A Novel Combination Therapy Tβ4/VIP Protects against Hyperglycemia-Induced Changes in Human Corneal Epithelial Cells

Despite the prevalence of diabetic retinopathy, the majority of adult diabetic patients develop visually debilitating corneal complications, including impaired wound healing. Unfortunately, there is limited treatment for diabetes-induced corneal damage. The current project investigates a novel, peptide-based combination therapy, thymosin beta-4 and vasoactive intestinal peptide (Tβ4/VIP), against high-glucose-induced damage to the corneal epithelium. Electric cell-substrate impedance sensing (ECIS) was used for real-time monitoring of barrier function and wound healing of human corneal epithelial cells maintained in either normal glucose (5 mM) or high glucose (25 mM) ± Tβ4 (0.1%) and VIP (5 nM). Barrier integrity was assessed by resistance, impedance, and capacitance measurements. For the wound healing assay, cell migration was also monitored. Corneal epithelial tight junction proteins (ZO-1, ZO-2, occludin, and claudin-1) were assessed to confirm our findings. Barrier integrity and wound healing were significantly impaired under high-glucose conditions. However, barrier function and cell migration significantly improved with Tβ4/VIP treatment. These findings were supported by high-glucose-induced downregulation of tight junction proteins that were effectively maintained similar to normal levels when treated with Tβ4/VIP. These results strongly support the premise that Tβ4 and VIP work synergistically to protect corneal epithelial cells against hyperglycemia-induced damage. In addition, this work highlights the potential for significant translational impact regarding the treatment of diabetic patients and associated complications of the cornea.

Vasoactive Intestinal Peptide Indirectly Elicits Pituitary LH Secretion Independent of GnRH in Female Zebrafish

Vasoactive intestinal peptide (Vip) regulates luteinizing hormone (LH) release through the direct regulation of gonadotropin-releasing hormone (GnRH) neurons at the level of the brain in female rodents. However, little is known regarding the roles of Vip in teleost reproduction. Although GnRH is critical for fertility through the regulation of LH secretion in vertebrates, the exact role of the hypophysiotropic GnRH (GnRH3) in zebrafish is unclear since GnRH3 null fish are reproductively fertile. This phenomenon raises the possibility of a redundant regulatory pathway(s) for LH secretion in zebrafish. Here, we demonstrate that VipA (homologues of mammalian Vip) both inhibits and induces LH secretion in zebrafish. Despite the observation that VipA axons may reach the pituitary proximal pars distalis including LH cells, pituitary incubation with VipA in vitro, and intraperitoneal injection of VipA, did not induce LH secretion and lhβ mRNA expression in sexually mature females, respectively. On the other hand, intracerebroventricular administration of VipA augmented plasma LH levels in both wild-type and gnrh3-/- females at 1 hour posttreatment, with no observed changes in pituitary GnRH2 and GnRH3 contents and gnrh3 mRNA levels in the brains. While VipA's manner of inhibition of LH secretion has yet to be explored, the stimulation seems to occur via a different pathway than GnRH3, dopamine, and 17β-estradiol in regulating LH secretion. The results indicate that VipA induces LH release possibly by acting with or through a non-GnRH factor(s), providing proof for the existence of functional redundancy of LH release in sexually mature female zebrafish.

Role of VIP and Sonic Hedgehog Signaling Pathways in Mediating Epithelial Wound Healing, Sensory Nerve Regeneration, and Their Defects in Diabetic Corneas

Diabetic keratopathy, a sight-threatening corneal disease, comprises several symptomatic conditions including delayed epithelial wound healing, recurrent erosions, and sensory nerve (SN) neuropathy. We investigated the role of neuropeptides in mediating corneal wound healing, including epithelial wound closure and SN regeneration. Denervation by resiniferatoxin severely impaired corneal wound healing and markedly upregulated proinflammatory gene expression. Exogenous neuropeptides calcitonin gene-related peptide (CGRP), substance P (SP), and vasoactive intestinal peptide (VIP) partially reversed resiniferatoxin's effects, with VIP specifically inducing interleukin-10 expression. Hence, we focused on VIP and observed that wounding induced VIP and VIP type 1 receptor (VIPR1) expression in normal (NL) corneas, but not corneas from mice with diabetes mellitus (DM). Targeting VIPR1 in NL corneas attenuated corneal wound healing, dampened wound-induced expression of neurotrophic factors, and exacerbated inflammatory responses, while exogenous VIP had the opposite effects in DM corneas. Remarkably, wounding and diabetes also affected the expression of Sonic Hedgehog (Shh) in a VIP-dependent manner. Downregulating Shh expression in NL corneas decreased while exogenous Shh in DM corneas increased the rates of corneal wound healing. Furthermore, inhibition of Shh signaling dampened VIP-promoted corneal wound healing. We conclude that VIP regulates epithelial wound healing, inflammatory response, and nerve regeneration in the corneas in an Shh-dependent manner, suggesting a therapeutic potential for these molecules in treating diabetic keratopathy.

Glucagon-like peptide-2 interferes with the neurally-induced relaxant responses in the mouse gastric strips through VIP release

Glucagon-like peptide-2 (GLP-2) has been reported to indirectly relax gastric smooth muscle. In the present study we investigated, through a combined mechanical and immunohistochemical approach, whether GLP-2 interferes with the electrical field stimulation (EFS)-induced vipergic relaxant responses and the mechanism through which it occurs. For functional experiments, strips from the mouse gastric fundus were mounted in organ baths for isometric recording of the mechanical activity. Vasoactive intestinal peptide (VIP) immunoreactivity in GLP-2 exposed specimens was also evaluated by immunohistochemistry. In carbachol pre-contracted strips, GLP-2 (20 nM) evoked a tetrodotoxin (TTX)-sensitive relaxation, similar in shape to the TTX-insensitive of 100 nM VIP. In the presence of GLP-2, VIP had no longer effects and no more response to GLP-2 was observed following VIP receptor saturation. EFS (4-16 Hz) induced a fast relaxant response followed, at the higher stimulation frequencies (≥ 8 Hz), by a slow one. This latter was abolished either by GLP-2 or VIP receptor saturation as well as by the VIP receptor antagonist, VIP 6-28 (10 μM). A decrease of VIP-immunoreactive nerve structures in the GLP-2 exposed specimens was observed. These results suggest that, in the mouse gastric fundus, GLP-2 influences the EFS-induced slow relaxant response by promoting neuronal VIP release.

Updating the picture of layer 2/3 VIP-expressing interneuron function in the mouse cerebral cortex

For years, interneurons expressing vasoactive intestinal peptide (VIP) interneurons and their function within the neocortex have been shrouded in mystery. Their relatively small size and minimal representation in the cortex have made investigation difficult. Due to their service role performed in co‑operation with glia and blood vessels to supply energy during neuronal activation in the brain, the contribution of VIP interneurons to local neuronal circuit function was not appreciated. VIP interneurons in the neocortex account for roughly 12% of all interneurons. They have been described as a subgroup of the third largest population of 5-hydroxytryptamine 3a (5HT3a) receptor‑expressing interneurons, non‑overlapping with interneuron populations expressing parvalbumin (PV) or somatostatin (SST). However, it was recently shown that only half of VIP interneurons display a 5HT3a receptor response and a subset of VIP interneurons in visual cortex co‑express SST. Over the last several years, due to new technical advancements, many facts have emerged relating to VIP interneuron phylogenetic origin, operational mechanisms within local circuits and functional significance. Some of these discoveries have dramatically shifted the perception of VIP interneurons. This review focuses on the function of the VIP interneurons residing in layer 2/3 of the mouse neocortex.

