The role of the lateral parabrachial nuclei in concurrent and sequential taste aversion learning in rats

The purpose of this study was to examine the role of the external lateral p arabrachial subnucleus (PBNLe) in two different taste aversion learning (TA L) procedures. For the first, short-term (concurrent) TAL, two different-fl avored stimuli were presented at the same time, one associated with simulta neous intragastric administration of an aversive product, hypertonic NaCl, and the other with saline. In the second, long-term (sequential/delayed) TA L, each gustatory stimulus was presented every other day and the intragastr ic products LiCl and saline were administered after a 15-min delay. Electro lytic lesions in the PBNLe blocked acquisition of concurrent TAL, in which the vagal visceral information is critical. But the same lesions failed to interrupt sequential TAL. This result was independent of the order in which the two tasks (concurrent and sequential) were presented. However, as foun d by other authors, the latter type of learning was impaired in the presenc e of larger lesions in this same area. This supports the existence of senso ry information needed to establish sequential TAL in other subnuclei of the parabrachial complex. The results of these experiments suggest that the di fferent modalities of TAL are anatomically specific.