Regional distribution of guanine nucleotide-sensitive and guanine nucleotide-insensitive vasoactive intestinal peptide receptors in rat brain

Unconventional binding sites and receptors for VIP and related peptides PACAP and PHI/PHM: an update

The 28-amino-acid neuropeptide VIP and related peptides PACAP and PHI/PHM modulate virtually all of the vital functions in the body. These peptides are also commonly recognized as major regulators of cell growth and differentiation. Through their trophic and cytoprotective functions, they appear to play major roles in embryonic development, neurogenesis and the progression of a number of cancer types. These peptides bind to three well-characterized subtypes of G-protein coupled receptors: VPAC1 and VPAC2 share a common high affinity in the nanomolar range for VIP and PACAP; a third receptor type, PAC1, has been characterized for its high affinity for PACAP but its low affinity for VIP. Complex effects and pharmacological behaviors of these peptides suggest that multiple subtypes of binding sites may cooperate to mediate their function in target cells and tissues. In this complex response, some of these binding sites correspond to the definition of the conventional receptors cited above, while others display unexpected pharmacological and functional properties. Here we present potential clues that may lead investigators to further characterize the molecular nature and functions of these atypical binding species.

Neonatal mice of the Down syndrome model, Ts65Dn, exhibit upregulated VIP measures and reduced responsiveness of cortical astrocytes to VIP stimulation

The Ts65Dn segmental mouse model of Down syndrome (DS) possesses a triplication of the section of chromosome 16 that is most homologous to the human chromosome 21 that is trisomic in DS. This model exhibits many of the characteristics of DS including small size, developmental delays, and a decline of cholinergic systems and cognitive function with age. Recent studies have shown that vasoactive intestinal peptide (VIP) systems are upregulated in aged Ts65Dn mice and that VIP dysregulation during embryogenesis is followed by the hypotonia and developmental delays as seen in both DS and in Ts65Dn mice. Additionally, astrocytes from aged Ts65Dn brains do not respond to VIP stimulation to release survival-promoting substances. To determine if VIP dysregulation is age-related in Ts65Dn mice, the current study examined VIP and VIP receptors (VPAC-1 and VPAC-2) in postnatal day 8 Ts65Dn mice. VIP and VPAC-1 expression was significantly increased in the brains of trisomic mice compared with wild-type mice. VIP-binding sites were also significantly increased in several brain areas of young Ts65Dn mice, especially in the cortex, caudate/putamen, and hippocampus. Further, in vitro treatment of normal neurons with conditioned medium from VIP-stimulated Ts65Dn astrocytes from neonatal mice did not enhance neuronal survival. This study indicates that VIP anomalies are present in neonatal Ts65Dn mice, a defect occurs in the signal transduction mechanism of the VPAC-1 VIP receptor, cortical astrocytes from neonatal brains are dysfunctional, and further, that VIP dysregulation may play a significant role in DS.

Receptors for VIP and PACAP in guinea pig cerebral cortex: effects on cyclic AMP synthesis and characterization by 125I-VIP binding

Receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) in guinea pig cerebral cortex were characterized by (1) radioreceptor binding of 125I-labeled VIP (human/rat/porcine), and (2) cyclic AMP (cAMP) formation. Saturation analysis of 125I-VIP binding to membranes of guinea pig cerebral cortex resulted in a linear Scatchard plot, suggesting the presence of a single class of high-affinity receptor-binding sites, with a Kd of 0.63 nM and a B(max) of 77 fmol/mg protein. Various peptides from the PACAP/VIP/secretin family displaced the specific binding of 125I-VIP to guinea pig cerebrum with the relative rank order of potency: chicken VIP (cVIP) > or = PACAP38 approximately PACAP27 approximately guinea pig VIP (gpVIP) > or = mammalian (human/rat/porcine) VIP (mVIP) > peptide histidine-methionine (PHM) > peptide histidine-isoleucine (PHI) > secretin. Analysis of the competition curves revealed displacement of 125I-VIP from high- and lower-affinity binding sites, with IC50 values in the picomolar and the nanomolar range, respectively. About 70% of the specific 125I-VIP-binding sites in guinea pig cerebral cortex were sensitive to Gpp(NH)p, a nonhydrolyzable analog of GTP. Pituitary adenylate cyclase-activating polypeptide 38 (PACAP38), PACAP27, cVIP, gpVIP, mVIP, PHM, and PHI stimulated cAMP production in [3H]adenine-prelabeled slices of guinea pig cerebral cortex in a concentration-dependent manner. Of the tested peptides, the most effective were PACAP38 and PACAP27, which at a 1 microM concentration produced a 17- to 19-fold rise in cAMP synthesis, increasing the nucleotide production to approx 11% conversion above the control value. The three forms of VIP (cVIP, mVIP, and gpVIP) at the highest concentration used, i.e., 3 microM, produced net increases in cAMP production in the range of 8-9% conversion, whereas 5 microM PHM and PHI, by, respectively, 6.7% and 4.9% conversion. It is concluded that cerebral cortex of guinea pig contains VPAC- type receptors positively linked to cAMP formation. In addition, the observed stronger action of PACAP (both PACAP38 and PACAP27), when compared to any form of VIP, on cAMP production in this tissue, suggests its interaction with both PAC1 and VPAC receptors.

