Hypophysectomy abolishes rhythms in rat thyroid hormones but not in the thyroid clock

The endocrine body rhythms including the hypothalamic-pituitary-thyroid axis seem to be regulated by the circadian timing system, and daily rhythmicity of circulating thyroid-stimulating hormone (TSH) is well established. The circadian rhythms are generated by endogenous clocks in the central brain oscillator located in the hypothalamic suprachiasmatic nucleus (SCN) as well as multiple peripheral clocks, but information on the existence and function of a thyroid clock is limited. The molecular machinery in all clock cells is composed of a number of clock genes and their gene products are connected by autoregulatory feedback loops. Here, we provide evidence for a thyroid clock in the rat by demonstrating 24-h antiphase oscillations for the mRNA of the canonical clock genes Per1 and Bmal1, which was unaffected by hypophysectomy. By immunostaining, we supported the existence of a core oscillator in the individual thyroid cells by demonstrating a daily cytoplasmatic-nuclear shuttling of PER1 protein. In normal rats, we found a significant daily rhythmicity in the circulating thyroid hormones preceded by a peak in TSH. In hypophysectomised rats, although the thyroid clock was not affected, the oscillations in circulating thyroid hormones were abolished and the levels were markedly lowered. No daily oscillations in the expression of TSH receptor mRNA were observed in neither control rats nor hypophysectomised rats. Our findings indicate that the daily rhythm of thyroid hormone secretion is governed by SCN signalling via the rhythmic TSH secretion rather than by the local thyroid clock, which was still ticking after hypophysectomy.

Altered Expression Pattern of Clock Genes in a Rat Model of Depression

BACKGROUND

Abnormalities in circadian rhythms may be causal factors in development of major depressive disorder. The biology underlying a causal relationship between circadian rhythm disturbances and depression is slowly being unraveled. Although there is no direct evidence of dysregulation of clock gene expression in depressive patients, many studies have reported single-nucleotide polymorphisms in clock genes in these patients.

METHODS

In the present study we investigated whether a depression-like state in rats is associated with alternations of the diurnal expression of clock genes. The validated chronic mild stress (CMS) animal model of depression was used to investigate rhythmic expression of three clock genes: period genes 1 and 2 (Per1 and Per2) and Bmal1. Brain and liver tissue was collected from 96 animals after 3.5 weeks of CMS (48 control and 48 depression-like rats) at a 4h sampling interval within 24h. We quantified expression of clock genes on brain sections in the prefrontal cortex, nucleus accumbens, pineal gland, suprachiasmatic nucleus, substantia nigra, amygdala, ventral tegmental area, subfields of the hippocampus, and the lateral habenula using in situ hybridization histochemistry. Expression of clock genes in the liver was monitored by real-time quantitative polymerase chain reaction (PCR).

RESULTS

We found that the effect of CMS on clock gene expression was selective and region specific. Per1 exhibits a robust diurnal rhythm in most regions of interest, whereas Bmal1 and in particular Per2 were susceptible to CMS.

CONCLUSION

The present results suggest that altered expression of investigated clock genes is likely associated with the induction of a depression-like state in the CMS model.

Vasoactive Intestinal Polypeptide Evokes Only a Minimal Headache in Healthy Volunteers

The role of the parasympathetic nervous system in the pathogenesis of migraine is disputed. The headache-eliciting effect of the parasympathetic neurotransmitter, vasoactive intestinal polypeptide (VIP), and its effect on cerebral arteries and brain haemodynamics has not been systematically studied in man. We hypothesized that infusion of VIP might induce headache in healthy subjects and cause changes in cerebral haemodynamics. VIP (8 pmol/kg per min) or placebo (0.9± saline) was infused for 25 min into 12 healthy young volunteers in a crossover, double-blind design. Headache was scored on a verbal rating scale from 0 to 10, regional cerebral blood flow (rCBF) was measured with single-photon emission computed tomography and 133Xe inhalation and mean flow velocity in the middle cerebral artery (VmeanMCA) was measured with transcranial Doppler ultrasonography. The headache was very mild with a maximum score of 2 and described as a pressing or throbbing sensation. Five participants developed headache during VIP and one during placebo. During the infusion, a significant drop in VmeanMCA was seen for VIP compared with placebo ( P < 0.001), but the effect quickly waned and no difference was found when comparing the time between 30 and 120 min. In addition, no significant difference in the diameter of the MCA could be found during the infusion. No significant differences in rCBF ( P = 0.10) were found between VIP and placebo. A marked dilation of the superficial temporal artery was seen ( P = 0.04) after VIP in the first 30 min but no difference was found when comparing the time between 30 and 120 min. We found no difference in mean arterial blood pressure between VIP and placebo days but the heart rate increased significantly on a VIP day compared with a placebo day (AUC0–30min, P < 0.001). Plasma VIP was significantly higher on a VIP day compared with placebo (AUC0–80min, P < 0.001). These results show that VIP causes a decrease in VmeanMCA without affecting rCBF. In spite of a marked vasodilator effect in the extracranial vessels and increased plasma VIP, healthy subjects developed only a very mild headache.

Restricted expression of Neuroglobin in the mouse retina and co-localization with Melanopsin and Tyrosine Hydroxylase

Neuroglobin (Ngb), a neuronal specific oxygen binding heme-globin, reported to be expressed at high levels in most layers of the murine retina. Ngb's function is presently unknown, but based on its high expression level and oxygen binding capabilities Ngb was proposed to function as an oxygen reservoir facilitating oxygen metabolism in highly active neurons or to function as a neuroprotectant. In the present study, we re-examined the expression pattern of Ngb in the retina using a highly validated antibody. Furthermore, intactness of retino-hypothalamic projections and the retinal expression level of Melanopsin and Tyrosine Hydroxylase were investigated in Ngb-null mice. Ngb-immunoreactivity was found in a few neurons of the ganglion cell and inner nuclear layers co-expressing Melanopsin and Tyrosine Hydroxylase, respectively. Ngb deficiency neither affected the level of Melanopsin and Tyrosine Hydroxylase proteins nor the intactness of PACAP-positive retinohypothalamic projections in the suprachiasmatic nucleus. Based on the present results, it seems unlikely that Ngb could have a major role in retinal oxygen homeostasis and neuronal survival under normal conditions. The present study suggests that a number of previously published reports have relied on antibodies with dubious specificity.

Streptozotocin treatment of a pancreatic tumour producing VIP and gastrin associated with Verner-Morrison syndrome

A 57-year-old male patient with metastasizing non-beta islet cell carcinoma of the pancreas is described. Both gastrin and VIP levels were elevated and the patient suffered from a syndrome of pancreatic cholera and hyperacidity. The tumour contained gastrin and VIP as demonstrated by immunofluorescence. The patient also had a history of familial renal stone formation and parathyroid nodular hyperplasia. Resection of pancreatic tumour in 1973 resulted in four years without symptoms. In 1977 definite signs of multiple hepatic metastases appeared. These signs disappeared after streptozotocin given in a dosage of 2 g three times at weekly intervals. The patient had remained well for 20 months after this treatment. The causative agents for the clinical syndrome in this case are discussed in view of circulating hormone levels.

