Biomedical subjects

J R Simon

Publications and source records attributed to J R Simon.

At least 19 recordsLinked to original sources

PubMed1995

Endogenous serotonin release from the dopamine-deficient striatum of the weaver mutant mouse.

In addition to an altered dopaminergic input, the striatum of the weaver mutant mouse (wv/wv) has increased serotonin tissue content and uptake compared to the wild-type mouse (+/+). To gain information regarding the functional status of serotonergic inputs to the wv/wv striatum, endogenous serotonin release from wv/wv and +/+ striatum was measured under basal conditions as well as in the presence of fenfluramine or elevated concentrations of potassium (K+). Fractional basal release of serotonin from the +/+ striatum was significantly greater than that from the wv/wv striatum. In the presence of K+, evoked release (stimulated release minus basal release) was greater from the +/+ striatum than from the wv/wv striatum. In the presence of fenfluramine, evoked serotonin release was greater from the wv/wv striatum compared to the +/+ striatum. These data are consistent with the involvement of an additional transmitter(s) in modulating serotonin release to a greater extent in the wv/wv than the +/+ striatum. The data on fenfluramine-stimulated serotonin release suggest that the additional serotonin content found in the wv/wv striatum is in a releasable pool but that striatal serotonin release might be attenuated more in wv/wv than in +/+ mice.

Animals↗

PubMed1994

Cholinergic innervation of the retrosplenial cortex via the fornix pathway as determined by high affinity choline uptake, choline acetyltransferase activity, and muscarinic receptor binding in the rat.

The cholinergic projections from basal forebrain nuclei to the retrosplenial cortex (RSC) have previously been studied using a variety of histological approaches. Studies using acetylcholinesterase (AChE) histochemistry and choline acetyltransferase (ChAT) immunocytochemistry have demonstrated that this projection travels via the cingulum on route to the RSC. Preliminary studies from our laboratory, however, have shown that the fornix may also be involved in this projection. The present study uses the combination of pathway lesions, and the analysis of cholinergic neurochemical markers in the RSC to determine the role of the fornix in the cholinergic projection to the RSC. High affinity choline uptake (HACU) and ChAT activity were measured in the RSC of control rats, animals with cingulate lesions, and animals with fornix plus cingulate lesions. Fornix plus cingulate lesions resulted in significant deceases in HACU and ChAT activity in comparison to cingulate lesions alone. Muscarinic receptor binding was also evaluated in combination with the various lesions, and a significant increase in retrosplenial receptor binding was noted following fornix lesions. Together, these results support the concept of a fornix-mediated cholinergic pathway to the RSC.

Animals↗

PubMed1992

Buffer conditions and non-tubulin factors critically affect the microtubule dynamic instability of sea urchin egg tubulin.

The dynamic instability of individual microtubules (Mts) in cytoplasmic extracts or assembled from highly purified sea urchin egg tubulin was examined using video-enhanced, differential-interference contrast (VE-DIC) light microscopy. Extract Mts (endogenous tubulin = 12.1 microM) displayed only plus-ended growth. The elongation velocity was 7.8 microns/min for an average duration of 1.3 min before switching (catastrophe) to rapid shortening, which occurred at 13.0 microns/min for an average duration of 0.5 min before switching (rescue) back to the elongation phase. These parameters are typical of interphase Mt dynamic instability. Surprisingly, Mts assembled from purified urchin egg tubulin in standard buffers were less dynamic that those reported for purified brain tubulin or Mts in the extract. Buffer parameters were changed in an attempt to mimic the extract Mt results. The pH buffer itself, Hepes or Pipes, drastically altered Mt dynamics but could not achieve high elongation velocity with high catastrophe frequencies. Calcium at 1 microM had negligible effects, while increasing pH from 6.9 to 7.2 stimulated elongation velocity. Finally, Mt dynamics of purified egg tubulin (11.9 microM) were assayed in ultrafiltrates (MW cut-off less than 30 kD) of the cytoplasmic extracts. Mts elongated slowly at 1.2 microns/min for 26 min before a catastrophe and rapid shortening at 11.8 microns/min. Rescue was less frequent than unfiltered extracts, minus-ended growth was observed, and self-assembly occurred at slightly higher tubulin concentrations. Therefore, the egg extracts and cytoplasm must contain non-buffer factors which stimulate elongation velocity by 6.5-fold without self-assembly, increase catastrophe frequency by 20-fold, and block minus-ended growth.

