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R C Roberts

Publications and source records attributed to R C Roberts.

At least 91 records · Page 5Linked to original sources
PubMed1990

Immunoreactive GAP-43 in the neuropil of adult rat neostriatum: localization in unmyelinated fibers, axon terminals, and dendritic spines.

GAP-43 is a neuron-specific phosphoprotein that has been implicated in neuronal development, axonal regeneration, and synaptic plasticity. Although in mammals the caudate-putamen is among those brain areas that retain a high content of GAP-43 throughout life, the role of the phosphoprotein in the neostriatum is unknown. In order to understand better the possible function(s) of GAP-43 in the adult striatum, its cellular localization was examined with immunohistochemistry at the light and electron microscopic levels by using a sheep polyclonal antibody. At the light microscopic level immunoreactive GAP-43 was abundant throughout the neostriatal neuropil but was absent from neuronal somata. At the ultrastructural level, labeling was most prevalent in small unmyelinated axons (0.12-0.15 microns diameter). Reaction product was distributed along fibers in discrete patches about 1 micron apart and in preterminal sites from which vesicle-filled boutons arose. Staining was also present in small (0.35 microns) axon terminals that contained round vesicles and formed asymmetric synapses, mostly with thin spines. Following unilateral cortical lesions, some degenerating cortical axons in the neostriatum exhibited GAP-43 labeling. Unexpectedly, in normal striatum, GAP-43 was also occasionally found in the heads of dendritic protrusions and in thin spines that received asymmetric contacts. We speculate that in the adult neostriatum, the protein may be important in the remodeling of synapses onto medium spiny neurons that involve, in part, the corticostriatal pathway.

Animals↗
PubMed1990

Long-term survival of GABA-, enkephalin-, NADPH-diaphorase- and calbindin-d28k-containing neurons in fetal striatal grafts.

Neurons in long-term striatal grafts were examined to determine if they retain the neurotransmitter characteristics of cells in younger grafts. In addition, calbindin-d28k, a ubiquitous marker of medium spiny neurons, was used to examine the overall frequency and ultrastructural characteristics of spiny neurons in the older grafts. Grafts from 17-day fetal striata were injected into the quinolinic acid-lesioned caudate nucleus in 5 adult rats. After 16 months, the neostriatum was processed for the localization of immunoreactive GABA, calbindin, enkephalin and NADPH-diaphorase (-d) activity. The proportions of GABA-, enkephalin- and NADPH-d-labeled neurons to total Nissl-stained neurons in the 16-month-old grafts (25 +/- 6, 13 +/- 4, and 3 +/- 3, respectively) were similar to findings in 2-month-old grafts. Calbindin-positive cells formed the highest proportion (36.3 +/- 3) of labeled neurons in the older grafts. Nuclear and spine morphology of immunoreactive calbindin cells varied more in the grafts than in host caudate. Results show that there is long-term survival and stability of GABA, enkephalin and NADPH-d cell populations in the grafts and that some grafted spiny neurons may exhibit altered phenotype from those of host striatum.

Animals↗
PubMed1990

GABAergic synapses in the brain identified with antisera to GABA and its synthesizing enzyme, glutamate decarboxylase.

GABA is a known inhibitory neurotransmitter in the mammalian brain. The site of GABAergic synapses can be determined with immunocytochemical methods that localize either GABA or its synthesizing enzyme, glutamate decarboxylase (GAD). In general, GABAergic axon terminals contain pleomorphic synaptic vesicles and form symmetric synapses. However, a small number of GABAergic axon terminals in selected brain regions (spinal cord, cerebellum, superior colliculus, striatum, globus pallidus, inferior olive, and substantia nigra) form asymmetric synapses. GAD- and GABA-immunoreactive processes that contain synaptic vesicles participate in every known morphological type of chemical synapse. These include axosomatic, axodendritic, axospinous, initial segment, axoaxonic, dendrodendritic, serial, reciprocal, and ribbon synapses. Although GABAergic synapses form a heterogeneous group, they most commonly form axosomatic, axodendritic, and initial segment synapses in the brain and spinal cord. These findings provide helpful guidelines for the identification of GABAergic synapses in future studies.

