Infusion of quinpirole and muscimol into the ventral tegmental area inhibits fear-potentiated startle: implications for the role of dopamine in fear expression.

Dopamine (DA) D2 and gamma-aminobutyric acid (GABA)A somatodendritic receptors tonically inhibit mesolimbic projection neurons in the A10 DA cell grouping of the ventral tegmentum. In the present study we determined the contribution of the ventral tegmental area (VTA) to the expression of a classically conditioned fear-induced increase in the acoustic startle reflex. Saline applied to VTA neurons did not modify the capacity of a light previously associated with footshock to potentiate acoustic startle amplitudes; conversely, bilateral administration of the DA D2/3 agonist quinpirole or the GABAA receptor agonist muscimol into the ventral tegmentum blocked fear-potentiated startle without altering baseline acoustic startle responding. It was suggested that DA VTA neurons regulate the excitatory aspects of fear expression by gating levels of aversive emotional arousal within the amygdala-based fear system.