Lateral parabrachial lesions impair lithium chloride-induced aversive responses but not saccharin-induced flavor preference.

Behavioral taste-guided experiments, as well as molecular studies employing c-FLI expression in response to aversive/appetitive unconditioned stimulus, have strongly suggested a visceral role for the lateral parabrachial subnuclei (lPB). The main objective in the present study was to further evaluate the functional role of the lPB in lithium chloride-induced behavioral/physiological responses. We employed a lesion/behavioral experimental strategy combining a lithium chloride-induced place aversion procedure together with the simultaneous evaluation of behavioral ("Lying on Belly", "LOB") and physiological (body temperature) responses elicited by the toxin. Data showed that lPB-lesioned animals failed to avoid the chamber previously paired with lithium chloride. Moreover, "LOB", and not hypothermia, in response to lithium chloride was impaired in parabrachial lesioned animals. Finally, all the animals were tested in a free discriminative flavor-preference task induced by saccharin, a non-caloric reinforcer, which precludes visceral feedback as essential in acquiring the learned response. As expected, both control and lesioned animals developed a clear flavor-preference to the flavor previously paired with saccharin, which shows normal gustatory and associative processing in lPB-lesioned animals. This study extends previous results on the functional visceral role of lPB subnuclei by providing alternative behavioral evidence other than taste-guided behavior, that the lPB is pivotal in visceral processing. Present data are discussed in the context of the visceral hypothesis that holds that the lPB is critically involved in processing post-oral visceral feedback.