Different regions of the periaqueductal grey are involved differently in the expression and conditioned inhibition of fear-potentiated startle

The fear-potentiated startle paradigm is a useful model for investigating the neural systems underlying the mediation and modulation of fear and anxiety. A series of previous studies showed that the periaqueductal grey is involved in the expression and inhibition of fear-potentiated startle, but it was uncertain whether the different columns of the periaqueductal grey play different roles, In the present study, picrotoxin, a GABA(A) (gamma-aminobutyric acid) chloride-channel blocker, was injected into the dorsal, lateral and ventrolateral columns of the periaqueductal grey in order to examine the effects of neural disinhibition on expression and conditioned inhibition of fear-potentiated startle, Picrotoxin injections into the lateral periaqueductal grey increase potentiation of the startle response by conditioned fear, injections into the ventrolateral periaqueductal grey block fear-potentiated startle. Picrotoxin injections into the dorsal periaqueductal grey decreased conditioned inhibition but did not affect expression of fear-potentiated startle. The baseline startle amplitude was not influenced by picrotoxin injections into the different columns of the periaqueductal grey. Picrotoxin injections into neighbouring brain areas did not have any effect on baseline startle amplitude nor did they have an effect on expression or conditioned inhibition of fear-potentiated startle. Based on the present results, the possible pathways underlying the expression and conditioned inhibition of fear-potentiated startle in rats are discussed.