Modulation of the Acetylcholine-Induced Input Current by Noopept in Helix Lucorum Neurons

Biophysics - Abstract—Possible causes of the positive modulating effect of noopept (in a concentration range of 0.1 to 10 nM) on the amplitude of the acetylcholine-induced input...     

Long-term potentiation of neuronal glutamate transporters

Persistent, use-dependent modulation of synaptic strength has been demonstrated for fast synaptic transmission mediated by glutamate and has been hypothesized to underlie persistent behavioral changes ranging from memory to addiction. Glutamate released at synapses is sequestered by the action of excitatory amino acid transporters (EAATs) in glia and postsynaptic neurons. So, the efficacy of glutamate transporter function is crucial for regulating glutamate spillover to adjacent presynaptic and postsynaptic receptors and the consequent induction of plastic or excitotoxic processes. Here, we report that tetanic stimulation of cerebellar climbing fiber-Purkinje cell synapses results in long-term potentiation (LTP) of a climbing fiber-evoked glutamate transporter current recorded in Purkinje cells. This LTP is postsynaptically expressed and requires activation of an mGluR1/PKC cascade. Together with a simultaneously induced long-term depression (LTD) of postsynaptic AMPA receptors, this might reflect an integrated antiexcitotoxic cellular response to strong climbing fiber synaptic activation, as occurs following an ischemic episode.     

Heterosynaptic potentiation of cholinergic excitatory postsynaptic responses in the Helix command neurons

Heterosynaptic potentiation of cholinergic excitatory postsynaptic currents and potentials evoked by electrical stimulation of visceral mass was discovered in command Helix neurons of escape reaction. The results suggest the involvement of mechanism of an increase in cholinosensitvity in postsynaptic membrane zones in potentiation of excitatory postsynaptic responses to sensory stimulation.     

Inhibition of apoptotic signaling cascades causes loss of trophic factor dependence during neuronal maturation

During development, neurons are acutely dependent on target-derived trophic factors for survival. This dependence on trophic support decreases dramatically with maturation in several neuronal populations, including sympathetic neurons. Analyses of nerve growth factor deprivation in immature and mature sympathetic neurons indicate that maturation aborts the cell death pathway at a point that is mechanistically indistinguishable from Bax deletion. However, neither the mRNA nor protein level of BAX changes with neuronal maturation. Therefore, BAX must be regulated posttranslationally in mature neurons.Nerve growth factor deprivation in immature sympathetic neurons induces two parallel processes: (a) a protein synthesis-dependent, caspase-independent translocation of BAX from the cytosol to mitochondria, followed by mitochondrial membrane integration and loss of cytochrome c; and (b) the development of competence-to-die, which requires neither macromolecular synthesis nor BAX expression. Activation of both signaling pathways is required for caspase activation and apoptosis in immature sympathetic neurons. In contrast, nerve growth factor withdrawal in mature sympathetic neurons did not induce the translocation of either BAX or cytochrome c. Moreover, mature neurons did not develop competence-to-die with cytoplasmic accumulation of cytochrome c. Therefore, inhibition of both BAX-dependent cytochrome c release and the development of competence-to-die contributed to the loss of trophic factor dependence associated with neuronal maturation.     

Identified neuronal individuals in the buccal ganglia of Helix pomatia.

The buccal ganglia of Helix pomatia are used as model nervous structures in neurophysiological and in epileptological studies. Many basic problems concerning membrane physics, functioning of the single neurons and of neuronal networks can be studied easily using these ganglia. The model character mainly comes from the relative simplicity of this nervous system and that it contains large visually identifiable neurons. As in other invertebrate nervous systems, the large neurons have proved to be individuals showing the same functional and structural properties from one animal to the next.     

