Poor sensitization of 50-kHz vocalization response to amphetamine predicts rat susceptibility to self-administration of the drug

Rationale: Our previous studies showed promise for using sensitization of the frequency-modulated 50-kHz vocalization response to amphetamine (AMPH) as an index of rat vulnerability to AMPH addiction.

Objective: This study aimed to test the utility of sensitizing frequency-modulated (FM) 50-kHz vocalization in the AMPH self-administration paradigm as well as the ability of N-acetylcysteine to prevent self-administration relapse.

Methods: Rats were subjected to the so-called two-injection protocol of sensitization (TIPS) using AMPH and were categorized as low-sensitized callers (LCTIPS) or high-sensitized callers (HCTIPS) based on the individual outcomes. Then, they were given 44 sessions of AMPH self-administration followed by a 17-session N-acetylcysteine-aided extinction course and a single session of AMPH-primed self-administration reinstatement.

Results: LCTIPS compared to HCTIPS rats showed no considerable difference in the FM 50-kHz vocalization rate during the self-administration training or extinction course, but they were considerably more likely to acquire AMPH self-administration and experience drug-induced reinstatement of this trait. Moreover, the LCTIPS rats were more likely than HCTIPS rats to have a markedly higher FM 50-kHz vocalization rate after AMPH reinstatement. N-acetylcysteine did not affect the course of self-administration extinction or the instrumental or FM 50-kHz vocalization responses to AMPH reinstatement.

Conclusions: There is no link between the FM 50-kHz vocalization and key characteristics of AMPH self-administration. Additionally, N-acetylcysteine does not help prevent AMPH self-administration relapse. However, there is a high predictive value for poor sensitization of the FM 50-kHz vocalization response to AMPH with respect to the acquisition and maintenance of self-administration of this psychostimulant.