Animals↗

PubMed1992

Topographic distribution of dopamine uptake, choline uptake, choline acetyltransferase, and GABA uptake in the striata of weaver mutant mice.

The topographic distribution of dopamine (DA) uptake, choline uptake, choline acetyltransferase (ChAT) activity and GABA uptake within the striata of weaver mutant mice and control mice was determined. Uptake of [3H]dopamine, [3H]choline and [14C]GABA, as well as ChAT activity were determined in samples prepared from the dorsolateral, dorsomedial, ventrolateral and ventromedial portions of the striatum. In 45-60 day old control mice, dopamine uptake was homogeneously distributed throughout the striatum. On the other hand, striata from weaver mice exhibited an uneven distribution with the ventral aspects having greater uptake activity than the dorsal regions. Thus, although the ventral portion of the striatum is less severely affected than the dorsal portion, all areas of the striatum exhibited significantly reduced uptake rates. In 9 and 12 month old mice, choline uptake was higher in lateral than medial zones of the striatum of both genotypes and no differences were observed between genotypes. GABA uptake was higher in the ventral striatum than in the dorsal striatum but again no differences were found between weaver and control mice. The results of this study indicate that the entire weaver striatum is severely deficient in its ability to recapture dopamine and thus is functionally compromised. The results also indicate that the striatal cholinergic and GABAergic interneurons are not directly or indirectly affected by the weaver gene.

Animals↗

PubMed1992

Comparison of alterations in tyrosine hydroxylase, dopamine levels, and dopamine uptake in the striatum of the weaver mutant mouse.

Previous reports have shown that among the markers for the nigro-striatal dopamine (DA) system measured in the striatum, dopamine uptake seems to be more severely affected than the others in the weaver mutant mouse. In the present study we examined DA levels, tyrosine hydroxylase (TH) activity, and high-affinity DA uptake to determine if the DA uptake is most affected when all the measurements are made in the same striatal homogenate in the same laboratory. We found that the DA uptake activity was most altered (93% lower) compared to DA levels (68% lower) and TH activity (64% lower). The DA uptake was so low in the weaver that we could not obtain reliable kinetic parameters. For TH activity we found that the Vmax was 36% lower while the Km for L-tyrosine was 92% higher in the weaver striatum. This lower affinity for substrate suggests that the TH enzyme itself may be altered in the nigro-striatal system of the weaver mutant mouse.

Animals↗

PubMed1992

Some regional anatomical relationships of TRH to 5-HT in rat limbic forebrain.

It is now a recognized principle that various neuropeptides are neuronally co-localized with biogenic amine or aminoacid neurotransmitters. In the rat CNS it has previously been shown that TRH is co-localized with 5-HT (and also with substance P) in cell bodies of the posterior raphe that project to the spinal cord. Although TRH cell bodies are known to be widely distributed throughout the forebrain there is no other known co-localization with 5-HT. In this study we further specify the forebrain there is no other known co-localization with 5-HT. In this study we further specify the anatomical relationship of TRH with 5-HT by use of surgical and neurotoxic lesioning with reference to limbic forebrain regions wherein TRH is greatly increased following seizures. In groups of rats, the fimbria-fornix was lesioned alone, or combined with a lesion of the dorsal perforant path or the ventral perforant path. There was a sham lesioned control group. Additional groups were lesioned with 5,7 dihydroxytryptamine, 100 micrograms i.v.t., 45 min. after i.p. desipramine, 25 mg/kg. All rats were sacrificed three weeks after lesions. Indoleamines were determined by HPLC in left anterior cortex, left pyriform/olfactory cortex, left dorsal hippocampus and left ventral hippocampus. TRH was determined by specific RIA in the corresponding right brain regions. The modal n was 7 rats.(ABSTRACT TRUNCATED AT 250 WORDS)

5,7-Dihydroxytryptamine↗

PubMed1992

Intrahippocampal grafts of cholinergic-rich striatal tissue ameliorate spatial memory deficits in rats with fornix lesions.

