Enhancing Effects of Sound on Methamphetamine-Induced Behavioral Aberrations in the Rat: A Model of Relapse of Schizophrenia-Like Symptoms

Abstract: Conditioning of methamphetamine (MAP)-induced behavioral aberrations, hyperactivity (HA), stereotyped (SB) and bizarre behavior (BB) in rats were examined using Pavlovian conditioning methods. A speaker-sound (SS) was used as the conditioning stimulus (CS) and MAP-induced behavior as the unconditioned stimulus (UCS). The rats belonging to the Sound Group were repeatedly administered with MAP or saline paired with SS in an observation room and those in the Soundless Group with MAP only in the housing room.
After chronic administration with MAP, conditioned behavioral responses (CBR) such as HA, SB, and BB were observed more intensely in the Sound Group than in the Soundless Group while being subjected to SS. CBR were greatest on the 30th day after the last MAP administration and they did not disappear for 120 days.
CBR were considered as analogous to the spontaneous relapse of schizophrenia-like symptoms.
Furthermore, as a certain behavior which had been conditioned could easily be observed as CBR with both specific (SS) and nonspecific environmental cues (handling), it is difficult to distinguish the withdrawal behavioral effects of MAP that lacks those of CBR.