Report on a patient with watery diarrhoea syndrome caused by a pancreatic tumour containing neurotensin, enkephalin and calcitonin

A patient with water diarrhoea syndrome (WDS) is described. A pancreatic tumour was found containing many cells with immunoreactivity to enkephalin and neurotensin, a few with immunoreactivity to calcitonin but none to vasoactive intestinal peptide (VIP). High levels of calcitonin, neurotensin, VIP and pancreatic polypeptide (PP) were present in plasma as measured by radioimmunoassay. After removal of the tumour, the plasma levels of the first three peptides returned to normal and the WDS disappeared. On the other hand, plasma PP did not change. No specific symptoms could be attributed to the new spectrum of peptides found in the tumour. This is the first report of a pancreatic tumour containing high levels of neurotensin.

Vasoactive Intestinal Peptide Causes Marked Cephalic Vasodilation, but does not Induce Migraine

We hypothesized that intravenous infusion of the parasympathetic transmitter, vasoactive intestinal peptide (VIP), might induce migraine attacks in migraineurs. Twelve patients with migraine without aura were allocated to receive 8 pmol kg-1 min-1 VIP or placebo in a randomized, double-blind crossover study. Headache was scored on a verbal rating scale (VRS), mean blood flow velocity in the middle cerebral artery ( Vmean mca) was measured by transcranial Doppler ultrasonography, and diameter of the superficial temporal artery (STA) by high-frequency ultrasound. None of the subjects reported a migraine attack after VIP infusion. VIP induced a mild immediate headache (maximum 2 on VRS) compared with placebo ( P = 0.005). Three patients reported delayed headache (3-11 h after infusion) after VIP and two after placebo ( P = 0.89). Vmean mca decreased (16.3 ± 5.9%) and diameter of STA increased significantly after VIP (45.9 ± 13.9%). VIP mediates a marked dilation of cranial arteries, but does not trigger migraine attacks in migraineurs. These data provide further evidence against a purely vascular origin of migraine.

Diurnal rhythmicity of the canonical clock genes Per1, Per2 and Bmal1 in the rat adrenal gland is unaltered after hypophysectomy

Circadian rhythms are generated by endogenous clocks in the central brain oscillator, the suprachiasmatic nucleus (SCN), and peripheral tissues. The molecular basis for the circadian clock consists of a number of genes and proteins that form transcriptional/translational feedback loops. Rhythmic expression of clock genes in the adrenal glands has previously been reported. Since the central clock in the SCN communicates with the adrenal glands via circadian release of adrenocorticotrophic hormone, we quantified the mRNAs for the canonical clock genes, Per1, Per2 and Bmal1 in the adrenal glands by real-time reverse transcription-polymerase chain reaction during a 24-h-cycle in normal and hypophysectomised rats. The mRNAs for all the three clock genes disclosed rhythmic oscillations with a period of 24 h and the phase did not differ between the hypophysectomised and intact rats. The expression pattern of Per1 and Bmal1 was in antiphase in both groups of animals. In situ hybridisation histochemistry using antisense RNA probes demonstrated that, at times of peak expression, mRNAs for all the three clock genes were expressed in the adrenal cortex with a particularly strong labelling in the zona reticularis. In accordance with the mRNA localisation, immunostaining for PER1 protein was visualised in cells of the adrenal cortex, being most intense in the inner zone. The immunostaining also demonstrated a translocation of PER1 protein from the cytoplasm to the nucleus during the daily cycle, supporting the existence of a core oscillator in the individual adrenal gland cells. Our findings support the existence of a circadian core oscillator in cells of the rat adrenal cortex and indicate that the activity of the oscillator is independent of SCN signalling via the pituitary gland. The adrenal cortical clock could be involved in rhythmic transcriptional activation of genes associated with hormonal biosynthesis, involved in gating of the response of the adrenal cortex to external cues or involved in apoptosis of adrenal cortical cells.

Expression of pituitary adenylate cyclase activating peptide in the uterine cervix, lumbosacral dorsal root ganglia and spinal cord of rats during pregnancy

The uterine cervix is highly innervated by the sensory nerves containing neuropeptides which change during pregnancy and are regulated, in part, by estrogen. These neuropeptides act as transmitters both in the spinal cord and cervix. The present study was undertaken to determine the expression pattern of the neuropeptide pituitary adenylate cyclase activating peptide (PACAP) in the cervix and its nerves during pregnancy and the influence of estrogen on this expression using immunohistochemistry, radioimmunoassay and RT-PCR. PACAP immunoreactivity was detected in nerves in the cervix, lumbosacral (L6-S1) dorsal root ganglia (DRG) and spinal cord. PACAP immunoreactivity was highest at day 15 of pregnancy in the cervix and dorsal spinal cord, but then decreased over the last trimester of pregnancy. However, levels of PACAP mRNA increased in the L6-S1 DRG at late pregnancy relative to early pregnancy. DRG of ovariectomized rats treated with estrogen showed increased PACAP mRNA synthesis in a dose-related manner, an effect partially blocked by the estrogen receptor (ER) antagonist ICI 182,780. We postulate that synthesis of PACAP in L6-S1 DRG and utilization in the cervix and spinal cord increase over pregnancy and this synthesis is the under influence of the estrogen-ER system. Since PACAP is expressed by sensory nerves and may have roles in nociception and vascular function, collectively, these data are consistent with the hypothesis that sensory nerve-derived neuronal factors innervate the cervix and play a role in cervical ripening.

Neuronal input pathways to the brain's biological clock and their functional significance

Circadian rhythms are entrained daily by environmental photic and non-photic cues. The present review describes the anatomy and functional characteristics of the three major input pathways to the circadian clock mediating entrainment: the retino-hypothalamic tract, the geniculo-hypothalamic tract and the midbrain raphe projection.

Light-induced phase shift in the Syrian hamster (Mesocricetus auratus) is attenuated by the PACAP receptor antagonist PACAP6-38 or PACAP immunoneutralization

Circadian rhythms generated by the suprachiasmatic nucleus (SCN) are daily adjusted (entrained) by light via the retinohypothalamic tract (RHT). The RHT contains two neurotransmitters, glutamate and pituitary adenylate cyclase-activating polypeptide (PACAP), which are believed to mediate the phase-shifting effects of light on the clock. In the present study we have elucidated the role of PACAP in light-induced phase shifting at early night in hamsters and shown that (i) light-induced phase delay of running-wheel activity was significantly attenuated by a specific PAC1 receptor antagonist (PACAP6-38) or by immunoblockade with a specific anti-PACAP antibody injected intracerebroventricularly before light stimulation; (ii) PACAP administered close to the SCN was able to phase-delay the circadian rhythm of running-wheel activity in a similar way to light; (iii) PACAP was present in the hamster RHT, colocalized with melanopsin, a recently identified opsin which has been suggested to be a circadian photopigment. The findings indicate that PACAP is a neurotransmitter of the RHT mediating photic information to the clock, possibly via melanopsin located exclusively on the PACAP-expressing cells of the RHT.

