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Biomedical subjects

W J Davis

Publications and source records attributed to W J Davis.

At least 19 recordsLinked to original sources
PubMed1991

Brachial plexus anesthesia for outpatient surgical procedures on an upper extremity.

We retrospectively reviewed 543 brachial plexus blocks performed on 526 outpatients. Most (98%) of the blocks were performed by means of the axillary approach. Various techniques were used, including paresthesia, transarterial fixation, nerve stimulation, or a combination of techniques; a high success rate was achieved with each of them. Only 7% of the blocks were incomplete and thus necessitated either general anesthesia or block supplementation with thiopental sodium and nitrous oxide. No persistent neurologic deficit was ascribed to the anesthetic technique. This review indicates that brachial plexus block, especially with use of the axillary approach, is a safe and effective option for outpatient surgical procedures on an upper extremity.

Adolescent↗
PubMed1991

Effect of phenethyl isothiocyanate on the metabolism of tobacco-specific nitrosamines by cultured rat oral tissue.

The effect of phenethyl isothiocyanate (PEITC) on the metabolism of N'-nitrosonornicotine (NNN) and 4-(methyl-nitrosamino)-1-(3-pyridyl)-1-butanone (NNK) by cultured rat oral tissue was investigated. Two protocols were used. In one, oral tissue from untreated rats was cultured in the presence of 10 or 50 microM PEITC and either NNN or NNK. The levels of NNN and NNK metabolites released into the culture media were determined by HPLC analysis. The presence of 10 microM PEITC inhibited the formation of all NNN metabolites from 45 to 70% when the concentration of NNN was 1 microM or 10 microM. When the concentration of PEITC was 50 microM the extent of inhibition was from 70 to 90%. alpha-Hydroxylation of NNK was inhibited 70 to 90% and N-oxidation of NNK was inhibited 80 to 90% by 10 microM PEITC. Carbonyl reduction of NNK to NNAL was unaffected by 10 microM PEITC and only slightly inhibited by 50 microM PEITC. In the second protocol, rats were fed NIH-07 diet containing 3 mumol PEITC/g for 1-14 days. The metabolism of NNN by cultured oral tissue from these rats was decreased from 40 to 90% relative to that by tissue from control rats. NNK metabolism was inhibited 40 to 60%. The extent of inhibition was the same when rats were fed PEITC containing diet for 1 or 14 days. NNN and NNK are the only tobacco constituents which induce oral cavity cancer in an animal model. The results of this study suggest the possibility that PEITC may be useful as a chemopreventive agent for oral cavity cancer.

Animals↗
PubMed1986

The mandibulo-stylohyoid ligament.

The mandibulo-stylohyoid ligament was studied in both sides of five cadavers, the surgical importance of the structure is confirmed and the anatomical importance as a landmark is emphasized.

Adult↗
PubMed1986

Tumor-localizing and photosensitizing properties of hematoporphyrin derivative in hamster buccal pouch carcinoma.

The tumor-localizing and photochemotherapeutic properties of hematoporphyrin derivative (HPD) were examined in 7, 12 dimethylbenzanthracene (DMBA)-induced oral cancers in the Syrian hamster. Oral tumors in hamsters injected with HPD (50 micrograms per gram of body weight) exhibited bright salmon pink fluorescence when exposed to long-wave ultraviolet light 24 hours after intraperitoneal HPD injection. Adjacent tumor-free mucosa did not fluoresce. Similarly, tumors not treated with HPD, normal mucosa treated with HPD, and normal mucosa not treated with HPD did not fluoresce. Tumors in animals that received HPD and photochemotherapy (PCT) were examined for gross and microscopic pathologic changes following the phototreatment. Tumors displayed edema, hemorrhage, and cellular necrosis that progressed with the time of sampling after photochemotherapy. Complete tumor necrosis was evident in the majority of oral tumors 24 hours after HPD PCT.

Animals↗
PubMed1986

Cholinergic suppression: a postsynaptic mechanism of long-term associative learning.

