Effects of arginine-vasopressin fragment 4-9 on rodent cholinergic systems

Therapeutic potential of vasopressin in the treatment of neurological disorders

Vasopressin (VP) is a nonapeptide made of nine amino acids synthesized by the hypothalamus and released by the pituitary gland. VP acts as a neurohormone, neuropeptide and neuromodulator and plays an important role in the regulation of water balance, osmolarity, blood pressure, body temperature, stress response, emotional challenges, etc. Traditionally VP is known to regulate the osmolarity and tonicity. VP and its receptors are widely expressed in the various region of the brain including cortex, hippocampus, basal forebrain, amygdala, etc. VP has been shown to modulate the behavior, stress response, circadian rhythm, cerebral blood flow, learning and memory, etc. The potential role of VP in the regulation of these neurological functions have suggested the therapeutic importance of VP and its analogues in the management of neurological disorders. Further, different VP analogues have been developed across the world with different pharmacotherapeutic potential. In the present work authors highlighted the therapeutic potential of VP and its analogues in the treatment and management of various neurological disorders.

Comparison of Neuroprotective and Cognition-Enhancing Properties of Hydrolysates from Soybean, Walnut, and Peanut Protein

Hydrolysates were prepared from soybean, walnut, and peanut protein by papain, respectively. Their amino acid compositions and molecular weight distributions, the effects of various hydrolysates on H2O2-induced injury PC12 cells, and cognition of mice were investigated, respectively. Results showed that the three hydrolysates were dominated by the peptides with 1–3 KDa with large amount of neurotrophic amino acids. All the hydrolysates exhibited much stronger inhibitory activity against H2O2-induced toxicity than cerebrolysin, and soy protein hydrolysate showed the highest activity. Moreover, the hydrolysates also could reduce the rate of nonviable apoptotic cells at the concentration of 2 mg/mL. The test of animal’s cognition indicated that three hydrolysates could present partly better effect of improving recurred memory ability of normal mice and consolidated memory ability of anisodine-treated mice than piracetam. Therefore, soybean, walnut, and peanut protein hydrolysates were recommended as a potential food raw material for prevention or treatment of neurodegenerative disorders.

Basal Forebrain Cholinergic System and Memory

Basal forebrain cholinergic neurons constitute a way station for many ascending and descending pathways. These cholinergic neurons have a role in eliciting cortical activation and arousal. It is well established that they are mainly involved in cognitive processes requiring increased levels of arousal, attentive states and/or cortical activation with desynchronized activity in the EEG. These cholinergic neurons are modulated by several afferents of different neurotransmitter systems. Of particular importance within the cortical targets of basal forebrain neurons is the hippocampal cortex. The septohippocampal pathway is a bidirectional pathway constituting the main septal efferent system, which is widely known to be implicated in every memory process investigated. The present work aims to review the main neurotransmitter systems involved in modulating cognitive processes related to learning and memory through modulation of basal forebrain neurons.

Arginine vasopressin in hypothalamic paraventricular nucleus is transferred to the caudate nucleus to participate in pain modulation

Arginine vasopressin (AVP), which is synthesized and secreted in the hypothalamic paraventricular nucleus (PVN), is the most important bioactive substance in the pain modulation. Our pervious study had shown that AVP plays an important role in pain modulation in caudate nucleus (CdN). The experiment was designed to investigate the source of AVP in CdN by the nucleus push-pull perfusion and radioimmunoassay. The results showed that: (1) pain stimulation increased the AVP concentration in the CdN perfusion liquid, (2) PVN decreased the effect of pain stimulation which was stronger in both sides than in one side of PVN cauterization; and (3) L-glutamate sodium would excited the PVN neurons by the PVN microinjection that could increase the AVP concentration in the CdN perfusion liquid. The data suggested that AVP in the CdN might come from the PVN in the pain process, i.e., AVP in the PVN might be transferred to the CdN to participate in the pain modulation.

