Figure 1 depicts the dose-response curves for the breaking points and the number of lever presses per reinforcer delivery for all rats.
Figure 2 depicts group data normalized as the percentage of control for the breaking points (top panel) and the lever presses per reinforcer (bottom panel).
Both investigations found that naloxone reduced breaking points in organisms responding for palatable food under PR schedules.
Although drug effects were generally orderly, considerable variability both within and across subjects in baseline breaking points may have limited our ability to detect the effects in some subjects of the smallest dose of naloxone tested (1.0 mg/ kg).
(2015), we found that arranging a progressive schedule based on response duration produced breaking points sensitive to experimental manipulations.
As naloxone decreased both breaking points and total lever presses in our study, we cannot argue for any direct relevance of our data for evaluating Bailey et al.
Paired t tests were also calculated using Prism Version 6.0 to compare the responses per reinforcer and breaking points obtained following food deprivation to those recorded under mean control.
Figure 3 depicts the breaking points and the number of lever presses divided by reinforcers earned for each rat at each condition.
Figure 4 depicts group data normalized as the percentage of control for the breaking points (top panel) and the lever presses per reinforcer (bottom panel).
Although the data suggested that caffeine increased breaking points overall, this effect was neither statistically significant nor consistent across all rats.
However, unlike our study, they found that caffeine convincingly increased breaking points at those doses.
Prior to the current study, breaking points under PD schedules were shown to be sensitive to both deprivation and reinforcer quality (Bailey et al.
We chose to examine naloxone and caffeine because we anticipated that they might elicit opposite effects on breaking points and because they were readily available to us.
1 Breaking points (left yaxis) and lever presses pa reinforcer (right y-axis) at all doses of naloxone for all rats.