Dexamethasone regulation of gastrin-releasing peptide receptor in human lung cells

Gastrin-releasing peptide receptor signaling in the integration of stress and memory

Neuropeptides act as signaling molecules that regulate a range of aspects of brain function. Gastrin-releasing peptide (GRP) is a 27-amino acid mammalian neuropeptide, homolog of the amphibian peptide bombesin. GRP acts by binding to the GRP receptor (GRPR, also called BB2), a member of the G-protein coupled receptor (GPCR) superfamily. GRP produced by neurons in the central nervous system (CNS) plays a role in synaptic transmission by activating GRPRs located on postsynaptic membranes, influencing several aspects of brain function. Here we review the role of GRP/GRPR as a system mediating both stress responses and the formation and expression of memories for fearful events. GRPR signaling might integrate the processing of stress and fear with synaptic plasticity and memory, serving as an important component of the set of neurobiological systems underlying the enhancement of memory storage by aversive information.

A role for glucocorticoid-signaling in depression-like behavior of gastrin-releasing peptide receptor knock-out mice

Abstract Background. The gastrin-releasing peptide receptor (GRPR) is highly expressed in the limbic system, where it importantly regulates emotional functions and in the suprachiasmatic nucleus, where it is central for the photic resetting of the circadian clock. Mice lacking GRPR presented with deficient light-induced phase shift in activity as well altered emotional learning and amygdala function. The effect of GRPR deletion on depression-like behavior and its molecular signature in the amygdala, however, has not yet been evaluated. Methods. GRPR knock-out mice (GRPR-KO) were tested in the forced-swim test and the sucrose preference test for depression-like behavior. Gene expression in the basolateral nucleus of the amygdala was evaluated by micorarray analysis subsequent to laser-capture microdissection-assisted extraction of mRNA. The expression of selected genes was confirmed by RT-PCR. Results. GRPR-KO mice were found to present with increased depression-like behavior. Microarray analysis revealed down-regulation of several glucocorticoid-responsive genes in the basolateral amygdala. Acute administration of dexamethasone reversed the behavioral phenotype and alterations in gene expression. Discussion. We propose that deletion of GRPR leads to the induction of depression-like behavior which is paralleled by dysregulation of amygdala gene expression, potentially resulting from deficient light-induced corticosterone release in GRPR-KO.

Gastrin-releasing peptide links stressor to cancer progression

INTRODUCTION

Gastrin-releasing peptide (GRP) plays an important role in cancer growth and metastasis; however, the mechanisms of how GRP affects cancer progression are not well understood. Recent studies revealed that chronic stress is a major risk factor for cancer progression, and this effect may be mediated by GRP. In this review, we will discuss the mechanisms and implications of GRP linking stressor to cancer progression.

MATERIALS AND METHODS

We retrieved the studies of the relationship between GRP, stress and cancers through PubMed using systematic methods to search, select, and evaluate the findings.

RESULTS

The results suggested that GRP can mediate the effects of stress on cancers at systemic, tissue and cellular levels: Stress elicits the secretion of GRP in the brain and GRP in turn activates the stress response pathways resulting in an elevation of stress hormones and GRP in the plasma and tissues. GRP in synergy with stress hormones stimulates the growth and invasion of cancer cells by suppressing the anti-tumor immune function and directly activating the pro-proliferative and pro-migratory signaling pathways in cancer cells.

CONCLUSION

GRP is a multi-functional peptide, which acts as a stress mediator as well as a growth factor linking stressor to cancer progression. GRP and its high-affinity receptor are useful targets for the diagnosis and treatment of cancers.

Effect of environmental enrichment on fearful behavior and gastrin-releasing peptide receptor expression in the amygdala of prenatal stressed rats

Prenatal stressed offspring exhibit more fearful behavior in behavioral tests, which can be reversed by environmental enrichment (EE). However, the physiological basis of these phenomena remains unclear. Previous studies revealed that abnormal fearful behavior of prenatally stressed offspring may be a consequence of increased activities of CRFergic systems (corticotropin-releasing factor and its receptors) in the amygdala. Gastrin-releasing peptide receptors (GRPR) also have an important role in regulating amygdala-dependent, fear-related learning. The aim of this study was to examine weather prenatal stress and EE can affect the expression of GRPR in the amygdala. We reported here that prenatal chronic stress (subjected to immobilization and bright light stress for 45 min three times per day) caused increased fearfulness in defensive withdrawal test but had no effect on the expression of GRPR in the amygdala. However, enriched environment housing treatment on postnatal days 21-60 can dramatically increase the expression of GRPR in amygdala and reduce fearfulness in the defensive withdrawal test. Our results demonstrate for the first time that EE can modify the expression of GRPR in the amygdala, which might contribute to our understanding of the physiological effects of environmental enrichment.