Coherency of circadian rhythms in the SCN is governed by the interplay of two coupling factors

Circadian clocks are autonomous oscillators driving daily rhythms in physiology and behavior. In mammals, a network of coupled neurons in the suprachiasmatic nucleus (SCN) is entrained to environmental light-dark cycles and orchestrates the timing of peripheral organs. In each neuron, transcriptional feedbacks generate noisy oscillations. Coupling mediated by neuropeptides such as VIP and AVP lends precision and robustness to circadian rhythms. The detailed coupling mechanisms between SCN neurons are debated. We analyze organotypic SCN slices from neonatal and adult mice in wild-type and multiple knockout conditions. Different degrees of rhythmicity are quantified by pixel-level analysis of bioluminescence data. We use empirical orthogonal functions (EOFs) to characterize spatio-temporal patterns. Simulations of coupled stochastic single cell oscillators can reproduce the diversity of observed patterns. Our combination of data analysis and modeling provides deeper insight into the enormous complexity of the data: (1) Neonatal slices are typically stronger oscillators than adult slices pointing to developmental changes of coupling. (2) Wild-type slices are completely synchronized and exhibit specific spatio-temporal patterns of phases. (3) Some slices of Cry double knockouts obey impaired synchrony that can lead to co–existing rhythms (“splitting”). (4) The loss of VIP-coupling leads to desynchronized rhythms with few residual local clusters. Additional information was extracted from co–culturing slices with rhythmic neonatal wild-type SCNs. These co–culturing experiments were simulated using external forcing terms representing VIP and AVP signaling. The rescue of rhythmicity via co–culturing lead to surprising results, since a cocktail of AVP-antagonists improved synchrony. Our modeling suggests that these counter-intuitive observations are pointing to an antagonistic action of VIP and AVP coupling. Our systematic theoretical and experimental study shows that dual coupling mechanisms can explain the astonishing complexity of spatio-temporal patterns in SCN slices.

The mammalian circadian clock is orchestrated by a network of coupled neurons. Brain slice preparations allow the analysis of coupling mechanisms mediated by neuropeptides. From bioluminescence recordings, we extract single cell characteristics such as period, amplitude and damping rate. Our data-based stochastic network model involves local coupling between cells and additional external forcing. Available experimental data guide our simulations with two distinct coupling and forcing mechanisms representing the neuropeptides VIP and AVP. We compare our simulations with experiments from neonatal and adult wild-type brain slices and multiple knockouts. Furthermore, we study co–culturing of slices with synchronized neonatal wild-type slices. The extreme complexity of the spatio-temporal patterns is quantified using empirical orthogonal functions (EOFs). The experimental reduction of AVP coupling leads to surprising observations. In double knockouts, inhibition of AVP signaling can improve synchrony, whereas, in triple knockouts, coherency is reduced. Our network modeling shows that these counter-intuitive observations can be explained by an antagonistic action of VIP and AVP signaling. The agreement of experiments and simulations suggests that quite complex spatio-temporal patterns can appear as emergent properties of oscillator networks with dual coupling mechanisms.

Sex- and sub region-dependent modulation of arcuate kisspeptin neurones by vasopressin and vasoactive intestinal peptide

A population of kisspeptin neurones located in the hypothalamic arcuate nucleus (ARN) very likely represent the gonadotrophin-releasing hormone pulse generator responsible for driving pulsatile luteinising hormone secretion in mammals. As such, it has become important to understand the neural inputs that modulate the activity of ARN kisspeptin (ARN^KISS ) neurones. Using a transgenic GCaMP6 mouse model allowing the intracellular calcium levels ([Ca²⁺ ]_i ) of individual ARN^KISS neurones to be assessed simultaneously, we examined whether the circadian neuropeptides vasoactive intestinal peptide (VIP) and arginine vasopressin (AVP) modulated the activity of ARN^KISS neurones directly. To validate this methodology, we initially evaluated the effects of neurokinin B (NKB) on [Ca²⁺ ]_i in kisspeptin neurones residing within the rostral, middle and caudal ARN subregions of adult male and female mice. All experiments were undertaken in the presence of tetrodotoxin and ionotropic amino acid antagonists. NKB was found to evoke an abrupt increase in [Ca²⁺ ]_i in 95%-100% of kisspeptin neurones throughout the ARN of both sexes. By contrast, both VIP and AVP were found to primarily activate kisspeptin neurones located in the caudal ARN of female mice. Although 58% and 59% of caudal ARN kisspeptin neurones responded to AVP and VIP, respectively, in female mice, only 0%-8% of kisspeptin neurones located in other ARN subregions responded in females and 0%-12% of cells in any subregion in males (P < 0.05). These observations demonstrate unexpected sex differences and marked heterogeneity in functional neuropeptide receptor expression amongst ARN^KISS neurones organised on a rostro-caudal basis. The functional significance of this unexpected influence of VIP and AVP on ARN^KISS neurones remains to be established.

Optogenetic dissection of roles of specific cortical interneuron subtypes in GABAergic network synchronization

KEY POINTS

An increase in the excitability of GABAergic cells has typically been assumed to decrease network activity, potentially producing overall anti-epileptic effects. Recent data suggest that inhibitory networks may actually play a role in initiating epileptiform activity. We show that activation of GABAergic interneurons can elicit synchronous long-lasting network activity. Specific interneuron subpopulations differentially contributed to GABA network synchrony, indicating cell type-specific contributions of interneurons to cortical network activity. Interneurons may critically contribute to the generation of aberrant network activity characteristic of epilepsy, warranting further investigation into the contribution of distinct cortical interneuron subpopulations to the propagation and rhythmicity of epileptiform activity.

ABSTRACT

In the presence of the A-type K+ channel blocker 4-aminopyrdine, spontaneous synchronous network activity develops in the neocortex of mice of either sex. This aberrant synchrony persists in the presence of excitatory amino acid receptor antagonists (EAA blockers) and is considered to arise from synchronous firing of cortical interneurons (INs). Although much attention has been given to the mechanisms underlying this GABAergic synchrony, the contribution of specific IN subtypes to the generation of these long-lasting discharges (LLDs) is incompletely understood. We employed genetically-encoded channelrhodopsin and archaerhodopsin opsins to investigate the sufficiency and necessity, respectively, of activation of parvalbumin (PV), somatostatin (SST) and vasointestinal peptide (VIP)-expressing INs for the generation of synchronous neocortical GABAergic discharges. We found light-induced activation of PV or SST INs to be equally sufficient for the generation of LLDs, whereas activation of VIP INs was not. By contrast, light-induced inhibition of PV INs strongly reduced LLD initiation, whereas suppression of SST or VIP IN activity only partially attenuated LLD magnitude. These results suggest neocortical INs perform cell type-specific roles in the generation of aberrant GABAergic cortical network activity.

Exercise-induced biochemical changes and their potential influence on cancer: a scientific review

AIM

To review and discuss the available international literature regarding the indirect and direct biochemical mechanisms that occur after exercise, which could positively, or negatively, influence oncogenic pathways.

METHODS

The PubMed, MEDLINE, Embase and Cochrane libraries were searched for papers up to July 2016 addressing biochemical changes after exercise with a particular reference to cancer. The three authors independently assessed their appropriateness for inclusion in this review based on their scientific quality and relevance.

RESULTS

168 papers were selected and categorised into indirect and direct biochemical pathways. The indirect effects included changes in vitamin D, weight reduction, sunlight exposure and improved mood. The direct effects included insulin-like growth factor, epigenetic effects on gene expression and DNA repair, vasoactive intestinal peptide, oxidative stress and antioxidant pathways, heat shock proteins, testosterone, irisin, immunity, chronic inflammation and prostaglandins, energy metabolism and insulin resistance.

SUMMARY

Exercise is one of several lifestyle factors known to lower the risk of developing cancer and is associated with lower relapse rates and better survival. This review highlights the numerous biochemical processes, which explain these potential anticancer benefits.

Neuroendocrine Control of Broodiness

In the majority of vertebrates, survival of offspring to sexual maturation is important for increasing population size, and parental investment in the young is important for reproductive success. Consequently, parental care is critical for the survival of offspring in many species, and many vertebrates have adapted this behavior to their social and ecological environments. Parental care is defined as any behavior that is performed in association with one's offspring (Rosenblatt, Mayer, Siegel. Maternal behavior among nonprimate mammals. In: Adler, Pfaff, Goy, editors. Handbook of behavioral neurobiology. New York: Plenum; 1985. p. 229-98) and is well characterized in mammals and birds. In birds (class Aves), this is due to the high level of diversity across species. Parental behavior in birds protects the young from intruders, and generally involves nest building, incubation, and broody behavior which protect their young from an intruder, and the offspring are reared to independence. Broodiness is complexly regulated by the central nervous system and is associated with multiple hormones and neurotransmitters produced by the hypothalamus and pituitary gland. The mechanism of this behavior has been extensively characterized in domestic chicken (Gallus domesticus), turkey (Meleagris gallopavo), and pigeons and doves (family Columbidae). This chapter summarizes broodiness in birds from a physiology, genetics, and molecular biology perspective.

