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Biomedical subjects

M Segal

Publications and source records attributed to M Segal.

At least 163 records · Page 9Linked to original sources
PubMed1992

Anti-Cdc25 antibodies inhibit guanyl nucleotide-dependent adenylyl cyclase of Saccharomyces cerevisiae and cross-react with a 150-kilodalton mammalian protein.

The CDC25 gene product of the yeast Saccharomyces cerevisiae has been shown to be a positive regulator of the Ras protein. The high degree of homology between yeast RAS and the mammalian proto-oncogene ras suggests a possible resemblance between the mammalian regulator of Ras and the regulator of the yeast Ras (Cdc25). On the basis of this assumption, we have raised antibodies against the conserved C-terminal domain of the Cdc25 protein in order to identify its mammalian homologs. Anti-Cdc25 antibodies raised against a beta-galactosidase-Cdc25 fusion protein were purified by immunoaffinity chromatography and were shown by immunoblotting to specifically recognize the Cdc25 portion of the antigen and a truncated Cdc25 protein, also expressed in bacteria. These antibodies were shown both by immunoblotting and by immunoprecipitation to recognize the CDC25 gene product in wild-type strains and in strains overexpressing Cdc25. The anti-Cdc25 antibodies potently inhibited the guanyl nucleotide-dependent and, approximately 3-fold less potently, the Mn(2+)-dependent adenylyl cyclase activity in S. cerevisiae. The anti-Cdc25 antibodies do not inhibit cyclase activity in a strain harboring RAS2Val-19 and lacking the CDC25 gene product. These results support the view that Cdc25, Ras2, and Cdc35/Cyr1 proteins are associated in a complex. Using these antibodies, we were able to define the conditions to completely solubilize the Cdc25 protein. The results suggest that the Cdc25 protein is tightly associated with the membrane but is not an intrinsic membrane protein, since only EDTA at pH 12 can solubilize the protein. The anti-Cdc25 antibodies strongly cross-reacted with the C-terminal domain of the Cdc25 yeast homolog, Sdc25. Most interestingly, these antibodies also cross-reacted with mammalian proteins of approximately 150 kDa from various tissues of several species of animals. These interactions were specifically blocked by the beta-galactosidase-Cdc25 fusion protein.

Adenylyl Cyclases↗
PubMed1992

Raphe grafts in the hippocampus, but not in the entorhinal cortex, reverse hippocampal hyperexcitability of serotonin-depleted rats and restore their responsiveness to fenfluramine.

We compared the effects of embryonic raphe grafted into either the hippocampus or the entorhinal cortex, on the responsiveness of dentate granule cells to stimulation of the perforant path. Raphe grafts in the hippocampus reversed the hyperexcitability of granule cells, resulting from depletion of the serotonergic innervation. Such grafts also restored the responsiveness of the granule cells to application of a serotonin releasing drug, fenfluramine (FFA). In contrast, hyperexcitability was not reversed when the graft was placed in the entorhinal cortex. Furthermore, although some increase in population spike size was observed in these rats after application of FFA, this increase had a response profile which was different from that of control and of lesioned rats that were grafted in the hippocampus. These results suggest that the serotonergic innervation, within the hippocampus and not in the entorhinal cortex, modulates granule cells excitability.

Animals↗
PubMed1992

A parametric family of correlation structures for the analysis of longitudinal data.

In epidemiological settings, we are often faced with numerous short time series, and a parsimonious parametrization of the correlation structure is desired in order to optimize the efficiency of the estimation procedure. We propose a damped exponential correlation structure for modeling multivariate Gaussian outcomes. The correlation between two observations separated by s units of time is modeled as gamma s theta, where gamma is the correlation between elements separated by one s-unit, and theta is a damping parameter. For (theta = 0), (theta = 1), and theta----infinity), the correlation structures of compound symmetry, first-order autoregressive, and first-order moving average processes are obtained. Although the AR(2) dependency structure, and the combination of random effects and AR(1) errors are not special cases of the proposed parametric family, these structures can be well approximated within the family for short time series. Maximum likelihood methods for parameter estimation and interpretations of intermediate models (0 less than theta less than 1) are discussed in the context of modeling pulmonary function in an adult population in The Netherlands and T-cell subsets in homosexual men infected with human immunodeficiency virus Type I.

Adult↗
PubMed1991

Restoration of serotonergic innervation underlies the behavioral effects of raphe grafts.