Caffeine and length dependence of staircase potentiation in skeletal muscle

Skeletal muscle sensitivity to Ca2+ is greater at long lengths, and this results in an optimal length for twitch contractions that is longer than optimal length for tetanic contractions. Caffeine abolishes this length dependence of Ca2+ sensitivity. Muscle length (ML) also affects the degree of staircase potentiation. Since staircase potentiation is apparently caused by an increased Ca2+ sensitivity of the myofilaments, we tested the hypothesis that caffeine depresses the length dependence of staircase potentiation. In situ isometric twitch contractions of rat gastrocnemius muscle before and after 10 s of 10-Hz stimulation were analyzed at seven different lengths to evaluate the length dependence of staircase potentiation. In the absence of caffeine, length dependence of Ca2+ sensitivity was observed, and the degree of potentiation after 10-Hz stimulation showed a linear decrease with increased length (DT = 1.47 - 0.05 ML, r2 = 0.95, where DT is developed tension). Length dependence of Ca2+ sensitivity was decreased by caffeine when caffeine was administered in amounts estimated to result in 0.5 and 0.75 mM concentrations. Furthermore, the negative slope of the relationship between staircase potentiation and muscle length was diminished at the lower caffeine dose, and the slope was not different from zero after the higher dose (DT = 1.53 - 0.009 ML, r2 = 0.43). Our study shows that length dependence of Ca2+ sensitivity in intact skeletal muscle is diminished by caffeine. Caffeine also suppressed the length dependence of staircase potentiation, suggesting that the mechanism of this length dependence may be closely related to the mechanism for length dependence of Ca2+ sensitivity.     

The dependence of thermopreferendum in Helix pomatia L. on air temperature

Behavioural tests with 192 specimen of the roman garden snail Helix pomatia L. were performed in order to clarify whether the thermopreferendum of this pulmonate is influenced not only by the temperature of the substratum but also by air temperature. For this purpose, the snails were exposed to a horizontal temperature gradient of the substratum at different air temperatures between 10 and 30 degrees C. The results show that the selection of substratum temperature depends on the air temperature: the lower the air temperature, the lower is the temperature of the substratum preferred by the snails. Obviously, the animals tend to keep the difference between air temperature and temperature of the substratum as small as possible. This behaviour might be a mechanism to reduce the temperature gradient in the snail's body and to adjust the metabolic rate to cardiac output.     

Satellite glial cell responses to neuronal firing in the nervous system of Helix pomatia

Patch clamp experiments were conducted on satellite glial cells attached to the cell body of neurons in place within the nervous system of the snail Helix pomatia. The glial cells were studied using cell-attached and whole-cell patch clamp configurations while the underlying neurons were under current or voltage clamp control.The resting potential of the glial cells (–69 mV) was more negative than that of the underlying neurons (–53 mV), due to their high K⁺ selectivity. Densely packed K⁺ channels were present, some of which were active at the cell resting potential. Neuronal firing elicited a cumulative depolarization of the glial cells. Large K⁺ currents flowing from V-clamped neurons depolarized the glial layer by up to 30 mV. The glial depolarization was directly correlated with the size of the neuronal K⁺ current. The glial cells recovered their resting potential within 2–5 sec. The neuronal depolarization induced a delayed (20–30 sec) and persistent (3–4 min) increase in the glial K⁺ channel opening probability. Likewise, pulses of K⁺ (20–50 mM)-rich saline activated the glial channels, unless the underlying neuron was held hyperpolarized. In low Ca²⁺-high Mg²⁺ saline, neuron depolarization and K⁺-rich saline did not activate the glial K⁺ channels.These data indicate that a calcium-dependent signal released from the neuronal cell body was involved in glial channel regulation. Neuron-induced channel opening may help eliminate the K⁺ ions flowing from active neurons.I. Gommerat is recipient of a fellowship from the Ministère de la Recherche et de la Technologie.This work was supported by the CNRS and by a grant from the Fondation pour la Recherche Médicale. We would like to thank Mrs. M. André and Mr. G. Jacquet for technical assistance and Mrs. J. Blanc for improving the English.     

Recording site dependence of the neuronal spiking statistics

Spiking characteristics of neurons in the middle temporal (MT) area and the medial superior temporal (MST) area in the visual cortex of a monkey are compared with the ones in the principal sulcus (PS) area in the prefrontal cortex. The comparison is based on the basis of three inter-spike interval statistical measures: the coefficient of variation (CV), the skewness coefficient (SK) and the correlation coefficient of consecutive intervals (COR). Even for the spike sequences recorded from the same neuron, three coefficients computed from 100 intervals do not always exhibit similar values, but distribute rather widely. The distribution of three coefficients obtained from a single neuron in the MST area does not largely deviate from the distribution obtained from multiple neurons in MT and MST areas. Those distributions, however, largely deviate from the distribution obtained from neurons in the PS area. In this way, the distribution of those statistical coefficients reflects the nature of the recording site.     