VIP Inhibits P. gingivalis LPS-induced IL-18 and IL-18BPa in Monocytes

IL-18 is a pro-inflammatory cytokine that is important in the regulation of T-cells and is elevated in inflammatory disorders such as periodontal disease. Vasoactive intestinal peptide (VIP) modulates immune responses to the periodontal pathogen Porphyromonas gingivalis ( Pg). Our objective was to investigate the effect of Pg LPS on IL-18 and its natural inhibitor, IL-18 binding protein (IL-18BPa), in human monocytes, and the effect of VIP on this system. We demonstrated that Pg LPS induced both IL-18 and IL-18BPa secretion in cultures of the human monocytic cell line THP-1, as measured by specific ELISA. The addition of antibodies to IL-18BPa to the stimulated THP-1 cultures resulted in increased levels of free IL-18, indicating a specific interaction between IL18 and IL-18BPa in this system. VIP (10−8M) inhibited both IL-18 and IL-18Bpa secretion by stimulated monocytes. We conclude that IL-18 and IL-18BPa secretion by monocytes is part of the immune response to Pg, and that VIP can inhibit this process.

Vasoactive Intestinal Peptide Excites GnRH Neurons in Male and Female Mice

A variety of external and internal factors modulate the activity of GnRH neurons to control fertility in mammals. A direct, vasoactive intestinal peptide (VIP)-mediated input to GnRH neurons originating from the suprachiasmatic nucleus is thought to relay circadian information within this network. In the present study, we examined the effects of VIP on GnRH neuron activity in male and female mice at different stages of the estrous cycle. We carried out cell-attached recordings in slices from GnRH-green fluorescent protein mice and calcium imaging in slices from a mouse line expressing the genetically encoded calcium indicator GCaMP3 selectively in GnRH neurons. We show that 50%-80% of GnRH neurons increase their firing rate in response to bath-applied VIP (1nM-1000nM) in both male and female mice and that this is accompanied by a robust increase in intracellular calcium concentrations. This effect is mediated directly at the GnRH neuron likely through activation of high-affinity VIP receptors. Because suprachiasmatic nucleus-derived timing cues trigger the preovulatory surge only on the afternoon of proestrus in female mice, we examined the effects of VIP during the estrous cycle at different times of day. VIP responsiveness in GnRH neurons did not vary significantly in diestrous and proestrous mice before or around the time of the expected preovulatory surge. These results indicate that the majority of GnRH neurons in male and female mice express functional VIP receptors and that the effects of VIP on GnRH neurons do not alter across the estrous cycle.

Encoding the Ins and Outs of Circadian Pacemaking

The SCN of the mammalian hypothalamus comprises a self-sustained, biological clock that generates endogenous ca. 24-h (circadian) rhythms. Circadian rhythmicity in the SCN originates from the interaction of a defined set of “clock genes” that participate in transcription/translation feedback loops. In order for the SCN to serve as an internal clock that times an internal day corresponding to the external solar day, the intracellular molecular oscillations must be output as physiological signals and be reset by appropriate environmental inputs. Here, the authors consider the mechanisms by which the SCN circadian pacemaker encodes rhythmic output and light input. In particular, they focus on the ionic mechanisms by which SCN neurons encode clock gene output as circa-dian rhythms in spike frequency, as well as cellular and molecular mechanisms by which SCN neurons encode circadian light input through phase heterogeneity in the SCN network. The authors propose that there are 2 distinct classes of ionic mechanisms supporting spike frequency rhythms output—modulation of basal membrane potential and conductance versus modulation of spike production—whereas light input is transformed by cellular communication within the SCN network and encoded by the relative phase relationships among SCN neurons.

Purinergic signalling in the gastrointestinal tract and related organs in health and disease

Purinergic signalling plays major roles in the physiology and pathophysiology of digestive organs. Adenosine 5'-triphosphate (ATP), together with nitric oxide and vasoactive intestinal peptide, is a cotransmitter in non-adrenergic, non-cholinergic inhibitory neuromuscular transmission. P2X and P2Y receptors are widely expressed in myenteric and submucous enteric plexuses and participate in sympathetic transmission and neuromodulation involved in enteric reflex activities, as well as influencing gastric and intestinal epithelial secretion and vascular activities. Involvement of purinergic signalling has been identified in a variety of diseases, including inflammatory bowel disease, ischaemia, diabetes and cancer. Purinergic mechanosensory transduction forms the basis of enteric nociception, where ATP released from mucosal epithelial cells by distension activates nociceptive subepithelial primary afferent sensory fibres expressing P2X3 receptors to send messages to the pain centres in the central nervous system via interneurons in the spinal cord. Purinergic signalling is also involved in salivary gland and bile duct secretion.

Circadian pacemaking in cells and circuits of the suprachiasmatic nucleus

The suprachiasmatic nucleus (SCN) of the hypothalamus is the principal circadian pacemaker of the brain. It co-ordinates the daily rhythms of sleep and wakefulness, as well as physiology and behaviour, that set the tempo to our lives. Disturbance of this daily pattern, most acutely with jet-lag but more insidiously with rotational shift-work, can have severely deleterious effects for mental function and long-term health. The present review considers recent developments in our understanding of the properties of the SCN that make it a robust circadian time-keeper. It first focuses on the intracellular transcriptional/ translational feedback loops (TTFL) that constitute the cellular clockwork of the SCN neurone. Daily timing by these loops pivots around the negative regulation of the Period (Per) and Cryptochrome (Cry) genes by their protein products. The period of the circadian cycle is set by the relative stability of Per and Cry proteins, and this can be controlled by both genetic and pharmacological interventions. It then considers the function of these feedback loops in the context of cytosolic signalling by cAMP and intracellular calcium ([Ca(2+) ]i ), which are both outputs from, and inputs to, the TTFL, as well as the critical role of vasoactive intestinal peptide (VIP) signalling in synchronising cellular clocks across the SCN. Synchronisation by VIP in the SCN is paracrine, operating over an unconventionally long time frame (i.e. 24 h) and wide spatial domain, mediated via the cytosolic pathways upstream of the TTFL. Finally, we show how intersectional pharmacogenetics can be used to control G-protein-coupled signalling in individual SCN neurones, and how manipulation of Gq/[Ca(2+) ]i -signalling in VIP neurones can re-programme the circuit-level encoding of circadian time. Circadian pacemaking in the SCN therefore provides an unrivalled context in which to understand how a complex, adaptive behaviour can be organised by the dynamic activity of a relatively few gene products, operating in a clearly defined neuronal circuit, with both cell-autonomous and emergent, circuit-level properties.

Neuropeptides in learning and memory

Dementia conditions and memory deficits of different origins (vascular, metabolic and primary neurodegenerative such as Alzheimer's and Parkinson's diseases) are getting more common and greater clinical problems recently in the aging population. Since the presently available cognitive enhancers have very limited therapeutical applications, there is an emerging need to elucidate the complex pathophysiological mechanisms, identify key mediators and novel targets for future drug development. Neuropeptides are widely distributed in brain regions responsible for learning and memory processes with special emphasis on the hippocampus, amygdala and the basal forebrain. They form networks with each other, and also have complex interactions with the cholinergic, glutamatergic, dopaminergic and GABA-ergic pathways. This review summarizes the extensive experimental data in the well-established rat and mouse models, as well as the few clinical results regarding the expression and the roles of the tachykinin system, somatostatin and the closely related cortistatin, vasoactive intestinal polypeptide (VIP) and pituitary adenylate-cyclase activating polypeptide (PACAP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY), opioid peptides and galanin. Furthermore, the main receptorial targets, mechanisms and interactions are described in order to highlight the possible therapeutical potentials. Agents not only symptomatically improving the functional impairments, but also inhibiting the progression of the neurodegenerative processes would be breakthroughs in this area. The most promising mechanisms determined at the level of exploratory investigations in animal models of cognitive disfunctions are somatostatin sst4, NPY Y2, PACAP-VIP VPAC1, tachykinin NK3 and galanin GALR2 receptor agonisms, as well as delta opioid receptor antagonism. Potent and selective non-peptide ligands with good CNS penetration are needed for further characterization of these molecular pathways to complete the preclinical studies and decide if any of the above described targets could be appropriate for clinical investigations.

