Atsuko Hayata

Lipopolysaccharide affects exploratory behaviors toward novel objects by impairing cognition and/or motivation in mice: Possible role of activation of the central amygdala.

Lipopolysaccharide (LPS) produces a series of systemic and psychiatric changes called sickness behavior. In the present study, we characterized the LPS-induced decrease in novel object exploratory behaviors in BALB/c mice. As already reported, LPS (0.3-5 μg/mouse) induced dose- and time-dependent decreases in locomotor activity, food intake, social interaction, and exploration for novel objects, and an increase in immobility in the forced-swim test. Although the decrease in locomotor activity was ameliorated by 10h postinjection, novel object exploratory behaviors remained decreased at 24h and were observed even with the lowest dose of LPS. In an object exploration test, LPS shortened object exploration time but did not affect moving time or the frequency of object exploration. Although pre-exposure to the same object markedly decreased the duration of exploration and LPS did not change this reduction, LPS significantly impaired the exploration of a novel object that replaced the familiar one. LPS did not affect anxiety-like behaviors in open-field and elevated plus-maze tests. An LPS-induced increase in the number of c-Fos-immunoreactive cells was observed in several brain regions within 6h of LPS administration, but the number of cells quickly returned to control levels, except in the central amygdala where the increase continued for 24h. These results suggest that LPS most prominently affects object exploratory behaviors by impairing cognition and/or motivation including continuous attention and curiosity toward objects, and that this may be associated with activation of brain nuclei such as the central amygdala.

PACAP is Implicated in the Stress Axes

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a highly conserved pleiotropic neuropeptide that functions as a neurotransmitter, neuromodulator and neurotrophic factor. Accumulating evidence implicates PACAP as an important regulator of both central and/or peripheral components of the stress axes, particularly exposure to prolonged or traumatic stress. Indeed, PACAP and its cognate receptors are widely expressed in the brain regions and peripheral tissues that mediate stress-related responses. In the sympathoadrenomedullary system, PACAP is required for sustained epinephrine secretion during metabolic stress. It is likely that PACAP regulates autonomic function and contributes to peripheral homeostasis by maintaining a balance between sympathetic and parasympathetic activity, favoring stimulation of the sympathetic system. Furthermore, PACAP is thought to act centrally on the paraventricular nucleus of the hypothalamus to regulate both the hypothalamic-pituitary-adrenal axis and the sympathetic nervous system. Intriguingly, PACAP is also active in brain structures that mediate anxiety- and fear-related behaviors, and the expression of PACAP and its receptors are dynamically altered under pathologic conditions. Thus PACAP may influence both hard-wired (genetically determined) stress responses and gene-environment interactions in stress-related psychopathology. This article aims to overview the molecular mechanisms and psychiatric implications of PACAP-dependent stress responses.

PACAP centrally mediates emotional stress-induced corticosterone responses in mice.

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a pleiotropic neuropeptide widely distributed in the nervous system. Recently, PACAP was shown to be involved in restraint stress-induced corticosterone release and concomitant expression of the genes involved in hypothalamic–pituitary–adrenal (HPA) axis activation. Therefore, in this study, we have addressed the types of stressors and the levels of the HPA axis in which PACAP signaling is involved using mice lacking PACAP (PACAP− / − ). Among four different types of stressors, open-field exposure, cold exposure, ether inhalation, and restraint, the corticosterone response to open-field exposure and restraint, which are categorized as emotional stressors, but not the other two, was markedly attenuated in PACAP− / − mice. Peripheral administration of corticotropin releasing factor (CRF) or adrenocorticotropic hormone induced corticosterone increase similarly in PACAP− / − and wild-type mice. In addition, the restraint stress-induced c-Fos expression was significantly decreased in the paraventricular nucleus (PVN) and medial amygdala (MeA), but not the medial prefrontal cortex, in PACAP− / − mice. In the PVN of PACAP− / − mice, the stress-induced c-Fos expression was blunted in the CRF neurons. These results suggest that PACAP is critically involved in activation of the MeA and PVN CRF neurons to centrally regulate the HPA axis response to emotional stressors.

