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The present study examined the effect of nimodipine on a reference memory task and on the induction and maintenance of long-term potentiation (LTP) in the hippocampal dentate gyrus. Young rats, subcutaneously implanted with either a 30 mg nimodipine or placebo pellet, were trained on the Barnes circular platform task. Retention was tested 15 days following acquisition. Following behavioural testing, recording and stimulating electrodes were implanted in the granule cell layer of the dentate gyrus and the perforant path, respectively. Pre-pellet baseline evoked potentials were collected. Nimodipine or placebo pellets were again subcutaneously implanted, according to the original groupings, and post-pellet baseline evoked potentials were obtained. LTP was then induced in the granule cell population by perforant path tetanization and the decay of LTP was followed for 15 days. Nimodipine significantly decreased the number of trials to reach both the acquisition and the retention criterion on the circular platform task, but did not alter granule cell excitability, LTP threshold, or the magnitude of LTP. Sustained nimodipine administration, however, increased the decay rate of LTP of the population spike, but did not affect the decay rate for LTP of the EPSP. No significant correlations were obtained between behavioural and electrophysiological measures. These results provide further evidence against a simple direct relationship between LTP and spatial learning.

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Earlier studies indicated that chemically crosslinking glomerular basement membrane (GBM) rendered it more permeable to water and to macromolecules. Here possible mechanisms for the introduction of crosslinks into GBM under pathological conditions were explored. Glycation with glucose and with fructose over periods of 2 wk (fructose) and 6 weeks (glucose) rendered the GBM more permeable to water and myoglobin as judged from in vitro ultrafiltration behaviour. The membranes were also made more permeable to serum following glycation. The permeation changes were shown to be dependent on glycoxidative reactions judging by their inhibition by EDTA and DTPA. Aminoguanidine also prevented glycation from altering the permeability of GBM. Fluorescence studies indicated the formation of bityrosine in glycated GBM. Studies with oxidants showed that while hydrogen peroxide superoxide and peroxynitrite had little effect on GBM, hypochlorite anion was capable of increasing GBM permeability to water, myoglobin, albumin and serum. Changes in permeation were induced by very low quantities of hypochlorite, well within the range of the amounts of hypochlorite formed by activated neutrophils. Thus glycoxidation, or oxidation by hypochlorite, are chemical mechanisms by which GBM permeability can be increased.

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The permeability of glomerular basement membrane (GBM) was assessed in vitro by the filtration of solutions of proteins across films formed from isolated pig GBM. Incubation of the films with fructose or glucose increased their permeability to water and serum albumin. The effect of fructose was similar to that previously noted for films crosslinked with glutaraldehyde. The metal chelator DTPA abolished the effects of glycation; EDTA was partially effective in this respect. Transition metal catalysed formation of glycoxidation induced crosslinks may explain the increased permeability of glycated GBM.

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The theoretical premise that the acquisition and storage of information occurs through the strengthening of synaptic connections has contributed to the popularity of long-term potentiation (LTP) as a candidate neural mechanism for associative learning. However, whether experimentally induced LTP facilitates, disrupts, or has no effect on subsequent learning is a controversial issue. The present study examined the reported facilitative effect of LTP within hippocampal perforant path-dentate gyrus synapses on subsequent discriminative conditioning of the rabbit nictitating membrane response. In addition, the effect of LTP on subsequent reversal learning of the initial discrimination was examined. LTP did not significantly affect acquisition of the initial discriminative response or subsequent reversal learning. Furthermore, the magnitude of LTP could not be used to predict the rate of acquisition of either task. The failure to find an effect of LTP on classical conditioning of the rabbit nictitating membrane response mirrors the recent failures to replicate the disruptive effect of LTP on spatial learning in the rat. Thus, the potential contribution of an LTP-like mechanism to associative learning remains equivocal.

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Mn(III)-salophen complex with superoxide scavenging activity was prepared from manganese(III) acetate dihydrate and salophen in ethanol. Visible absorption spectrum of the red-brown complex exhibits a shoulder at 430 nm which was absent with either salophen or manganic acetate alone. Titration of salophen with manganese(III) is consistent with a 1:1 Mn to salophen stoichiometry of the complex based on changes in the absorbance at 500 nm or of superoxide scavenging activity. The superoxide dismutase (SOD)-like activity of the complex in the xanthine-xanthine oxidase/cytochrome c assay was 1450 units/mg salophen. The SOD activity of the complex was suppressed 50% in the presence of EDTA (1 mM), but was not altered in the presence of bovine serum albumin (1 mg/ml) or crude protein extract of Escherichia coli QC779 sodA-sodB- (1 mg/ml). E. coli QC779 sodA-sodB- grew scantily after an 8-h lag phase in aerobic M63 glucose minimal medium. The aerobic growth of the E. coli SOD double mutant in glucose minimal medium was greatly enhanced in the presence of 5 or 10 microM Mn-salophen complex compared to that of control after 24 h incubation. Mn-desferal green complex (10 microM) and pink complex (5 microM) also increased growth rate of E. coli QC779 sodA-sodB- but to a lesser extent than Mn-salophen complex. However, the growth was completely inhibited by 50 microM Mn-salophen complex, 100 microM Mn-desferal green complex, or 10 microM Mn-desferal pink complex.

