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M Chesler

Publications and source records attributed to M Chesler.

At least 55 records · Page 3Linked to original sources
PubMed1991

Elevation and clearance of extracellular K+ following contusion of the rat spinal cord.

The elevation and clearance of extracellular potassium following a standard contusion injury was studied in the thoracic spinal cord of rats. Animals were anesthetized, paralyzed, laminectomized at T9-T11, then artificially ventilated. A 10-g rod was released 5.0 cm above the cord with the dura intact. After impact, the dura-arachnoid and pial membranes were incised to allow penetration of K(+)-selective microelectrodes. Electrodes utilized a valinomycin ionophore and were double-barreled, with tip diameters of 3-5 microns. Extracellular potassium activity ([K+]o) increased with the depth of penetration. The maximum values of [K+]o occurred at depths greater than 500 microns, and remained so with time after injury. These data indicate that a dorsal-ventral gradient of [K+]o develops in spinal cords contused from the dorsal surface, with the greatest elevation of [K+]o in the gray matter. In 8 preparations, the maximum [K+]o was 65 +/- 8 mM (mean +/- S.E.M.) at 5 +/- 1 min after injury. The [K+]o peak values decayed with a half-time of 11.0 +/- 3.4 min. Compared with data available for the injured cat spinal cord, the peak [K+]o recovered relatively rapidly. Although a simple diffusion model could account for the rapid clearance of [K+]o, the persistence of dorsal-ventral [K+]o gradients could not be explained by such a model. It is postulated that secondary injury processes contributed to the persistent [K+]o gradients.

Animals↗
PubMed1991

GABA-sensitivity of dorsal column axons: an in vitro comparison between adult and neonatal rat spinal cords.

In neonatal rat spinal cord, conduction in the dorsal column is reversibly depressed by GABA. We compared the GABA-sensitivity of dorsal columns in neonate versus adult rats, using in vitro isolated dorsal column preparations. The extracellular compound action potential evoked by submaximal stimuli was recorded with a glass micropipette. GABA (10(-4)-10(-3) M) reversibly depressed the compound action potential of both neonatal and adult rat dorsal columns. The GABA-induced reduction of dorsal column compound action potential amplitudes was blocked by the GABAA antagonist picrotoxin (10(-3) M) and mimicked by the GABAA agonist isoguvacine (10(-4-10(-3) M). The compound action potential reduction by GABA was far less pronounced on adult dorsal columns. The reduction of compound action potential amplitudes by isoguvacine (10(-4)-10(-3) M) was also significantly less in adult dorsal columns. These data suggest that GABAA receptors may play a role in extrasynaptic modulation of spinal long tract conduction in an age-dependent manner.

Action Potentials↗
PubMed1991

GABAA receptors modulate axonal conduction in dorsal columns of neonatal rat spinal cord.

gamma-Aminobutyric acid (GABA) can influence conduction in a number of axonal preparations from the peripheral and central nervous system. In the spinal cord, the excitability of primary afferent terminals has long been known to be affected by GABA. Whether conduction in the long fiber tracts of the spinal cord can be similarly modulated is unknown. Since GABA causes a pronounced depression of excitability in preparations of unmyelinated axons, and myelination is incomplete in the neonatal rat, we tested whether GABA can modulate conduction in the dorsal columns of 10-17-day-old rats. Experiments were performed in vitro, on isolated dorsal column segments (n = 18). The extracellular compound action potential evoked by submaximal stimuli was recorded with a glass micropipette positioned 0.5-2.0 mm from a stimulating electrode. At concentrations of 10(-4) - 10(-3) M, GABA decreased excitability, reversibly depressing the compound action potential amplitude, and increasing the latency by 47 +/- 11% and 22 +/- 9% (mean +/- S.E.M., n = 5, 10(-3) M), respectively. These effects were blocked by picrotoxin and mimicked by isoguvacine (10(-4) M), which decreased the compound action potential amplitude by 44 +/- 10% and increased the latency by 9 +/- 4% (n = 5). Lower concentrations of these agents caused a modest increase in excitability. At 10(-5) M, GABA increased the compound action potential amplitude by 14 +/- 2% and decreased the latency by 3 +/- 2% (n = 5). Our results demonstrate that functional GABAA receptors are present in neonatal dorsal columns.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1991

Extracellular alkaline-acid pH shifts evoked by iontophoresis of glutamate and aspartate in turtle cerebellum.

