CRF1 and CRF2 receptors are required for potentiated startle to contextual but not discrete cues.

Corticotropin-releasing factor (CRF) peptides and their receptors have crucial roles in behavioral and endocrine responses to stress. Dysregulation of CRF signaling has been linked to post-traumatic stress disorder, which is associated with increased startle reactivity in response to threat. Thus, understanding the mechanisms underlying CRF regulation of startle may identify pathways involved in this disorder. Here, we tested the hypothesis that both CRF1 and CRF2 receptors contribute to fear-induced increases in startle. Startle responses of wild type (WT) and mice with null mutations (knockout, KO) for CRF1 or CRF2 receptor genes were measured immediately after footshock (shock sensitization) or in the presence of cues previously associated with footshock (ie fear-potentiated startle, FPS). WT mice exhibited robust increases in startle immediately after footshock, which was dependent upon contextual cues. This effect was completely absent in CRF1 KO mice, and significantly attenuated in CRF2 KO mice. In contrast, CRF1 and CRF2 KO mice exhibited normal potentiation of startle by discrete conditioned cues. Blockade of both receptors via CRF1 receptor antagonist treatment in CRF2 KO mice also had no effect on FPS. These results support an additive model of CRF1 and CRF2 receptor activation effects on potentiated startle. These data also indicate that both CRF receptor subtypes contribute to contextual fear but are not required for discrete cued fear effects on startle reactivity. Thus, we suggest that either CRF1 or CRF2 could contribute to the increased startle observed in anxiety disorders with CRF system abnormalities

Relations of combat stress and posttraumatic stress disorder to 24-h plasma and cerebrospinal fluid interleukin-6 levels and circadian rhythmicity

Background: Acute and chronic stress can lead to a dysregulation of the immune response. Growing evidence suggests peripheral immune dysregulation and low-grade systemic inflammation in posttraumatic stress disorder (PTSD), with numerous reports of elevated plasma interleukin-6 (IL-6) levels. However, only a few studies have assessed IL-6 levels in the cerebrospinal fluid (CSF). Most of those have used single time-point measurements, and thus cannot take circadian level variability and CSF-plasma IL-6 correlations into account. Methods: This study used time-matched, sequential 24-h plasma and CSF measurements to investigate the effects of combat stress and PTSD on physiologic levels and biorhythmicity of IL-6 in 35 male study volunteers, divided in 3 groups: (PTSD = 12, combat controls, CC = 12, and non-deployed healthy controls, HC = 11). Results: Our findings show no differences in diurnal mean concentrations of plasma and CSF IL-6 across the three comparison groups. However, a significantly blunted circadian rhythm of plasma IL-6 across 24 h was observed in all combat-zone deployed participants, with or without PTSD, in comparison to HC. CSF IL-6 rhythmicity was unaffected by combat deployment or PTSD. Conclusions: Although no significant group differences in mean IL-6 concentration in either CSF or plasma over a 24-h timeframe was observed, we provide first evidence for a disrupted peripheral IL-6 circadian rhythm as a sequel of combat deployment, with this disruption occurring in both PTSD and CC groups. The plasma IL-6 circadian blunting remains to be replicated and its cause elucidated in future research. © 201