Stress responses are elicited by a variety of stimuli and are aimed at counteracting direct or perceived threats to the well-being of an organism. In the mammalian central and peripheral nervous systems, specific cell groups constitute signaling circuits that indicate the presence of a stressor and elaborate an adequate response, ultimately restoring homeostasis. Pituitary adenylate cyclase-activating polypeptide (PACAP) is expressed in central and peripheral parts of these circuits and has recently been identified as a candidate for regulation of the stress axis. In the present experiments, we tested the involvement of PACAP in the response to a psychological stressor in vivo. We used a restraint paradigm and compared PACAP-deficient mice (PACAP−/−) to wild-type controls (PACAP+/+). Acute secretion of corticosterone elicited by 1h of restraint was found to be identical between genotypes, whereas sustained secretion provoked by 6h of unrelieved restraint was 48% lower in PACAP−/− mice. Within the latter time frame, expression of mRNA encoding corticotropinreleasing hormone (CRH) was increased in the hypothalamus of wild-type, but not PACAP-deficient mice. Expression of hypothalamic activity-regulated transcription factors (Egr1, Fos) was rapidly and transiently induced by restraint in a PACAP-dependent fashion, a pattern that was also found in the adrenal glands. Here, abundance of transcripts encoding enzymes required for adrenomedullary catecholamine biosynthesis (TH, PNMT) was higher in PACAP+/+ mice after 6h of unrelieved restraint. Our results suggest that sustained corticosterone secretion, synthesis of the hypophysiotropic hormone CRH in the hypothalamus, as well as enzymes producing the hormone adrenaline in the adrenal medulla, are controlled by PACAP signaling in the mouse. These findings identify PACAP as a major potential contributor to the stimulus-secretion-synthesis coupling that supports stress responses in vivo.

The neuropeptide PACAP is an informational molecule released from stress-transducing neurons. It exerts post-synaptic effects required to complete hypothalamo-pituitary-adrenocortical (HPA) and hypothalamo-splanchnico-adrenomedullary (HSA) circuits activated by psychogenic and metabolic stressors. PACAP-responsive (in cell culture models) and PACAP-dependent (in vivo) transcriptomic responses in the adrenal gland, hypothalamus, and pituitary upon activation of these circuits have been identified. Gene products produced in response circuits during stress include additional neuropeptides and neurotransmitter biosynthetic enzymes and neuroprotective factors. Major portions of HPA and HSA stress responses are abolished in PACAP-deficient mice. This deficit occurs at the level of both the adrenal medulla (HSA axis) and the hypothalamus (HPA axis). PACAP-dependent transcriptional stress responses are conveyed through noncanonical cyclic AMP-and calcium-initiated signaling pathways within the HSA circuit. PACAP transcriptional regulation of the HPA axis, in the hypothalamus, is likely to be mediated via canonical cyclic AMP (cAMP) signaling through protein kinase A. Keywords PACAP; stress; HPA axisThe stress response may be defined operationally as the response of the neuroendocrine network to systemic or environmental perturbations outside of the normal physiological range. Stress responses in mammals are mediated through specific neural and neuroendocrine circuits. The propagation of signaling through these circuits is itself a cellular stressor. In other words, a 'stressed neuron' is one propagating an organismic stress response through a neuronal stress circuit. Thus, the cellular stress response is a point of entry to identifying targets for pharmacological modulation of organismic stress perception and processing.Neuropeptides play a special role in the stress response. As informational molecules stored in large dense-core vesicles, neuropeptides are released preferentially at higher firing rates, as occur during neurotransmission activated by stress in both the central and peripheral nervous systems. Fast and slow transmission are the two major modes of intercellular communication that underlie nervous system function. Fast transmission by glutamate, GABA, and acetylcholine involves direct gating of plasma membrane ionic channels for Correspondence: Lee E. Eiden, Section on Molecular Neuroscience, Laboratory of Cellular and Molecular Regulation, NIMH-IRP, NIH, Bethesda, Maryland 20892, eidenl@mail.nih.gov. This contribution summarizes the State-of-the-Art Lecture "Signaling in Stress: The 'emergency response' transcriptome" presented by L.E.E. at The 7 th International Congress of Neuroendocrinology, July 11-15, 2010, Rouen, France. NIH Public Access Author ManuscriptAnn N Y Acad Sci. Author manuscript; available in PMC 2012 March 1. Bloom et al. made the acute observation that neuropeptides represent the language of stress because the enhanced neuronal firing required to message systemic or environmen...