Impairments of social behavior and memory after neonatal gastrin-releasing peptide receptor blockade in rats: Implications for an animal model of neurodevelopmental disorders

The gastrin-releasing peptide receptor (GRPR) has been implicated in central nervous system (CNS) diseases, including neurodevelopmental disorders associated with autism. In the present study we examined the effects of GRPR blockade during the neonatal period on behavioral measures relevant to animal models of neurodevelopmental disorders. Male Wistar rats were given an intraperitoneal (i.p.) injection of either saline (SAL) or the GRPR antagonist [D-Tpi(6), Leu(13) psi(CH(2)NH)-Leu(14)] bombesin (6-14) (RC-3095; 1 or 10mg/kg) twice daily for 10days from postnatal days (PN) 1 to 10. Animals treated with RC-3095 showed pronounced deficits in social interaction when tested at PN 30-35 and impaired 24-h retention of memory for both novel object recognition (NOR) and inhibitory avoidance (IA) tasks tested at PN 60-71. Neither short-term memory tested 1.5h posttraining nor open field behavior were affected by neonatal GRPR blockade. The implications of the findings for animal models of neurodevelopmental disorders are discussed.

Sensitization of pulmonary chemosensitive neurons by bombesin-like peptides in rats

Small cell lung cancer (SCLC) patients suffer from pulmonary stresses such as dyspnea and chest pain, and the pathogenic mechanisms are not known. SCLC cells secrete a variety of bioactive neuropeptides, including bombesin-like peptides. We hypothesize that these peptides may enhance the sensitivity of the pulmonary chemosensitive nerve endings, contributing to the development of these pulmonary stresses in SCLC patients. This study was therefore carried out to determine the effects of bombesin and gastrin-releasing peptide (GRP), a major bombesin-like peptide, on the sensitivities of pulmonary chemoreflex and isolated pulmonary vagal chemosensitive neurons. In anesthetized, spontaneously breathing rats, intravenous infusion of bombesin or GRP significantly amplified the pulmonary chemoreflex responses to chemical stimulants such as capsaicin and ATP. The enhanced responses were completely abolished by perineural capsaicin treatment of both cervical vagi, suggesting the involvement of pulmonary C-fiber afferents. In isolated pulmonary vagal chemosensitive neurons, pretreatment with bombesin or GRP potentiated the capsaicin-induced Ca(2+) transient. This sensitizing effect was further demonstrated in patch-clamp recording studies; the sensitivities of these neurons to both chemical (capsaicin and ATP) and electrical stimuli were significantly enhanced by the presence of either bombesin or GRP. In summary, our results have demonstrated that bombesin and GRP upregulate the pulmonary chemoreflex sensitivity in vivo and the excitability of isolated pulmonary chemosensitive neurons in vitro.

Dexamethasone reverses the memory impairment induced by antagonism of hippocampal gastrin-releasing peptide receptors

Storage of emotionally influenced memory is regulated by activation of glucocorticoid receptors (GRs) as well as of gastrin-releasing peptide receptors (GRPRs) in the dorsal hippocampus. In the present study, male Wistar rats were given a bilateral infusion of saline or the GRPR antagonist (D-Tpi6, Leu13 psi[CH2NH]-Leu14) bombesin (6-14) (RC-3095) (1.0 microg/side) into the dorsal hippocampus 10 min before training on an inhibitory avoidance task, followed by an immediate post-training i.p. injection of vehicle or the GR agonist dexamethasone (0.3 mg/kg). A retention test trial, carried out 24 h after training, indicated that intrahippocampal infusion of RC-3095 impaired inhibitory avoidance retention. Post-training administration of dexamethasone induced an enhancement of retention regardless of whether the animals had received saline or RC-3095 into the hippocampus before training. The findings indicate that hippocampal GRPR blockade does not prevent memory enhancement induced by dexamethasone. Together with previous results, these findings suggest that endogenous activation of GRPRs in the hippocampus modulates the consolidation of emotional memory, but is not a critical receptor system mediating memory formation.