ZNC(C)PR affects developmental changes of P46 phosphorylation in rat hippocampus

AVP(4-8) Improves Cognitive Behaviors and Hippocampal Synaptic Plasticity in the APP/PS1 Mouse Model of Alzheimer's Disease

Memory deficits with aging are related to the neurodegeneration in the brain, including a reduction in arginine vasopressin (AVP) in the brain of patients with Alzheimer's disease (AD). AVP(4-8), different from its precursor AVP, plays memory enhancement roles in the CNS without peripheral side-effects. However, it is not clear whether AVP(4-8) can improve cognitive behaviors and synaptic plasticity in the APP/PS1 mouse model of AD. Here, we investigated for the first time the neuroprotective effects of AVP(4-8) on memory behaviors and in vivo long-term potentiation (LTP) in APP/PS1-AD mice. The results showed that: (1) APP/PS1-AD mice had lower spontaneous alternation in the Y-maze than wild-type (WT) mice, and this was significantly reversed by AVP(4-8); (2) the prolonged escape latency of APP/PS1-AD mice in the Morris water maze was significantly decreased by AVP(4-8), and the decreased swimming time in target quadrant recovered significantly after AVP(4-8) treatment; (3) in vivo hippocampal LTP induced by high-frequency stimulation had a significant deficit in the AD mice, and this was partly rescued by AVP(4-8); (4) AVP(4-8) significantly up-regulated the expression levels of postsynaptic density 95 (PSD95) and nerve growth factor (NGF) in the hippocampus of AD mice. These results reveal the beneficial effects of AVP(4-8) in APP/PS1-AD mice, showing that the intranasal administration of AVP(4-8) effectively improved the working memory and long-term spatial memory of APP/PS1-AD mice, which may be associated with the elevation of PSD95 and NGF levels in the brain and the maintenance of hippocampal synaptic plasticity.

Cloning of cytidine triphosphate: phosphocholine cytidylyltransferase mRNA upregulated by a neuropeptide arginine-vasopressin((4-8)) in rat hippocampus

Neuropeptide arginine-vasopressin((4-8)) (AVP(4-8)) is a metabolite of arginine-vasopressin which has been shown to have potent memory-enhancing activity, facilitate neurite elongation and prolongate cell aging. Identification of differentially expressed genes in hippocampus induced by AVP(4-8) is important for understanding the molecular basis of AVP(4-8) function. Differential display PCR and 5'rapid amplification of cDNA Ends were used. One new full length cDNA encoding rat cytidine triphosphate: phosphocholine cytidylyltransferase (CCT) beta was thus obtained. Northern blot analysis demonstrated that it was upregulated by AVP(4-8) in mature rat hippocampus. The study of tissue distribution with reverse transcription PCR showed that the gene was abundant in brain. Since CCT catalyzes the formation of cytidine diphosphate choline, which was reported to have a beneficial therapeutic effect on Alzheimer's disease, so we speculated that AVP(4-8) may be a potential candidate for treating Alzheimer's disease by upregulating CCT mRNA level.

Biochemistry of vasopressin fragments

Vasopressin (VP) undergoes a step-wise aminopeptidase conversion process in the brain, leading to accumulation of several metabolites. Some of these metabolites, in particular [pGlu4,Cyt6]VP 4-9 and 4-8, show behavioral effects comparable to VP, but are more potent and selective than VP. Most data favor the existence of a separate receptor for the VP metabolites distinct of the classical VP and oxytocin receptors, although its identity has remained obscure thus far. The characterization of this receptor is a major challenge to understand how the brain VP system generates and regulates divers central functions.

Function and molecular basis of action of vasopressin 4-8 and its analogues in rat brain

VP 4-8 as a highly potent behavioral-active metabolite of arginine-vasopressin (VP) has been studied in detail at four levels, i.e. ligand level, membrane binding level, intracellular level and nuclear level. The purpose of this chapter is to review and discuss the main results obtained from our recent pharmacological and biochemical investigations which are described as follows: 1, structure-function relationship of VP 4-8 and its analogs; 2, some characters of VP 4-8-specific binding, the distribution of the binding sites in the rat brain and the consequent effect on long-term potentiation of synaptic transmission; 3, a putative receptor-mediated signaling pathway involving second messenger IP3, immediately-early gene c-fos transcription and protein kinase PKC, CaMKII and MAPK; 4, peptide-induced enhancement of some crucial functional proteins such as calmodulin, nerve growth factor (NGF) and brain-derived nerve growth factor (BDNF). The physiological significance of the events following VP 4-8 administration and particularly, its possible role in learning and memory processes are discussed.

Facilitation of AVP(4-8) on gene expression of BDNF and NGF in rat brain

In situ hybridization and Northern blot assay were used to evaluate the effects of exogenous AVP(4-8) on the transcription of mRNAs for nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT-3) in the adult rat brain. NGF and BDNF expression was found to be significantly enhanced by AVP(4-8) administration in the cerebral cortex and hippocampus, but NT-3 expression was not changed. In the same conditions, behavior-active arginine-vasopressin (AVP) showed a small effect and its behavior-inactive homologue, oxytocin did not. Our results suggest that selective regulation of neurotrophin gene expression by the peptides may be responsible for its memory-enhancing function.

Molecular neurobiology and pharmacology of the vasopressin/oxytocin receptor family

1. VP and OT mediate their wealth of effects via 4 receptor subtypes V1a, V1b, V2, and OT receptors. 2. We here review recent insights in the pharmacological properties, structure activity relationships, species differences in ligand specificity, expression patterns, and signal transduction of VP/OT receptor. 3. Furthermore, the existence of additional VP/OT receptor subtypes is discussed.

Enhancement of NGF gene expression in rat brain by the memory-enhancing peptide AVP(4-8)

Northern blot analysis of nerve growth factor (NGF) was used to evaluate the effect of exogenous AVP(4-8) on the transcription of NGF gene in rat brain. NGF expression was found to be significantly enhanced by exogenous AVP(4-8) in the hippocampus as well as in the cerebral cortex in a time period of 12 h. This effect was inhibited by an antagonist to AVP(4-8). In addition, gel mobility shift assay was also used to observe the in vitro expression of c-fos gene in rat hippocampal slices. Our results suggest that NGF gene is one of the target genes responsible for memory-enhancing responses induced by AVP(4-8) and that the enhancement of NGF gene expression may share the signaling pathway mediated by AVP(4-8) receptor and c-fos gene expression.

Characterization of binding sites of a memory-enhancing peptide AVP(4-8) in rat cortical synaptosomal membranes

The pentapeptide pGlu-Asn-Cyt-Pro-Arg [AVP(4-8), termed ZNC(C)PR in this article] has been found as a metabolite of arginine-vasopressin (AVP) in rat brain and has been shown to have potent memory-enhancing activity and to yield a series of biochemical events in brain tissues. [35S]ZNC(C)PR was chemically synthesized with high specific activity (232 Ci/mmol), and specific binding sites for ZNC(C)PR were located in synaptosomal membrane preparations of rat brain. We identified a specific binding site for ZNC(C)PR with a Kd of 3.12 nM and Bmax of 31 fmol/mg protein in anterior cortical synaptosomal membranes in the presence of 5 mM Ni2+. A comparison of synthetic analogues of ZNC(C)PR competing with [35S]ZNC(C)PR for binding to anterior cortical receptor are presented. ZDC(C)PR, a 2-aspartyl substitute of the 2-asparaginyl residue in ZNC(C)PR, had the most potent competition, but AVP did not show significant ability to compete for the receptor with ZNC(C)PR.