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The primary culture of rat renal glomeruli was found to result in the ready outgrowth of two cells types. One type designated c-cells were cytokeratin positive and exhibited microvilli and cilia. The second type designated f-cells were vimentin positive and showed rugose surfaces. C-cells were polygonal in culture on plastic surfaces and were derived from cells of parietal epithelial origin. F-cells assumed a more extended form on plastic and were judged to be a sub-set of parietal epithelial cells. Neither cell type was derived from the visceral epithelium which was found to have been destroyed during isolation of the glomeruli. When cultured on isolated glomerular basement membrane both the c-cells and f-cells assumed a polygonal morphology but when grown on Matrigel the cells assumed the form of long strands interconnecting the outgrowths between the glomeruli. The appearance of the cells in the strands, judged from scanning electron microscopy, suggested that these were formed from f-cells but other cell types were entrained in the structures. Glomeruli subjected to vigorous proteinase digestion of the basement membrane allowed culture of a wider variety of cells. These included endothelial cells, judged by OX-43 antibody and anti-von Willebrand Factor staining, and mesangial cells. In cultures from glomeruli polygonal cells are often assumed to be visceral epithelial cells, the results from this study indicate that this assumption is unsound. The very different behaviour of cells grown on isolated basement membrane as compared with cells grown on Matrigel suggests that Matrigel may not faithfully mimic basement membrane with respect to cell response in culture.

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The present experiment compared the long-lasting with the short-lasting effects of kindling the perforant path input to the hippocampal formation on the acquisition of two radial maze tasks. Animals in the long-term group were fully kindled (i.e., Stage 5 motor seizures were evoked) prior to a stimulation-free training period. Animals in the short-term group were kindled 30-45 min prior to each learning trial. A third group of animals served as controls and were never kindled. On both 8-arm and 4/8-arm radical maze tasks, learning impairments were apparent only in the short-term group. Thus, the impaired learning is more likely related to the short-term aftereffects of an afterdischarge than to any long-term alterations in the neuronal status of the brain caused by kindling.

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Hippocampal dentate granule cell responsivity to excitatory input from entorhinal perforant path fibers was examined in the chronic rabbit preparation following norepinephrine (NE) depletion induced with the neurotoxin DSP4. To examine granule cell responsivity as a function of perforant path activation, constant low frequency stimulation (0.1 Hz) was applied to the perforant path using an ascending intensity series. To examine granule cell responsivity to more complex patterns of stimulation, a train of impulses, with a random interstimulus interval (Poisson distribution; mean frequency of 2 Hz), was applied to the perforant path. Both single impulse and random interval impulse stimulation revealed that NE depletion increased the average amplitude of the perforant path-granule cell population spike. The random interval impulse stimulation revealed that NE depletion also increased the magnitude and duration of second order inhibitory interactions. These changes were transient, however, and recovered over the 21 day test period. Hippocampal NE levels were reduced an average of 80% between 23 and 38 days post-DSP4. The activity of the rate-limiting enzyme for NE synthesis, tyrosine hydroxylase (TH), was reduced an average of 60%. That NE levels were reduced to a greater extent than was TH activity is suggestive of increased NE synthesis within the remaining nerve terminals. Such an increase in NE synthesis may reflect a compensatory response underlying the functional recovery of electrophysiological responsiveness following partial NE depletion.

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The present experiment examined the anterograde effect of bilateral saturation of long-term potentiation (LTP) of the rat perforant path-granule cell response on acquisition of the eight-arm radial maze. To ensure maintained saturation, high-frequency stimulation was applied to the perforant path immediately prior to each trial. LTP did not significantly increase the number of trials required for acquisition of the standard eight-arm radial maze task. Furthermore, the magnitude of LTP did not correlate with the rate of acquisition. LTP also did not significantly affect the number of either working or reference memory errors during subsequent training with only four of the eight arms baited; both control and LTP rats made significantly more reference memory than working memory errors, with the number of both types of errors decreasing as training progressed. These results indicate that prior saturation of LTP within the perforant path-dentate granule cell circuit does not affect acquisition of either the reference or working memory components of the radial maze task. The results are discussed in relation to the role of LTP in acquisition of the eight-arm radial maze.