Animals↗
PubMed1990

Endogenous event-related potentials from sphenoidal electrodes.

Event-related potentials (ERPs) were recorded from left and right sphenoidal electrodes during 2 cognitive tasks (visual oddball and a word repetition procedure) known to evoke endogenous ERP activity in the medial temporal lobe. Both tasks gave rise to large, reliable modulations of scalp-recorded ERPs. In the oddball task, no consistent task-related ERP activity could be recorded from the sphenoidal electrodes concurrently with the scalp-recorded P3 component, although in the latency region following the peak of P3 these electrodes exhibited an enhanced late negative wave to target stimuli. In the word repetition task, no consistent repetition-related ERP effects of any kind were observed from the sphenoidal electrodes. Sphenoidal electrodes do not appear to detect the endogenous ERP components that are generated in the medial temporal lobe concurrently with scalp-recorded components.

Acoustic Stimulation↗
PubMed1990

Evidence for synaptic proliferation, reorganization, and growth in the excitotoxic lesioned adult rat caudate nucleus.

Functional recovery following brain injury depends, in part, on the reestablishment of synaptic connections by surviving neurons. In this study we used quantitative methods to examine the synaptic organization of the caudate neuropil at 2, 7, and 30 weeks following excitotoxic injury. Results showed that in regions of severe to moderate neuronal depletion caused by intrastriatal injections of quinolinic acid, synaptic density was significantly reduced relative to controls but was significantly greater than neuronal density (percentage of control) at all postlesion intervals. Moreover, there was a marked increase in synaptic density (percentage of control), but not neuronal density (percentage of control), in the lesion periphery between 7 and 30 weeks postlesion. The relative proportion of axospinous synapses to total synapses was significantly reduced in the center of the lesion at all postlesion intervals but was similar to controls in regions of neuropil that were less severely affected. In the lesion and its borders there was also a significant increase in the proportion of short synaptic contacts between axons and spines and a proliferation of small unmyelinated fibers. Furthermore, after 30 weeks postlesion, regions of severe neuronal depletion developed aberrant synaptic contacts between vesicle-containing profiles which were significantly larger than those in normal caudate. We conclude that excitotoxic lesions of the neostriatum precipitate a variety of responses in injured neuropil including synaptic proliferation, growth, and altered circuitry.

Animals↗
PubMed1990

Genetic characterization of the stabilizing functions of a region of broad-host-range plasmid RK2.

One of the regions responsible for the stable inheritance of the broad-host-range plasmid RK2 is contained within the PstI C fragment, located from coordinates 30.8 to 37.0 kb (P.N. Saurugger, O. Hrabak, H. Schwab, and R.M. Lafferty, J. Biotechnol. 4:333-343, 1986). Genetic analysis of this 6.2-kb region demonstrated that no function was present that stabilized by selectively killing plasmid-free segregants. The sequence from 36.0 to 37.0 kb mediated a twofold increase in plasmid copy number, but this region was not required for stabilization activity. The PstI C fragment was shown to encode a multimer resolution system from 33.1 to 35.3 kb. The resolution cis-acting site was mapped to 140 bp, sequenced, and observed to contain two directly repeated sequences of 6 and 7 bases and two perfect inverted repeats of 6 and 8 bases. The trans-acting factor(s) was mapped and functionally determined to encode a resolvase capable of catalyzing recombination at high frequency between cis-acting sites in either direct or inverted orientation. Multimer resolution alone did not account for complete plasmid stabilization by the PstI C fragment, since removal of regions adjacent to the 35.3-kb border of the minimal mrs locus dramatically reduced stabilization. The minimal region required for complete stabilization, from 32.8 to 35.9 kb, was capable of fully stabilizing plasmids independently of the replicon or the recA proficiency of the host. Stabilization activity was also fully expressed in several diverse gram-negative bacteria, whereas the F plasmid par locus functioned only in Escherichia coli. On the basis of these observations, we conclude that under the growth conditions used, the minimal stabilization locus encodes both an mrs activity and a stabilization activity that has the properties of a par locus.

