PACAP type I receptor gene expression in the paraventricular and supraoptic nuclei of rats

Hypothalamic Regulation of Corticotropin-Releasing Factor under Stress and Stress Resilience

This review addresses the molecular mechanisms of corticotropin-releasing factor (CRF) regulation in the hypothalamus under stress and stress resilience. CRF in the hypothalamus plays a central role in regulating the stress response. CRF stimulates adrenocorticotropic hormone (ACTH) release from the anterior pituitary. ACTH stimulates glucocorticoid secretion from the adrenal glands. Glucocorticoids are essential for stress coping, stress resilience, and homeostasis. The activated hypothalamic-pituitary-adrenal axis is suppressed by the negative feedback from glucocorticoids. Glucocorticoid-dependent repression of cAMP-stimulated Crf promoter activity is mediated by both the negative glucocorticoid response element and the serum response element. Conversely, the inducible cAMP-early repressor can suppress the stress response via inhibition of the cAMP-dependent Crf gene, as can the suppressor of cytokine signaling-3 in the hypothalamus. CRF receptor type 1 is mainly involved in a stress response, depression, anorexia, and seizure, while CRF receptor type 2 mediates “stress coping” mechanisms such as anxiolysis in the brain. Differential effects of FK506-binding immunophilins, FKBP4 and FKBP5, contribute to the efficiency of glucocorticoids under stress resilience. Together, a variety of factors contribute to stress resilience. All these factors would have the differential roles under stress resilience.

Protective Effects of Pituitary Adenylate Cyclase-Activating Polypeptide and Vasoactive Intestinal Peptide Against Cognitive Decline in Neurodegenerative Diseases

Cognitive impairment is one of the major symptoms in most neurodegenerative disorders such as Alzheimer’s (AD), Parkinson (PD), and Huntington diseases (HD), affecting millions of people worldwide. Unfortunately, there is no treatment to cure or prevent the progression of those diseases. Cognitive impairment has been related to neuronal cell death and/or synaptic plasticity alteration in important brain regions, such as the cerebral cortex, substantia nigra, striatum, and hippocampus. Therefore, compounds that can act to protect the neuronal loss and/or to reestablish the synaptic activity are needed to prevent cognitive decline in neurodegenerative diseases. Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are two highly related multifunctional neuropeptides widely distributed in the central nervous system (CNS). PACAP and VIP exert their action through two common receptors, VPAC1 and VPAC2, while PACAP has an additional specific receptor, PAC1. In this review article, we first presented evidence showing the therapeutic potential of PACAP and VIP to fight the cognitive decline observed in models of AD, PD, and HD. We also reviewed the main transduction pathways activated by PACAP and VIP receptors to reduce cognitive dysfunction. Furthermore, we identified the therapeutic targets of PACAP and VIP, and finally, we evaluated different novel synthetic PACAP and VIP analogs as promising pharmacological tools.

Current State of Understanding of the Role of PACAP in the Hypothalamo-Hypophyseal Gonadotropin Functions of Mammals

PACAP was discovered 30 years ago in Dr. Akira Arimura's laboratory. In the past three decades since then, it has become evident that this peptide plays numerous crucial roles in mammalian organisms. The most important functions of PACAP are the following: 1. neurotransmitter, 2. neuromodulator, 3. hypophysiotropic hormone, 4. neuroprotector. This paper reviews the accumulated data regarding the distribution of PACAP and its receptors in the mammalian hypothalamus and pituitary gland, the role of PACAP in the gonadotropin hormone secretion of females and males. The review also summarizes the interaction between PACAP, GnRH, and sex steroids as well as hypothalamic peptides including kisspeptin. The possible role of PACAP in reproductive functions through the biological clock is also discussed. Finally, the significance of PACAP in the hypothalamo-hypophysial system is considered and the facts missing, that would help better understand the function of PACAP in this system, are also highlighted.

Discovery of PACAP and its receptors in the brain

Pituitary adenylate-cyclase-activating polypeptide (PACAP) is a 27- or 38-amino acid neuropeptide, which belongs to the vasoactive intestinal polypeptide (VIP)/glucagon/secretin family. PACAP shows particularly high homology (~ 68%) to VIP. Because of the high homology of the amino acid sequences of PACAP and VIP, these peptides share three class B-G-protein coupled receptors: the PAC1-Receptor (PAC1-R), the VPAC1-Receptor (VPAC1-R) and VPAC2-Receptor (VPAC2-R). These receptors have high homology to each other, and their high homology is utilized for these discoveries. This review provides mainly an overview of the history of the discovery of PACAP and its three receptors.

Regulation of bed nucleus of the stria terminalis PACAP expression by stress and corticosterone

Single-nucleotide polymorphisms (SNPs) in the genes for pituitary adenylyl cyclase-activating peptide (PACAP) and the PAC1 receptor have been associated with stress-related psychiatric disorders. Although, from recent work, we have argued that stress-induced PACAP expression in the bed nucleus of the stria terminalis (BNST) may mediate stress-related psychopathology, it is unclear whether stress-induced increases in BNST PACAP expression require acute or repeated stressor exposure and whether increased BNST PACAP expression is related to stress-induced increases in circulating glucocorticoids. In the current work, we have used real-time quantitative polymerase chain reaction (qPCR) to assess transcript expression in brain punches from rats after stressor exposure paradigms or corticosterone injection. BNST PACAP and PAC1 receptor transcript expression was increased only after 7 days of repeated stressor exposure; no changes in transcript levels were observed 2 or 24 hours after a single-restraint session. Moreover, repeated corticosterone treatment for 7 days was not sufficient to reliably increase BNST PACAP transcript levels, suggesting that stress-induced elevations in corticosterone may not be the primary drivers of BNST PACAP expression. These results may help clarify the mechanisms and temporal processes that underlie BNST PACAP induction for intervention in stress-related anxiety disorders.

