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Biomedical subjects

M Davis

Publications and source records attributed to M Davis.

At least 451 records · Page 25Linked to original sources
PubMed1987

Pertussis toxin or 8-bromo-cAMP block inhibition of the acoustic startle response by the alpha 2-adrenergic agonist ST-91.

Stimulation of supraspinal alpha 2-adrenergic receptors by intraventricular infusion of the alpha 2-adrenergic agonist ST-91 depresses a simple vertebrate behavior, the acoustic startle response. Intraventricular pretreatment with pertussis toxin, an agent known to inactivate the inhibitory guanine nucleotide binding protein (Gi) which can inhibit adenylate cyclase, completely prevented the depressant behavioral effect of ST-91. In contrast, pertussis toxin did not alter the depressant effect of intraventricular infusion of the 5-HT 1B agonist 1-m-chlorophenylpiperazine (mCPP). Intraventricular infusion of the cyclic adenosine monophosphate (cAMP) analog 8-bromo-cAMP also reversed the depressant effect of ST-91 without altering the effect of mCPP. These data suggest that inhibition of adenylate cyclase may be involved in the effect of activation of central alpha 2-adrenergic receptors.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1987

Mescaline: excitatory effects on acoustic startle are blocked by serotonin2 antagonists.

The ability of serotonin2 (5-HT2) antagonists to block the excitatory effects of mescaline on the acoustic startle reflex were analyzed. Mescaline (20 mg/kg) caused a consistent increase in the amplitude of the acoustic startle reflex. This effect was blocked in a dose-related fashion by the 5-HT2 antagonist ritanserin (ED50 dose = 0.25 mg/kg IP). In contrast, even a high dose of ritanserin (2.0 mg/kg) did not block the excitatory effects of amphetamine on startle. Other 5-HT2 antagonists (ketanserin, cinanserin, LY 53857) also blocked mescaline's effect, whereas the 5-HT1 antagonist pindolol (5 mg/kg) did not. These results support the hypothesis that the behavioral effects of hallucinogens are mediated by agonist actions at 5-HT2 receptors.

Animals↗
PubMed1987

Cavernous lymphangioma of the duodenum: case report and review of the literature.

Lymphangiomas of the gastrointestinal tract are extremely rare benign tumors. There have been 39 cases of solitary intestinal lymphangiomas reported, 8 of which were found in the duodenum; only 3 of these were seen radiographically. A case of cavernous lymphangioma of the duodenum is presented, the roentgenographic and pathologic findings are described, and the literature is reviewed.

Duodenal Neoplasms↗
PubMed1987

Actions of calcium ions and a calcium-influx blocker on basal and TRH- and GnRH-stimulated hormone release in patients with pituitary adenomas.

We investigated the influence of calcium ions on the secretion of anterior pituitary hormones basally and in response to exogenous hypothalamic releasing factors in 6 men with pituitary tumors. To this end, concentrations of LH, FSH, TSH, growth hormone and prolactin were measured in blood collected at 10-min intervals basally and during a continuous infusion of combined TRH (2 micrograms/min) and GnRH (1 microgram/min). Study sessions were randomized to iv saline, calcium, or diltiazem infusions or oral diltiazem administration. Our results indicate that in contrast to responses in normal men, iv calcium injections do not suppress circulating prolactin concentrations in patients with prolactin-secreting pituitary tumors. Moreover, neither oral diltiazem administration for one week nor acute iv diltiazem infusion suppressed the hyperprolactinemia of tumor patients. However, there were significant effects of drug and calcium treatments on serum concentrations of FSH, GH and testosterone, but not LH or TSH. Moreover, during GnRH-TRH stimulation, there were significant differences in LH, TSH, and testosterone responses in tumor patients compared to normal men. In summary, iv calcium infusion was associated with invariant basal release of anterior pituitary tumoral hormones in patients with pituitary adenomas. However, there were significant differences in the GnRH/TRH-stimulated release of certain anterior pituitary hormones in tumor patients compared to normal men in response to iv calcium and the calcium-channel antagonist, diltiazem.

Adenoma↗
PubMed1987

Respiration-dependent uptake and extrusion of Mg2+ by isolated heart mitochondria.

It has been known for some time that isolated heart mitochondria can both take up and extrude Mg2+ by respiration-dependent, uncoupler-sensitive processes. A re-examination of these reactions reveals that the respiration-dependent uptake of Mg2+ can be quite rapid and efficient and is apparently preceded by a passive binding to the inner membrane. The rate of Mg2+ uptake can exceed 30 ng ion/min/mg protein at an efficiency of about 1 ng ion Mg2+ accumulated per ng atom O2 consumed. Passive binding and respiration-dependent accumulation of Mg2+ are strongly inhibited by K+ and other monovalent cations and the uptake reaction is further decreased by the presence of ATP or ADP. Under conditions approaching those faced by mitochondria in situ (state 3 respiration in a KCl medium) the rate of Mg2+ uptake, as estimated from 28Mg2+ distribution, is no more than 0.25 ng ion/min/mg. When heart mitochondria are suspended in a Mg2+-free medium, a slow, respiration-dependent Mg2+ efflux is seen. This reaction is quite insensitive to external K+ and otherwise shows an inhibitor profile markedly different from that of the Mg2+ accumulation reaction. Neither the uptake nor the loss of Mg2+ is inhibited by ruthenium red or diltiazem. These reactions therefore appear unrelated to those involved in the uptake and release of Ca2+. It is concluded that heart mitochondria have separate pathways available for Mg2+ uptake and release.

