Taste responses in the nucleus of the solitary tract in saccharin-preferring and saccharin-averse rats

A minority of rats consistently reject the taste of sodium saccharin at concentrations that the majority find palatable. We chose rats that selected either water (WP), or 0.03 M NaSaccharin (SP) in two-bottle preference tests and monitored single unit responses to a range of taste qualities in the nucleus of the solitary tract. WP rats gave significantly greater responses to Na/Li salts and QHCl. Their responses to sugars were equal to those from SP rats. Total activity to NaSaccharin did not differ between the two groups, but its distribution across the three identified neuron types did. The response was skewed from one in which sugar (5) and sodium salt (N) participated nearly equally (SP) to one dominated by the activity of N cells and nearly devoid of an S cell contribution (WP rats). Accordingly, the response profile for NaSaccharin was correlated nearly as well with those of the sugars (+ 0.60) as with the Na/Li salts (+ 0.73) in SP rats, but was reshaped in WP rats to be nearly identical with those of the salts (+ 0.85) and unlike sugars (+ 0.30). In their heightened sensitivity to stimuli that humans call salty and bitter, and in their rejection of the complex taste of NaSaccharin, WP rats showed many of the characteristics of human tasters of PTC/PROP.