Serotonin inhibits glutamate- but not PACAP-induced per gene expression in the rat suprachiasmatic nucleus at night

Circadian rhythms of physiology and behaviour generated by the brain's biological clock located in the suprachiasmatic nucleus are entrained by light via the retinohypothalamic tract. Two neurotransmitters, glutamate and pituitary adenylate cyclase-activating polypeptide (PACAP), found in this monosynaptic pathway mediate the effects of light to the clock. It is well known that not only light entrains the clock. Nonphotic cues mediated by neurotransmitters such as serotonin reaching the suprachiasmatic nucleus from the midbrain raphe nucleus modulate light-induced phase shifts at night. Two clock genes, per1 and per2, have been attributed a role in light-induced phase shift. In the present study, using an in vitro brain slice model and quantitative in situ hybridization for per1 and per2, we have shown that serotonin induces per1 gene expression at late subjective night but not at early night. Furthermore, serotonin application before glutamate or PACAP blocked glutamate-induced per1 expression at early night and per2 gene expression at late night. In contrast, serotonin did not influence PACAP-induced per gene expression at late night. Triple antigen immunohistochemistry and confocal microscopy supported both a pre- and post-synaptic interaction of retinohypothalamic tract (PACAP-immunoreactive) and serotonin projections on vasoactive intestinal peptide- and gastrin-releasing peptide-containing cell bodies in the ventro-lateral suprachiasmatic nucleus. Our findings suggest that the per genes could be the molecular target for the modulatory effects of serotonin on light signalling to the clock.

On the Role of Galanin, Substance P and Other Neuropeptides in Primary Sensory Neurons of the Rat: Studies on Spinal Reflex Excitability and Peripheral Axotomy

The interaction of intrathecally (i.t.) applied galanin (GAL) with substance P (SP), calcitonin gene-related peptide (CGRP), vasoactive intestinal polypeptide (VIP), somatostatin (SOM) and C-fibre conditioning stimulation (CS) with regard to their effects on the spinal nociceptive flexor reflex was studied in decerebrate, spinalized, unanaesthetized rats with intact or sectioned sciatic nerves. SP, CGRP, VIP and SOM applied onto the surface of lumbar spinal cord or a brief CS train (1 Hz, 20 s) to the sural nerve facilitated the flexor reflex for several minutes in animals with intact or sectioned nerves. Pretreatment with GAL, which by itself had a biphasic effect on the flexor reflex in a dose-dependent manner, antagonized the reflex facilitation induced by sural CS before and after sciatic nerve section. SP-induced facilitation of the flexor reflex was antagonized by GAL in rats with intact sciatic nerves, but not after nerve section. In contrast, VIP-induced reflex facilitation was antagonized by GAL only after sectioning of the sciatic nerve. GAL was effective in antagonizing the facilitatory effect of CGRP under both situations, but had no effect on SOM-induced facilitation. A parallel immunohistochemical study revealed that after sciatic nerve section GAL-like immunoreactivity (LI) and VIP-LI are increased in the dorsal root ganglia and that these two peptides coexist in many cells. The present results indicate that GAL antagonizes the excitatory effect of some neuropeptides which exist in the spinal cord. This antagonism could explain the inhibitory effect of GAL on C-fibre CS-induced facilitation of the flexor reflex, which is presumably due to the release of some of these neuropeptides from the terminals of primary afferents. Furthermore, the interaction between GAL and other neuropeptides is altered by sciatic nerve section, paralleling changes in the levels of these neuropeptides in primary afferents and their pattern of coexistence after nerve section. It is proposed that SP and CGRP are important mediators of the spinal flexor reflex in intact rats. However, after axotomy VIP may replace SP in this capacity, paralleling the decrease in SP and marked increase in VIP levels. In general the study provides further support for involvement of peptides in sensory function.

Gut/brain peptides in the genital tract: VIP and PACAP

The two structurally related gut/brain peptides vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) are pleiotropic peptides with a wide-spread occurrence. Besides their presence and functions in the gut and the brain VIP and PACAP have distinct physiological roles in the genital tract. VIP seems to be involved in the nervous control of ovum transportation, sexual arousal in women and penile erection in men. Dysfunction of the VIP nerves can lead to erectile failure and VIP in combination with phentolamine can be successfully used as self-injection therapy of impotence. PACAP could be a co-transmitter with VIP in a number of functions involving nervous control of blood flow and motility, but in addition PACAP is a sensory neurotransmitter. The most fascinating role for PACAP is, however, its auto- or paracrine function in the peri- and postovulatory events involving acute progesterone production and subsequent luteinization in periovulatory granulosa/lutein cells.

Characterization of a G protein coupling "YL" motif of the human VPAC1 receptor, equivalent to the first two amino acids in the "DRY" motif of the rhodopsin family

The conserved residues Y239 and L240 of human VPAC1 receptor are predicted to be at the same location as the asparagine and arginine in the "DRY" motif in the Rhodopsin family of G protein-coupled receptors. By comparing vasoactive intestinal peptide (VIP) binding with or without the presence of GTP-gamma-S, it was found that the deltadelta G(o) for the endogenous G-protein coupling was 1.5 kJ/mol, 0.95 kJ/mol, and 3.4 kJ/mol for theY239A, L240A, and wild-type receptor, respectively. VIP-induced cAMP production in whole cells support the results of the binding studies, as Y239A had a moderate and L240A a pronounced impaired ability to produce cAMP. The mutants had a minor influence on the intrinsic "low affinity to high affinity equilibrium," suggesting that the dominating effect of these mutants is a perturbation of the G protein-binding site. Thus, the highly diverged chemical properties of the hydrophobic "YL" motif and charged "DR(Y)" motif could be a crucial difference between the Secretin Receptor Family and the Rhodopsin Family with respect to receptor activation and G-protein coupling.

Light-dependent induction of cFos during subjective day and night in PACAP-containing ganglion cells of the retinohypothalamic tract

Environmental light stimulation via the retinohypothalamic tract (RHT) is necessary for stable entrainment of circadian rhythms generated in the suprachiasmatic nucleus (SCN). In the current report, the authors characterized the functional activity and phenotype of retinal ganglion cells that give rise to the RHT of the rat. Retinal ganglion cells that give rise to the RHT were identified by transsynaptic passage of an attenuated alpha herpesvirus known to have selective affinity for this pathway. Dual labeling immunocytochemistry demonstrated co-localization of viral antigen and pituitary adenylate cyclase activating polypeptide (PACAP) in retinal ganglion cells. This was confirmed using the anterograde tracer cholera toxin subunit B (ChB). In normal and retinally degenerated monosodium glutamate (MSG)-treated rats, ChB co-localized with PACAP in axons of the retinorecipient zone of the SCN. Light-induced Fos-immunoreactivity (Fos-IR) was apparent in all PACAP-containing retinal ganglion cells and a population of non-PACAP-containing retinal ganglion cells at dawn of normal and MSG-treated animals. Within the next 3 h, Fos disappeared in all non-PACAP-immunoreactive cells but persisted in all PACAP-containing retinal ganglion cells until dusk. When animals were exposed to constant light, Fos-IR was sustained only in the PACAP-immunoreactive (PACAP-IR) retinal ganglion cells. Darkness eliminated Fos-IR in all PACAP-IR retinal ganglion cells, demonstrating that the induction of Fos gene expression was light dependent. When animals were maintained in constant darkness and exposed to light pulses at ZT 14, ZT 19, or ZT 6, Fos-IR was induced in PACAP-IR retinal ganglion cells in a pattern similar to that seen at dawn. Collectively, these data indicate that PACAP is present in ganglion cells that give rise to the RHT and suggest a role for this peptide in the light entrainment of the clock.