Food avoidance learning in the mollusc Pleurobranchaea entails reduction in the responsiveness of key brain interneurons in the feeding neural circuitry, the paracerebral feeding command interneurons (PCNs), to the neurotransmitter acetylcholine (AcCho). Food stimuli applied to the oral veil of an untrained animal depolarize the PCNs and induce the feeding motor program (FMP). Atropine (a muscarinic cholinergic antagonist) reversibly blocks the food-induced depolarization of the PCNs, implicating AcCho as the neurotransmitter mediating food detection. AcCho applied directly to PCN somata depolarizes them, indicating that the PCN soma membrane contains AcCho receptors and induces the FMP in the isolated central nervous system preparation. The AcCho response of the PCNs is mediated by muscarinic-like receptors, since comparable depolarization is induced by muscarinic agonists (acetyl-beta-methylcholine, oxotremorine, pilocarpine), but not nicotine, and blocked by muscarinic antagonists (atropine, trifluoperazine). The nicotinic antagonist hexamethonium, however, blocked the AcCho response in four of six cases. When specimens are trained to suppress feeding behavior using a conventional food-avoidance learning paradigm (conditionally paired food and shock), AcCho applied to PCNs in the same concentration as in untrained animals causes little or no depolarization and does not initiate the FMP. Increasing the concentration of AcCho 10-100 times, however, induces weak PCN depolarization in trained specimens, indicating that learning diminishes but does not fully abolish AcCho responsiveness of the PCNs. This study proposes a cellular mechanism of long-term associative learning--namely, postsynaptic modulation of neurotransmitter responsiveness in central neurons that could apply also to mammalian species.

Acetylcholine↗
PubMed1986

Food avoidance learning is accompanied by synaptic attenuation in identified interneurons controlling feeding behavior in Pleurobranchaea.

Identified paracerebral feeding command interneurons (PCNs) in the brain of the mollusc Pleurobranchaea excite other identified PCNs by means of a chemical polysynaptic pathway whose efficacy is reduced by food avoidance training (conditionally paired food and electric shock). The purpose of the present study was to identify the neurons comprising this pathway and to localize learning-induced changes to single identified neurons. We found that associative training strongly attenuates or abolishes a unitary excitatory postsynaptic potential (EPSP) at a single identified synapse in this polysynaptic pathway, but does not alter other synapses. The PCNs descend to the buccal ganglion, where they monosynaptically excite each member of a set of four identified neurons (two per hemiganglion) that belong to the corollary discharge population described previously. The strength of ascending and descending synapses involving identified PCNs is greatest ipsilaterally and is proportional to relative command efficacy established in previous studies. These findings suggest that command efficacy results directly from synaptic strength. The pair of corollary discharge neurons on each side of the buccal ganglion sends axons to the opposite side and thence up the contralateral cerebrobuccal connective to the brain. These neurons have therefore been termed the contralateral corollary discharge (CCD) neurons. Each CCD monosynaptically excites every PCN on both sides of the brain. Contralateral synaptic influences on identified PCNs are larger than ipsilateral ones. Each of the four identified CCD neurons is electrically coupled to all other members of the subset, including the contralateral homologue (based on simultaneous intracellular recording) and the ipsilateral partner (based on dye coupling). Hyperpolarizing a single CCD eliminates the polysynaptic response of PCNs to stimulation of other PCNs, whereas depolarizing a single CCD mimics the polysynaptic response. The CCD neurons are therefore necessary and sufficient to the polysynaptic response. Consistent with this role, the CCDs discharge in phase with the PCNs during the feeding motor program, and hyperpolarizing a CCD abolishes the cycle discharge of PCNs and weakens the feeding rhythm. Of the several reciprocal synapses identified between the PCNs and CCDs, only one was significantly altered by associative training in the food avoidance paradigm developed previously. This synapse, from the polysynaptic excitor (PSE) to the ipsilateral CCD, was also the strongest in this recurrent positive-feedback loop. In brains taken from conditioned specimens, the mean EPSP amplitude induced by a PSE action potential in ipsi

Action Potentials↗
PubMed1985

Learning: neural analysis in the isolated brain of a previously trained mollusc, Pleurobranchaea californica.

