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Biomedical subjects

G Lynch

Publications and source records attributed to G Lynch.

At least 397 records · Page 22Linked to original sources
PubMed1983

Regulation by calcium ions of glutamate receptor binding in hippocampal slices.

Hippocampal slices were incubated in a Krebs-bicarbonate buffer with various concentrations of calcium and [3H]glutamate receptor binding was measured in crude synaptic membranes derived from these slices. Increasing the calcium concentration from 0 to 2.5 mM resulted in a 2.2-fold increase in the maximal number of the Na-independent [3H]glutamate binding sites without changes in their affinity for [3H]glutamate. This effect was totally blocked by the addition of the protease inhibitor leupeptin (50 microM) to the slice incubation medium. No effect was observed on the Na-dependent [3H]glutamate binding nor on the Na-independent [ 3H ]glutamate binding measured in the presence of a concentration of calcium of 250 microM. Increasing the calcium concentration also resulted in an increased proteolytic activity which was inhibited by about 70% by the addition of leupeptin. Finally, increasing the calcium concentration induced the degradation of high-molecular weight proteins, the microtubule-associated proteins (MAPs) and the 220 000 dalton doublet protein corresponding to fodrin. Both effects were partially prevented by the addition of leupeptin in the slice incubation medium. These results indicate that the same calcium-dependent processes which were previously shown to regulate [ 3H ]glutamate receptor binding to hippocampal membranes occur in the hippocampal slice preparation, and they suggest a mechanism by which fluctuations in calcium levels can activate a calcium-dependent proteinase, the degradation of cytoskeletal-associated proteins and the unmasking of additional glutamate receptors. The participation of such processes in various forms of plasticity is discussed.

Animals↗
PubMed1983

Antiseptics in the treatment of bacterial peritonitis in rats.

A controlled mixed peritoneal infection was produced by inoculation of bacteria into the peritoneum and peritonitis was allowed to become established. A laparotomy was performed and peritoneal toilet with a variety of agents was carried out. Local povidone-iodine in the inflamed peritoneum proved to be not only of no benefit but, in fact, to be toxic. In the standard concentrations recommended it proved lethal. Noxythiolin 2.5 per cent also had no beneficial effect. There was a significant difference between the effect of povidone-iodine when instilled into an inflamed peritoneum and instillation into the intact peritoneal cavity. We would advise caution in the use of these antiseptics in any situation in which local defence mechanisms have been compromised as a result of established infection.

Animals↗
PubMed1983

Cervix carcinoma: treatment with combination cisplatin and bleomycin.

Thirty patients with metastatic carcinoma of the cervix were treated with a combination of cisplatin and bleomycin. Thirty patients were evaluable for toxicity and 24 were evaluable for response. Thirteen patients achieved a partial remission for an objective response rate of 54% with a median duration of 3.5 months. The response rate for extrapelvic disease without prior radiation was 57% while the response rate for disease recurring in the previously irradiated pelvic area was only 36%. Response rates were higher in tumors with nonsquamous histology. Survival times for responders and nonresponders were not significantly different. Significant toxicity was observed. It is concluded that the combination of high-dose cisplatin and bleomycin infusion in patients with recurrent cervix cancer has an improved response rate. However, these responses are of short duration and drug toxicity is significant. The role of this combination for adjuvant studies is discussed.

Adult↗
PubMed1983

Purification from synaptosomal plasma membranes of calpain I, a thiol protease activated by micromolar calcium concentrations.

Synaptosomal plasma membranes (SPMs) were prepared from whole rat brain and assayed for calcium-stimulated proteolytic activity. Addition of calcium to SPMs caused a dose-dependent increase in trichloroacetic acid-soluble protein. Two peaks of protease activity directed against a casein substrate were detectable when SPMs were incubated with low-ionic-strength buffer and the extract was fractionated on DEAE-cellulose. The enzyme in peak 1 required less than 1/10 the calcium concentration for activation as the peak 2 protease (Kact1 = 35 microM; Kact2 = 500 microM). The specific thiol-protease inhibitors leupeptin and antipain and the alkylator iodoacetate blocked enzyme activity. The low-sensitivity protease was converted to a high-sensitivity enzyme (Kact = 20 microM) by substrate affinity chromatography in the presence of calcium. This protease was purified 550-fold from SPMs. The high- and low-sensitivity membrane-associated calcium-dependent proteases are part of a family of enzymes, the calpains, previously reported in cytosolic fractions of several tissues.