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The following experiment examined the effects of kindled seizures on reversal learning and the effects of both kindling and classical conditioning of the rabbit nictitating membrane on granule cell responsivity to perforant path input. Kindling resulted in significant potentiation of the population spike, the excitatory postsynaptic potential (EPSP) and the magnitude of twin pulse inhibition. Following kindling, rabbits were trained in a discrimination-reversal paradigm with either a tone or light paired with a corneal airpuff. Kindling did not affect acquisition of the initial discriminative response but did retard the rate of reversal learning. Kindling-induced potentiation, within dentate excitatory and inhibitory circuits, persisted for the duration of training. Thus, these results do not distinguish between the contribution of kindling-induced potentiation within dentate excitatory and inhibitory circuits to discrimination-reversal training. Spikes evoked during tone presentations were of reduced amplitude compared to spikes evoked either between trials or during light trials. The EPSP was not affected by stimulus conditions. In control rabbits, the magnitude of both the spike and EPSP increased across training. Training-related potentiation, in kindled rabbits, could not be separated from kindling-induced potentiation. These results demonstrate that an LTP-like effect of both the population spike and EPSP occurs with discrimination-reversal training.

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Cross-linking glomerular basement membrane (GBM) has been shown to render it more permeable to protein. Isolated pig GBM was cross-linked with dimethylmalonimidate which reacts selectively with lysine epsilon-NH2 groups or with glutaraldehyde, a less selective cross-linking agent. Studies of the ultrafiltration properties of these materials in vitro using cytochrome c, myoglobin, bovine serum albumin and immunoglobulin showed that cross-linking had markedly increased solvent and protein fluxes as compared with native membranes particularly at higher pressures. Filtration studies with serum demonstrated that the cross-linked membranes were more permeable to serum proteins. Thickness measurements under pressure indicated that cross-linked membrane was less compressed than native membrane as pressure was increased. Pore theory did not provide a suitable model for analysis of the results, but analysis of the results using the fibre-matrix hypothesis indicated that cross-linking had the effect of bundling together the fibres (type IV collagen) in the GBM matrix. The effect of cross-linking on filtration could be explained by a combination of contraction of the membrane, fibre bundling and increased rigidity compared with native membrane. Cross-linking of GBM might lead to long-term damage of the glomerular capillary wall in nephritis, so promoting proteinuria.

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Several investigations have shown that the N-methyl-D-aspartate (NMDA) antagonist MK-801 interferes both with learning and a candidate neural mechanism for learning, the long-term potentiation (LTP) phenomenon. The low doses of MK-801 reported to block learning, however, may not be sufficient to block LTP. The present experiments examined the effects of 4 doses (0.05, 0.10, 0.50 and 1.00 mg/kg) of MK-801 on LTP of the perforant path-granule cell population excitatory postsynaptic potential (EPSP) and spike in unanesthetized rabbits. MK-801 did not significantly affect the threshold intensity for LTP of the population EPSP but the 3 highest doses did increase the threshold for LTP of the population spike. The 3 highest doses also reduced the peak magnitude and the duration of LTP of the spike to less than 24 h. The 0.05 m/kg dose did not affect the threshold or peak magnitude of spike LTP, but did decrease the decay time constant to 10.4 days, compared to 20.8 days in control rabbits. Only the 1.00 mg/kg dose reduced the magnitude of LTP of the EPSP. It was not possible to determine if MK-801 altered the longer-lasting component of LTP of the EPSP as it never persisted for longer than 24 h. These studies demonstrate that MK-801 disrupts LTP at doses also known to interfere with learning.

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Epileptiform activity is known to alter both excitatory and inhibitory circuits within the network of neurons that comprise the hippocampal formation. In the present experiment, kindling-induced alterations in the functional properties of the rabbit perforant path-dentate circuit were analyzed using non-linear system analytic procedures. System input consisted of a random train of impulses applied to the perforant path. System output was the perforant path-granule cell population spike amplitude evoked by each impulse in the train. The results of non-linear systems analysis were compared with the results from twin impulse analysis of kindling-induced alterations within the hippocampal dentate gyrus. Compared to twin impulse procedures, non-linear systems analytic procedures revealed a reduced duration and magnitude of kindling-induced inhibitory interactions to interstimulus intervals of 10-200 ms. The increased magnitude of inhibitory interactions did not decay to prekindled magnitude until 16 weeks postkindling. In contrast, kindling-induced potentiation of the population spike had decayed within 10 weeks of the last stage 5 seizure. Despite the decay of electrophysiological responses to prekindled levels, only a few kindling stimulations were required to evoke fully kindled seizures. Thus, electrophysiological alterations within the first synaptic relay of the hippocampal trisynaptic circuit, the dentate gyrus, cannot explain the long duration of the kindling effect.