Azotobacter↗
PubMed1990

Thyroid function and treatment in premenstrual syndrome.

In 1986 it was reported that a high percentage of women with premenstrual syndrome (PMS) were found to have thyroid hypofunction (TH), mostly subclinical hypothyroidism, as defined by an augmented response of TSH to TRH, and that all affected women had complete relief of PMS symptoms with L-T4 therapy. We studied baseline thyroid function (T4, T3 uptake, T3, TSH, and TSH response to TRH) in 15 normal women (group 1) and 44 women with PMS and treated 22 of the PMS women with L-T4 (group 2; 1.6 micrograms L-T4/kg dose) and the other half with placebo (group 3) for 2 months in a double blinded protocol. We found no evidence of thyroid dysfunction in group 2 or 3, except for 1 subject with slightly elevated TSH (6.2 microIU/mL) and moderate augmented response to TRH (change in TSH, 65 microIU/mL). During the treatment phase we found a complete relief of symptoms in 6 (27%), a partial relief of symptoms in 6 (27%), and some relief of symptoms in 12 (54%) in group 2. Whereas in group 3, 10 (45%) had complete relief, 5 (23%) had partial relief, and 15 (68%) had some relief of symptoms. These results show that 1) there is no significant thyroid disease in PMS; and 2) L-T4 is no better than placebo in treatment of PMS. We conclude that the high incidence of thyroid hypofunction previously reported in PMS is due to an unusually low TSH level for the limit of the normal range for the TRH stimulation test.

Adult↗
PubMed1989

Phosphate promotes glycation of antithrombin III which interferes with heparin binding.

Nonenzymatic glycation of antithrombin III has been reported to cause the reduction of heparin-catalyzed thrombin-inhibiting activity in diabetes. The effect of in vitro nonenzymatic glycation of pure antithrombin III on heparin binding and heparin-potentiated activity under a variety of buffers and pH values was studied to further clarify the physiological significance of this reaction. The extent of glycation, measured by the fructosamine assay and [14C]glucose binding, was enhanced by the presence of phosphate ion (pH 7.45, 8.5 and 9.5) and increased linearly with increasing phosphate ion concentration from 0.01 to 0.2 M phosphate. Conversely, the heparin-catalyzed antithrombin activity decreased from 93.1% of controls for 0.01 M phosphate to 73.5% for 0.2 M phosphate as the extent of glycation increased. The increase in intrinsic fluorescence induced by binding of heparin to antithrombin III was also moderated by glycation of antithrombin III in a dose-dependent manner with a negative correlation coefficient of -0.94. Direct measurement of the heparin binding by affinity chromatography showed a decrease in the heparin-binding fraction which correlated with the degree of glycation and the decrease in heparin-catalyzed activity. These studies suggest that nonenzymatic glycation may be responsible for the reduction in antithrombin III activity observed in some diabetics.

Antithrombin III↗
PubMed1989

Short- and long-term survival of large neurons in the excitotoxic lesioned rat caudate nucleus: a light and electron microscopic study.

Large striatal neurons are spared in caudate tissue from postmortem brain of patients with Huntington's disease (HD) and in the rat caudate lesioned with excitotoxins at short postlesion intervals. In order to determine the survival of large neurons and other effects of excitotoxicity at longer postlesion intervals the rat caudate nucleus was examined 2, 7, and 30 weeks after intrastriatal injections of the excitotoxin, quinolinic acid. The caudate nucleus diminished in size progressively up to 30 weeks postlesion due to 1) shrinkage and compacting of the lesion zone and 2) reduction in area of intact caudate, apparently due to gradual loss of the remaining caudate neurons. In Nissl-stained sections of the lesion zone where total neuronal density was less than 5% of contralateral control, large neurons were present at all postlesion intervals, forming 38-58% of the remaining neurons. Unexpectedly, a fivefold reduction in the number of large neurons was observed between 2 and 30 weeks postlesion. Also, at 7 and 30 weeks postlesion most of the large neurons were confined to the peripheral region of the lesion. At all postlesion intervals, large neurons retained ultrastructural integrity and some synaptic inputs despite the severe disruption of the surrounding neuropil. Surrounding the lesion zone was a transition zone which exhibited a decrease in total neuronal density to 53-74% of control. In this region the density of large neurons was not diminished, and the proportion of large neurons was elevated in comparison to that of controls at all postlesion intervals. Findings suggest that following excitotoxic lesion of the caudate nucleus there are marked differences between short- and long-term postlesion intervals in the survival and distribution of large neurons. We speculate that an imbalance in the synaptic connections with other caudate neurons leads to the persistent loss of large neurons in the lesion zone at long postlesion intervals. A transition zone surrounding the lesion, where cell loss is less severe than in the lesion zone, exhibits features more characteristic of the neuropathology of HD.

