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Cephalopod NeurobiologyNeuroscience Studies in Squid, Octopus and Cuttlefish$
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N. Joan Abbott, Roddy Williamson, and Linda Maddock

Print publication date: 1995

Print ISBN-13: 9780198547907

Published to Oxford Scholarship Online: March 2012

DOI: 10.1093/acprof:oso/9780198547907.001.0001

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Diffusion properties of the microenvironment of cephalopod brain

Diffusion properties of the microenvironment of cephalopod brain

23 Diffusion properties of the microenvironment of cephalopod brain
Cephalopod Neurobiology

Charles Nicholson

Jaleel A. Miyan

Katherine T. Potter

Roddy Williamson

N. Joan Abbott

Oxford University Press

The diffusion characteristics of brain extracellular space can be summarized by two parameters, the tortuosity (λ) and the volume fraction (α). Volume fraction is a measure of the volume of extracellular space relative to whole tissue volume, while tortuosity measures the extent to which diffusion is hindered by cellular obstruction in comparison to a free medium. By using local iontophoresis of tetramethylammonium from a micropipette in conjunction with suitable ionselective microelectrodes, λ and α can be determined. The λ and α in an invertebrate neural mass is measured in this chapter to determine whether the parameters had similar values to those previously found in vertebrates. The cephalopod vertical lobe and optic lobes were chosen because of their size and accessibility. The average value of the diffusion parameters in the vertical lobe of intact anaesthetized Sepia (cuttlefish), intact anaesthetized Eledone (octopus), and isolated slices of Sepia were λ = 1.65 and α = 0.10. In isolated slices from the optic lobes of Sepia the average values were λ = 1.86 and α = 0.29. These data suggest that while there may be definite structural differences between the two neural lobes of these cephalopods, the diffusion characteristics are quite similar to those in vertebrates.

Keywords:   Cephalopod, volume fraction, iontophoresis, tetramethylammonium, micropipette, Sepia, Eledone

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