Vasoactive intestinal peptide in the brain of a mouse model for Down syndrome

The most common genetic cause of mental retardation is Down syndrome, trisomy of chromosome 21, which is accompanied by small stature, developmental delays, and mental retardation. In the Ts65Dn segmental trisomy mouse model of Down syndrome, the section of mouse chromosome 16 most homologous to human chromosome 21 is trisomic. This model exhibits aspects of Down syndrome including growth restriction, delay in achieving developmental milestones, and cognitive dysfunction. Recent data link vasoactive intestinal peptide malfunction with developmental delays and cognitive deficits. Blockage of vasoactive intestinal peptide during rodent development results in growth and developmental delays, neuronal dystrophy, and, in adults, cognitive dysfunction. Also, vasoactive intestinal peptide is elevated in the blood of newborn children with autism and Down syndrome. In the current experiments, vasoactive intestinal peptide binding sites were significantly increased in several brain areas of the segmental trisomy mouse, including the olfactory bulb, hippocampus, cortex, caudate/putamen, and cerebellum, compared with wild-type littermates. In situ hybridization for VIP mRNA revealed significantly more dense vasoactive intestinal peptide mRNA in the hippocampus, cortex, raphe nuclei, and vestibular nuclei in the segmental trisomy mouse compared with wild-type littermates. In the segmental trisomy mouse cortex and hippocampus, over three times as many vasoactive intestinal peptide-immunopositive cells were visible than in wild-type mouse cortex. These abnormalities in vasoactive intestinal peptide parameters in the segmental trisomy model of Down syndrome suggest that vasoactive intestinal peptide may have a role in the neuropathology of Down-like cognitive dysfunction.

Characterization of vasoactive intestinal peptide/pituitary adenylate cyclase-activating polypeptide receptors in chick cerebral cortex

In this study receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating polypeptide (PACAP) were characterized in chick cerebral cortex by an in vitro binding technique, using 125I-labeled VIP ([125I]-VIP) as a ligand. The specific binding of [125I]-VIP to chick cerebral cortical membranes was found to be rapid, stable, saturable, reversible, and of high affinity. Saturation analysis resulted in a linear Scatchard plot, suggesting binding to a single class of receptor binding sites with high affinity (Kd = 0.21 nM) and low capacity (Bmax = 19.5 fmol/mg protein). The relative rank order of potency of the tested peptides to inhibit [125I]-VIP binding to chick cerebrum was VIP (chicken) > or = VIP (mammalian) > or = PACAP27 > or = PACAP38 >> VIP6-28 (mammalian) > PHI (porcine) >> neurotensin6-11-chicken VIP7-28 > neurotensin6-11-mammalian VIP7-28 >>> VIP16-28 (chicken; inactive) approximately secretin (inactive). About 60% of [125I]-VIP-binding sites in chick cerebral cortex were sensitive to Gpp(NH)p, a nonhydrolyzable analog of GTP. It has been concluded that the cerebral cortex of chick, in addition to PAC1 receptors, contains a population of VPAC-type receptors.

VIP as a trophic factor in the CNS and cancer cells

The effects of vasoactive intestinal peptide (VIP) on the proliferation of central nervous system (CNS) and cancer cells were investigated. VIP has important actions during CNS development. During neurogenesis, VIP stimulates the proliferation and differentiation of brain neurons. Addition of VIP to embryonic mouse spinal cord cultures increases neuronal survival and activity dependent neurotrophic factor (ADNF) secretion from astroglial cells. VIP is an integrative regulator of brain growth and development during neurogenesis and embryogenesis. Also, VIP causes increased proliferation of human breast and lung cancer cells in vitro. VIP binds with high affinity to cancer cells, elevates the cAMP and increases gene expression of c-fos, c-jun, c-myc and vascular endothelial cell growth factor. The effects of VIP on cancer cells are reversed by VIPhybrid, a synthetic VPAC(1) receptor antagonist. VIPhyb inhibits the basal growth of lung cancer cells in vitro and tumors in vivo and potentiates the ability of chemotherapeutic drugs to kill cancer cells. Due to the high density of VPAC(1) receptors in cancer cells, VIP has been radiolabeled with 123I, 18F and 99mTc to image tumors. It remains to be determined if radiolabeled VIP analogs will be useful agents for early detection of cancer in patients.

