Electrical Properties Of Neurons Research Articles

Synaptic interactions between mammalian central neurons in cell culture. I. Reversal potential for excitatory postsynaptic potentials.

Intracellular recording and stimulation techniques were used to study the electrical properties of neurons in cell cultures from fetal mouse spinal cord (SC). The morphology of SC neurons and the distribution on SC neurons of boutons formed by synaptically connected SC or dorsal root ganglion (DRG) neurons were demonstrated with horseradish peroxidase (HRP) injection. Postsynaptic polarization in conjunction with synaptic activation of SC neurons was used to determine the reversal potential for excitatory postsynaptic potentials (EPSPs). Tetraethylammonium ions were injected postsynaptically in order to obtain reversal of the EPSPs. Both SC-SC and DRG-SC excitatory connections could be reversed by postsynaptic depolarization. The average reversal potential for the SC-SC EPSP was -4 +/- 12.2 (SD) mV and that for the DRG-SC EPSP was +8 +/- 7.9 (SD) mV, a statistically significant difference (Wilcoxon two-sample rank; P less than 0.05). Scatter was quite large, particularly for the SC-SC connection. While some neurons gave clear electrophysiological evidence of significant dendritic effects, the average total electrotonic length was small (0.58 +/- 0.65 (SD) of a length constant). The morphological extent of the dendrites of SC neurons was substantially less than that of mature motoneurons in vivo. We concluded that both SC-SC and DRG-SC EPSPs were mediated by a conventional conductance increase and that most synaptic input was not far removed electrically from the recording site in the neuron cell body.

Serotonin alters the phosphorylation of specific proteins inside a single living nerve cell.

The large size and ready identifiability of molluscan neurones have made it possible to investigate the hypothesis1,2 that cyclic AMP-dependent protein phosphorylation may regulate neuronal electrical properties. For example, it has been found recently that intracellular application of the catalytic subunit of cyclic AMP-dependent protein kinase can alter the electrical activity of various molluscan neurones (refs 3, 4; J. De Peyer, H. Reuter and I.B.L., unpublished). We have recently demonstrated5 that injection of a specific protein kinase inhibitor into identified Aplysia neurone R15 blocks the increase in K+ conductance normally elicited in R15 by serotonin6, implicating protein phosphorylation in the regulation of a specific ion channel by a neurotransmitter. We report here attempts to identify phosphoproteins which may be involved in such regulation, by measuring protein phosphorylation in R15 following the intracellular injections of γ[-32P]ATP. The results indicate that we can indeed measure protein phosphorylation inside an individual living nerve cell, and that the extent of phosphorylation of several proteins in R15 is influenced by serotonin.

Acute effects of intravenous glucocorticoid on cat spinal motor neuron electrical properties

The acute effects of a single large intravenous dose of methylprednisolone were examined on the resting membrane potentials and the antidromic action potentials characteristics in cat lumbar spinal motor neurons via intracellular recording. A 30 mg/kg glucocorticoid dose was found to cause a 3.5 mV hyperpolarization of the resting membrane potential. An examination of the effects of the single dose on the conduction and generation of an antidromic action potential revealed an increased conduction velocity along the myelinated motor axon, a decreased conduction rate through the unmyelinated initial axon segment, an increased threshold for antidromic soma-dendritic activation, a decreased action potential zero overshoot and a faster repolarization. All of these effects were greatest after the 30 mg/kg methylprednisolone dose except for the increase in the antidromic soma-dendritic threshold which was even greater after 60 mg/kg. The 30 mg/kg dose also caused a stimulus-bound repetitive discharge in a third of the motor neurons which appeared to arise in the myelinated motor axon or initial axon segment. The neurophysiological implications of these acute glucocorticoid actions are discussed.

Electrical properties of neurones in the olfactory cortex slice in vitro.

1. Slices of guinea-pig olfactory cortex were maintained in vitro. Electrical properties of neurones in the prepyriform region were studied using single high resistance glass micro-electrodes filled with potassium acetate, connected to a resistance-compensating circuit to allow passage of current through the electrode. 2. Neurones showed a high, stable resting membrane potential (75.4 +/- 2.7 mV, mean +/- S.D.; n = 47). Input resistance measured with small depolarizing currents varied over a range of 9-280 Momega. The time constant for decay of depolarizing potentials was 19.4 +/- 7.5 msec (mean +/- S.D.).. 4. Depolarization produced repetitive action potentials (maximum frequency of 85 Hz) having peak amplitudes of +16 to +47 mV. The action potential was followed by a depolarizing after potential of about 20 mV positive to the membrane potential. 5. In these and other respects, the prepyriform neurones appear to behave like most other neurones in the mammalian brain, after allowing for the more stable recording conditions in this preparation.

Interaction between inhibitory and excitatory synaptic potentials at a peripheral neurone.

1. The interaction between inhibitory and excitatory synaptic potentials in neurones lying in the submucous plexus of guinea-pig ileum has been examined. 2. It was found that during an inhibitory conductance change, electrotonic potentials were more depressed in amplitude than were excitatory synaptic potentials. 3. It is suggested that inhibitory conductance changes may have only a slight effect on the impedance seen by excitatory synaptic currents as much of the excitatory synaptic current flow is likely to be capacitive. 4. A part of the depression of excitatory synaptic potential amplitude was not associated with changes in electrical properties of neurones and it is suggested that inhibitory transmitter may reduce the release of excitatory transmitter.