PACAP 1-38 as neurotransmitter in the porcine antrum

The concentration of PACAP 1-38 in porcine antrum amounted to 15.4+/-7.9 and 20.3+/-8 pmol/g tissue in the mucosal and muscular layers. PACAP immunoreactive (IR) fibres innervated the muscular (co-localised with VIP) and submucosal/mucosal layers (some co-storing VIP and CGRP) including myenteric and submucosal plexus and blood vessels. Only myenteric nerve cell bodies contained PACAP-IR (co-storing VIP). In isolated perfused antrum, vagus nerve stimulation (8 Hz) and capsaicin (10(-5) M) increased PACAP 1-38 release. PACAP 1-38 (10(-9) M) increased substance P (SP), gastrin releasing peptide (GRP) and VIP release. PACAP 1-38 (10(-8) M) inhibited gastrin secretion and stimulated somatostatin secretion and motility dose-dependently. PACAP-induced motility was strongly inhibited by the antagonist PACAP 6-38 but also by atropine and substance P-antagonists (CP99994/SR48968) but PACAP 6-38 had no effect on vagus-induced secretion or motility.

CONCLUSION

PACAP 1-38 may be involved in antral motility and secretion by interacting with cholinergic, SP-ergic, GRP-ergic and/or VIP-ergic neurones, and may also be involved in afferent reflex pathways.

Functional roles of conserved transmembrane prolines in the human VPAC(1) receptor

The importance of three conserved transmembrane prolines of the human vasoactive intestinal polypeptide (VPAC)(1) receptor was examined by single alanine substitution. P266A, P300A and P348A reduced the expression level, but maintained the binding to VIP. P266A showed decreased ability to stimulate cAMP, while P300A and P348A displayed an increased potency in cAMP production combined with a high sensitivity towards GTP compared to the wild type receptor. In addition, substitutions of two conserved leucines located in position -2 and +1 from P348 were investigated. L346A and L349A reduced the receptor expression, influenced the G protein coupling and decreased the receptor activity. These observations, which are the first on conserved transmembrane prolines within this family of receptors, indicate that these residues are important for receptor expression, G protein coupling and receptor activity.

Dissociation between light-induced phase shift of the circadian rhythm and clock gene expression in mice lacking the pituitary adenylate cyclase activating polypeptide type 1 receptor

The circadian clock located in the suprachiasmatic nucleus (SCN) organizes autonomic and behavioral rhythms into a near 24 hr time that is adjusted daily to the solar cycle via a direct projection from the retina, the retinohypothalamic tract (RHT). This neuronal pathway costores the neurotransmitters PACAP and glutamate, which seem to be important for light-induced resetting of the clock. At the molecular level the clock genes mPer1 and mPer2 are believed to be target for the light signaling to the clock. In this study, we investigated the possible role of PACAP-type 1 receptor signaling in light-induced resetting of the behavioral rhythm and light-induced clock gene expression in the SCN. Light stimulation at early night resulted in larger phase delays in PACAP-type 1 receptor-deficient mice (PAC1(-)/-) compared with wild-type mice accompanied by a marked reduction in light-induced mPer1, mPer2, and c-fos gene expression. Light stimulation at late night induced mPer1 and c-fos gene expression in the SCN to the same levels in both wild type and PAC1(-)/- mice. However, in contrast to the phase advance seen in wild-type mice, PAC1(-)/- mice responded with phase delays after photic stimulation. These data indicate that PAC1 receptor signaling participates in the gating control of photic sensitivity of the clock and suggest that mPer1, mPer2, and c-fos are of less importance for light-induced phase shifts at night.

Pituitary adenylate cyclase-activating polypeptide induces period1 and period2 gene expression in the rat suprachiasmatic nucleus during late night

The suprachiasmatic nucleus generates circadian rhythms which are synchronized to the environmental light-dark cycle via the retinohypothalamic tract. Pituitary adenylate cyclase-activating polypeptide and glutamate, two neurotransmitters co-stored in the retinohypothalamic tract of the rat, are able to phase shift the endogenous rhythm similar to light. The "clock genes" period1 (per1) and per2, which show circadian oscillation within the suprachiasmatic nucleus, have been attributed a role in light-induced resetting of the mammalian circadian clock due to rapid induction of the period (per) genes after light stimulation at night. Using a rat in vitro brain slice model, we demonstrate by quantitative in situ hybridization histochemistry that the diurnal alteration in expression of both per genes in the suprachiasmatic nucleus was retained in vitro. In the model, we examined the effects of pituitary adenylate cyclase-activating polypeptide and glutamate alone and in combination on per1 and per2 gene expression at late subjective night (circadian time 19). Glutamate administration (10(-3)M) induced both per1 and per2 gene expression in the suprachiasmatic nucleus of the brain slice within 1h. The per gene responses were similar to the induction of gene expression observed after light stimulation in vivo at late night. Pituitary adenylate cyclase-activating polypeptide (10(-6)M) administered alone had no effect on the per gene expression, but when pituitary adenylate cyclase-activating polypeptide in micromolar concentration was applied before glutamate, the neuropeptide blocked the glutamate-induced per1 and per2 gene expression in the suprachiasmatic nucleus. In contrast to the lack of effect of pituitary adenylate cyclase-activating polypeptide itself in micromolar concentration, pituitary adenylate cyclase-activating polypeptide (10(-9)M) induced both per1 and per2 gene expression, an effect which was not augmented by co-application of glutamate. Our results provide the molecular substrate for the previous electrophysiological findings that pituitary adenylate cyclase-activating polypeptide in high concentration is able to block glutamate-induced phase advance at late night, and that the peptide in low concentration can induce a phase advance similar to light and glutamate.

Downregulation of VPAC1R expression in breast cancer cell lines

The breast carcinoma cell line T47D was tested for 17 beta-estradiol (E2) mediated regulation of vasoactive intestinal polypeptide receptor type-1 (VPAC1) expression. E2 was found to downregulate the mRNA level. The number of VIP binding sites was reduced 66% on treatment with E2 for 72 h. Experiments with cycloheximide suggested that the effect was independent (at least partly so) of protein synthesis. Experiments with the transcriptional inhibitor, actinomycin D, showed that E2 did not influence the VPAC1 mRNA halflife. Both of two antiestrogens, ICI 182,780 and 4-hydroxy-tamoxifen, mediated a concentration dependent inhibition of the effect of E2 on the mRNA level. Transient transfection with reporter-gene constructs containing various portions of the VPAC1 5'-flanking sequence revealed the most proximal 100 bp to be essential for the basal transcriptional activity. However, E2 did not influence the expression of the reporter gene using up to 3,250 bp of the VPAC1 5'-flanking region.

Estradiol down regulates expression of vasoactive intestinal polypeptide receptor type-1 in breast cancer cell lines

Three breast carcinoma cell lines were tested for 17beta-estradiol (E(2)) mediated regulation of vasoactive intestinal polypeptide receptor type-1 (VPAC(1)) expression. In all three, E(2) was found to down-regulate the mRNA level. We studied T47D cells in more details and found a 25 and 70% decrease in the VPAC(1) mRNA level upon 7 and 48 h of E(2) treatment, respectively. The number of vasoactive intestinal polypeptide (VIP) binding sites was reduced 66% upon treatment with E(2) for 72 h. After cycloheximide pretreatment, the E(2) mediated mRNA reduction was attenuated from 50% to 25% after 24 h suggesting the effect to be at least partly independent of protein synthesis. Experiments with the transcriptional inhibitor actinomycin D showed that E(2) did not influence the VPAC(1) mRNA half-life while nuclear run-on experiments indicated that E(2) decreased the VPAC(1) transcription rate. Two antiestrogens: ICI 182780 (ICI) and 4-hydroxy-tamoxifen (4-OHT) mediated a concentration dependent inhibition of E(2)'s effect on the mRNA level. Transient transfection with reporter-gene constructs containing various portions of the VPAC(1) 5'-flanking sequence revealed the most proximal 100 bp to be essential for the basal transcriptional activity. However, E(2) did not influence the expression of the reporter gene using up to 3250 bp of the VPAC(1) 5'-flariking region.

