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18. Advances in understanding the mechanisms underlying synaptic plasticity
A8
Abstracts/Journal of Neuroscience Methods (1994) A 1-A28
16. IMAGING CALCIUM VARIATIONS IN DENDRITES AND SPINES OF CENTRAL N E U R O N S IN VITRO
M. Segal
Department of Neurobiology, The Weizman Institute of Science, RehoL,ot, 76100 Israel Dendritic spines have attracted neuroscientists ever since their first description by Cajal nearly a century ago. They are assumed to play a major role in neuronal plasticity and have been shown to undergo some morphological variations in plasticity-related events. Their small size, at the limit of optical resolution, prohibited their systematic study in live tissue at the light microscope level and restricted their analysis to the fixed tissue, at the electron microscope level. With the advent of improved calcium-sensitive dyes and imaging technologies, the dendritic spine became accessible to a systematic analysis. Studies employing the in vitro slice preparation as well as cultured central neurons are being used in several laboratories in an attempt to elucidate the role(s) of the spine in neuronal functions. The slice offers the advantage of studying 'normal' neurons with known electrophysiological properties where plasticity-evoking stimuli can be easily applied. The disadvantage of the slice is its three-dimensionality, where high-power objectives are limited by the working distance in the tissue. The cultured neuron is essentially two-dimensional, so that application of high-resolution optics is relatively easy. The cultured neuron is different from the neuron in the slice in several morphological and functional respects. We have compared the different methods used to measure calcium in dendrites and spines of live neurons. The results obtained thus far indicate that the spine constitutes a unique calcium compartment in that it can regulate calcium independently of the parent dendrite. Also, the spine appears to contain voltage-sensitive calcium channels and mechanisms for fast removal of excess calcium. The relationship between calcium regulation and the morphological changes seen in dendritic spines is subject for further studies. 17. HIPPOCAMPAL SLICES: EVALUATION OF SODIUM CHANNEL MODULATORS AS THERAPEUTIC TREATMENTS FOR ISCHEMIC STROKE
C.P. Taylor, M.L. Weber
Department of Neuroscience Pharmacology, Park-Davis Research, Div. of Warner-Lambert, 2800 Plymouth Road, Ann Arbor, MI 48105, USA Hippocampal slices have been used to study potential treatments (hypothermia, N M D A antagonists,
AMPA antagonists, sodium channel modulators) for ischemia. We have used extracellular field potential recordings, histological and histochemical techniques, and biochemical studies of glutamate release to evaluate various treatments. The sodium channel blocker tetrodotoxin (TTX, 1 ~M) reduced glutamate release from deprivation of oxygen and glucose while calcium channel blockade was ineffective. Voltage-dependent sodium channel modulators (TTX, 100-600 nM; phenytoin, 5-100 /zM; lidocaine, 2-200 /zM) each prevented damage to the CA1 area, as measured by preventing the irreversible loss of synaptic potentials and preventing histological damage without interfering with normal synaptic function. Calcium channel blockers (nimodipine, 10 /zM; w-Conus toxin (CTxMVIIC), 2 ~ M ) were ineffective despite the almost total blockade of glutamatergic synaptic potentials by CTxMVIIC. These results suggests that glutamate release and cellular damage from "ischemia" in vitro is not dependent on calcium-dependent exocytosis of glutamate, but both glutamate release and cellular damage from "ischemia" can be reduced by the modulation of voltage-activated sodium channels.
18. ADVANCES IN UNDERSTANDING THE MECHANISMS UNDERLYING SYNAPTIC PLASTICITY
T.J. Teyler ~, I. Cavus % C. Coussens % P.G. DiScenna % L. Grover b, y . Lee a and Z. Little ~
~'Neurobiology Department, Northeastern Ohio Universities, College of Medicine, Rootstown, OH 44272, USA; b Physiology Department, Marshall University, Medical School, Huntington, WV25755, USA
Hippocampal CA1 cells possess several varieties of long-lasting synaptic plasticity: two different forms of long-term potentiation (LTP) and at least one form of long-term depression (LTD). All forms of synaptic plasticity are induced by afferent activation, all involve Ca 2+ influx, all can be blocked by Ca 2+ chelators and all activate Ca 2+ dependent mechanisms. The question arises as how different physiological responses can be initiated by activation of the same second messenger. We consider two hypotheses which could account for these phenomena: voltage-dependent differences in cytosolic Ca 2+ concentration acting upon Ca 2+ substrates of differing Ca 2 + affinities, and compartmentalization of the Ca 2+ and its substrates.
