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Biomedical subjects

M Davis

Publications and source records attributed to M Davis.

At least 415 records · Page 23Linked to original sources
PubMed1989

Footshock-induced sensitization of electrically elicited startle reflexes.

The acoustic startle reflex can be facilitated by the presentation of a train of footshocks presented in rapid succession (footshock sensitization). Acoustic startle is a short-latency reflex mediated by a neural circuit consisting of the ventral cochlear nucleus (VCN), ventral nucleus of the lateral lemniscus (VLL), the nucleus reticularis pontis caudalis (RPC), and the spinal cord. The present study sought to determine the point along this pathway where footshocks might ultimately alter neural transmission to affect startle response. Rats were implanted bilaterally with stimulating electrodes in either the VCN, VLL, or RPC. Startle could be elicited acoustically with a noise burst or electrically with a single-pulse stimulus to either the VCN, VLL, or RPC before and after a train of ten 0.6-mA, 500-ms shocks presented at a rate of 1 shocks/s. Startle elicited acoustically or electrically in the VCN or VLL was significantly elevated following shocks. In contrast, startle elicited from the RPC showed no sensitization, even though startle elicited acoustically from the same animals during the same test session was facilitated. These data suggest that footshock sensitization ultimately alters transmission in the startle circuit at the RPC.

Acoustic Stimulation↗
PubMed1989

Sensitization of the startle reflex by footshock: blockade by lesions of the central nucleus of the amygdala or its efferent pathway to the brainstem.

Bilateral electrolytic lesions of the central, but not the lateral, nucleus of the amgydala blocked shock sensitization of startle (the increase in startle produced by presentation of ten 0.6-mA footshocks in rapid succession). Lesions of the central nucleus also decreased reactivity to shock (jumping and flinching) during shock presentation. However, this decrease in reactivity cannot account for the blockade of shock sensitization, because when a higher shock intensity (1.0 mA) was used, producing equivalent reactivity to that of controls at 0.6 mA, central nucleus lesions still blocked shock sensitization. Moreover, lesions of the caudal part of the ventral amygdalofugal pathway, which carries central nucleus efferents to the startle reflex pathway, also blocked shock sensitization. It is hypothesized that shock activates the central nucleus of the amygdala, which increases startle through modulation of the startle pathway. Activation of the amygdala by shock may be the unconditioned response relevant for fear conditioning.

Acoustic Stimulation↗
PubMed1989

In vitro NMR evaluation of human thyroid lesions.

In vitro analysis of spin-lattice relaxation times (T1), water self-diffusion coefficients (DH2O), and proton NMR spectroscopy were performed in a study of 88 patients with thyroid lesions in order to determine the usefulness of these parameters in the differentiation of benign and malignant tissues. Thyroid tissue sample proton NMR spectral patterns were examined at 360 MHz. Proton NMR spectra were different for normal thyroid tissues, benign, and cancerous lesions. Significantly prolonged T1 (0.5T) and decreased DH2O were found in cancerous thyroid lesions relative to normal thyroid tissues. Considerable overlap was found, however, in comparing T1 and DH2O values for benign and malignant thyroid lesions. This study suggests that proton NMR spectroscopy may be more useful than T1 and DH2O in differentiating benign and malignant thyroid lesions.

Adenoma↗
PubMed1989

Neural systems involved in fear-potentiated startle.

The acoustic startle reflex offers a number of advantages for analyzing the neural bases of behavior. Startle apparently is mediated by excitatory amino acids at several of the synapses that comprise the short-latency startle pathway. The reflex is modulated by a variety of neurotransmitters at both the spinal and the supraspinal levels. In addition to showing habituation and sensitization, startle is increased in the presence of a fear stimulus. This may result from activation of the central nucleus of the amygdala which projects directly tot he acoustic startle pathway. A major challenge for future studies will be to determine what neurotransmitters, which are known to modulate startle, are involved in habituation, sensitization, and fear conditioning and to begin to analyze these processes at a cellular level.