New cancer cachexia rat model generated by implantation of a peritoneal dissemination-derived human stomach cancer cell line

Cancer cachexia (CC), a syndrome characterized by anorexia and body weight loss due to low fat-free mass levels, including reduced musculature, markedly worsens patient quality of life. Although stomach cancer patients have the highest incidence of cachexia, few experimental models for the study of stomach CC have been established. Herein, we developed stomach CC animal models using nude rats subcutaneously implanted with two novel cell lines, i.e., MKN45c185, established from the human stomach cancer cell line MKN-45, and 85As2, derived from peritoneal dissemination of orthotopically implanted MKN45c185 cells in mice. Both CC models showed marked weight loss, anorexia, reduced musculature and muscle strength, increased inflammatory markers, and low plasma albumin levels; however, CC developed earlier and was more severe in rats implanted with 85As2 than in those implanted with MKN45cl85. Moreover, human leukemia inhibitory factor (LIF), a known cachectic factor, and hypothalamic orexigenic peptide mRNA levels increased in the models, whereas hypothalamic anorexigenic peptide mRNA levels decreased. Surgical removal of the tumor not only abolished cachexia symptoms but also reduced plasma LIF levels to below detectable limits. Importantly, oral administration of rikkunshito, a traditional Japanese medicine, substantially ameliorated CC-related anorexia and body composition changes. In summary, our novel peritoneal dissemination-derived 85As2 rat model developed severe cachexia, possibly caused by LIF from cancer cells, that was ameliorated by rikkunshito. This model should provide a useful tool for further study into the mechanisms and treatment of stomach CC.

Water deprivation induces appetite and alters metabolic strategy in Notomys alexis: unique mechanisms for water production in the desert

Like many desert animals, the spinifex hopping mouse, Notomys alexis, can maintain water balance without drinking water. The role of the kidney in producing a small volume of highly concentrated urine has been well-documented, but little is known about the physiological mechanisms underpinning the metabolic production of water to offset obligatory water loss. In Notomys, we found that water deprivation (WD) induced a sustained high food intake that exceeded the pre-deprivation level, which was driven by parallel changes in plasma leptin and ghrelin and the expression of orexigenic and anorectic neuropeptide genes in the hypothalamus; these changed in a direction that would stimulate appetite. As the period of WD was prolonged, body fat disappeared but body mass increased gradually, which was attributed to hepatic glycogen storage. Switching metabolic strategy from lipids to carbohydrates would enhance metabolic water production per oxygen molecule, thus providing a mechanism to minimize respiratory water loss. The changes observed in appetite control and metabolic strategy in Notomys were absent or less prominent in laboratory mice. This study reveals novel mechanisms for appetite regulation and energy metabolism that could be essential for desert rodents to survive in xeric environments.

Signal transduction in the hypothalamic corticotropin-releasing factor system and its clinical implications

Corticotropin-releasing factor (CRF) is a major regulatory peptide in the hypothalamic-pituitary-adrenal (HPA) axis under stress conditions. In response to stress, CRF is produced in the hypothalamic paraventricular nucleus. Forskolin- or pituitary adenylate cyclase-activating polypeptide-stimulated CRF gene transcription is mediated by the cyclic AMP (cAMP) response element on the CRF 5'-promoter region. Estrogens enhance activation of the CRF gene in stress, while inducible cAMP-early repressor suppresses the stress response via inhibition of the cAMP-dependent CRF gene. Glucocorticoid-dependent repression of cAMP-stimulated CRF promoter activity is mediated by both the negative glucocorticoid-response element and the serum-response element, while interleukin-6 (IL-6) stimulates the CRF gene. Suppressor of cytokine signaling-3, stimulated by IL-6 and cAMP, is involved in the negative regulation of CRF gene expression. Such complex mechanisms contribute to stress responses and homeostasis in the hypothalamus. Moreover, disruption of the HPA axis may cause a number of diseases related to stress. For example, CRF-induced p21-activated kinase 3 mRNA expression may be related to the proliferation of corticotrophs in Nelson's syndrome. A higher molecular weight form of immunoreactive β-endorphin, putative proopiomelanocortin (POMC), is increased in CRF-knockout mice, suggesting the important role of CRF in the processing of POMC through changes in prohormone convertase type-1 expression levels.

Similar changes of hypothalamic feeding-regulating peptides mRNAs and plasma leptin levels in PTHrP-, LIF-secreting tumors-induced cachectic rats and adjuvant arthritic rats

Parathyroid hormone-related protein (PTHrP) is a causative factor of humoral hypercalcemia in malignancy. However, it is difficult to explain the mechanism of anorexia/cachexia with PTHrP secretion in detail. Previously, we demonstrated that the expressions of orexigenic peptides increased and anorexigenic peptides decreased under cachectic conditions in rats carrying tumors secreting PTHrP. In this study, we investigated whether such changes in the expression of hypothalamic feeding-regulating peptides can be solely attributed to PTHrP or are a general response under cachectic conditions. Cachectic syndromes were induced in rats by: (i) inoculation of human lung cancer LC-6 cells that secreted PTHrP, (ii) inoculation of human melanoma SEKI cells that secrete not PTHrP but LIF1, (iii) injection of heat-killed Mycobacterium leading to arthritis (AA) and (iv) oral administration of a high dose of 1α,25(OH)(2)D(3) that resulted in hypercalcemia. The LC-6-bearing rats and AA rats were treated with or without anti-PTHrP antibody and indomethacin, respectively, and the expression of the hypothalamic feeding-regulating peptide mRNAs were examined by in situ hybridization histochemistry. The orexigenic peptide mRNAs, such as neuropeptide Y and agouti-related protein, were significantly increased, and that of anorexigenic peptide mRNAs, such as proopiomelanocortin, cocaine- and amphetamine-regulated transcript and corticotropin-releasing hormone were significantly decreased when they developed cachectic syndromes and AA. A high dose of 1α,25(OH)(2)D(3) caused hypercalcemia and body weight loss but did not affect the expression of hypothalamic feeding-regulating peptide mRNAs. The expressions of the hypothalamic feeding-regulating peptides change commonly in different chronic cachectic models without relating to serum calcium levels.

PACAP neurons in the hypothalamic ventromedial nucleus are targets of central leptin signaling

The adipose-derived hormone, leptin, was discovered over 10 years ago, but only now are we unmasking its downstream pathways which lead to reduced energy intake (feeding) and increased energy expenditure (thermogenesis). Recent transgenic models have challenged the long-standing supposition that the hypothalamic arcuate nucleus (Arc) is omnipotent in the central response to leptin, and research focus is beginning to shift to examine roles of extra-arcuate sites. Dhillon et al. (2006) demonstrated that targeted knock out of the signaling form of the leptin receptor (lepr-B) in steroidogenic factor 1 (SF-1) cells of the hypothalamic ventromedial nucleus (VMN) produces obesity of a similar magnitude to the pro-opiomelanocortin (POMC)-driven lepr-B deleted mouse, via a functionally distinct mechanism. These findings reveal that SF-1 cells of the VMN could be equally as important as POMC cells in mediating leptin's anti-obesity effects. However, the identification of molecular and cellular correlates of this relationship remains tantalizingly unknown. Here, we have shown that mRNA expression of the VMN-expressed neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) is regulated according to energy status and that it exerts catabolic effects when administered centrally to mice. Furthermore, we have shown that SF-1 and PACAP mRNAs are colocalized in the VMN, and that leptin signaling via lepr-B is required for normal PACAP expression in these cells. Finally, blocking endogenous central PACAP signaling with the antagonist PACAP(6-38) markedly attenuates leptin-induced hypophagia and hyperthermia in vivo. Thus, it appears that PACAP is an important mediator of central leptin effects on energy balance.

