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

Postweaning Development Influences Endogenous VPAC1 Modulation of LTP Induced by Theta-Burst Stimulation: A Link to Maturation of the Hippocampal GABAergic System

Long-term potentiation (LTP) induced by theta-burst stimulation (TBS) undergoes postweaning developmental changes partially linked to GABAergic circuit maturation. Endogenous vasoactive intestinal peptide (VIP) acting on its VPAC1 receptor strongly influences LTP induced by theta-burst stimulation (TBS), an effect dependent on GABAergic transmission. Although VPAC1 receptor levels are developmentally regulated during embryogenesis, their variation along postweaning development is unknown, as is the VPAC1 modulation of LTP or its relation to hippocampal GABAergic circuit maturation. As such, we investigated how VPAC1 modulation of LTP adjusts from weaning to adulthood along with GABAergic circuit maturation. As described, LTP induced by mild TBS (5 bursts, 4 pulses delivered at 100 Hz) was increasingly greater from weaning to adulthood. The influence of the VPAC1 receptor antagonist PG 97-269 (100 nM) on TBS-induced LTP was much larger in juvenile (3-week-old) than in young adult (6-7-week-old) or adult (12-week-old) rats. This effect was not associated with a developmental decrease in synaptic VPAC1 receptor levels. However, an increase in pre and post-synaptic GABAergic synaptic markers suggests an increase in the number of GABAergic synaptic contacts that is more prominent than the one observed in glutamatergic connections during this period. Conversely, endogenous VPAC2 receptor activation did not significantly influence TBS-induced LTP. VPAC2 receptor levels enhance pronouncedly during postweaning development, but not at synaptic sites. Given the involvement of VIP interneurons in several aspects of hippocampal-dependent learning, neurodevelopmental disorders, and epilepsy, this could provide important insights into the role of VIP modulation of hippocampal synaptic plasticity during normal and altered brain development potentially contributing to epileptogenesis.

Advantages of Vasoactive Intestinal Peptide for the Future Treatment of Parkinson's Disease

Parkinson's disease is the second most common neurodegenerative disorder in adults over the age of 65. The characteristic symptoms of Parkinson's disease, such as resting tremor, muscular rigidity, bradykinesia, postural instability and gait imbalance, are thought to be a result of the progressive degeneration of the dopaminergic neurons of the substantia nigra compacta, resulting in insufficient dopamine integrated signalling on GABAergic medium spiny neurons in the striatum. Despite tremendous research, the molecular mechanisms underlying the pathogenesis of neurodegeneration in Parkinson's disease have remained largely unknown. Although a variety of possible pathogenic mechanisms have been proposed over the years, including excessive release of oxygen free radicals, impairment of mitochondrial function, loss of trophic support, abnormal kinase activity, disruption of calcium homeostasis, dysfunction of protein degradation and neuroinflammation, the pathogenesis is still largely uncertain, and there is currently no effective cure for Parkinson's disease. To develop potential therapies for Parkinson's disease, inflammatory processes, mitochondrial dynamics, oxidative stress, production of reactive aldehydes, excitotoxicity and synucleinopathies are to be targeted. In this respect, vasoactive intestinal peptide has beneficial effects that provide an advantage for the treatment of Parkinson's disease. Vasoactive intestinal peptide is a major neuropeptide-neurotransmitter having antioxidant, anti-inflammatory, neurotropic, neuromodulator, and anti-apoptotic properties. In addition to its direct neuroprotective actions regulating the activity of astrocytes, microglia and brain mast cells, it also plays important roles for neuronal adaptation, maintenance and survival.

