Cerebral Substrates Of Conditioned Taste Aversion Induced By Physical-exercise In Rats

When taste stimulus is combined with gastrointestinal malaise, animals will refuse to ingest it and escape. This behavior is described as conditioned taste aversion (CTA). It is studied recently that the CTA can also be induced by the association of the gustatory stimulus and the physical exercise, but the brain structures taking part in the CTA are not clear yet. So SD rats used by my experiments were divide into four groups, and they were the control group,the saccharin stimulus group,the CTA group and the CTA with saccharin stimulus group. The rats of the CTA group and the CTA with saccharin stimulus group were given the saccharin solution before a 20 min swimming treatment until the predilection ratio of the saccharin solution was lower than 30%. While the brains of the control group and the CTA group were directly dislodged to be made into sections. The other groups were given the same procedures after intraoral stimuli with 5 ml of the saccharin solution through intraoral cannulas. Fos expression was examined by the immunohistochemistry and explored the change of Fos expression in brains of rats that had been lesioned the area postrema (AP)after having acquired CTA. The results suggested:1. Fos expression induce by both the seet taste stimulus and the establishment of the CTA increased in the external part of the lateral parabrachial nucleus (LPBE), external part of the medial parabrachial nucleus (MPBE), central medial thalamic nucleus (CM), paraventricular thalamic nucleus(PV), lateral hypothalamic area (LH), basolateral amygdaloid nucleus(BLA), shell area of nucleus accumbens (AcbSh) and ventral part of the lateral septal nucleus (LSV). The sweet taste stimulus and the establishment of CTA were not interactional. This denoted that these brain areas were associated with the discrimination of the gustatory quality, reward value of the taste and the behavioral expression after having acquired CTA. They effected on these brain areas independently.2. Fos expression enhanced in the central part of the lateral parabrachial nucleus (LPBC) when rats were stimulated by the sweet taste, and Fos expression increased in the anterodorsal thalamic nucleus (AD), central amygdaloid nucleus (CeA) and dorsal part of dorsomedial hypothalamic nucleus (DMD) when rats established the CTA. The sweet taste stimulus interacted with the establishment of the CTA. It is said that Fos expression induced by the sweet taste stimulus increased in these areas above, but did not rise any more after the CTA had been set up. The results suggested that the LPBC, CeA, AD and DMD were involved in integrating the sense information and the information of the behavioral expression.3. More Fos expression induced by the sweet taste stimulus in the medial amygdaloid nucleus (Me) was not involved in establishing the CTA or not. The increase in Fos expression in the intermediate nucleus of the solitary traits (SolIM) and the zona incerta (ZI) generated after rats had set up the CTA. There was not interaction between the establishment of the CTA and the sweet taste stimulus. This indicated that the sweet taste stimulus was critical for the change of Fos expression in the Me, and the establishment of the CTA was a primary factor for Fos expression in SolIM and ZI.4. The destruction of the AP could accelerate the extinction of the acquired CTA and decreased aversive reactions when rats were given the conditioned taste stimulus. Fos expression of rats with lesions of the AP was higher significantly than the Sham- lesioned group in the LPBC, but was lower significantly than the Sham- lesioned group in the MPBE, LPBE, BLA, AcbSh, core area of accumbens nucleus (AcbC) and central part of dorsal tegmental nucleus (DTgC). The results suggested that brain areas taking part in the establishment of the CTA were associated with brain areas participating in the extinction of the CTA, but there were differences between them.