Neuropeptides and hippocampal neurogenesis

Hippocampal neurogenesis is important for modulating the behavioural responses to stress and for certain forms of learning and memory. The mechanisms underlying the necessary coupling of neuronal activity to neural stem/progenitor cell (NSPC) function remain poorly understood. Within the dentate subgranular stem cell niche, local interneurons appear to play an important part in this excitation-neurogenesis coupling via GABAergic transmission, which promotes neuronal differentiation and integration. Neuropeptides such as neuropeptide Y (NPY), vasoactive intestinal peptide (VIP) and galanin have emerged as important mediators for signalling local and extrinsic interneuronal activity to subgranular zone precursors. Here we review the distribution of these neuropeptides and their receptors in the neurogenic area of the hippocampus and their precise effects on hippocampal neurogenesis. We also discuss neuropeptides' potential involvement in functional aspects of hippocampal neurogenesis particularly their involvement in the modulation of learning and memory and behavior responses.

Can traumatic injury trigger psoriatic arthritis? A review of the literature

Traumatic injury as a trigger for the subsequent development of psoriatic arthritis (PsA) has been implicated by several case reports and case series. However, it is still unclear whether trauma is the inciting event or just an incidental finding. It is thought that the interplay of genetic, immunologic, and environmental factors, such as trauma, may trigger the development of PsA. At least two hypotheses of how trauma may be linked to the development of PsA have surfaced and involve a "deep Koebner effect," the concept of a synovio-entheseal complex and activation of the innate immune system by biomechanical factors. The role of neuropeptides such as substance P and vasoactive intestinal peptide has been highlighted in the synovium after trauma. Better understanding of this phenomenon would shed light into the pathophysiology of Psa and help the development of preventive and therapeutic strategies.

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide (PACAP) in humans with multiple sclerosis

Multiple sclerosis (MS) is a chronic neuroinflammatory disease of the central nervous system that leads to demyelination and neurodegeneration. VIP and PACAP are structurally related neuropeptides with neuroprotective and anti-inflammatory activities. To evaluate VIP and PACAP-38 in plasma and CSF in humans in correlation with IL-6, IL-10 and TNFα, we compared 20 MS individuals with 27 healthy controls. In MS, a decrease in PACAP-38 in CSF and a decrease in plasma IL-6 concentration were seen. A positive correlation between plasma VIP and plasma IL-6 was identified. We conclude that VIP and PACAP may influence the course of MS.

Vasoactive intestinal peptide increases VEGF expression to promote proliferation of brain vascular endothelial cells via the cAMP/PKA pathway after ischemic insult in vitro

Vasoactive intestinal peptide (VIP) enhances angiogenesis in rats with focal cerebral ischemia. In the present study, we investigated the molecular mechanism of the proangiogenic action of VIP using an in vitro ischemic model, in which rat brain microvascular endothelial cells (RBMECs) are subjected to oxygen and glucose deprivation (OGD). Western blotting and immunocytochemistry were carried out to examine the expression of VIP receptors and vascular endothelial growth factor (VEGF) in cultured RBMECs. The cell proliferation was assessed by the MTT assay. Cyclic adenosine monophosphate (cAMP) and VEGF levels were measured by using the enzyme-linked immunosorbent assay. The cultured RBMECs expressed VPAC1, VPAC2 and PAC1 receptors. Treatment with VIP significantly promoted the proliferation of RBMECs and increased OGD-induced expression of VEGF, and this effect was antagonized by the VPAC receptor antagonist VIP6-28 and VEGF antibody. VIP significantly increased contents of cAMP in RBMECs and VEGF in the culture medium. The VIP-induced VEGF production was blocked by H89, a protein kinase A (PKA) inhibitor. These data suggest that treatment with VIP promotes VEGF-mediated endothelial cell proliferation after ischemic insult in vitro, and this effect appears to be initiated by the VPAC receptors leading to activation of the cAMP/PKA pathway.

Ameliorative effect of PACAP and VIP against increased permeability in a model of outer blood retinal barrier dysfunction

Breakdown of outer blood retinal barrier (BRB) due to the disruption of tight junctions (TJs) is one of the main factors accounting for diabetic macular edema (DME), a major complication of diabetic retinopathy. Previously it has been shown that PACAP and VIP are protective against several types of retinal injuries. However, their involvement in the maintenance of outer BRB function during DME remains uncovered. Here, using an in vitro model of DME, we explored the effects of both PACAP and VIP. Human retinal pigment epithelial cells (ARPE19) were cultured for 26 days either in normal glucose (5.5 mM, NG) or in high glucose (25 mM, HG). In addition, to mimic the inflammatory aspect of the diabetic milieu, cells were also treated with IL-1β (NG+IL-1β and HG+IL-1β). Effects of PACAP or VIP on cells permeability were evaluated by measuring both apical-to-basolateral movements of fluorescein isothyocyanate (FITC) dextran and transepithelial electrical resistance (TEER). Expression of TJ-related proteins was evaluated by immunoblot. Results demonstrated that NG+IL-1β and, to a greater extent, HG+IL-1β significantly increased FITC-dextran diffusion, paralleled by decreased TEER. PACAP or VIP reversed both of these effects. Furthermore, HG+IL-1β-induced reduction of claudin-1 and ZO-1 expression was reversed by PACAP and VIP. Occludin expression was not affected in any of the conditions tested. Altogether, these finding show that both peptides counteract HG+IL-1β-induced damage in ARPE19 cells, suggesting that they might be relevant to the maintenance of outer BRB function in DME.

17β-estradiol protects the lung against acute injury: possible mediation by vasoactive intestinal polypeptide

Beyond their classical role as a class of female sex hormones, estrogens (e.g. 17β-estradiol) exert important biological actions, both protective and undesirable. We have investigated the ability of estradiol to protect the lung in three models of acute injury induced by 1) oxidant stress due to the herbicide paraquat; 2) excitotoxicity, caused by glutamate agonist N-methyl-d-aspartate; and 3) acute alveolar anoxia. We also assessed the role of estrogen receptors (ER) ERα and ERβ and the neuropeptide vasoactive intestinal peptide (VIP) in mediating this protection. Isolated guinea pig or rat lungs were perfused in situ at constant flow and mechanically ventilated. The onset and severity of lung injury were monitored by increases in pulmonary arterial and airway pressures, wet/dry lung weight ratio, and bronchoalveolar lavage fluid protein content. Estradiol was infused into the pulmonary circulation, beginning 10 min before induction of injury and continued for 60-90 min. Lung injury was marked by significant increases in the above measurements, with paraquat producing the most severe, and excitotoxicity the least severe, injury. Estradiol significantly attenuated the injury in each model. Both ER were constitutively expressed and immunohistochemically demonstrable in normal lung, and their selective agonists reduced anoxic injury, the only model in which they were tested. As it protected against injury, estradiol rapidly and significantly stimulated VIP mRNA expression in rat lung. Estradiol attenuated acute lung injury in three experimental models while stimulating VIP gene expression, a known mechanism of lung protection. The up-regulated VIP expression could have partially mediated the protection by estrogen.

Effects of vasoactive intestinal peptide genotype on circadian gene expression in the suprachiasmatic nucleus and peripheral organs

The neuropeptide vasoactive intestinal polypeptide (VIP) has emerged as a key candidate molecule mediating the synchronization of rhythms in clock gene expression within the suprachiasmatic nucleus (SCN). In addition, neurons expressing VIP are anatomically well positioned to mediate communication between the SCN and peripheral oscillators. In this study, we examined the temporal expression profile of 3 key circadian genes: Per1, Per2 , and Bmal1 in the SCN, the adrenal glands and the liver of mice deficient for the Vip gene (VIP KO), and their wild-type counterparts. We performed these measurements in mice held in a light/dark cycle as well as in constant darkness and found that rhythms in gene expression were greatly attenuated in the VIP-deficient SCN. In the periphery, the impact of the loss of VIP varied with the tissue and gene measured. In the adrenals, rhythms in Per1 were lost in VIP-deficient mice, while in the liver, the most dramatic impact was on the phase of the diurnal expression rhythms. Finally, we examined the effects of the loss of VIP on ex vivo explants of the same central and peripheral oscillators using the PER2::LUC reporter system. The VIP-deficient mice exhibited low amplitude rhythms in the SCN as well as altered phase relationships between the SCN and the peripheral oscillators. Together, these data suggest that VIP is critical for robust rhythms in clock gene expression in the SCN and some peripheral organs and that the absence of this peptide alters both the amplitude of circadian rhythms as well as the phase relationships between the rhythms in the SCN and periphery.

