Cortical cooling induces conditioned consumption reduction in male rats

Previous studies have shown that male rats acquire a conditioned reduction in consumption of a sucrose solution when consumption of that taste solution is followed by cooling the caudate putamen. Because the shaft of the cold probe was not insulated, this cooling also included the cortex and meninges overlying the caudate putamen. When cooling the meninges was eliminated as a factor, the conditioned consumption reduction was weaker but it was not abolished. This suggests that meninges cooling contribute to the conditioned consumption reduction induced when all three structures are cooled, but it is not sufficient. Five experiments were designed to determine whether cooling the cortex also contributes. In the first experiment, the temperature of the cortex and meninges overlying the caudate putamen was measured during cooling. In the following three experiments the ability of male rats to acquire a conditioned consumption reduction was determined after pairing a sucrose solution with cooling the cortex and meninges overlying the caudate putamen, cooling the cortex with and without cooling the dura meninges membrane, and cooling the cortex with and without cooling the entire meninges. When the cortex was cooled without cooling the caudate putamen, dura, or entire meninges, a conditioned consumption reduction was acquired. The last experiment demonstrated that contingent pairing of sucrose and cortical cooling was required to obtain consumption reduction. These results clearly indicate that cortical cooling contributes to the acquisition of conditioned consumption reduction induced when the caudate putamen and overlying cortex and meninges are cooled. Two hypotheses are suggested to account for the ability of neural cooling to act as an unconditioned stimulus in the conditioned consumption reduction paradigm: (1) neuronal inactivation produces physiological changes that can serve as unconditioned stimuli and (2) cooling itself produces physiological changes that can serve as unconditioned stimuli.