Exposure to the predator odor TMT induces early and late differential gene expression related to stress and excitatory synaptic function throughout the brain in male rats

Abstract

Persistent changes in brain stress and glutamatergic function are associated with post-traumatic stress disorder (PTSD). Rodent exposure to the predator odor trimethylthiazoline (TMT) is an innate stressor that produces lasting behavioral consequences relevant to PTSD. As such, the goal of the present study was to assess early (6 hours and 2 days) and late (4 weeks) changes to gene expression (RT-PCR) related to stress and excitatory function following TMT exposure in male, Long-Evans rats. During TMT exposure, rats engaged in stress reactive behaviors, including digging and immobility. Further, the TMT group displayed enhanced exploration and mobility in the TMT-paired context one week after exposure, suggesting a lasting contextual reactivity. Gene expression analyses revealed upregulated FKBP5 6 hours post-TMT in the hypothalamus and dorsal hippocampus. Two days after TMT, GRM3 was downregulated in the prelimbic cortex and dorsal hippocampus, but upregulated in the nucleus accumbens. This may reflect an early stress response (FKBP5) that resulted in later glutamatergic adaptation (GRM3).Finally, four weeks after TMT exposure, several differentially expressed genes known to mediate excitatory tripartite synaptic function were observed. Specifically in the prelimbic cortex (GRM5, DLG4 and SLC1A3 upregulated), infralimbic cortex (GRM2 downregulated, Homer1 upregulated), nucleus accumbens (GRM7 and SLC1A3 downregulated), dorsal hippocampus (FKBP5 and NR3C2 upregulated, SHANK3 downregulated) and ventral hippocampus (CNR1, GRM7, GRM5, SHANK3, and Homer1 downregulated). These data demonstrate that TMT exposure stress induces early and late stress and excitatory molecular adaptations, which may help us understand the persistent glutamatergic dysfunction observed in PTSD.

The effects of predator odor (TMT) exposure and mGlu3NAM pretreatment on lasting behavioral and molecular adaptations in the insular cortex and BNST

“…Consistent with previous findings, the TMT exposure produced engagement in stressreactive behaviors (immobility, digging, avoidance, and decreased grooming, distance traveled and midline crossings), indicating that TMT exposure is an acute stressor [56,58]. Pretreatment with the mGlu 3 NAM (VU6010572) did not affect any of these behaviors, suggesting that mGlu 3 -signaling during the stressor does not contribute to the engagement of acute stressreactive behaviors.…”

“…It is made regions [58]. Of relevance to the present work, we have reported decreased Grm3 gene expression 2 days after TMT exposure [58]. Given recent physiology findings previously discussed [29], we hypothesized that this change may reflect a transcriptional mechanism for loss of function following stressor-induced activation of mGlu 3 .…”

“…CC-BY-ND 4.0 International license available under a was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made regions [58]. Of relevance to the present work, we have reported decreased Grm3 gene expression 2 days after TMT exposure [58].…”

“…These studies show that mGlu 3 -signaling during exposure to the TMT predator odor stressor contributes to both behavioral (context reactivity) and molecular (glutamate receptor gene expression) adaptations approximately 2 weeks after the stressor exposure in male rats. Rats engaged in stress-reactive behaviors during the TMT exposure, and a hyperactive behavioral phenotype during the context re-exposure (in the absence of TMT) two weeks later, which may reflect hypervigilance to the stressor context [58]. TMT exposure did not produce differences in the zero maze or ASR test, but a single administration of the mGlu 3 contrast to the insular cortex, glutamate receptor gene expression in the BNST was more sensitive to mGlu 3 NAM than to the TMT exposure.…”

“…freezing behavior during the TMT exposure [58]. Time spent digging in the bedding (see [56,58]) and time spent grooming were quantified manually by an experimenter blind to experimental conditions. For the context re-exposure, two rats were removed from analysis due…”