PACAP-(1-38) as neurotransmitter in the porcine adrenal glands

The concentration of pituitary adenylyl cyclase-activating polypeptide [PACAP-(1-38)] in porcine adrenal glands amounted to 14 +/- 3 pmol/g tissue. PACAP immunoreactive (PACAP-IR) fibers innervated adrenal chromaffin cells (often co-localized with choline acetyltransferase). Subcapsular fibers traversed the cortex-innervating endocrine cells and blood vessels [some co-storing mainly calcitonin gene-related peptide but also vasoactive intestinal polypeptide (VIP)]. PACAP-IR fibers were demonstrated in the splanchnic nerves, whereas IR adrenal nerve cell bodies were absent. In isolated, vascularly perfused adrenal gland, splanchnic nerve stimulation (16 Hz) and capsaicin (10(-5) M) increased PACAP-(1-38) release (1.6-fold and 6-fold respectively, P = 0.02). PACAP-(1-38) dose-dependently stimulated cortisol (2 x 10(-10) M; 24-fold increase, P = 0.02) and chromogranin A fragment (2 x 10(-9) M; 15-fold increase, P = 0.05) secretion. Both were strongly inhibited by the PAC(1)/VPAC(2) receptor antagonist PACAP-(6-38) (10(-7) M). PACAP-(6-38) also inhibited splanchnic nerve (10 Hz)-induced cortisol secretion but lacked any effect on splanchnic nerve-induced pancreastatin secretion. PACAP-(1-38) (2 x 10(-10) M) decreased vascular resistance from 5.5 +/- 0.6 to 4.6 +/- 0.4 mmHg. min. ml(-1). PACAP-(6-38) had no effect on this response. We conclude that PACAP-(1-38) may play a role in splanchnic nerve-induced adrenal secretion and in afferent reflex pathways.

Creation of a selective antagonist and agonist of the rat VPAC(1) receptor using a combinatorial approach with vasoactive intestinal peptide 6-23 as template

We have used combinatorial chemistry with amino acid mixtures (X) at positions 6 to 23 in vasoactive intestinal peptide (VIP) to optimize binding affinity and selectivity to the rat VPAC(1) receptor. The most efficient amino acid replacement was a substitution of alanine at position 18 to diphenylalanine (Dip), increasing the displacement efficiency of (125)I-VIP by 370-fold. The [Dip(18)]VIP(6-23) was subsequently used to find a second replacement, employing the same approach. Tyrosine at position 9 was selected and the resulting [Tyr(9),Dip(18)]VIP(6-23) analog has a K(i) value of 90 nM. This analog was unable to stimulate cAMP production at 10(-6) M but was able to inhibit VIP-induced cAMP stimulation (K(b) = 79 nM). The K(i) values of [Tyr(9),Dip(18)]VIP(6-23) using the rat VPAC(2) and PAC(1) receptors were 3,000 nM and >10,000 nM, respectively. Thus, [Tyr(9),Dip(18)]VIP(6-23) is a selective VPAC(1) receptor antagonist. The C-terminally extended form, [Tyr(9),Dip(18)]VIP(6-28), displays improved antagonistic properties having a K(i) and K(b) values of 18 nM and 16 nM, respectively. On the contrary, the fully extended form, [Tyr(9),Dip(18)]VIP(1-28), was a potent agonist with improved binding affinity (K(i) = 0.11 nM) and ability to stimulate cAMP (EC(50) = 0.23 nM) compared with VIP (K(i) = 1.7 nM, EC(50) = 1.12 nM). Furthermore, the specificity of this agonist to the VPAC(1) receptor was high, the K(i) values for the VPAC(2) and PAC(1) receptors were 53 nM and 3,100 nM, respectively. Seven other analogs with the [Tyr(9),Dip(18)] replacement combined with previously published VIP modifications have been synthesized and described in this work.

Immunohistochemical localization of the VIP1 receptor (VPAC1R) in rat cerebral blood vessels: relation to PACAP and VIP containing nerves

The two structurally related peptides, vasoactive intestinal polypeptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP), are present in cerebral vascular nerve fibers. Biologic actions of VIP are exerted through two receptors, VPAC1 and VPAC2, having similar binding affinity for both VIP and PACAP. In the current study, the authors have developed a specific antibody against the rVPAC1 receptor to examine the localization of rVPAC1 immunoreactivity in cerebral arteries and arterioles of the rat by immunohistochemistry using fluorescence confocal microscopy. Specificity of the antiserum was ensured by immunoblotting and immunocytochemistry of cells transfected with cDNA encoding the different PACAP-VIP receptor subtypes. The rVPAC1 receptor immunoreactivity was localized to the plasmalemma of circularly orientated smooth muscle cells on superficial cerebral arteries and arterioles taken from the basal surface of the brain. By double immunostaining VIP immunoreactive nerve fibers and, to a lesser extent, those containing PACAP were shown to have intimate contact with the receptor protein. Vasoactive intestinal polypeptide and PACAP containing cerebrovascular nerve fibers were found in separate nerve populations with different distribution pattern and density. In brain sections processes of cortical VIP-, but not PACAP-, containing neurons seemed to innervate the rVPAC1 receptor of pial arterioles on the brain surface. The current findings provide the neuroanatomical substrate for a role of VIP and maybe PACAP in the regulation of cerebral blood flow.

Pituitary adenylate cyclase-activating peptide stimulates acute progesterone production in rat granulosa/Lutein cells via two receptor subtypes

Pituitary adenylate cyclase-activating peptide (PACAP) is transiently expressed in ovarian granulosa/lutein cells from eCG/hCG-treated rats, and in vitro immunoneutralization of endogenously released PACAP inhibits acute progesterone secretion and subsequent luteinization in such cells. This suggests that PACAP mediates locally some of the effects of the LH surge, but the putative PACAP receptor(s) involved in such an auto or paracrine activity is presently unknown. Reverse-transcription polymerase chain reaction with specific primers to the three cloned PACAP-binding receptors called PAC(1), VPAC(1), and VPAC(2) demonstrated both PAC(1) and VPAC(2) mRNA in extracts from preovulatory follicular cells. Radioligand-binding assays revealed the presence of high-affinity binding sites with characteristics of these two receptors on the intact cells, and autoradiography demonstrated that the binding was restricted to a minor proportion of the follicular cells as well as the oocytes. Pituitary adenylate cyclase-activating peptide and vasoactive intestinal peptide (VIP) dose-dependently stimulated cAMP accumulation and acute progesterone accumulation. Forskolin and db-cAMP also stimulated acute progesterone accumulation, and the protein kinase A inhibitor H89 dose-dependently inhibited peptide induced acute progesterone accumulation, suggesting involvement of cAMP and the protein kinase A pathway in the process. In conclusion, two of the three PACAP binding receptors are present on preovulatory follicular cells and are involved in the effects of PACAP on acute progesterone production. The data provide further evidence to establish PACAP as an auto- or paracrine regulator of LH-induced acute progesterone production in rat preovulatory follicles.

