EXCITOTOXIC LESIONS OF THE PARABRACHIAL NUCLEI PREVENT CONDITIONED TASTE-AVERSIONS AND SODIUM APPETITE IN RATS

Electrolytic lesions of the parabrachial nuclei (PEN) disrupt conditio ned taste aversion (CTA) in the rat, but it is not known whether this effect is due to damaging axons of passage or to destruction of intrin sic neurons. We tested 10 rats with electrophysiologically guided, ibo tenic acid lesions of the PEN (PBNx) to determine whether they could a cquire a LiCl-induced CTA to l-alanine (0.3 M) or demonstrate a sodium appetite following furosemide treatment and overnight access to sodiu m deficient chow. Vehicle-treated and nonsurgical controls were includ ed in the design. PBNx rats failed to develop a CTA, even after 3 cond itioning trials. Moreover, more than 8 months later, a subset of the P BNx rats were again unable to learn a CTA using NaCl as the conditiona l stimulus (CS). After the furosemide treatment, the control rats dran k an average of 20.3 mi of strong salt in 24 hr. The PBNx rats drank v irtually no NaCl during the first 2 hr and averaged only 4.0 mi in 24 hr. In the PEN, damage to neuronal somata is more critical than interr upting fibers of passage for producing deficits in taste-guided behavi ors.