It has been previously demonstrated that an embryonic raphe grafted into a serotonin-depleted hippocampus restores normal serotonin innervation of the hippocampus and behaviors associated with serotonin. To test the possibility that the behavioral effects of these grafts result from non-specific actions of the grafted tissue or the grafting procedure itself, we compared raphe grafts with septal grafts, in serotonin-depleted rats. We also compared the effects of a serotonin synthesis inhibitor, p-chlorophenylalanine, on the behavior of normal, serotonin-depleted and raphe-grafted rats. The results indicate that the bulk of behavioral effects of raphe grafts are due to the serotonergic nature of the graft.

5,7-Dihydroxytryptamine↗
PubMed1991

Independent regulation of calcium revealed by imaging dendritic spines.

The dendritic spine is a basic structural unit of neuronal organization. It is assumed to be a primary locus of synaptic plasticity, and to undergo long-term morphological and functional changes, at least some of which are regulated by intracellular calcium concentrations. It is known that physiological stimuli can cause marked increases in intracellular calcium levels in hippocampal dendritic shafts, but it is completely unknown to what extent such changes in the dendrites would also be seen by calcium-sensing structures within spines. Will calcium levels in all spines change in parallel with the dendrite or will there be a heterogeneous response? This study, through direct visualization and measurement of intracellular calcium concentrations in individual living spines, demonstrates that experimentally evoked changes in calcium concentrations in the dendritic shaft ([Ca2+]d).

Animals↗
PubMed1991

An alpha 2 antagonist, idazoxan, enhances EPSP-spike coupling in the rat dentate gyrus.

The effect of the alpha 2 antagonist, idazoxan (IDA), on the excitability of neurons in the dentate gyrus of the hippocampus was studied. Population field potentials (PS) evoked by stimulation of the perforant pathway were measured before and after drug treatment. IDA enhanced the amplitude of the PS, while decreasing the slope of the EPSP. Neurotoxic destruction of noradrenergic nerve terminals completely abolished the IDA effect, arguing that its mechanism of action is through enhanced release of noradrenaline (NA). It is proposed that NA enhances the EPSP-to-spike coupling component of the PS.

Adrenergic alpha-Antagonists↗
PubMed1991

Calcimycin potentiates responses of rat hippocampal neurons to N-methyl-D-aspartate.

We examined the effect of elevating intracellular calcium ([Ca2+]i) on responses to iontophoretically applied N-methyl-D-aspartate (NMDA), and quisqualate in CA1 neurons of the hippocampal slice. Topical application of calcimycin (A23187), a calcium ionophore, potentiated responses to NMDA but not to quisqualate. This potentiation was prevented by loading cells with the calcium chelator, BAPTA, suggesting that the action of calcimycin on NMDA receptors was mediated by an elevation of [Ca2+]i in the recorded cell. The potentiation was also recorded in voltage-clamped and in cesium-loaded cells, suggesting that it was not mediated by non-specific changes in voltage or input resistance of the cell that may have resulted from the rise in [Ca2+]i. We propose that intracellular calcium plays a crucial role in regulating the activity of the NMDA subtype of L-glutamate receptor.

Animals↗
PubMed1991

Phase II study of pibenzimol in pancreatic cancer. A Southwest Oncology Group study.

Twenty-three patients with advanced pancreatic adenocarcinoma were treated with Pibenzimol utilizing a daily intravenous schedule for five days. There were no objective responses seen. The major toxicity was pancreatic with grade 3 hyperglycemia in eleven patients. Pibenzimol is inactive in patients with advanced pancreatic adenocarcinoma.

Adenocarcinoma↗
PubMed1991

Endometriosis in episiotomy scar with anal sphincter involvement. Report of a case.

A case of endometriosis in an episiotomy scar with involvement of the external anal sphincter is presented. The clinical, operative, and pathologic findings are reported. The question of etiology and treatment is discussed, and the literature is reviewed. Wide excision of the ectopic endometrial tissue with primary reconstruction of the external sphincter was curative, and the functional result was excellent. It is suggested that this treatment policy should be recommended for these cases.

Adult↗
PubMed1991

Bleeding after intravascular transfusion: experimental and clinical observations.