Previous studies have shown that cholinergic grafts derived from the medial septal nucleus are capable of restoring behavioral function in rats with lesions that sever the cholinergic inputs to the hippocampal formation. In this study, we demonstrate that intrahippocampal grafts of cholinergic-rich striatal tissue also ameliorate spatial memory deficits of rats with fornix lesions. We also found that atropine administration dramatically disrupted spatial navigation performance of rats with striatal grafts and control rats, thus suggesting that the striatal graft effects are mediated by cholinergic mechanisms of action. Measurements of high affinity choline uptake (HACU) and muscarinic receptor binding revealed that intrahippocampal striatal grafts increased HACU and normalized muscarinic receptor binding in animals with fornix lesions. Regression analyses demonstrated significant correlations between the amelioration of spatial memory deficits and hippocampal HACU and receptor binding. We conclude that intrahippocampal grafts of cholinergic-rich striatal tissue can ameliorate spatial memory deficits and that this amelioration is associated with the reinstatement of functional cholinergic terminations.

Animals↗

PubMed1991

Intrahippocampal transplants of septal cholinergic neurons: high-affinity choline uptake and spatial memory function.

Recent studies have demonstrated that intrahippocampal cholinergic septal grafts can ameliorate deficits in spatial memory function and hippocampal cholinergic neurochemical activity in animals with disruptions of the septohippocampal system. However, no study has determined if the restoration of spatial memory function is correlated to the restoration of cholinergic activity, as measured by high-affinity choline uptake (HACU). The present study was designed to determine if such a correlation between behavioral and neurochemical restoration exists. Male Sprague-Dawley rats received either sham lesions (SHAM), bilateral lesions of the septohippocampal pathway (LES), or bilateral lesions along with intrahippocampal septal grafts (SG). After 8 months, rats were tested for their ability to perform spatial reference, spatial navigation and working memory tasks. Upon completion of the behavioral testing, neurochemical activity of the hippocampus was measured by HACU. The results indicate that animals in the SG group had significantly higher behavioral scores and hippocampal HACU rates than animals in the LES group. Regression analysis indicates that a significant correlation exists between performance on each behavioral task and HACU rates. These results demonstrate that hippocampal cholinergic activity, as measured by HACU, correlates significantly with performance on tests of spatial memory function.

Animals↗

PubMed1991

In vitro release of endogenous dopamine from the striatum of the weaver mutant mouse.

The weaver mutant mouse has a genetically determined defect in the nigrostriatal dopaminergic system. The present study was undertaken to test the hypothesis that in the weaver mutant mouse, striatal nerve terminals undergo compensatory changes in response to this deficiency. To test this hypothesis, we studied the basal and stimulated release of dopamine from striatal slices of weaver mutant mice and matched controls. By using a superfusion system and concentrating the superfusate by passage over alumina, resting dopamine release could be determined in the weaver mutant despite the fact that striatal tissue content of dopamine in these mice is reduced by greater than 75% compared with control mice. Fractional resting release of dopamine in weaver striatal slices was significantly elevated compared with that in controls, suggesting that the release mechanisms in the weaver may be adapting to overcome the dopamine deficit. Potassium-evoked release (24 and 48 mM potassium) was not significantly different between the two genotypes. In contrast, amphetamine-evoked release (1 microM) was significantly greater in the weaver mice than in controls. In both genotypes, release evoked by amphetamine was completely inhibited by cocaine, implicating the dopamine uptake carrier in this release process. These findings suggest that fundamental differences in dopamine release mechanisms exist between weaver and control mice and support the hypothesis that compensatory mechanisms may develop in neurons in response to dopamine deficits.

Amphetamine↗

PubMed1990

Age-related changes in striatal dopamine D2 receptor binding in weaver mice and effects of ventral mesencephalic grafts.