Pituitary adelylate cyclase-activating peptide is an activator of vasoactive intestinal polypeptide gene transcription in human neuroblastoma cells

In many ganglia, the neuropeptide pituitary adenylate cyclase-activating peptide (PACAP) innervates nerve cell bodies containing the homologous neuropeptide vasoactive intestinal polypeptide (VIP). We therefore investigated whether PACAP affected the VIP gene expression and elucidated the molecular mechanisms using the human neuroblastoma cell line NB-1. A concentration dependent induction of the VIP mRNA level was found upon PACAP stimulation. Five nM PACAP mediated transient elevation of the VIP mRNA being evident after 2 h, the maximal 65-fold induction was reached after 6-8 h and hereafter the level decreased rapidly. In cell extracts, the concentration of immunoreactive VIP was elevated four-fold upon PACAP stimulation for 8 h, and it remained elevated during the next 40 h. In conditioned medium, a stable 20-fold VIP increase was seen after 8-24 h. Experiments with the translational inhibitor cycloheximide showed a direct effect of PACAP on the VIP mRNA level, and nuclear run-on assays revealed a three- to four-fold enhancement of the VIP gene transcription rate after PACAP stimulation. The VIP mRNA induction was abolished by transcriptional inhibition with the actinomycin D, and PACAP did not seem to mediate any changes in the VIP mRNA half-life. However, the VIP mRNA level seemed very stable during the transcriptional cessation. Reporter gene constructs were used to evaluate involvement of the VIP CRE site in the PACAP mediated induction of the VIP gene transcription. Mutation of the CRE site did not abolish the induction suggesting it to be of minor if any importance for the induction. In conclusion, the PACAP mediated induction of the VIP gene expression suggests that PACAP released from nerve terminals could influence the function of VIP'ergic neurons in target tissues.

Role of second extracellular loop in the function of human vasoactive intestinal polypeptide/pituitary adenylate cyclase activating polypeptide receptor 1 (hVPAC1R)

To elucidate the functional role of the second extracellular loop of human vasoactive intestinal polypeptide/pituitary adenylate cyclase-activating polypeptide (VIP/PACAP) receptor (hVPAC1R), surface expression, ligand binding, and receptor activation were analyzed. Amino acids in the entire second extracellular loop were individually substituted by alanine by site-directed mutagenesis. The mutant and wild-type receptors were transiently expressed in HEK293 cells and purified cell membranes were tested for the ability to bind VIP, while the receptor activity was measured as potency of cAMP production analysed on intact cells. Surface expression of the substituted conserved residues, W286A, I289A, W294A, and W295A, was evidently decreased to 20-30% compared to the wild-type expression. W286A also showed an significantly reduced potency of cAMP production. Substituted residues as F280A, E281A, and G284A showed a significant reduction in the potency of stimulated cAMP production amounting to 8-46-fold, compared to the wild-type with unaffected surface expression and VIP binding. These results indicate that some residues in the second extracellular loop of the human VPAC1R participate in the active mechanism of a ligand-mediated response without being directly involved in the binding of VIP.

PACAP and glutamate are co-stored in the retinohypothalamic tract

The retinohypothalamic tract (RHT) relays photic information from the eyes to the suprachiasmatic nucleus (SCN). Activation of this pathway plays a role in adjusting circadian timing to the light/dark environment. Two transmitters, glutamate and pituitary adenylate cyclase activating polypeptide (PACAP) having phase shifting capacity during the night and day, respectively, are located in the RHT. Using double staining immunohistochemistry at the light and electron microscopic level, we showed that PACAP was co-stored with glutamate in a subset of retinal ganglion cells and in nerve terminals in the retino-recipient area of the SCN. These findings provide an anatomical basis for the recent demonstration of the interaction between these two transmitters on the SCN phase response at night.

Innervation pattern and Ca2+ signalling in labial salivary glands of healthy individuals and patients with primary Sjögren's syndrome (pSS)

We have characterised the innervation pattern and intracellular Ca2+-signalling in labial salivary glands (LSG) of 16 patients with primary Sjögren's syndrome (pSS) and 27 healthy controls. Numerous immunoreactive nerve fibers (IRF) containing vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating peptide (PACAP) were found around acini, ducts and blood vessels. Substance P (SP)-, neuropeptide Y-, tyrosine hydroxylase- and nitric oxide synthase-IRF were mainly surrounding ducts and blood vessels. The majority of pSS patients had inflamed LSG and the presence of focal lymphocytic infiltrates (FI) were more frequent and pronounced as compared with healthy controls. In areas with normal or diffusely inflamed LSG tissue, pSS patients demonstrated the same distribution of IRF as healthy controls with similar histology. However, IRF were absent in central areas of FI both in pSS and age-matched healthy controls. Although all pSS patients had hyposalivation, stimulation with acetylcholine, norepinephrine, phenylephrine, isoproterenol, VIP, PACAP, SP, adenosine 5'-triphosphate and uridine 5'-triphosphate induced the same increase in the intracellular free Ca2+ concentration in LSG acini from both pSS patients and healthy controls, indicating the presence of functional receptor systems in vitro.

Pituitary adenylate cyclase-activating polypeptide in intrinsic and extrinsic nerves of the rat pancreas

Pituitary adenylate cyclase-activating polypeptide (PACAP) is the latest member of the vasoactive intestinal polypeptide (VIP) family of neuropeptides present in nerve fibres in many peripheral organs. Using double immunohistochemistry, with VIP as a marker for intrinsic innervation and calcitonin-gene related peptide (CGRP) as a marker for mainly extrinsic innervation, the distribution and localization of PACAP were studied in the rat pancreas. PACAP was demonstrated in nerve fibres in all compartments of the pancreas and in a subpopulation of intrapancreatic VIP-containing ganglion cells. PACAP and VIP were co-stored in intra- and interlobular nerve fibres innervating acini, blood vessels, and in nerve fibres within the islets of Langerhans. No PACAP immunoreactivity was observed in the islet cells. Another population of PACAP-immunoreactive nerve fibres co-localized with CGRP innervated ducts, blood vessels and acini. PACAP/CGRP-positive nerve fibres were also demonstrated within the islets. Neonatal capsaicin reduced the PACAP-38 concentration by approximately 50%, and accordingly a marked reduction in PACAP/CGRP-immunoreactive nerve fibres in the exocrine and endocrine pancreas was observed. Bilateral subdiaphragmatic vagotomy caused a slight but significant decrease in the PACAP-38 concentration compared with controls. In conclusion, PACAP-immunoreactive nerve fibres in the rat pancreas seem to have dual origin: extrinsic, most probably sensory fibres co-storing CGRP; and intrinsic, constituting a subpopulation of VIP-containing nerve cell bodies and fibres innervating acinar cells and islet cells. Our data provide a morphological basis for the reported effects of PACAP in the pancreas and suggest that PACAP-containing nerves in the rat pancreas may have both efferent and sensory functions.

