Expression and conditioned inhibition of fear-potentiated startle after stimulation and blockade of AMPA/Kainate and GABA(A) receptors in the dorsal periaqueductal gray

Previous work showed that the dorsal periaqueductal gray is involved in the inhibition of fear-potentiated startle. The present study investigated the effects of blockade and stimulation of Kainate/AMPA and GABA(A) receptors within the dorsal periaqueductal gray on expression and conditioned inhibit ion of fear-potentiated startle. Blockade of the Kainate/AMPA receptors enh anced whereas stimulation of the Kainate/AMPA receptors decreased expressio n of fear-potentiated startle. These effects do not reflect conditioned inh ibition since this modulation was not changed by injections of Kainate/AMPA receptor agonists or antagonists into the dorsal periaqueductal gray. Stim ulation and blockade of GABA(A) receptors within the dorsal periaqueductal gray neither affected expression of fear-potentiated startle nor its condit ioned inhibition. The present results together with findings from the liter ature indicate that glutamate in the dorsal periaqueductal gray is a critic al substrate for the expression and modulation of fear-related behaviours. (C) 2000 Elsevier Science B.V. All rights reserved.