Chemokine release is associated with the protective action of PACAP-38 against HIV envelope protein neurotoxicity

The envelope protein (gp120) of the human immunodeficiency virus produces neuronal cell death in cultures that can be prevented by co-treatment with pituitary adenylate activating peptide-38 (PACAP-38) or chemokines. To investigate the hypothesis that a functional relationship exists between these two protectants, the release of chemokines was measured in rat astrocyte cultures after PACAP-38 treatment. Chemokine analyses were performed by immunoaffinity capillary electrophoresis. Bell-shaped dose-responses for PACAP-mediated release of chemokines into the culture medium were observed with EC(50)'s of 3 x 10(15) M (RANTES: regulated upon activation normal T cell expressed and secreted), 3 x 10(-11) M (MIP-1 beta) and 10(-7)M (MIP-1 alpha). In addition, PACAP-mediated depletion of chemokines from cultured astrocytes exhibited inverted bell-shaped curves, with similar EC(50)'s to those observed for chemokine measurements of the medium. Comparative studies with structurally related peptides (vasoactive intestinal peptide [VIP] and secretin) revealed that PACAP was the most potent secretagogue for RANTES on astrocyte cultures. Gp120-mediated neuronal cell death was prevented by co-treatment with PACAP-38, although the efficacy of protection varied significantly among the gp120 isolates. A bi-model dose-response was observed with EC(50)'s of 3 x 10(-15) and 3 x 10(-11) M. Co-treatment with neutralizing antiserum to RANTES attenuated PACAP-mediated protection from toxicity associated with gp120. In contrast to previous studies with VIP and gp120 toxicity, co-treatment with anti-MIP-1 alpha did not affect PACAP-induced protection. These studies support the hypothesis that PACAP produces neuroprotection from gp120 toxicity, in part, through the release of RANTES and this mechanism is distinct from that observed with VIP.

The polypeptide PHI discriminates a GTP-insensitive form of VIP receptor in liver membranes

In early reports on 125I-VIP binding experiments in liver membranes, it has been proposed that, the VIP binding sites were partially sensitive to GTP. Here we confirm that the VIP binding sites of chicken liver membranes consisted mainly in bivalent VIP/PACAP receptors and that about 50% of the 125I-VIP binding capacity was not affected by the GTP analogue GppNHp. Part of these bivalent receptors also appeared to represent PHI binding sites. In GppNHp-treated membranes, the GTP-insensitive VIP binding sites displayed a 17-fold higher relative affinity than in control membranes for the VIP analogue PHI. Such data suggested that GTP-insensitive VIP receptors may correspond to a subclass of high-affinity PHI receptors. Cross-linking of 125 I-VIP or 125 I-PHI to their receptors, revealed 2 components of 48 and 60 kDa. The radiolabelling of the 60 kDa component was strongly affected by increasing concentrations of the GTP analogue but was modestly abolished by an excess of PHI. Conversely, the radiolabelling of the 48 kDa molecular form was not affected by the GTP analogue but was efficiently abolished by increasing concentrations of PHI. Taken together, the data suggest that the 48 kDa component expressed in chicken liver membranes display the properties of a GTP-insensitive VIP/PHI receptor that can be pharmacologically discriminated from the GTP-sensitive 60 kDa form, through its much higher affinity for PHI.

Pharmacologically distinct vasoactive intestinal peptide binding sites: CNS localization and role in embryonic growth

In vitro autoradiography with [125I]vasoactive intestinal peptide revealed that the vasoactive intestinal peptide analogue, stearyl-norleucine17 vasoactive intestinal peptide, reported to be inactive at adenylyl cyclase-linked receptors in astrocytes, displaced a subset of vasoactive intestinal peptide binding sites on rat brain sections. These sites were widespread in adult rat brains and enriched in the olfactory bulb and thalamus, and corresponded to previously demonstrated GTP-insensitive vasoactive intestinal peptide binding sites. Stearyl-norleucine17 vasoactive intestinal peptide also identified receptors in rat lung and liver. In the adult brain, the stearyl-norleucine analog displaced only GTP-insensitive vasoactive intestinal peptide binding sites. In contrast, stearyl-norleucine17 vasoactive intestinal peptide-displaceable sites in the embryonic day 9 mouse appeared to include both GTP-sensitive and GTP-insensitive binding sites. This observation suggested the presence of an embryonic vasoactive intestinal peptide receptor with distinct pharmacological properties. Treatment of whole cultured mouse embryos with stearyl-norleucine17 vasoactive intestinal peptide resulted in stimulation of embryonic growth, with the stearyl-norleucine analog equipotent to vasoactive intestinal peptide, but less efficacious at higher concentrations (10(-7) M). Embryonic growth was inhibited by pituitary adenylyl cyclase-activating peptide and 8-bromoadenosine 3',5'-cyclic monophosphate. In addition, 8-bromoadenosine 3',5'-cyclic monophosphate inhibited stearyl-norleucine17 vasoactive intestinal peptide-stimulated growth. The results of the current study support the hypothesis that vasoactive intestinal peptide regulation of early postimplantation embryonic growth occurs, at least in part, independently of adenylyl cyclase stimulation.

Expression of vasoactive intestinal peptide (VIP) receptors in human uterus

We show the existence of functional vasoactive intestinal peptide (VIP) receptors in normal human female genital tract (endometrium, myometrium, ovary and Fallopian tube) as well as in leiomyoma (a frequent uterine pathology). The correlation between VIP binding and stimulation of adenylyl cyclase activity for all studied tissues was linear (r = 0.86) suggesting the expression of VIP receptors throughout the human female genital tract. Immunodetection of VIP receptor subtypes gave different molecular weights for VPAC(1) (47 kDa primarily) and VPAC(2) (65 kDa), which may be due to different glycosylation extents. In conclusion, this study demonstrates the expression of both subtypes of VIP receptors and their functionality in human female genital tract, suggesting that this neuropeptide could play an important physiological and pathophysiological role at this level.

