Ipsilateral connections between the gustatory cortex, amygdala and parabrachial nucleus are necessary for acquisition and retrieval of conditioned taste aversion in rats

Acquisition and retrieval of conditioned taste aversion (CTA) is implemented by the interaction of several brain structures. In order to clarify the role of 3 important gustatory and visceral relays, gustatory neocortex (GC), amygdala (AM) and parabrachial nucleus (PB), two experimental series were carried out. In Expt. 1 reversible unilateral lesions of the PB and AM or of AM and GC were induced by 10 ng of tetrodotoxin (TTX) either in the same hemisphere or in the opposite hemispheres during CTA acquisition. It was found that contralateral TTX injections into the above structures caused a complete blockade of CTA acquisition which was not affected by ipsilateral TTX administration. In Expt. 2, retrieval of CTA acquired during unilateral blockade of the PB or AM in one hemisphere has been examined during unilateral TTX blockade of GC alone, AM alone or during combined GC and AM inactivation either in the same or in the contralateral hemispheres. A clear CTA retrieval impairment was found only when structures in the opposite hemispheres were blocked. These results indicate a complete lateralization of CTA acquisition and retrieval processes and suggest that the long-term CTA engram can be formed in each hemisphere separately without participation of the contralateral hemisphere.