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Biomedical subjects

J Larson

Publications and source records attributed to J Larson.

At least 19 recordsLinked to original sources
PubMed1992

Theta burst stimulation is optimal for induction of LTP at both apical and basal dendritic synapses on hippocampal CA1 neurons.

The efficacy of stimulation patterns consisting of brief high frequency bursts repeated at various intervals to induce long-term potentiation (LTP) at synapses on apical and basal dendrites of CA1 hippocampal neurons was tested in vitro. Both apical and basal dendritic synapses exhibited maximal LTP after bursts repeated at 5-10 Hz, i.e. close to the frequency of the endogenous hippocampal theta rhythm. As at apical dendritic synapses, LTP at basal dendritic synapses was blocked by an antagonist of NMDA receptors. Basal dendritic LTP was significantly greater in magnitude than apical dendritic LTP, although the reason for this is unknown.

2-Amino-5-phosphonovalerate↗
PubMed1992

Handwashing practices and resistance and density of bacterial hand flora on two pediatric units in Lima, Peru.

The handwashing practices and bacterial hand flora of 62 pediatric staff members of a teaching hospital in Lima, Peru, were studied. Handwashing followed patient contact 29.3% of the time (204/697 contacts). Mean duration was 14.5 seconds, and significant differences in practices were found by unit (rehydration or neonatal intensive care), type of staff member (nurses or physicians), and type and duration of patient contact. Mean count of colony-forming units was log10 5.87 +/- 0.41, with significant differences in density of flora found between patient care and kitchen staffs. There was no significant effect of handwashing on counts of colony-forming units. Significant differences were also found by unit and by staff position with regard to species isolated and antimicrobial resistance of isolates. A more efficacious and cost-effective form of hand hygiene and a more prudent use of antimicrobial agents are indicated.

Colony Count, Microbial↗
PubMed1992

Improving elders' continence state.

A 6-month study was conducted to assess the effects that noninvasive self-managed interventions on 12 remediable risk factors had on elder's urinary continence status. Each remediable risk factor was linked with a criterion meeting normal and if not normal, one or more interventions. Continence history assessments were conducted monthly on 31 elders (M age = 67.65 years). After the first assessment, elders were identified as continent, incontinent or at risk for loss of continence. At the end of the 6 months, 9 of the 11 incontinent elders moved to the at-risk group and the other 2 remained incontinent, and 12 of the 20 at-risk elders became continent. Both the elders who were initially at risk and those who were incontinent had a statistically significant reduction in the number of remediable risk factors reported at the end of the study period. The assessments and interventions are useful.

Aged↗
PubMed1992

The healing web. A transformative model for nursing. Part II.

The author and contributors continue the article that began in the February issue of Nursing & Health Care on the Healing Web project, "a collaborative effort of creative spinning and weaving." The purpose of the creative web management is to facilitate the healing of wounds within nursing and between nursing and medicine.

Education, Nursing, Associate↗
PubMed1991

A test of the spine resistance hypothesis for LTP expression.

Long-term potentiation (LTP) consists of an enhanced response to released transmitter by the quisqualate/AMPA subclass of glutamate receptors with little change in the slower currents generated by the NMDA receptor subclass. Recent computer simulations suggest that a decrease in the resistance of dendritic spines would selectively augment fast synaptic currents and this could produce the pattern of results found with LTP. The present experiments tested this hypothesis by asking whether non-NMDA responses slowed by low temperature to resemble NMDA responses could express LTP. Slow non-NMDA responses recorded at 25 degrees C did express LTP, indicating that the time courses of NMDA responses cannot explain why they do not express LTP. The results, therefore, do not support the hypothesis that spine resistance changes are responsible for the enhanced transmission.

Animals↗
PubMed1991

Evidence that changes in spine neck resistance are not responsible for expression of LTP.

From modeling studies it is known that changes in spine neck resistance can influence the shape of the non-linear curve relating synaptic current to synaptic conductance if the resistance of the neck approaches the synaptic input resistance. Such work also indicates that the effects of resistance will be much more pronounced for fast rather than slow synaptic currents. Accordingly, a reduction in neck resistance could produce an increase in the rapid responses generated by the quisqualate/AMPA class of glutamate receptors while only minimally affecting the slower NMDA receptor-mediated responses and thus account for the pattern of changes known to be associated with long-term potentiation (LTP). This hypothesis predicts that large reductions in synaptic conductance should have disproportionate effects on potentiated versus control responses. This was tested by using field potential recordings of synaptic currents in CA1 pyramidal cells in hippocampal slices in response to stimulation of Schaffer/commissural inputs that either received LTP-inducing stimulation or did not. Two manipulations were used to systematically reduce synaptic conductances: reductions of extracellular Ca++ and partial blockade of postsynaptic receptors. Reductions of synaptic field potentials by 40-75% by either method at control synapses were accompanied by equivalent reductions at previously potentiated synapses. These results suggest that LTP expression is not due to a change in the curves relating synaptic current to synaptic conductance as would be predicted by the spine resistance hypothesis.