Regulatory mechanisms underlying corticotropin-releasing factor gene expression in the hypothalamus

The hypothalamic-pituitary-adrenal (HPA) axis is activated under various stressors. Corticotropin-releasing factor (CRF) plays a central role in controlling stress response, and regulating the HPA axis. CRF, produced in the hypothalamic paraventricular nucleus (PVN), stimulates adrenocorticotropic hormone (ACTH) production via CRF receptor type 1 (CRF(1) receptor) from the corticotrophs of the anterior pituitary (AP). Cyclic AMP (cAMP)-protein kinase A (PKA) pathway takes a main role in stimulating CRF gene transcription. Forskolin and pituitary adenylate cyclase-activating polypeptide (PACAP) stimulate adenylate cyclase, intracellular cAMP production, and then CRF and arginine vasopressin (AVP) gene expression in hypothalamic 4B cells. Interleukin (IL)-6, produced in the PVN, both directly and indirectly stimulates CRF and AVP gene expression. Estradiol may enhance the activation of CRF gene expression in response to stress. The HPA axis is regulated by a negative feedback mechanism, because glucocorticoids inhibit both CRF production in the hypothalamic PVN and ACTH production in the pituitary. Hypothalamic parvocellular neurons in the PVN are known to express glucocorticoid receptors, and glucocorticoids are able to regulate CRF gene transcription and expression levels directly in the PVN. Glucocorticoids-dependent repression of cAMP-stimulated CRF promoter activity is mainly localized to promoter sequences between -278 and -233 bp. Both negative glucocorticoid regulatory element (nGRE) and serum response element (SRE) are involved in the repression of the CRF gene in the hypothalamic cells.

Response of substances co-expressed in hypothalamic magnocellular neurons to osmotic challenges in normal and Brattleboro rats

The intention of this review is to emphasize the current knowledge about the extent and importance of the substances co-localized with magnocellular arginine vasopressin (AVP) and oxytocin (OXY) as potential candidates for the gradual clarification of their actual role in the regulation of hydromineral homeostasis. Maintenance of the body hydromineral balance depends on the coordinated action of principal biologically active compounds, AVP and OXY, synthesized in the hypothalamic supraoptic and paraventricular nuclei. However, on the regulation of water-salt balance, other substances, co-localized with the principal neuropetides, participate. These can be classified as (1) peptides co-localized with AVP or OXY with unambiguous osmotic function, including angiotensin II, apelin, corticotropin releasing hormone, and galanin and (2) peptides co-localized with AVP or OXY with an unknown role in osmotic regulation, including cholecystokinin, chromogranin/secretogranin, dynorphin, endothelin-1, enkephalin, ferritin protein, interleukin 6, kininogen, neurokinin B, neuropeptide Y, vasoactive intestinal peptide, pituitary adenylate cyclase-activating polypeptide, TAFA5 protein, thyrotropin releasing hormone, tyrosine hydroxylase, and urocortin. In this brief review, also the responses of these substances to different hyperosmotic and hypoosmotic challenges are pointed out. Based on the literature data published recently, the functional implication of the majority of co-localized substances is still better understood in non-osmotic than osmotic functional circuits. Brattleboro strain of rats that does not express functional vasopressin was also included in this review. These animals suffer from chronic hypernatremia and hyperosmolality, accompanied by sustained increase in OXY mRNA in PVN and SON and OXY levels in plasma. They represent an important model of animals with constantly sustained osmolality, which in the future, will be utilizable for revealing the physiological importance of biologically active substances co-expressed with AVP and OXY, involved in the regulation of plasma osmolality.

Parathyroid hormone-related protein induces cachectic syndromes without directly modulating the expression of hypothalamic feeding-regulating peptides

PURPOSE

Parathyroid hormone-related protein (PTHrP) is a causative factor of humoral hypercalcemia of malignancy (HHM) and concurrent anorexia and wasting. Because changes in the expression of hypothalamic feeding-regulating peptides can directly affect appetites and thereby can cause anorexia and wasting, we addressed whether the cachectic syndromes induced by PTHrP rely on the action of hypothalamic feeding-regulating peptides.

EXPERIMENTAL DESIGN

Rats were inoculated with a LC-6 human cancer xenograft that secreted PTHrP, and the mRNA levels of the hypothalamic feeding-regulating peptide genes and serum leptin levels were examined before and after the development of HHM by in situ hybridization histochemistry and ELISA, respectively. Some rats were given the anti-PTHrP antibody.

RESULTS AND CONCLUSION

The mRNA levels for the orexigenic peptides, such as the agouti-related protein and the neuropeptide Y in the arcuate nucleus (Arc), were significantly increased after the development of HHM, whereas the mRNA levels for the anorexigenic peptides, such as the proopiomelanocortin in the Arc, the cocaine and amphetamine-regulated transcript in the Arc, and the corticotropin-releasing factor in the paraventricular nucleus, were significantly decreased after the development of HHM. Plasma leptin levels were also reduced in cachectic rats, and the administration of anti-PTHrP antibody to the cachectic rats not only improved the cachectic symptoms but also restored the mRNA levels of these orexigenic and anorexigenic peptides, except for orexin. Thus, PTHrP induces HHM and concurrent cachectic syndromes by mechanisms other than directly modulating the leptin or hypothalamic feeding-regulated peptides.

