N-methyl-D-aspartate receptor-mediated component of synaptic responses to single-pulse stimulation in rat hippocampal slices.
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2-Amino-5-phosphonovalerate↗
Biomedical subjects
G Lynch
Publications and source records attributed to G Lynch.
Long-term potentiation: persisting problems and recent results.
In this paper we discuss recent experimental results pertinent to three unresolved issues regarding the long-term potentiation (LTP) effect: the nature of its enduring substrates, the biochemical mechanisms that produce it, and its potential role in memory. LTP appears to be triggered by a postsynaptic influx of calcium and is associated with alterations in the shape of dendritic spines and probably the formation of new synapses. We discuss the possibility that morphological reorganization also modifies membrane surface chemistry of synaptic elements. Evidence is presented that LTP is not associated with changes in presynaptic calcium currents. Activation of protein kinase C is shown to be insufficient for the induction of LTP, although it may play a modulatory role. The hypothesis that activation of a calcium-sensitive protease (calpain) is pivotal to the establishment of LTP is supported by experiments showing that a calpain inhibitor, leupeptin, blocks LTP. Furthermore, activation of NMDA receptors, an event implicated in LTP induction, is accompanied by calcium-sensitive proteolysis of spectrin, a major dendritic cytoskeletal protein. The finding that stimulation patterns designed to mimic naturally-occurring cell discharge patterns are highly effective for LTP induction greatly strengthens the hypothesis that LTP actually occurs during the encoding of information in cortical systems. Potential contributions of LTP to learning are explored using computer simulations of a simple cortical network.
Animals↗
Phorbol ester-induced synaptic facilitation is different than long-term potentiation.
The studies described here tested the hypothesis that the changes in synaptic efficacy produced by phorbol esters in hippocampal slices are equivalent to the long-term potentiation (LTP) induced by high-frequency stimulation. In contrast to the extremely stable synaptic potentiation induced by electrical stimulation, the facilitatory effects of phorbol 12,13-diacetate and phorbol 12,13-dibutyrate were transient: washout of the drugs restored normal responses in approximately 1-2 and 2-4 hr for phorbol diacetate and phorbol dibutyrate, respectively. It is noteworthy that the more liposoluble of the phorbol esters required longer washout periods. Robust LTP still occurred in response to high-frequency stimulation after washout of phorbol esters and to a lesser degree during their application. Treatment of slices with H-7, an inhibitor of protein kinase C, did not prevent LTP induction although it significantly affected neuronal excitability and produced effects opposite to those of phorbol esters. Finally, phorbol esters altered responses to repetitive stimulation in a way that could account for the reduced LTP elicited in their presence. These results indicate that the increases in synaptic responses caused by phorbol esters and high-frequency electrical stimulation are quite different and thus do not support the hypothesis that activation of protein kinase C, the presumed target of the phorbol esters, triggers LTP.
1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
Long-term potentiation differentially affects two components of synaptic responses in hippocampus.
We have used low magnesium concentrations and the specific antagonist D-2-amino-5-phosphonopentanoate (D-AP5) to estimate the effects of long-term potentiation (LTP) on the N-methyl-D-aspartate (NMDA) and non-NMDA receptor-mediated components of postsynaptic responses. LTP induction resulted in a considerably larger potentiation of non-NMDA as opposed to NMDA receptor-related currents. Increasing the size of postsynaptic potentials with greater stimulation currents or with paired-pulse facilitation produced opposite effects; i.e., those aspects of the response dependent on NMDA receptors increased to a greater degree than did those components mediated by non-NMDA receptors. These results pose new constraints on hypotheses about the locus and nature of LTP and strongly suggest that postsynaptic modifications are part of the effect.
2-Amino-5-phosphonovalerate↗
Transperineal 125iodine endocurietherapy of prostate cancer.
We present the improved implant technique, intraoperative and postoperative complications, local control, and survival of 67 patients with cancer of the prostate treated by means of percutaneous transperineal template permanent 125iodine interstitial endocurietherapy (ECT). This ECT technique is a simple, easily learned, accurate and rapid procedure that can be performed without subjecting the patient to celiotomy. The use of vicryl carriers for permanent 125iodine implantation of the prostate with the percutaneous transperineal template technique prevents seed loss and permits implantation of patients after transurethral resection of the prostate (TURP).
Brachytherapy↗
Effects of thiol-reagents on [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid binding to rat telencephalic membranes.