Neuropeptides shaping the central nervous system development: Spatiotemporal actions of VIP and PACAP through complementary signaling pathways

Pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal peptide (VIP) are neuropeptides with wide, complementary, and overlapping distributions in the central and peripheral nervous systems, where they exert important regulatory roles in many physiological processes. VIP and PACAP display a large range of biological cellular targets and functions in the adult nervous system including regulation of neurotransmission and neuroendocrine secretion and neuroprotective and neuroimmune responses. As the main focus of the present review, VIP and PACAP also have been long implicated in nervous system development and maturation through their interaction with the seven transmembrane domain G protein-coupled receptors, PAC1, VPAC1, and VPAC2, initiating multiple signaling pathways. Compared with PAC1, which solely binds PACAP with very high affinity, VPACs exhibit high affinities for both VIP and PACAP but differ from each other because of their pharmacological profile for both natural accessory peptides and synthetic or chimeric molecules, with agonistic and antagonistic properties. Complementary to initial pharmacological studies, transgenic animals lacking these neuropeptides or their receptors have been used to further characterize the neuroanatomical, electrophysiological, and behavioral roles of PACAP and VIP in the developing central nervous system. In this review, we recapitulate the critical steps and processes guiding/driving neurodevelopment in vertebrates and superimposing the potential contribution of PACAP and VIP receptors on the given timeline. We also describe how alterations in VIP/PACAP signaling may contribute to both (neuro)developmental and adult pathologies and suggest that tuning of VIP/PACAP signaling in a spatiotemporal manner may represent a novel avenue for preventive therapies of neurological and psychiatric disorders. © 2016 Wiley Periodicals, Inc.

Altered distribution of hippocampal interneurons in the murine Down Syndrome model Ts65Dn

Down Syndrome, with an incidence of one in 800 live births, is the most common genetic alteration producing intellectual disability. We have used the Ts65Dn model, that mimics some of the alterations observed in Down Syndrome. This genetic alteration induces an imbalance between excitation and inhibition that has been suggested as responsible for the cognitive impairment present in this syndrome. The hippocampus has a crucial role in memory processing and is an important area to analyze this imbalance. In this report we have analysed, in the hippocampus of Ts65Dn mice, the expression of synaptic markers: synaptophysin, vesicular glutamate transporter-1 and isoform 67 of the glutamic acid decarboxylase; and of different subtypes of inhibitory neurons (Calbindin D-28k, parvalbumin, calretinin, NPY, CCK, VIP and somatostatin). We have observed alterations in the inhibitory neuropil in the hippocampus of Ts65Dn mice. There was an excess of inhibitory puncta and a reduction of the excitatory ones. In agreement with this observation, we have observed an increase in the number of inhibitory neurons in CA1 and CA3, mainly interneurons expressing calbindin, calretinin, NPY and VIP, whereas parvalbumin cell numbers were not affected. These alterations in the number of interneurons, but especially the alterations in the proportion of the different types, may influence the normal function of inhibitory circuits and underlie the cognitive deficits observed in DS.

Endogenous inhibition of hippocampal LTD and depotentiation by vasoactive intestinal peptide VPAC1 receptors

Vasoactive intestinal peptide (VIP), an important modulator of hippocampal synaptic transmission, influences exploration and hippocampal-dependent learning in rodents. Homosynaptic long-term depression (LTD) and depotentiation are two plasticity phenomena implicated in learning of behavior flexibility and spatial novelty detection. In this study, we investigated the influence of endogenous VIP on LTD and depotentiation induced by low-frequency stimulation (1 Hz, 900 pulses) of the hippocampal CA1 area in vitro in juvenile and young adult rats, respectively. LTD and depotentiation were enhanced by the VIP receptor antagonist Ac-Tyr(1) , D-Phe(2) GRF (1-29), and the selective VPAC1 receptor antagonist, PG 97-269, but not the selective VPAC2 receptor antagonist, PG 99-465. This action was mimicked by an anti-VIP antibody, suggesting that VIP, and not pituitary adenylate cyclase-activating polypeptide (PACAP), is the endogenous mediator of these effects. Selective inhibition of PAC1 receptors with PACAP (6-38) enhanced depotentiation, but not LTD. VPAC1 receptor blockade also revealed LTD in young adult rats, an effect abolished by the GABAA antagonist bicuculline, evidencing an involvement of GABAergic transmission. We conclude that inhibition of LTD and depotentiation by endogenous VIP occurs through VPAC1 receptor-mediated mechanisms and suggest that disinhibition of pyramidal cell dendrites is the most likely physiological mechanism underlying this effect. As such, VPAC1 receptor ligands may be considered promising pharmacological targets for treatment of cognitive dysfunction in diseases involving altered GABAergic circuits and pathological saturation of LTP/LTD like Down's syndrome and temporal lobe epilepsy.