Characteristics of postpuncture bleeding of umbilical vessels were evaluated with an in vitro cord perfusion model and in vivo by ultrasonographic observation of bleeding duration after intravascular transfusion. Ultrasonographic determination of blood loss in vitro was very sensitive (0.01 ml/sec). In vitro blood loss varied directly with perfusion rate, but there were wide variations between cord specimens. Observed clinical bleeding occurred in 43% of cases; the duration of bleeding varied by vessel punctured, needle size, and fetal platelet count. The combined in vitro and clinical data help define the range of duration of bleeding and the probable volume of loss.

Bleeding Time↗
PubMed1991

Extremely large number of twists of the umbilical cord causing torsion and intrauterine fetal death.

Extremely large number of twists of the umbilical cord causing torsion of the entire length of the umbilical cord was found in two cases of intrauterine fetal death. It was twisted in one case 35 times and in the other 20 times. No additional pathology, such as stricture or abnormality of the Wharton's jelly, was found. The two mothers complained of decreased fetal movements and both newborns were found later to be growth retarded. A long cord of 120 cm was present in one case and normal length of 70 cm in the other. Close antenatal care in cases with growth retarded fetuses or decreased fetal movements may help in avoiding fetal demise in such rare cases.

Adult↗
PubMed1991

Activity of hippocampal extract on development of [3H]5-HT high-affinity uptake in dissociated microcultures.

Specific and localized lesions of the 5-HT fibers in the hippocampus induce homotypic collateral sprouting and enhance serotonergic fiber outgrowth from adult neurons and transplanted fetal tissue. In this study, hippocampal extracts were prepared and applied to primary cultures of fetal serotonergic neurons. The effects of plating density and serum additives were examined. The growth of the serotonergic neurons in the rostral brainstem dissociated cultures were estimated by measuring the specific uptake of [3H]5-HT. The results indicate the presence of a trypsin-sensitive factor which is active when prepared fresh at dilutions up to 1/10,000. The factor is higher in hippocampus than cerebellum. Young male tissue contained more activity than either female or aged hippocampus. Although both positive and negative effects are described, higher dilutions of factor (1/1,000) were generally stimulatory in high density cultures while lower dilutions (1/10) were inhibitory in low density cultures. Specific removal of 5-HT hippocampal afferents with fornix-fimbria microinjections of 5,7-dihydroxytryptamine resulted in an initial loss of activity (2 days and 2 weeks) followed by an enhanced activity (2 months) compared to normal hippocampal extract. Several possibilities are discussed as to the identity of the serotonergic growth factor from hippocampal supernatant.

5,7-Dihydroxytryptamine↗
PubMed1991

Actions of norepinephrine in the rat hippocampus.

Acting at postsynaptic alpha 1- and beta 1-receptors, norepinephrine (NE) exerts a complex action in rat hippocampus. It is currently believed that beta 1-receptor activation enhances excitability of recorded neurons, whereas alpha 1 activation suppresses reactivity to afferent stimulation. These reported effects of alpha-agonists are not consistent with alpha 1 effects found elsewhere in the brain. We have conducted experiments in the anesthetized rat and found that an amphetamine-induced increase in the dentate gyrus population spike can be blocked by a beta-antagonist but also by an alpha 1-antagonist. We have conducted experiments in the brain slide preparation and found that an alpha-agonist, phenylephrine (PHE), selectively enhances responses to N-methyl-D-aspartate (NMDA) but not to quisqualate. We propose that the product of activation of both alpha- and beta-receptor types will enhance reactivity of hippocampal cells to afferent stimulation.

Afferent Pathways↗
PubMed1991

Plasticity of sensory responses of locus coeruleus neurons in the behaving rat: implications for cognition.

The gating and tuning actions of noradrenaline (NA) at post-synaptic sites have been highly suggestive of an important role for the locus coeruleus (LC) in attention, learning and memory. By recording the activity of single units in the LC in behaving rats in a strictly controlled conditioning paradigm, direct evidence was provided that this nucleus is engaged during specific aspects of learning. The neuronal response to a discrete sensory stimulus was monitored as a function of the changing significance of the stimulus i.e., when it was novel, during habituation, associative learning, reversal and extinction. Both appetitive and aversive paradigms were used. We consistently observed differential conditioned responding with food reinforcement, while when footshock reinforcement was used, there was an increase in response to both CS+ and CS-. In both paradigms, the LC response disappeared when the conditioning was expressed at a behavioral level, to reappear vigorously as soon as the stimulus reinforcement contingencies were changed, i.e., during reversal or extinction. These results suggest that the LC does not mediate specific sensory or associative information necessary for ongoing performance but shows remarkable plasticity of sensory responding as a function of changing cognitive significance of the stimulus.