The neural manifestations of food avoidance learning in the mollusc, Pleurobranchaea, survive the surgical reduction of the preparation to the nearly isolated brain. These manifestations include increased synaptic inhibition and reduced synaptic excitation of the phasic paracerebral feeding command interneurons (PCps) in the brain in response to food stimulation of chemosensory structures left attached to the brain. The same changes are not evident, however, in brains removed from naive, control or satiated specimens. Therefore the nearly isolated brain preparation permits analysis of the cellular substrates of learning in relative isolation from non-associative motivational variables. The isolated brain preparation is here used to show that the increased synaptic inhibition consequent to associative training is distributed not only to the PCps but also to their identified central presynaptic inputs, including other identified feeding command interneurons (PSEs and ETIIs; ref. 21). The decrease in PCp excitation is explained in part by a training-induced inhibition of excitatory inputs to the PCps, and in part by a training-induced reduction in the efficacy of an identified polysynaptic excitatory pathway presynaptic to the PCps.

Animals↗
PubMed1985

Neural mechanisms of motor program switching in the mollusc Pleurobranchaea. I. Central motor programs underlying ingestion, egestion, and the "neutral" rhythm(s).

The buccal musculature of the carnivorous gastropod Pleurobranchaea is used in three cyclic patterns of coordination underlying, respectively, ingestion, egestion, and a third, unknown behavior(s) (Croll, R. P., and W. J. Davis (1981) J. Comp. Physiol. 145: 277-287; Croll, R. P., and W. J. Davis (1982) J. Comp. Physiol. 147: 143-154). The corresponding three motor programs can be identified and distinguished in the intact animal (Croll, R. P., and W. J. Davis (1981) J. Comp. Physiol. 145: 277-287), the reduced preparation (Croll, R. P., and W. J. Davis (1982) J. Comp. Physiol. 147: 143-154, and the present paper), and the isolated CNS (present paper), on the basis of several qualitative and quantitative criteria. Distinguishing parameters developed here include: the activity of the salivary duct, which bursts in phase with protraction during ingestion, is silent during egestion, and usually bursts biphasically and in antiphase with protraction during the third ("neutral") rhythm(s); and the protractor duty cycle, which is generally 33 to 50% during ingestion, greater than 50% during egestion, and less than 33% during the neutral rhythm(s). Retractor duty cycles did not differ significantly between the three motor programs. The neutral rhythm(s) may be a low-intensity version of the ingestion motor program, with which it shares most features. The three buccal motor programs can be elicited in the reduced preparation (sensory feedback intact) and in the isolated, deafferented CNS. Therefore, multiple motor programs in this metastable motor system are each endogenous to the CNS; i.e., they can each be generated by a central pattern generator(s) in the absence of sensory feedback.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Neural mechanisms of motor program switching in the mollusc Pleurobranchaea. II. Role of the ventral white cell, anterior ventral, and B3 buccal neurons.

Identified buccal neurons in the mollusc Pleurobranchaea were stimulated and recorded intracellularly while recording the resultant identified motor program from buccal muscles (reduced preparation) or nerves (isolated central nervous system). Neurons studied included the ventral white cell (VWC), members of the anterior ventral (AV) population, and interneuron B3. Each of these neurons elicited the egestion motor program or its characteristic components when stimulated intracellularly. The characteristic prolonged plateau potential of the VWC was frequently associated with the egestion motor program but never with the ingestion motor program or its characteristic components. Intracellular recordings from these same neurons during spontaneous or induced buccal motor programs were consistent with the view that these neurons participate in production of the egestion motor program. The VWC discharged also during the neutral buccal rhythm, although in a different pattern from that seen during the egestion motor program, suggesting that it is multifunctional. Synaptic targets of the VWC are unknown, but synaptic influences of the AV and B3 neurons were found and are appropriate to their proposed role in egestion. This study therefore indicates that an interrelated cluster of buccal neurons is specialized to command the egestion motor program.

Animals↗
PubMed1985

Neural mechanisms of motor program switching in the mollusc Pleurobranchaea. III. Role fo the paracerebral neurons and other identified brain neurons.

