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M Segal

Publications and source records attributed to M Segal.

At least 127 records · Page 7Linked to original sources
PubMed1994

Differential effects of serotonin and raphe grafts in the hippocampus and hypothalamus: a combined behavioural and anatomical study in the rat.

Combined with a partial cholinergic deficiency, serotonergic lesions induce severe spatial learning deficits. Serotonergic lesions, however, have additional effects, such as reduced body weight and disruption of thermoregulation, which may be the cause of the observed learning deficits. Restoration of the serotonergic innervation of the hippocampus by raphe grafts reduces these learning deficits. The effects of the grafts may result from a direct support of spatial learning but may also be an indirect result of preventing some of the other effects of serotonergic lesions. In the present study we used raphe grafts to examine the selectivity and specificity of the effects of serotonergic lesions in the rat, and used the behavioural effects as an indication of successful transplantation in order to examine the fine details of such grafts. Raphe grafts in the hippocampus did not prevent the effects of the lesions on body weight, thermoregulation and exploratory behaviour but did minimize the effects of the lesions on spatial learning. In contrast, raphe grafts in the hypothalamus reduced the effects of the lesions on thermoregulation but failed to support learning. The grafted fibres showed termination specificity with the interneurons, which is typical of the serotonergic innervation of the normal hippocampus. The results indicate that the serotonergic innervation of the hippocampus functions locally to support spatial learning. This role of serotonin is independent of its involvement in modulation of body weight, thermoregulation or exploratory behaviour. The results confirm that the modes of serotonergic action in the hippocampus include the selective innervation of specific interneuron subpopulations.

5,7-Dihydroxytryptamine↗
PubMed1994

Interactions among calcium compartments in C6 rat glioma cells: involvement of potassium channels.

1. Variations in intracellular free Ca2+ concentration ([Ca2+]i) induced by alteration of the extracellular concentrations of Ca2+ ([Ca2+]o) and K+ ([K+]o) were imaged in single fluo-3-loaded C6 glioma cells. In addition, the effect of membrane potential on [Ca2+]i was investigated in fura-2-loaded, voltage-clamped cells. 2. Step alterations of [Ca2+]o from 0 to 10 nM were followed by proportional variations in [Ca2+]i, with a maximum 7-fold increase and an apparent half-maximum at [Ca2+]o of 1.5 mM. 3. The time to half-maximum change (t1/2) of [Ca2+]o-associated [Ca2+]i variations ranged between 10 and 50 s, and was inversely related to the amplitude of [Ca2+]o steps. 4. Transient, serotonin-induced [Ca2+]i elevations, used as a measure of Ca2+ availability in inositol 1,4,5-trisphosphate-sensitive stores, were diminished within 10 min in 0 mM [Ca2+]o, but were unaffected by [Ca2+]o changes in the 1-5 mM range. 5. Restoration of normal [Ca2+]i following its elevation by serotonin was delayed by removal of external Na+ or Cl- and was enhanced by warming the medium to 37 degrees C. These conditions did not affect [Ca2+]o-associated [Ca2+]i variations. 6. [Ca2+]o-associated [Ca2+]i variations were depressed by La3+ and Ba2+, while blockers of voltage-activated Ca2+ channels were ineffective. 7. Elevated [K+]o depressed the basal level of [Ca2+]i, and in high concentrations (70-140 mM) also diminished the response to serotonin. 8. Depolarizing the membrane potential of voltage-clamped cells reversibly reduced [Ca2+]i. These membrane-potential associated [Ca2+]i variations were blocked by La3+, Ba2+ and TEA, all of which also depolarized membrane resting potential. 9. Apamin (at 1-10 microM), a blocker of [Ca2+]i-activated K+ channel, totally and reversibly prevented [Ca2+]o-associated [Ca2+]i variations. 10. These studies indicate that C6 cells are responsive to variations in [Ca2+]o, and that a K+ channel is a possible path through which Ca2+ penetrates into the cell.

Animals↗
PubMed1994

The effects of general and restricted serotonergic lesions on hippocampal electrophysiology and behavior.

