Serotonin modulates oscillations of the membrane potential in isolated spinal neurons from lampreys.

Studies were performed on spinal neurons from lampreys isolated by an enzymatic/mechanical method using pronase. The effects of 100 microM serotonin (5-HT) on membrane potential oscillations induced by a variety of excitatory amino acids were studied. 5-HT was found to depolarize branched cells (presumptive motoneurons and interneurons) by 2-6 mV without inducing membrane potential oscillations.

The effects of serotonin on functionally diverse isolated lamprey spinal cord neurons.

The experiments reported here showed that application of serotonin (5-hydroxytryptamine, 5-HT) (100 microM) did not induce any significant current through the membranes of any of the spinal neurons studied (n = 62). At the same time, the membranes of most motoneurons and interneurons (15 of 18) underwent slight depolarization (2-6 mV) in the presence of 5-HT, which was not accompanied by any change in the input resistance of the cells. Depolarization to 10-20 mV occurred in some cells (3 of 18) of these functional groups, this being accompanied by 20-60% decreases in input resistance.

[Serotonin modulates oscillation parameters of the membrane potential in isolated spinal neurons in the lamprey].

The 5-HT was shown to depolarize branch cells (supposedly motoneurones and interneurones) by 2-6 mV, inducing, however, no MP oscillations. In case the MP oscillations were present (induced by the NMDA, for instance), the 5-HT altered their parameters: increased the amplitude of all types of oscillations, frequency of irregular oscillations, and duration of the depolarising plateau with the AP discharges. This modulation of the induced oscillations may enhance activity of neuronal locomotor network and thus reinforce muscle contractions and increase the intensity of the animal's movements.

[Effect of serotonin on isolated cells with the various functionality from the lamprey spinal cord].

The differential actions of 5-hydroxytryptamine (5-HT) (100 microM) were investigated on isolated motoneurons, interneurons, and primary sensory neurons from the lamprey spinal cord using patch-clamp techniques. Application of 5-HT did not evoke membrane currents in any of the spinal neurons tested (n = 62). However, in most motoneurons and interneurons (15 of 18), 5-HT produced a small depolarization (2-6 mV), which was not accompanied by a change in input resistance.

[Inhibition in the lamprey spinal cord].

Glycine and GABA play the role of inhibitory transmitters in the lamprey spinal cord. The mechanisms of action of both amino acids to the membrane receptors producing the postsynaptic inhibition as well as role and mechanism of GABA action producing the presynaptic inhibition are considered in this paper. The data concerned with morphological substrates of both type inhibitions are discussed.

Physiological and morphological correlates of presynaptic inhibition in primary afferents of the lamprey spinal cord.

Patch-clamp recordings in a whole-cell mode were performed on dorsal sensory cells enzymatically isolated from the spinal cord of two lamprey species, Ichthyomyzon unicuspis and Lampetra fluviatilis. The voltage-activated currents through calcium channels were analysed. GABA and the specific GABA(B) receptor agonist baclofen reduced the peak amplitude of inward Ba2+ current, as a robust alternate charge carrier through voltage-dependent Ca2+ channels.

The effects of baclofen on calcium channel currents in dorsal sensory cells of the spinal cord in the lamprey.

Dorsal sensory cells isolated from the spinal cord of the lamprey species Ichthyomyzon unicuspis and Lampetra fluviatilis were used for whole-cell patch-clamp studies of the effects of baclofen on calcium channel currents, evoked in conditions in which Na+, K+ currents were blocked, by depolarizing membranes from constant holding potentials of -100 or -80 mV to +30 mV. Ba ions were used as carriers of currents through calcium channels. These studies demonstrated that baclofen (0.

Calcium currents and GABAB receptors in the dorsal sensory cells of the lamprey spinal cord.

Patch-clamp studies were performed on the isolated dorsal sensory cells of the spinal cords of three species of lamprey, Ichthyomyzon unicuspis, Petromyzon marinus, and Lampetra fluviatilis, to measure changes in the amplitudes of calcium current induced by GABA and its specific antagonists and agonists. The experiments showed that GABA (4 mM) reduced the peak amplitude of the calcium current by 28.5 +/- 4.

[Effect of baclofen on calcium channel currents in dorsal sensory cells of the lamprey spinal cord].

delta-Baclofen reduced the peak amplitude of the barium current in the DSCs from Lunicuspis and L.fluviatilis. The membrane conductance was not altered either by baclofen or GABA.

[Calcium current and GABA(B) receptors in dorsal sensory cells of the lamprey spinal cord].

GABA and GABAB receptor agonists were shown to reduce the peak calcium current amplitude with its subsequent recovery, whereas glycine and taurine, the GABAA receptor agonists, did not modify the current. The findings suggest that the GABAB receptors mediate a presynaptic inhibition by suppression of the Calcium currents in the cyclostome spinal cord.

[Potential-gated currents in isolated spinal cord neurons of the river lamprey Lampetra fluviatilis].

