title: The Effects of Electrical and Optical Stimulation of Midbrain Dopaminergic Neurons on Rat 50-kHz Ultrasonic Vocalizations.
abstract: BACKGROUND
  Adult rats emit ultrasonic vocalizations (USVs) at around 50-kHz; these commonly occur in contexts that putatively engender positive affect. While several reports indicate that dopaminergic (DAergic) transmission plays a role in the emission of 50-kHz calls, the pharmacological evidence is mixed. Different modes of dopamine (DA) release (i.e., tonic and phasic) could potentially explain this discrepancy.
  
  
  OBJECTIVE
  To investigate the potential role of phasic DA release in 50-kHz call emission.
  
  
  METHODS
  In Experiment 1, USVs were recorded in adult male rats following unexpected electrical stimulation of the medial forebrain bundle (MFB). In parallel, phasic DA release in the nucleus accumbens (NAcc) was recorded using fast-scan cyclic voltammetry. In Experiment 2, USVs were recorded following response-contingent or non-contingent optogenetic stimulation of midbrain DAergic neurons. Four 20-s schedules of optogenetic stimulation were used: fixed-interval, fixed-time, variable-interval, and variable-time.
  
  
  RESULTS
  Brief electrical stimulation of the MFB increased both 50-kHz call rate and phasic DA release in the NAcc. During optogenetic stimulation sessions, rats initially called at a high rate comparable to that observed following reinforcers such as psychostimulants. Although optogenetic stimulation maintained reinforced responding throughout the 2-h session, the call rate declined to near zero within the first 30 min. The trill call subtype predominated following both electrical and optical stimulation.
  
  
  CONCLUSIONS
  The occurrence of electrically-evoked 50-kHz calls, time-locked to phasic DA (Experiment 1), provides correlational evidence supporting a role for phasic DA in USV production. However, in Experiment 2, the temporal dissociation between calling and optogenetic stimulation of midbrain DAergic neurons suggests that phasic mesolimbic DA release is not sufficient to produce 50-kHz calls. The emission of the trill subtype of 50-kHz calls potentially provides a marker distinguishing positive affect from positive reinforcement.
authors.affiliation: Department of Pharmacology and Therapeutics, Neuropsychopharmacology, McGill University Montreal, QC, Canada.
authors.forename: Tina
authors.initials: T
authors.lastname: Scardochio
authors.affiliation: Department of Psychology, Center for Studies in Behavioral Neurobiology, Concordia University Montreal, QC, Canada.
authors.forename: Ivan
authors.initials: I
authors.lastname: Trujillo-Pisanty
authors.affiliation: Department of Psychology, Center for Studies in Behavioral Neurobiology, Concordia University Montreal, QC, Canada.
authors.forename: Kent
authors.initials: K
authors.lastname: Conover
authors.affiliation: Department of Psychology, Center for Studies in Behavioral Neurobiology, Concordia University Montreal, QC, Canada.
authors.forename: Peter
authors.initials: P
authors.lastname: Shizgal
authors.affiliation: Department of Pharmacology and Therapeutics, Neuropsychopharmacology, McGill University Montreal, QC, Canada ; Department of Psychology, Center for Studies in Behavioral Neurobiology, Concordia University Montreal, QC, Canada.
authors.forename: Paul B S
authors.initials: PB
authors.lastname: Clarke
keywords: fast-scan cyclic voltammetry; midbrain dopaminergic neurons; nucleus accumbens; optogenetics; phasic dopamine; ultrasonic vocalizations