Depletion of the forebrain serotonergic system was found in previous studies to induce an increased excitability of the dentate gyrus (DG) granule cells and, when combined with a cholinergic deficiency, to impair spatial learning. We now compared the effects of general forebrain serotonergic lesions induced by intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT), to those of a more restricted injection of 5,7-DHT into fornix-fimbria and cingulum, to eliminate hippocampal serotonergic innervation. Control and lesioned rats were injected with atropine and tested in the spatial learning water-maze task. Following the behavioral tests, rats were anesthetized and the responsiveness of the DG to perforant path (PP) stimulation was measured. To assess the lesions functionally, responses to application of the serotonin releasing drug fenfluramine (FFA) were measured. Finally, the reduction, in the hippocampus, of serotonergic innervation was evaluated by [3H]imipramine binding. The effects of the lesions on the responsiveness to FFA confirmed that the ICV lesions were functionally more general than the FF lesions. [3H]Imipramine binding indicated that both lesions reduced the serotonergic innervation of the hippocampus significantly. Behaviorally, both lesioned groups were impaired in the water-maze. Electrophysiologically, in both DG excitability was higher than in controls and in both hyperexcitability was associated with an increase in feed-forward inhibition. The results suggest that the serotonergic innervation of the hippocampus proper is involved in cognitive functions associated with the hippocampus.

Action Potentials↗
PubMed1994

Locus coeruleus (LC)--target interaction and cAMP in control of LC development.

The epigenetic stimuli that regulate the development of noradrenergic LC neurons were studied in an vitro system of LC primary cultures. Noradrenergic cells were identified using immunocytochemical staining for tyrosine hydroxylase (TH). Maturation of noradrenergic neurons was assessed by measuring the high affinity uptake of norepinephrine (NE). Coculturing target cells with LC neurons exerts both stimulatory and inhibitory effects on NE uptake, depending on the density of plated cells. The target stimulatory effect may be mediated by glial soluble factors, whereas the inhibitory effect may be mediated by glial membranal molecules. In addition to target derived trophic factors, the effect of elevated cAMP levels was examined. cAMP analogs and forskolin dramatically increase the number of TH+ cells, possibly by supporting their survival. This phenomenon is not dependent on calcium or calcium requiring processes and is not mediated by glial cells. The trophic activity of cAMP appears to be exerted by protein phosphorylation via cAMP dependent protein kinase. Norepinephrine is suggested to be one signal that triggers cAMP elevation through the beta-adrenergic receptor and thereby affects LC development. Morphine, which is known to inhibit adenylate cyclase, reduces NE uptake and number of TH+ neurons. Morphine also inhibits the NT-3 induced increase in noradrenergic survival. We hypothesize that morphine exerts these effects by modulating the cAMP cascade.

Animals↗
PubMed1994

Unusual bleeding manifestations of amyloidosis in patients with multiple myeloma.

We describe two patients who developed severe haemorrhagic complications. One manifested massive vaginal bleeding and the second haemopericardium with cardiac tamponade. In both cases histopathological examination showed subendothelial deposits of amyloid. Since other local and systemic causes of the haemorrhagic complications were excluded the bleeding was most probably due to amyloid angiopathy. Therefore, amyloid angiopathy should be considered in the differential diagnosis of bleeding in patients with amyloidosis associated with multiple myeloma.

Aged↗
PubMed1994

A novel cholinergic induction of long-term potentiation in rat hippocampus.