The neuropeptide PACAP (pituitary adenylate cyclase-activating polypeptide) is a cotransmitter of acetylcholine at the adrenomedullary synapse, where autonomic regulation of hormone secretion occurs. We have previously reported that survival of prolonged metabolic stress in mice requires PACAP-dependent biosynthesis and secretion of adrenomedullary catecholamines (CAs). In the present experiments, we show that CA secretion evoked by direct high-frequency stimulation of the splanchnic nerve is abolished in native adrenal slices from male PACAP-deficient mice. Further, we demonstrate that PACAP is both necessary and sufficient for CA secretion ex vivo during stimulation protocols designed to mimic stress. In vivo, up-regulation of transcripts encoding adrenomedullary CA-synthesizing enzymes (tyrosine hydroxylase, phenylethanolamine N-methyltransferase) in response to both psychogenic and metabolic stressors (restraint and hypoglycemia) is PACAP-dependent. Stressor-induced alteration of the adrenomedullary secretory cocktail also appears to require PACAP, because up-regulation of galanin mRNA is abrogated in male PACAP-deficient mice. We further show that hypoglycemia-induced corticosterone secretion is not PACAP-dependent, ruling out the possibility that glucocorticoids are the main mediators of the aforementioned effects. Instead, experiments with bovine chromaffin cells suggest that PACAP acts directly at the level of the adrenal medulla. By integrating prolonged CA secretion, expression of biosynthetic enzymes and production of modulatory neuropeptides such as galanin, PACAP is crucial for adrenomedullary function. Importantly, our results show that PACAP is the dominant adrenomedullary neurotransmitter during conditions of enhanced secretory demand.

External and internal stimuli that threaten homeostasis trigger coordinated stress responses through activation of specialised neuroendocrine circuits. In mammals, the hypothalamic-pituitary-adrenal (HPA) axis mediates responses to stressors such as restraint, ultimately enhancing adrenocortical hormone secretion. Pituitary adenylate cyclase-activating polypeptide (PACAP) has been implicated in central control of the HPA axis, and we have recently shown PACAP-dependent expression of corticotropin-releasing hormone (CRH) and secretion of corticosterone in response to restraint. We now provide a more detailed analysis of PACAP-dependent HPA axis stimulation in the mouse, indicating that the hypothalamic paraventricular nucleus (PVN) is the primary site of action. We demonstrate by quantitative PCR and in situ hybridisation that upregulation of mRNAs encoding CRH and inducible transcription factors from the Nr4a family (Nur77, Nor1) in the PVN is PACAP-dependent. Furthermore, CRH hnRNA is rapidly upregulated in cultured hypothalamic neurones after treatment with PACAP. Induction of Nr4a factors (Nur77, Nurr1) in response to restraint is attenuated in the pituitary gland of PACAP-deficient mice. In the adrenal glands, restraint elicits a marked PACAP-dependent increase in adrenocortical mRNA levels of all three Nr4a transcription factors, SF-1 (steroidogenic factor 1; Nr5a1), steroidogenic acute regulatory protein (StAR) and steroid 21-hydroxylase. Taken together, our results show that PACAP controls HPA responses to restraint primarily at the level of the hypothalamus by upregulating CRH, possibly involving transcription factors such as Nur77 and Nor1. Subsequent adrenocortical steroidogenesis also appears to involve PACAP-dependent stimulus-transcription coupling, suggesting a mechanism by which PACAP exerts control over HPA axis function during stress.

Background: Intracellular GPR37 accumulation is neurotoxic and associated with parkinsonism, whereas plasma membrane association is protective. Results: The endogenous GPR37 ligand prosaposin promotes GPR37 surface density and association with GM1-enriched lipid rafts. Conclusion: GPR37, prosaposin, and GM1 constitute a pathway that improves cell viability through GPR37 trafficking to the plasma membrane. Significance: Targeting this pathway could reduce toxic intracellular GPR37 accumulation observed in parkinsonism.