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. 2021 Jun 15;22(12):6416.
doi: 10.3390/ijms22126416.

Is PTSD-Phenotype Associated with HPA-Axis Sensitivity?: The Endocannabinoid System in Modulating Stress Response in Rats

Dor Danan  1 , Doron Todder  1 , Joseph Zohar  2 , Hagit Cohen  1
Affiliations

Is PTSD-Phenotype Associated with HPA-Axis Sensitivity?: The Endocannabinoid System in Modulating Stress Response in Rats

Dor Danan et al. Int J Mol Sci. .

Abstract

Endocannabinoids play a role in adaptation to stress and regulate the release of glucocorticoids in stressed and unstressed conditions. We recently found that basal corticosterone pulsatility may significantly impact the vulnerability for developing post-traumatic-stress-disorder (PTSD), suggesting that the endocannabinoid system may contribute to its development. To examine this, we exposed rats to predator scent stress (PSS). Behavioral reactions were recorded seven days post-PSS. Cerebrospinal fluid (CSF) was collected from anesthetized rats shortly after PSS exposure to determine the levels of 2-arachidonoyl glycerol (2-AG) and anandamide (AEA). To correlate between endocannabinoids and corticosterone levels, rats were placed in metabolic cages for urine collection. To assess the levels of endocannabinoids in specific brain regions, rats' brains were harvested one day after behavioral analysis for staining and fluorescence quantification. Moreover, 2-AG was elevated in the CSF of PTSD-phenotype rats as compared with other groups and was inversely correlated with corticosterone urinary secretion. Eight days post-PSS exposure, hippocampal and hypothalamic 2-AG levels and hippocampal AEA levels were significantly more reduced in the PTSD-phenotype group compared to other groups. We posit that maladaptation to stress, which is propagated by an abnormal activation of endocannabinoids, mediates the subsequent stress-induced behavioral disruption, which, later, reduces neuronal the expression of endocannabinoids, contributing to PTSD symptomology.

Keywords: 2-arachidonoyl glycerol; anandamide; animal model; corticosterone; endocannabinoids; hypothalamus-pituitary-adrenal axis; posttraumatic stress disorder; pulsatility.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Timeline of the experiment after a 7-day habitation period; rats were exposed to predator scent stress (PSS)/sham PSS. Cerebrospinal fluid (CSF) samples were collected 60–120 min after PSS for evaluated levels of 2-arachidonoyl glycerol (2-AG) and anandamide (AEA). Urine corticosterone levels 60–120 min following exposure were also monitored. Behavioral assessments were conducted 7 days post-exposure to PSS, first in the Elevated Plus Maze (EPM) paradigm, and, 1 h later, in the Acoustic startle response (ASR) paradigm; on the following day, rats were executed and their brains were harvested for analysis.
Figure 2
Figure 2
Behavioral responses Effects of the predator scent stress paradigm on overall anxiety-like behavior and startle response. Three-dimensional parameters: The X-axis represents time spent in the open arms (min), the Y-axis represents acoustic startle amplitude, the Z-axis represents startle habituation. Squares represent the exposed group that exhibited an extreme behavioral disruption (EBR) (PTSD phenotype) on the elevated plus-maze, and a pattern of exaggerated startle responses with significantly reduced habituation, 7 days after exposure. Triangles represent the exposed group that exhibited partial behavioral response patterns (PBR). Circles represent the exposed group that exhibited minimal behavioral disruption (MBR). The stress response was not homogeneous, and several subgroups were identifiable in the population.
Figure 3
Figure 3
Cerebrospinal fluid (CSF) endocannabinoid levels shortly after predator scent stress (PSS) exposure (A) Graph showing 2-arachidonoyl glycerol (2-AG) levels in the CSF 60–120 min following PSS, in controls and in the different cut-off behavioral criteria (CBC) groups. Significant differences are shown on the graph. (B) Graph showing anandamide (AEA) levels in the CSF 60–120 min following PSS, in controls and in the different CBC groups. C.
Figure 4
Figure 4
Urine corticosterone concentrations shortly after predator scent stress (PSS) exposure. (A) Urine corticosterone concentrations 60–90 min following PSS in controls and in the different cut-off behavioral criteria (CBC) groups. Significant differences are shown on the graph. (B) Correlation between 2-arachidonoyl glycerol (2-AG) levels in the cerebrospinal fluid (CSF) and urine corticosterone shortly after PSS. Significant values are shown in the graphs.
Figure 5
Figure 5
Brain endocannabinoid levels 8 days post-PSS exposure. (A) Graph showing 2-AG levels in the hippocampus 8 days post-PSS exposure. (B) Graph showing 2-AG levels in the hypothalamus 8 days post-PSS exposure. (C) Graph showing AEA levels in the hippocampus 8 days post-PSS exposure. (D) Graph showing AEA levels in the hypothalamus 8 days post-PSS exposure. Significant values are shown in the graphs.
Figure 5
Figure 5
Brain endocannabinoid levels 8 days post-PSS exposure. (A) Graph showing 2-AG levels in the hippocampus 8 days post-PSS exposure. (B) Graph showing 2-AG levels in the hypothalamus 8 days post-PSS exposure. (C) Graph showing AEA levels in the hippocampus 8 days post-PSS exposure. (D) Graph showing AEA levels in the hypothalamus 8 days post-PSS exposure. Significant values are shown in the graphs.
Figure 6
Figure 6
Fixation of rats in a stereotactic device during puncture of the great cerebral cistern. Adapted from ref. [70].
See this image and copyright information in PMC

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