tetrodotoxin and Motion-Sickness

The aversive effects of bilateral transient blockade of the lateral vestibular nucleus caused by tetrodotoxin microinjections were tested using conditioned taste aversion in the first experiment. Male Wistar rats received tetrodotoxin injections (10 ng) after drinking a coffee solution (0.5%), either 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 receiving the injection in the lateral vestibular nucleus displayed a coffee aversion. In a second experiment the role of the peripheral vestibular symptoms induced by LVN inactivation on substituting the aversive stimulus was explored 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 differ to those animals receiving only anesthesia or those that remained undisturbed. These results showed that the bilateral blockade of the vestibular nuclei may induce peripheral vestibular symptoms that that may substitute the aversive stimulus in taste aversion learning.

Topics: Animals; Avoidance Learning; Male; Motion Sickness; Rats; Rats, Wistar; Taste; Tetrodotoxin; Vestibular Nuclei

The role of the parabrachial area in conditioned taste aversion (CTA) induced by motion-sickness was studied in male Wistar rats. In the first experiment, one-trial conditioned taste aversion, to a 0.5% decaffeinated coffee solution, was induced by 30 min of vertical rotatory motion (80 rev./min) in intact rats. In the second experiment, reversible blockade of the neural activity in various brainstem sites was induced by bilateral intracerebral injections of tetrodotoxin (TTX) (10 ng/microl) after conditioning. Blockade of the parabrachial area, but neither A8 nor lateral vestibular nucleus, disrupted the acquisition of (CTA). The results are discussed in terms of an associative role of the parabrachial area in body rotation-induced taste aversion learning, as the area was intact during sensory processing and testing.

Topics: Analysis of Variance; Animals; Avoidance Learning; Conditioning, Operant; Male; Motion Sickness; Pons; Rats; Rats, Wistar; Taste; Tetrodotoxin