Corticotropin-Releasing Factor-Producing Cells in the Paraventricular Nucleus of the Hypothalamus and Extended Amygdala Show Age-Dependent FOS and FOSB/DeltaFOSB Immunoreactivity in Acute and Chronic Stress Models in the Rat.

Corticotropin-releasing factor (CRF) immunoreactive (ir) neurons of the paraventricular nucleus of the hypothalamus (PVN) play pivotal role in the coordination of stress response. CRF-producing cells in the central nucleus of amygdala (CeA) and oval division of the bed nucleus of stria terminalis (BNSTov) are also involved in stress adaptation and mood control. Immediate early gene products, subunits of the transcription factor activator protein 1 (AP1) are commonly used as acute (FOS) and/or chronic (FOSB/deltaFOSB) markers for the neuronal activity in stress research. It is well known that the course of aging affects stress adaptation, but little is known about the aging-related stress sensitivity of CRF neurons. To the best of our knowledge, the stress-induced neuronal activity of CRF neurons in the course of aging in acute and chronic stress models was not studied systematically yet. Therefore, the aim of the present study was to quantify the acute restraint stress (ARS) and chronic variable mild stress (CVMS) evoked neuronal activity in CRF cells of the PVN, CeA, and BNSTov using triple-label immunofluorescence throughout the whole lifespan in the rat. We hypothesized that the FOS and FOSB content of CRF cells upon ARS or CVMS decreases with age. Our results showed that the FOS and FOSB response to ARS declined with age in the PVN-CRF cells. BNSTov and CeA CRF cells did not show remarkable stress-induced elevation of these markers neither in ARS, nor in CVMS. Exposure to CVMS resulted in an age-independent significant increase of FOSB/delta FOSB immunosignal in PVN-CRF neurons. Unexpectedly, we detected a remarkable stress-independent FOSB/deltaFOSB signal in CeA- and BNSTov-CRF cells that declined with the course of aging. In summary, PVN-CRF cells show decreasing acute stress sensitivity (i.e., FOS and FOSB immunoreactivity) with the course of aging, while their (FOSB/deltaFOSB) responsivity to chronic challenge is maintained till senescence. Stress exposure does not affect the occurrence of the examined Fos gene products in CeA- and BNSTov-CRF cells remarkably suggesting that their contribution to stress adaptation response does not require AP1-controlled transcriptional changes.

Construct and face validity of a new model for the three-hit theory of depression using PACAP mutant mice on CD1 background.

Major depression is a common cause of chronic disability. Despite decades of efforts, no equivocally accepted animal model is available for studying depression. We tested the validity of a new model based on the three-hit concept of vulnerability and resilience. Genetic predisposition (hit 1, mutation of pituitary adenylate cyclase-activating polypeptide, PACAP gene), early-life adversity (hit 2, 180-min maternal deprivation, MD180) and chronic variable mild stress (hit 3, CVMS) were combined. Physical, endocrinological, behavioral and functional morphological tools were used to validate the model. Body- and adrenal weight changes as well as corticosterone titers proved that CVMS was effective. Forced swim test indicated increased depression in CVMS PACAP heterozygous (Hz) mice with MD180 history, accompanied by elevated anxiety level in marble burying test. Corticotropin-releasing factor neurons in the oval division of the bed nucleus of the stria terminalis showed increased FosB expression, which was refractive to CVMS exposure in wild-type and Hz mice. Urocortin1 neurons became over-active in CMVS-exposed PACAP knock out (KO) mice with MD180 history, suggesting the contribution of centrally projecting Edinger-Westphal nucleus to the reduced depression and anxiety level of stressed KO mice. Serotoninergic neurons of the dorsal raphe nucleus lost their adaptation ability to CVMS in MD180 mice. In conclusion, the construct and face validity criteria suggest that MD180 PACAP HZ mice on CD1 background upon CVMS may be used as a reliable model for the three-hit theory.

Reduced response to chronic mild stress in PACAP mutant mice is associated with blunted FosB expression in limbic forebrain and brainstem centers.

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been implicated in stress adaptation with potential relevance in mood disorder management. PACAP deficient (KO) mice on CD1 background were shown to have depression-like phenotype. Here we aimed at investigating effects of chronic variable mild stress (CVMS) in non-injected, vehicle and imipramine-treated KO mice vs. wildtype (WT) counterparts. We hypothesized reduced FosB neuronal activity in stress-related centers, altered activity and peptide/neurotransmitter content of corticotropin-releasing factor (CRF) cells of the oval (ovBST) bed nucleus of stria terminalis (BST), urocortin 1 (Ucn1) neurons of centrally projecting Edinger-Westphal nucleus (cpEW) and serotonin (5HT) cells of dorsal raphe (DR) in PACAP deficiency. CVMS caused decreased body weight and increased adrenal size, corticosterone (CORT) titers and depression-like behavior in WT mice, in contrast to KO animals. CVMS increased FosB in the central (CeA) and medial amygdala, dorsomedial (dmBST), ventral (vBST), ovBST, CA1 area, dentate gyrus (DG), ventral lateral septum, parvo- (pPVN) and magnocellular paraventricular nucleus, lateral periaqueductal gray, cpEW and DR. Lack of PACAP blunted the CVMS-induced FosB rise in the CeA, ovBST, dmBST, vBST, CA1 area, pPVN and DR. The CVMS-induced FosB expression in ovBST-CRF and cpEW-Ucn1 neurons was abolished in KO mice. Although CVMS did not induce FosB in 5HT-DR neurons, PACAP KO mice had increased 5HT cell counts and 5HT content. We conclude that PACAP deficiency affects neuronal reactivity in a brain area-specific manner in stress centers, as well as in ovBST-CRF, cpEW-Ucn1 and 5HT-DR neurons leading to reduced CVMS response and altered depression level.