Stimuli present during this time period were the self-administration chamber and lever.
Animals were housed in the self-administration chamber during the self-administration phase of the experiment.
Thus, the SD, but not the lever press or self-administration chamber, was highly correlated with the outcome, or infusion of cocaine.
Each self-administration chamber was also equipped with two pairs of infrared beams 2 cm above the grid floor (Imétronic, France).
Furthermore, during the self-administration phase of the experiment, animals lived in the self-administration chamber, spending 18 hours of each training day not self-administering.
Subsequently, animals were returned to the self-administration chamber 18 to 72 hours before the test of cue-induced responding (details of test in [22]).
Other methods such as LiCl delivery following cocaine self-administration (i.e. punishment) pair LiCl-induced illness with cocaine, instrumental responding, the self-administration chamber, and the prior presentations of the discriminative stimuli, which would generate ambiguous interpretations of testing data.
The weak correlation of these environmental cues with the cocaine infusion may be a factor in the development of habitual behavior [7], [27], [28] and the reason why the lever and self-administration chamber did not apparently evoke a representation of the devalued cocaine in the paired group and thereby influence response rates in the test hour prior to SD presentations.
This may be especially important because our prior investigation on SD-induced responding yielded markedly diminished responding during the first hour of testing when animals were housed in the self-administration chamber over 30 days of forced abstinence prior to the cue-presentation test [22].
During the cue-elicited test sessions, rats were placed into the self-administration chamber connected to the tethers for a 1 h test session during which active lever responses on an FR1 schedule of reinforcement resulted in response-contingent presentations of the same stimulus complex that had been previously paired with cocaine infusions.
Again, the rats were put in the self-administration chambers and connected to the microdialysis systems the night before testing and perfused at 0.4 µl/min overnight.
