Altered pontine taste processing in a rat model of obesity

The increased palatability of modern diet contributes to eating beyond homeostatic need and in turn to the growing prevalence of obesity. How palatability is coded in taste-evoked neural activity and whether this activity differs between obese and lean remains unknown. To investigate this, we used extracellular single-unit recording in the second central gustatory relay, the pontine parabrachial nucleus while stimulating the tongue with various concentrations of sucrose (0.01-1.5 M) in Otsuka Long Evans Tokushima Fatty (OLETF) rats, lacking CCK-1R. The analyses included a total of 179 taste-responsive neurons in age-matched prediabetic, obese OLETF and lean Long Evans Tokushima Otsuka (LETO) controls. Compared with LETO, we found more NaCl-, and fewer sucrose-responsive neurons (67 vs. 47% and 14 vs. 32%), and an overall reduced response magnitude to sucrose in the OLETF rats. Further, in the obese rats there was a rightward shift in sucrose concentration-response functions relative to lean controls with a higher response-threshold (0.37 ± 0.05 vs. 0.23 ± 0.2 M, P < 0.05) and maximal neural response to higher sucrose concentrations (0.96 ± 0.07 vs. 0.56 ± 0.5 M, P < 0.001). These findings demonstrate altered central gustatory processing for sucrose in obese OLETF rat and further support the notion that palatability is encoded in the across neuron pattern.