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APOE-Deficient mice are oxidatively stressed and their antioxidants response to closed head injury is deranged
S33 change in the turn direction. Unlike the other interneurons in the group, that showed a change in turning size with addition of spikes, GI2 did not. A possible explanation for that could be the disruption of a fine temporal pattern that exists in the wind response of this interneuron. We tested this possibility by photoablating the posterior part of the neuron and injecting spikes to the undamaged more anterior part. Injection of constant frequency spike trains restored about 80% of the change in turn size caused by the GI2 ablation. Therefore, it is suggested that the fine temporal pattern is not crucial for the accurate coding of wind direction in this neuron. CA2+-INDEPENDENT SYNAPTIC VESICLE FUSION INDUCED BY D-LATROTOXIN IN P19 DEVELOPING NEURONS M. Linial and A. Citri Dept. of Biological Chemistry, The Institute of Life Sciences, The Hebrew University of Jerusalem, Jerusalem, Israel
D-Latrotoxin, the major component of black widow spider venom, is a 120 kDa protein that stimulates massive exocytosis of small synaptic vesicles. In the presence of extracellular Ca2+, D-latrotoxin induces release mainly via receptor-toxin clustering, the formation of nonselective cation channels and a subsequent Ca2+ induced release. However, the toxin also stimulates release in the absence of Ca2+ and with no apparent changes in intracellular Ca2+. This Ca2+-independent mode of release is still an enigma. We set out to investigate the α-latrotoxin Ca2+-independent mode of action in a neuronal context, in developing P19 neurons. P19 cells mature into functional neurons as determined by their ability to release neurotransmitters in a Ca2+ and depolarization dependent manner. We observed that mature P19 neurons express high affinity binding sites (Kd = 10–9–10–10 M). We determined the expression of its recently discovered Ca2+-independent receptor, named CIRL, during differentiation and maturation of P19 neurons. A novel in-vivo antibody uptake assay coupled to ELISA measurements was used to monitor the extent of Ca2+-independent synaptic vesicle fusion induced by D-latrotoxin. We observed that under such conditions (Dlatrotoxin at 0.15 nM), the pool of vesicles released is large compared to vesicles fused under physiological stimulation (80 mM KCl in the presence of Ca2+). We studied the potential involvement of G-proteins in the release induced by the toxin in order to understand the mechanism that allows the toxin to bypass the tight control of neurotransmitter release in nerve terminals. EFFECT OF SOCIAL ENVIRONMENT ON NEURONAL RECRUITMENT IN THE ADULT AVIAN BRAIN D. Lipkind1, R. Rado1, A. Barnea2 1 Dept. of Zoology, Tel-Aviv University, Tel Aviv, Israel;2 Dept. of Natural & Life Sciences, The Open University of Israel, Tel-Aviv, Israel Neurogenesis and neuronal replacement are known to occur in the adult avian brain (Alvarez-Buylla and Nottebohm, 1988; Kirn and Nottebohm, 1993). A possible explanation for this phenomenon is that creation of new neurons is necessary for acquiring long-term memories (Nottebohm, 1989). Therefore, we hypothesized that the rate of neuronal production and/or survival must increase in response to environmental changes that require the acquisition of new information. We used zebra finches (Taeniopygia guttata), a highly social estrildine bird to test this hypothesis. Adult individuals, reared under the same conditions, were introduced to different levels of social environments: (a) with no other birds present; (b) with a single, unfamiliar bird of the opposite gender; (c) with a group of 40 unfamiliar birds; (d) a control group which included birds that were kept in their native nesting colony. All experimental birds received intramuscular injections of 3Hthymidine, a marker of cell birth, during six days before or after they were introduced to the new social environment. Their brains were processed for autoradiographic and histological analysis, and quantification of the radioactively labeled neurons was obtained. Various behavioral parameters (feeding, locomotion, preening, mutual preening, fighting)
of the experimental birds were also monitored. Preliminary results indicate that there are differences both in neuronal and behavioral parameters between the various experimental groups. APOE-DEFICIENT MICE ARE OXIDATIVELY STRESSED AND THEIR ANTIOXIDANTS RESPONSE TO CLOSED HEAD INJURY IS DERANGED L. Lomnitski1, S. Chapman1, A. Hochman2, E. Shohami4, R. Kohen3, and D.M. Michaelson1 Depts. of Neurobiochemistry1 and Biochemistry2, Tel-Aviv University, Tel Aviv, Israel, and depts. of Pharmaceutics3 and Pharmacology4, The Hebrew University of Jerusalem, Jerusalem, Israel Apolipoprotein E (apoE)-deficient mice have distinct memory deficits and neurobiochemical derangements, and their recovery from closed head injury is impaired. The present study examined the possibility that these derangements are associated with changes in