Helix bending as a factor in protein/DNA recognition

Normal vectors perpendicular to individual base pairs are a powerful tool for studying the bending behavior of B-DNA, both in the form of normal vector plots and in matrices that list angles between vectors for all possible base pair combinations. A new analysis program, FREEHELIX, has been written for this purpose, and applied to 86 examples of sequence-specific protein/DNA complexes whose coordinates are on deposit in the Nucleic Acid Data Base. Bends in this sample of 86 structures almost invariably follow from roll angles between adjacent base pairs; tilt makes no net contribution. Roll in a direction compressing the broad major groove is much more common than that which compresses the minor groove. Three distinct types of B-DNA bending are observed, each with a different molecular origin: (1) Localized kinking is produced by large roll at single steps or at two steps separated by one turn of helix. (2) Smooth, planar curvature is produced by positive and negative roll angles spaced a half-turn apart, with random side-to-side zigzag roll at intermediate points, rather than a tilt contribution that might have been expected theoretically. (3) Three-dimensional writhe results from significant roll angles at a continuous series of steps. Writhe need not change the overall direction of helix axis, if it is continued indefinitely or for an integral number of helical turns. A-DNA itself can be formally considered as possessing uniform, continuous writhe that yields no net helix bending. Smooth curvature is the most intricate deformation of the three, and is least common. Writhe is the simplest deformation and is most common; indeed, a low level of continuous writhe is the normal condition of an otherwise unbent B-DNA helix of general sequence. With one exception, every example of major kinking in this sample of 86 structures involves a pyrimidine–purine step: C–A/T–G, T–A, or C–G. Purine–purine steps, especially A–A, show the least tendency toward roll deformations. © 1998 John Wiley & Sons, Inc. Biopoly 44: 361–403, 1997     

Competitive potentiation of acetylcholine effects on neuronal nicotinic receptors by acetylcholinesterase-inhibiting drugs

The effects of the acetylcholinesterase inhibitors physostigmine and tacrine on alpha4beta2 and alpha4beta4 subtypes of neuronal nicotinic acetylcholine (ACh) receptors, expressed in Xenopus laevis oocytes, have been investigated. In voltage-clamp experiments low concentrations of physostigmine and tacrine potentiate ion currents induced by low concentrations of ACh, whereas at high concentrations they inhibit ACh-induced ion currents. These dual effects result in bell-shaped concentration-effect curves. Physostigmine and tacrine, by themselves, do not act as nicotinic receptor againsts. The larger potentiation is observed with 10 microM: physostigmine on alpha4beta4 nicotinic receptors and amounts to 70% at 1 microM: ACh. The mechanism underlying the effects of physostigmine on alpha4beta4 ACh receptors has been investigated in detail. Potentiation of ACh-induced ion current by low concentrations of physostigmine is surmounted at elevated concentrations of ACh, indicating that this is a competitive effect. Conversely, inhibition of ACh-induced ion current by high concentrations of physostigmine is not surmounted at high concentrations of ACh, and this effect appears mainly due to noncompetitive, voltage-dependent ion channel block. Radioligand binding experiments demonstrating displacement of the nicotinic receptor agonist (125)I-epibatidine from its recognition sites on alpha4beta4 ACh receptors by physostigmine confirm that physostigmine is a competitive ligand at these receptors. A two-site equilibrium receptor occupation model, combined with noncompetitive ion channel block, accounts for the dual effects of physostigmine and tacrine on ACh-induced ion currents. It is concluded that these acetylcholinesterase-inhibiting drugs interact with the ACh recognition sites and are coagonists of ACh on alpha4-containing nicotinic ACh receptors.     

Humoral factor activating the Sarcophaga lectin gene in cultured fat body

On culture of the fat body of Sarcophaga peregrina (flesh fly) larvae in modified Grace's medium, the Sarcophaga lectin gene was activated only when the medium was supplemented with larval hemolymph. The expressions of the genes for the storage protein and the sarcocystatin A were not affected by supplementing the medium with the hemolymph. Thus the hemolymph contained a factor that specifically activated the Sarcophaga lectin gene. This factor seemed to be a heat-stable, low molecular weight compound that was probably not a peptide, and to activate genes in the fat body for defense proteins that are known to be expressed in response to injury of Sarcophaga larvae.     