A novel role for endogenous pituitary adenylate cyclase activating polypeptide in the magnocellular neuroendocrine system

Central release of vasopressin (VP) by the magnocellular neuroendocrine cells (MNCs) responsible for systemic VP release is believed to be important in modulating the activity of these neurons during dehydration. Central VP release from MNC somata and dendrites is stimulated by both dehydration and pituitary adenylate cyclase activating polypeptide (PACAP). Although PACAP is expressed in MNCs, its potential role in the magnocellular response to dehydration is unexplored. The current study demonstrates that prolonged dehydration increases immunoreactivity for PACAP-27, PACAP-38, and the type I PACAP receptor in the supraoptic nucleus (SON) of the rat. In addition, PACAP stimulates local VP release in the euhydrated rat SON in vitro, and this effect is reduced by the PACAP receptor antagonist PAC(6-27) (100 nm), suggesting the participation of PACAP receptors. Concomitant with its effects on local VP release, PACAP also reduces basal glutamate and aspartate release in the euhydrated rat SON. Furthermore, somatodendritic VP release elicited by acute dehydration is blocked by PAC(6-27), suggesting that endogenous PACAP participates in this response. Consistent with this, RIA revealed that local PACAP-38 release within the SON is significantly elevated during acute dehydration. These results suggest that prolonged activation of hypothalamic MNCs is accompanied by up-regulation of PACAP and the type I PACAP receptor in these cells and that somatodendritic VP release in response to acute dehydration is mediated by activation of PACAP receptors by endogenous PACAP released within the SON. A potential role for PACAP in promoting efficient, but not exhaustive, systemic release of VP from MNCs during physiological challenge is discussed.

Behavioral effects of local microinfusion of pituitary adenylate cyclase activating polypeptide (PACAP) into the paraventricular nucleus of the hypothalamus (PVN)

Pituitary adenylate cyclase activating polypeptide (PACAP) has been implicated in the regulation of several autonomic and neuroendocrine functions. In the hypothalamic paraventricular nucleus (PVN), for example, PACAP-immunoreactive fibers densely innervate corticotropin-releasing hormone (CRH)-containing neurons in the medial parvocellular region, suggesting that PACAP acts to mediate stress responses. Therefore, we examined the behavioral effects of an intra-PVN PACAP injection (25 pmol) in combination with a mild stressor. PACAP or artificial cerebrospinal fluid (aCSF) was microinjected into the PVN (0.25 l) and then animals were restrained or placed in their home cage for 5 min. Exploratory activity (total distance traveled) and scored behaviors (face washing, body grooming, wet dog shakes, and rearing) were observed in a familiar open field for 10 min. In animals receiving aCSF, there were no behavioral differences between restrained and unrestrained groups. For the entire 10-min observation period, animals receiving PACAP, whether restrained or not, displayed elevated face washing and body grooming with decreased locomotor activity and rearing. Among PACAP-injected animals, restrained animals displayed increased body grooming compared to unrestrained animals during the first 2 min in the open field suggesting a summation of the effects of peptide injection and stressor. The observed elevation in grooming is consistent with previous studies reporting similar increases following electrical-, NMDA-, CRH-, or stressor-induced activation of the PVN. Thus, at the level of the PVN, PACAP may act as an excitatory neuropeptide and augment behavioral responses to stressors.

Pituitary adenylate cyclase-activating polypeptide (PACAP) mimics neuroendocrine and behavioral manifestations of stress: Evidence for PKA-mediated expression of the corticotropin-releasing hormone (CRH) gene

The physiologic response to stress is highly dependent on the activation of corticotropin-releasing hormone (CRH) neurons by various neurotransmitters. A particularly rich innervation of hypophysiotropic CRH neurons has been detected by nerve fibers containing the neuropeptide PACAP, a potent activator of the cAMP-protein kinase A (PKA) system. Intracerebroventricular (icv) injections of PACAP also elevate steady-state CRH mRNA levels in the paraventricular nucleus (PVN), but it is not known whether PACAP effects can be associated with acute stress responses. Likewise, in cell culture studies, pharmacologic activation of the PKA system has stimulated CRH gene promoter activity through an identified cAMP response element (CRE); however, a direct link between PACAP and CRH promoter activity has not been established. In our present study, icv injection of 150 or 300 pmol PACAP resulted in robust phosphorylation of the transcription factor CREB in the majority of PVN CRH neurons at 15 to 30 min post-injection and induced nuclear Fos labeling at 90 min. Simultaneously, plasma corticosterone concentrations were elevated in PACAP-injected animals, and significant increases were observed in face washing, body grooming, rearing and wet-dog shakes behaviors. We investigated the effect of PACAP on human CRH promoter activity in alphaT3-1 cells, a PACAP-receptor expressing cell line. Cells were transiently transfected with a chloramphenicol acetyltransferase (CAT) reporter vector containing region - 663/+124 of the human CRH gene promoter then treated for with PACAP (100 nM) or with the adenylate cyclase activating agent, forskolin (2.5 muM). Both PACAP and forskolin significantly increased wild-type hCRH promoter activity relative to vehicle controls. The PACAP response was abolished in the CRE-mutant construct. Pretreatment of transfected cells with the PKA blocker, H-89, completely prevented both PACAP- and forskolin-induced increases in CRH promoter activity. Furthermore, CREB overexpression strongly enhanced PACAP-mediated stimulation of hCRH promoter activity, an effect which was also lost with mutation of the CRE. Thus, we demonstrate that icv PACAP administration to rats under non-stressed handling conditions leads to cellular, hormonal and behavioral responses recapitulating manifestations of the acute stress response. Both in vivo and in vitro data point to the importance of PACAP-mediated activation of the cAMP/PKA signaling pathway for stimulation of CRH gene transcription, likely via the CRE.

Expression of pituitary adenylate cyclase activating polypeptide type 1 receptor (PAC1R) in the ewe hypothalamus: distribution and colocalization with tyrosine hydroxylase-immunoreactive neurones

We have examined the distribution of the pituitary adenylate cyclase activating polypeptide type I receptor (PAC1R) in the ewe hypothalamus by reverse transcription-polymerase chain reaction, in situ hybridization and immunohistochemistry. PAC1R mRNA was highly expressed in the mediobasal hypothalamus of the ewe, particularly in the arcuate nucleus and ventromedial hypothalamus, compared to other hypothalamic regions. Similar results were obtained from immunohistochemistry using a specific PAC1R antibody. Intense immunolabelling was observed in the arcuate nucleus, external zone of the median eminence and ventromedial hypothalamus. Only relatively weak immunolabelling was observed in other hypothalamic regions, including the paraventricular nucleus and supraoptic nucleus. In the ewe, PACAP acts via the arcuate nucleus to suppress prolactin secretion. Therefore we examined whether PAC1R was present on the tuberoinfundibular dopamine (TIDA) neurones in this nucleus. Dual immunofluorescence labelling for PAC1R and tyrosine hydroxylase revealed that 21.2 +/- 1.7% of dopaminergic neurones in the arcuate nucleus (A12 cell group) also stained for PAC1R. By contrast, other hypothalamic dopaminergic cell groups (A11, A13, A14 and A15) exhibited little (< 3%) or no colocalization. Overall, our results indicate that, in the ewe hypothalamus, PAC1R is most concentrated in the arcuate nucleus, where it is localized on a substantial proportion of dopaminergic neurones. These observations, together with previous in vivo studies, suggest that PACAP could act directly on TIDA neurones via PAC1R to increase dopamine release and consequently inhibit prolactin secretion in the sheep.

