligand and that this is dependent, at least in part, on interaction with residues constrained within the alpha-helix of the peptide.

Animals↗
PubMed1999

Respiratory morbidity of hospitalized children with Trisomy 21.

OBJECTIVE: To review the respiratory morbidity in children with Trisomy 21 admitted to a teaching hospital. METHODOLOGY: A retrospective chart review of 232 admissions to John Hunter Children's Hospital during a 6.5-year period (1991-98). The primary outcome measures included: (i) primary reason for admission, (ii) concomitant respiratory pathology, (iii) admission to the Intensive Care Unit (ICU), (iv) length of stay and (v) costs of admission. RESULTS: Fifty-four per cent of admissions were primarily for respiratory tract pathology, dominated by pneumonia, bronchiolitis and croup. Admission to the ICU was required for 10% of admissions, most commonly for pneumonia (10/23). Congenital heart disease (CHD) was present in 33% of patients. The median length of stay and cost of admission for a child with Trisomy 21 (without CHD) with common respiratory conditions such as bronchiolitis, asthma or pneumonia was two to three times greater than in patients without Trisomy 21. CONCLUSION: Lower respiratory pathology is most common cause for acute hospital admission in children with Trisomy 21. The presence of CHD did not influence admission rates to hospital. However, patients with CHD had longer lengths of stay, appeared to have more severe illness, were more likely to require admission to an ICU and were more likely to require ventilatory support.

Adolescent↗
PubMed1998

Prevalence of Wernicke-Korsakoff syndrome in Australia: has thiamine fortification made a difference?

OBJECTIVE: To determine the prevalence of the Wernicke-Korsakoff syndrome (WKS) in Australia and compare this with previous studies. DESIGN AND SETTING: Prospective autopsy study at the New South Wales Institute of Forensic Medicine, 1996-1997. METHODS: Brains of deceased people (aged over 15 years) derived from 2212 sequential autopsies performed between 1 January 1996 and 31 December 1997 were studied macroscopically and microscopically to identify cases of WKS. MAIN OUTCOME MEASURES: Standard histological criteria for WKS and any available clinical data. RESULTS: Twenty-five cases of WKS were identified (prevalence, 1.1%), mostly among the 5.9% of the 2212 people who had a history suggestive of alcohol abuse. Only four cases (16%) had been diagnosed during life. CONCLUSIONS: There has been a significant reduction in the prevalence of WKS in Australia since the introduction of thiamine enrichment of bread flour. While the prevalence is still higher than in most other Western countries, further research is needed before adding thiamine to alcoholic beverages can be recommended.

Adolescent↗
PubMed1998

Purification of calcitonin-like peptides from rat brain and pituitary.

Accumulating evidence supports the existence of nonthyroidal calcitonin (CT)-like peptides, more similar to fish CTs, which may act as endogenous regulators of CT receptors in brain and other tissues. In this study, we have carried out large-scale extractions from Sprague-Dawley rat brain diencephalon and pituitary, and purified a novel, biologically active, CT-like peptide from pituitary. Monitoring of the calcitonin-like activity of the peptides from rat brain and pituitary required different detection systems. While the brain CT cross-reacted with C-terminally directed salmon CT-specific antisera, the pituitary CT did not. However, the pituitary CT was biologically active, exhibiting specific interaction with CT receptors to activate adenylate cyclase. Conventional chromatographic techniques were employed to purify the CT-like peptides. Although the brain CT was not purified to homogeneity, size exclusion chromatography revealed the presence of multiple molecular weight forms of immunoreactive CT. Of these, only the lowest molecular weight form was biologically active. Purification from the pituitary resulted in the isolation of a biologically active peptide with a mass of 3267 Da. This mass differs from the mass of both salmon and thyroid-derived rat CT. Initial amino acid sequencing of the pituitary CT indicated that it was N-terminally blocked. Following aminopeptidase digestion, a unique six amino acid sequence, EKSQSP, was identified. Elucidation of the amino acid composition provided supporting evidence that the peptide was novel and was consistent with a full length peptide of approximately 30 amino acids. These data support the existence of novel, nonthyroidal, CTs which are potential regulators of CT receptor-mediated functions.