VIP and PACAP: recent insights into their functions/roles in physiology and disease from molecular and genetic studies

PURPOSE OF REVIEW

Vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) as well as the three classes of G-protein-coupled receptors mediating their effects, are widely distributed in the central nervous system (CNS) and peripheral tissues. These peptides are reported to have many effects in different tissues, which are physiological or pharmacological, and which receptor mediates which effect, has been difficult to determine, primarily due to lack of potent, stable, selective agonists/antagonists. Recently the use of animals with targeted knockout of the peptide or a specific receptor has provided important insights into their role in normal physiology and disease states.

RECENT FINDINGS

During the review period, considerable progress and insights has occurred in the understanding of the role of VIP/PACAP as well as their receptors in a number of different disorders/areas. Particularly, insights into their roles in energy metabolism, glucose regulation, various gastrointestinal processes including gastrointestinal inflammatory conditions and motility and their role in the CNS as well as CNS diseases has greatly expanded.

SUMMARY

PACAP/VIP as well as their three classes of receptors are important in many physiological/pathophysiological processes, some of which are identified in these studies using knockout animals. These studies may lead to new novel treatment approaches. Particularly important are their roles in glucose metabolism and on islets leading to possible novel approaches in diabetes; their novel anti-inflammatory, cytoprotective effects, their CNS neuroprotective effects, and their possible roles in diseases such as schizophrenia and chronic depression.

Decreased REM sleep and altered circadian sleep regulation in mice lacking vasoactive intestinal polypeptide

OBJECTIVES

Vasoactive intestinal polypeptide (VIP) has been implicated in sleep regulation as a promoter of rapid eye movement (REM) sleep. Previous work has shown that the amount of time spent in REM sleep is increased by intracerebroventricular administration of VIP, and reduced by treatment with VIP antagonists or antibodies against VIP. A variety of evidence suggests that VIP is critical for normal expression of circadian rhythmicity of diverse physiological and behavioral parameters. In the present study, we investigated the role of this peptide in sleep regulation using VIP-deficient (VIP-/-) mice.

METHODS

EEG/EMG sleep-wake patterns were recorded in VIP-/- mice and their wild-type littermate controls under normal light-dark (LD), constant darkness (DD) and sleep deprivation conditions.

RESULTS

VIP-/- mice exhibited reduced REM sleep time over the 24-h cycle while total daily amounts of NREM sleep and wakefulness were not altered significantly. The reduced REM sleep time in VIP-/- mice occurred entirely during the day due to a reduction in the duration, but not the frequency, of REM sleep bouts. In response to sleep deprivation, compensatory rebounds in NREM sleep and REM sleep were also attenuated in VIP-/- mice. Finally, the loss of VIP altered the temporal distribution of sleep in that the VIP -/- mice exhibited smaller amplitude rhythms in total sleep, NREM sleep, and REM sleep under both LD and DD.

CONCLUSIONS

These results indicate that VIP regulates the duration of REM sleep, sleep homeostatic mechanisms as well as the temporal patterning of sleep.

Vasoactive intestinal peptide induces surfactant protein A expression in ATII cells through activation of PKC/c-Fos pathway

Vasoactive intestinal peptide (VIP) is a major neurotransmitter in the lungs and regulates many aspects of pulmonary functions. Pulmonary surfactant (PS), a complex mixture of lipids and proteins, produced by the alveolar type II (ATII) cells maintains alveolar integrity and plays important roles in the control of host defense and inflammation in the lungs. Surfactants deficiency or dysfunction is associated with occurrence and development of many pulmonary diseases. We reported previously that VIP enhanced the synthesis of pulmonary surfactants phospholipid in ATII cells. In this study, the effect of VIP on the expression of pulmonary surfactant protein A (SP-A) in lung explants was investigated. Firstly, we found that VIP elevated SP-A expression in ATII cells which was mediated by enhanced sp-a gene transcription. Furthermore, we identified that c-Fos protein was essential for VIP induced SP-A expression in ATII cells. Finally, we provided evidence to show that activation of c-Fos expression by PKC was required for VIP induced SP-A expression. Altogether, our work showed that VIP regulated the function of pulmonary surfactant system in the lungs and further investigation of the underlying mechanism would provide important clues for better therapeutic strategy design for pulmonary disorders caused by surfactant deficiency.

Nuclear localization of vasoactive intestinal peptide (VIP) receptors in human breast cancer

Vasoactive intestinal peptide (VIP) and its receptors (VPACs) are involved in proliferation, survival, and differentiation in human breast cancer cells. Its mechanism of action is traditionally thought to be through specific plasma membrane receptors. There is compelling evidence for a novel intracrine mode of genomic regulation by G-protein-coupled receptors (GPCRs) that implies both endocytosis and nuclear translocation of peripheral GPCR and/or the activation of nuclear-located GPCRs by endogenously-produced, non-secreted ligands. Regarding to VPAC receptors, which are GPCRs, there is only a report suggesting them as a dynamic system for signaling from plasma membrane and nuclear membrane complex. In this study, we show that VPAC(1) receptor is localized in cell nuclear fraction whereas VPAC(2) receptor presents an extranuclear localization and its protein expression is lower than that of VPAC(1) receptor in human breast tissue samples. Both receptors as well as VIP are overexpressed in breast cancer as compared to non-tumor tissue. Moreover, we report the markedly nuclear localization of VPAC(1) receptors in estrogen-dependent (T47D) and independent (MDA-MB-468) human breast cancer cell lines. VPAC(1) receptors are functional in plasma membrane and nucleus as shown by VIP stimulation of cAMP production in both cell lines. In addition, VIP increases its own intracellular and extracellular levels, and could be involved in the regulation of VPAC(1)-receptor traffic from the plasma membrane to the nucleus. These results support new concepts on function and regulation of nuclear GPCRs which could have an impact on development of new therapeutic drugs.

Role of VPAC1 and VPAC2 in VIP mediated inhibition of rat pulmonary artery and aortic smooth muscle cell proliferation

Recent studies have suggested the potential use of vasoactive intestinal peptide (VIP) in the treatment of pulmonary arterial hypertension (PAH). An understanding of the mechanism of action of VIP is important for the development of new therapies for PAH. The biological effects of VIP are mediated by two type II guanine nucleotide binding protein (G-protein)-coupled receptors VIP/PACAP (pituitary adenylate cyclase activating peptide) receptor type1 (VPAC1) and VIP/PACAP receptor type 2 (VPAC2). In the present study, the distribution and role of these receptors were investigated and compared in cultured smooth muscle cells from rat aorta and pulmonary artery, as well as in fixed tissue sections of the aorta and pulmonary artery. Western blot analysis, RT-PCR and immunohistochemistry showed the expression of both VIP receptors in tissue sections of the aorta and pulmonary artery as well as in cultured smooth muscle cells from these vessels. The application of a specific antagonist of VPAC1 resulted in a small release from VIP induced inhibition of cell proliferation. In contrast (VIP 6-28; 300nM) which is an antagonist against both receptors resulted in a significant restoration of proliferation. The expression of cAMP was reduced in the presence of VIP 6-28 and slightly decreased by VPAC1 antagonist. These findings suggest a dual role for VPAC1 and VPAC2 receptors in mediating the antiproliferative effects of VIP with VPAC2 appearing to play a more dominant role.

