Search PubMed⌕ Search

Biomedical subjects

D Smyth

Publications and source records attributed to D Smyth.

At least 19 recordsLinked to original sources
PubMed1998

Spatial-frequency tuning and geniculocortical projections in the visual cortex (areas 17 and 18) of the pigmented ferret.

We have examined the spatial-frequency selectivity of neurons in areas 17 and 18 of the adult pigmented ferret, by measuring how the amplitude of response depends on the spatial-frequency of moving sinusoidal gratings of optimal orientation and fixed contrast. Neurons in area 17 of the ferret respond optimally to low spatial frequencies [average 0.25 cycles per degree (c/deg)], much lower than the optima for cat area 17. The tuning curves are of the same form as those found in cat and monkey: unimodal with bandwidths in the range 0.8-3.5 octaves. Neurons in area 18 of the ferret respond optimally to even lower spatial frequencies (average 0.087 c/deg) than area 17 neurons, and the distributions of optimal spatial frequency for areas 17 and 18 hardly overlap. In both cortical areas, the bandwidth of the tuning curves is inversely correlated with optimal spatial frequency. This marked difference in tuning between the two cortical areas is probably attributable to differential geniculo-cortical projections. Small injections of fluorescent latex microspheres or horseradish peroxidase (HRP) were made into area 17 or area 18 in order to investigate the populations of geniculate neurons projecting to the two cortical areas. After injections into area 17, labelled neurons are found predominantly in the geniculate A layers, with a few neurons labelled in the C layers. Conversely, after an area 18 injection, similar numbers of labelled neurons are found in the C layers as in the A layers. Soma-size analysis of the neurons in the A-layers suggests the existence of two populations of relay neurons, which project differentially to areas 17 and 18. The different geniculate inputs and the different spatial-frequency tuning in areas 17 and 18 may imply that the two cortical areas process visual information more in parallel than in series.

Animals↗
PubMed1997

Recurrent laryngeal nerve dysfunction following carotid endarterectomy.

Recurrent laryngeal nerve dysfunction is a significant complication of carotid endarterectomy and vocal cord paralysis is a major source of morbidity. This study prospectively assessed patients undergoing carotid endarterectomy to determine the nature and frequency of vocal cord damage and attempt to identify avoidable factors. Fifty consecutive patients undergoing carotid endarterectomy for symptomatic disease were studied. A standardized surgical technique was used emphasizing identification of the vagus nerve and minimal disturbance of the surrounding tissues. All patients underwent pre-operative and post-operative (day 2) indirect laryngoscopy and videostroboscopy. Pre-operative assessment found asymptomatic compensated vocal cord paralysis in one patient who had previously had a stroke. Post-operative laryngoscopy revealed asymptomatic impaired vocal cord mobility in three patients (6%) all of whom recovered completely. In addition six patients (12%) developed post-operative hoarseness of whom five have fully recovered. The remaining patient (2%) developed vocal cord paralysis which is permanent to date. This prospective study demonstrates that recurrent laryngeal nerve dysfunction is a common but often transient complication of carotid endarterectomy. The incidence of vocal cord paralysis in this group was less than many of the reported series. This could be due to the technique of minimal dissection which may prevent disturbance of the vagal segmental blood supply. Pre-operative vocal cord assessment is essential in all patients undergoing carotid endarterectomy.

Aged↗
PubMed1996

The TRH-like peptides in rabbit testis are different from the TRH-like peptide in the prostate.