Abstracts/Journal of Neuroscience Methods (1994) A 1-A28
16. IMAGING CALCIUM VARIATIONS IN DENDRITES AND SPINES OF CENTRAL N E U R O N S IN VITRO
M. Segal
Department of Neurobiology, The Weizman Institute of Science, RehoL,ot, 76100 Israel Dendritic spines have attracted neuroscientists ever since their first description by Cajal nearly a century ago. They are assumed to play a major role in neuronal plasticity and have been shown to undergo some morphological variations in plasticity-related events. Their small size, at the limit of optical resolution, prohibited their systematic study in live tissue at the light microscope level and restricted their analysis to the fixed tissue, at the electron microscope level. With the advent of improved calcium-sensitive dyes and imaging technologies, the dendritic spine became accessible to a systematic analysis. Studies employing the in vitro slice preparation as well as cultured central neurons are being used in several laboratories in an attempt to elucidate the role(s) of the spine in neuronal functions. The slice offers the advantage of studying 'normal' neurons with known electrophysiological properties where plasticity-evoking stimuli can be easily applied. The disadvantage of the slice is its three-dimensionality, where high-power objectives are limited by the working distance in the tissue. The cultured neuron is essentially two-dimensional, so that application of high-resolution optics is relatively easy. The cultured neuron is different from the neuron in the slice in several morphological and functional respects. We have compared the different methods used to measure calcium in dendrites and spines of live neurons. The results obtained thus far indicate that the spine constitutes a unique calcium compartment in that it can regulate calcium independently of the parent dendrite. Also, the spine appears to contain voltage-sensitive calcium channels and mechanisms for fast removal of excess calcium. The relationship between calcium regulation and the morphological changes seen in dendritic spines is subject for further studies. 17. HIPPOCAMPAL SLICES: EVALUATION OF SODIUM CHANNEL MODULATORS AS THERAPEUTIC TREATMENTS FOR ISCHEMIC STROKE
C.P. Taylor, M.L. Weber
Department of Neuroscience Pharmacology, Park-Davis Research, Div. of Warner-Lambert, 2800 Plymouth Road, Ann Arbor, MI 48105, USA Hippocampal slices have been used to study potential treatments (hypothermia, N M D A antagonists,
AMPA antagonists, sodium channel modulators) for ischemia. We have used extracellular field potential recordings, histological and histochemical techniques, and biochemical studies of glutamate release to evaluate various treatments. The sodium channel blocker tetrodotoxin (TTX, 1 ~M) reduced glutamate release from deprivation of oxygen and glucose while calcium channel blockade was ineffective. Voltage-dependent sodium channel modulators (TTX, 100-600 nM; phenytoin, 5-100 /zM; lidocaine, 2-200 /zM) each prevented damage to the CA1 area, as measured by preventing the irreversible loss of synaptic potentials and preventing histological damage without interfering with normal synaptic function. Calcium channel blockers (nimodipine, 10 /zM; w-Conus toxin (CTxMVIIC), 2 ~ M ) were ineffective despite the almost total blockade of glutamatergic synaptic potentials by CTxMVIIC. These results suggests that glutamate release and cellular damage from "ischemia" in vitro is not dependent on calcium-dependent exocytosis of glutamate, but both glutamate release and cellular damage from "ischemia" can be reduced by the modulation of voltage-activated sodium channels.
18. ADVANCES IN UNDERSTANDING THE MECHANISMS UNDERLYING SYNAPTIC PLASTICITY
T.J. Teyler ~, I. Cavus % C. Coussens % P.G. DiScenna % L. Grover b, y . Lee a and Z. Little ~
~'Neurobiology Department, Northeastern Ohio Universities, College of Medicine, Rootstown, OH 44272, USA; b Physiology Department, Marshall University, Medical School, Huntington, WV25755, USA
Hippocampal CA1 cells possess several varieties of long-lasting synaptic plasticity: two different forms of long-term potentiation (LTP) and at least one form of long-term depression (LTD). All forms of synaptic plasticity are induced by afferent activation, all involve Ca 2+ influx, all can be blocked by Ca 2+ chelators and all activate Ca 2+ dependent mechanisms. The question arises as how different physiological responses can be initiated by activation of the same second messenger. We consider two hypotheses which could account for these phenomena: voltage-dependent differences in cytosolic Ca 2+ concentration acting upon Ca 2+ substrates of differing Ca 2 + affinities, and compartmentalization of the Ca 2+ and its substrates.