Distinct Populations of Identified Glial Cells in the Developing Rat Spinal Cord Slice: Ion Channel Properties and Cell Morphology

Abstract

Four types of glial cells could be distinguished in the grey matter of rat spinal cord slices at postnatal days 1-19 (P1-P19), based on their pattern of membrane currents as revealed by the whole cell patch clamp technique, and by their morphological and immunocytochemical features. The recorded cells were labelled with Lucifer Yellow, which allowed the subsequent identification of cells using cell-type-specific markers. Astrocytes were identified by positive staining for glial fibrillary acidic protein (GFAP). These were morphologically characterized by multiple, very fine and short processes and electrophysiologically by symmetrical, non-decaying K+ selective currents. Oligodendrocytes were identified by a typical oligodendrocyte-like morphology, lack of GFAP staining and positive labelling with a combination of O1 and O4 antibodies (markers of the oligodendrocyte lineage), and their membrane was dominated by symmetrical, passive, decaying K+ currents. The third population of glial cells was also characterized by positive staining for O1/O4 or only for O4 antigens, lack of GFAP staining and, in some cells, oligodendrocyte-like morphology. However, these cells could be distinguished by the presence of inwardly rectifying (KIR), delayed outwardly rectifying (KDR) and A-type K+ currents (KA), representing the most likely glial precursor cells of the oligodendrocyte lineage. The fourth population of glial cells had small somata and a widespread network of long processes with no apparent orientation preference. In one case, processes were positively labelled with GFAP, while 30% were characterized by faint, diffuse staining. These cells expressed a complex pattern of voltage-gated channels, namely Na+, KDR, KA and KIR channels. In contrast to neurons, the amplitude of Na+ currents was at least one order of magnitude smaller than the K+ currents, and none of these cells showed the ability to generate action potentials in the current clamp mode. Since none of these cells could be labelled by oligodendrocyte markers we assume that they were either astrocytes or glial precursor cells of the astrocyte lineage. The four cell types were found in all regions of the grey matter. When randomly accessing the glial cells, the probability of recording from the oligodendrocyte precursor cells and the glial cells with Na+ currents decreased during development. At P1-P3, 50% of the cells revealed the Na+ current, while at P13-P15 only 18% did. Concomitantly, the number of glial cells with astrocyte- and oligodendrocyte-like membrane currents increased from 19 and 12% to 41 and 35.5% respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

Gap Junction-Mediated Astrocytic Networks in the Mouse Barrel Cortex

“…This identification was confirmed by the lack of action potential in response to depolarizing current injections, the absence of spontaneous electrical activity, and the negative resting potential (ϽϪ70 mV). Furthermore, in voltage-clamp mode, the absence of typical off-set currents indicated that these cells were not oligodendrocytes (Chvatal et al, 1995). When whole-cell recording of a glial cell was performed with a biocytin-filled pipette, this intercellular tracer was detected in surrounding cells after fixation and biocytin revelation (Fig.…”

Synaptically Evoked GABA Transporter Currents in Neocortical Glia

“…1A), electrophysiological characterization of membrane properties, and labeling with Lucifer yellow or Alexa 594 in a number of cells and confirming ultrastructure post hoc. Neocortical astrocytes are known to be relatively small cells, with cell bodies in the range of 6 -15 m. This size criterion was the basis for the initial selection of an experimental cell; identity was also established electrophysiologically: astrocytes are characterized by their high negative resting membrane potentials (RMPs), low input resistances, and passive, linear currentvoltage relationships (e.g., Chvatal et al 1995;D'Ambrosio et al 1998;Schwartzkroin and Prince 1979;but see Bordey and Sontheimer 1998). Based on these electrophysiological criteria, we characterize the cells in this study as neocortical astrocytes.…”

Phosphatase inhibitors remove the run-down of γ-aminobutyric acid type A receptors in the human epileptic brain

“…On the other hand, glial cells could be recognized because they had hyperpolarized resting potentials (Ϫ87.8 Ϯ 2.9 mV), lower resistance (33 Ϯ 16 m⍀; n ϭ 5; see refs. 19 and 20), and were unable to elicit full action potentials in current-clamp mode (21). The current run-down protocol adopted was the following: after current amplitude stabilization with repetitive applications every 120 s, a sequence of 10 GABA applications every 15 s was delivered.…”