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Biomedical subjects

S C Robertson

Publications and source records attributed to S C Robertson.

10 recordsLinked to original sources
PubMed1997

Hemorrhagic complications in association with silastic dural substitute: pediatric and adult case reports with a review of the literature.

OBJECTIVE AND IMPORTANCE: Delayed intracranial hemorrhage is an unusual complication associated with the use of silastic dural substitute. CLINICAL PRESENTATION: We present three patients with this complication. Two adult patients developed subdural and epidural hemorrhages 9 months and 10 years after posterior fossa surgery for Chiari malformations. The remaining patient, a 13-month-old child, is the youngest reported patient to develop an epidural hematoma 8 months after a craniosynostosis repair. INTERVENTION: The hematomas were removed with the silastic dural substitute from all three patients, and the dural defect was repaired with autologous paracervical fascia. CONCLUSION: Silastic dural grafts have an increased incidence of hemorrhage associated with their use. A slight increase in the prevalence of hemorrhagic complications with silastic dural substitute was observed in women. We report our radiographic and surgical findings, including an extensive review of the literature.

Adult↗
PubMed1996

Identification of an autoinhibitory region in the activation loop of the Mos protein kinase.

The Mos protein is a serine/threonine protein kinase which acts to regulate progression through meiosis in vertebrate oocytes. Although Mos function is dependent on its ability to act as a protein kinase, little is known about the factors which regulate Mos kinase activity. To understand the mechanism by which Mos kinase activity is regulated, we have used molecular modeling to construct a three-dimensional model of Mos based on the crystallographic coordinates of cyclic AMP-dependent kinase (PKA). This model identified a loop in Mos which is positioned near the active site and appears capable of blocking substrate access to the active site. Mutagenesis was used to construct altered forms of the Mos protein with deletions of parts or all of the loop. In vitro kinase assays showed that Mos proteins with the loop removed had up to a fourfold increase in kinase activity compared with the wild-type protein, indicating that the loop acts in an autoinhibitory manner for Mos kinase activity. Point mutations were also made on individual residues of the loop which were determined from the molecular model to be capable of reaching the active site. Determination of the kinase activities of these mutants showed that individual mutations in the loop region are capable of either increasing or decreasing kinase activity with regard to the wild-type protein. These data suggest that the loop identified in Mos acts as an autoinhibitor of kinase activity.

Amino Acid Sequence↗
PubMed1996

Profound ligand-independent kinase activation of fibroblast growth factor receptor 3 by the activation loop mutation responsible for a lethal skeletal dysplasia, thanatophoric dysplasia type II.

Thanatophoric dysplasia type II (TDII) is a neonatal lethal skeletal dysplasia caused by a recurrent Lys-650-->Glu mutation within the highly conserved activation loop of the kinase domain of fibroblast growth factor receptor 3 (FGFR3). We demonstrate here that this mutation results in profound constitutive activation of the FGFR3 tyrosine kinase, approximately 100-fold above that of wild-type FGFR3. The mechanism of FGFR3 activation in TDII was probed by constructing various point mutations in the activation loop. Substitutions at position 650 indicated that not only Glu but also Asp and, to a lesser extent, Gln and Leu result in pronounced constitutive activation of FGFR3. Additional mutagenesis within the beta10-beta11 loop region (amino acids Tyr-647 to Leu-656) demonstrated that amino acid 650 is the only residue which can activate the receptor when changed to a Glu, indicating a specificity of position as well as charge for mutations which can give rise to kinase activation. Furthermore, when predicted sites of autophosphorylation at Tyr-647 and Tyr-648 were mutated to Phe, either singly or in combination, constitutive kinase activity was still observed in response to the Lys-650-->Glu mutation, although the effect of these mutations on downstream signalling was not investigated. Our data suggest that the molecular effect of the TDII activation loop mutation is to mimic the conformational changes that activate the tyrosine kinase domain, which are normally initiated by ligand binding and autophosphorylation. These results have broad implications for understanding the molecular basis of other human developmental syndromes that involve mutations in members of the FGFR family. Moreover, these findings are relevant to the study of kinase regulation and the design of activating mutations in related tyrosine kinases.

Amino Acid Sequence↗
PubMed1992

Crystal structure of the phosphotyrosine recognition domain SH2 of v-src complexed with tyrosine-phosphorylated peptides.

Three-dimensional structures of complexes of the SH2 domain of the v-src oncogene product with two phosphotyrosyl peptides have been determined by X-ray crystallography at resolutions of 1.5 and 2.0 A, respectively. A central antiparallel beta-sheet in the structure is flanked by two alpha-helices, with peptide binding mediated by the sheet, intervening loops and one of the helices. The specific recognition of phosphotyrosine involves amino-aromatic interactions between lysine and arginine side chains and the ring system in addition to hydrogen-bonding interactions with the phosphate.