Animals↗
PubMed1983

Biochemical effects of high-frequency synaptic activity studied with in vitro slices.

Brain slices have a number of features that may be of value in the analysis of how physiological events affect neuronal chemistry. This paper discusses this topic and describes slice experiments concerned with the chemical events responsible for long-term potentiation (LTP) of synaptic responses found in hippocampus after brief episodes of high-frequency stimulation. Work with two variants of the slice procedure indicated that LTP is accompanied by an increase in the sodium-independent binding of [3H]glutamate to partially purified synaptic membranes; this effect very likely results from an increase in the numbers of a particular postsynaptic receptor. Stimulation that produces long-term potentiation also causes a significant change in the endogenous phosphorylation of pyruvate dehydrogenase (PDH), a key mitochondrial enzyme. Inasmuch as the phosphorylated state of PDH is strongly correlated with calcium sequestration by mitochondria, it is possible that LTP is triggered by a transient perturbation of the calcium buffering function provided by mitochondria. Low micromolecular levels of calcium increase glutamate binding to purified membranes apparently via the activation of a calcium-sensitive thiol proteinase. This mechanism could account for the increase in glutamate binding found in slices exhibiting LTP. These experiments suggest a possible explanation for long-term potentiation and indicate that slices can be used to detect at least some of the biochemical consequences of repetitive synaptic activity.

Animals↗
PubMed1983

Classification and properties of acidic amino acid receptors in hippocampus. III. Supersensitivity during the postnatal period and following denervation.

The effects of excitatory amino acids on 22Na efflux rate in rat hippocampal slices were determined at various postnatal days and following removal of a major afferent system. Two weeks after a unilateral hippocampal aspiration, the 22Na efflux induced by potassium ions, D-glutamate, N-methylaspartate, and kainate is significantly decreased in the contralateral intact hippocampus whereas the effect of L-glutamate is substantially increased. Analysis of concentration-response curves suggests that the increased responsiveness to L-glutamate is due to an increase in the maximal effect rather than to changes in the half-maximal concentration for the amino acid. Partial denervation does not detectably change efflux elicited by D,L-homocysteic acid nor does it modify the properties of [3H]glutamate binding to hippocampal membranes. The effects of potassium ions, N-methylaspartate, and kainate but not of D,L-homocysteate are significantly decreased in slices incubated in the absence of calcium. All of the amino acids tested are considerably more potent in slices prepared from 11-day-old rats than in those from adult rats; the differences in responsiveness reflect an increase in maximal effect without changes in the half-maximal concentration. The responses to L-glutamate and D,L-homocysteate decline steadily between postnatal days 11 and 30, at which time adult values are reached. Together, the results from the denervation and development studies suggest a different localization and different modes of regulation for various classes of excitatory amino acid receptors.

Aging↗
PubMed1983

Classification and properties of acidic amino acid receptors in hippocampus. II. Biochemical studies using a sodium efflux assay.

The properties of excitatory amino acid receptors in hippocampal slices were analyzed using agonist-induced stimulation of 22Na efflux rate. Several amino acids (L- and D-glutamate, N-methylaspartate) produce progressively smaller responses upon successive applications, whereas D,L-homocysteate does not. Several lines of evidence suggest that depletion of an intracellular pool of 22Na is not responsible for the apparent desensitization. Addition of the amino acids in the presence of an antagonist does not affect the response of the slices to subsequent applications, indicating that desensitization is dependent upon the interaction of the agonist with its receptor. The antagonist D-alpha-aminoadipate discriminates between various excitatory amino acids, completely blocking the responses to N-methylaspartate, D-glutamate, and D,L-homocysteate; partially antagonizing those of quisqualate and kainate; and being without effect on L-glutamate. The order of potency of several excitatory amino acids on the stimulation of 22Na efflux rate in hippocampal slices is highly correlated with their relative effects measured with electrophysiological techniques, but does not correlate with their relative potencies to inhibit [3H]glutamate binding to hippocampal membranes. The similarities in the properties of excitatory amino acid receptors evidenced with the 22Na efflux assay or with the electrophysiological approach in the in vitro hippocampal slice preparation indicate that the same receptors are sampled by the two techniques. The results are discussed in terms of a classification of these receptors into four different groups: a synaptic receptor, activated by D,L-homocysteate (tentatively defined as a G1 receptor), an extrasynaptic glutamate receptor (defined as a G2 receptor), an N-methylaspartate receptor, and a kainate receptor.