Length dependence of staircase potentiation: interactions with caffeine and dantrolene sodium

In skeletal muscle, there is a length dependence of staircase potentiation for which the mechanism is unclear. In this study we tested the hypothesis that abolition of this length dependence by caffeine is effected by a mechanism independent of enhanced Ca2+ release. To test this hypothesis we have used caffeine, which abolishes length dependence of potentiation, and dantrolene sodium, which inhibits Ca2+ release. In situ isometric twitch contractions of rat gastrocnemius muscle before and after 20 s of repetitive stimulation at 5 Hz were analyzed at optimal length (Lo), Lo - 10%, and Lo + 10%. Potentiation was observed to be length dependent, with an increase in developed tension (DT) of 78 +/- 12, 51 +/- 5, and 34 +/- 9% (mean +/- SEM), at Lo - 10%, Lo, and Lo + 10%, respectively. Caffeine diminished the length dependence of activation and suppressed the length dependence of staircase potentiation, giving increases in DT of 65+/-13, 53 +/- 11, and 45 +/- 12% for Lo - 10%, Lo, and Lo + 10%, respectively. Dantrolene administered after caffeine did not reverse this effect. Dantrolene alone depressed the potentiation response, but did not affect the length dependence of staircase potentiation, with increases in DT of 58 +/- 17, 26 +/- 8, and 18 +/- 7%, respectively. This study confirms that there is a length dependence of staircase potentiation in mammalian skeletal muscle which is suppressed by caffeine. Since dantrolene did not alter this suppression of the length dependence of potentiation by caffeine, it is apparently not directly modulated by Ca2+ availability in the myoplasm.     

Quantal analysis of long-term potentiation of combined neuronal postsynaptic potentials on hippocampal slices in vitro

Excitatory postsynaptic potentials (EPSP) were recorded from 14 neurons in guinea pig hippocampal slices (area CAl) after stimulating the stratum radiatum (Schaffer collaterals) and stratum oriens. An increase occurring in EPSP amplitude in 7 units (9 pathways) recorded 15–45 min after tetanic stimulation of Schaffer collaterals is viewed as long-term potentiation (LTP). Statistical analysis conducted according to two sets of quantal theory (histogram and variance methods) showed an increase in mean quantal content (m) during LTP. An increase in quantal size, found only when using the histogram method, did not correlate with LTP level. This increase is thought to be associated with the considerably greater sensitivity of the histogram method to noise level in comparison with the variance method, the latter being more reliable with signals of high noise level. The increase found in m using both methods matches findings previously obtained for the whole brain; it also points to presynaptic location of mechanisms responsible for raised synaptic efficacy during LTP.Institute for Brain Research, All-Union Mental Health Research Center, Academy of Medical Sciences of the USSR, Moscow. Max-Planck Institute of Biophysical Chemistry, Göttingen, West Germany. Institute of Zoology, Jagiellonian University, Cracow, Poland. Translated from Neirofiziologiya, Vol. 22, No. 4, pp. 465–472, July–August, 1990.     

CO2 chemosensitivity in Helix aspersa: three potassium currents mediate pH-sensitive neuronal spike timing

Elevated levels of carbon dioxide increase lung ventilation in Helix aspersa. The hypercapnic response originates from a discrete respiratory chemosensory region in the dorsal subesophageal ganglia that contains CO₂-sensitive neurons. We tested the hypothesis that pH-dependent inhibition of potassium channels in neurons in this region mediated the chemosensory response to CO₂. Cells isolated from the dorsal subesophageal ganglia retained CO₂ chemosensitivity and exhibited membrane depolarization and/or an increase in input resistance during an acid challenge. Isolated somata expressed two voltage-dependent potassium channels, an A-type and a delayed-rectifier-type channel (I_KA and I_KDR). Both conductances were inhibited during hypercapnia. The pattern of voltage dependence indicated that I_KA was affected by extracellular or intracellular pH, but the activity of I_KDR was modulated by extracellular pH only. Application of inhibitors of either channel mimicked many of the effects of acidification in isolated cells and neurons in situ. We also detected evidence of a pH-sensitive calcium-activated potassium channel (I_KCa) in neurons in situ. The results of these studies support the hypothesis that I_KA initiates the chemosensory response, and I_KDR and I_KCa prolong the period of activation of CO₂-sensitive neurons. Thus multiple potassium channels are inhibited by acidosis, and the combined effect of pH-dependent inhibition of these channels enhances neuronal excitability and mediates CO₂ chemosensory responses in H. aspersa. We did not find a single "chemosensory channel," and the chemosensitive channels that we did find were not unique in any way that we could detect. The protein "machinery" of CO₂ chemosensitivity is probably widespread among neurons, and the selection process whereby a neuron acts or does not act as a respiratory CO₂ chemosensor probably depends on the resting membrane potential and synaptic connectivity. carbon dioxide