Human seminal fluid contains a number of tripeptide amides with similar structures to thyrotropin releasing hormone (TRH), two of which have been identified as pGlu-Glu-Pro amide and pGlu-Phe-Pro amide. To determine whether these peptides originate in the same tissues and have the same molecular origin, TRH-immunoreactive peptides were extracted from the prostate and testis of the rabbit, purified by ion exchange chromatography and HPLC, and identified by co-chromatography with 3H-labelled marker peptides. In addition, trypsin digestion was used to release TRH-like tripeptides from N-extended forms of these peptides. The sole TRH-like peptide in the prostate was shown to be pGlu-Glu-Pro amide; it was not accompanied by a detectable amount of pGlu-Phe-Pro amide. The prostate also appeared to contain a very small amount of N-extended forms of these peptides. In contrast to the prostate, the testis contained high concentrations of N-extended forms of pGlu-Phe-Pro amide but essentially no tripeptide. The testis also contained N-extended forms of two other neutral TRH-like peptides which were less hydrophobic than pGlu-Phe-Pro amide. Neither the prostate nor the testis contained a significant amount of TRH. The results show that in the rabbit the TRH-like peptides pGlu-Glu-Pro amide and pGlu-Phe-Pro amide occur in different tissues and appear to be formed from different precursors.

Amino Acid Sequence↗
PubMed1996

Exfoliated malignant cells in glove and instrument washings following head and neck surgery.

Loco-regional recurrence following resection of squamous cell carcinoma of the upper aero-digestive tract is a major problem. Cells exfoliated from malignant tumours have been considered capable of implanting and giving rise to local recurrence or metastatic deposits. A prospective study was performed examining washings from the gloves and instruments used in major head and neck operations to determine if exfoliated cells were indeed present. Following removal of the main tumour specimen all surgeons washed their hands in a solution containing a cell fixative and all instruments were soaked in the solution. Samples were then centrifuged and stained using a modified PAP technique. On occasions nuclear fragments consistent with squamous cell carcinoma were present in both glove and instrument washings. We recommend that all surgeons change gloves and instruments following removal of the main tumour specimen and prior to irrigation of the operative field with a tumoricidal agent.

Carcinoma, Squamous Cell↗
PubMed1994

Traumatic posterior cerebral artery aneurysm secondary to an intracranial nail: case report.

We present the case of a traumatic posterior cerebral artery aneurysm from a self-inflicted pneumatic nail-gun missile injury through the roof of the mouth. The patient presented to us in a coma with subarachanoid and intraventricular hemorrhage. Cerebral angiography revealed an aneurysm of the left posterior cerebral artery with no distal filling. The patient died 6 days after admission. At autopsy, a pseudoaneurysm of the posterior cerebral artery was seen. This aneurysm resulted from direct disruption of the arterial wall by the intracranial nail.

Adult↗
PubMed1992

Cocaine use, risk taking, and fatal Russian roulette.

OBJECTIVE: To examine the association between recent cocaine use and risk taking, particularly in the form of playing Russian roulette, a paradigm for extreme risk-taking behavior. DESIGN: A case-control study. CASES AND CONTROLS: The prevalence of cocaine use among all Russian roulette fatalities (N = 14) was compared with a demographically similar, randomly selected sample (N = 54) of all suicides by handgun during a contemporaneous 4-year period in New York City, NY. RESULTS: Recent use of cocaine, the most common drug found at autopsy, was detected in 64% of Russian roulette fatalities and in 35% of the control group (P less than .05). All Russian roulette fatalities were male and usually young and unemployed. Blacks and Hispanics accounted for 80% of all cases and were overrepresented compared with their numbers in the general population. CONCLUSION: In some populations cocaine may be associated with life-threatening risk-taking behaviors.

Adolescent↗
PubMed1991

Increased vasopressin immunoreactivity in the rat brain after a postmortem interval of 6 hours.