Prenatal treatment prevents learning deficit in Down syndrome model

Down syndrome is the most common genetic cause of mental retardation. Active fragments of neurotrophic factors release by astrocyte under the stimulation of vasoactive intestinal peptide, NAPVSIPQ (NAP) and SALLRSIPA (SAL) respectively, have shown therapeutic potential for developmental delay and learning deficits. Previous work demonstrated that NAP+SAL prevent developmental delay and glial deficit in Ts65Dn that is a well-characterized mouse model for Down syndrome. The objective of this study is to evaluate if prenatal treatment with these peptides prevents the learning deficit in the Ts65Dn mice. Pregnant Ts65Dn female and control pregnant females were randomly treated (intraperitoneal injection) on pregnancy days 8 through 12 with saline (placebo) or peptides (NAP 20 µg +SAL 20 µg) daily. Learning was assessed in the offspring (8–10 months) using the Morris Watermaze, which measures the latency to find the hidden platform (decrease in latency denotes learning). The investigators were blinded to the prenatal treatment and genotype. Pups were genotyped as trisomic (Down syndrome) or euploid (control) after completion of all tests. Statistical analysis: two-way ANOVA followed by Neuman-Keuls test for multiple comparisons, P<0.05 was used to denote statistical significance. Trisomic mice who prenatally received placebo (Down syndrome -placebo; n = 11) did not demonstrate learning over the five day period. DS mice that were prenatally exposed to peptides (Down syndrome-peptides; n = 10) learned significantly better than Down syndrome -placebo (p<0.01), and similar to control-placebo (n = 33) and control-peptide (n = 30). In conclusion prenatal treatment with the neuroprotective peptides (NAP+SAL) prevented learning deficits in a Down syndrome model. These findings highlight a possibility for the prevention of sequelae in Down syndrome and suggest a potential pregnancy intervention that may improve outcome.

Cognitive and pharmacological insights from the Ts65Dn mouse model of Down syndrome

Down syndrome (DS) is a multi-faceted condition resulting in the most common genetic form of intellectual disability. Mouse models of DS, especially the Ts65Dn model, have been pivotal in furthering our understanding of the genetic, molecular and neurobiological mechanisms that underlie learning and memory impairments in DS. Cognitive and pharmacological insights from the Ts65Dn mouse model have led to remarkable translational progress in the development of therapeutic targets and in the emergence of DS clinical trials. Unravelling the pathogenic role of trisomic genes on human chromosome 21 and the genotype-phenotype relationship still remains a pertinent goal for tackling cognitive deficits in DS.

Molecular and cellular alterations in Down syndrome: toward the identification of targets for therapeutics

Down syndrome is a complex disease that has challenged molecular and cellular research for more than 50 years. Understanding the molecular bases of morphological, cellular, and functional alterations resulting from the presence of an additional complete chromosome 21 would aid in targeting specific genes and pathways for rescuing some phenotypes. Recently, progress has been made by characterization of brain alterations in mouse models of Down syndrome. This review will highlight the main molecular and cellular findings recently described for these models, particularly with respect to their relationship to Down syndrome phenotypes.