Amygdala↗
PubMed1989

Influence of non-steroidal anti-inflammatory drugs and disease activity on serum alkaline phosphatase concentrations in rheumatoid arthritis, osteoarthritis, and polymyalgia rheumatica.

The influence of non-steroidal anti-inflammatory drugs (NSAIDs) and of disease activity on the serum alkaline phosphatase concentration was examined in patients with rheumatoid arthritis, osteoarthritis, and polymyalgia rheumatica. Concentrations of serum alkaline phosphatase were similar both in patients with rheumatoid arthritis taking NSAIDs and in those not taking NSAIDs. In patients with osteoarthritis NSAID use was not associated with a significant increase in serum alkaline phosphatase. In rheumatoid arthritis no correlation was found between clinical indices of disease activity and serum alkaline phosphatase concentrations. There was significant correlation with plasma viscosity in rheumatoid arthritis, both in those taking and not taking NSAIDs, and in polymyalgia rheumatica. Serum alkaline phosphatase concentrations are not influenced by NSAIDs. Concentrations correlate with laboratory parameters, but not clinical indices of disease activity.

Aged↗
PubMed1989

Mammalian tissue culture growth, viral replication, and cultivation using serum replacement factor.

Variability, cost, and availability of fetal bovine serum are in question; thus, we examined whether using a serum replacement factor in multiple mammalian tissue cultures could support not only cell growth, but also viral replication, expression, and retention of phenotypic markers. By using a serum replacement in defined media, we demonstrated multipassage cell growth of several different cell lines and viral cultivation and replication equivalent to fetal bovine serum. Moreover, by supplementing media with a serum replacement factor we observed at least a 28% financial savings.

Animals↗
PubMed1989

Pulmonary needle embolism from intravenous drug abuse.

Although the embolization of catheters and other foreign bodies in blood vessels is a well-known happening, needle embolization has rarely been reported. We describe here an instance in which a hypodermic needle broke in a man's skin during cocaine injection. The needle fragment was observed to migrate within a short time to the periphery of the left lung. The patient did not develop complications. The limited literature available indicates that such peripheral embolization usually follows a benign course.

Adult↗
PubMed1989

Sensitization of the acoustic startle reflex by footshock.

Administration of footshock (500-ms duration, 0.2-1.4 mA) increased the amplitude of the startle reflex for a long time after its presentation. The effect occurred with a single footshock, although its magnitude and consistency across animals was greater with 5 or 10 footshocks presented 1/s. The facilitatory effect came on within 2-4 min with a 0.6-mA shock, peaking in about 10 min and then dissipating over the next 40 min. Stronger shocks also increased startle, but with a more delayed onset of facilitation (8-10 min). Footshocks increased startle in rats not previously given startle-eliciting stimuli, indicating sensitization rather than dishabituation. The facilitatory effect may not be attributable to a rapid conditioning to the experimental context, because a change in lighting conditions from shock presentation to testing did not attenuate shock sensitization. This excitatory effect of shock on startle may represent the unconditioned effect of shock that can become associated with a neutral stimulus to support classical fear conditioning.

Acoustic Stimulation↗
PubMed1989

Temporal specificity of fear conditioning: effects of different conditioned stimulus-unconditioned stimulus intervals on the fear-potentiated startle effect.

Separate groups of rats were given 30 pairings of a light (conditioned stimulus, CS) and 500-ms shock (unconditioned stimulus, US) at CS-US intervals of 0, 25, 50, 100, 200, 800, 3,200, 12,800, or 51,200 ms. Other groups had lights and shocks inconsistently paired. The startle reflex was elicited 2-4 days later with a noise burst alone or 25-51,200 ms after light onset. After CS-US pairings over a wide range of intervals (25-51,200 ms), startle was potentiated in testing, sometimes as rapidly as 50 ms after light onset. Magnitude of potentiation and resistance to extinction were generally greater with longer CS-US intervals. In several groups, potentiation was maximal at a test interval that matched the CS-US interval used in training. This temporal specificity sharpened with increasing numbers of training trials but even occurred with a single training trial in which a 51,200-ms CS-US interval was used. The data indicate that even during simple fear conditioning, animals rapidly learn a temporal CS-US relationship. This has important implications for understanding the neural mechanisms of fear conditioning.