Regulation of postimplantation mouse embryonic growth by maternal vasoactive intestinal peptide

Vasoactive intestinal peptide (VIP) is an identified regulator of growth in the embryonic day (E) 9-11 mouse. Mouse embryonic and extra-embryonic tissues were studied to identify the source of VIP at this critical time. VIP and mRNA was detected in the decidua/trophoblast at E8 and declined until E10, after which it was not detectable. VIP mRNA was not apparent in the embryo until E11-E12. At E9, cells in decidua had VIP as well as lymphocyte marker (delta and CD3) immunoreactivity. VIP binding sites were dense in the decidua/trophoblast at E6, which gradually decreased until E10. VIP binding sites were detected in embryonic neuroepithelium by E9. The transient presence of VIP binding sites and mRNA in the decidua/trophoblast correlate with the identified period of VIP growth regulation, when VIP mRNA is absent in the embryo. Therefore, these findings suggest that maternal decidual lymphocytes are the source of VIP that regulate early postimplantation embryonic growth.

Maternal regulation of embryonic growth: the role of vasoactive intestinal peptide

Vasoactive intestinal peptide (VIP) is an important growth regulator of the embryonic day (E)9-E11 mouse. In comparably aged rat embryos, VIP messenger RNA (mRNA) is not detectable; however, peak concentrations of VIP in maternal rat serum indicate a nonembryonic source. In the current study, mouse maternal and embryonic tissues were examined from E6-E12. Although RT-PCR revealed VIP mRNA in E6-E7 conceptuses, by E8 (when extraembryonic tissues could be separated from the embryo), VIP mRNA was detected only in the decidua/trophoblast. Decidual/trophoblastic VIP mRNA decreased until E10, after which it was not detectable. VIP mRNA was not apparent in the embryo until E11-E12. At E9, VIP immunoreactivity was localized to abundant, diffuse cells in the decidua basalis, which were also immunoreactive for T cell markers. VIP binding sites were dense in the decidua/trophoblast at E6, but gradually decreased until E10, after which they were not apparent. VIP binding sites were detected in embryonic neuroepithelium by E9. The transient presence of VIP binding sites and mRNA in the decidua/trophoblast correlate with the critical period of VIP growth regulation, when VIP mRNA is absent in the embryo. These findings suggest that maternal lymphocytes are the source of VIP's regulating early postimplantation embryonic growth.

Vasoactive intestinal peptide shortens both G1 and S phases of neural cell cycle in whole postimplantation cultured mouse embryos

Vasoactive intestinal peptide, a trophic and mitogenic factor, stimulates growth in whole cultured mouse embryos. Inhibition of this growth function between embryonic days 9 and 11 induces growth retardation accompanied by severe microcephaly. In the present study, to determine the effects of this peptide on the different phases of the cell cycle of neural cells, embryonic day 9.5 cultured mouse embryos were cumulatively labelled with bromodeoxyuridine. Vasoactive intestinal peptide (10(-7)M) shortened S phase and G1 phase of neuroepithelial cells by 50% (4.8-2.4 h) and 58% (1.9-0.8 h), respectively, compared with controls. G2 and M phases were not modified by vasoactive intestinal peptide treatment. Total cell cycle length was consequently reduced by 43% (8.2-4.7 h) in vasoactive intestinal peptide treated embryos, compared with controls. In contrast, vasoactive intestinal peptide did not modify the rate of neuroepithelial cell death as assessed by the proportion of nuclei containing fragmented DNA. These data suggest that vasoactive intestinal peptide stimulates growth in premigratory stages of nervous system development by shortening S and G1 phases of the cell cycle and that S phase duration can be regulated by a physiological peptide.

Circadian changes in the expression of vasoactive intestinal peptide 2 receptor mRNA in the rat suprachiasmatic nuclei

The suprachiasmatic nuclei (SCN) in the hypothalamus function as the primary circadian pacemaker. A receptor for vasoactive intestinal peptide (VIP), denoted as VIP2, is abundantly expressed in the SCN. Since the rodent circadian clock demonstrates phase-dependent sensitivity to exogenous VIP, we investigated the possibility that VIP2 receptor mRNA is differentially expressed in the SCN across the 24 h cycle. To establish whether VIP2 receptor mRNA levels change across the 12:12 h light-dark (LD) cycle (lights on designated as Zeitgeber time (ZT)O), rats were killed at ZT 0, 2, 6, 10, 12, 14, 18 and 22. To determine if variation in this mRNA occurs in the absence of LD entrainment cues, lights were not turned on at the time of transition from dark to light (designated as CT O); the animals in this group were killed in constant darkness (DD) at CT 0, 2, 6, 10, 12, 14, 18 and 22. In situ hybridization histochemistry indicated no variations in VIP2 receptor mRNA in the cingulate cortex under either LD or DD conditions. There was, however, significant variation in the expression of VIP2 receptor mRNA within the SCN during the LD cycle, with one peak at ZT 6 and at ZT 22. A comparable biphasic pattern of mRNA expression was observed in DD animals with peaks at CT 10 and another at CT 22. The results suggest that the phase-dependent actions of VIP on the clock may involve phase-specific changes in the availability of VIP2 receptor within the SCN.

