Diffusion properties of the microenvironment of cephalopod brain
Nicholson, C.; Miyan, J.A.; Potter, K.T.; Williamson, R.; Abbott, N.J. (1995). Diffusion properties of the microenvironment of cephalopod brain, in: Abbott, N.J. et al. (Ed.) Cephalopod neurobiology: neuroscience studies in squid, octopus and cuttlefish. pp. 383-397
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| Authors | | Top |
- Nicholson, C.
- Miyan, J.A.
- Potter, K.T.
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- Williamson, R.
- Abbott, N.J.
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| Abstract |
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. This study sought to measure λ and α in an invertebrate neural mass to determine if 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. We found that 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 (typically, λ = 1.60 and α = 0.20). This implies that the connectivity and size of the extracellular space is conserved in neuronal aggregates and that this has functional consequences for the movement of metabolic substrates and chemical signals in the extracellular microenvironment. |
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