The effect of glutamate and aspartate iontophoresis on extracellular pH was investigated in the turtle cerebellum in vitro. Both amino acids produced a rapid alkaline transient, typically followed by a prolonged acidification. These responses could be evoked in all layers of the cerebellum. Transition from bicarbonate to N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered media amplified the pH shifts. Similar alkaline-acid transients could be evoked in the molecular layer by electrical stimulation of the parallel fibers or the ipsilateral peduncle, or by superfusion of glutamate or aspartate. However, no alkaline shifts were evoked in the granular layer by either parallel fiber or peduncle stimulation. In contrast, the iontophoretically induced alkaline shifts were largest in the granular layer. Compared with the stimulus-evoked alkalinizations, the iontophoretic alkaline shifts were relatively insensitive to Mn2+ or Cd2+. These data suggest that the activity-dependent alkalinization of brain extracellular space is generated by a bicarbonate-independent mechanism related to excitatory synaptic transmission. The results are consistent with a flux of hydrogen ions through cationic channels, but do not support a direct role for voltage-dependent Ca2+ channels. In view of the sensitivity of ion channels to changes in external pH, and the magnitude of the amino acid-induced pH shifts, these results indicate that extracellular pH could play an important modulatory role in excitatory synaptic transmission.

Animals↗
PubMed1991

Extracellular alkalinization evoked by GABA and its relationship to activity-dependent pH shifts in turtle cerebellum.

1. The effect of gamma-aminobutyric acid (GABA) on extracellular pH (pHo) was investigated in the turtle cerebellum, in vitro, using double-barrelled, H(+)-selective microelectrodes. Responses evoked by GABA were compared with pHo shifts evoked by repetitive stimulation of the parallel fibres. 2. In media buffered with 35 mM-HCO3- and 5% CO2, superfusion of GABA (1 mM) elicited an abrupt alkaline shift in the molecular layer, which averaged 0.05 +/- 0.02 pH units (+/- S.D., range 0.02-0.12 pH units). pHo often recovered in the continued presence of GABA, and displayed a rebound acidification upon wash-out. 3. The GABA-evoked alkaline shift was blocked by picrotoxin and was mimicked by the GABAA agonists isoguvacine and muscimol. The GABAB agonist baclofen did not elicit an alkaline shift. Alkaline shifts evoked by stimulation of the parallel fibres were unaffected by picrotoxin. 4. In nominally HCO3(-)-free solutions, buffered with 35 mM-HEPES, superfusion of GABA caused either no pHo change or a slow acid shift. In contrast, the alkaline shift evoked by stimulation of the parallel fibres became enhanced in HEPES-buffered media. 5. The alkaline shift evoked by GABA was accompanied by an increase in extracellular K+ ([K+]o) which averaged 1.7 mM above baseline. Experimental elevation of [K+]o to a comparable level always caused a pure acid shift in the extracellular space. 6. The GABA-evoked alkaline shift persisted when synaptic transmission was blocked using 4 mM-kynurenic acid or saline prepared with nominally zero Ca2+ and 10 mM-Mg2+. The alkaline shift evoked by repetitive stimulation of the parallel fibres was completely abolished in these media. 7. Although the GABA-evoked alkaline shift was blocked in nominally HCO3(-)-free media, substitution of 35 mM-formate for HCO3- restored the GABA response. Superfusion of 1 mM-GABA in formate saline produced an alkaline shift of 0.040 +/- 0.034 pH units. 8. These results indicate that gating of GABAA channels in the vertebrate CNS gives rise to an HCO3- efflux which can significantly increase the pH of the brain microenvironment. However, this mechanism cannot account for the extracellular alkalinization caused by parallel fibre stimulation. Extracellular alkaline shifts capable of modulating local synaptic operations may therefore be a consequence of either excitatory or inhibitory synaptic transmission.

