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Biomedical subjects

G A Davis

Publications and source records attributed to G A Davis.

At least 19 recordsLinked to original sources
PubMed1996

Neuroanatomical distribution of androgen and estrogen receptor-immunoreactive cells in the brain of the male roughskin newt.

Immunohistochemistry was used to investigate the neuroanatomical distribution of androgen and estrogen receptors in brains of adult male roughskin newts, Taricha granulosa, collected during the breeding season. Immunoreactive cells were found to be widely distributed in specific brain areas of this urodele amphibian. Androgen receptor-immunoreactive (AR-ir) cells were observed in the olfactory bulbs, habenula, pineal body, preoptic area, hypothalamus, interpeduncular nucleus, area acusticolateralis, cerebellum, and motor nuclei of the medulla oblongata. Estrogen receptor-immunoreactive (ER-ir) cells were found in the lateral septum, amygdala pars lateralis, pallium, preoptic area, hypothalamus, and dorsal mesencephalic tegmentum. This immunocytochemical study of the newt brain reveals AR-ir and ER-ir cells in several regions that have not been previously reported to contain androgen and estrogen receptors in non-mammalian vertebrates. Additionally, the distribution of AR-ir and ER-ir cells in the newt brain, in general, is consistent with previous studies, suggesting that the distribution of sex steroid receptor-containing neurons in some brain regions is relatively conserved among vertebrates.

Animals↗
PubMed1996

Comparison of creatinine clearance estimation methods in patients with trauma.

The abilities of a modified Cockcroft-Gault equation and the standard equation to estimate creatinine clearance (CLcr) in trauma patients were compared. The medical records of patients with stable renal function who had been treated for trauma and had had a 24-hour urine collection for creatinine measurement were reviewed. Creatinine concentrations in urine and serum were used to calculate the actual CLcr, which was normalized to 1.73 sq m. CLcr was estimated by the modified equation (which normalized body weight to 72 kg) and by the standard equation using ABW, IBW, and dosing body weight (DBW). Values derived with the standard equation were normalized to 1.73 sq m. The predictive performances of the modified and standard equations in estimating the actual CLcr were then compared. Fifty patients were enrolled. The standard equation using IBW or DBW produced estimates that differed significantly from the actual CLcr. The modified equation and the standard equation using ABW did not differ significantly in bias or precision, but both were significantly less biased than the standard equation using IBW or DBW. The only significant difference among equations in precision was between the modified equation (the more precise) and the standard equation using IBW. There were no clinically significant differences among methods in gentamicin dosing simulations. The modified Cockcroft-Gault equation can be used to estimate CLcr in trauma patients with stable renal function.

Adult↗
PubMed1995

Comparison of fluid volumes with whole bowel irrigation in a simulated overdose of ibuprofen.

OBJECTIVE: To determine the effect of 2 different fluid volumes of polyethylene glycol whole bowel irrigation (WBI) solution on absorption of an ingested toxin in a simulated overdose model. DESIGN: Prospective, randomized, crossover trial. SETTING: Clinical research unit. PARTICIPANTS: Nine adult men. INTERVENTIONS: On 2 separate days, volunteers ingested approximately 75 mg/kg of ibuprofen. In treatment 1, 30 minutes after ingestion of ibuprofen, a 3-L WBI at 2 L/h was begun. This procedure was repeated in treatment 2 with an 8-L. WBI administered at 2 L/h. Fourteen timed serum samples were collected prior to and after drug ingestion for a 24-hour period and analyzed for ibuprofen concentration. The peak serum concentration, time to peak concentration, total area under the serum concentration-time curve (AUC), clearance, and volume of distribution were compared. RESULTS: The mean +/- SD AUCs did not differ between the 3-L (1185.3 +/- 216.9 mg.h/L) and 8-L (1153.5 +/- 251.5 mg.h/L) treatments (p = 0.710). Time to peak serum concentration, peak serum concentration, clearance, and volume of distribution were comparable for the 2 treatments (p > 0.05). CONCLUSIONS: These data indicated that a total WBI volume of 3 L would be expected to perform as well as 8 L administered at the same rate. We recommend that further research define the optimal dose of WBI in acute ingestion of toxins.