Dopamine (DA) D2 receptor binding is increased in the striatum of 5-6 months old weaver mutant mice (Kaseda et al. 1987). This may occur in response to the loss of DA neurons in the midbrain and the decrease in DA content in the striatum of homozygous mutants. One purpose of the present study was to determine if the diminished DA innervation is associated with changes in D2 receptors at earlier ages and if the increase in DA D2 receptor binding seen at 5-6 months is a lasting phenomenon. Specific [3H]spiperone binding was measured in the dorsolateral (DL), dorsomedial (DM) and ventrolateral (VL) striatum and in the nucleus accumbens (AC) of homozygous weaver mutant mice (wv/wv), heterozygous littermates (wv/+) and wild-type controls (+/+). Mice were studied at 20 days and 1, 3, 6, 9 and 12 months of age. The difference in specific [3H]spiperone binding in DL striatum between wv/wv and +/+ mice was significantly greater at 6 months than the difference at 1 month and at 12 months of age. Foetal ventral mesencephalic grafts survive and establish functional innervation in the striatum of weaver mice as shown by the induction of a contralateral turning bias (Low et al. 1987). The second aim of the present studies was to determine if such grafts would also reverse the increase in DA D2 receptor binding in the striatum. Aspiration cavities were prepared in the cortex of weaver mice, and ventral mesencephalic tissue from E14-E15 +/+ foetuses was subsequently placed on the surface of the right dorsal striatum when the recipients were 3 months old.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1990

Transformation and recombination in rad mutants of Saccharomyces cerevisiae.

Disruption/deletion mutations in genes of the RAD52 epistasis group of Saccharomyces cerevisiae were examined for their effects on recombination between single- and double-stranded circular DNA substrates and chromosomal genes in a transformation assay. In rad50 mutants there was a small reduction in recombination with single-stranded DNA at the leu2-3, 112 allele; in addition there was an almost complete elimination of recombination at trp1-1 for both single- and double-stranded DNA. Reintroduction of a wild-type RAD50 gene on a replicating plasmid carrying CEN4 restored recombinational competence at trp1-1, indicating that rad50 is defective in gene replacement of this allele. In rad52 mutants a reduction of 30%-50% in recombination involving either single- or double-stranded circular DNA was observed in each experiment when compared to the wild type. This reduction of recombination in rad52 mutants was similar for recombination at the ura3-52 mutant locus where only integration events have been observed, and at the trp1-1 mutant locus, where recombination occurs predominantly by gene replacement. Neither the rad54 nor the rad57 mutations had a significant effect on recombination with single- or double-stranded DNA substrates.

Genes, Fungal↗

PubMed1990

Effect of conflicting cues on information processing: the 'Stroop effect' vs. the 'Simon effect'.

This study examined the relationship between two sources of interference in human information processing: the Stroop effect and the Simon effect. Forty subjects pressed a left- or right-hand key in response to a Stroop color word located on the left or right side of a screen. For one group, ink color was the relevant cue and, for another group, word meaning was the relevant cue. Independent variables were: congruence, i.e., agreement or lack thereof between the ink color and meaning of the Stroop word; spatial correspondence, i.e., agreement or lack thereof between the location of the Stroop word and the location of the key used to make the response; and stimulus duration, i.e., 400 or 100 ms. Each of these variables had a significant effect on RT, and there were no significant interactions. According to Sternberg's additive-factor logic, these findings suggest that the Stroop effect (congruence) and the Simon effect (spatial correspondence) involve separate stages of processing. If one assumes that manipulation of stimulus duration effects the encoding stage, then results also suggest that neither the Stroop effect nor the Simon effect involves the stimulus encoding stage.

Attention↗

PubMed1990

The structure of microtubule ends during the elongation and shortening phases of dynamic instability examined by negative-stain electron microscopy.

