Tegmental pedunculopontine lesions in rats decrease saccharin's rewarding effects but not its memory-improving effect.

The tegmental pedunculopontine nucleus (TPP) of the brainstem has been identified as a critical substrate for both opiate and food reward in nondeprived rats. In this study of rats, TPP lesions blocked saccharin-conditioned place preferences, in both the presence and the absence of water deprivation. TPP lesions also attenuated the unconditioned intake of saccharin and water over several hours after recovery from food and water deprivation. TPP lesions did not block saccharin preferences over water in short-duration tests. The researchers propose that the absence of a lesion effect may reflect previously conditioned discriminations. TPP lesions had no effect on the ability of posttrial presentations of a 3.2% saccharin solution to improve lithium-chloride-conditioned taste aversions. TPP lesions dissociate 2 behavioral processes elicited by saccharin: One mediates unconditioned-reward-conditioned-reinforcing effects, and another mediates the memory-improving effect.