Animals↗
PubMed1989

The natural history of late-onset epilepsy secondary to vascular disease.

Twenty-nine patients with late-onset epilepsy were followed prospectively for a mean period of 4.9 years; 14 had CT evidence of occult cerebral infarction and 15 had normal scans. The prognosis was similar in the 2 groups; 57% and 53% respectively became seizure-free. One patient in each group had a myocardial infarction and one patient with occult cerebrovascular disease had a stroke. A separate study was made of the prognosis of 24 patients with epilepsy following stroke (mean follow-up 5.9 years). Twelve of 12 patients with seizure onset within 2 weeks of the stroke became seizure-free, compared with 7/12 with more delayed onset. Late-onset epilepsy has a favourable prognosis, and excellent control should be expected if seizures commence within 2 weeks of stroke.

Aged↗
PubMed1989

Autogenetic inhibition from contraction receptors in the decerebrate cat.

1. Autogenetic inhibition from contraction receptors was measured by eliciting contractions of the soleus muscle in the decerebrate cat. Inhibitory feedback was detected when the tension increment f, produced by stimulating motor fibres in the presence of a background reflex contraction, was smaller than the tension d elicited by the same stimulus in the absence of reflex action. Tendon vibration was applied throughout to clamp primary spindle afferents at a constant firing rate, thereby preventing spindle unloading from disfacilitating the reflex contraction. 2. The reduction in tension d--f varied roughly linearly with the size of the tension stimulus f. Feedback gain was proportional to d--f/f, i.e. the ratio of inhibited tension to stimulus tension. It was computed by averaging over several measurements obtained with stimuli of different sizes, and ranged between 0 and 0.88 in ten animals. The average gain, 0.39, implies that voluntary muscle force is reduced by approximately 27% through the direct inhibition of alpha-motoneurones from homonymous contraction receptors. 3. Inhibitory feedback gain did not appear to co-vary with the background reflex contraction. When measured without vibration, however, a positive covariance did emerge, suggesting that this is due to unloading of muscle spindles, either by extrafusal muscle shortening or by inhibition of fusimotor neurones. 4. Inhibited tension varied linearly with the estimated increment in Ib afferent firing. On the assumption that group Ib afferents carried the entire inhibitory signal, inhibitory feedback gain measured with vibration was used to predict the size of the gain if vibration had not been applied. Feedback gain calculated in this way was reduced by still did not vary with reflex tension. 5. In one animal with signs of brain stem trauma, feedback gain was increased to around six. It is argued that inhibitory feedback in the intact animal can rise to comparable values, as a result both of convergence of signals from different muscles and of supraspinal facilitation.

Animals↗
PubMed1989

The effects of lesions on autogenetic inhibition in the decerebrate cat.