Pituitary adenylate cyclase-activating polypeptide in intrinsic and extrinsic nerves of the rat pancreas

Pituitary adenylate cyclase-activating polypeptide (PACAP) is the latest member of the vasoactive intestinal polypeptide (VIP) family of neuropeptides present in nerve fibres in many peripheral organs. Using double immunohistochemistry, with VIP as a marker for intrinsic innervation and calcitonin-gene related peptide (CGRP) as a marker for mainly extrinsic innervation, the distribution and localization of PACAP were studied in the rat pancreas. PACAP was demonstrated in nerve fibres in all compartments of the pancreas and in a subpopulation of intrapancreatic VIP-containing ganglion cells. PACAP and VIP were co-stored in intra- and interlobular nerve fibres innervating acini, blood vessels, and in nerve fibres within the islets of Langerhans. No PACAP immunoreactivity was observed in the islet cells. Another population of PACAP-immunoreactive nerve fibres co-localized with CGRP innervated ducts, blood vessels and acini. PACAP/CGRP-positive nerve fibres were also demonstrated within the islets. Neonatal capsaicin reduced the PACAP-38 concentration by approximately 50%, and accordingly a marked reduction in PACAP/CGRP-immunoreactive nerve fibres in the exocrine and endocrine pancreas was observed. Bilateral subdiaphragmatic vagotomy caused a slight but significant decrease in the PACAP-38 concentration compared with controls. In conclusion, PACAP-immunoreactive nerve fibres in the rat pancreas seem to have dual origin: extrinsic, most probably sensory fibres co-storing CGRP; and intrinsic, constituting a subpopulation of VIP-containing nerve cell bodies and fibres innervating acinar cells and islet cells. Our data provide a morphological basis for the reported effects of PACAP in the pancreas and suggest that PACAP-containing nerves in the rat pancreas may have both efferent and sensory functions.

Pituitary adenylate cyclase activating polypeptide (PACAP) in the rat mammary gland

Pituitary adenylate cyclase activating polypeptide (PACAP), a member of the vasoactive intestinal polypeptide (VIP) family of peptides, is present in the brain and in neuronal elements of a number of peripheral organs. Since no information on PACAP in the mammary gland exists, we have investigated, by radioimmunoassay and immunohistochemistry, the occurrence and distribution of PACAP immunoreactivity in the mammary gland of lactating and non-lactating rats. A specific monoclonal mouse anti-PACAP antibody'has been used to show that the peptide is located in nerve fibres associated with bundles of circular and longitudinal smooth muscle surrounding the lactiferous duct of the nipple. PACAP-immunoreactive nerve fibres and nerve bundles are present in the subepidermal connective tissue of the nipple and in the mammary parenchyma, some of the fibres being in close contact with blood vessels. Occasionally, a few delicate varicose fibres are associated with secretory alveoli and lactiferous ducts. The majority of PACAP-positive nerve fibres are, however, located in the glabrous skin of the nipple and the hairy skin adjacent to the nipple forming a subepithelial plexus from which delicate varicose nerve fibres enter the overlying epithelium. Double immunostaining for PACAP and a marker for sensory neurons, calcitonin gene-related peptide, has disclosed that the two peptides are almost completely co-localized. A minor population of the PACAP-immunoreactive nerve fibres shows co-existence with VIP. Although no obvious changes at the immunohistochemical level could be observed during pregnancy or lactation, elevated concentrations of immunoreactive PACAP-38 in mammary extracts have been found during lactation. Our data suggest that PACAP is involved in the nervous control of mammary gland function, probably in the transmission of suckling stimuli.

Functional expression of rat VPAC1 receptor in Saccharomyces cerevisiae

The yeast Saccharomyces cerevisiae was examined as host for heterologous expression of the G protein-coupled VPAC1 receptor. Rat VPAC1 receptor cDNA and two chimeric constructs encoding the yeast mating factor pre-pro alpha-leader peptide fused in-frame to rat VPAC1 receptor were expressed in yeast cells under control of a galactose inducible promoter. The rat VPAC1 receptor was fused to the HSV tag epitope to ensure proper immunological detection of the receptor. Crucial conditions for high-level expression of active rat VPAC1 receptor included growth in amino acid supplemented minimal medium, fusion to the yeast alpha-leader peptide and a temperature shift from 30 degrees C to 15 degrees C before promoter induction. Western blotting showed that the expressed receptor was highly glycosylated and a band of 47 kDa was obtained upon endoglycosidase H treatment. Binding with radioiodinated vasoactive intestinal polypeptide revealed a KD of 2.5 nM and an IC50 of 15 nM when displacing with unlabeled vasoactive intestinal polypeptide. VPAC1 receptor density quantified by Western blotting was 510 pmol/mg membrane protein of which only 66 pmol/mg were able to bind vasoactive intestinal polypeptide.

Identification of pituitary adenylate cyclase-activating polypeptide1-38-binding factor in human plasma, as ceruloplasmin

125I-Pituitary adenylate cyclase-activating polypeptide (PACAP) 1-38 is able to bind a factor in human plasma, which can be displaced by unlabelled PACAP 1-38 and PACAP 28-38 but not by the other biologically active form, PACAP 1-27. Likewise, 125I-PACAP 28-38 binds this plasma factor, whereas 125I-PACAP 1-27 does not. Apparent Kd values were measured to be 12.0+/-1.3 and 3.4+/-1.5 nM for PACAP 1-38 and PACAP 28-38, respectively, using a competition assay with 125I-PACAP 28-38. Purification of the PACAP 1-38-binding factor from human blood was made by ethanol precipitation of serum followed by Ni2+-chelating and anion-exchange chromatography. A 120-kDa band on SDS/PAGE, as well as some proteolytic products, was blotted on to PVDF membrane and their N-terminal amino acid sequences determined. In combination with a mass-spectrometric fingerprinting of a tryptic digest of the 120-kDa band, this PACAP 1-38-binding factor was identified as ceruloplasmin. Purified commercial ceruloplasmin shows identical mobility on SDS/PAGE to the PACAP 1-38-binding factor and the same binding characteristics to PACAP 1-38, 1-27 and 28-38, using the same amount of ceruloplasmin as was expected to be found in the human plasma. Furthermore, the ability of plasma to bind 125I-PACAP 1-38 or 28-38 disappeared when ceruloplasmin was immunoprecipitated from plasma with rabbit anti-human ceruloplasmin Ig.

PACAP gene expression in neurons of the rat hypothalamo-pituitary-adrenocortical axis is induced by endotoxin and interleukin-1beta

Inflammatory stress due to infection by various micro-organisms is known to activate the hypothalamo-pituitary-adrenocortical (HPA) axis through inflammatory mediators. Recently, pituitary-adenylate-cyclase-activating polypeptide (PACAP) was shown to be located in corticotropin-releasing factor containing neurons of the medial parvocellular part of the hypothalamic paraventricular nucleus (mpPVN). In the present study, we demonstrate that PACAP gene expression is induced in neurons of the mpPVN after intraperitoneal administration of bacterial lipopolysaccharide (LPS) which was accompanied by a marked increase in PACAP immunoreactivity in the external zone of the median eminence. As determined by quantitative in situ hybridization, PACAP gene expression was rapidly induced after 4 h and was elevated for 48 h, declining to normal levels after 72 h. A significant increase in PACAP mRNA was also observed following intraperitoneal injection of interleukin-1beta. PACAP gene expression was not induced by LPS in vagotomized animals, suggesting that the increase in PACAP mRNA following immune activation by LPS is mediated via the vagus nerve. The findings suggest that PACAP may function as a hypothalamo-pituitary-releasing factor during acute inflammation.

