Intracerebral injection of R-(-)-Apomorphine into the nucleus accumbens decreased carbachol-induced 22-kHz ultrasonic vocalizations in rats

Publication date: Available online 26 January 2019

Source: Behavioural Brain Research

Author(s): Michael Silkstone, Stefan M. Brudzynski

Abstract

Rats can produce ultrasonic vocalizations (USVs) in a variety of different contexts that signal their emotional state to conspecifics. Under distress, rats can emit 22-kHz USVs, while during positive pro-social interactions rats can emit frequency-modulated (FM) 50-kHz USVs. It has been previously reported that rats with increasing emission of FM 50-kHz USVs in anticipation of rewarding electrical stimulation or positive pro-social interaction decrease the number of emitted 22-kHz USVs. The purpose of the present investigation was to determine, in a pharmacological-behavioural experiment, if the positive emotional arousal of the rat indexed by the number of emitted FM 50-kHz USVs can decrease the magnitude of a subsequent negative emotional state indexed by the emission of 22-kHz USVs. To induce the positive emotional arousal, an intracerebral injection of a known D₁/D₂ agonist R-(-)-apomorphine (3.0 µg/0.3 µl) into the medial nucleus accumbens shell was used, while the negative emotional arousal was induced by intracerebral injection of carbachol (1.0 µg/0.3 µl), a known broad-spectrum muscarinic agonist, into the anterior hypothalamic-medial preoptic area. Our results demonstrated that initiation of a positive emotional state was able to significantly decrease the magnitude of subsequently expressed negative emotional state measured by the number of emitted 22-kHz USVs. The results suggest the neurobiological substrates that initiate positive emotional state antagonize the brain regions that initiate negative emotional states.

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