Adenine Nucleotides↗
PubMed1987

Fear-potentiated startle using an auditory conditioned stimulus: effect of lesions of the amygdala.

The effect of lesions of the amygdala on fear-potentiated startle using an auditory conditioned stimulus (CS) was evaluated, after replicating and extending previous findings that a tone is an effective CS for fear-potentiated startle. Rats received 10 tone-shock pairings on 2 successive days. At 24-48 hr following training, they received bilateral electrolytic lesions of the central nucleus of the amygdala or sham operations, and then were tested for fear-potentiated startle 4-5 days later. Lesions of the amygdala impaired fear-potentiated startle using an auditory CS, consistent with the previous findings using a visual CS. These data indicate that the effect of lesions of the amygdala on fear-potentiated startle is not specific to one sensory modality, consistent with the hypotheses that the amygdala is involved in processing multimodal information related to conditioned fear, or is part of an output pathway for motor and autonomic expressions of conditioned fear.

Acoustic Stimulation↗
PubMed1987

A technique to restrain awake rats for recording single-unit activity with glass micropipettes and conventional microdrives.

A technique has been developed which permits the study of single-unit activity using glass micropipettes and conventional microdrives in restrained, awake rats. A unique feature of this preparation is that the rats are kept still during electrophysiological recording by infusing a small amount of local anesthetic through a catheter chronically implanted into the epidural space of the spinal cord resulting in a temporary mid-body to hind-limb motor blockade. The animal is held in a slightly modified stereotaxic device by a bolt attached to the top of its skull. The rats are responsive to acoustic, visual, or tactile stimulation, permitting the simultaneous recording of electrophysiological activity and behavioral or electromyographical activity rostral to the level of motor blockade. By employing the epidural anesthesia the animals are healthy and mobile prior to and following each recording session and can be tested across a number of days. Single unit activity recorded from the facial motor nucleus in response to an acoustic click is presented as an example of the viability of this preparation. Therefore, this preparation seems suitable for a variety of investigations involving neurophysiological recording with glass micropipettes or the correlation of such recording with simple behaviors in awake, restrained rats.

Anesthesia, Epidural↗
PubMed1987

Three-phase radionuclide bone scanning in evaluation of local radiation injury. A case report.

The management of local radiation injuries is influenced by the degree of vascular compromise within the skin and underlying tissues. Other authors have used thermography and angiography in assessing the blood flow to radiation damaged tissues. This report describes the use of radionuclide imaging in the evaluation of a patient who developed necrosis of his distal digits following a radiation accident. In addition to determining the vascular status of the hands, imaging helped indicate an appropriate level for amputation.

Accidents, Occupational↗
PubMed1987

Analytical modeling of worldwide medical radiation use.

An analytical model was developed to estimate the availability and frequency of medical radiation use on a worldwide basis. This model includes medical and dental x-ray, nuclear medicine, and radiation therapy. The development of an analytical model is necessary as the first step in estimating the radiation dose to the world's population from this source. Since there is no data about the frequency of medical radiation use in more than half the countries in the world and only fragmentary data in an additional one-fourth of the world's countries, such a model can be used to predict the uses of medical radiation in these countries. The model indicates that there are approximately 400,000 medical x-ray machines worldwide and that approximately 1.2 billion diagnostic medical x-ray examinations are performed annually. Dental x-ray examinations are estimated at 315 million annually and approximately 22 million in-vivo diagnostic nuclear medicine examinations. Approximately 4 million radiation therapy procedures or courses of treatment are undertaken annually.

Africa↗
PubMed1987

Treatment of gram-positive peritonitis with two intraperitoneal doses of vancomycin in continuous ambulatory peritoneal dialysis patients.

Eight patients with end-stage renal failure on continuous ambulatory peritoneal dialysis (CAPD), who developed peritonitis, received an intraperitoneal dose of vancomycin (30 mg/kg body weight) with 6 h of peritoneal dwell and then resumed their routine CAPD schedule. Vancomycin concentration in serum, peritoneal dialysate (PD) from an overnight dwell and 1, 2 and 3 h after a new exchange was measured at 48 h (in 5 patients) and 7 days (in 6 patients). Except for an occasional 1-hour peritoneal fluid sample on the 7th day, all samples had satisfactory vancomycin levels. Five of the 8 patients who had gram-positive peritonitis and 1 with 'sterile' peritonitis received another similar intraperitoneal dose of vancomycin at the 7th day. All of these patients had good therapeutic response with a negative PD culture 3 weeks after the cessation of therapy and no relapse of infection in at least 1 month of follow-up. We conclude that 2 intraperitoneal doses of vancomycin (30 mg/kg body weight) given 1 week apart with 6 h of intraperitoneal dwell is an effective and adequate treatment for gram-positive and 'sterile' peritonitis in CAPD patients.

