Involvement of forebrain in parabrachial neuronal activation induced by aversively conditioned taste stimuli in the rat.

We previously have shown that forebrain inputs increase responses of amiloride-sensitive NaCl-best neurons to the conditioned stimulus (CS) in the rat parabrachial nucleus (PBN) after the establishment of conditioned taste aversion (CTA) to NaCl. In the present study, we examined the effects of aversively-conditioned NaCl taste stimulation on Fos-like immunoreactivity (FLI) in the PBN using awake intact and decerebrate rats. In Experiment 1, the CTA-trained and sham-conditioned control rats were intraorally infused with 0.1 M NaCl or 0.1 M NaCl mixed with 10(-4) M amiloride, a sodium-channel blocker. Significantly more NaCl-stimulated FLI was observed in the central medial (cms) and external lateral subnuclei (els) of PBN in the CTA-trained group than in the control group. In both groups, amiloride markedly reduced NaCl-stimulated FLI in the cms but not in the els. In Experiment 2, we found that after decerebration, there was no significant difference in FLI between the CTA-trained and sham-conditioned groups. These results suggest that (1) amirolide-sensitive taste information of NaCl projects mainly to the cms; (2) sensory information of aversive taste stimuli is likely to be represented in the els; and (3) forebrain inputs are required for elevated FLI in the PBN after CTA.