A method of direct chemical brain stimulation in behavioral studies using microiontophoresis

A method of microiontophoresis for direct chemical brain stimulation in chronic, awake animals for behavioral studies is described. Carbachol-induced drinking was employed to test the method. Fluid-filled micropipettes (tip diameters: 5-15 mu) were stereotaxically implanted in the region of the nucleus of the diagonal band. Up to 3 weeks after recovery, ions could be ejected directly into the brain of awake animals by passing a direct current through the pipette. Iontophoretic ejection of carbachol in doses as low as 0.05 mug elicited drinking. This effect could be blocked by intraperitoneal injection of 0.5 mg/kg scopolamine. Passage of choline ions produced no detectable effect. The microiontophoretic technique allows direct chemical brain stimulation in chronic, awake animals without major changes in tonicity or volume that can occur with crystalline or fluid implants through cannulae. Additionally, the technique allows precise localization, precise control of dosage, and minimal damage at the site of stimulation.