The binding of [3H]alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid ([3H]AMPA), a ligand for the quisqualate subtype of excitatory amino acid receptors, was measured after chemical modifications of rat brain synaptic membranes. Treatment with oxidizing or thiol-alkylating agents did not modify [3H]AMPA binding, whereas treatment with several sulfhydryl reagents produced marked increases in binding. The involvement of free sulfhydryl groups in the regulation of the properties of [3H]AMPA binding sites was suggested by the specificity of p-chloromercuribenzoic acid (PCMB), its sulfonate analog p-chloromercuriphenyl-sulfonic acid (PCMBS), and HgCl2, plus the reversal of their effects after reduction with dithiothreitol. Pretreatment of synaptic membranes with the oxidizing agent 5,5'-dithiobis(2-nitrobenzoic acid) or the alkylating agent N-ethylmaleimide did not significantly affect [3H]AMPA binding but markedly reduced the enhancing effect of PCMBS. On the other hand, the increase in [3H]AMPA binding produced by PCMBS was not prevented by treatment with agonists such as quisqualate or L-glutamate and was produced equally well in resealed postsynaptic membranes with both lipophilic or nonlipophilic SH-reagents. Using filtration assays, two types of binding sites could be detected with high and low affinity for [3H]AMPA. Treatment with SH-reagents produced an increase in the Bmax for the high affinity component and a decrease in the Bmax for the low affinity component, accompanied by an increase in its affinity for the ligand. Using centrifugation assays, the same two types of sites could be detected under control conditions but treatment with SH-reagents produced an increase in affinity of the large component that prevented the analytical differentiation of the two sites. Treatment with SH-reagents also increased the binding of [3H] glutamate to the N-methyl-D-aspartate receptors but did not modify the binding of [3H]kainate to the kainate receptors or the strychnine-insensitive [3H]glycine binding. These results suggest that free sulfhydryl groups allosterically modulate the affinity of the quisqualate subtype of excitatory amino acid receptors and also indicate that different types of glutamate receptors might be differentially affected by chemical modification.
Allosteric Regulation↗
Wear, creep, and frictional heating of femoral implant articulating surfaces and the effect on long-term performance--Part II, Friction, heating, and torque.
In Part I, (J.A. Davidson and G. Schwartz, "Wear, creep, and frictional heating of femoral implant articulating surfaces and the effect on long-term performance--Part I, A review," J. Biomed. Mater. Res., 21, 000-000 (1987) it was shown that lubrication of the artificial hip joint was complex and that long-term performance is governed by the combined wear, creep, and to a lesser extent, oxidation degradation of the articulating materials. Importantly, it was shown that a tendency for heating exists during articulation in the hip joint and that elevated temperatures can increase the wear, creep, and oxidation degradation rate of UHMWPE. The present study was performed to examine closely the propensity to generate heat during articulation in a hip joint simulator. The systems investigated were polished Co-Cr-Mo alloy articulating against UHMWPE, polished alumina ceramic against UHMWPE, and polished alumina against itself. Frictional torque was also evaluated for each system at various levels of applied loads. A walking load history was used in both the frictional heating and torque tests. The majority of tests were performed with 5 mL of water lubricant. However, the effect of various concentrations of hyaluronic acid was also evaluated. Results showed frictional heating to occur in all three systems, reaching an equilibrium after roughly 30 min articulation time. Ceramic systems showed reduced levels of heating compared to the cobalt alloy-UHMWPE system. The level of frictional torque for each system ranked similar to their respective tendencies to generate heat. Hyaluronic acid had little effect, while dry conditions and the presence of small quantities of bone cement powder in water lubricant significantly increased frictional torque.
Hip Prosthesis↗
Stable hippocampal long-term potentiation elicited by 'theta' pattern stimulation.
The stability of long-term potentiation (LTP) elicited by a stimulation paradigm in which short high-frequency bursts of pulses were given in a 'theta' pattern (i.e. 5 bursts/s) was tested in a chronic recording study. Stimulation electrodes were implanted bilaterally in the Schaffer-commissural system while the recording electrode was placed in the apical dendritic field of the Ca1 zone of the hippocampus. Following 4 days of baseline testing, 'theta' stimulation was applied to one electrode for a total of 2 s (ten 30 ms bursts), after which testing was continued for 3 weeks or until the responses fell to below baseline levels. Data were collected from 25 animals and 3 types of results were obtained: (1) no LTP (n = 4), (2) LTP that decreased steadily from 24 h after high frequency stimulation onward (n = 4), and (3) LTP that was stable until recording was terminated or until the responses began a precipitous decrease to below baseline values (n = 17). The mean of the slopes of the curves relating degree of potentiation to days after 'theta' stimulation was less than 1%/day with a mean correlation coefficient of only 0.1 prior to the point at which the responses began their rapid decline. Control responses were unaffected by the induction of LTP in neighboring CA1 afferents and did not exhibit a reliable relationship with time. These results suggest that, for most rats, LTP elicited by theta pattern stimulation is stable until such time that stimulation-recording arrangements begin to deteriorate.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Functional reconstitution of N-methyl-D-aspartate receptors in artificial lipid bilayers.