Trophic Effects of PACAP on Pancreatic Islets: A Mini-Review

Progressive beta-cell insufficiency in the pancreas is a hallmark of both types I and II diabetes, and agents that protect against beta-cell dysfunction are potential drug targets for diabetes mellitus. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a strong secretagogue of insulin from pancreatic islets and is suggested to be involved in physiological blood glucose homeostasis and the pathology of diabetes. Recent studies in genetically engineered animal models have shown that PACAP stimulates pancreatic functions, especially in cooperation with other regulatory factors including glucose. Furthermore, chronic activation of PACAP signaling regulates pancreatic islet mass in a context-dependent manner. Accumulating in vivo and in vitro evidence suggest that PACAP has trophic effects and regulates both proliferation and cell viability of beta-cells and thereby contributes to protection against diabetes. This review focuses on such trophic actions of PACAP on pancreatic beta-cells and discusses the pathophysiological significance of pancreatic PACAP, with the aim to provide information for future development of treatment for diabetes.

Central PACAP mediates the sympathetic effects of leptin in a tissue-specific manner

We previously demonstrated that the peptidergic neurotransmitter pituitary adenylate cyclase-activating polypeptide (PACAP) affects the autonomic system and contributes to the control of metabolic and cardiovascular functions. Previous studies have demonstrated the importance of centrally-mediated sympathetic effects of leptin for obesity-related hypertension. Here we tested whether PACAP signaling in the brain is implicated in leptin-induced sympathetic excitation and appetite suppression. In anesthetized mice, intracerebroventricular (ICV) pre-treatment with PACAP6-38, an antagonist of the PACAP receptors (PAC1-R and VPAC2), inhibited the increase in white adipose tissue sympathetic nerve activity (WAT-SNA) produced by ICV leptin (2μg). In contrast, leptin-induced stimulation of renal sympathetic nerve activity (RSNA) was not affected by ICV pre-treatment with PACAP6-38. Moreover, in PACAP-deficient (Adcyap1-/-) mice, ICV leptin-induced WAT-SNA increase was impaired, whereas RSNA response was preserved. The reductions in food intake and body weight evoked by ICV leptin were attenuated in Adcyap1-/- mice. Our data suggest that hypothalamic PACAP signaling plays a key role in the control by leptin of feeding behavior and lipocatabolic sympathetic outflow, but spares the renal sympathetic traffic.

Central CRTH2, a Second Prostaglandin D2 Receptor, Mediates Emotional Impairment in the Lipopolysaccharide and Tumor-Induced Sickness Behavior Model

Chemoattractant receptor-homologous molecule expressed on T helper type 2 cells (CRTH2) is a second prostaglandin D2 receptor involved in mediating the allergic response; however, its central function is not yet known. Here, we demonstrate that central CRTH2 mediates emotional impairment. Lipopolysaccharide (LPS)-induced decreases in social interaction and novel exploratory behavior were observed in wild-type (CRTH2+/+) mice but not CRTH2-deficient (CRTH2−/−) mice, but both genotypes showed hypolocomotion and anorexia following LPS injection. Tumor (colon 26) inoculation, a more pathologically relevant model, induced decreases in social interaction and novel exploratory behavior in CRTH2+/+, but not CRTH2−/− mice. In addition, the CRTH2 antagonists including clinically available ramatroban reversed impaired social interaction and novel exploratory behavior after either LPS or tumor inoculation in CRTH2+/+ mice. Finally, LPS-induced c-Fos expression in the hypothalamic paraventricular nucleus (PVN) and central amygdala (CeA) was selectively abolished in CRTH2−/− mice. These results show that CRTH2 participates in LPS-induced emotional changes and activation in the PVN and CeA. Our study provides the first evidence that central CRTH2 regulates specific emotional behaviors, and that CRTH2 antagonism has potential as a therapeutic target for behavioral symptoms associated with tumors and infectious diseases.

Increased ethanol preference and serotonin 1A receptor-dependent attenuation of ethanol-induced hypothermia in PACAP-deficient mice.