Adult↗
PubMed1994

The role of echocardiography in blunt chest trauma: a transthoracic and transesophageal echocardiographic study.

Previous studies assessing the value of transthoracic echocardiography (TTE) in blunt chest trauma are limited because patients with severe chest wall injury often have suboptimal echocardiographic findings. Transesophageal echocardiography (TEE) can provide high quality images when the transthoracic image quality is poor. To provide complete echocardiographic assessment of cardiac structure and function we prospectively performed TTE in 105 patients with severe blunt chest trauma and TEE in 20 of the 105 patients (19%) whose TTE examination results were suboptimal. Myocardial contusion was diagnosed in 31 patients (30%), 22 by TTE and nine by TEE. Cardiac complications developed in 8 of 31 patients (26%) with myocardial contusion compared with 2 of 74 patients (3%) with normal echocardiographic findings (p = 0.001). Cardiac complications required treatment in only four patients. Echocardiography was of value in detecting severe right ventricular dysfunction as the cause of hypotension in two patients with suspected cardiac tamponade. Four patients with myocardial contusion died compared with two patients with normal echocardiographic findings (p = NS). No death was related to the cardiac status. In addition, TEE detected aortic injury in five patients, four with focal intimal tears and one with an aortic transection. We conclude that myocardial contusion is common following blunt chest trauma, rarely requires treatment, and is associated with a favorable prognosis. Only patients who develop cardiac complications benefit from echocardiography. Transesophageal echocardiography is of value when the TTE examination results are suboptimal and when aortic injury is suspected.

Abbreviated Injury Scale↗
PubMed1993

Stability of flumazenil with selected drugs in 5% dextrose injection.

The compatibility and stability of flumazenil mixed with aminophylline, dobutamine hydrochloride, dopamine hydrochloride, cimetidine hydrochloride, famotidine, ranitidine hydrochloride, heparin sodium, lidocaine hydrochloride, or procainamide hydrochloride were studied. Flumazenil (1.0 mg) was mixed with each of the other drugs in polyvinyl chloride minibags containing 50 mL of 5% dextrose injection to achieve concentrations commonly used when the drugs are administered by continuous i.v. infusion. All admixtures were analyzed for color change, pH, and particulate matter. Flumazenil concentrations were measured by a stability-indicating high-performance liquid chromatographic assay at baseline and 2, 4, 8, 12, and 24 hours after mixing. No detectable changes in color, pH, or particulate matter were observed. In the presence of each drug except dopamine hydrochloride, at least 95% of initial flumazenil concentration was present 24 hours after mixing. Flumazenil in the presence of dopamine hydrochloride was stable for 12 hours. Flumazenil was visually compatible and chemically stable when admixed with 5% dextrose injection and selected drugs.

Chemistry, Pharmaceutical↗
PubMed1989

Effects of age on comprehension of complex sentences in adulthood.

This study was designed to determine effects of aging on comprehension of complex sentences. In particular, we were interested in whether normal aging modifies a subsystem of comprehension (i.e., syntactic or semantic) or places unusual demand on working memory related to the distance between constituents that must be integrated. Five age-defined groups of healthy adults were asked questions about thematic roles of nouns in sentences with center-embedded or right-branching subordinate clauses. Results indicated that comprehension accuracy declines after age 60. Although aging did not affect the semantic component, it did affect the syntactic component when evaluated with sentences representing implausible events. There appeared to be an effect of distance between constituents in the 70s decade that was not related solely to embedding of a subordinate clause. Instead of affecting a single component of the language system, normal aging may have an impact on interactions between components.

