Determination of steady-state transcriptome modifications associated with repeated homotypic stress in the rat rostral posterior hypothalamic region
Chronic stress is epidemiologically correlated with physical and psychiatric disorders. Whereas many animal models of chronic stress induce symptoms of psychopathology, repeated homotypic stress typically fails to induce these symptoms and may even protect against the effects of subsequent stress exposures. Recent results indicate that the rostral posterior hypothalamic (rPH) region is a significant component of the brain circuitry underlying response reductions (habituation) associated with repeated homotypic stress. To test whether posterior hypothalamic transcriptional regulation associates with the behavioral modifications induced by repeated homotypic stress, RNA-seq was performed in the rPH dissected from adult male rats that experienced either no stress, 1, 3, or 7 stressful loud noise exposures. Plasma samples displayed reliable increases of corticosterone in all stressed groups, with the smallest increase in the group exposed to 7 loud noises, indicating significant habituation compared to the other stressed groups. While no differentially expressed genes were detected 24-hrs after a single loud noise exposure, 36 and 405 transcripts were differentially expressed between the control vs 3-stress and control vs 7-stress groups, respectively, which correlated with the corticosterone habituation observed. Gene ontology analyses indicated multiple significant functional terms related to neuron differentiation, neural membrane potential, pre- and post-synaptic elements, chemical synaptic transmission, vesicles, axon guidance and projection, glutamatergic and GABAergic neurotransmission. Some of the differentially expressed genes (Zmat4, Dlx6) encoded transcription factors that were independently predicted by transcription factor enrichment analysis to target other differentially regulated genes in the set. A similar experiment employing in situ hybridization histochemical analysis in additional animals validated the direction of change of the 5 transcripts investigated (Camk4, Gabrb2, Gad1, Grin2a and Slc32a) with a high level of temporal and regional specificity for the rPH. In aggregate, the results suggest that distinct patterns of gene regulation are obtained in response to repeated homotypic vs. heterotypic stress regimens; they also point to a significant reorganization of the rPH region that may critically contribute to the phenotypic modifications associated with repeated homotypic stress habituation. Overall design: Gene expression profiling of RNA-seq data generated from 4 groups (n=6/group) of independent rat brains in the rostral posterior hypothalamic region after control, 1, 3 or 7 30-loud noise presentations.