Animals↗
PubMed1991

Regulation of the development of locus coeruleus neurons in vitro.

Primary dissociated cultures of embryonic locus coeruleus (LC) neurons were established. Norepinephrine (NE) uptake was used as an index of maturation of the noradrenergic (NA) neurons from the LC. When LC cells were cocultured with a low density of hippocampal target cells, NE uptake was stimulated. However, increasing the concentration of hippocampal cells resulted in a significant decrease in NE uptake. The target stimulatory effect was mediated by both neurons and glia, whereas the inhibitory effect was mediated by direct contact between target glia and LC neurons and detected only in the presence of serum. In addition to the effect of target, we also tested the effect of elevated intracellular cAMP levels on NE uptake versus GABA uptake. GABA uptake was an index of development of non-NA cells. Increasing intracellular cAMP resulted in selective stimulation of NE uptake. These studies illustrate the potential of dissociated LC cultures in studying the regulation of NA axonal outgrowth.

Animals↗
PubMed1991

The effects of serotonin depletion and raphe grafts on hippocampal electrophysiology and behavior.

The involvement of the serotonergic system in spatial learning and a possible correlation between serotonergic modulation of hippocampal electrical activity and spatial learning were studied in rats. Control, partial septal-lesioned (SL), 5,7-dihydroxytryptamine (5,7-DHT)-injected (DHT), double-lesioned (5,7-DHT and SL; DL), and DL rats that were transplanted with embryonic raphe grafts into the hippocampus (RG) were tested in a spatial task in a water maze and in an active avoidance shuttle-box task. The responses of the dentate gyrus (DG) to perforant-path (PP) stimulation were examined in the same rats, under the following conditions: (1) priming stimulation of the PP (testing feedback inhibition), (2) priming stimulation of the commissural pathway (testing feedforward inhibition), (3) during repeated stimulation of the PP at 7 Hz (frequency potentiation), and (4) following tetanic stimulation [long-term potentiation (LTP)]. DL, but not DHT or SL, treatment severely impaired the performance of rats in both reference- and working-memory tasks in the water maze. This effect was not seen in the shuttle box. The ability of the DG to exhibit LTP, which was reduced in the DHT and SL rats, was apparently similar to controls in the DL group, DL, but not DHT or SL alone, resulted in a reduction of inhibition in the DG. Both the behavioral deficits and the reduction in hippocampal inhibition were ameliorated by intrahippocampal raphe grafts. These results indicate that the serotonergic innervation of the hippocampus plays a role in spatial learning when the septohippocampal neurotransmission systems are disrupted. Furthermore, these results suggest that restoration of modulation of hippocampal inhibition, by raphe grafts, underlies the behavioral recovery observed in these rats.

5,7-Dihydroxytryptamine↗
PubMed1991

Control of the maturation and the survival of central noradrenergic neurons in culture.

Central noradrenergic neurons from the locus coeruleus express unique plastic properties. The aim of this study was to identify factors that specifically regulate the development and the survival of the noradrenergic cells. Primary dissociated cultures of embryonic locus coeruleus (LC) neurons were established. Norepinephrine (NE) uptake was used as an index of maturation of the noradrenergic neurons. The noradrenergic cells were identified and quantified following immunocytochemical staining for tyrosine hydroxylase antibody. We have examined the effect of hippocampal target tissue and of cyclic-AMP (cAMP) on the development of these cells. Coculturing LC cells with a low density of hippocampal target cells, resulted in a significant increase in NE uptake. However, when the amount of hippocampal target cells was doubled an enormous decrease in NE uptake occurred. The target stimulatory effect was mediated by both neurons and glia, whereas the inhibitory effect was mediated by direct contact between target glia and LC neurons and detected only in the presence of serum. In addition to target effect, we also tested the effect of elevated intracellular cAMP level on NE uptake versus GABA uptake. GABA uptake served as a developmental index of the non noradrenergic cells. Increasing the intracellular cAMP level, by application of the membrane permeable analog dibutyryl cyclic AMP (DbcAMP), resulted in a selective stimulation of NE uptake, due to enhanced survival of noradrenergic neurons. GABA uptake and the number of non-noradrenergic cells were not changed in the presence of DbcAMP. DbcAMP could maintain the survival of LC neurons in the absence of glial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