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The effect of the non-competitive N-methyl-D-aspartate antagonist MK-801 on the early development of kindling-induced potentiation was examined in the rabbit hippocampal dentate gyrus. MK-801 (0.5 mg/kg) was administered 2 h before each daily kindling stimulation was applied to the perforant path. This treatment continued for the first 10 days of kindling. MK-801 depressed the growth of the afterdischarge duration and suppressed development of behavioral seizures. MK-801 did not block kindling-induced potentiation of either the perforant path-dentate granule cell population spike or excitatory postsynaptic potential. Random impulse train stimulation and non-linear systems analytic techniques were used to examine kindling-induced potentiation of presumed GABAergic recurrent inhibitory circuits. Both the magnitude and duration of kindling-induced response inhibition, to the second of each pair of impulses within the train, were reduced in rabbits pretreated with MK-801. These results suggest that MK-801 differentially affects kindling-induced potentiation of excitatory and inhibitory circuits within the rabbit hippocampal dentate gyrus.

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The ultrafiltration properties of isolated glomerular basement membrane were studied in vitro by forming membrane fragments into thin films for use as ultrafiltration membranes. The filtration properties of the films were examined using cytochrome c, myoglobin, lysozyme, ovalbumin, lactoglobulin, and serum albumin. The films behaved as compressible filters showing size-dependent rejection of the proteins. The behavior of the films was modelled using the fiber matrix hypothesis which gave good prediction of film behavior. The membrane behaved as a random fiber matrix composed of fibers of 0.8-1.0 nm in radius.

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The effect of kindling the hippocampal perforant path-dentate projection on subsequent discrimination-reversal conditioning of the rabbit nictitating membrane (NM) response was examined. Kindling facilitated acquisition of the initial discriminative response but severely impaired performance during reversal training. The facilitative effect on initial acquisition is highly similar to previously reported effects of long-term potentiation on NM discrimination learning, and thus may reflect a kindling-induced increase in perforant path-dentate synaptic strength. The learning deficit during reversal training is similar to the effects of hippocampal ablation; i.e. characterized by a continued high response rate to the CS- rather than an inability to respond to the CS +. These findings demonstrate that kindling-induced seizures can have profound effects on associative learning. The effects are different for the discrimination and reversal phases of the task, however, which may reflect the multi-dimensional effects of kindling at the cellular level.

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Rat neutrophils added to 3H-labelled glomerular basement membrane (GBM) treated with rabbit anti-rat GBM antiserum degraded the GBM as judged by the release of 3H-labelled peptides. Cells from female animals promoted a more marked degradation than cells from males. This correlated with measurements of higher levels of elastase in granule fractions from the cells. The subcellular distributions of granule marker enzymes was found not to differ between the sexes. Levels of myeloperoxidase, lysozyme, cathepsin G, alkaline phosphatase, gamma-glutamyltranspeptidase and N-acetyl-beta-glucosaminidase showed no sex-based differences. No alpha-mannosidase could be detected in the cells.

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1. Nonlinear systems analytic procedures, based on an orthogonalized functional power series approach, were developed for study of the transformational properties of the hippocampal formation. As a testing stimulus, the procedures utilize a train of electrical impulses with randomly varying interimpulse intervals. The specific case was considered of applying such a stimulus to the perforant path, a major afferent to the hippocampal dentate gyrus that arises from the entorhinal cortex. Resulting field potentials evoked within the dentate gyrus are recorded to all impulses in the train. Computational algorithms based on cross-correlations determine the relationship between the interimpulse interval within the random train and amplitude of the evoked dentate potentials. The calculations, which reduce to averaging procedures, were derived for first- and second-order terms, or kernels, of the orthogonalized functional power series. 2. It is proposed that such an approach can be applied to a single component of the complex field potential evoked in the dentate gyrus. This component, the population spike, reflects the action potential discharge of dentate granule cells. Thus, a field potential component for which the underlying neuronal generator is well-known can be analyzed with respect to the transformational characteristics of the network of neurons that influence that generator. Other components of the complex field potential produced by other generators can be ignored. It is shown that this adaptation has the effect of greatly simplifying both the computation and presentation of kernels. 3. As a further consequence of this adaptation, the resulting first- and second-order kernels were shown to have specific interpretations. The first-order kernel represents the average response of the orthodromically driven granule cells to the set of stimuli comprising the random impulse train. The second-order kernel quantitatively characterizes the nonlinearity of the granule cell response, and may be interpreted as a generalized recovery function; i.e., the first input of any pair of stimuli in the train activates the newtork, and the second input tests the modulatory influence of the network excited by the initial input. 4. Most past investigations of nonlinearities of the perforant path-dentate projection have utilized pairs of stimulus impulses. We show here that, for a second-order system, the expected results from paired impulse experiments may be predicted from second-order kernels. Disagreement between the measured and predicted results reflects interactions of a higher order, and thus, greater system complexity.(ABSTRACT TRUNCATED AT 400 WORDS)

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