Microtubules (MTs) are dynamic polymers that can exist in phases of elongation and rapid-shortening at steady-state. These phases have been observed in vitro and in living cells, and this property of MTs has been termed 'dynamic instability'. The purpose of this study was to use negative-stain electron microscopy (EM) to test if there are structural differences between the ends of MTs in the elongation and shortening phases, which could provide insight into the mechanisms of dynamic instability. MTs in the elongation phase were obtained by seeding either highly purified porcine brain tubulin (PC-tubulin) or tubulin containing microtubule-associated proteins (MTP), from isolated Tetrahymena axonemes. The results are that, in addition to intact cylindrical MTs, a significant fraction of the tubulin polymer in the elongation phase occurred as sheets of parallel protofilaments, as found in previous investigations with self-assembled MTs. Therefore, sheet formation is an intrinsic property of MT assembly that does not depend on the tubulin purity or the method of nucleation. Also, since sheets lack helical symmetry, at least a fraction of tubulin polymers seeded from axonemes did not assemble by helical addition of tubulin dimers to the ends, an assumption often made in mathematical models of dynamic instability. Sheets and intact MTs that were seeded from isolated axonemes, emanated both from the intact MT wall of the axoneme A-subfiber and from the incomplete wall of the B-subfiber. Therefore, axoneme seeds do not provide a homogeneous nucleation site for tubulin growth, or produce a homogeneous population of tubulin polymers under our conditions. Previous evidence has indicated that MT disassembly can occur by a segmental release of tubulin oligomers from the ends and at sites along the length of MTs. However, these studies were performed with MTP, and disassembly was induced by cold depolymerization. We examined MT shortening under conditions that closely represent shortening via dynamic instability, namely isothermal dilution at 37 degrees C of self-assembled MTs. This was compared with the morphology of cold-disassembled MTs. The cold-depolymerization of MTs composed of MTP showed rings and protofilament curls as previously observed using similar methods. Surprisingly, cold-depolymerization of MTs assembled from PC-tubulin induced not only shortening, but also the opening of a large fraction of MTs into sheets, suggesting that the MT lattice contains a cold-labile seam. Under conditions that mimic stochastic shortening, MTs were intact, closed cylinders with ends that were approximately blunt. Therefore, rapid shortening occurs at the ends of the MT, without a long-range disruption of the MT wall. In conclusion, MTs in the elongation phase can have highly irregular ends and need not elongate by a helical assembly process. Conversely, MTs in the shortening phase can have relatively blunt, even ends and can depolymerize in a relatively uniform fashion.

Animals↗

PubMed1989

A rapid and efficient procedure for transformation of intact Saccharomyces cerevisiae by electroporation.

A rapid and efficient procedure is described for transforming Saccharomyces cerevisiae using electroporation to render intact cells permeable to DNA. The technique uses relatively low voltages and is particularly sensitive to low concentrations of plasmid DNA. At the highest voltage used (400 volts), the frequency of transformation increased with the amount of plasmid DNA between 25 ng and 100 ng. At higher concentrations of DNA (1-1.5 micrograms) electroporation yielded one-third to one-half the number of transformants obtained with a standard lithium acetate pretreatment. Because this method requires neither pretreatment of cells nor addition of polyethylene glycol (PEG), it has several advantages over currently used transformation procedures.

Electric Stimulation↗

PubMed1989

Activity-wheel stress and serotonergic hypersensitivity in rats.

Adult male Wistar rats were subjected to activity wheel stress: unlimited access to an activity wheel for up to twelve days and food for 30 to 60 min each day. Each treated rat was paired with a control, the latter being housed in home cages and given sufficient food to maintain a weight similar to the stressed partner. All rats were previously trained on a variable interval schedule for milk reinforcement. When the activity of the stressed rat increased rapidly then decreased suddenly, the pair was decapitated for biochemical analysis. Levels of the serotonin metabolite, 5-hydroxyindoleacetic acid, decreased by 50%, and the Bmax for ketanserin binding increased by 19% in frontal cortical homogenates from the stressed rats when compared to controls. These data support the concept that stress increases the sensitivity of central serotonin receptors.

Animals↗

PubMed1989

Restoration of high affinity choline uptake in the hippocampal formation following septal cell suspension transplants in rats with fimbria-fornix lesions.