1. We studied long-term cholinergic effects on synaptic transmission in submerged hippocampal slices using intra- and extracellular recording techniques. 2. Bath application of submicromolar concentrations of carbachol (CCh) produced a gradually developing, long-lasting increase in the CA1 excitatory postsynaptic potential and population spike. This potentiation was blocked by atropine and, hence, named muscarinic long-term potentiation (LTPm). Application of DL-2-amino-5-phosphonovaleric acid had no effect on LTPm, indicating that this phenomenon is N-methyl-D-aspartate receptor independent. 3. These effects of CCh were not likely to be due to the blockade of one of several K+ conductances by the drug; the time and concentration dependence of LTPm were different from those associated with cholinergic blockade of K+ conductances. 4. Removal of extracellular calcium (Cao2+) from the bath blocked synaptic transmission. CCh added in calcium-free medium induced LTPm, which was revealed upon removal of the drug by washing with normal calcium-containing medium. Neither cutting CA1-CA3 connections nor cessation of synaptic stimulation interfered with LTPm induction. 5. Application of thapsigargin or H-7 together with CCh blocked LTPm, suggesting the involvement of intracellular calcium (Cai2+) stores and protein kinases, respectively, in the LTPm mechanism. 6. Subthreshold cholinergic stimulation coupled with subthreshold tetanic stimulation caused LTP. CCh had no effect when administered after the LTP mechanism had been saturated by repeated suprathreshold tetani. Tetanic stimulation failed to cause LTP when applied after LTPm had been induced by CCh. These experiments indicate that tetanus-induced potentiation and LTPm share a common mechanism and provide a direct link between ACh and mechanisms of synaptic plasticity.

Acetylcholine↗
PubMed1994

Changes in cytosolic sodium caused by a toxic glutamate treatment of cultured hippocampal neurons.

Changes in cytosolic Na+ ([Na+]i) caused by a toxic glutamate (GLU) or NMDA treatment of cultured hippocampal neurons were monitored by using SBFI fluorescent probe and imaging microscopy. Both GLU and NMDA (50 or 100 microM in Mg(2+)-free solution, 15 min) induced a marked increase in [Na+]i (from 6-8 to 30-45 mM) which persisted after the termination of a treatment. The competitive NMDA antagonist, APV (100 microM) when applied in the post-NMDA period failed to decrease the elevated [Na+]i. The results obtained strongly suggest that the main reason for an impairment of Na+/Ca2+ exchange in the post-glutamate period (see Febs Letters 1993, 324, 271-273) is a reduction of the transmembrane Na+ gradient caused apparently by inhibition of Na(+)-K+ pump.

2-Amino-5-phosphonovalerate↗
PubMed1994

Selective elimination of hypothalamic neurons by grafted hypertension-inducing neural tissue.

Embryonic hypothalamic tissue originating from spontaneously hypertensive rats (SHR) was implanted in young normotensive Wistar Kyoto rats in an attempt to localize hypothalamic regions directly responsible for the induction of hypertension. A 25% increase in host systolic blood pressure as compared with the controls was recorded 3 months after implantation in the animals receiving rostral hypothalamic tissue (R-SHR), whereas blood pressure was not affected in the animals grafted with caudal hypothalamic tissue (C-SHR). The hypertension in the R-SHR group was accompanied by hypertrophy of the heart and kidneys. The number of vasopressin-immunopositive (VPi) parvocellular cells in the hypothalamic paraventricular nucleus (PVN) of the R-SHR group was massively reduced (by 72%), while that of the tyrosine hydroxylase-immunopositive cells displayed no change. In the suprachiasmatic nucleus of these animals the VPi cell number was unaltered. In the C-SHR, the amount of parvocellular VPi cells was also unaltered. Likewise, oxytocin-containing cells were the same in all groups. DNA nick-end labeling of the tissue revealed that PVN cells are undergoing programmed cell death. These results implicate a selective degeneration by hypothalamic PVN cells in the pathogenesis of hypertension.

Animals↗
PubMed1993

Extracellular recordings in the colchicine-lesioned rat dentate gyrus following transplants of fetal dentate gyrus and CA1 hippocampal subfield tissue.