Upregulation of corticotropin-releasing hormone gene expression in the paraventricular nucleus of cyclophosphamide-induced cystitis in male rats

We examined the effects of cyclophosphamide (CP)-induced cystitis on the expression of corticotropin-releasing hormone (CRH) mRNA in the paraventricular nucleus (PVN) and the serum levels of adrenocorticotropic hormone (ACTH) using in situ hybridization histochemistry and radioimmunoassay. In addition, the expression of AVP heteronuclear (hn) RNA and neuronal nitric oxide synthase (nNOS) mRNA was also examined in the PVN of a CP-induced cystitis model. We found that the levels of CRH mRNA were significantly increased in the PVN at 2 h after intraperitoneal administration of CP compared to those in saline-treated rats. The CRH mRNA levels in the PVN peaked at 12 h after CP administration and the levels were still significantly higher than those in saline-treated group at 24 h after CP administration. The serum ACTH levels in CP-treated group were also significantly higher compared to those in saline-treated group at any of the time points examined. Unlike previous findings showing upregulation of nNOS mRNA and AVP hnRNA under somatic nociceptive states, the levels of nNOS mRNA and AVP hnRNA were unchanged in the PVN following CP-induced cystitis, visceral nociceptive stimulation. These results suggest that visceral nociceptive stimulation as well as somatic nociceptive stimulation may activate the hypothalamo-pituitary axis but the hypothalamic neuroendocrine responses produced by visceral nociceptive stimulation may be different from those produced by somatic nociceptive stimulation.

Enhanced up-regulation of corticotropin-releasing hormone gene expression in response to restraint stress in the hypothalamic paraventricular nucleus of oxytocin gene-deficient male mice

The neuropeptide oxytocin is released not only into the blood, but also within the brain in response to various stressors. Accumulating evidence suggests that central oxytocin may play a major role in the regulation of neuroendocrine responses to stress. In the present study, using the oxytocin knockout mouse model, we tested whether oxytocin might act to attenuate stress-induced up-regulation of corticotropin-releasing hormone (CRH) mRNA expression in the brain. The expression of CRH mRNA in the paraventricular nucleus (PVN) after 4 h of restraint stress was examined in oxytocin gene-deficient (OTKO), wild-type and heterozygous male mice using in situ hybridization histochemistry. We found that basal levels of CRH mRNA were not different among the three genotypes. Although restraint stress resulted in a significant increase of CRH mRNA expression in the PVN regardless of genotype, the degree of stress induced-up-regulation was significantly higher in OTKO mice than in wild-type mice. The effects of restraint stress on the expression of the arginine vasopressin (AVP) and the oxytocin genes were also examined. Unlike CRH mRNA, basal expression (in nonstressed control groups) of AVP mRNA in OTKO mice, as well as oxytocin mRNA in heterozygous mice, was significantly lower in the PVN and the supraoptic nucleus than in wild-type mice. After restraint stress, the expression of AVP mRNA was significantly increased in the PVN of OTKO mice compared to the nonstressed control group, whereas the expression of both AVP and oxytocin mRNA were unchanged in the PVN and the supraoptic nucleus of wild-type and heterozygous mice. Finally, in a separate set of mice, restraint stress-induced Fos expression was also examined in several brain regions involved in stress response, including the lateral septum, the bed nucleus of the stria terminalis (BNST), the medial preoptic area, the PVN, the medial and central amygdala using immunohistochemistry. After 90 min of restraint stress, the number of Fos-expressing cells significantly increased in all brain regions examined regardless of genotype. However, the number of stress-induced Fos-expressing cells in the BNST and the medial amygdala of OTKO mice was significantly lower than in wild-type mice. Collectively, the findings in the present study suggest that oxytocin may regulate stress-induced CRH gene expression in the PVN. Furthermore, neuronal activity in the BNST and the medial amygdala may be involved in this neuroendocrine regulatory system.

Impaired somatodendritic responses to pituitary adenylate cyclase-activating polypeptide (PACAP) of supraoptic neurones in PACAP type I -receptor deficient mice

The role of pituitary adenylate cyclase-activating polypeptide (PACAP) type I receptor (PAC1 receptor) in regulating hypothalamic supraoptic neurones was investigated using PAC1 receptor-deficient male mice (PAC1-/-). The effects of PACAP on [Ca2+]i were investigated in freshly dissociated supraoptic neurones and on the somatodendritic release of vasopressin and oxytocin, examined on intact supraoptic nuclei. In supraoptic neurones from wild-type mice (PAC1+/+), 100 nm PACAP induced an increase in [Ca2+]i and release of vasopressin and oxytocin, whereas in heterozygous (PAC1+/-) and null-mutant mice (PAC1-/-), PACAP was much less effective. PACAP had no effect on these two parameters when applied to isolated neurohypophysial nerve terminals of PAC1+/+ and PAC1-/- mice, and rats. In conclusion, the PAC1 receptor is solely responsible for the PACAP-induced [Ca2+]i signalling and secretion of vasopressin and oxytocin in the somatodendritic region of supraoptic neurones.