High affinity choline uptake (HACU) was investigated in the hippocampal formation following fetal septal cell suspension transplants into rats with fimbria-fornix lesions. Nine-14 weeks after transplantation, HACU was markedly decreased in hippocampi from animals with fimbria-fornix lesions; this decrease was ameliorated by fetal septal cells transplanted into the host hippocampus. HACU related to septal transplantation was activated in vitro by K+, and in vivo by the administration of scopolamine and picrotoxin. These findings suggest that fetal septal cell transplantation can restore HACU in the host hippocampus following fimbria-fornix lesions, and that HACU related to the graft has pharmacological properties similar to those of the normal adult HACU system. The activation of HACU by picrotoxin, a gamma-aminobutyric acid (GABA) antagonist, suggests that transplanted cholinergic neurons receive either direct or indirect functional input from GABAergic afferents from the transplant and/or host hippocampus. Lesions of the fimbria-fornix also resulted in an increased binding to muscarinic receptors in the dorsal hippocampus. This increase in binding was not significantly ameliorated by intrahippocampal grafts of cholinergic neurons.

Animals↗

PubMed1989

The effect of prediction accuracy on choice reaction time.

In this study, we examined the effect of prediction accuracy on reaction time (RT). Subjects performed on three blocks of choice RT trials, all of which involved the mapping of four stimuli (red, green, 1, or 0) onto two response keys. The subjects were told that the four stimuli were equally probable and that their task was to respond to each stimulus onset by pressing the correct key. In one block (stimulus-prediction), the subjects predicted, prior to each trial, the precise stimulus that would appear. In a second block (category-prediction), the subjects predicted the category of the stimulus (i.e., color or digit) that would appear. In a third block (no-prediction), the subjects simply responded to each stimulus without making a prior prediction. In the stimulus-prediction block, RT was faster for correct predictions than for incorrect predictions. In addition, RT was faster on trials in which an incorrect prediction involved the correct category than on trials in which it involved the incorrect category: that is, a "half-wrong" prediction was better than an "all-wrong" prediction. In the category-prediction block, RT was faster when the stimulus category was predicted correctly than when it was not. There was little evidence of a response-facilitation contribution to the correct-prediction effect. These results permit inferences concerning the encoding and organization of information in memory.

Adult↗

PubMed1988

The molecular mobility of alpha-actinin and actin in a reconstituted model of gelation.

Dictyostelium discoideum alpha-actinin (D.d. alpha-actinin) is a calcium and pH-regulated actin-binding protein that can cross-link F-actin into a gel at a submicromolar free calcium concentration and a pH less than 7 [Fechheimer, et al., 1982]. We examined mixtures of actin and D.d. alpha-actinin at four pH and calcium concentrations that exhibited various degrees of gelation or solation. The macroscopic viscosities of these mixtures were measured by falling ball viscometry (FBV) and compared to the translational diffusion coefficients measured by gaussian spot and periodic-pattern fluorescence photobleaching recovery (FPR) of both the actin filaments and D.d. alpha-actinin. A homogeneous, macroscopic gel was not composed of a static actin network. Instead, the filament diffusion coefficient decreased to approximately 65% of the control value. If the D.d. alpha-actinin concentration was increased, the solution became inhomogeneous, consisting of domains of higher actin concentration. These domains were often composed of a static actin network. The mobility of D.d. alpha-actinin consisted of a major fraction that freely diffused and a minor fraction that appeared immobile under the conditions employed. This suggested that D.d. alpha-actinin binding to the actin filaments was static over the time course of measurement (approximately 5 sec). Under solation conditions, there was no apparent interaction of actin with D.d. alpha-actinin. These results demonstrate that 1) actin filaments need not be cross-linked into an immobile, static array in order to have macroscopic properties of a gel; 2) interpretation of the rheological properties of actin:alpha-actinin gels are complicated by spatial heterogeneity of the filament concentration and mobility; and 3) a fraction of D.d. alpha-actinin binds statically to actin in undisturbed gels. The implications of these results are discussed in relation to cytoplasmic structure and contractility.

Actinin↗