Animals↗
PubMed1990

Development of hippocampal long-term potentiation is reduced by recently introduced calpain inhibitors.

The effects of two recently synthesized inhibitors of calpains, calpain inhibitor I (CiI) and calpain inhibitor II (CiII) were tested on the development of long-term potentiation (LTP) in region CA1 of rat hippocampus. Slices maintained in 100 microM of CiI or CiII showed an initial degree of potentiation after theta burst stimulation that, in contrast to controls, slowly decayed across time. The effects of CiI and CiII appeared to be independent of possible actions on the physiological mechanisms that take place during the induction stage of LTP. Since these inhibitors are more potent and specific than leupeptin in blocking calpain activity, their effects on LTP can be more convincingly ascribed to a selective blockade of the calcium-sensitive protease. Accordingly, the results favor the idea that a proteolytic event of the kind found after N-methyl-D-aspartate receptor activation is an intermediary step in the development of LTP.

Animals↗
PubMed1990

Extended-field radiation therapy for carcinoma of the cervix.

The survival of cervical carcinoma patients with paraaortic/high common iliac nodal metastases was evaluated by retrospective chart review during a 13-year interval. Thirty-three patients with cervical carcinoma and surgically documented nodal metastases received primary, extended-field radiation therapy. Overall 2-year and 5-year actuarial survival rates after diagnosis were 37% and 31%, respectively. Survival was analyzed in terms of the variables patient age, clinical stage, tumor histologic type, the presence of enlarged paraaortic/high common iliac lymph nodes, the extent of nodal involvement (microscopic versus macroscopic), the presence of intraperitoneal disease, and whether intracavitary brachytherapy was administered. The use of intracavitary radiation therapy was associated with improved local control and survival (P = 0.017). None of the other variables were statistically related to patient survival. Twenty-two of the patients died of cervical cancer and five are surviving without evidence of cancer. Four patients died of intercurrent disease. Two patients developed bowel-related radiation complications; both patients received chemotherapy concurrent with the radiation therapy. One of the two patients died of radiation enteritis. The use of extended-field radiation therapy does benefit a small group of patients and may result in extended patient survival.

Adenocarcinoma↗
PubMed1990

Identification of a rabies virus T cell epitope on the basis of its similarity with a hepatitis B surface antigen peptide presented to T cells by the same MHC molecule (HLA-DPw4).

The antigenic determinant recognized by a HLA-DPw4-restricted human T cell clone specific for rabies virus was identified by using a vaccinia-rabies nonstructural phosphoprotein recombinant virus and synthetic peptides of the sequence of rabies nonstructural Ag. These peptides were selected on the basis of three models that predict T cell epitopes. The antigenic determinant recognized by the rabies virus-specific T cell clone contained a five-amino acid segment highly homologous to a sequence found in a hepatitis B surface Ag epitope that stimulates human T cells in the context of the HLA-DPw4. A preliminary model of DPw4-restricted T cell determinants is elaborated based on a hypothesis of how the 2 alpha-helical peptides may bind to this MHC molecule. Results are further discussed in the context of the usefulness in identifying DPw4-restricted T cell epitopes for the production of synthetic vaccines because this MHC class II molecule is found with high frequency in the population.

Amino Acid Sequence↗
PubMed1990

Anoxia reveals a vulnerable period in the development of long-term potentiation.

Transient anoxia occurring 1-2 min after high-frequency stimulation selectively prevented the stable expression of long-term potentiation (LTP). Anoxia occurring after this brief vulnerable period did not reverse LTP. Experiments on the duration of anoxia necessary to block LTP expression indicated that simply reducing synaptic transmission was insufficient but that membrane depolarization was not required. The effects of anoxia on LTP were blocked by antagonists of A1 adenosine receptors. It is concluded that LTP develops in about one minute and that the chemistries operating in this period are easily disrupted by an event triggered by adenosine receptors.

Action Potentials↗
PubMed1990

Glycine site associated with the NMDA receptor modulates long-term potentiation.