Animals↗
PubMed1990

A bicarbonate-dependent increase in extracellular pH mediated by GABAA receptors in turtle cerebellum.

The gamma-aminobutyric acid (GABA)-gated anion channel has been found to have a significant permeability to bicarbonate in isolated nerve cells and crayfish muscle. We have studied the extracellular pH of the in vitro turtle cerebellum to determine whether the extracellular pH of vertebrate brain can be modulated by GABA. Exposure to 10(-3) M GABA produced an extracellular alkaline transient with a mean amplitude of 0.054 +/- 0.19 pH units (n = 49, range 0.018-0.091 pH units). The GABA-evoked alkaline shift was blocked by picrotoxin and was dependent on the presence of HCO3- in the bathing media. These data suggest that GABAA receptors gate an HCO3(-)-efflux which is sufficient to modulate brain pH.

Animals↗
PubMed1990

Astrocytic acidosis in hyperglycemic and complete ischemia.

Nearly complete brain ischemia under normoglycemic conditions results in death of only selectively vulnerable neurons. With prior elevation of brain glucose, such injury is enhanced to include pancellular necrosis (i.e., infarction), perhaps because an associated, severe lactic acidosis preferentially injures astrocytes. However, no direct physiologic measurements exist to support this hypothesis. Therefore, we used microelectrodes to measure intracellular pH and passive electrical properties of cortical astrocytes as a first approach to characterizing the physiologic behavior of these cells during hyperglycemic and complete ischemia, conditions that produce infarction in reperfused brain. Anesthesized rats (n = 26) were made extremely hyperglycemic (blood glucose, 51.4 +/- 2.8 mM) so as to create potentially the most extreme acidic conditions possible; then ischemia was induced by cardiac arrest. Two loci more acidic than the interstitial space (6.17-6.20 pH) were found. The more acidic locus [4.30 +/- 0.19 (n = 5); range: 3.82-4.89] was occasionally seen at the onset of anoxic depolarization, 3-7 min after cardiac arrest. The less acidic locus [5.30 +/- 0.07 (n = 53); range 4.46-5.93)] was seen 5-46 min after cardiac arrest. A small negative change in DC potential [8 +/- 1 mV (n = 5); range -3 to -12 mV and 7 +/- 2 mV (n = 53); range +3 to -31 mV, respectively] was always seen upon impalement of acidic loci, suggesting cellular penetration. In a separate group of five animals, electrical characteristics of these cells were specifically measured (n = 17): membrane potential was -12 +/- 0.2 mV (range -3 to -24 mV), input resistance was 114 +/- 16 M omega (range 25-250 M omega), and time constant was 4.4 +/- 0.4 ms (range 3.0-7.9 ms). Injection of horseradish peroxidase into cells from either animal group uniformly stained degenerating astrocytes. These findings establish previously unrecognized properties of ischemic astrocytes that may be prerequisites for infarction from nearly complete ischemia: the capacity to develop profound cellular acidosis and a concomitant reduction in cell membrane ion permeability.

Acid-Base Equilibrium↗
PubMed1989

Intracellular pH transients of mammalian astrocytes.

Intracellular pH (pHi) is an important physiologic variable that both reflects and influences cell function. Glial cells are known to alter their functional state in response to a variety of stimuli and accordingly may be expected to display corresponding shifts in pHi. We used fine-tipped, double-barreled, pH-sensitive microelectrodes to continuously monitor pHi in glial cells in vivo from rat frontal cortex. Cells were identified as glia by a high membrane potential and lack of injury discharge or synaptic potentials. Continuous, stable recordings of pHi from astrocytes were obtained for up to 80 min but typically lasted for approximately 10 min. Resting pHi was 7.04 +/- 0.02 with a membrane potential of 73 +/- 0.9 mV (mean +/- SEM; n = 51). With cortical stimulation, glia depolarized and became more alkaline by 0.05-0.40 pH (n = 50). During spreading depression (SD), glia shifted more alkaline by 0.11-0.78 pH (n = 26). After stimulation or SD, glia repolarized and pHi became more acidic than at resting levels. Superfusion of the cortical surface with 0.5-2 mM Ba2+ caused glia to hyperpolarize during stimulation and completely abolished the intracellular alkaline response. The predominant pH response of the interstitial space during stimulation or SD was a slow acidification. With superfusion of Ba2+ an early stimulus-evoked interstitial alkaline shift was revealed. The mechanism of the intracellular alkaline shift is likely to involve active extrusion of acid. However, internal consumption of protons cannot be excluded. The sensitivity of the response to Ba2+ suggests that it is triggered by membrane depolarization. These results suggest that glial pHi is normally modulated by the level of local neuronal activity.

