Fig. 2.
Diluted Ensure®-maintained responding under a multi-day progressive-ratio schedule for 18% (top panel) or 56% (bottom panel) diluted Ensure® in male (circles; n = 6) and female (squares; n = 6) rats. a, d depict aggregate demand functions and nonlinear regression using the exponential model of demand for 18 and 56% diluted Ensure®, respectively. Ordinate: number of reinforcers earned per 120-min behavioral session. Abscissa: response requirement. Individually determined essential values for 18 and 56% diluted Ensure® are depicted in b and e, respectively. Individually determined Q0 values for 18 and 56% diluted Ensure® are depicted in c and f, respectively. *denotes significant (p < 0.05) difference between male and female rats