Recent work has shown that kynurenic acid and several quinoxaline derivatives act as non-competitive NMDA receptor antagonists by binding to the glycine site associated with this receptor. In this study, we have tested the effect of the most potent and selective of these compounds, 7-chlorokynurenic acid (Cl-Kyn), on the induction of long-term potentiation, an event known to involve activation of NMDA receptors. It was found that 30 microM Cl-Kyn reversibly abolished the development of both short-term and long-term potentiation in the CA1 region of hippocampal slices. The effectiveness of Cl-Kyn matched its ability to inhibit 3H-glycine binding and the association of 3H-TCP with the NMDA receptor in binding experiments (Ki 0.7-1 microM). Weak interactions of Cl-Kyn with AMPA receptor sites were observed and may account for a partial, reversible reduction in the epsp. However, blockade of long-term potentiation by Cl-Kyn was completely reversed by simultaneous application of the glycine site agonist D-serine and thus must be attributed to its interaction with the glycine site. These results indicate that the glycine site coupled to the NMDA receptor potently modulates channel function during physiological events related to synaptic activation.

Adaptation, Physiological↗
PubMed1990

Long-term potentiation of monosynaptic EPSPs in rat piriform cortex in vitro.

Induction of long-term potentiation (LTP) by burst stimulation patterned after the limbic system theta rhythm was studied in slices of piriform cortex. Monosynaptic responses were evoked by stimulation of afferent fibers of the lateral olfactory tract (LOT) or the intrinsic associational (ASSN) feedback system. LTP was difficult to elicit at LOT synapses in the presence of 2.5 mM extracellular Mg2+, and when it was induced potentiation increased for 20-30 min after burst stimulation before stabilizing. The probability of inducing LTP was increased when the extracellular Mg2+ concentration was reduced to 50 microM. In ASSN synapses LTP developed in about 1 min after burst stimulation and then remained stable. ASSN system LTP was more readily induced in slices from caudal than rostral piriform. Induction of LTP at both LOT and ASSN synapses was blocked by D-2-amino-5-phosphonopentanoate, indicating that NMDA receptor activation was required. Neither system exhibited the decremental short-term potentiation effect observed after burst stimulation of inputs to the CA1 field of hippocampus.

2-Amino-5-phosphonovalerate↗
PubMed1990

Role of NMDA and non-NMDA receptors in synaptic transmission in rat piriform cortex.

The pharmacology of synaptic transmission was studied in slices of rat piriform cortex using the selective non-NMDA glutamate receptor antagonist 6.7-dinitroquinoxaline-2,3-dione (DNQX) and the selective NMDA receptor antagonist D-2-amino-5-phosphonopentanoate (D-AP5). DNQX produced a dose-dependent blockade of synaptic transmission at both lateral olfactory tract and associational system synapses with half-maximal effects at about 2.5 microM. D-AP5 had no significant effects on field potentials recorded in medium containing 2.5 mM Mg++. However in low Mg++ (100-200 microM) medium, D-AP5 did reduce a slow component of postsynaptic responses in both synaptic systems. In Mg(++)-free medium, 20 microM DNQX did not completely block transmission; the remaining response components were blocked by D-AP5. These results suggest that normal synaptic transmission in the two main inputs to the superficial layers of piriform cortex is mediated by non-NMDA receptors but that NMDA receptors can also participate under conditions where the Mg++ block of the NMDA channel is alleviated.

2-Amino-5-phosphonovalerate↗
PubMed1990

Survival of patients with ovarian epithelial carcinomas after second-look laparotomy.

Survival of ovarian carcinoma patients undergoing second-look laparotomy after primary surgery and adjunctive chemotherapy was evaluated by retrospective chart review. From August 1976 to August 1987, 102 patients with stage I-IV disease underwent second-look laparotomy. Optimal tumor debulking and early (stage I or II) disease were positively correlated with a negative second-look laparotomy. Of the 49 patients with a "negative" second look, 15 demonstrated recurrent tumor from 12.5 to 52.5 months after laparotomy. Of the 15 recurrences, 6 were documented more than 3 years following second look. Half of the 28 patients with stage III disease and a "negative" second look have demonstrated recurrent tumor. Fifty-three patients (52%) were found to have residual disease at second-look laparotomy. Initial chemotherapy (melphalan or multiple agent) and the adequacy of primary debulking surgery (optimal vs suboptimal) were not significant factors contributing to patient survival after a positive second look. However, the size of residual disease at second-look laparotomy was a significant factor in subsequent patient survival (P less than or equal to 0.01). Fifteen patients were free of gross disease at laparotomy, but had residual tumor on microscopic examination of the specimens submitted. These patients had a 2-year actuarial survival of 78%. Forty-seven percent have survived 5 or more years after second look. Nineteen patients with tumor implants 2 cm or smaller had 2- and 5-year actuarial survivals of 61 and 31%, respectively. Nineteen patients with tumor nodules larger than 2 cm in diameter had a 2-year actuarial survival of 6%. Only 1 of 19 patients with nodules greater than 2 cm could be effectively redebulked.

Carcinoma↗