Animals↗
PubMed1988

Activity-related extracellular potassium transients in the neonatal rat spinal cord: an in vitro study.

Transient increases and decreases in extracellular potassium (delta[K+]o) were recorded from the gray matter of hemisected, neonatal rat spinal cords isolated from 3, 4, 9- and 10-day-old pups. delta[K+]o were evoked in both the ventral and dorsal regions of the gray matter by electrical stimulation. In the ventral horn, repetitive stimulation of the ventral root was required to elicit detectable delta[K+]o. By contrast, single dorsal root stimuli evoked clear delta[K+]o. In the dorsal horn, single orthodromic stimuli elicited delta[K+]o as large as 4-5 mM from a baseline of 4.5 mM. With repetitive stimulation the [K+]o reached, but never exceeded, a ceiling of 10-11 mM. Undershoots were seen only after repetitive stimulation. Spontaneous delta[K+]o were observed in the ventral horn and were well correlated with ventral root activity. Spontaneous delta[K+]o were rare in the dorsal cord, but were recorded after bath application of apamin or tetraethylammonium. The magnitude and distribution of evoked K+ transients and postsynaptic components of the evoked field potential were well correlated in both the dorsal and the ventral gray matter. delta[K+]o were reversibly blocked by 1 mM CdCl2 in the bath and diminished by 1 mM BaCl2. Bath application of mephenesin, apamin or tetraethylammonium diminished evoked delta[K+]o in a stimulus-dependent manner. In apamin and tetraethylammonium, decreases from control responses were largest with high intensity stimulation, the opposite was the case with mephenesin. These results are interpreted in terms of the spinal circuits activated by high- and low-intensity electrical stimulation. We conclude that activity-related delta[K+]o in neonatal spinal cord are large enough to modulate neuronal electrical activity and the [K+]o is well regulated compared to other immature CNS regions studied. Thus, local increases in [K+]o may, by modulating neuronal activity, play a role in neonatal spinal cord developmental processes.

Action Potentials↗
PubMed1988

Stimulus-induced extracellular pH transients in the in vitro turtle cerebellum.

In a number of CNS preparations, neuronal activation has been shown to result in a rapid extracellular alkaline transient, followed by a prolonged acid shift. The isolated turtle cerebellum was used to investigate the early alkaline transient. Double-barreled ion-sensitive microelectrodes for H+, K+ and tetramethylammonium were used to measure field potentials and extracellular ion and volume shifts in response to bipolar electrical stimulation of the parallel fibers. Transition from 15 mM HEPES to 35 mM HCO3- -buffered Ringer decreased the amplitude of the alkaline shift, presumably due to a marked increase in extracellular buffering power. In HEPES-buffered Ringer, repetitive stimulation produced alkaline shifts as large as 0.3-0.4 pH. Single shocks produced an alkaline shift of 0.006 +/- 0.0002 pH with a latency as short as 70 ms. Kynurenic acid (an excitatory amino acid antagonist), or Mn2+, blocked the alkaline shift and the postsynaptic component of the field potential. The alkaline shift was not blocked by the Na-H exchange inhibitor amiloride. The relationship between pHo and extracellular volume transients was studied using tetramethylammonium as an extracellular volume indicator. In nominally HCO3-free Ringer, stimulation at 5 Hz for 10 s caused a decrease in extracellular volume of 3.0 +/- 0.2 per cent. The volume transient was unaffected by 3 mM Mn2+, while the alkaline shift was completely abolished. The data for the alkaline shift are consistent with a channel-mediated transmembrane flux of proton equivalents. The size of the pH change and the underlying perturbation it represents, indicate that acid-base shifts may be a functionally important consequence of neuronal activity.