Vasoactive intestinal peptide prevents excitotoxic cell death in the murine developing brain

Excitotoxic damage may be a critical factor in the formation of brain lesions associated with cerebral palsy. When injected at birth, the glutamatergic analog ibotenate induces mouse brain lesions that strikingly mimic human microgyria. When ibotenate is injected at postnatal day 5, it produces transcortical necrosis and white matter cysts that mimic human perinatal hypoxic-like lesions. Vasoactive intestinal peptide (VIP) has potent growth-related actions and neuroprotective properties that influence mitosis and neuronal survival in culture. The goal of this study was to assess the protective role of VIP against excitotoxic lesions induced by ibotenate in developing mouse brain. VIP cotreatment reduced ibotenate-induced microgyric-like cortical lesions and white matter cysts by up to 77 and 85%, respectively. VIP protective effects were reproduced by a peptide derived from activity-dependent neurotrophic factor (ADNF), a trophic factor released by VIP-stimulated astrocytes, and by stearyl norleucine VIP, a specific VIP agonist that does not activate adenylate cyclase. Neither forskolin, an adenylate cyclase activator, nor pituitary adenylate cyclase-activating peptide, provided VIP-like protection. VIP and neurotrophic analogs, acting through a cAMP-independent mechanism and inducing ADNF release, could represent new avenues in the understanding and prevention of human cerebral palsy.

Sites of gene expression for vasoactive intestinal polypeptide throughout the brain of the chick (Gallus domesticus)

The peptide neurotransmitter vasoactive intestinal polypeptide (VIP) has several important functions in vertebrates, particularly, influencing the neuroendocrine and autonomic nervous systems both in developing and in adult animals. To document potential brain areas that might play significant functional roles, the distribution of VIP mRNA was examined throughout the entire chick brain by using in situ hybridization histochemistry (ISHH). In addition, a VIP binding-site study was completed that focused on the lateral septal organ (LSO), a circumventricular organ of potential significance in avian species. The areas where VIP message was found included the olfactory bulbs, posterior hippocampus, parahippocampal area, hyperstriatum, archistriatum/nucleus (n.) taenia (amygdala), medial part of the LSO, organum vasculosum of the lamina terminalis, medial preoptic region, bed n. of the pallial commissure, anterior hypothalamic (hypo.) n., lateral hypo. area (most extensive and dense message), periventricular hypo. n., lateral to the paraventricular n., ventromedial hypo. n., stratum cellulare externum, inferior hypo. n., infundibular hypo. n., median eminence, three layers within the stratum griseum et fibrosum superficiale, area ventralis of Tsai, n. tegmenti pedunculopontinus pars compacta (substantia nigra), intercollicular n., central gray, locus ceruleus, parabrachial n., ventrolateral medulla, reticular pontine area, in and about the n. vestibularis descendens. When compared with immunocytochemistry that detected the presence of the peptide product VIP, more areas of the brain were found to contain perikarya expressing VIP by using ISHH, particularly in the telencephalon and the mesencephalon. VIP binding sites were found in the lateral portion of the LSO where the blood-brain barrier is not fully developed. Hence, the LSO was found to contain neural elements that synthesize as well as bind VIP. VIP appears to be a useful peptide for defining major components of the visceral forebrain system in birds.

Decreased absolute levels of ascorbic acid and unaltered vasoactive intestinal polypeptide receptor binding in the frontal cortex in acquired immunodeficiency syndrome

VIP receptor binding in the frontal cortex, a region with substantial neuronal loss, was unaltered in individuals who had died of acquired immunodeficiency syndrome (AIDS) neurotoxicity. In contrast, ascorbic acid, which suppresses human immunodeficiency virus (HIV) replication and modulates glutamatergic neuronal activity, was reduced by nearly 60% in the same brain region. These findings indicate that while neurons containing ascorbic acid may be lost, vasoactive intestinal polypeptide (VIP) receptor bearing cells remain viable. This finding supports previous observations that VIP prevents HIV induced neuronal death. The reduced ascorbic acid levels may contribute to particular neurons being vulnerable to damage from oxidative stress and possibly clinically to the development of dementia.

Neurobehavioral development of neonatal mice following blockade of VIP during the early embryonic period

Previous work has shown that blockade of VIP function in the early postimplantation embryo results in growth retardation and microcephaly. In the present work, the neurobehavioral development of neonatal mice was examined following treatment of dams with a VIP antagonist during this period. Inhibition of VIP functions during early embryogenesis impaired the performance of 5 of 10 developmental behaviors. These behaviors included developmental milestones (first appearance of ear twitch and eye opening) and complex motor behaviors (negative geotaxis, surface righting, and air righting). The retardation of neurobehavioral development produced by inhibition of VIP action indicates that this peptide is important to the progression of embryonic development.