Animals↗
PubMed1988

Continuous slow release of low levels of diazepam produces tolerance to its depressant and anxiolytic effects on the startle reflex.

Development of tolerance to the depressant effects of diazepam on the acoustic startle reflex and to the blockade of fear-potentiated startle, a measure of fear or anxiety in rodents, was evaluated after chronic administration via continuous release from implanted diazepam-filled silastic capsules or daily intraperitoneal (i.p.) injections. After continuous exposure to diazepam via capsule implants, complete tolerance occurred to the depressant effects of diazepam on startle and partial tolerance occurred to the antifear effects. In contrast, no tolerance was observed after daily i.p. injection with comparable amounts of diazepam (5 mg/kg) although tolerance could be produced by daily i.p. injections of a much higher dose of diazepam (20 mg/kg). These data suggest that tolerance to at least some behavioral effects may be much easier to produce with continuous rather than intermittent occupation of benzodiazepine receptors.

Animals↗
PubMed1988

Neuroleptic malignant syndrome: a review of the Wellington experience.

The neuroleptic malignant syndrome is a potentially lethal complication of central dopamine antagonism. We report five cases, occurring in the Wellington region in the last 4 years. Three of the cases are reported in detail and the diagnostic difficulties and therapeutic strategies are reviewed. Particular attention is drawn to the use of the depot intramuscular phenothiazine formulations which were clearly implicated in our experience.

Adult↗
PubMed1988

Excitatory amino acid antagonists depress acoustic startle after infusion into the ventral nucleus of the lateral lemniscus or paralemniscal zone.

Rats were implanted with bilateral cannulas in an area just medial to the ventral nucleus of the lateral lemniscus, an obligatory relay along the acoustic startle pathway. Bilateral infusions of excitatory amino acid transmitter antagonists into this region (10, 25 or 50 nmol per side) produced a rapid, dose-dependent depression of acoustic startle. gamma-D-Glutamylglycine, gamma-D-glutamylaminomethyl sulfonate and 2-amino-5-phosphonovalerate were equally effective in depressing the startle response over this dose range. These results indicate that excitatory amino acid transmitters play an important role in the expression of acoustic startle at this part of the startle pathway.

2-Amino-5-phosphonovalerate↗
PubMed1988

Complement C4B-null alleles in Felty's syndrome.

C4A and C4B allotypes were compared in 20 patients with Felty's syndrome (FS), 52 patients with rheumatoid arthritis (RA), and 55 control subjects. Nineteen of the FS patients had HLA-DR4. A C4B-null allele was more frequent in the patients with FS (60%) than in either the RA patients (15%) or the control subjects (26%). Only the differences between patients with FS and those with RA remained statistically significant when DR4 positive subjects were compared. The C4B null allele may identify individuals within the rheumatoid population who are at risk of developing particular systemic complications.

Alleles↗
PubMed1988

Gadolinium-labeled liposomes containing paramagnetic amphipathic agents: targeted MRI contrast agents for the liver.

Unique paramagnetic liposomal contrast agents were synthesized and utilized for selective augmentation of T1 MR imaging of the livers of normal Balb/c mice. Amphipathic gadolinium complexes, which mimic phospholipids, were incorporated into the lamella of small unilamellar liposomes (SUV) such that they became an integral part of its surface. T1 signal enhancement of normal liver approached 150% after iv administration of the paramagnetic liposomes, determined by experiments performed on a 1.9-T, experimental whole-body MRI unit. Tracer studies utilizing gadolinium-153-tagged SUV revealed that the agents exhibited excellent in vivo stability, compared to liposomal preparations in which paramagnetic agents are simply entrapped in the aqueous core of the liposome vesicle.

Animals↗