Simultaneous recording of somatic and dendritic field potentials and combined microiontophoresis in the rat Ammon's horn in situ: effects of GABA and acetylcholine.

In rats under urethane anesthesia, a twin set of multibarreled micropipettes was used to record simultaneously in situ the somatic population spike, the positive field and the dendritic negative field (EPSP) evoked by commissural stimulation, and to apply microiontophoretically GABAergic and cholinergic agents at each level. Relying on the typical somatic responses evoked by local application of GABA and acetylcholine (ACh), an electrode can be positioned in the pyramidal layer with good accuracy (in the range of 50 microns) and the pharmacology of the excitatory drive impinging upon the apical dendrite concomitantly investigated.