Search PubMed⌕ Search

Biomedical subjects

B R Ransom

Publications and source records attributed to B R Ransom.

123 records · Page 7Linked to original sources
PubMed1977

Mouse spinal cord in cell culture. I. Morphology and intrinsic neuronal electrophysiologic properties.

1. Reliable methods for establishing fetal mouse spinal cord (SC) and dorsal root ganglion (DRG) cells in long term (greater than 1 mo) dissociated cell cultures are described. These cells have been studied by morphologic and intracellular electrophysiologic techniques. 2. Cells studied electrophysiologically can be relocated after preparation for electron microscopy and examined in thin sections. The electron microscope shows that the surface membranes of these cells were directly accessible to the culture medium. The surfaces of SC cells were studded with synaptic boutons, whereas the DRG cell surfaces generally had none. 3. Current-voltage relationships and linear electrotonic properties of the neurons are described. Delayed and anomalous rectification were seen in both cell types. The length of SC cell dendrites was about one characteristic electrotonic length, while little or no contribution of the relatively sparse DRG cell processes was seen in the transient responses of the DRG cells. 4. Postspike and posttetanic hyperpolarizations in DRG cells were due to a surface membrane conductance increase; this was probably primarily an increase in K+ conductance. Post-activation hyperpolarization in SC cells was primarily due to activation of an electrogenic Na+ pump.

Animals↗
PubMed1977

Mouse spinal cord in cell culture. II. Synaptic activity and circuit behavior.

1. Neurons in cell cultures of fetal mouse spinal cord (SC) and dorsal root ganglia (DRG) develop extensive synaptic interconnections. 2. No spontaneous synaptic activity was detectable in the presence of tetrodotoxin or an elevated magnsium ion concentration, but statistical analysis of evoked excitatory postsynaptic potentials (EPSPs) indicates that the quantal size was 200-250 muV, which was below the noise level of the recording system used. 3. In a sample of eight RDG-SC and seven SC-SC cell pairs linked by EPSPs, the quantal content of the SC-SC EPSPs was about 3.5-fold larger than for the DRG-SC EPSPs. 4. The extrapolated equilibrium potential for the SC-SC EPSP was about 20 mV positive. The IPSP reversed at a membrane potential of 60-80 mV negative. 5. Some examples of the types of synaptic circuits commonly encountered are given. Only one case of electrical coupling between neurons was found.

Animals↗
PubMed1977

Mouse spinal cord in cell culture. III. Neuronal chemosensitivity and its relationship to synaptic activity.

1. Mouse spinal cord (SC) cells in dissociated cell cultures showed strong electrophysiologic responses to glutamate, gamma-aminobutyric acid (GABA), and glycine when these were iontophoretically applied to the neurons. 2. The extrapolated reversal potential for the glutamate response was 20-30 mV negative in contrast to the positive extrapolated reversal potential for the SC-SC excitatory postsynaptic potential. The data are interpreted as indicating different ionic mechanisms for the glutamate response and the EPSP. 3. The reversal potentials for the glycine and GABA responses were similar to one another and to the IPSP reversal potential. The time course of the glycine and GABA responses were quite different from each other, however. 4. While some SC cells showed a relatively uniform sensitivity over their surfaces to iontophoretically applied glutamate, discrete regions of higher sensitivity occurred on most cells. 5. Release of excitatory and inhibitory transmitter could be elicited by focal application of glutamate and, in favorable instances, this could be shown to be due to the sensitivity of presynaptic terminals to the applied glutamate. Considerable spatial resolution of regions from which transmitter release could be elicited was achieved by this technique. Some correspondence between glutamate "hot spots" and such release sites was found.

Acetylcholine↗
PubMed1975

Neurons from fetal rat brain in a new cell culture system: a multidisciplinary analysis.

A new culture system for cells from the mammalian brain was developed by a modification of a previously established technique. This modification involved the use of fluorodeoxyuridine and adult horse serum. The cultures contained large, easily visualized neurons both isolated from other neurons and in networks of varying complexity. These cells were large enough to permit reliable intracellular electrophysiologic recording and were often sufficiently dispersed to allow examination of membrane responses to iontophoretically applied neurotransmitter candidates. Many responses characteristic of central neurons in situ were seen, including evoked and spontaneous action potentials, complex patterns of inhibitory and excitatory post-synaptic potentials, and neurotransmitter-induced membrane responses. These preparations were examined by phase contrast microscopy, by light microscopy after silver impregnation and by Nomarski interference optics. Total choline acetyltransferase (CAT) activity was little changed and specific activity was increased in the new culture system as compared with the earilier system. Conditions which gave the highest specific activity of CAT also provided the best cultures from the standpoint of electrophysiologic and morphologic analysis. This new approach will allow, in culture, detailed multidisciplinary analyses of individual neurons and small networks of neurons from the mammalian brain.

Acetylcholine↗
PubMedDate not supplied

A simple method for making ion-selective microelectrodes suitable for intracellular recording in vertebrate cells.

A simple procedure for manufacturing Cl-, K+, and pH liquid membrane ion-sensitive microelectrodes is presented in detail. Electrodes suitable for recording from the specimen of interest are back-filled with a small amount of silane solution and heated for 5 min on a hot plate at a temperature between 400 and 500 degrees C, after which they are injected with the ion-sensitive resin. The procedure is adaptable to many different glass stocks, e.g., single-barreled, double-barreled, or theta glass, and can be used to produce electrodes having a wide range of tip sizes for recording either extracellular or intracellular ion activities. Another advantage of the method is speed; up to 10 electrodes can be prepared simultaneously, permitting over 40 functional electrodes to be made per hour.

Animals↗