Functional reconstitution of the N-methyl-D-aspartate (NMDA) receptors was achieved by adding synaptic membranes from rat brain to large planar bimolecular lipid membranes (BLMs). The reconstituted receptors exhibited several properties of the NDMA receptors described using a variety of biochemical and electrophysiological techniques. Addition of NMDA at concentrations between 5 and 50 microM produced large, voltage-dependent increases in membrane conductivity. The selective antagonist of NMDA receptors, amino-2-phosphonopentanoate (AP-7), totally blocked the response of the bilayers to NMDA as did micromolar concentrations of magnesium; this latter effect was also voltage-dependent. These results indicate that BLMs can be used to study the ion channels and regulatory processes associated with NMDA receptors from adult brain in ways that could not be accomplished with conventional neurophysiological techniques.
Aspartic Acid↗
Use of cystine to distinguish glutamate binding from glutamate sequestration.
Cystine is shown to be a high-affinity substrate for the chloride-dependent glutamate exchange system in brain membranes, which mediates what has previously been considered chloride-dependent glutamate 'binding'. Similarities in the pharmacological profile and in kinetic properties suggest that this transport system may be a high-affinity adaptation of the transport system xc- present in somatic cells. Since cystine selectively inhibits glutamate sequestration and does not interact with the major glutamate binding sites, it can be used to assess the contribution of sequestration to overall 'binding' of glutamate or glutamate-analogs or to suppress sequestration in receptor binding assays. As an example, it is shown that more than 90% of 'bound' [3H]aminophosphonobutyrate [( 3H]APB) is displaced by cystine and should be interpreted as APB sequestration.
Animals↗
Evidence for synaptic potentiation in a cortical network during learning.
The connections between the lateral olfactory tract (LOT) and layer I of the piriform cortex were used to test the idea that certain forms of learning involve potentiation of cortical synapses. Rats were trained on a series of two-odor discriminations over a period of several days after which patterned electrical stimulation (short, high frequency bursts with 5-6 bursts per second) of the LOT was used as a discriminative cue. The animals reacted to the stimulation as though it were an odor and quickly learned to respond appropriately and to distinguish between 'positive' and 'negative' electrodes. Comparisons of the monosynaptic responses in the piriform cortex evoked by single pulse stimulation of the LOT before and after learning revealed that the population synaptic responses were substantially potentiated by the training. This effect was present in an unchanged form 24 h later. Responses elicited by control stimulating electrodes were slightly or not at all affected by training to stimulation with another electrode. Synaptic potentiation was not found in a small group of rats that did not learn to respond to patterned stimulation and was also absent when the stimulation was applied to naive rats. These results provide evidence that rapid learning of a specific cue potentiates cortical synapses in a defined terminal field.
Animals↗
Optimising antiemesis in cancer chemotherapy.
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Acupuncture Therapy↗
Calmodulin stimulates the degradation of brain spectrin by calpain.
Brain spectrin has been shown to be a preferential substrate of calcium-dependent proteases (Baudry, Bundman, Smith, and Lynch: Science 212:937-938, 1981) and a major calmodulin-binding protein (Kakiuchi, Sobue, and Fujita: FEBS Lett. 132:144-148, 1981). Since calmodulin, spectrin, and a proteolytically derived spectrin fragment are all components of isolated postsynaptic density preparations (Grab, Berzins, Cohen, and Siekevitz: J. Biol. Chem. 254:8690-8696, 1979; Carlin, Bartelt, and Siekevitz: J. Cell Biol. 96:443-448, 1983), we investigated the functional role of calmodulin binding to brain spectrin with respect to its susceptibility to digestion by proteases. We report that calmodulin's interaction with brain spectrin results in a marked acceleration of the rate of spectrin degradation by calcium-dependent proteases (calpains I and II), but not by chymotrypsin. The cleavage of erythrocyte spectrin (which lacks a high-affinity calmodulin binding site) by calpain I is unaffected by the presence of calmodulin. The stimulatory effect of calmodulin is blocked by trifluoperazine, a calmodulin antagonist, which by itself does not modify brain spectrin proteolysis by calcium-dependent proteases. These results suggest a novel role for calmodulin in neuronal function--namely, a synergistic interaction with calcium-dependent proteases in the regulation of cytoskeletal integrity.
Animals↗
A critical level of protein synthesis is required for long-term potentiation.
