To spritz or not to spritz: The doubtful value of aimless iontophoresis

Abstract

Publisher Summary This chapter discusses the different aspects of iontophoresis. The response of a neuron to a drug applied by iontophoresis can be determined by the changes in any parameter of cell activity. For cells with spontaneous electrical activity, changes in discharge pattern can be determined from interspike interval histograms and poststimulus time histograms can be used when test cells can be influenced by defined, isolated, monosynaptic inputs. In each case, accuracy of response measurements requires continuous detection of distinguishable action potentials of a constant spike height. With the recording barrel of a multibarrel electrode used in iontophoresis, extracellular spikes often have low signal to noise ratios and more than one cell can be recorded simultaneously. These signals can be improved electronically with gate or window discriminators provided that spike size remains constant. In iontophoretic tests, spike size can change by drift in the spatial relation between electrode and cell, by interaction between ejection or retention currents and the spike generating mechanisms of the cell, or when the drug to be tested has membrane anesthetizing properties. Noise levels are frequently increased during iontophoretic tests, especially when the drug solution has a high electrical impedance from low solubility or low ionization constants.