Action Potentials↗
PubMed1987

pH regulation in the vertebrate central nervous system: microelectrode studies in the brain stem of the lamprey.

Studies of intracellular pH (pHi) in nervous tissue are summarized and recent investigation of intracellular and extracellular pH (pHo) in the isolated brain stem of the lamprey is reviewed. In the lamprey, pHi regulation was studied in single reticulospinal neurons using double-barrel ion-selective microelectrodes (ISMs). In nominally HCO3(-)-free HEPES-buffered media, acute acid loading was followed by a spontaneous recovery of pHi requiring 10-20 min and was associated with a prolonged rise in intracellular Na+. The recovery of pHi was blocked by 1-2 mM amiloride. Amiloride also caused a small rise in pHo. Substitution of external Na+ caused a slow intracellular acidification and extracellular alkalinization. Return of external Na+ reversed these effects. Transition from HEPES to HCO3(-)-buffered media increased the rate of acid extrusion during recovery of pHi. Recovery in HCO3(-)-buffered media was inhibited by 4,4'-diisothio-cyanostilbene-2,2'-disulfonic acid and was slowed after exposure to Cl(-)-free media. Following inhibition of acid extrusion by amiloride, transition to HCO3- media restored pHi recovery. These data indicate that lamprey neurons recover from acute acid loads by both Na+-H+ exchange and an independent HCO3(-)-dependent mechanism. Evidence for HCO3(-)-dependent acid extrusion in other vertebrate cells and the protocols of pHi studies using ISMs are discussed.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1987

Intracellular pH of astrocytes increases rapidly with cortical stimulation.

Modulation of intracellular pH is widely implicated in the control of cell growth and metabolism, yet little is known about intracellular pH and brain function. To determine how stimulation of brain may affect the intracellular pH of mammalian glial cells, rat cortical astrocytes were studied for the first time in vivo using pH-sensitive electrodes of submicron caliber. Stimulation of the cortical surface caused a cytoplasmic alkaline shift of tenths of a pH within seconds. Cessation of induced electrical activity was followed by pH recovery and a small acid rebound. Recordings obtained during cortical-spreading depression revealed similar but generally larger intracellular pH shifts. Production of metabolic acids is known to occur when the brain is stimulated and has led to the long-held presumption that brain cells accordingly become more acidic. The observation that glia initially become more alkaline during electrical activity is thus paradoxical. The correlation of glial alkalinization with evoked electrical activity suggests that modulation of intracellular pH of glia may have important functional implications.

Animals↗
PubMed1986

The medical context of parental coping with childhood cancer.

This research assessed the extent to which contextual factors, especially the medical context, are related to the use of specific coping strategies by 74 parents of surviving children with cancer. Parents reported that they coped reasonably well by using information-seeking, problem-solving, help-seeking, maintaining emotional balance, relying on religion, being optimistic, denying, and accepting. More highly educated parents tended to use problem solving, optimism, and information seeking significantly more and denial significantly less than well-educated parents. However, gender and income were unrelated to coping. The use of specific coping strategies was not related to severity of the child's medical condition, stress level, or parents' own evaluations of their coping effectiveness. However, the quality of relations with the medical staff was strongly related to coping strategies. Use of passive coping strategies was positively related to good relations with the medical staff.

Adaptation, Psychological↗
PubMed1986

Regulation of intracellular pH in reticulospinal neurones of the lamprey, Petromyzon marinus.