Adult↗
PubMed1988

Breast specimen radiography: evaluation of a compression device.

The irregular shape and uneven tissue thickness of excised breast specimens makes radiographic evaluation difficult, especially when calcifications are not present. Xeroradiographs before and after compression of 20 separate excised breast specimens were compared, and 17 of the same specimens were compared after compression combined with immersion in water. Specimen compression improved visibility of the lesion on average in 88% of cases, and visibility was equal in 12%. Combined compression/immersion further improved visibility of the lesion on average in 37% of cases. More significantly, evaluation of the compressed specimen led to a change in interpretation of the radiographs in 45% of cases. Compression of the specimen in specimen radiography is recommended in all cases in which pre-biopsy localization is performed.

Biopsy↗
PubMed1988

Norepinephrine is a possible neurotransmitter stimulating pulsatile release of luteinizing hormone-releasing hormone in the rhesus monkey.

The hypothesis that norepinephrine (NE) plays a facilitatory role in controlling the pulsatile release of LHRH was tested with a modified push-pull perfusion technique in conscious rhesus monkeys. The in vivo LHRH release in perfusate samples collected from the stalk-median eminence of ovariectomized females was pulsatile and synchronous with pulsatile LH release. Catecholamines measured in aliquots of perfusate samples revealed that in vivo NE release was also pulsatile and was synchronous with LHRH release. Local infusion of NE or methoxamine (an alpha 1-adrenergic stimulant) through a push cannula stimulated LHRH release, while iv injection of prazosin (an alpha 1-adrenergic blocker) suppressed LHRH release. It is concluded that NE is a possible neurotransmitter stimulating pulsatile LHRH release.

Animals↗
PubMed1987

Stimulation of sentence production in a case with agrammatism.

A multiple base-line single-subject experimental design was employed to study effects of a sentence stimulation treatment on sentence production in an aphasic patient with agrammatism. Prior to this seven-week study, the subject had not been using speech functionally for six months. Treatment was applied sequentially across three sets of picture stimuli. Performance was measured with probes of verbal description for each set. Results showed that treatment influenced description of the pictures being treated and that some generalization occurred with sets not being treated. However, formal pre-post testing indicated that a broader effect had not been obtained.

Adult↗
PubMed1985

Nicotine stimulation of protein secretion from isolated rat pancreatic acini.

The secretion of amylase and trypsinogen from isolated rat pancreatic acini was greatly stimulated by 3-25 mM nicotine. In the presence of 12.5 mM nicotine, a concentration used in the study, amylase and trypsinogen release was increased by 95 and 400%, respectively, when compared with the corresponding control and showed further a preferential release of trypsinogen. A 90-min time course release of the enzymes revealed that in the presence of nicotine trypsinogen-to-amylase ratio remained two- to threefold elevated over that of the control throughout the incubation period. The nicotine-induced stimulation of trypsinogen and amylase release from the acini could not be blocked by 2.5 mM cycloheximide, a dose that inhibited overall acinar protein synthesis by about 85%. When isolated acini were incubated with [3H]leucine in the presence of nicotine, the released proteins revealed a fourfold higher radioactivity (dpm/microgram acinar DNA) than the control. Cycloheximide dramatically decreased this increment. The rate of release of 3H-pulse-labeled proteins from the acini was greatly accelerated by nicotine. It is concluded that nicotine stimulates the secretion of preformed zymogen granules and newly synthesized proteins from dispersed rat pancreatic acini in vitro.

Amylases↗
PubMed1983

The LHRH neuronal system in female rats: relation to the medial preoptic nucleus.