Estrogen receptor-beta regulates transcript levels for oxytocin and arginine vasopressin in the hypothalamic paraventricular nucleus of male mice

Estrogen receptor (ER)-beta, unlike ER-alpha, is localized in the hypothalamic paraventricular nucleus (PVN) which also contains neuropeptide synthesizing neurons, such as oxytocin (OT), arginine vasopressin (AVP) and corticotropin-releasing hormone (CRH). Although it is known that some ER-beta containing neurons co-express OT and AVP, but not CRH, in the PVN, it is not yet determined whether ER-beta activation may indeed play a role in estrogenic regulation on syntheses of these neuropeptides. In the present study, we tested this hypothesis by comparing the effects of estrogen on the levels of OT, AVP and CRH messenger RNA (mRNA) between ER-beta knockout (betaERKO) and wild type (WT) control male mice. Mice were gonadectomized and implanted with either a pellet containing estradiol benzoate (2.5-5.0 microg/day) or a placebo pellet for 21 days. In situ hybridization histochemistry revealed that estrogen treatment resulted in a significant increase in OT transcripts (151.6+/-6.0%) and a decrease in AVP transcripts (77.8+/-5.2%) in the PVN of WT mice, compared to the placebo control group. This estrogenic regulation of OT and AVP mRNA levels in the PVN was completely abolished in betaERKO mice. Similar genotype differences in the effects of estrogen on the numbers of OT- and AVP-containing cells were found in immunocytochemical studies performed in a separate set of mice. On the other hand, the expression of CRH mRNA in the PVN was not affected by estrogen treatment in either WT or betaERKO mice. Furthermore, estrogen did not cause any changes in the levels of OT or AVP mRNA, regardless of genotype, in the supraoptic nucleus where, unlike in rats, ER-beta containing neurons are rarely found in mice. Finally, estrogen significantly increased OT mRNA levels in both betaERKO and WT in the medial preoptic area, which contains both ER-alpha and ER-beta. These results suggest that ER-beta activation may play a critical role in estrogenic regulation of OT and AVP gene expression in the PVN.

Upregulation of CRH gene expression and downregulation of arginine vasopressin gene expression in the hypothalamus of bilateral nephrectomized rats

The expression of the corticotropin-releasing hormone (CRH) gene and the arginine vasopressin (AVP) gene in the hypothalamus examined in bilateral nephrectomized rats by in situ hybridization histochemistry. The expression of the CRH gene was significantly increased in the parvocellular part of the paraventricular nucleus (PVN) 12 and 20 h after bilateral nephrectomy in comparison with that after sham operation. The plasma concentration of adrenocorticotropic hormone (ACTH) in nephrectomized rats was significantly higher than that in sham operated rats 20 h after surgery. In contrast, the expression of the AVP gene in both the parvocellular and magnocellular parts of the PVN and throughout the supraoptic nucleus (SON) was significantly decreased 20 h after bilateral nephrectomy in comparison with that after sham operation. These results suggest that nephrectomy-induced upregulation of the CRH gene with elevation of plasma ACTH may be due to the activation of the hypothalamo-pituitary adrenal (HPA) axis.

Effects of vasoactive intestinal polypeptide on neurones of the rat suprachiasmatic nuclei in vitro

The suprachiasmatic nuclei (SCN) of the hypothalamus house the main circadian pacemaker in mammals. Vasoactive intestinal polypeptide (VIP) is the most abundant neuropeptide in the SCN and has been shown to phase-shift the electrical activity rhythm of SCN cells in vitro. However, the effects of VIP on the cellular activity of rat SCN neurones are unknown. In this study, we examined the acute effects of VIP on the extracellularly recorded spontaneous firing rate of SCN neurones in an in-vitro hypothalamic slice preparation. Furthermore, with the use of receptor-selective agonists and antagonists, we determined which receptors might mediate the effects of VIP in the SCN. Approximately 50% of cells responded to VIP; the main type of response was suppression in firing rate, although a few cells were activated. Suppression responses to VIP were mimicked by the VPAC(2) receptor agonist Ro 25-1553 and blocked by the selective VPAC(2) receptor antagonist PG 99-465. The PAC(1) receptor agonist maxadilan evoked responses from 40% of SCN cells, and activations to this agonist were not altered by PG 99-465. Responses to VIP were not blocked by antagonists to ionotropic glutamate receptors, but the duration of suppression was modulated by the GABA(A) receptor antagonist bicuculline. Our data indicate that VIP alters the electrical activity of rat SCN neurones in vitro, via both VPAC(2) and PAC(1) receptors.

Neurotransmitter/neuropeptide interactions in the regulation of neurohypophyseal hormone release

Regulation of neurohypophyseal hormone release reflects the convergence of a large number of afferent pathways on the vasopressin (VP)- and oxytocin-producing neurons. These pathways utilize a broad range of neurotransmitters and neuropeptides. In this review, the mechanisms by which this information is coordinated into appropriate physiological responses is discussed with a focus on the responses to agents that are coreleased from A1 catecholamine nerve terminals in the supraoptic nucleus. The A1 pathway transmits hemodynamic information to the vasopressin neurons by releasing several neuroactive agents including ATP, norepinephrine, neuropeptide Y, and substance P. These substances stimulate VP release from explants of the hypothalamo-neurohypophyseal system and certain combinations of these agents elicit potent but selective synergism. Evaluation of the signal cascades elicited by these agents provides insights into mechanisms underlying these synergistic interactions and suggests mechanisms responsible for coordinated responses of the VP neurons to activation of a range of ion-gated ion channel and G-protein-coupled receptors.

Pre- and postsynaptic modulation of the electrical activity of rat supraoptic neurones

The release of vasopressin and oxytocin is regulated by the electrical activity of magnocellular neurosecretory cells in the supraoptic and paraventricular nuclei, which is under the control of a great variety of neurotransmitters and neuromodulators. The major neural signals to the supraoptic nucleus are from excitatory glutamate inputs and inhibitory GABA inputs. In recent studies, the voltage-clamp mode of the whole-cell patch-clamp technique has been applied to slice preparations from rat hypothalamus to monitor synaptic inputs to supraoptic neurones. Spontaneous excitatory and inhibitory postsynaptic currents (EPSCs and IPSCs) are abolished by CNQX and picrotoxin, respectively, but are insensitive to tetrodotoxin, indicating that they represent quantal release of glutamate and GABA, respectively, from nerve terminals of presynaptic neurones. GABA and glutamate show remarkable suppressive effects on both EPSCs and IPSCs via presynaptic GABA(B) and mGlu receptors, respectively. Noradrenaline, which excites supraoptic neurones via postsynaptic alpha1-receptors, also suppresses IPSCs and potentiates EPSCs. On the other hand, prostaglandin E2, which excites supraoptic neurones via postsynaptic prostaglandin E2 (EP) receptors of the EP4 subclass, also suppresses IPSCs via EP3 receptors but has little effect on EPSCs. Thus pre- and postsynaptic mechanisms may act cooperatively to excite supraoptic neurones. Nitric oxide, which inhibits supraoptic neurones, potentiates IPSCs without affecting EPSCs. This provides another example for the preferential modulation of IPSCs of supraoptic neurones. On the other hand, PACAP, which causes a long-lasting increase in the firing frequency via the postsynaptic receptors, has no effect on EPSCs and IPSCs, suggesting that some ligands act only at postsynaptic receptors. Thus multiple patterns for pre- and postsynaptic modulation are present in the supraoptic nucleus, and the electrical activity of supraoptic neurones is regulated via complex mechanisms at both pre- and postsynaptic sites.