2-Aminoadipic Acid↗
PubMed1983

Denervation-induced decrease in mitochondrial calcium transport in rat hippocampus.

Calcium accumulation by mitochondria and the activity and in vitro phosphorylation of pyruvate dehydrogenase were measured in control and partially denervated hippocampus. Calcium uptake was measured with a calcium-sensitive electrode and 45Ca2+ accumulation; both methods indicated that lesions of the entorhinal cortex produced a sizable reduction of calcium transport when mitochondria were fueled with pyruvate while much smaller changes were observed using succinate or ATP as energy sources. The decrease in calcium transport was evident by 24 hr after the lesion and was still present 6 months later. Synaptic and nonsynaptic mitochondria were similarly affected by the lesions. The activity and in vitro phosphorylation of pyruvate dehydrogenase were also significantly reduced following lesions of the entorhinal cortex, suggesting that denervation altered the endogenous state of phosphorylation of the mitochondrial enzyme. Commissural lesions but not septal lesions also resulted in a decrease in mitochondrial calcium transport when mitochondria were fueled with pyruvate. These findings suggest that denervation disturbs mitochondrial regulation of free calcium via an action on enzymes which regulate pyruvate dehydrogenase phosphorylation and activity. The potential relationship of this effect to degenerative changes associated with deafferentation and certain disease states is discussed.

Adenosine Triphosphate↗
PubMed1982

Combination chemotherapy of advanced sarcomas in adults with "CYOMAD" (S7).

Response rates of metastatic soft part sarcomas to chemotherapy have varied from 27 and 44% for our ALOMAD and OMAD protocols to 46-55% reported for CYVADIC. The present combination, CYOMAD, consists of the induction part of ALOMAD (vincristine, high-dose methotrexate with citrovorum factor rescue, Adriamycin and DTIC) alternating with a condensed version of CYVADIC (cyclophosphamide, vincristine, adriamycin and DTIC). Forty-one patients with advanced soft-part sarcomas were entered on the CYOMAD program of whom 36 were considered evaluable. Complete responses (CR) were seen in four patients had partial (PR) in five patients for a major response rate of 25%. Responders had an overall longer survival than nonresponders (20 versus 13 months). Toxicity was substantial with both gastrointestinal side effects and myelosupression common. Possible Adriamycin cardiotoxicity was noted in four patients. Cyomad offered no therapeutic advantage over previous protocols and was even less well tolerated than some.

Adolescent↗
PubMed1982

Vincamine: a psychogeriatric agent blocking synaptic potentiation in hippocampus.

The action of vincamine on the physiology of the CA1 region of the in vitro hippocampal slice preparation was investigated. At concentrations of 1, 10 and 100 microM, a five-minute perfusion with vincamine did not affect the synaptically-mediated activation of pyramidal neurons evoked by stimulation of the Schaffer-commissural fiber system. The effect of vincamine on the excitability of the pyramidal neurons was investigated by studying its effect on the antidromically-elicited field potential and the input-output relation of Schaffer-commissural fiber input. No effect on either of the two parameters was seen at a concentration of 100 microM of vincamine. Vincamine did, however, attenuate both the post-tetanic (PTP) and long-term potentiation (LTP) evoked by repetitive stimulation of the Schaffer-commissural fiber system. At a concentration of 100 microM of vincamine, PTP was significantly reduced and LTP was almost completely suppressed.

Action Potentials↗
PubMed1982

Effects of high-frequency synaptic stimulation on glumate receptor binding studied with a modified in vitro hippocampal slice preparation.

Slices of the field CA1 minus the stratum moleculare were prepared from the rat hippocampus and maintained in an in vitro recording chamber. The physiological properties of these "minislices" were similar to those reported for non-dissected hippocampal slices. Slices receiving various patterns of electrical stimulation through multiple electrodes were subsequently homogenized and crude membrane fractions prepared; the binding of [3H]glutamate was measured by a rapid filtration assay. Binding in membranes prepared from control slices exhibited kinetic properties and sensitivities to pharmacological and ionic manipulations which were comparable to those found in previous studies using conventional fractionation and assay techniques. Brief bursts of high-frequency stimulation increased [3H]glutamate binding compared to non-stimulated controls in 3 separate experiments. Stimulation at low frequency or at high frequency in low calcium medium did not produce this effect. In addition to suggesting that glutamate binding sites are regulated by patterns of afferent activity, these findings indicate that the minislice preparation should be of general utility in relating synaptic physiology to synaptic chemistry.

Animals↗