Association of medial corticostriatal regions with amphetamine-induced emission of 50 kHz vocalizations as studied by Zif-268 expression in the rat brain

Behavioural sensitization of locomotion and 50 kHz ultrasonic vocalizations (USVs) following repeated amphetamine (AMPH) injections in rats has been extensively demonstrated. These two behaviours appear dissociable in their sensitization patterns and are thought to be reflective of underlying emotional states of the organism. Although AMPH is often used to induce 50 kHz USVs there is little research to date on the extent of cortical and subcortical forebrain region involvement in 50 kHz call production associated with the drug. Nor has general ergometric activity (a measure that in addition to locomotor activity includes all major muscular activity of the body) been investigated in such a framework. The present study sought to address this by performing a minimal sensitization protocol, utilizing only two injections, to investigate expression of the inducible transcription factor Zif-268 (Zif) among brain regions thought to be associated with 50 kHz USV emission. It was found that animals that spent a longer time emitting 50 kHz calls after a second AMPH injection showed statistically significant correlative patterns of Zif expression in medial prefrontal and striatal regions. These associations were not significant in animals that spent a shorter period of time calling after AMPH. There was also no significant correlation between any ergometric activity and time spent calling. The results provide evidence that the medial prefrontal cortices (prelimbic and infralimbic regions) of the rat may be involved with 50 kHz USV emission induced by AMPH in association with medial portions of the ventral and dorsal striatum.