Intracellular calcium signalling in magnocellular neurones of the rat supraoptic nucleus: understanding the autoregulatory mechanisms

Oxytocin and vasopressin, released at the soma and dendrites of neurones, bind to specific autoreceptors and induce an increase in [Ca2+]i. In oxytocin cells, the increase results from a mobilisation of Ca2+ from intracellular stores, whereas in vasopressin cells, it results mainly from an influx of Ca2+ through voltage-dependent channels. The response to vasopressin is coupled to phospholipase C and adenylyl-cyclase pathways which are activated by V1 (V1a and V1b)- and V2-type receptors respectively. Measurements of [Ca2+]i in response to V1a and V2 agonists and antagonists suggest the functional expression of these two types of receptors in vasopressin neurones. The intracellular mechanisms involved are similar to those observed for the action of the pituitary adenylyl-cyclase-activating peptide (PACAP). Isolated vasopressin neurones exhibit spontaneous [Ca2+]i oscillations and these are synchronised with phasic bursts of electrical activity. Vasopressin modulates these spontaneous [Ca2+]i oscillations in a manner that depends on the initial state of the neurone, and such varied effects of vasopressin may be related to those observed on the electrical activity of vasopressin neurones in vivo.

Effects of leptin on fasting-induced inhibition of neuronal nitric oxide synthase mRNA in the paraventricular and supraoptic nuclei of rats

Fasting induced a reduction in neuronal nitric oxide synthase (nNOS) mRNA in the paraventricular nucleus (PVN) and supraoptic nucleus (SON) of rats. The effect of intracerebroventricular (i.c.v.) administration of leptin on the nNOS mRNA level in the PVN and SON of fasting rats was studied by in situ hybridization histochemistry. Leptin (10 microg/kg b.wt) or vehicle was administered i.c.v. at 1700 h on two successive days fasting for 2 days. Fasting for 2 days with i.c.v. administration of vehicle induced a significant reduction of nNOS mRNA in the PVN and SON. Central administration of leptin prevented the fasting-induced reduction of nNOS mRNA in the PVN and SON. Administration of leptin also prevented the fasting-induced reductions of thyrotropin-releasing hormone (TRH) and corticotropin-releasing hormone (CRH) mRNAs in the parvocellular division of the PVN. These results suggest that leptin is associated with fasting-induced reduction of nNOS mRNA in the PVN and SON as well as TRH and CRH mRNAs in the PVN.

Activation of multiple intracellular transduction signals by vasopressin in vasopressin-sensitive neurones of the rat supraoptic nucleus

1. The intracellular mechanisms activated by the binding of vasopressin to its receptor(s) and which result in the increase of [Ca2+]i were investigated in freshly dissociated supraoptic nucleus neurones. Various pharmacological agents were used to investigate the possible involvement of phospholipase C (PLC) and adenylate cyclase (AC) intracellular pathways in the transduction of the vasopressin action. 2. Both the PLC inhibitor U-73122 and the protein kinase C (PKC) inhibitor calphostin C, reduced the [Ca2+]i rise elicited by vasopressin. The cAMP analogue, 8-Br-cAMP produced an increase in [Ca2+]i and IBMX, a phosphodiesterase inhibitor, potentiated the response to vasopressin. 3. After pre-incubation with the AC inhibitor SQ-22536, 7 out of 18 vasopressin-sensitive neurones showed no inhibition of the vasopressin response, while the response to vasopressin was reduced by greater than 35 % in each of the other 11 neurones. 4. The activation of protein kinase A (PKA) with Sp-cAMPS caused an increase in [Ca2+]i which was additive to the vasopressin-elicited [Ca2+]i increase. After incubation with the PKA inhibitors Rp-cAMPS or H-89, the [Ca2+]i responses triggered by Sp-cAMPS and vasopressin were, respectively, abolished and greatly reduced. 5. A combined administration of SQ-22536 (AC inhibitor) followed by U-73122 (PLC inhibitor), or U-73122 followed by H-89 (PKA inhibitor), virtually abolished the response to vasopressin. 6. In vasopressin-responsive neurones, the pituitary adenylate cyclase-activating polypeptide (PACAP) induced a [Ca2+]i increase similar to the response to vasopressin and in both cases the increase was inhibited to the same extent by a combination of U-73122 and Rp-cAMPS. 7. In conclusion, we suggest that the autoregulation exerted specifically by vasopressin on vasopressin-sensitive neurones involves the activation of both PLC- and AC-linked pathways.

Is there appetite after GLP-1 and PACAP?

Anitobesity drugs must increase the sensitivity of the hypothalamic satiety center towards leptin and antagonize the synthesis and action of NPY. The array of pharmacologic tools available is vast and presently ineffective. Among peptide analogs considered for evaluation [NPY-5 antagonists and CCK-A, bombesin, amylin and melanocyte-stimulating hormone-4 (or melanin-concentrating hormone?) agonists], is there a place for GLP-1 and PACAP? GLP-1 receptors present in ARC, PVN, VMN, and SON are the target for both central and blood-borne GLP-1 in those hypothalamic neurons endowed with GLUT-2 and glucokinase. GLP-1, hypersecreted by L-cells after a meal, is a potent insulinotropic agent and, together with glucose, reduces food intake and induces c-fos in the ARC. PACAP is present in the ARC, PVN, and SCH, and its hypothalamic type I receptor elevates cAMP and inositol triphosphate in the PVN, where it may perhaps antagonize NPY-induced food intake and hyperinsulinemia. However, irrelevant neuroendocrine, autonomic, and circadian functions are also activated by this peptide, making it a less than ideal base on which to build an obesity treatment.