Bacterial Infections↗
PubMed1987

Drugs as probes of organ function: evaluation of the hepatobiliary axis using oral rifampicin and novel high performance liquid chromatography.

Investigation of the uptake and metabolism of drugs by organs such as the liver may allow assessment of specific aspects of organ function. Rifampicin, when orally administered, is transported into the hepatocyte from portal blood and thence passes, with its deacetylated metabolite, into the systemic circulation and into bile. This paper reports an investigation of the pharmacokinetics of a sub-therapeutic oral dose of rifampicin in healthy subjects, in patients with cirrhosis and in subjects with Gilbert's syndrome. The areas under the plasma concentration curves (AUC) in patients with cirrhosis were significantly greater than in healthy subjects. Subjects with Gilbert's syndrome had decreased AUCs compared with healthy subjects and were clearly distinguished from patients with cirrhosis. Rifampicin concentration in serum was measured by HPLC using a novel direct injection technique.

Acetylation↗
PubMed1987

Evidence for lipid peroxidation in man following paraquat ingestion.

Four patients were investigated for evidence of lipid peroxidation between 4.5 and 36 h (mean 22 h) after ingestion of paraquat by measuring plasma phospholipid-2-esterified, diene-conjugated 18:2 delta 9,11-linoleic acid (9,11-LA) and expressing it also as a ratio R (9,11-LA/9,12-LA X 100) of the 'parent' linoleic acid. The mean value for R was 4.73 (range 3.7-7.1) at presentation and 6.91 at peak values (range 3.8-13.4) which occurred at a mean of 34 h after ingestion. Both values were significantly higher (P less than 0.001) than that of 107 healthy controls (1.94, range 0.67-3.8). Parallel changes in plasma vitamin E and 9,11-LA occurred in the 2 patients in whom serial measurements were made suggesting an involvement of vitamin E in the formation of this isomer. These findings support the hypothesis that lipid peroxidation occurs during paraquat poisoning in man and the early appearance of 9,11-LA suggests that it may be a primary event.

Adult↗
PubMed1986

Campylobacter pyloridis and associated gastritis: investigator blind, placebo controlled trial of bismuth salicylate and erythromycin ethylsuccinate.

An investigator blind trial was performed comparing bismuth salicylate, erythromycin ethylsuccinate, and placebo in the treatment of Campylobacter pyloridis associated gastritis in patients without peptic ulceration. Fifty patients fulfilled the study criteria. There was a strong correlation between the presence of C pyloridis and histologically confirmed gastritis. Clearance of organisms led to improvement of the gastritis. C pyloridis was cleared from 15 patients; of these, 13 had gastritis initially, which resolved in 12. Conversely, gastritis resolved in only four of 32 patients not cleared of organisms (p less than 0.0001). There was significantly greater improvement in endoscopic appearances in the patients cleared of C pyloridis compared with those whose infection persisted (p less than 0.001). In the three treatment groups organisms were cleared from 14 of 18 patients receiving the locally active bismuth salicylate, only one of 15 patients receiving erythromycin ethylsuccinate, and none of 17 patients taking placebo. These findings suggest that the ideal antimicrobial for the successful eradication of C pyloridis associated gastritis should be locally active, stable at low pH, and should penetrate gastric mucus. The resolution of gastritis and improvement in endoscopic appearances associated with clearance of C pyloridis support the view that these organisms may play a part in this condition.

Adult↗
PubMed1986

Differential effects of dopamine agonists on acoustically and electrically elicited startle responses: comparison to effects of strychnine.

This study sought to determine where drugs that are known to alter sensorimotor reactivity measured with the acoustic startle reflex ultimately act within the acoustic startle pathway. To do this, startle was elicited either acoustically or electrically within various nuclei believed to comprise the acoustic startle pathway. Direct infusion of serotonin into the subarachnoid space of the lumbar spinal cord increased acoustic startle and startle elicited electrically through the ventral cochlear nucleus (VCN) to a comparable degree. Subconvulsant doses of strychnine increased startle elicited acoustically or electrically through either the VCN or the nucleus reticularis pontis caudalis (RPC), pointing to a spinal locus of action of strychnine after systemic administration. In marked contrast, the dopamine agonists d-amphetamine and apomorphine consistently increased acoustic startle but actually depressed startle elicited electrically through the VCN or the RPC. These later results suggest that dopamine agonists increase sensorimotor reactivity measured with acoustic startle by acting on sensory rather than motor parts of the reflex arc.

Acoustic Stimulation↗