Amino Acid Sequence↗
PubMed1992

Mechanisms of cardiovascular responses to glycine injected into the dorsal vagal motor nucleus in rat.

Microinjection of glycine into the dorsal vagal motor nucleus of anesthetized rats elicits increases in arterial pressure and heart rate. In the nucleus tractus solitarii, where cardiovascular responses to injection of glycine may be mediated through release of acetylcholine, there is a dense concentration of glycinergic nerve terminals and glycine receptors. In this study, using immunohistochemical methods, we show that glycine terminals and receptors are present in caudal dorsal vagal motor nucleus, although the concentration of both terminal elements is less than in adjacent nucleus tractus solitarii. Responses to glycine microinjected into the dorsal vagal motor nucleus are blocked by the muscarinic antagonist atropine microinjected at the same site; but, unlike responses to glycine in the nucleus tractus solitarii, responses to glycine in the dorsal vagal motor nucleus are not prolonged by physostigmine. These data support the possibility that endogenous glycine may play a role as a transmitter in the dorsal vagal motor nucleus. Responses to glycine may be mediated through actions at muscarinic receptors but not through acetylcholine itself.

Animals↗
PubMed1991

Glycine microinjected into nucleus tractus solitarii of rat acts through cholinergic mechanisms.

Previous studies have demonstrated the release of glycine from neurotransmitter pools in the region of the nucleus tractus solitarii (NTS) where cardiovascular afferents terminate. Microinjection of glycine into NTS elicits decreases in arterial pressure and heart rate; these effects are also produced by glutamate or acetylcholine. As glycine may act both at the N-methyl-D-aspartate (NMDA)-receptor complex and centrally to release acetylcholine, we have sought to determine whether the cardiovascular responses to exogenous glycine are mediated through glutamatergic or cholinergic mechanisms. Responses to glycine microinjected into the NTS of anesthetized rats were not affected by blockade of the NMDA receptor complex but, like acetylcholine, were blocked by muscarinic receptor blockade. Physostigmine prolonged responses to glycine. Subthreshold doses of glycine, which augmented responses to acetylcholine microinjected into NTS, either decreased or had no effect on glutamate or NMDA. This study supports a role for glycine in cardiovascular regulation by the NTS and suggests that the actions of glycine may be effected, at least in part, through cholinergic mechanisms.

Acetylcholine↗
PubMed1991

Nucleus prepositus hypoglossi. A medullary pressor region.

Electrical stimulation of fibers of passage through the fastigial nucleus increases arterial pressure. To identify nuclei that may project through the pressor region of the fastigial nucleus, we injected the retrograde tracer fast blue unilaterally at confirmed pressor sites in the nucleus. In seven rats, we found dense fluorescent labeling bilaterally in the external cuneate, lateral reticular, medial vestibular, and caudal prepositus hypoglossi nuclei, and contralaterally in the inferior olivary nucleus. There had been no reports of a cardiovascular role for the nucleus prepositus hypoglossi; thus, we sought to determine if electrical or chemical stimulation of that nucleus or the adjacent medial vestibular nucleus altered arterial pressure or heart rate in 24 anesthetized rats. Both types of stimuli to the caudal, but not the rostral, pole of the nucleus prepositus hypoglossi or to the medial vestibular nucleus elicited an increase in arterial pressure; bradycardia accompanied the former and tachycardia the latter. Both the nucleus prepositus hypoglossi and medial vestibular nucleus may participate in central cardiovascular regulation.

Animals↗
PubMed1989

Glycine, like glutamate, microinjected into the nucleus tractus solitarii of rat decreases arterial pressure and heart rate.

Glycinergic mechanisms have been implicated in central cardiovascular regulation. However, the inhibitory amino acid's role in the nucleus tractus solitarii (NTS), the site of termination of cardiovascular afferents, has not been clarified. Thus, we sought to determine if the microinjection of glycine into the NTS alters arterial pressure and heart rate. Microinjections of glycine, like glutamate, confined to the NTS decreased arterial pressure and heart rate in a neurally mediated, dose-dependent manner. The glycine antagonist strychnine completely blocked these effects of glycine but did not itself alter arterial pressure or heart rate, or interfere with the baroreceptor reflex. The acute hypotensive, bradycardic response to glycine was followed by a period during which glycine essentially eliminated the cardiovascular responses to the microinjection into the NTS of glutamate, an amino acid reputed to be a transmitter in the baroreceptor reflex arc. These data suggest that glycine is involved in cardiovascular regulation by the NTS but do not support its being an integral transmitter in the baroreceptor reflex.

Animals↗