1. The effects of spinal and brain lesions on autogenetic inhibition from contraction receptors were studied in the decerebrate cat. Inhibitory feedback gain was estimated by measuring the effect of tension perturbations on reflex contractions of the soleus muscle. Tendon vibration was used to clamp the firing rate of primary spindle afferents, to prevent spindle unloading from disfacilitating the reflex contraction. In addition, secondary spindle afferents could be selectively excited by stimulating fusimotor fibres during muscle vibration. 2. Following an acute contralateral or bilateral dorsal transection of the spinal cord at L3, the vibration reflex tension fell by between 50 and 74% in three decerebrate animals. This was accompanied by a variable increase in inhibitory feedback, ranging between 180 and 360%. 3. In two animals, selective stimulation of fusimotor fibres supplying soleus muscle was without effect in the presence of muscle vibration both before and after the spinal lesion. In the third animal, a small and variable reduction in tension could be obtained only after the lesion, implying that an inhibitory pathway from homonymous secondary spindle afferents to alpha-motoneurones was released. 4. In a separate series of experiments, contralateral cerebral lesions were made 2-12 months prior to the acute inhibitory feedback measurement. Inhibitory feedback gain was increased, on average twofold in decerebrate animals with chronic cerebral lesions, when compared to control decerebrate animals. 5. Selective stimulation of fusimotor fibres to excite spindle secondary afferents was uniformly without effect in decerebrate animals with chronic cerebral lesions. In one animal spinal transection had only a minor effect on extensor tone and on inhibitory feedback gain, in contrast to the control decerebrate cats. 6. The implications of these findings are discussed in relation to the use of animals with spinal and supraspinal lesions as models of spasticity.

Animals↗
PubMed1989

99Tcm-HMPAO single photon emission computed tomography in partial epilepsy: a preliminary report.

In the pre-operative assessment of patients being considered for temporal lobe surgery, accurate lateralization and localization of the epileptic focus is mandatory. Surface electroencephalography (EEG) can be misleading and confirmatory evidence, preferably non-invasive, of the site of the epileptic focus is valuable. Sixteen patients with partial epilepsy, six of whom were considered to be good surgical candidates, had technetium-99m hexamethylpropylene amine oxime (99Tcm-HMPAO) scanning. In those patients with poor epileptic control and a well localized EEG focus, there was a correlation between EEG and HMPAO scan abnormalities, whilst in all patients where no correlation existed, the HMPAO scan was normal. We conclude that 99Tcm-HMPAO single photon emission computed tomography may be a useful non-invasive, adjunctive investigation in the preoperative assessment of patients with partial epilepsy.

Adolescent↗
PubMed1989

A redetermination of the concentration of alpha 2-macroglobulin in human plasma.

The concentration of alpha 2-macroglobulin in human plasma has been remeasured utilizing a carefully isolated and characterized sample of alpha 2-macroglobulin as a standard. A highly purified sample of alpha 2-macroglobulin with a total trypsin binding capacity of 1.7 mol trypsin/mol alpha 2-macroglobulin was used as a standard for both a radial immunodiffusion and a rocket immunoelectrophoresis technique. With this preparation as a standard, the concentration of alpha 2-macroglobulin in a normal plasma pool over 10,000 donors was found to be about 1.2 mg/ml. A similar concentration (1.3 mg/ml) was found when using a functional trypsin binding assay. This concentration is considerably less than the usually accepted mean of the normal range for alpha 2-macroglobulin.

Adolescent↗
PubMed1989

Enhanced streptokinase-induced thrombolysis using heparin in a rabbit model.

Heparin potentiation of clot lysis by streptokinase was studied in a rabbit model. Clot was initiated in the rabbit aorta with stasis and thrombin and allowed to naturally propagate proximally until stasis met flow. The clot was allowed to age for 1 h before assigning treatment. Fifteen rabbits (group I) were given streptokinase (10,000 IU/h) and 11 rabbits (group II) were given streptokinase (10,000 IU/h) plus sodium-heparin (120 IU/h). Thrombolytic therapy was continued for 5 h. Clot lysis averaged 30% in group I and 70% in group II. Ten of 11 rabbits in group II had more than 50% clot lysis, whereas only 4 of 15 in group I had this degree of lysis. One group II rabbit and four group I rabbits died prematurely; each was noted to have clot propagation at the time of death. While a trend for amelioration of hypofibrinogenemia was observed in the group receiving both streptokinase and heparin, this difference was not statistically significant. We conclude, in the animal model, that thrombolysis by a combination of heparin and streptokinase is more effective than streptokinase alone. Systemic effects are apparently no worse with the combination.