VIP regulation of embryonic growth

Vasoactive intestinal peptide (VIP) plays a regulatory role in the growth of early postimplantation rodent embryos through its action on receptors localized to the central nervous system (CNS). However, the origin of the VIP influencing embryonic growth is unknown. VIP binding sites have been found prenatally; however, VIP mRNA was not detected in the rat CNS before birth and has been detected in peripheral organs only during the final third of gestation. Recent studies have revealed that VIP receptors were limited to the CNS in the embryonic day 11 (E11) rat embryo/trophoblast, which, in addition, had almost four times the VIP concentration of the E17 fetus. However, neither in situ hybridization or reverse transcriptase-polymerase chain reaction methods detected VIP mRNA in the E11 rat embryo or embryonic membranes. Rat maternal serum revealed a peak in VIP concentration at days E10-E12 of pregnancy, with VIP levels 6- to 10-fold higher than later during pregnancy. Radiolabeled VIP, administered intravenously to pregnant female mice, was found in the E10 embryo. These results suggest that VIP produced by extraembryonic tissues may regulate embryonic growth during the early postimplantation stage of development in the rodent.

Maternal vasoactive intestinal peptide and the regulation of embryonic growth in the rodent

Vasoactive intestinal peptide (VIP) has been shown to regulate early postimplantation growth in rodents through central nervous system receptors. However, the source of VIP mediating these effects is unknown. Although VIP binding sites are present prenatally, VIP mRNA was not detected in the rat central nervous system before birth and was detected in the periphery only during the last third of pregnancy. In the present study, the embryonic day (E11) rat embryo/trophoblast was shown to have four times the VIP concentration of the E17 fetus and to have VIP receptors in the central nervous system. However, no VIP mRNA was detected in the E11 rat embryo or embryonic membranes by in situ hybridization or reverse transcriptase-PCR. RIA of rat maternal serum revealed a peak in VIP concentration at days E10-E12 of pregnancy, with VIP rising to levels 6-10-fold higher than during the final third of pregnancy. After intravenous administration of radiolabeled VIP to pregnant female mice, undegraded VIP was found in the E10 embryo. These results suggest that maternal tissues may provide neuroendocrine support for embryonic growth through a surge of VIP during early postimplantation development in the rodent.

Photoperiodic exposure and time of day modulate the expression of arginine vasopressin mRNA and vasoactive intestinal peptide mRNA in the suprachiasmatic nuclei of Siberian hamsters

In hamsters, changes in ambient photoperiod lead to alterations in the circadian rhythm of pineal melatonin secretion and subsequent changes in reproductive function. The present study examined whether photoperiod also alters 24-h rhythms in neuropeptide mRNA levels in the SCN of Siberian hamsters. In situ hybridization and quantitative autoradiography were used to assess messenger RNA levels for vasopressin (AVP) and vasoactive intestinal peptide (VIP) in the SCN of hamsters sacrificed at six times of day following exposure to long (16 h light/day) or short (10 h light/day) photoperiod for 2 weeks. Both AVP mRNA and VIP mRNA in the SCN were significantly affected by time of day and photoperiodic exposure. The 24-h profiles of AVP mRNA and VIP mRNA showed different relationships to the light: dark cycle, suggesting that these profiles are differentially regulated. In general, short photoperiod tended to suppress AVP mRNA and VIP mRNA in the SCN; this effect on AVP mRNA was significant at two times of day. These results complement and extend previous findings of 24-h h profiles in neuropeptide mRNA expression in the rat SCN by showing that these 24-h profiles are also characteristic of the Siberian hamster SCN and that they can be modulated by photoperiod.

The distribution of vasoactive intestinal peptide2 receptor messenger RNA in the rat brain and pituitary gland as assessed by in situ hybridization

The distribution of rat vasoactive intestinal peptide2 (VIP2) receptor messenger RNA in the brain and the pituitary gland was examined by in situ hybridization and by ribonuclease protection assay. labelled cells were found chiefly in the suprachiasmatic nucleus, the central nucleus of the amygdala and the thalamus (the lateral geniculate nucleus, and the paraventricular, mediodorsal and ventral nuclei of the thalamus). The distribution of the VIP2 receptor overlaps only in part with that of the VIP1 receptor, for example in the hippocampus, where VIP2 receptor messenger RNA was found in the pyramidal cells of the CA1-CA3 subfields and in the granule cells of the dentate gyrus. Small numbers of neurons containing high concentrations of VIP2 receptor messenger RNA were present in the brainstem in the principal sensory trigeminal nucleus and in the substantia gelatinosa of the spinal cord, suggesting a role for the VIP2 receptor in the processing of sensory information. The presence of the VIP2 receptor in the suprachiasmatic nucleus suggests that it is this receptor subtype which is involved in the control of circadian rhythms.

