Changes at glutamate tripartite synapses in the prefrontal cortex of a new animal model of resilience/vulnerability to acute stress

Abstract

Stress represents a main risk factor for psychiatric disorders. Whereas it is known that even a single trauma may induce psychiatric disorders in humans, the mechanisms of vulnerability to acute stressors have been little investigated. In this study, we generated a new animal model of resilience/vulnerability to acute footshock (FS) stress in rats and analyzed early functional, molecular, and morphological determinants of stress vulnerability at tripartite glutamate synapses in the prefrontal cortex (PFC). We found that adult male rats subjected to FS can be deemed resilient (FS-R) or vulnerable (FS-V), based on their anhedonic phenotype 24 h after stress exposure, and that these two populations are phenotypically distinguishable up to two weeks afterwards. Basal presynaptic glutamate release was increased in the PFC of FS-V rats, while depolarization-evoked glutamate release and synapsin I phosphorylation at Ser9 were increased in both FS-R and FS-V. In FS-R and FS-V rats the synaptic expression of GluN2A and apical dendritic length of prelimbic PFC layers II–III pyramidal neurons were decreased, while BDNF expression was selectively reduced in FS-V. Depolarization-evoked (carrier-mediated) glutamate release from astroglia perisynaptic processes (gliosomes) was selectively increased in the PFC of FS-V rats, while GLT1 and xCt levels were higher and GS expression reduced in purified PFC gliosomes from FS-R. Overall, we show for the first time that the application of the sucrose intake test to rats exposed to acute FS led to the generation of a novel animal model of resilience/vulnerability to acute stress, which we used to identify early determinants of maladaptive response related to behavioral vulnerability to stress.

Molecular signatures of astrocytes and microglia maladaptive responses to acute stress are rescued by a single administration of ketamine in a rodent model of PTSD

“…Recently, we introduced the use of the sucrose intake test in rats exposed to acute FS as a rapid screening tool to distinguish acute stress-vulnerable from -resilient animals and to identify early determinants of a pro-adaptive or maladaptive stress response [43]. As previously shown, a single session of acute inescapable FS selectively triggers anhedonic behavior in a subpopulation of stressed rats, thus considered FS-V. We have also previously reported that the anhedonia observed in FS-V lasts more than a week and is reversible, that glutamate release is differentially activated in neurons and astrocytes, and that FS-R and FS-V differ in expression levels of astrocytic proteins that regulate glutamate homeostasis, suggesting glial involvement in promoting a pro-adaptive or maladaptive response to FS [43]. Notably, a multiomics study has shown that glial cells are the major contributors to the transcriptional bulk sequencing signal observed after acute stress [65].…”

“…Adult male Sprague-Dawley rats (175-200 g at the beginning of the protocol) were exposed to acute inescapable FS and deemed FS-R or FS-V as reported in Bonifacino et al [43]. After obtaining the required licenses (N 521/2015-PR and 140/2014-B-DGSAF24898), all experimental procedures were performed following the European Community Council Directive 2010/63/UE and the Italian D.L.26/2014.…”

“…We have previously shown that FS causes shortening and simpli cation of apical dendrites in PFC pyramidal neurons as early as 24 h after stress [42,43]. Our previous data showing a greater reduction in the number of intersections selectively in FS-V suggest subtle stress-induced differences in dendritic remodeling [43]. Here, we found a signi cant increase in the dendritic marker MAP2 and the neurotrophin BDNF exclusively in FS-R (24 hours after stress that persisted up to 48 hours after stress), suggesting activation of trophic mechanisms that presumably counteract the effects of stress.…”

Molecular signatures of astrocytes and microglia maladaptive responses to acute stress are rescued by a single administration of ketamine in a rodent model of PTSD

“…Adult male Sprague-Dawley rats (175–200 g at the beginning of the protocol) were exposed to acute inescapable FS and deemed FS-R or FS-V as reported in Bonifacino et al [ 50 ]. After having obtained the licenses required (N 521/2015-PR and 140/2014-B-DGSAF24898), all experimental procedures were performed according to the European Community Council Directive 2010/63/UE and the Italian D.L.26/2014.…”

“…In the present study, we used a recently validated rat model of resilience/vulnerability to acute inescapable footshock stress (FS) [ 50 ] to investigate the functional, molecular, and morphological determinants of the adaptive/maladaptive response to traumatic stress. Our experiments were performed in the rat prefrontal cortex (PFC) where we examined the density and function of astrocytes, microglia, and neurons.…”