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. Author manuscript; available in PMC: 2009 Nov 30.
Published in final edited form as: Physiol Rev. 2008 Oct;88(4):1277–1340. doi: 10.1152/physrev.00027.2007

Fig. 4.

Fig. 4

The RTI method. A. Original setup. Paired iontophoretic and ion-selective microelectrodes (ISM) are glued together and lowered into rat cerebellum in vivo. The iontophoretic microelectrode passes a current pulse controlled by a constant current circuit. The signals from the ion-sensing and reference barrels of the ISM are impedance-buffered and subtracted to remove contribution of local potential in brain. This results in an output that is proportional to the logarithm of the local ion concentration. Electrode array is withdrawn into agar for control measurements. (Modified from Ref. 257). B. Examples of RTI records using four different ions. All records taken in rat cerebellum in vivo. Each record in each set was taken at a different spacing between source electrode and ISM. Ordinate is concentration, abscissa is time. See original paper for details. (Modified from Ref. 257). C. Part of a frontal section through the cerebellum of a lizard. This cerebellum is very similar to that of the turtle. A, Molecular layer; B, Purkinje cells; C, granular layer; D, ependyma (Modified from Ref. 56). D. Diffusion anisotropy demonstrated by theoretical concentration-time profiles derived from average diffusion parameters measured in the turtle cerebellum and control medium. Theoretical records illustrate the relative concentration reached during the iontophoresis of TMA+ in the x-, y- and z-axes of the molecular layer, the granular layer (GrL) and agar gel. Diffusion distance used to calculate the curves was 120 μm. The tortuosity values were: molecular layer, λx = 1.44, λy = 1.95, λz = 1.58, α = 0.31 and granular layer, λ = 1.77, α = 0.22. (Modified from Ref. 314). E. Setup used to measure anisotropy in rat corpus callosum in vivo with the RTI-TMA method. The design is similar to that shown in panel A except that two iontophoresis microelectrodes are used to allow simultaneous measurements in the x- and y- or x- and z-axes (Modified from Ref. 410). F. Example of measurements in rat corpus callosum with the RTI-TMA method. In this record, λx = 1.44, λy = 1.70, λz = 1.72, α = 0.24. Ordinate is TMA+ concentration, abscissa is time. (Modified from Ref. 358).