Pavlovian conditioning of eating induced by spreading depression in cortex, striatum and hippocampus of rats.

A single wave of unilateral spreading depression in the cortex, hippocampus or caudate nucleus of rats elicits eating after 2-6 min. The present experiments provide evidence that such spreading depression-induced eating can be classically conditioned to a complex conditioned stimulus. A wave of spreading depression was triggered by injection of 0.5-2.0 mul of 25 percent KCl solution. In a first experiment successful conditioning was demonstrated in 20 rats, involving 7 cortical, 5 caudate and 8 hippocampal spreading depression sites. Four animals failed to show any conditioned eating. A control group of 8 animals, in which cortical spreading depression did not induce eating, showed no increase in eating in the presence of the CS after conditioning trials. A second experiment, which included pseudoconditioning and NaCl control groups, confirmed the results obtained in Experiment 1. Classical conditioning was successful in 11 animals, involving 6 cortical and 5 caudate spreading depression sites. Neither the pseudoconditioning (14 animals, involving 8 cortical and 6 caudate spreading depression sites) not the NaCl control group (8 animals, all with cortical sites), showed eating in the presence of the CS. In both experiments the conditioned eating underwent gradual extinction.