Potential-gated currents in the membranes of enzymatically isolated neurons from the lamprey spinal cord were investigated using the whole cell variant of the patch-clamp technique. As it was revealed the main currents underlying action potential (AP) in the dorsal sensory cells as well as in branched cells are inward Na(+)- and outward K(+)-currents. Sodium current has the duration 4-9 ms, it was rapidly activated and inactivated and blocked by TTX.

[The pathways of the stabilization of the amplitude of postsynaptic potentials in the interneuronal synapses of vertebrates].

The influence of various factors on the degree of stabilization of postsynaptic potential amplitude has been studied by mathematical modelling. Increasing of transmitter release probability in single boutons, spatial non-uniformity of these probabilities, interaction of release sites, non-linear summation of potentials lead to amplitude stabilization. Temporal fluctuations of the release probability, failures of responses from contact groups and activation of a variable number of the fibers have the opposite influence.

[Effect of penicillin on the synaptic activity of isolated spinal cord motor neurons in the lamprey].

Penicillin (PCN) has been studied for its effect on the membrane potential (MP) and synaptic activity of lamprey spinal cord motoneurons using intracellular recording in the in vitro spinal cord-notochord preparation. In one group of motoneurons with relative low MP (58.7 +/- 5.

[The effect of glycine and gamma-aminobutyric acid on the excitatory postsynaptic potentials of the spinal motor neurons in the lamprey in the presence of antagonists].

Effect of bath application of the inhibitory amino acids (glycine and GABA) on motoneurons of EPSPs was studied in the normal physiological solutions and after preliminary administration of antagonists: strychnine (10(-6) mol/l), bicuculline (10(-4) mol/l) or picrotoxin (10(-4) mol/l). All these antagonists diminished the depression of monosynaptic EPSPs which were elicited by both amino acids (glycine and GABA). Data obtained in this study and previously reported ones permit concluding that motoneuron membranes in the spinal cord of lamprey possess the unit receptor channel complex sensitive to both amino acids.

[The effect of glycine and gamma-aminobutyric acid on the evoked activity of the spinal cord motor neurons in the lamprey].

The influence of bath application of glycine (10(-5)-10(-3) mol/l) and gamma-aminobutyric acid (10(-5)-10(-2) mol/l) on the monosynaptic EPSPs evoked in motoneurons by stimulation of a descending tract and individual Müller axons was studied in spinal cord-notochord preparation of lamprey (Lampetra fluviatilis). Both amino acids hyperpolarized the motoneuron membrane and depressed the evoked synaptic activity. But the inhibitory effect of glycine was stronger and it was revealed at lower concentrations as compared to that of GABA.

Peculiarities of receptor-channel complexes for inhibitory mediators in the membranes of lamprey spinal cord neurones.

Effects of inhibitory mediators on the membranes of isolated lamprey spinal cord neurones were investigated by means of whole-cell recording and concentration clamp techniques. Glycine and gamma-aminobutyric acid (GABA) applications evoked desensitizing chloride currents. The concentrations at half-maximum effects were 16 microM for glycine- and 1.

[Characteristics of the effect of glycine and gamma-aminobutyric acid on the spinal cord neurons in the lamprey].

Responses of isolated spinal cord neurons of lamprey on glycine and gamma-aminobutyric acid (GABA) were investigated by means of intracellular perfusion and concentration clamp techniques. Responses on both amino acids exhibited fast but not full desensitization. Preincubation of neurons in the solution of one mediator led to full disappearance of the response to other mediator.

[Action of l-DOPA and acidic amino acids on isolated neurons of spinal cord in the lamprey].

Ionic currents induced by application of L-3, 4-dihydroxyphenylalanine (L-DOPA) and acidic amino acids: L-glutamate, kainate, N-methyl-D-aspartate (NMDA) were investigated in experiments on isolated spinal cord neurons of the lamprey by means of whole-cell recording and concentration clamp methods. L-DOPA was found to activate glycine, but not excitatory amino acid receptors.

[Quantitative study of the reticular-motor neuronal contacts in the spinal cord of the lampern].

The number and location of contacts which are made by two HRP-labelled motoneurons with the individual Müller axons in lamprey was investigated. Each motoneuron had contacting zones with the ventromedial and ventrolateral Müller axons, but had no contacts with the dorsolateral Müller axon. The contacting zones which were extended for 0.

[Inhibitory effects of taurine on spinal cord motoneurons of the lamprey].

The influence of bath application of taurine (1-10 X 10(-4) mol/l) on the activity of motoneurons was studied in the isolated lamprey spinal cord. EPSPs evoked by stimulation of the descending tract as well as unitary EPSPs evoked by intracellular depolarization of the individual Müller axons were depressed, whereas conduction of action potentials in the Müller axons and antidromic action potentials of motoneurons were practically unchanged. A deep depression of electrical, in addition to chemical, components of EPSPs and comparison of the obtained results with the available morphological data on the structure of reticulomotor synapses in lamprey, allow concluding that the inhibitory synapses can be located near the excitatory ones on the motoneuron dendrites.