Long-term potentiation (LTP) of the hippocampal population spike in area CA1 was studied in the hippocampal slice before, during, and after inhibition of protein synthesis. LTP was tested 15 and 30 min following addition of the protein synthesis inhibitor cycloheximide (CXM) to the bathing medium. Stimulation-induced LTP of the population spike was reduced in slices incubated in CXM for 15 min and completely blocked if incubated for 30 min. Measures of protein synthesis inhibition under the same conditions showed 79% at 15 min and 85% after 30 min. Tests of the effects of repeated LTP treatments at these same time points in the absence of CXM and evaluation of the time course of recovery of LTP from CXM blockade were also conducted. The results confirm previous observations and indicate that a critical amount of protein synthesis inhibition is required to completely block LTP in the hippocampal slice.
Animals↗
Subcellular compartmentalization of calcium-dependent and calcium-independent neutral proteases in brain.
In the present experiments, we studied the subcellular distribution of three types of extralysosomal, neutral proteolytic activities in rat telencephalon: (1) nonthiol proteases (NTP), (2) thiol proteases (TP), and (3) calcium-activated thiol proteases (calpains I and II). Subcellular fractionation was performed by using conventional differential and sucrose-gradient centrifugation techniques. The only significant proteolytic activity detected in crude homogenates could be assigned to calpain II, the high-threshold calcium-activated protease. Within the primary fractions prepared from the homogenates, the highest levels of calpain II were found in S3, or the soluble cytoplasmic fraction. Significant activity of the enzyme was also present in P2, the crude mitochondrial/synaptosomal fraction. In contrast, the specific activity of calpain I was greatest in P2 with somewhat lesser enzymatic activity in P1 and S3. Most of the calpain I in P2 was recovered after differential centrifugation through sucrose gradients and lysis of the resultant subfractions. In marked contrast, only a small percentage of the calpain II activity was recovered in the gradient bands. In all, calpain II appears to be predominantly localized in the soluble cytoplasmic compartment while the greatest concentrations of calpain I are found in the soluble components of small glial and neuronal processes (pinched off during homogenization) that constitute the P2 fraction. The highest specific activity of the calcium-independent proteases was obtained in P3, a fraction essentially devoid of calpain, with a secondary peak in P2. Subfractionation of P2 revealed that calcium-independent TP in P2 was associated with mitochondria while the calcium-independent NTP was more uniformly distributed across myelin, synaptosomes, and mitochondria.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
A possible second messenger system for the production of long-term changes in synapses.
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Animals↗
Brain spectrin, calpain and long-term changes in synaptic efficacy.
This chapter discusses the possibility that proteolytic digestion of cytoskeletal proteins, in particular spectrin, is part of the mechanisms through which physiological activity elicits structural and chemical changes in brain synapses. Recent work from several laboratories has produced a description of the initial events that trigger the long-term potentiation (LTP) of synaptic responses that appears in hippocampus after brief episodes of high frequency electrical stimulation. A likely sequence is as follows: suppression of IPSPs, prolongation of EPSPs, activation of N-methyl-D-aspartate (NMDA) receptors, influx of calcium into target cells. After briefly describing the evidence for this triggering sequence, the review takes up the question of what types of calcium sensitive chemistries are available to synaptic region that could produce functional changes lasting for weeks (i.e., for LTP). It is argued that the partial degradation of spectrin by a calcium-activated protease (calpain) provides a mechanism of this type. Spectrin is a substrate for calpain and both it and a breakdown product comparable to that produced by calpain are found in postsynaptic densities. Moreover, there is substantial evidence that spectrin regulates the surface chemistry and morphology of cells and thus its partial degradation would be expected to produce pronounced and persistent modifications in synapses. To reinforce this point, the review discusses recent findings suggesting that calpain mediated proteolysis of spectrin and other cytoskeletal proteins produces substantial changes in the shape of blood-borne cells and the distribution of their surface receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗
Olfaction and the "data" memory system in rats.
A set of studies was conducted to characterize the memory system involved in successive olfactory discrimination learning in rats. Two odors emanated from different arms of a radial maze; one of the arms contained a water reward. After training on four or five pairs of odors (20 trials per day), rats learned to discriminate the members of a new pair in 5-10 trials. Experiments in which either member of the pair was compared with a novel cue indicated that the rats learn both positive and negative odors, rather than simply ignoring the negative cue. The memories for the odors were apparently persistent, and no evidence for retroactive interference from subsequent training was obtained. Training on 30 pairs did not result in any slowing of subsequent learning, which suggest that the capacity of the memory system for odors is substantial. In a second group of experiments, we tested whether rats distinguish between odors by identifying unshared subcomponents or instead treat odors in a gestalt (i.e., unitary) fashion. Animals trained on three component odors with two in common did not recognize the elements that were unshared when these were presented by themselves. Even when one of the two shared components was combined with the differentiating component into a cue (i.e., two thirds of the original three-component odor), the new cue was treated as a novel odor. However, inclusion of a previously learned simple odor in a complex odor did affect the learning of that odor.(ABSTRACT TRUNCATED AT 250 WORDS)
Animals↗