The contribution by glial cells to surface recordings from the optic nerve of an amphibian

Abstract

SUMMARY1. The contribution by glial cells to surface recordings has been examined in the optic nerve of the amphibian Necturuws maculosus. The method of current injection was employed selectively to alter the membrane potential of glial cells without affecting that of the axons. The resulting changes in potential were recorded simultaneously from the surface of the nerve using the sucrose gap method and intracellularly from a glial cell near the gap.2. The sucrose gap method recorded 40 % of the changes in glial membrane potential. This percentage was not affected when the current electrode was inserted into different glial cells while maintaining the recording conditions constant.3. Following axonal degeneration, produced by removing the eye 2-3 months earlier, the percentage contribution by glia increased to 84 %.4. By measuring sucrose gap responses to changes in Ko it was possible to estimate that the sucrose gap method recorded 31-60 % of changes in axonal membrane potential. It was also determined that the axons, unlike glial cells, are relatively insensitive to reductions in K.. Surface responses to decreases in external potassium thus reflect the magnitude of the glial contribution. 5. It is concluded that changes in glial membrane potential contribute about as much to surface recordings from the optic nerve of Necturus as do equivalent changes in axonal membrane potential. The contributions by the glial cells and axons are related to the relative volumes of tissue they respectively occupy. The significance of these findings to the analysis of surface recordings from the mammalian brain is discussed. Since mammalian glial cells, like those in Amphibia and the leech, become depolarized during neuronal activity and on the basis of electron microscopic evidence

Oscillatory potentials as predictors to amplitude and peak time of the photopic b-wave of the human electroretinogram

“…The OPs would reflect the primary retinal events (excited retinal neurons), which would be integrated by the Miiller cells to yield the b-wave. Supportive of this interpretation of the b-wave genesis are previous reports, which suggested that the OPs were closely linked to the primary retinal events [1] and that the Mfiller cells (like other glial cells) had a very slow time constant, which demonstrated some integrating (summating) capabilities [15,16].…”

Noninactivating, tetrodotoxin-sensitive Na+ conductance in rat optic nerve axons.

“…Glial cells are known to be coupled (25,26) and possess TTX-sensitive Na+ channels (27); it is possible that glia might have contributed to the effects we describe (28). We attempted to demonstrate electrical coupling of optic nerve glia across the 2-mm width of the grease gap, by recording from optic nerves devoid of axons [created by enucleating newborn animals and allowing the axons to degenerate (29)].…”

PRESYNAPTIC Γ-Aminobutyric ACID RESPONSES IN THE OLFACTORY CORTEX

“…Since application of GABA to either end of the LOT produced equivalent depolarizations, it seems that GABA receptors may not be exclusive to nerve terminals but may be present all over the axonal membrane. Less likely alternative explanations for the recorded signal are electrogenic uptake (Kehoe, 1975), which could well apply to the glycine response, or glial responses (Cohen, 1970). Postsynaptic responses might have been recorded along centrifugal axons in the LOT (Heimer, 1968) although the lack of effect of glutamate, a potent depolarizing agent of neurones in the olfactory cortex (Richards, 1978), weighs against this.…”