Bilateral tetrodotoxin blockade of the rat vestibular nuclei substitutes the natural unconditioned stimulus in taste aversion learning

The aversive effects of bilateral transient blockade of the lateral vestibu lar nucleus caused by tetrodotoxin microinjections were tested using condit ioned taste aversion in the first experiment. Male Wistar rats received tet rodotoxin injections (10 ng) after drinking a coffee solution (0.5%), eithe r in the lateral vestibular nucleus (LVN), the parabrachial nucleus or the dopaminergic area A8. Two days later they drank a cider vinegar solution (3 %) not followed by injections. In a later choice test, only the group recei ving the injection in the lateral vestibular nucleus displayed a coffee ave rsion. In a second experiment the role of the peripheral vestibular symptom s induced by LVN inactivation on substituting the aversive stimulus was exp lored in the same behavioral task. Rats anesthetized (Pentobarbital, 25 mg/ kg) before tetrodoxin LVN blockade, that did not show peripheral symptoms, did not develop learned aversions. The coffee preference ratios did not dif fer to those animals receiving only anesthesia or those that remained undis turbed. These results showed that the bilateral blockade of the vestibular nuclei may induce peripheral vestibular symptoms that that may substitute t he aversive stimulus in taste aversion learning. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.