VIP as a cell-growth and differentiation neuromodulator role in neurodevelopment

In addition to its commonly recognized status as a neuromodulator of virtually all vital functions, including neurobiological, the neuropeptide VIP plays a role in the control of cell growth and differentiation and of neuronal survival. Through these actions, VIP, whose impact appears early in ontogeny, may possess developmental functions. VIP can be stimulatory or inhibitory on cell growth in function of the model considered. The growth regulatory actions of VIP, which are often independent of cAMP, are most likely significant when mitogenic or trophic factors, eventually released by nontarget cells, are simultaneously present in the extracellular medium. The intracellular mechanisms that mediate these actions of VIP may involve different transduction cascades triggered by subsets of VIP binding sites that may coexist in the same tissue.

Severe microcephaly induced by blockade of vasoactive intestinal peptide function in the primitive neuroepithelium of the mouse

Vasoactive intestinal peptide (VIP) has potent growth-related actions that influence cell mitosis, neuronal survival, and neurodifferentiation in cell culture. VIP can also produce dramatic growth in postimplantation mouse embryos in vitro, characterized by large increases in cell number. The goal of the present study was to assess the role of VIP on early nervous system development in vivo. Pregnant mice were treated with a specific antagonist to VIP. Prenatal administration of the antagonist early in development (E9-E11) produced severe microcephaly characterized by decreased embryonic brain weight with reduced DNA and protein content. The retardation of growth was disproportionally manifested in the brain compared with the body and was prevented by co-treatment with VIP. Identical treatment with the antagonist later in gestation had no detectable effect on embryonic growth. VIP receptors, which were restricted to the central nervous system during this stage of embryonic development, were increased in the neuroepithelium of antagonist-treated embryos while the number of cells in S-phase was significantly decreased. Thus, VIP regulates brain growth in vivo and inhibition of its action provides new insight into a molecular mechanism for microcephaly.

Distribution of VIP mRNA and two distinct VIP binding sites in the developing rat brain: relation to ontogenic events

The peptide neurotransmitter vasoactive intestinal peptide (VIP) has neurotrophic properties and influences neurobehavioral development. To assess the role of VIP during neural ontogeny, the present work traces the development of VIP mRNA with in situ hybridization and VIP receptors with in vitro autoradiography in rat central nervous system (CNS) from embryonic day 14 (E14) to the adult. VIP mRNA was not evident in the CNS until birth. Postnatally, it was expressed in several distinct brain regions, but its distribution bore little relation to that of VIP receptors. VIP receptors were present and expressed changing patterns of distribution throughout CNS development. The changing patterns were the result of 1) the transient appearance of GTP-insensitive VIP receptors in several regions undergoing mitosis or glial fasciculation and 2) the transient appearance of GTP-sensitive VIP receptors homogeneously distributed throughout the CNS during the first 2 postnatal weeks, the period of the brain growth spurt. At E14-16 VIP binding was dense throughout the brainstem and spinal cord, but limited in the rest of the brain. From E19 to postnatal day 14 (P14), while VIP binding was higher in germinal zones, it tended to be uniformly dense throughout the remainder of the brain. By P21 the adult pattern began to emerge; VIP binding was unevenly distributed and was related to specific cytoarchitectural sites. Since the expression of VIP in the CNS is limited to postnatal development but VIP receptors are abundant prenatally, we suggest that extraembryonic VIP may act upon prenatal VIP receptors to regulate ontogenic events in the brain.

Molecular cloning and functional characterization of a human liver vasoactive intestinal peptide receptor

We have isolated a cDNA from a human liver library which is 2349 base pairs in length and encodes a near-full length seven transmembrane receptor (432 amino acids), 85% homologous to the amino acid sequence for the rat vasoactive intestinal peptide (VIP) receptor. Northern blot analysis identifies a major species at 3.3 kb in lung, and to a lesser extent in brain, heart and liver. In order to confirm the identity of this human clone, double-stranded oligonucleotides encoding the signal peptide of the rat VIP receptor were constructed by polymerase chain reaction and attached to the 5' end of the human clone. COS cells transiently transfected with this human VIP receptor chimera, express a single binding site for 125I-VIP with a Kd of 9.2 +/- 2 nM. Related peptides displace 125I-VIP with a relative potency of VIP = PACAP > helodermin >> PHM > secretin, which is similar to the binding profile seen in human tissues. This human chimeric receptor is functionally coupled to the stimulation of adenylyl cyclase in transfected COS cells, as evidenced by a dose-dependent increase in intracellular cAMP accumulation. These studies indicate that this cDNA encodes a human liver VIP receptor which is functionally coupled to the activation of adenylyl cyclase.

Rapid alterations in cAMP accumulation in brain nuclei of rats following microinjections of vasoactive intestinal polypeptide (VIP) into the lateral ventricle

The in vivo effect of exogenous vasoactive intestinal polypeptide (VIP) on the accumulation of cAMP in 21 microdissected brain nuclei was investigated 3 and 7 min after intraventricular injections in rats. VIP elicited significant (up to 20-fold) increases in cAMP levels. This effect is region specific varying considerably among the brain regions investigated. VIP dramatically increased the cAMP content of the lateral septal nucleus, several hypothalamic nuclei, the habenula, the midbrain central gray and the locus coeruleus. Smaller increases were observed elsewhere including some VIP-rich brain areas such as the cerebral cortex and the hippocampus.