Amino Acid Sequence↗
PubMed1997

Hydroxychloroquine therapy of diffuse pulmonary sarcoidosis in two Australian male children.

Sarcoidosis is a chronic granulomatous disease, seen infrequently in children, with the capacity to affect multiple systems. The incidence and prevalence of the disease in children is largely unknown but is dependent on many factors including: age, race and geographical location. There have been very few studies of sarcoidosis in Australian (Aboriginal or white) children. Diffuse pulmonary sarcoidosis is very rare in non-Scandinavian white Caucasian children, yet in the winter of 1992 two Caucasian males, aged 11.1 and 10.5 years were seen at the John Hunter Hospital in Newcastle. Both boys had pulmonary sarcoidosis and after an initial trial of treatment with steroids responded well to hydroxychloroquine therapy.

Antimalarials↗
PubMed1997

Structure/function relationships of calcitonin analogues as agonists, antagonists, or inverse agonists in a constitutively activated receptor cell system.

The structure/function relationship of salmon calcitonin (sCT) analogues was investigated in heterologous calcitonin receptor (CTR) expression systems. sCT analogues with progressive amino-terminal truncations intermediate of sCT-(1-32) to sCT-(8-32) were examined for their ability to act as agonists, antagonists, or inverse agonists. Two CTR cell clones, B8-H10 and G12-E12, which express approximately 5 million and 25,000 C1b receptors/cell, respectively, were used for this study. The B8-H10 clone has an approximately 80-fold increase in basal levels of intracellular cAMP due to constitutive activation of the overexpressed receptor. In whole-cell competition binding studies, sCT-(1-32) was more potent than any of its amino-terminally truncated analogues in competition for 125I-sCT binding. In cAMP accumulation studies, sCT-(1-32) and modified analogues sCT-(2-32) and sCT-(3-32) had agonist activities. SDZ-216-710, with an amino-terminal truncation of four amino acids, behaved as a partial agonist/antagonist, whereas amino-terminal truncations of six or seven amino acid residues produced a 16-fold reduction in basal cAMP levels and attenuated the response to the agonist sCT-(1-32) in the constitutively active CTR system. This inverse agonist effect was insensitive to pertussis toxin inhibition. In contrast, the inverse agonist activity of these peptides was not observed in the nonconstitutively active CTR system, in which sCT analogues with amino-terminal truncations of four or more amino acids behaved as neutral competitive antagonists. These results suggest that the inverse agonist activity is mediated by stabilization of the inactive state of the receptor, which does not couple to G protein, and attenuates basal signaling initiated by ligand-independent activation of the effector adenylyl cyclase.

Animals↗
PubMed1995

In vitro autoradiographic localization of the calcitonin receptor isoforms, C1a and C1b, in rat brain.

In this study the distribution of the calcitonin receptor isoforms, C1a and C1b, were mapped in rat brain using in vitro autoradiography and manipulation of their different pharmacological specificities. While salmon calcitonin binds to both receptors with high affinity, only the C1a receptor interacts with human calcitonin. Thus, the distribution of C1a specific binding sites was mapped using [125I]human calcitonin. The C1b receptors were mapped using [125I]salmon calcitonin in the presence of unlabelled human calcitonin and rat amylin, displacing binding of [125I]salmon calcitonin to C1a and C3 (amylin) sites, respectively. The distribution of C1a and C1b receptors was found to predominantly overlap. Brain regions displaying C1a, but little or no C1b, binding sites included the nucleus of the solitary tract, area postrema and the intermediate lobe of the pituitary. Although there were no nuclei expressing exclusively C1b receptors, parts of the mesencephalic and pontine reticular formation, and the thalamic paraventricular nucleus were enriched in C1b receptors relative to the density of C1a receptors in other brain regions. These data indicate that the relative expression of the two receptor isoforms, although predominately parallel, is not uniform in the rat brain.

Animals↗
PubMed1994

Medicolegal postmortem examinations in rural New South Wales. Another rural health problem.