Altered expression of neuropeptides in the primary somatosensory cortex of the Down syndrome model Ts65Dn

Down syndrome is the most common genetic disorder associated with mental retardation. Subjects and mice models for Down syndrome (such as Ts65Dn) show defects in the formation of neuronal networks in both the hippocampus and the cerebral cortex. The principal neurons display alterations in the morphology, density and distribution of dendritic spines in the cortex as well as in the hippocampus. Several evidences point to the possibility that the atrophy observed in principal neurons could be mediated by changes in their inhibitory inputs and, in fact, an imbalance between excitation and inhibition has been observed in Ts65Dn mice in these regions, which are crucial for learning and information processing. These animals have an increased density of interneurons in the primary somatosensory cortex, especially of those expressing calretinin and calbindin D-28k. Here, we have analysed the expression and distribution of several neuropeptides in the primary somatosensory cortex of Ts65Dn mice in order to investigate whether these subpopulations of interneurons are affected. We have observed an increase in the total density of somatostatin expressing interneurons and of those expressing VIP in layer IV in Ts65Dn mice. The typology of the somatostatin and VIP interneurons was unaltered as attested by the pattern of co-expression with other markers. Somatostatin immunoreactive neurons co-express mainly D-28k calbindin and VIP expressing interneurons maintain its pattern of co-expression with calcium binding proteins. These alterations, in case they were also present in subjects with Down syndrome, could be related to their impairment in cognitive profile and could be involved in the neurological defects observed in this disorder.

Prevention of developmental delays in a Down syndrome mouse model

OBJECTIVE

To estimate whether prenatal treatment with neuroprotective peptides prevents the developmental delay and the glial deficit in the Ts65Dn mouse model for Down syndrome and to explore the peptides' effects on achievement of normal development.

METHODS

Pregnant Ts65Dn females were randomly assigned to NAPVSIPQ+SALLRSIPA or control and were treated by investigators blinded to treatment and genotype on gestational days 8-12. Offspring were tested from postnatal day 5 to 21 for motor and sensory milestones with standardized tests by operators blinded to the pup's treatment and genotype. The pup's genotype was determined after completion of all tests. Activity-dependent neurotrophic factor, glial fibrillary acidic protein, and vasoactive intestinal peptide expression were determined using real-time polymerase chain reaction.

RESULTS

Trisomic mice achieved milestones with a significant delay in four of five motor and sensory milestones. Trisomic mice that were prenatally exposed to NAPVSIPQ+SALLRSIPA achieved developmental milestones at the same time as the controls in three of four motor and one of four sensory milestones (P<.01). Euploid pups prenatally treated with NAPVSIPQ+SALLRSIPA achieved developmental milestones significantly earlier than the euploid pups prenatally treated with placebo. Activity-dependent neurotrophic factor expression was significantly downregulated in the Ts65Dn brains compared with the controls, prenatal treatment with NAPVSIPQ+ SALLRSIPA prevented the activity-dependent neurotrophic factor decrease in the Ts65Dn brains, and the expression was not different from the controls. The glial marker glial fibrillary acidic protein demonstrated the known glial deficit in the Ts65Dn mice, and treatment with NAPVSIPQ+ SALLRSIPA prevented its downregulation. Lastly, vasoactive intestinal peptide levels were increased in the trisomic brains, whereas treatment with NAPVSIPQ+SALLRSIPA did not prevent its upregulation.

CONCLUSION

Prenatal treatment with NAPVSIPQ and SALLRSIPA prevented developmental delay and the glial deficit in Down syndrome. These findings highlight a possibility for the prevention of developmental sequelae in Down syndrome and suggest a potential intervention during pregnancy that may improve the outcome.

Regardless of genotype, offspring of VIP-deficient female mice exhibit developmental delays and deficits in social behavior