Pituitary adenylate cyclase-activating polypeptide is an auto/paracrine stimulator of acute progesterone accumulation and subsequent luteinization in cultured periovulatory granulosa/lutein cells

Recently, we have demonstrated that pituitary adenylate cyclase-activating polypeptide (PACAP) is transiently expressed in steroidogenic ovarian cells during the periovulatory period. This prompted us to establish an in vitro system in which the potential local regulatory role of PACAP during periovulatory progesterone production could be examined. Granulosa/lutein cells from PMSG- and human CG (hCG)-stimulated immature rats were used. The cells were isolated from preovulatory follicles 4-6 h after the hCG injection, at which time the transient ovarian PACAP expression begins in vivo. By immunocytochemistry on intact cells and RIA on cell extracts and culture medium, granulosa/lutein cells were found to accumulate and secrete PACAP during incubation. Furthermore, the cells responded to exogenous PACAP 38 with a rapid (10(-7) M induced a peak value 20-fold higher than controls at 2 h) and dose-dependent accumulation of progesterone. PACAP 38 (5 x 10(-9) M), in combination with an approximately half-maximal dose of hCG (1 ng/ml), showed an additive effect on progesterone accumulation. Immunoneutralization of endogenously released PACAP was performed using the IgG fraction from a specific PACAP antiserum that dose-dependently inhibits the progesterone accumulating effect of exogenous PACAP 38. The acute effects of endogenously released PACAP were studied during 8 h of incubation of granulosa/lutein cells with anti-PACAP IgG (100 microg/ml). A significant reduction in progesterone accumulation was observed after 4, 6, and 8 h [38.7% (P < 0.05), 41.2% (P < 0.02), and 50% (P < 0.002), respectively], compared with nonimmune IgG (100 microg/ml) treated cultures. The long-term effects on luteinization induced by endogenously released PACAP were studied after incubation of the cells with anti-PACAP IgG or nonimmune IgG for 24 h, followed by incubation for 9 days in serum-containing medium. Under these conditions, nonimmune IgG-treated cells assumed a luteal phenotype, accumulating large and stable amounts of progesterone and acquiring hypertrophic cell bodies with numerous lipid droplets and distinct nucleoli in the large nuclei. Anti-PACAP IgG-treated cells displayed morphological and functional signs of impaired luteinization being smaller and more irregular and with progesterone accumulation being significantly lower throughout the incubation period [56.4% (P < 0.02), 69.2% (P < 0.05), 43.8% (P < 0.02), and 52.2% (P < 0.02) at 1, 4, 7, and 10 days, respectively]. Together, these findings support an auto- or paracrine role for PACAP during gonadotropin-induced acute periovulatory progesterone production and subsequent luteinization in granulosa/lutein cells.

Innervation of the rat pineal gland by pituitary adenylate cyclase-activating polypeptide (PACAP)-immunoreactive nerve fibres

Pituitary adenylate cyclase-activating polypeptide (PACAP)-immunoreactive nerve fibres were demonstrated in the rat pineal gland. These fibres entered the pineal gland through the conarian nerve at the distal tip of the gland. A high density of the fibres was observed in the capsule of the gland, from where the immunoreactive elements penetrated into the pineal perivascular spaces and parenchyma. The majority of PACAP-immunoreactive nerve fibres also contained calcitonin gene-related peptide (CGRP). Some PACAP-immunoreactive nerve fibres contained neuropeptide Y (NPY), but only occasionally was PACAP colocalized with vasoactive intestinal peptide (VIP). After removal of both superior cervical ganglia, a high number of PACAP-containing nerve fibres were still present in the gland. In the nervous system PACAP is present in two isoforms, PACAP-38 and PACAP-27. The concentration of PACAP-38 in the superficial pineal gland was determined by radioimmunoassay to be 20.4 pmol/g tissue at midday and 18.9 pmol/g tissue at midnight. The concentration of PACAP-27 was only about 3% of the concentration of PACAP-38. In summary, this study is the first demonstration of a PACAP-containing innervation of the rat pineal gland. The PACAP concentration in the pineal gland does not exhibit a day-night difference. The colocalization of PACAP with calcitonin gene-related peptide in the pincalopetal nerve fibres indicates that the majority of PACAP-immunoreactive nerve fibres might originate from the trigeminal ganglion.

Increased expression, axonal transport and release of pituitary adenylate cyclase-activating polypeptide in the cultured rat vagus nerve

The expression and axonal transport of pituitary adenylate cyclase-activating polypeptide (PACAP) was studied in the cultured vagus nerve of the rat by immunocytochemistry and in situ hybridization. The number of neurons immunoreactive for PACAP increased markedly within the nodose ganglion during a 24-48 h culture period, as did the number of cells containing messenger RNA for PACAP. PACAP was found to be axonally transported and accumulated at the site of a crush injury. The peptide was also released at this site. Addition of PACAP to regenerating nerves in culture did not affect axonal outgrowth, neither did antibodies against PACAP. Separate experiments showed that neither PACAP-27 nor PACAP-38 affected proliferation of non-neuronal cells measured as the incorporation of [3H]thymidine. In contrast, forskolin, another potent stimulator of adenylate cyclase besides PACAP, dramatically decreased [3H]thymidine incorporation. The results showed that, during regeneration of peripheral nerves, PACAP expression increases and the peptide is transported into the regenerating nerve, where it is released. The functional significance of this release is unknown, but it does not seem to be directly related to the initiation of proliferation of Schwann cells or initial axonal outgrowth.

Pituitary adenylate cyclase activating peptide (PACAP) in the retinohypothalamic tract: a daytime regulator of the biological clock

The retinohypothalamic tract (RHT) relays photic information from the eyes to the brain biological clock in the suprachiasmatic nucleus (SCN). Activation of this pathway by light plays a role in adjusting circadian timing to light exposure at night. Here we report a new signaling pathway by which the RHT regulates circadian timing in the daytime as well. Using dual-immunocytochemistry for PACAP and the in vivo tracer Cholera toxin subunit B (ChB), intense PACAP immunoreactivity (PACAP-IR) was observed in retinal afferents at the rat SCN as well as in the intergeniculate leaflet (IGL) of the thalamus. This PACAP-IR was nearly lost upon bilateral eye enucleation. PACAP afferents originated from ganglion cells distributed throughout the retina. The phase of circadian rhythm measured as SCN neuronal activity in vitro was significantly advanced by application of PACAP-38 during the subjective day, but not at night. The effect is channelled to the clock via a PACAP 1 receptor-cAMP signaling mechanism. Thus, in addition to its role in nocturnal regulation by glutamatergic neurotransmission, the RHT can adjust the biological clock by a PACAP-cAMP-dependent mechanism during the daytime.

Importance of conserved cysteines in the extracellular loops of human PACAP/VIP1 receptor for ligand binding and stimulation of cAMP production

The importance of two highly conserved cysteines in the human pituitary adenylate cyclase activating polypeptide (PACAP)/vasoactive intestinal peptide 1 (VIP1) receptor was examined. Using site-directed mutagenesis, each Cys residue was converted into Ala or Ser. The mutant and wildtype genes were transfected into HEK293 cells and tested for the ability to bind VIP and to activate cAMP production. Cys215Ala/Ser and Cys285Ala/Ser showed at least a tenfold decrease in binding affinity and receptor potency when compared to the wildtype. In contradiction to the wildtype receptor, both mutations were insensitive to dithiothreitol (DTT). The results indicate the existence of a disulfide bond between Cys215 and Cys285, which is important for stabilizing the receptor in the correct conformation for ligand binding and activation.