Enhanced immunocytochemical staining of vasopressin-containing neurons was observed after incubation of rat brain slices in Ringer medium for 6 h at room temperature, as compared to brain tissue fixed immediately after death. Hypothalamic vasopressin neurons in the supraoptic nucleus, the paraventricular nucleus and the suprachiasmatic nucleus stained more intensely after a postmortem interval of 6 h. Extrahypothalamic vasopressin neurons (VP) in the bed nucleus of the stria terminalis, the medial amygdala and the locus coeruleus proved to be stained as well. Extrahypothalamic VP neurons in the locus coeruleus could, until now, only be visualized after in vivo pretreatment with colchicine. In addition, staining was observed at two new sites, the dorsal raphe nucleus and the lateral septum. Staining of VP was corroborated by application of different antibodies directed against the intact vasopressin molecule as well as by antibodies directed against the other parts of the vasopressin precursor molecule, i.e. neurophysin and glycopeptide. The specificity of the VP-staining was validated by using pre-immune serum and using Brattleboro rat brain tissue, resulting in a negative staining in both cases. Furthermore, homogenated punches of the suprachiasmatic nucleus were submitted to iso-electric focussing on polyacrylamide gel, followed by press blotting and subsequent immunocytochemical staining for vasopressin. Iso-electric foccussing enabled us to characterize and quantify peptides in the suprachiasmatic nucleus. The vasopressin content increased 6 h postmortem, while c-terminal glycopeptide and neurophysin levels remained stable. Similar results were observed in the suprachiasmatic nucleus from decapitated rats whose brains were left intact in the skull for 6 h at room temperature.

Animals↗
PubMed1988

An unfortunate complication of self-therapy for seborrheic dermatitis.

The death of a young boy who practiced self-therapy of seborrheic dermatitis of the scalp is reported. Practitioners should be aware that peer pressure in today's teenage society, coupled with misinterpretation of therapeutic protocols, may result in the application of unorthodox treatment regimens.

Adolescent↗
PubMed1987

Vasopressin coexists in half of the corticotropin-releasing factor axons present in the external zone of the median eminence in normal rats.

Electron-microscopic immunocytochemistry of serial thin sections showed that, in normal rats, approximately 50% of corticotropin-releasing factor (CRF) axons in the external zone of the median eminence contained vasopressin (AVP) and AVP precursor-derived peptides coexistent in the same secretory vesicles as CRF. The other 50% of the CRF axons contained little or no detectable AVP or AVP precursor-derived peptides. Differential activation of these subpopulations of CRF axons could provide a mechanism by which levels of CRF and AVP in portal plasma could be varied independently.

Animals↗
PubMed1979

Proton magnetic resonance studies on [methionine]-enkephalin and beta-endorphin in aqueous solution.

Proton magnetic resonance studies of [Met5]-enkephalin (lipotropin 61-65) in aqueous solution indicate a conformational preference for the pentapeptide backbone. The structural differences between [Met5]-enkephalin and other, more flexible peptides have been investigated using paramagnetic probe techniques. An outline structure for beta-endorphin (lipotropin 61-91) in aqueous solution is obtained from binding studies using Gd(III) as a relaxation probe.

Animals↗
PubMed1979

Distribution of active and inactive forms of endorphins in rat pituitary and brain.

The recent isolation and identification of alpha-N-acetyl forms of the C-Fragment of lipotropin (beta-endorphin, residues 61-91) and the C'-Fragment (residues 61-87) [Smyth, D.G., Massey, D.E., Zakarian, S. & Finnie, M. (1979) Nature (London) 279, 252-254] has led to a study of their distribution in the pituitary and brain of the rat. Regions were mapped by the method of immunofluorescent staining and the reactive peptides were determined by immunoassay after extraction, gel filtration, and ion exchange chromatography. The major immunoreactive peptides in both lobes of the pituitary were found to be C'-Fragment and N-acetyl C'-Fragment, which are weakly active or inactive as opiates; the C-Fragment and its N-acetyl derivative represented minor components. This indicates that in the rat the circulating "endorphins" released from pituitary would have little morphinomimetic activity. The same four immunoreactive peptides were observed in rat brain. In the hippocampus the C'-Fragment was the principal component in the midbrain there was more C-Fragment but C'-Fragment predominated; in the hypothalamus the C-Fragment was the major peptide, almost to the exclusion of the other peptides. The results demonstrate that the processing of lipotropin is under differential control in anatomically distinct regions of the central nervous system. The processing of lipotropin in the hypothalamus is directed specifically to the production of lipotropin C-Fragment.

Amino Acid Sequence↗