Role of VIP, PACAP, and related peptides in the regulation of the hypothalamo-pituitary-adrenal axis

Vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) are members of a family of regulatory peptides that are widely distributed in the body and share numerous biologic actions. The two peptides display a remarkable amino acid-sequence homology, and bind to a class of G protein-coupled receptors, named PACAP/VIP receptors (PVRs), whose signaling mechanism mainly involves the activation of adenylate-cyclase and phospholipase-C cascades. A large body of evidence suggests that VIP and PACAP play a role in the control of the hypothalamo--pituitary-adrenal (HPA) axis, almost exclusively acting in a paracrine manner, since their blood concentration is very low. VIP and PACAP are contained in both nerve fibers and neurons of the hypothalamus, and VIP, but not PACAP, is also synthesized in the pituitary gland. Both peptides are expressed in the adrenal gland, and especially in medullary chromaffin cells. All the components of the HPA axis are provided with PVRs. VIP and PACAP enhance pituitary ACTH secretion, VIP by eliciting the hypothalamic release of CRH and potentiating its secretagogue action, and PACAP by directly stimulating pituitary corticotropes. Through this central mechanism, VIP and PACAP may increase mineralo- and glucocorticoid secretion of the adrenal cortex. VIP but not PACAP also exerts a weak direct secretagogue action on adrenocortical cells by activating both PVRs and probably a subtype of ACTH receptors. VIP and PACAP raise aldosterone production via a paracrine indirect mechanism involving the stimulation of medullary chromaffin cells to release catecholamines, which in turn enhance the secretion of zona glomerulosa cells via a beta-adrenoceptor-mediated mechanism. PACAP appears to be able to evoke a glucocorticoid response through the activation, at least in the rat, of the intramedullary CRH/ACTH system. The relevance of these effects of VIP and PACAP under basal conditions is questionable, although there are indications that endogenous VIP is involved in the maintenance of the normal growth and steroidogenic capacity of rat adrenal cortex. However, indirect evidence suggests that these peptides might play a relevant role under paraphysiological conditions (e.g., in the mediation of HPA axis responses to cold and inflammatory stresses) or may be somehow involved in the pathogenesis of Cushing disease or some case of hyperaldosteronism associated with secreting pheochromocytomas.

PACAP increases the cytosolic Ca2+ concentration and stimulates somatodendritic vasopressin release in rat supraoptic neurons

Pituitary adenylate cyclase activating polypeptide (PACAP)-like immunoreactivity and its receptor mRNA have been reported in the supraoptic and the paraventricular nucleus (SON and PVN, respectively) and PACAP has been implicated in the regulation of magnocellular neurosecretory cell function. To examine the site and the mechanism of the action of PACAP in the neurosecretory cells, we measured AVP release from SON slice preparations and the cytosolic Ca2+ concentration ([Ca2+]i) from single dissociated SON neurons. PACAP at concentrations from 10(-12) to 10(-7) M increased [Ca2+]i in dissociated SON neurons in a dose-dependent manner. The patterns of the PACAP-induced [Ca2+]i increase were either sustained increase or cytosolic Ca2+ oscillations. PACAP (10[-7] M) increased [Ca2+]i in 27 of 27 neurons and glutamate (10[-4] M) increased [Ca2+]i in 19 of 19 SON neurons examined, whereas angiotensin II (10[-7] M) increased [Ca2+]i in only 15 of 60 SON neurons examined. PACAP at lower concentrations (10[-10] to 10[-8] M) increased [Ca2+]i in 70-80% of neurons examined. Although the onset and recovery of the PACAP-induced [Ca2+]i increase were slower than those observed with glutamate, the spatial distribution of the [Ca2+]i increases in response to the two ligands were similar: [Ca2+]i increase at the proximal dendrites was larger and faster and that at the center of the soma was smaller and slower. The PACAP-induced [Ca2+]i responses were abolished by extracellular Ca2+ removal, the L-type Ca2+-channel blocker, nicardipine, or by replacement of extracellular Na+ with N-methyl D-glucamine, and were partially inhibited by the Na+-channel blocker, tetrodotoxin. The N-type Ca2+-channel blocker, omega-conotoxin GVIA did not significantly inhibit the PACAP-induced [Ca2+]i responses. Furthermore, PACAP (10[-7] M) as well as glutamate (10[-4] M) increased AVP release from SON slice preparations, and extracellular Ca2+ removal or nicardipine inhibited the AVP release in response to PACAP. These results indicate that PACAP enhances Ca2+ entry via voltage-gated Ca2+ channels and increases [Ca2+]i, which, in turn, stimulates somatodendritic vasopressin release by directly activating PACAP receptors on SON neurons. The results also suggest that PACAP in the SON may play a pivotal role in the control of the neurohypophyseal function at the level of the soma or the dendrites.

Pituitary adenylate cyclase-activating polypeptide potentiation of Ca2+ entry via protein kinase C and A pathways in melanotrophs of the pituitary pars intermedia of rats

Pituitary adenylate cyclase-activating polypeptide (PACAP) has been reported to stimulate melanotroph secretion, and PACAP-like immunoreactivity and expression of PACAP type I receptor messenger RNA have been identified in the pituitary pars intermedia (PI). The present study showed that PACAP messenger RNA is also expressed in the PI. To examine the mechanism of PACAP action in the PI, cytosolic Ca2+ concentrations ([Ca2+]i) and ionic currents were measured in acutely dissociated rat melanotrophs. In about 40% of the melanotrophs studied, PACAP induced an increase in [Ca2+]i, which was suppressed by extracellular Ca2+ removal; extracellular Na+ replacement; the blocker of L-type Ca2+ channels, nicardipine; or the secreto-inhibitory neurotransmitter, dopamine. The PACAP-induced [Ca2+]i increase was mimicked by activators of protein kinase A (PKA) and protein kinase C (PKC), Sp-diastereomer of cAMP and 1-oleoyl-2-acetyl-sn-glycerol, and was reduced by inhibitors of PKA and PKC, Rp-diastereomer of cAMP and staurosporine. Patch-clamp analysis revealed that PACAP caused inward currents with a reversal potential of -0.8 mV and facilitated voltage-dependent Ba2+ currents. It further revealed that PACAP-induced inward currents were mimicked by 1-oleoyl-2-acetyl-sn-glycerol and inhibited by staurosporine, and that Sp-diastereomer of cAMP facilitated Ba2+ currents. These results suggest that PACAP potentiates Ca2+ entry mechanisms of rat melanotrophs by activation of nonselective cation channels via PKC and facilitation of voltage-dependent Ca2+ channels via PKA.