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The role of post‐ingestive cues in feeding preferences by mice that lack taste capabilities

The gustatory nerves of mice lacking P2X2 and P2X3 purinergic receptor subunits (P2X‐KO) are unresponsive to taste stimulation (Finger et al., 2005). Surprisingly, P2X‐KO mice show residual behavioral responses to concentrated tastants, presumably from post‐ingestive detection. Therefore, the current study tested whether tastant‐evoked gut signaling is functional in P2X‐KO mice. WT and P2X‐KO mice were given eight training sessions on alternating days either with an odor alone or with a different odor mixed with 150 mM monosodium glutamate (MSG). Then all animals were given preference tests consisting of both odors without MSG. Both WT and P2X‐KO animals preferred the odor previously paired with MSG showing post‐ingestive cues were detected and associated with an odor. Further, we measured MSG‐evoked brain activation, by expression of the immediate early gene c‐Fos (cFLI), in the n. of the solitary tract (nTS) ‐ the primary taste/viscerosensory nucleus. In gustatory levels of the nTS, significantly less cFLI was present in P2X‐KO animals compared to WT controls. In contrast, in the viscerosensory part of nTS, cFLI did not differ between WT and P2X‐KO mice. Together, these results suggest that P2X‐KO mice can form preferences based on post‐ingestive cues and that post‐ingestive detection of MSG does not require purinergic signaling that is crucial for the taste system. Supported by NIH and 3ARP grants to T.E.F.