[P3-3-10] Responses to conditioned taste stimuli of amygdalar neurons defined by genetic tracing after acquisition and extinction of conditioned taste aversion memory
Keywords:味覚、ニューロン、味覚嫌悪学習
Sweet and bitter taste stimuli innately evoke attractive and aversive behavioral responses, respectively. In the experimental model of conditioned taste aversion (CTA) in mice, oral application of saccharin, a novel sweet tastant (conditioned stimulus [CS]), is followed by intraperitoneal injection of lithium chloride that induces illness (unconditioned stimulus [US]), resulting in that mice acquire one-trial learning of CTA to the CS saccharin. Although the association of CS and US in a subset of CREB-overexpressing neurons in the basolateral amygdala (BLA) appears to be required for acquisition of CTA memory, it remains elusive how the BLA neurons receiving the convergent input and their downstream neurons could induce plastic changes in activities to respond to the CS. Here we combined genetic tracing and immunohistochemical analyses to examine whether the subsets of bitter taste-relaying neurons in the amygdala changed their responses to orally-applied saccharin after CTA learning, and after extinction of CTA memory. Bitter taste-relaying neurons in the amygdala were defined in the transgenic mice expressing the transneuronal tracer WGA-DsRed in bitter taste receptor cells by detecting the neurons labeled by WGA-DsRed that originated from bitter taste receptor cells. WGA-DsRed-labeled neurons were found in the medial amygdala. To clarify whether the bitter taste-relaying neurons in the medial amygdala were activated by oral application of saccharin, we detected the expression of Zif268, an immediate early gene, in the WGA-DsRed-labeled neurons. Immunohistochemical detection of Zif268 induction revealed that in the anterodorsal, anteroventral, and posterodorsal regions of the medial amygdala, more bitter taste-relaying neurons were activated by saccharin after CTA acquisition, compared with those observed before CTA. The increased ratios of the saccharin-activated neurons among bitter taste-relaying neurons in those regions of the medial amygdala persisted after extinction of CTA memory.