Identified neurons in the cerebropleural ganglion (brain) of the mollusc Pleurobranchaea were stimulated and recorded from intracellularly while recording the identified motor program from buccal muscles (reduced preparation) or nerves (isolated central nervous system). Neurons studied included the metacerebral giant neurons (MCGs), phasic paracerebral neurons (PCp's), polysynaptic excitors of the PCp's (PSEs), type II electrotonic neurons (ETII's), type I electrotonic neurons (ETI's) and several other identified neurons or neuronal classes. Intracellular stimulation of the above identified neurons generally elicited the ingestion motor program or its characteristic components, but never the egestion motor program and seldom its characteristic components. Intracellular recordings from these neurons in the isolated central nervous system preparation while eliciting the ingestion and egestion motor program generally showed cyclic membrane potential oscillations in phase with both motor programs, indicating that these neurons receive synaptic feedback from the ingestion and egestion central pattern generator(s). This study is therefore consistent with the view that an interrelated cluster of brain neurons is specialized to command the ingestion motor program. A neural model of motor program switching in the buccal motor system is formulated, comprising separate command pathways for ingestion and egestion that converge on a common central pattern generator(s).

Animals↗
PubMed1985

Recurrent aphthous stomatitis.

Aphthous ulcers are of unknown etiology; both genetic and immunologic origins have been proposed. Lesions are painful, tend to recur and may last up to six weeks. Recurrent aphthous stomatitis must be differentiated from herpesvirus infections and herpangina. No treatment has been uniformly successful, but levamisole shows promise.

Adult↗
PubMed1984

Fenoterol dose-response study in children with asthma.

We have studied the effect of fenoterol, a selective beta-2 adrenergic agent, on airway obstruction in children with asthma. The drug was administered orally in single doses of 2.5, 5, and 7.5 mg to 20 children with chronic stable asthma of moderate severity. The mean age of the children was 11.6 yr. Pulmonary function tests were performed as baseline at zero time and at intervals over a 6-hour period after drug administration. Onset of action for all doses was within 1 hr with a peak effect noted at 1.5 to 3 hr, and sustained improvement was observed over the entire 6 hr. The doses of 5 mg and 7.5 mg were equally effective in producing significant improvement of pulmonary function compared to 2.5 mg (p less than 0.05). Side effects remained acceptable for all patients. The 5 and 7.5 mg doses produced significant adverse effects that involved the central nervous and musculoskeletal systems, whereas the 7.5 mg dose caused a significant incidence of tachycardia. Our findings indicate: (1) fenoterol is a potent oral bronchodilator for large and small airways in children, (2) the 7.5 mg dose does not achieve any additive effect over a 5 mg dose; and (3) 5 mg is the optimal oral dose of fenoterol for children from age 8 to 12 yr.

Adolescent↗
PubMed1984

Brain oscillator(s) underlying rhythmic cerebral and buccal motor output in the mollusc, Pleurobranchaea californica.

Tonic (d.c.) intracellular depolarization of the previously identified phasic paracerebral feeding command interneurones (PCps) in the brain of the carnivorous gastropod Pleurobranchaea causes oscillatory neural activity in the brain, both before and after transecting the cerebrobuccal connectives. Therefore, cycle-by-cycle ascending input from the buccal ganglion is not essential to cyclic brain activity. Instead the brain contains an independent neural oscillator(s), in addition to the oscillator(s) demonstrated previously in the buccal ganglion (Davis et al. 1973). Transection of the cerebrobuccal connectives immediately reduces the previously demonstrated (Kovac, Davis, Matera & Croll, 1983) long-latency polysynaptic excitation of the PCps by the polysynaptic excitors (PSEs) of the PCps. Therefore polysynaptic excitation of the PCps by the PSEs is mediated by an ascending neurone(s) from the buccal ganglion. The capacity of feeding command interneurones to induce neural oscillation in the isolated brain declines to near zero within 1 h after transection of the cerebrobuccal connectives, suggesting that this capacity is normally maintained by ascending information from the buccal ganglion. The results show that this motor system conforms to a widely applicable general model of the neural control of rhythmic behaviour, by which independent neural oscillators distributed widely in the central nervous system are coupled together to produce coordinated movement.

Action Potentials↗