THE FUNCTIONAL RELEVANCE OF MEDIAL PARABRACHIAL NUCLEUS IN INTRAGASTRIC SODIUM CHLORIDE-INDUCED SHORT-TERM (CONCURRENT) AVERSION LEARNING

The functional meaning of the visceral information processing in the m edial parabrachial nucleus (PBNm) was analyzed in this study through a short-term aversion learning task. In this short-term task the animal s (Wistar rats) had to learn to discriminate between two different gus tatory-olfactory stimuli presented simultaneously (two graduated buret tes); one of the stimuli was associated with the concurrent intragastr ic administration of an aversive chemical agent (hypertonic NaCl) and the other stimulus was paired with no injection. In the first experime nt, the PBNm-lesioned animals are unable to learn the task using gusta tory stimuli (saccharin and quinine) that surpassed the detection thre shold of parabrachial-lesioned rats. Moreover, in a second experiment, the PBNm-lesioned animals were unable to learn the task when there wa s no initial preference for either of the gustatory-olfactory stimuli presented (strawberry or coconut). However, this short-term task is le arned by lateral parabrachial nucleus (PBNl) lesioned animals. The pos sibility that the PBNm and the PBNl are involved in distinct mechanism s of visceral processing is discussed. (C) 1997 Academic Press.