the levels of distinct brain antioxidants and that the increased susceptibility of the apoE-deficient mice to closed head injury is related to these antioxidant alterations. Measurements of the levels of brain Mn-superoxide dismutase and catalase activities revealed them to be significantly elevatedin apoE-deficient mice, as compared to control mice (134 ± 7 and 122 ± 8 percent of control, respectively; P < 0.01). Brain glutathione reductase activity was also significantly higher in the apoE-deficient mice (167 ± 7 percent of control; P < 0.01) whereas glutathione peroxidase and glucose-6-phosphate dehydrogenase activities were found to be similar in both groups of mice. Analysis of the brain membranes revealed that the total phospholipid level of apoE-deficient mice was markedly decreased (55 ± 15 percent of control; P < 0.01) ,whereas the levels of non-esterified cholesterol of the two groups of mice were similar. Further measurements revealed an increase of 132 ± 15 percent (P < 0.01) of the levels of the conjugated diene oxidative products of phospholipids in the apoE-deficient mice , relative to the control. Exposure of the mice to closed head injury resulted in a marked decrease in the levels of brain ascorbic acid of the two groups of mice, which was apparent at 5 min after head injury. However, whereas the brain ascorbic acid levels of the injured control mice recovered at 24 h post-injury, those of the injured apoE-deficient mice did not recover and remained low. Measurement of the levels of reduced brain glutathione in the two groups revealed slight and similar decreases at 24 h following head injury. Catalase and glutathione peroxidase of the two injured groups were both elevated about two-fold, relative to the sham controls, whereas superoxide dismutase activity was unaffected by the trauma. Glutathione reductase activity increased significantly (139 ± 7 percent of sham control at 24 h following injury; P < 0.01) in the control group , while that of the apoE-deficient mice was moderately reduced postinjury. These findings suggest that the antioxidant system of apoEdeficient mice is altered prior to and following head trauma, a phenomenon which may contribute to the diminished recovery capacity of apoE-deficient mice from acute oxidative stress induced by closed head injury. PLASMA NEUROSTEROIDS (DHEA AND DHEA-S) AS MARKERS OF SUCCESSFUL RESPONSIVENESS TO ECT (ELECTROCONVULSIVE THERAPY) IN PSYCHIATRIC PATIENTS R. Maayan I. Yagorowsky, I. Gil-Ad, B. Shtaif, A. Weizman Laboratory of Psychiatric Biology, Felsenshtein Medical Research Center, Beilinson Campus, Petah Tiqva and Tel-Aviv University, Tel Aviv, Israel Dehydroepiandrosterone (DHEA) and its derivative sulfate (DHEAS) are neuroactive neurosteroids. In the brain these steroids were found to interact with GABAa receptors which are involved in regulation of mood and anxiety. The significance of plasma levels of these steroids in psychiatric patients is obscure. We have studied basal plasma levels of DHEA, DHEA-S and their ratio in 17 psychiatric patients, and the
D-Latrotoxin, the major component of black widow spider venom, is a 120 kDa protein that stimulates massive exocytosis of small synaptic vesicles. In the presence of extracellular Ca2+, D-latrotoxin induces release mainly via receptor-toxin clustering, the formation of nonselective cation channels and a subsequent Ca2+ induced release. However, the toxin also stimulates release in the absence of Ca2+ and with no apparent changes in intracellular Ca2+. This Ca2+-independent mode of release is still an enigma. We set out to investigate the α-latrotoxin Ca2+-independent mode of action in a neuronal context, in developing P19 neurons. P19 cells mature into functional neurons as determined by their ability to release neurotransmitters in a Ca2+ and depolarization dependent manner. We observed that mature P19 neurons express high affinity binding sites (Kd = 10–9–10–10 M). We determined the expression of its recently discovered Ca2+-independent receptor, named CIRL, during differentiation and maturation of P19 neurons. A novel in-vivo antibody uptake assay coupled to ELISA measurements was used to monitor the extent of Ca2+-independent synaptic vesicle fusion induced by D-latrotoxin. We observed that under such conditions (Dlatrotoxin at 0.15 nM), the pool of vesicles released is large compared to vesicles fused under physiological stimulation (80 mM KCl in the presence of Ca2+). We studied the potential involvement of G-proteins in the release induced by the toxin in order to understand the mechanism that allows the toxin to bypass the tight control of neurotransmitter release in nerve terminals. EFFECT OF SOCIAL ENVIRONMENT ON NEURONAL RECRUITMENT IN THE ADULT AVIAN BRAIN D. Lipkind1, R. Rado1, A. Barnea2 1 Dept. of Zoology, Tel-Aviv University, Tel Aviv, Israel;2 Dept. of Natural & Life Sciences, The Open University of Israel, Tel-Aviv, Israel Neurogenesis and neuronal replacement are known to occur in the adult avian brain (Alvarez-Buylla and Nottebohm, 1988; Kirn and Nottebohm, 