Pituitary adenylate cyclase-activating polypeptide (PACAP)-deficient mice display remarkable behavioral changes including increased novelty-seeking behavior and reduced hypothermia induced by either serotonin (5-HT)(1A) receptor agonists or ethanol. Because 5-HT(1A) receptors have been implicated in the development of alcohol dependence, we have examined ethanol preference in PACAP-deficient mice using a two-bottle choice and a conditioned place preference test, as well as additive effects of ethanol and 5-HT(1A) receptor agents on hypothermia. PACAP-deficient mice showed an increased preference towards ethanol compared with wild-type mice. However, they showed no preference for the ethanol compartment after conditioning and neither preference nor aversion to sucrose or quinine. The 5-HT(1A) receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) restored the attenuated hypothermic response to ethanol in the mutants to similar levels in wild-type mice, with no effect in wild-types. In contrast, the 5-HT(1A) receptor antagonist WAY-100635 attenuated the ethanol-induced hypothermia in wild-type mice, with no effect in the mutants. These results demonstrate increased ethanol preference in PACAP-deficient mice that may be mediated by 5-HT(1A) receptor-dependent attenuation of ethanol-induced central inhibition.

Pathophysiological implication of the VPAC2 receptor in psychiatric disorders

The advent of the genomic era has led to the discovery of linkages of several genes and pathways to schizophrenia and autism spectrum disorder (ASD) that may serve as new biomarkers or therapeutic targets for these diseases. Two large-scale genetic studies published early in 2011 provided evidence that functional microduplications at 7q36.3, containing VIPR2, are a risk factor for schizophrenia. 7q36.3 microduplications were also reported to be significantly increased in ASD. VIPR2 encodes VPAC2, a seven transmembrane heterotrimeric G protein-coupled receptor that binds two homologous neuropeptides with high affinity, PACAP and VIP. These clinical studies demonstrate a VIPR2 genetic linkage to schizophrenia and ASD and should lead to novel insights into the etiology of these mental health disorders. However, the mechanism by which overactive VPAC2 signaling may lead to schizophrenia and ASD is unknown. In the present review, we will describe recent advances in the genetics of schizophrenia and attempt to discuss the pathophysiological role of altered VPAC2 signaling in psychiatric disorders.

Involvement of a prostanoid receptor CRTH2 in the LPS-induced decrease in object exploration behavior

or phosphorylation of the translation initiation factor eIF2 . Total mRNA also was isolated from the cells for measure of level of tau mRNAs by the TaqMan real-time PCR. The cells were pulse-labeled in media containing 35S-methionin/cystein and chased in media with ER stress.Results:Tau protein levels were significantly elevated in response to ER stress compared with controls in parallel with phosphorylation of eIF2&alpha. There were little apparent differences in tau mRNAs levels between cells with or without ER stress, verifying that ER stress did not increase tau gene transcription or mRNA stability. Moreover there were no apparent differences between the half-lives of tau protein under with and without ER stress, indicating that the tau increase is not due to tau protein stabilization.Conclusions: ER stress may increase tau levels via the protein synthesis steps, which could be initiating molecular mechanism in tauopathies.

Interaction between genetic and non-genetic factors modulates psychomotor behaviors in PACAP-heterozygous knockout mice

Method: Male 8-weeks old C57BL/6J mice were purchased from CLEA (Japan Inc.). They were housed under a standardized light/dark cycle at room temperature of 24 ± 1 ◦C and a humidity of 60 ± 10% with food and water ad libitum. CPu and SCN were obtained at 09:00, 13:00, 17:00, 21:00, 01:00, 05:00. The mRNA levels of clock genes and PD-related genes in CPu and SCN were measured by RT-PCR. Result: MPTP-treated mice exhibited a loss of TH-immunoreactive neurons in the SN and TH-immunoreactive fibers in CPu. The levels of DA, DOPAC and HVA in CPu of MPTP-treated mice dramatically decreased. 24-hr rhythms in body temperature and locomotor activity were changed in MPTP-induced PD model mouse. Furthermore, 24-hr rhythm of clock genes in CPu and SCN were altered in MPTP-induced PD model mouse. Conclusions: These findings indicate that the circadian clock system is altered in PD. On the other hand, such disruption in 24-hr rhythm of clock genes may be underlying the several non-motor symptoms such as sleep disturbances and depression in PD.