Neurogenic regulation of dendritic cells in the intestine

Antigen presenting cells like dendritic cells (DC) are responsible for the initiation of adaptive immune responses via the T helper cells they activate. The type of T cell responses DC induce is dependent on the local immunological environment where antigen has been taken up. In the gut, resident DC are phenotypically and functionally shaped by epithelial and stromal cell derived signals, the cytokine microenvironment, and neuronal products. These factors can control the activation state of DC thereby inducing tolerance for food and commensal organisms or immunity against pathogenic microbes. The enteric nervous system (ENS) is increasingly recognized as an important regulatory factor in intestinal immune cell control. Neurotransmitters and neuropeptides like acetylcholine (ACh), norepinephrine (NE) and vasoactive intestinal peptide (VIP) are released by neurons of the ENS and can affect the function of DC and subsequent immune responses. The critical balance between tolerance and protective immunity is disrupted in inflammatory bowel disease, which results in an exaggerated immune response against commensal bacteria. In this review we discuss the effects of ACh, VIP, and NE on DC function. DC express various receptors for these neuron derived products and can alter DC co-stimulatory molecule expression, cytokine release and subsequent T cell activation in an anti-inflammatory fashion. Knowledge about these interactions will help find new drug targets and may facilitate the development of specific therapies for diseases like inflammatory bowel disease (IBD).

Thermoregulatory and thermal control in the human cutaneous circulation

The past 10-15 years has been a time of focus on the mechanisms of control in the human cutaneous circulation. Methodological developments have provided powerful means for resolving the important contributors to the reflex control of skin blood flow (thermoregulatory control) and also for the equally impressive effects of direct heating and cooling of the skin (thermal control). This review is devoted largely to that recent literature. We treat the sympathetic vasoconstrictor system and its transmitters and modulatory factors and the sympathetic active vasodilator system and its abundant mysteries, with focus on the putative transmitters and cotransmitters, the involvement of nitric oxide and the relationship to sweating and modulatory factors. We also deal with the current understanding of the mechanisms of vasoconstriction and vasodilation that accompany direct skin cooling and heating, noting that adrenergic function, afferent nerve function and the nitric oxide system are involved in the vascular responses to both thermal stimuli.

[Relevance of vasoactive intestinal peptide and total bronchial mucin in rat lung.]

Vasoactive intestinal peptide (VIP) is a neuropeptide with potent bronchodilator, immunomodulator, and anti-inflammatory properties, and thus has biological properties capable of counteracting all major features of the asthmatic response. However, the effect of VIP on bronchial mucin secretion remains unclear. In order to observe the influence of VIP on bronchial mucin, the present study was designed to observe the correlation between VIP and total bronchial mucin changes under different time of ozone stress in rat lung. Sixty-four Sprague-Dawley rats were used in the experiment. Under different time of ozone stress, VIP content in lung homogenate was analyzed by radioimmunoassay, and changes in total bronchial mucin in the lung were analyzed by calculating the goblet cell hyperplasia ratio and the epithelial cell mucus occupying ratio from the periodic acid-Schiff reaction (PAS) staining. The results showed that, at early stage of respiratory tract injury, VIP did not change significantly, while the total bronchial mucin secretion increased; with the development of damage, the secretion of VIP increased by compensation, followed by a decrease in total bronchial mucin; with further injury, the numbers of pulmonary endocrine VIP positive nerve fibers and endocrine cells decreased, but bronchial mucin volume gradually increased. It is concluded that the secretion of VIP is negatively correlated with the secretion of bronchial mucin during the development of inflammation.

Multifunctional role of VIP in prostate cancer progression in a xenograft model: suppression by curcumin and COX-2 inhibitor NS-398

We used an in vivo model of human experimental prostate cancer in order to shed a new light on the effects of vasoactive intestinal peptide (VIP) on tumor growth as well as its pro-metastatic potential in this disease. We used nude mice subcutaneously injected with prostate cancer androgen-independent PC3 cells for 30 days. The regulatory role of VIP on cyclooxygenase-2 (COX-2) and vascular endothelial growth factor (VEGF) expression as well as on matrix metalloproteinase-2 and 9 (MMP-2 and 9) activities was examined. A selective COX-2 inhibitor, NS-398, and curcumin were used to block VIP effects. Xenografts of VIP-treated PC3 prostate cancer cells in nude mice gave tumors that grew significantly faster than those in the untreated group. It is conceivably a result of both the trophic effect of VIP on prostate cancer cells and the proangiogenic action of the neuropeptide in the growing tumor. We show the overexpression at mRNA and/or protein levels of VIP, its main receptor VPAC(1), the major angiogenic factor VEGF, and the pro-inflammatory enzyme COX-2 as well as the increased activity of MMP-2 and 9 in tumors derived from VIP-treated PC3 cells as compared with control group. The overexpression of the above biomarkers was suppressed in tumors derived from VIP-treated PC3 cells that had been previously incubated with curcumin or NS-398. Thus, the potential therapeutic role of curcumin and selective COX-2 inhibitors in combination with available VIP antagonists should be considered in prostate cancer therapy as supported by their inhibitory activities on tumor cell growth.

Adenoviral transfer of vasoactive intestinal peptide (VIP) gene inhibits rat aortic and pulmonary artery smooth muscle cell proliferation

Vasoactive intestinal peptide (VIP), a 28 amino acid peptide, has been shown to inhibit proliferation of vascular smooth muscle cells. In previous studies VIP and VIP analogs have been used to study the effects of the peptide on vascular smooth muscle cell function. In this study an adenovirus encoding the VIP gene was used to investigate the mechanism of the antiproliferative action of VIP in vascular smooth muscle cells. Primary cultures of aortic and pulmonary artery smooth muscle cells from male Sprague-Dawley rats were transfected with varying concentrations of serotype 5 adenovirus encoding human VIP (Ad5CMVhVIP). Transfection efficiency and subsequently VIP gene expression were confirmed by western blot analysis and immunohistochemistry. In this study a decrease in vascular smooth muscle cell proliferation at vector concentrations of 150, 300 and 600MOI (multiplicity of infection) was observed. In addition, there was increased production of cAMP in pulmonary artery and aortic smooth muscle cells transfected with VIP. Treatment of cells with a PKA inhibitor (Rp-8-BrcAMPs) restored proliferation to about 80% of control whereas treatment with the PKG inhibitor Rp-8-BrcGMPs had no significant effect suggesting the involvement of the PKA pathway in the antiproliferative actions of VIP.

Regulation of vasoactive intestinal peptide and substance P in the human pyloric sphincter

BACKGROUND/AIMS

Brain-gut hormones (i.e., neuropeptides) such as vasoactive intestinal peptide (VIP) and substance P (SP) have been shown to exist in the enteric nervous system (ENS) of the pyloric sphincter (PS) in studies of immunohistochemistry. To clarify the role of neuropeptides in the ENS of the normal human PS, we investigated the enteric nerve responses to VIP and SP in normal human PS specimens in vitro.

METHODOLOGY

Normal human PS specimens derived from 45 patients with early gastric cancer (35 men and 10 women aged from 44 to 65 years, average 57.4 years) were used. A total of 120 PS muscle strips were made from 45 PS. A mechanographic technique was used to evaluate in vitro muscle strip responses to VIP and SP before and after treatment with various autonomic nerve blockers.

RESULTS

Responses to VIP and SP after blockade of the adrenergic and cholinergic nerves: Relaxation was elicited by VIP in 41.7% at 1 x 10(-8), 62.5% at 1 x 10(-7), and 83.3% at 1 x 10(-6) g/ml. Differences were noted in the percentages showing relaxation between 1 x 10(-8) and 1 x 10(-7) g/ml, between 1 x 10(-8) and 1 x 10(-6) g/ml, and between 1 x 10(-7) and 1 x 10(-6) g/ml (p = 0.0012, p < 0.0001, p = 0.0002, respectively). Contraction was elicited by administration of by SP in 31.7% at 1 x 10(-8), 58.3% at 1 x 10(-7), and 79.2% at 1 x 10(-6) g/ml, respectively. Differences were noted in the percentages showing contraction between 1 x 10(-8) and 1 x 10(-7) g/ml, between 1 x 10(-8) and 1 x 10(-6) g/ml, and between 1 x 10(-7) and 1 x 10(-6) g/ml (p = 0.0001, p < 0.0001, p = 0.0004, respectively). VIP caused relaxation and substance P caused contraction of the PS in a concentration-dependent manner. Response to VIP and SP at 1 x 10(-6) g/ml after blockade of the ENS by tetrodotoxin (TTX): The relaxation to VIP and contraction to SP following administration of TTX were weaker than after blockade of the adrenergic and cholinergic nerves. In the normal human PS, VIP and SP may act both via NANC nerves and directly on the muscle strips.