1993). A possible explanation for this phenomenon is that creation of new neurons is necessary for acquiring long-term memories (Nottebohm, 1989). Therefore, we hypothesized that the rate of neuronal production and/or survival must increase in response to environmental changes that require the acquisition of new information. We used zebra finches (Taeniopygia guttata), a highly social estrildine bird to test this hypothesis. Adult individuals, reared under the same conditions, were introduced to different levels of social environments: (a) with no other birds present; (b) with a single, unfamiliar bird of the opposite gender; (c) with a group of 40 unfamiliar birds; (d) a control group which included birds that were kept in their native nesting colony. All experimental birds received intramuscular injections of 3Hthymidine, a marker of cell birth, during six days before or after they were introduced to the new social environment. Their brains were processed for autoradiographic and histological analysis, and quantification of the radioactively labeled neurons was obtained. Various behavioral parameters (feeding, locomotion, preening, mutual preening, fighting)
of the experimental birds were also monitored. Preliminary results indicate that there are differences both in neuronal and behavioral parameters between the various experimental groups. APOE-DEFICIENT MICE ARE OXIDATIVELY STRESSED AND THEIR ANTIOXIDANTS RESPONSE TO CLOSED HEAD INJURY IS DERANGED L. Lomnitski1, S. Chapman1, A. Hochman2, E. Shohami4, R. Kohen3, and D.M. Michaelson1 Depts. of Neurobiochemistry1 and Biochemistry2, Tel-Aviv University, Tel Aviv, Israel, and depts. of Pharmaceutics3 and Pharmacology4, The Hebrew University of Jerusalem, Jerusalem, Israel Apolipoprotein E (apoE)-deficient mice have distinct memory deficits and neurobiochemical derangements, and their recovery from closed head injury is impaired. The present study examined the possibility that these derangements are associated with changes in the levels of distinct brain antioxidants and that the increased susceptibility of the apoE-deficient mice to closed head injury is related to these antioxidant alterations. Measurements of the levels of brain Mn-superoxide dismutase and catalase activities revealed them to be significantly elevatedin apoE-deficient mice, as compared to control mice (134 ± 7 and 122 ± 8 percent of control, respectively; P < 0.01). Brain glutathione reductase activity was also significantly higher in the apoE-deficient mice (167 ± 7 percent of control; P < 0.01) whereas glutathione peroxidase and glucose-6-phosphate dehydrogenase activities were found to be similar in both groups of mice. Analysis of the brain membranes revealed that the total phospholipid level of apoE-deficient mice was markedly decreased (55 ± 15 percent of control; P < 0.01) ,whereas the levels of non-esterified cholesterol of the two groups of mice were similar. Further measurements revealed an increase of 132 ± 15 percent (P < 0.01) of the levels of the conjugated diene oxidative products of phospholipids in the apoE-deficient mice , relative to the control. Exposure of the mice to closed head injury resulted in a marked decrease in the levels of brain ascorbic acid of the two groups of mice, which was apparent at 5 min after head injury. However, whereas the brain ascorbic acid levels of the injured control mice recovered at 24 h post-injury, those of the injured apoE-deficient mice did not recover and remained low. Measurement of the levels of reduced brain glutathione in the two groups revealed slight and similar decreases at 24 h following head injury. Catalase and glutathione peroxidase of the two injured groups were both elevated about two-fold, relative to the sham controls, whereas superoxide dismutase activity was unaffected by the trauma. Glutathione reductase activity increased significantly (139 ± 7 percent of sham control at 24 h following injury; P < 0.01) in the control group , while that of the apoE-deficient mice was moderately reduced postinjury. These findings suggest that the antioxidant system of apoEdeficient mice is altered prior to and following head trauma, a phenomenon which may contribute to the diminished recovery capacity of apoE-deficient mice from acute oxidative stress induced by closed head injury. PLASMA NEUROSTEROIDS (DHEA AND DHEA-S) AS MARKERS OF SUCCESSFUL RESPONSIVENESS TO ECT (ELECTROCONVULSIVE THERAPY) IN PSYCHIATRIC PATIENTS R. Maayan I. Yagorowsky, I. Gil-Ad, B. Shtaif, A. Weizman Laboratory of Psychiatric Biology, Felsenshtein Medical Research Center, Beilinson Campus, Petah Tiqva and Tel-Aviv University, Tel Aviv, Israel Dehydroepiandrosterone (DHEA) and its derivative sulfate (DHEAS) are neuroactive neurosteroids. In the brain these steroids were found to interact with GABAa receptors which are involved in regulation of mood and anxiety. The significance of plasma levels of these steroids in psychiatric patients is obscure. We have studied basal plasma levels of DHEA, DHEA-S and their ratio in 17 psychiatric patients, and the