The VIP2 receptor: molecular characterisation of a cDNA encoding a novel receptor for vasoactive intestinal peptide

We have cloned and sequenced a cDNA (RPR4) encoding a new member of the secretin/calcitonin/parathyroid hormone (PTH) receptor family. RPR4 was identified by PCR of rat pituitary cDNA, and a full-length clone was isolated from a rat olfactory bulb cDNA library. When RPR4 was functionally expressed in COS 7 cells, cyclic adenosine monophosphate (cAMP) production was stimulated by vasoactive intestinal peptide (VIP), pituitary adenylate cyclase activating peptides (PACAP-38 and PACAP-27) and helodermin, with equal potency. Peptide histidine isoleucine (PHI) and rat growth hormone releasing hormone (rGHRH) also stimulated cAMP production at lower potency. This suggests that RPR4 encodes a novel VIP receptor which we have designated the VIP2 receptor. In situ hybridisation showed that mRNA for this receptor was present mainly in the thalamus, hippocampus and in the suprachiasmatic nucleus.

Expression of multiple alpha adrenergic receptor subtype messenger RNAs in the adult rat brain

Multiple subtypes of alpha adrenergic receptors with CNS expression (alpha 1A, alpha 1B, alpha 2A and alpha 2C) have been identified through pharmacological and molecular biological means. To characterize the localization of these subtypes and attempt to correlate subtype expression with physiological significance, the expression of the mRNAs encoding the alpha 1A, alpha 1B, alpha 2A and alpha 2C adrenergic receptor subtypes was examined in the adult rat brain by in situ hybridization histochemistry. Each subtype demonstrated a unique pattern of distribution, with the alpha 1 adrenergic receptors more restricted in their distribution and the alpha 2 receptors more widespread. The alpha 1A was primarily localized in the olfactory bulb, intermediate layers of the cortex, the hippocampus and the reticular nucleus of the thalamus. The alpha 1B was expressed in intermediate and deep layers of the cortex, thalamus, hippocampus, dorsal raphe and cerebellum. Although the alpha 2A message was relatively low in abundance, it was identified in the olfactory bulb, cortex, hippocampus, locus coeruleus, pons and cerebellum. The alpha 2C messenger RNA was localized in the cortex (particularly cingulate), hippocampus, caudoputamen, pons and cerebellum. Multiple alpha adrenergic receptor subtypes have significant sequence homology and similar pharmacologic properties; however, they each possess a unique pattern of messenger RNA distribution throughout the brain. The multiplicity of subtypes of alpha adrenergic receptors in specific brain regions may dictate the physiological and pharmacological responses to catecholamines.

[125I]Vasoactive intestinal peptide binding in rodent suprachiasmatic nucleus: developmental and circadian studies

The suprachiasmatic nucleus (SCN) of rat and hamster have been studied extensively and shown to play critical roles in circadian rhythmicity. [125I]Vasoactive intestinal peptide (VIP) binding levels are high in the rat SCN, suggesting that VIP receptors may be an important component of SCN function. In contrast to previously demonstrated diurnal variations in VIP immunoreactivity and VIP mRNA, the present study found [125I]VIP binding to be stable across the light-dark cycle in both rat and hamster SCN. High [125I]VIP labeling appeared to be coextensive with the rat SCN but extended somewhat beyond the cytoarchitectonic boundaries of the hamster SCN. Binding density in hamster SCN was slightly higher than in rat. In the developing rat SCN, [125I]VIP binding levels distinguished the SCN on embryonic day 18, and appeared to increase to postnatal day 10 before declining to adult levels. The early presence of [125I]VIP binding suggests possible involvement of VIP receptors in fetal entrainment of circadian rhythms.

Growth factor function of vasoactive intestinal peptide in whole cultured mouse embryos

Factors controlling central nervous system (CNS) growth immediately after neurulation are mostly unknown. Vasoactive intestinal peptide (VIP) receptors are widely distributed in the embryonic nervous system, and VIP has trophic and mitogenic properties on embryonic neural tissues but inhibits growth and mitosis in certain tumours. To address the potential effects of VIP on embryonic growth, we used whole postimplantation embryo cultures. After a 4-h incubation, VIP stimulated growth, increasing somite number, embryonic volume, DNA and protein content, and number of cells in S-phase. A VIP antagonist substantially inhibited these VIP-mediated increments in growth. The VIP antagonist completely suppressed VIP-stimulated mitosis in the CNS while decreasing the same in non-neuronal tissues by 38%. In vitro autoradiography revealed GTP-sensitive and GTP-insensitive VIP receptors which were differentially regulated in VIP antagonist-treated embryos. The present study suggests that VIP acts as a growth factor on early postimplantation embryos through multiple VIP receptors that exhibit tissue-specific responses.