CONCLUSIONS

Relaxation reaction via VIP nerves and contraction via SP nerves might be involved in regulation of ENS in the normal human PS.

VIP, vagina, clitoral and periurethral glans--an update on human female genital arousal

The sexually quiescent human vagina is a just moist, potential space with a minimal blood flow and very low luminal oxygen tension. The first measurable sign of sexual arousal is an increase in the blood flow. This creates the engorged condition, elevates the luminal oxygen tension and stimulates the production of surface vaginal fluid by an increased plasma transudation that saturates the fluid reabsorptive capacity of the epithelium. The vaginal lubrication created allows painless penile penetration and coital movements. The mechanisms underlying the changes appear to be mediated by Vasoactive Intestinal Peptide (VIP). VIP is present in nerves closely applied to blood vessels in the vaginal wall. Administration of VIP either intravenously, or by subepithelial injection in the vaginal wall, increases vaginal blood flow and induces vaginal fluid production. Increases in vaginal blood flow by sexual arousal are not blocked by atropine injection indicating that cholinergic mechanisms are unimportant. All the present evidence suggests that the local vaginal release of VIP induces the vaginal changes of arousal. Discourse on vaginal and pudendal anatomy (Sevely, 1987) has proposed that the female glans of the clitoris is not the true homologue of the penile glans because it has no urethral opening. The speculative suggestion is that the true female glans is the area surrounding the urethral opening (which has no specific anatomical name). Preliminary studies indicate that the area of this tissue (periurethral glans) decreases on vaginal penile insertion and reappears on withdrawal indicating that it is moved during coitus. How important such movement is to stimulate erotic sensation and how sensitive this area is to erotic stimulation are unanswered questions.

[Roles of enteric nervous system neurotransmitters and interstitial cells of Cajal in the colon in slow transit constipation in rats]

OBJECTIVE

To evaluate the roles of enteric nervous system neurotransmitters, nitric oxide (NO), substance P (SP) and vasoactive intestinal polypeptide (VIP), and interstitial cells of Cajal (ICC) in the colon in slow transit constipation in rats.

METHODS

Thirty-two healthy Wistar rats were randomly assigned to control and constipated groups. In the constipated group, the rats were daily administered with diphenoxylate (8 mg/kg) to develop slow transit constipation, while the control rats were fed with water. The number and the weight of fecal granule and the body weight of rats were recorded every 5 days for 90 days. Transit functions of intestinal movement were examined by an activated charcoal suspension pushing test one week after stopping the administration of diphenoxylate. The levels of NO and SP in the colonic mucosa were measured by nitrate reductase methods and ELISA respectively. The distribution of VIP and ICC positive cells confirmed with symbolic c-kit+ cells in the colonic wall were observed by immunohistochemical methods.

RESULTS

The daily number of fecal granule in the constipated group was significantly less than that in the control group (P<0.01). The mean weight of each fecal granule in the constipated group was significantly higher than that in the control group (P<0.01). The discharge time of the first granule of black faeces in the constipated group (430.2+/- 132.1 min) was significantly longer than that in the control group (337.2+/- 74.7 min; P<0.05). There were no significant differences in NO and SP levels and the density of VIP positive cells in the distal colonic segment between the two groups. The number of c-kit+ cells in the distal colonic wall in the constipated group was significantly reduced compared with that in the control group (P<0.05).

CONCLUSIONS

The reduction of ICC number in the distal colon may be contributed to the pathogenesis of slow transit constipation in rats.

Population encoding by circadian clock neurons organizes circadian behavior

Mammalian circadian rhythms are orchestrated by the suprachiasmatic nuclei (SCN) of the hypothalamus. The SCN are composed of circadian clock neurons, but the mechanisms by which these populations of neuronal oscillators encode rhythmic behavior are incompletely understood. We have used ex vivo real-time gene expression imaging of the neural correlates of circadian behavior, combined with genetic disruption of vasoactive intestinal polypeptide, a key SCN signaling molecule, to examine the neural basis of circadian organization in the SCN. We show that the coherence and timing of clock neuron rhythms are correlated with the coherence and timing of behavioral rhythms within individual mice and that the degree of disruption of SCN neuronal organization correlates with the degree of behavioral disruption within individuals. Our results suggest that the SCN encode circadian phase as a temporal population vector of its constituent neurons; such that as the neuronal population becomes desynchronized, phase information becomes ambiguous.

Vasoactive intestinal peptide and its role in continuous and seasonal reproduction in birds

Native Thai chicken, an equatorial species breeds throughout the year, whereas turkeys are seasonal temperate zone breeder whose reproductive cycle is terminated by the onset of photorefractoriness. This study investigated VIPergic activity throughout a reproductive cycle in both species, hypothesizing that the differential expression of vasoactive intestinal peptide (VIP) would provide an insight into the differing reproductive strategies of the two species. Distribution of VIP neurons in the native Thai chicken and a comparison of VIPergic activity in the nucleus inferioris hypothalami (IH) and nucleus infundibuli hypothalami (IN) were investigated. VIP immunoreactivity was found throughout the native Thai chicken brain, predominantly located within the IH-IN. The pattern of VIP distribution in the native Thai chicken supports the findings reported in temperate zone species. Unlike the turkey, where there is a dissociation between VIPergic activity and prolactin levels during photorefractoriness, in the native Thai chicken, which do not express photorefractoriness, changes in VIP immunoreactive (VIP-ir) neurons within the IH-IN were directly correlated with prolactin throughout the reproductive cycle. VIPergic activity reached its lowest level after hatching of the chicks in the native Thai chicken, while in the turkey VIPergic activity was lowest only after exposure to a short day photoperiod and the acquisition of photosensitivity. This suggests that VIP neurons in the IH-IN may play a pivotal role in regulating the reproductive cycle and its differential expression following hatching of the young may, in part, account for the difference in reproductive mode between equatorial, continually breeding, non-photoperiodic birds and seasonally breeding, photoperiodic birds.

Cutaneous neurovascular interaction involved in tactile sensation

The sense of touch is one of the most vital; still, it is incompletely understood. We review the afferent function that allows for the relay of sensory information from the periphery (the skin) to the central nervous system. Within this afferent function, we examine the different integrating levels including several candidates for cutaneous transducers, the conduction of the information via the afferent nervous fibres and the transmission of the sensory stimuli to higher brain structures, resulting in the perception of the different senses. We then examine the efferent system that stimulates the skin by secreting neurotransmitters. Finally, we discuss the tools available to study the cutaneous neurovascular interaction and conclude on a novel test that assesses this interaction triggered by the application of a local non noxious pressure (tactile stimulation).

Vasoactive peptides in the pathogenesis of psoriasis

Psoriasis, a chronic inflammatory skin disease, is believed to be exacerbated by stress. The exact mechanism of this phenomenon is not fully understood, however, it has been postulated that different substances released from dermal nerve endings during stress may take part in initiation or modulation of psoriasis. One of the most interesting group of mediators are polypeptides, also named as neuropeptides, that possess vasoactive properties. It was documented that these polypeptides could not only be released from nerve endings, but may also be directly synthesised in the skin and liberated from numerous dermal cells. Moreover, these substances are not only released by different cells, but may activate various cell types showing a wide spectrum of biological actions. Thus, this complex system of interactions seems to be important component of psoriatic pathological reaction. The significant role of these neuromediators has also been postulated in other chronic skin diseases, like palmoplantar pustulosis, atopic and irritant eczema, rosacea, lichen sclerosus, vitiligo, pigmented urticaria or prurigo nodularis. Among different neuropeptides, substance P, calcitonin gene-related peptide, vasoactive intestinal peptide (VIP) and neuropeptide Y have been mostly studied in psoriasis.