Grafts of fetal dentate gyrus (DG) and CA1 hippocampal subfield tissue were extruded into the dentate gyri of adult male Sprague-Dawley rats, 7-10 days after lesioning the granule cells with colchicine (0.06 microliter of 7 mg/ml solution at each of 5 sites/hippocampus). Graft area-host and host-graft area connectivities were investigated 4-6 months post-transplantation by recoding extracellular evoked response in hippocampal slice preparations. Following stimulation of the host mid-molecular layer, evoked field potential responses, showing considerable variation, were recorded in both types of graft. Evoked responses in the lesioned DG without grafts were recorded in very few slices. Stimulation of the area of DG tissue grafts occasionally evoked responses in the host CA3/CA4 and there was no evidence for CA1 graft area-CA3/CA4 connectivity; stimulation of DG and CA1 graft areas occasionally evoked responses in the host CA1. Responses in the area of both DG and CA1 grafts supported short-term potentiation following stimulation of the host mid-molecular layer but only DG graft areas supported long-term potentiation of the population spike amplitude. In the area of both types of transplant a tonic bicuculline-sensitive inhibition was present and paired-pulse stimulation paradigms provided some evidence for inhibition. It is possible that responses recorded within the area of grafted tissue to stimulation of the host are attributable to host-graft connectivity and similarly, responses recorded in the host to stimulation of the area of the graft may be attributable to graft-host connectivity. Only DG graft areas received host inputs which were capable of sustaining a long-term potentiation and establishing efferent contacts with the host CA3/CA4 subfield, suggesting that these would be more likely than CA1 grafts to reinstate normal functional circuitry.

Animals↗
PubMed1993

Age-related cognitive deficits in rats are associated with a combined loss of cholinergic and serotonergic functions.

The cholinergic hypothesis of senile dementia proposes that an age-dependent reduction of central cholinergic functions accounts for the severe cognitive deficits seen in aged rats. A careful examination of the experimental evidence cited in support of this hypothesis reveals that it cannot account for some behavioral observations. We have modified this hypothesis and wish to propose that serotonin and acetylcholine interact to allow normal cognitive functions in the brain. Thus, a partial reduction in both cholinergic and serotonergic functions will cause severe memory impairment in young as well as in aged rats. We found that restoration of the serotonergic innervation in the hippocampus of serotonin depleted rats, using tissue transplants, can restore impaired behavior. We have localized a memory-related interaction between serotonin and acetylcholine in the hippocampus and are in the process of identifying a physiological function which may underly this interaction.

Acetylcholine↗
PubMed1993

Selective signaling via unique M1 muscarinic agonists.

Rigid analogs of acetylcholine (ACh) were designed for selective actions at muscarinic receptor (mAChR) subtypes and distinct second messenger systems. AF102B, AF150, and AF151 are such rigid analogs of ACh. AF102B, AF150 and AF151 are centrally active M1 agonists. AF102B has a unique agonistic profile showing, inter alia: only part of the M1 electrophysiology of ACh and unusual binding parameters to mAChRs. AF150 and AF151 are more efficacious agonists than AF102B for M1 AChRS in rat cortex and in CHO cells stably transfected with the m1 AChR subtype. Notably, the selectivity of the new m1 agonists is reflected also by activation of select second messenger systems via distinct G-proteins. These compounds reflect a new pharmacological concept, tentatively defined as ligand-selective signaling. Thus, agonist/m1AChR complexes may activate different combinations of signaling pathways, depending on the ligand used. Rigid agonists may activate a limited repertoire of signaling systems. In various animal models for Alzheimer's disease (AD) the agonists AF102B, AF150 and AF151, exhibited positive effects on mnemomic processes and a wide safety margin. Such agonists, and especially AF102B, can be considered as a rational treatment strategy for AD.

Acetylcholine↗
PubMed1993

Neurotrophic effects of cAMP generating systems on central noradrenergic neurons.