Arginine vasopressin induces rat caudate nucleus releasing acetylcholine to participate in pain modulation

A lot of studies have pointed that acetylcholine (Ach), a classic neurotransmitter can regulate pain process in the caudate nucleus (CdN). Our previous report has proven that arginine vasopressin (AVP) effects on pain modulation in the CdN. The communication was designed to investigate the interaction between AVP and Ach in the rat CdN during the pain process. AVP concentration was determined by radioimmunoassay (RIA) and Ach concentration by high performance liquid chromatography (HPLC). The results showed that pain stimulation increased both AVP and Ach concentrations in the CdN perfusion liquid; AVP increased Ach concentration in the CdN perfusion liquid, while AVP receptor antagonist including d(CH(2))(5)Tyr(Me)AVP (V(1) receptor antagonist) and d(CH(2))(5)[D-Ile(2), Ile(4), Ala-NH(2)(9)]AVP (V(2) receptor antagonist) decreased Ach concentration in the CdN perfusion liquid. The data indicated that the analgesic effect of AVP might be involved in the Ach system in the CdN.

Ameliorative effect of NC-1900, a new AVP4-9 analog, through vasopressin V1A receptor on scopolamine-induced impairments of spatial memory in the eight-arm radial maze

The mechanism by which NC-1900, a new pGlu-Asn-Cys(Cys)-Pro-Arg-Gly-NH(2) (AVP(4-9)) analog, improves spatial memory in rats using an eight-arm radial maze was examined. Even at very low doses (0.2 ng/kg for s.c., 1 microg/kg for p.o., 1 fg for i.c.v.) NC-1900 improved scopolamine-induced impairment of spatial memory. NC-1900 (1 ng/kg, s.c.) also improved impairment of spatial memory induced by pirenzepine, a muscarinic(1) (M(1)) receptor antagonist, and by KN-62, a Ca2+/calmodulin (CaM)-dependent protein kinase II inhibitor. [Pmp(1), Tyr(Me)(2)]-Arg(8)-vasopressin, a vasopressin(1A) (V(1A)) receptor antagonist, and nicardipine, L-type Ca2+ blocker, but not OPC-31260, a V(2) antagonist, suppressed the effect of NC-1900 on scopolamine-induced impairment of spatial memory. A microdialysis study showed that NC-1900 did not affect acetylcholine release in the ventral hippocampus (VH) of intact rats or of scopolamine-treated rats. NC-1900 (1 microM) increased [Ca2+](i) in the VH than in the dorsal hippocampus (DH). Pretreatment with nicardipine (1 microM) and Ca2+ -free conditions inhibited the NC-1900-induced [Ca2+](i) response in the VH. Whereas co-administration of NC-1900 (1 microM) and carbachol (500 microM) increased [Ca2+](i) in the VH. Moreover, nicardipine concentration-dependently inhibited the increase in [Ca2+](i) induced by the co-administration of NC-1900 and carbachol in the VH. These results suggest that NC-1900 activates the V(1A) receptor at the postsynaptic cholinergic nerve, and causes a transient influx of intracellular Ca2+ through L-type Ca2+ channels, to interact with the M(1) receptor. The activation of these Ca2+ -dependent processes induced by NC-1900 may be involved in the positive effect of NC-1900 on scopolamine-induced impairment of spatial memory.

Ameliorative effect of vasopressin-(4-9) through vasopressin V(1A) receptor on scopolamine-induced impairments of rat spatial memory in the eight-arm radial maze