Neurotransmitters of the non-adrenergic non-cholinergic relaxation of proximal stomach

The proximal third of the stomach (fundus plus oral corpus) relaxes during swallowing so that it can hold large amounts of food with limited increases in intraluminal pressure. This mechanism has been called "receptive relaxation" and is mediated by a vago-vagal reflex. When the food bolus reaches the stomach, gastric relaxation is maintained by another reflex starting from mechanoreceptors in the gastric wall. This second mechanism has been named "adaptive relaxation" or "gastric accommodation" and involves both intramural and vagal reflex pathways, whose inhibitory neurons are always intramural. There was initially a great deal of controversy about the identity of the neurotransmitter/s released by inhibitory neurons, but at present nitric oxide (NO) and vasoactive intestinal polypeptide (VIP) are considered to be the most likely candidates. Several lines of evidence indicate that adenosine triphosphate (ATP) might be implicated too. It seems that these neurotransmitters are co-released from the inhibitory motor neurons and are responsible for the different features of the NANC relaxation induced by low- or high-frequency neuronal firing. NO (and perhaps ATP) would be responsible for the rapid beginning and the initial rapid development of the relaxation evoked by neuronal firing at low- or high-frequency and VIP for the long duration of the relaxation evoked by high-frequency neuronal activation. This review will deal mainly with the physiological characteristics and pharmacological features of the NANC relaxation of the proximal stomach and the evidences favoring or excluding a role as inhibitory neurotransmitters of ATP, NO and VIP in different species.

Vasoactive intestinal polypeptide can excite gonadotropin-releasing hormone neurons in a manner dependent on estradiol and gated by time of day

A surge of GnRH release signals the LH surge that triggers ovulation. The GnRH surge is dependent on a switch in estradiol feedback from negative to positive and, in rodents, a daily neural signal, likely from the suprachiasmatic nuclei. Vasoactive intestinal polypeptide (VIP) may be involved in suprachiasmatic nuclei-GnRH neuron communication. Here we assessed the effects of acute VIP (5 min treatment) on GnRH neuron function using targeted extracellular recordings of firing activity of GnRH neurons in brain slices. We examined the effect of VIP on firing rate at different times of day using an established ovariectomized, estradiol-treated (OVX+E) mouse model that exhibits daily LH surges timed to the late afternoon. Cells from OVX animals (no estradiol) did not respond to VIP, regardless of time of day. With estradiol, the effect of VIP on GnRH neurons was dependent on the time of recording. During negative feedback, OVX+E cells did not respond. VIP increased firing in cells recorded during surge onset, but this excitatory response was reduced at surge peak. Acute treatment of OVX+E cells during surge peak with a VIP receptor antagonist decreased GnRH neuron firing. This suggests endogenous VIP may both increase GnRH neuron firing during the surge and occlude response to exogenous VIP. These data provide functional evidence for VIP effects on GnRH neurons and indicate that both estradiol and time of day gate the GnRH neuron response to this peptide. VIP may provide an excitatory signal from the circadian clock that helps time the GnRH surge.

Role of vasoactive intestinal peptide and pituitary adenylate cyclase activating polypeptide in the vaginal wall of women with stress urinary incontinence and pelvic organ prolapse

Pelvic floor connective tissue degeneration is closely associated with retrogradation of its dominating nerve fibers. We hypothesized that some neuropeptides from pelvic floor tissue might be involved in the pathological progress of stress urinary incontinence (SUI) and pelvic organ prolapse (POP) in women. Thirty premenopausal and 31 postmenopausal patients participated in the study. The morphological appearance in the vaginal tissue was examined. The vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase activating polypeptide-38 (PACAP) immunoreactivities (ir-VIP, ir-PACAP) were tested by immunohistochemistry and radioimmunoassay. We found that the VIP and PACAP immunostainings were weaker and sparser, and ir-VIP and ir-PACAP levels were significantly decreased in the anterior vaginal wall in the premenopausal and postmenopausal SUI or POP patients. Ir-VIP and ir-PACAP levels were reversely correlated with the age and menopausal status in the SUI or POP patients. Our data suggest that VIP and PACAP may participate in the pathophysiological process of SUI and POP.

Regulation of the peptidergic nerves (substance P and vasoactive intestinal peptide) in the colon of women patients with slow transit constipation: an in vitro study

BACKGROUND/AIMS

In histological studies, there is evidence to suggest a diminution of the peptidergic nerves such as vasoactive intestinal peptide (VIP) and substance P (SP) in the enteric nervous system in the colon of patients with slow transit constipation (STC). To clarify the pathophysiological significance of peptidergic nerves in the colon of patients with STC, we investigated the enteric nerve responses on pathological and normal bowel segments derived from patients with STC and patients who underwent colon resection for colon cancers, respectively.

METHODOLOGY

Twenty-eight preparations were taken from the pathological sigmoid colon of 16 women with STC (aged 40-58 years, average 48.8 years). Forty-eight preparations were taken from the normal sigmoid colon of 20 women with colonic cancer (aged 40-55 years, average 49.6 years). A mechanographic technique was used to evaluate in vitro muscle responses to VIP and SP of adrenergic and cholinergic nerves before and after treatment with various autonomic nerve blockers.

RESULTS

Responses mediated by non-adrenergic non-cholinergic (NANC) inhibitory nerves were found in the normal colon, but were more frequently in the colon with STC than in the normal colon (p < 0.01). Responses mediated by excitatory nerves such as cholinergic nerves were more dominant in the normal colon than in the STC colon. At 1 x 10(-8), 1 x 10(-7), 1 x 10(-6) g/mL, VIP and SP in both the normal and STC colonic muscle strips produced a concentration-dependent relaxation to VIP and contraction to SP. In addition, the relaxation reaction to VIP in the colon with STC was also weaker than in the normal colon (p < 0.01). The contraction reaction to SP in the colon with STC was weaker than in the normal colon (p < 0.01). VIP acts through neural mechanisms, whereas SP may act both through nerves and also directly on both the normal and STC muscle strips.

CONCLUSIONS

Responses mediated by NANC inhibitory nerves were significantly increased in the colon with STC compared with the normal colon. A decrease of responses to peptidergic nerves such as SP and VIP may also play an important role in the impaired motility observed in the colon of patients with STC. These results indicate that the disturbances in the neural component of the enteric nervous system in the colon of women patients with STC may initiate or contribute to the functional changes.

[Neurologic inflammation and oral disease. An aetiopathogenic hypothesis]

The nervous system contributes to the pathophysiology of peripheral inflammation and a neurogenic component has been implicated in many inflammatory disease, including oral diseases. Neurogenic inflammation should be regarded as a protective mechanism wich forms the first line of defense and protects tissue integrity. However, prolonged noxius stimulation may result in the inflammatory response. This review focuses on the evidence suggesting that neuropeptides have a pivotal role in the complex cascade of chemical activity associated with oral diseases. The pathophysiology is complex and neuropeptides are not solely responsible for the initiation and progression of the disease. However, since neuropeptides and inflammatory modulators are released together during the inflammatory response, it will be impossible to assign a specific role to each until work with selective antagonists is completed.

CGRP, PACAP, and VIP Modulate Langerhans Cell Function by Inhibiting NF-κB Activation

The neuropeptides calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase-activating polypeptide (PACAP), and vasoactive intestinal peptide (VIP) suppress Langerhans cell (LC) antigen presentation and modulate cytokine production. We have tested the hypothesis that these neuropeptides (NP) inhibit LC function by modulating activation of NF-kappaB. Lipopolysaccharide (LPS) activates NF-kappaB in both a LC-like cell line (XS52) and epidermal LC enriched to approximately 95% and this effect is inhibited by each of the NP. Furthermore, CGRP, PACAP, and VIP suppress phosphorylation of IkappaB kinase beta (P-IKKbeta), prevent degradation of the IkappaB alpha, and inhibit activation of NF-kappaB. Thus, these NP modulate LC function by reducing NF-kappaB activation. Bay 11-7085, an inhibitor of IKK, reduced tumor necrosis factor-alpha (TNFalpha) production from LPS-stimulated XS52 cells and inhibited the ability of LC to present antigen to a T-cell clone in vitro. Each NP also inhibited LPS-induced secretion of TNFalpha by XS52 cells and LC enriched to approximately 95% homogeneity. We suggest that the inhibitory activities of CGRP, PACAP, and VIP on LC function are mediated, at least in part, by inhibition of P-IKKbeta, which prevents IkappaB alpha degradation and activation of NF-kappaB. Modulation of this signaling pathway may be useful for therapeutic modulation of immunity in the skin.