Regulation of conditioned and unconditioned fear in rats by 5-HT1A receptors in the dorsal periaqueductal gray.

Studies on the involvement of 5-HT1-mediated mechanisms in the dorsal periaqueductal gray (dPAG) of animals with past stressful experiences have not been conducted so far. We investigated the role of 5-HT1 receptors in the dPAG of rats previously submitted to contextual fear conditioning. Defensive behaviors induced by activation of the dPAG were assessed by measuring the lowest electric current applied to this structure (threshold) able to produce freezing and escape responses during testing sessions of contextual fear conditioning, in which animals were placed in a context previously paired to footshocks.

5-HT2 receptor mechanisms of the dorsal periaqueductal gray in the conditioned and unconditioned fear in rats.

Rationale: It is well known that 5-HT(2) mechanisms modulate the defensive behavior produced by the stimulation of the dorsal periaqueductal gray (dPAG). However, in spite of the notion that past stressful experiences play a role in certain types of anxiety, only studies with the stimulation of the dPAG of rats without previous aversive experience have been conducted so far.

Objectives: We investigated the mediation of 5-HT(2) receptors of the dPAG in rats previously submitted to contextual fear conditioning (CFC).