Animals↗
PubMed1988

Localization of immunoreactive GABA and enkephalin and NADPH-diaphorase-positive neurons in fetal striatal grafts in the quinolinic-acid-lesioned rat neostriatum.

Fetal striatal tissue grafts have been shown to partially reverse the biochemical and behavioral deficits induced by excitotoxic lesions. To determine if grafted striatal neurons contain neurochemical markers similar to those in neurons in the caudate nucleus and to establish the morphological characteristics and relative frequency of labeled neurons in the grafts, the localization of immunoreactive GABA and leucine-enkephalin (ENK) and of NADPH-diaphorase (NADPH-d) activity was examined in fetal striatal grafts at the light and electron microscopic levels. Striatal tissue from 17-day fetuses was grafted into the caudate nucleus of adult rats 1 week after intracaudate injections of either a low or high dose of quinolinic acid. At the light microscopic level, immunoreactive GABA and ENK and NADPH-d-positive neurons, processes, and punctate structures were present within adjacent sections of the same grafts. The frequency and morphological features of these labeled cell populations were similar in grafts placed into either minimally or extensively lesioned striata. Immunoreactive GABA and ENK neurons in the grafts constituted 28% and 13.5%, respectively, of the neuronal population of the graft and their mean diameters were 22 and 14% larger, respectively, than neostriatal neurons that contained the same chemical markers. NADPH-d-positive neurons in the grafts formed 3.5% of total grafted neurons and exhibited characteristics of neostriatal NADPH-d-containing aspiny cells, including medium-sized somata, indented nuclei, and varicose dendrites. At the electron microscopic level most GABA-positive neurons in the grafts contained indented nuclei and most immunoreactive ENK somata had unindented nuclei. Dendrites and dendritic spines with GABA or ENK immunoreactivity were present in the grafts where they were postsynaptic to unlabeled axons. Immunoreactive GABA and ENK axon terminals formed synapses with unlabeled neuronal profiles in the grafts. These findings demonstrate that fetal striatal grafts contain chemically defined neuronal populations that form synaptic connections within the graft and share some features with corresponding cell groups in the neostriatum. These results provide an anatomical basis for the graft-induced recovery from behavioral and biochemical deficits caused by instrastriatal lesions reported in other studies.

Animals↗
PubMed1987

GABAergic neurons and axon terminals in the brainstem auditory nuclei of the gerbil.

The anatomical localization of glutamic acid decarboxylase (GAD), the synthesizing enzyme for GABA, was analyzed in the brainstem auditory nuclei of the adult gerbil. GAD-positive terminals and somata were present in the cochlear nucleus, superior olivary complex, lateral lemniscus, and inferior colliculus in varying concentrations and patterns. One of the highest densities of GAD-positive terminals is found in the superficial layers of the dorsal cochlear nucleus (DCN), whereas the ventral cochlear nucleus (VCN) has somewhat fewer terminals that are arranged in pericellular plexuses. GAD-positive neurons occur mainly in the superficial and fusiform layers of the DCN and are scattered throughout the VCN. Within the superior olivary complex, the highest concentration of immunoreactive terminals and neurons occurs in the ventral and lateral nuclei of the trapezoid body. In contrast, the medial nucleus of the trapezoid body and the medial superior olive contain fewer GAD-positive puncta and probably no immunoreactive somata. The lateral superior olive and superior periolivary nucleus contain a few immunoreactive puncta but a large number of immunoreactive somata. In the midbrain, the nuclei of the lateral lemniscus contain a moderate number of GAD-positive puncta and a large number of different types of GAD-positive neurons. The inferior colliculus also contains a heterogeneous population of labeled somata, most of which are multipolar neurons. In addition, a high concentration of immunoreactive puncta occurs in this region. These data demonstrate a diverse distribution of GAD-positive neurons and puncta throughout the brainstem auditory nuclei and suggest that GABA might be an important neurotransmitter in the processing of auditory information.

Animals↗