The environmental signals which regulate the development of central noradrenergic neurons are largely unknown. The aim of the present study was to search for factors affecting the development of these cells. Dissociated cultures of embryonic dorsal brainstem tissue, containing the nucleus locus coeruleus (LC), were established; norepinephrine (NE) and GABA uptake were assessed, and noradrenergic versus total neurons were identified and counted following immunocytochemical staining with tyrosine hydroxylase (TH) and neuron specific enolase (NSE) antibodies, respectively. Application of dibutyryl cAMP (dbcAMP), other cAMP analogs, or forskolin, to LC cultures resulted in a significant increase in NE uptake which was associated with up to a 4-fold increase in the number of TH immunoreactive cells (TH+). dbcAMP treatment caused an increase in the number of TH+ cells in LC cultures by enhancing their survival and/or by upregulating their phenotypic differentiation. A possible effect of dbcAMP on cell proliferation and transformation of non-noradrenergic cells to noradrenergic TH+ cells were examined and suggested not to underlie this effect of cAMP. Glial cells may mediate the effect of cAMP on noradrenergic neurons. Calcium was not involved in the trophic activity of dbcAMP, which was probably mediated by protein phosphorylation via cAMP dependent protein kinase. Insulin (25 micrograms/ml) was found to increase the number of TH+ cells by 73%. The beta-adrenergic agonist isoproterenol also increased the number of TH+ cells by 53%. We propose a neurotrophic role for NE during development of central noradrenergic neurons.

Adenylyl Cyclases↗
PubMed1993

Residues crucial for Ras interaction with GDP-GTP exchangers.

Cdc25 is essential for Ras-mediated activation of adenylyl cyclase in the yeast Saccharomyces cerevisiae. This protein acts by catalyzing GDP-GTP exchange on yeast Ras. Harvey (Ha) ras expressed in S. cerevisiae is also recognized by both Cdc25 and Sdc25, a yeast homolog of Cdc25. Thus it is feasible to examine molecular aspects of mammalian Ras modulation by Cdc25 using the RAS/cAMP pathway in yeast as a model system. Here, we describe mutational analysis of Ha-ras for the identification of residues critical for the ability of Ras to interact with Cdc25 and related guanine nucleotide-release proteins. Mutations within codons 97-108 impaired Ras-mediated activation of adenylyl cyclase in the presence but not in the absence of mammalian GTPase-activating protein. Such mutations, therefore, affected the ability of Ras to undergo GDP-GTP exchange catalyzed by the guanine nucleotide exchanger without preventing Ras activation of the effector. Similar mutations were previously shown to impair the ability of c-ras to transform mammalian cells while having a less drastic effect on v-ras.

Adenylyl Cyclases↗
PubMed1993

GABA induces a unique rise of [Ca]i in cultured rat hippocampal neurons.

GABA evoked a reversible rise of free intracellular calcium concentration ([Ca]i) in cultured rat hippocampal neurons, detected with Fluo-3 fluorescence in a confocal laser scanning microscope. The GABA-evoked change of [Ca]i was mimicked by muscimol and not by baclofen, but was only minimally affected by picrotoxin or bicuculline, indicating that this effect of GABA is not likely to be mediated by activation of GABAB receptor or by a conventional chloride-linked GABAA receptor. GABA-evoked rise of [Ca]i expressed a marked desensitization; only 10-20 minutes after a previous exposure to GABA was the response to a subsequent application fully expressed. This desensitization was not seen in electrophysiological responses to GABA or in [Ca]i changes evoked by NMDA in the same neurons. The GABA response appeared to be developmentally regulated and was seen in 1-7-day-old more than in 21-28-day-old cells. It is suggested that GABA evokes a unique change of [Ca]i in young hippocampal neurons.

Animals↗
PubMed1993

Regional specificity of raphe graft-induced recovery of behavioral functions impaired by combined serotonergic/cholinergic lesions.

We compared the effects of embryonic raphe grafted into either the hippocampus or the entorhinal cortex on the ability of rats to perform a spatial memory water-maze task. Serotonin depletion or partial cholinergic lesion of the hippocampus (by injection of colchicine into the septum) did not affect the ability of rats to perform the task, but the combined treatment did. Double-lesioned rats, with raphe grafts in the hippocampus, but not in the entorhinal cortex, performed similar to control or single-lesioned rats. The results suggest that the functioning of the serotonergic innervation of the hippocampus, and not of its afferents, is crucial for the ability of rats to perform spatial memory tasks, especially when the septohippocampal cholinergic connection is disrupted.

5,7-Dihydroxytryptamine↗