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 t he neural systems underlying the mediation and modulation of fear and anxie ty. A series of previous studies showed that the periaqueductal grey is inv olved 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-aminob utyric acid) chloride-channel blocker, was injected into the dorsal, latera l and ventrolateral columns of the periaqueductal grey in order to examine the effects of neural disinhibition on expression and conditioned inhibitio n of fear-potentiated startle, Picrotoxin injections into the lateral peria queductal grey increase potentiation of the startle response by conditioned fear, injections into the ventrolateral periaqueductal grey block fear-pot entiated startle. Picrotoxin injections into the dorsal periaqueductal grey decreased conditioned inhibition but did not affect expression of fear-pot entiated startle. The baseline startle amplitude was not influenced by picr otoxin injections into the different columns of the periaqueductal grey. Pi crotoxin injections into neighbouring brain areas did not have any effect o n baseline startle amplitude nor did they have an effect on expression or c onditioned inhibition of fear-potentiated startle. Based on the present res ults, the possible pathways underlying the expression and conditioned inhib ition of fear-potentiated startle in rats are discussed.