OBJECTIVE: To investigate the quality of coronial postmortem examinations performed in rural New South Wales by Government Medical Officers. METHODS: We reviewed 100 cases, examining the history of the case provided by police officers, referral letters from Government Medical Officers and macroscopic reports of the postmortem findings. Tissue specimens received were correlated with histological findings. RESULTS: Only 11 cases were adequately recorded. Macroscopic description was poor in 42 cases. Major deficiencies identified included illegible hand written reports, inadequate description of organ systems, incorrect description of pathological findings and incorrect formulation of cause of death. Major diagnostic errors were identified in referred tissue samples in 13 cases--most commonly, mistaking postmortem blood clot for massive pulmonary embolism. Often organs were insufficiently or incorrectly dissected. CONCLUSIONS: Coronial postmortem examinations performed by Government Medical Officers in rural New South Wales are generally of a lower standard than should be accepted by the medicolegal community. These examinations should be viewed as specialist procedures and be performed by specialist pathologists only.

Autopsy↗
PubMed1994

Brains at necropsy: to fix or not to fix?

AIM: To investigate whether routine formalin fixation of all brains coming to necropsy increases the rate of detection of brain abnormalities relative to either selective formalin fixation of brain tissue or fresh dissection of all brain tissue at the time of post mortem examination. METHODS: A retrospective study of 300 medicolegal necropsies was performed. One hundred cases were examined by doctors with little or no formal training in necropsy pathology. One hundred cases were examined by forensic pathologists, who used their discretion as to whether to fix the brain in formalin. A further 100 cases were examined by neuropathologists; all the brains had already been fixed at the time of necropsy. RESULTS: When examined by doctors with little or no formal necropsy pathology training, only 15% of brains were found to be abnormal. In the case of selective fixation, 33% were found to be abnormal. When there was obligatory fixation of all brains, 51% of all brains were found to be abnormal. CONCLUSIONS: It is concluded that formalin fixation of the whole brain at the time of necropsy, followed by detailed examination of the brain by a neuropathologist, significantly increases the detection rate of brain pathology at necropsy.

Autopsy↗
PubMed1994

The clinical features of Ehlers-Danlos syndrome type VIIB resulting from a base substitution at the splice acceptor site of intron 5 of the COL1A2 gene.

The features of a 32 year old woman with Ehlers-Danlos syndrome type VIIB and affected members of her family, resulting from a mutation in one COL1A2 allele, were studied. Her dermal type I collagen contained alpha 2(I) chains and mutant pN-alpha 2(I) chains in which the amino-terminal propeptide remained attached to the alpha 2(I) chain. She was heterozygous for an AG-->AC mutation at the splice acceptor site of intron 5 of the COL1A2 gene. The mutation activated a cryptic AG splice acceptor site corresponding to positions +14 and +15 of exon 6 of the COL1A2 gene. In contrast to previous reports only five, rather than all 18, amino acids encoded by exon 6 were deleted in the proband. The deleted peptide removed the amino-proteinase cleavage site, but not the nearby lysine cross linking site in the amino-telopeptide of the alpha 2(I) chain. She was born with bilateral hip dislocations, knee subluxations, and generalised joint hypermobility. Bilateral inguinal herniae and an umbilical hernia were present at birth. Facial features included a depressed nasal bridge with prominent paranasal folds. The skin was soft, moderately hyperelastic, and sagged over the face. Skin fragility and easy bruising were apparent from childhood. Skin wounds healed slowly and with broad, paper thin scars. Throughout her life, she had multiple fractures of the small bones of her hands and feet following moderate trauma. Electron microscopy of the proband's dermis as well as deep fascia and hip joint capsule from her affected brother showed that collagen fibrils in transverse section were nearly circular but with irregular margins. Light microscopy of bone from her affected brother and son showed normal Haversian systems and lamellar bone. All of these tissues contained approximately equal amounts of the normal and mutant alpha2(I) chains. The findings of this study confirm that loss of the amino-proteinase cleavage site of the pro alpha2(I) collagen chains, owing to anomalous splicing of exon 6 sequences in the conversion of pre-mRNA to mRNA, produces the clinical features of Ehlers-Danlos syndrome type VIIB. The history of frequent fractures found in this family is atypical and indicates an overlap with osteogenesis imperfecta.

Adult↗