1. The regulation of intracellular pH (pHi) in lamprey reticulospinal neurones was investigated with pH-sensitive micro-electrodes based on a neutral carrier liquid membrane. Experiments were performed using an in vitro brain-stem preparation. 2. In HEPES-buffered solutions, extracellular pH (pHo) was consistently more acidic than the pH of the bathing solution (pHb). In HCO3(-)-buffered solutions, the brain was also relatively acidic, but the brain pH gradient was smaller. 3. In HEPES- and HCO3(-)-buffered solutions, mean pHi was 7.40-7.50. This range was too high to be explained by a passive distribution of H+, OH- or HCO3-. 4. In nominally HCO3(-)-free, HEPES-buffered solution, cells were acid loaded by addition and subsequent withdrawal of NH4+ from the superfusate. pHi recovered from acid loading by an energy-dependent process in 10-20 min. Recovery from acid loading in HEPES-buffered solutions was blocked by exposure to amiloride. 5. Removal of extracellular Na+ caused a slow, accelerating fall of pHi. Return of Na+ to the bath caused an immediate reversal of this acidification, followed by a slow recovery of pHi. Measurement with Na+-sensitive micro-electrodes during acid loading showed a rapid rise in the intracellular Na+ activity [( Na+]i). 6. Following acid loading, transition from HEPES- to HCO3(-)-buffered solutions caused an increase in the acid extrusion rate of at least 48%. The effect of these solution changes was dependent on pHo. After blocking pHi recovery with amiloride, transition from HEPES- to HCO3(-)-buffered Ringer plus amiloride produced a slow recovery of pHi. 7. Recovery from acid loading in HCO3(-)-buffered solutions was inhibited 65% by the anion transport blocker DIDS (4,4'-diisothiocyanostilbene-2,2'-disulphonic acid). Recovery from acid loading after incubation in Cl(-)-free solution was slower than recovery after replenishment of Cl-. 8. It is concluded that in HCO3(-)-free solutions, pHi regulation is accomplished by a Na-H exchange mechanism. In the presence of extracellular HCO3- an additional mechanism can operate to extrude intracellular acid.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1985

Organization of the filum terminale in the frog.

The histological organization of the filum terminale of the spinal cord in Rana catesbeiana and Rana pipiens was characterized to determine if this region possessed an organized neuropil or whether it was merely a glial remnant that persisted after absorption of the larval tail. The excised filum was maintained in vitro. Intracellular electrophysiological recording was performed with horseradish peroxidase injection. Tyrosine hydroxylase and serotonin distribution were revealed by immunocytochemical methods. Astroglia were the dominant cell type and displayed an elaborate variety of forms. The mean membrane potential was logarithmically related to the extracellular potassium concentration but displayed a sub-Nernstian slope. Oligodendroglia were also seen, as well as ependyma that extended from the central canal to the pial surface. Neuronal activity was revealed by occasional intracellular penetration of elements that displayed spontaneous excitatory postsynaptic or action potentials. The major evidence for the presence of neurons was the demonstration of tyrosine hydroxylase (TH) immunoreactivity in a large population of cerebrospinal fluid-contacting neurons that abutted the ventral half of the central canal. The axons of these cells entered a ventral bundle and ascended the cord; some fibers left this tract and apparently terminated on large arcuate neurons within the filum. Serotoninergic fibers were primarily confined to a subpial location at the dorsal midline. We conclude that the filum terminale of the frog has a sparse but functional neuropil that is organized around the central canal and supported by a profusion of elaborate glial forms.

Animals↗
PubMed1985

Regulation of intracellular pH in vertebrate central neurons.

The regulation of intracellular pH (pHi) was investigated in reticulospinal neurons of the lamprey using ion-selective microelectrodes. Steady-state pHi in 23 mM HCO-3-buffered Ringer was 7.44 +/- 0.03 with a membrane potential of 54 +/- 4 mV (mean +/- S.E.M., n = 6). In nominally HCO-3-free solutions, pHi recovery from acid loading was blocked by 10(-3)M amiloride. Recovery was stimulated by transition to HCO-3-containing solutions. Results suggest that pHi regulation in lamprey reticulospinal neurons is mediated by a Na+-H+ exchanger. The presence of a distinct, HCO-3-dependent pHi regulatory mechanism is postulated.

Amiloride↗