Functional Connectivity from the Amygdala to the Hippocampus Grows Stronger after Stress

Abstract

The cellular and molecular effects of stress on the amygdala are strikingly different compared with those in the hippocampus. Previous findings on stress-induced plasticity were based primarily on postmortem analysis within individual areas. However, little is known about how stress affects dynamic changes and interactions in neuronal activity between the two areas. Hence, we simultaneously monitored in vivo activity of neuronal populations located in hippocampal areas CA1 and CA3 and the lateral amygdala (LA) in rats during and after chronic immobilization stress. The amplitude of auditory-evoked potentials (AEPs) in the hippocampus increased transiently only after a single 2 h stress but not when it was repeated for 10 d. In contrast, both acute and chronic stress caused a persistent increase in AEPs in the LA. Chronic stress also elicited a sustained increase in the LA but a decrease in the hippocampus in the evoked power of gamma and beta frequencies. Moreover, beta and gamma synchrony was reduced between areas CA1 and CA3 but enhanced between the LA and hippocampus after chronic stress. Granger causality spectra revealed a strong directional influence from the LA to area CA1 that persisted throughout and even 10 d after chronic stress. However, directional coupling from hippocampal area CA3 to CA1 became weaker at the end of chronic stress. Thus, our findings suggest that the growing dominance of amygdalar activity over the hippocampus during and even after chronic stress may contribute to the enhanced emotional symptoms, alongside impaired cognitive function, seen in stressrelated psychiatric disorders.

Role of FKBP5 in emotion processing: results on amygdala activity, connectivity and volume

“…Hence, differential connectivity patterns between the amygdala and the hippocampus may provide a neural model underlying the increased risk of stress-related disorders in T homozygotes. Crucially, this coupling has been demonstrated to increase after stress (Ghosh et al 2013;Vaisvaser et al 2013), which is in line with the prolonged stress response in T homozygotes (Binder 2009). …”

“…The amygdala-hippocampus connection has been demonstrated to be critically involved in the formation of emotional memory (Hooker et al 2008;Phelps 2004). Moreover, amygdala-hippocampus connectivity has been shown to be influenced by stress exposure (Ghosh et al 2013;Vaisvaser et al 2013). …”

Hippocampal structural plasticity accompanies the resulting contextual fear memory following stress and fear conditioning

“…Furthermore, muscimol infusion into the BLA blocks stress-induced impairments in hippocampal long-term potentiation and spatial memory (Kim et al 2005). Hence, there is growing evidence that the amygdala has a prominent role in the influence of stress on hippocampal function (Kim et al 2005;Ghosh et al 2013). To sum up, these findings highlight the key role played by BLA in coordinating structural plasticity in the downstream areas involved in memory processing and storage (McIntyre et al 2003;McGaugh 2004).…”

Effects of post-encoding stress on performance in the DRM false memory paradigm

“…Evidence suggests that brain regions involved in emotional (e.g., amygdala) and neutral memory consolidation (e.g., hippocampus) are differentially impacted by elevated stress and cortisol (Payne et al 2004(Payne et al , 2006(Payne et al , 2007. For example, while high levels of stress and cortisol often disrupt hippocampal function, they potentiate activity in the amygdala (e.g., Vyas et al 2002;van Stegeren et al 2007a,b;Pruessner et al 2008;Ghosh et al 2013). Our results are consistent with this idea in that, using only neutral lists, impairment of hippocampal processing by stress may have disrupted veridical memory for studied words (see also Smeets et al 2006), while the emotional words used by Smeets et al (2008) may have benefited from stress, because they rely on amygdala activation.…”