In order to clarify the mechanism by which pGlu-Asn-Cys(Cys)-Pro-Arg-Gly-NH(2) (vasopressin-(4-9)), a major metabolite C-terminal fragment of [Arg(8)]-vasopressin (vasopressin-(1-9)), improves learning and memory, we used several different drugs such as an acetylcholine receptor antagonist, a Ca(2+)/calmodulin-dependent protein kinase II inhibitor, vasopressin receptor antagonists and L-type Ca(2+) channel blocker to disrupt spatial memory in rats. Moreover, we examined the effect of vasopressin-(4-9) on acetylcholine release in the ventral hippocampus using microdialysis. Vasopressin-(4-9) (10 fg/brain, i.c.v.) improved the impairment of spatial memory in the eight-arm radial maze induced by scopolamine, pirenzepine and Ca(2+)/calmodulin -dependent protein kinase II inhibitor. Pirenzepine, a vasopressin V(1A) receptor antagonist, and L-type Ca(2+) channel blocker, but not a vasopressin V(2) receptor antagonist, suppressed the effects of vasopressin-(4-9) on scopolamine-induced impairment of spatial memory. Moreover, vasopressin-(4-9) did not affect acetylcholine release in the ventral hippocampus of intact rats or of scopolamine-treated rats as assessed by microdialysis. These results suggest that vasopressin-(4-9) activates vasopressin V(1A) receptors on the postsynaptic membrane of cholinergic neurons, and induces a transient influx of intracellular Ca(2+) through L-type Ca(2+) channels to interact with muscarinic M(1) receptors. The activation of these processes by vasopressin-(4-9) is critically involved in the positive effect of vasopressin-(4-9) on scopolamine-induced impairment of spatial memory.

Role of corticotropin-releasing factor, vasopressin and the autonomic nervous system in learning and memory

Learning and memory are essential requirements for every living organism in order to cope with environmental demands, which enables it to adapt to changes in the conditions of life. Research on the effects of hormones on memory has focused on hormones such as adrenocorticotropic hormone (ACTH), glucocorticoids, vasopressin, oxytocin, epinephrine, corticotropin-releasing factor (CRF) that are released into the blood and brain following arousing or stressful experiences. Most of the information have been derived from studies on conditioned behavior, in particular, avoidance behavior in rats. In these tasks, an aversive situation was used as a stimulus for learning. Aversive stimuli are associated with the release of stress hormones and neuropeptides. Many factors play a role in different aspects of learning and memory processes. Neuropeptides not only affect attention, motivation, concentration and arousal or vigilance, but also anxiety and fear. In this way, they participate in learning and memory processes. Furthermore, neuropeptides such as CRF and vasopressin modulate the release of stress hormones such as epinephrine. In turn, systemic catecholamines enhance memory consolidation. CRF and vasopressin are colocalized in neurons from the nucleus paraventricularis, which project to nuclei in the brainstem involved in autonomic regulation. The objective of this paper is to discuss the role of CRF, vasopressin, and the autonomic nervous system (ANS) in learning and memory processes. Both CRF and vasopressin have effects in the same direction on behavior, learning and memory processes and stress responses (release of catecholamines and ACTH). These neuropeptides may act synergistically or in a concerted action aimed to learn to adapt to environmental demands.

Effects of prolyl endopeptidase inhibitors and neuropeptides on delayed neuronal death in rats

We investigated the effects of the prolyl endopeptidase inhibitors 1-[1-(Benzyloxycarbonyl)-L-prolyl]prolinal (Z-Pro-Prolinal) and N-benzyloxycarbonyl-thioprolyl-thioprolinal-dimethylaceta l (ZTTA) on delayed neuronal death induced by four-vessel-occlusion transient ischemia in rats. We also examined the effects of [pGlu4, Cyt6, ArgS]vasopressin (vasopressin-(4-9)) and thyrotropin-releasing hormone (TRH) on the delayed neuronal death. Furthermore, we investigated the role of vasopressin receptors in the effects of vasopressin and prolyl endopeptidase inhibitors. Z-Pro-Prolinal, vasopressin-(4-9) and TRH protected pyramidal cells in the CA1 subfield of the rat hippocampus from delayed neuronal death after 10-min ischemia. The effect of vasopressin-(4-9) was abolished by vasopressin receptor antagonists. The effect of Z-Pro-Prolinal was also abrogated by the antagonists. These results suggest that the neuroprotective effect of prolyl endopeptidase inhibitors is mediated by neuropeptides such as [Arg8]vasopressin and TRH, and indicate the involvement of vasopressin receptors in the neuroprotective effect of vasopressin-(4-9) and prolyl endopeptidase inhibitors.