Previously we have found that small lesions confined to the medial preoptic nucleus (MPN) or the suprachiasmatic nucleus (SCN) blocked the cyclic release of gonadotropins in the female rat, inducing a persistent estrous state. Since the MPN is located just caudal to the organum vasculosum of the lamina terminalis (OVLT) where LHRH cell bodies are most concentrated, we applied an immunocytochemical technique to examine the possibility that the lesions had simply disrupted LHRH neurons or fibers. Using a new anti-LHRH provided by Dr. V. D. Ramirez, we found that the distribution pattern of immunoreactive LHRH cell bodies and fibers was similar to that previously reported, although the staining was more intense and extensive with low background. There was no concentration of LHRH cell bodies and fibers in the MPN or SCN and, in fact, these nuclei generally showed a lower density of stained elements than did surrounding tissue. In persistent estrous animals with lesions confined to the MPN there was no detectable reduction of stained fibers in the median eminence. These results, along with the results of other workers, suggest that persistent estrus following lesions of the MPN or SCN is not due to reduction of LHRH neurons or fibers. Rather, they support the hypothesis that these nuclei are critical for triggering the ovulatory release of LHRH.

Animals↗
PubMed1981

Prostaglandins, clonidine and sexual receptivity in the guinea pig.

Prostaglandins E1 and F2 alpha suppressed lordosis in ovariectomized guinea pigs brought into estrus with estradiol benzoate and progesterone. Pretreatment with clonidine prevented this action of the prostaglandins, but if the animals were first given prostaglandin and allowed to go out of estrus, then clonidine did not restore lordosis. In a previous study it was found that the abbreviation of estrus induced by copulation was also blocked by clonidine, again only if it were given before the inhibitory treatment. These results suggest tht prostaglandin, perhaps released from the female reproductive tract, could mediate the inhibitory effect of copulation, and radioimmunoassays of prostaglandin F2 alpha and its principal metabolite PGFM revealed substantial elevations in the concentrations of these materials in trunk blood after copulation. We discuss the possibility that prostaglandins may suppress sexual receptivity by interfering with an alpha-adrenergic mechanism.

Animals↗
PubMed1981

Effects of ovarian steroids on serotonin metabolism within grossly dissected and microdissected brain regions of the ovariectomized rat.

Brain serotonin (5-HT) levels and accumulation rate within the dorsal raphe nucleus (DR) were elevated in ovariectomized (OVX) rats after ovarian steroid treatment, which consisted of estradiol benzoate (EB) followed by progesterone (P) 48 hr later. Some animals were also given the monoamine oxidase (MAO) inhibitor pargyline at designated times 10-40 min prior to sacrifice. Decapitation occurred 5 hr following the second steroid injection and 4-6 hr into the dark phase of a 14:10 light/dark cycle. Basal 5-HT levels and the rate of 5-HT accumulation (5-HTr) following MAO inhibition were estimated by radioenzymatic assay of brain tissue punched from frozen sections or dissected freehand. Within the DR, 5-HT levels and 5-HTr rates were respectively 13.8% (p less than 0.001) and 23.2% (p less than 0.025) higher in EB+P treated females compared with oil controls. Differences in basal 5-HT were found within the median raphe nucleus, but these were inconsistent from experiment to experiment. No differences were found in tissue immediately adjacent to these nuclear regions or within other brain regions including the ventral medial nucleus and suprachiasmatic nucleus of the hypothalamus. Increased levels of 5-HT were also found in grossly dissected tissue containing the mesencephalic raphe nuclei.

Amygdala↗
PubMed1980

Copulation-induced abbreviation of estrus in the female guinea pig: block by clonidine.

In the female guinea pig, copulation produces a rapid inhibition of subsequent sexual receptivity. Injection of the alpha adrenergic agonist clonidine before mating blocked the early inhibitory effects of coital stimulation, while the serotonergic antagonist methysergide, and the dopaminergic antagonist pimozide were without effect. The effects of clonidine were prevented by pretreatment with the alpha adrenergic antagonist yohimbine. These results suggest that an adrenergic system is involved in the copulation-induced inhibition of receptivity and provide further evidence that such a system has an important facilitative role in the control of female sexual behavior in the guinea pig.

Animals↗