Pharmacological studies indicate that vasoactive intestinal peptide (VIP) may be necessary for normal embryonic development in the mouse. For example, VIP antagonist treatment before embryonic day 11 resulted in developmental delays, growth restriction, modified adult brain chemistry and reduced social behavior. Here, developmental milestones, growth, and social behaviors of neonates of VIP-deficient mothers (VIP +/-) mated to VIP +/- males were compared with the offspring of wild type mothers (VIP +/+) mated to VIP +/+ and +/- males, to assess the contributions of both maternal and offspring VIP genotype. Regardless of their own genotype, all offsprings of VIP-deficient mothers exhibited developmental delays. No delays were seen in the offspring of wild type mothers, regardless of their own genotype. Body weights were significantly reduced in offspring of VIP-deficient mothers, with VIP null (-/-) the most affected. Regardless of genotype, all offspring of VIP-deficient mothers expressed reduced maternal affiliation compared with wild type offspring of wild type mothers; +/- offspring of wild type mothers did not differ in maternal affiliation from their wild type littermates. Play behavior was significantly reduced in all offsprings of VIP-deficient mothers. Maternal behavior did not differ between wild type and VIP-deficient mothers, and cross-fostering of litters did not change offspring development, indicating that offspring deficits were induced prenatally. This study illustrated that the VIP status of a pregnant mouse had a greater influence on the growth, development and behavior of her offspring than the VIP genotype of the offspring themselves. Deficiencies were apparent in +/+, +/- and -/- offspring born to VIP-deficient mothers; no deficiencies were apparent in +/- offspring born to normal mothers. These results underscore the significant contribution of the uterine environment to normal development and indicate a potential usefulness of the VIP knockout mouse in furthering the understanding of neurodevelopmental disorders with social behavior deficits such as autism.

Blockage of VIP during mouse embryogenesis modifies adult behavior and results in permanent changes in brain chemistry

Vasoactive intestinal peptide (VIP) regulates growth and development during the early postimplantation period of mouse embryogenesis. Blockage of VIP with a VIP antagonist during this period results in growth restriction, microcephaly, and developmental delays. Similar treatment of neonatal rodents also causes developmental delays and impaired diurnal rhythms, and the adult brains of these animals exhibit neuronal dystrophy and increased VIP binding. These data suggest that blockage of VIP during the development of the nervous system can result in permanent changes to the brain. In the current study, pregnant mice were treated with a VIP antagonist during embryonic days 8 through 10. The adult male offspring were examined in tests of novelty, paired activity, and social recognition. Brain tissue was examined for several measures of chemistry and gene expression of VIP and related compounds. Glial cells from the cortex of treated newborn mice were plated with neurons and examined for VIP binding and their ability to enhance neuronal survival. Treated adult male mice exhibited increased anxiety-like behavior and deficits in social behavior. Brain tissue exhibited regionally specific changes in VIP chemistry and a trend toward increased gene expression of VIP and related compounds that reached statistical significance in the VIP receptor, VPAC-1, in the female cortex. When compared to control astrocytes, astrocytes from treated cerebral cortex produced further increases in neuronal survival with excess synaptic connections and reduced VIP binding. In conclusion, impaired VIP activity during mouse embryogenesis resulted in permanent changes to both adult brain chemistry/cell biology and behavior with aspects of autism-like social deficits.

Vasoactive intestinal peptide antagonist treatment during mouse embryogenesis impairs social behavior and cognitive function of adult male offspring

Vasoactive intestinal peptide (VIP) is a regulator of rodent embryogenesis during the period of neural tube closure. VIP enhanced growth in whole cultured mouse embryos; treatment with a VIP antagonist during embryogenesis inhibited growth and development. VIP antagonist treatment during embryogenesis also had permanent effects on adult brain chemistry and impaired social recognition behavior in adult male mice. The neurological deficits of autism appear to be initiated during neural tube closure and social behavior deficits are among the key characteristics of this disorder that is more common in males and is frequently accompanied by mental retardation. The current study examined the blockage of VIP during embryogenesis as a model for the behavioral deficits of autism. Treatment of pregnant mice with a VIP antagonist during embryonic days 8 through 10 had no apparent effect on the general health or sensory or motor capabilities of adult offspring. However, male offspring exhibited reduced sociability in the social approach task and deficits in cognitive function, as assessed through cued and contextual fear conditioning. Female offspring did not show these deficiencies. These results suggest that this paradigm has usefulness as a mouse model for aspects of autism as it selectively impairs male offspring who exhibit the reduced social behavior and cognitive dysfunction seen in autism. Furthermore, the study indicates that the foundations of some aspects of social behavior are laid down early in mouse embryogenesis, are regulated in a sex specific manner and that interference with embryonic regulators such as VIP can have permanent effects on adult social behavior.