The role of the dorsal-most part of the lateral parabrachial nucleus in the processing of hypertonic NaCl using different conditioned flavor avoidance paradigms.

The parabrachial nucleus (PBN) has been strongly associated with taste aversion learning (TAL) acquisition. Independent of its suggested associative functions, this brain stem centre plays a key role in the sensorial processing of both gustatory and visceral information. The sensory visceral functions have been attributed to the lateral area of the PBN (PBNl) but, recently, it has been proposed that within this area a form of anatomical and functional segregation may also exist, determined by factors such as, the learning paradigm used, the nature of aversive agent used, or the route chosen for the administration of this agent. This study used a lesion approach in rats to address the question of whether the dorsal most portion of the PBNl plays a key role in the acquisition of a conditioned avoidance to flavored stimuli induced by hypertonic sodium chloride (intra gastric), and whether this role is dependent on the flavor avoidance learning (FAL) paradigm used, concurrent (experiment 1) or delayed-sequential FAL (experiment 2). Results showed a clear disruptive effect of the PBNl electrolytic lesion on the acquisition of the concurrent FAL, but hardly any attenuation of the delayed-sequential FAL. This finding is discussed in the context of the hypothesis that two separate and apparently non-redundant routes exist for the processing of the visceral information.