Vasoactive intestinal peptide (VIP), a putative neurotransmitter of nonadrenergic, noncholinergic (NANC) inhibitory innervation and its relevance to therapy

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.

Alteration in nerves and neurotransmitter stimulation of lacrimal gland secretion in the TSP-1-/- mouse model of aqueous deficiency dry eye

The purpose of this study is to determine neural, vascular, protein secretion, and cellular signaling changes with disease progression in lacrimal glands of the thrombospondin-1-/- (TSP-1-/-) mouse model of dry eye compared to C57BL/6 wild-type (WT) mice. Neural innervation was reduced in TSP-1-/- lacrimal glands compared to WT controls, whereas the number of blood vessels was increased. Intracellular Ca2+ stores and the amount of lysosomes, mitochondria, and secretory granules, but not the endoplasmic reticulum, were reduced in TSP-1-/- compared to WT acini at 12 weeks of age. Ex vivo high KCl-evoked secretion was decreased in TSP-1-/- compared to WT lacrimal gland tissue pieces. The α1D-adrenergic agonist-stimulated response was increased in TSP-1-/- at 4 and 24 weeks but decreased at 12 weeks, and the ATP and MeSATP-stimulated peak [Ca2+]i responses were decreased at 24 weeks. These changes were observed prior to the appearance of mononuclear infiltrates. We conclude that in the lacrimal gland the absence of TSP-1: injures peripheral nerves; blocks efferent nerve activation; decreases protein secretion; and alters intracellular Ca2+ stores. Through these effects the absence of TSP-1 leads to disruption of ocular surface homeostasis and development of dry eye.

Contribution of nitric oxide and sensory transmitters to non-adrenergic, non-cholinergic innervation of nasal blood vessels

The possible contribution of a non-adrenergic, non-cholinergic (NANC) vasodilator mechanism in human nasal mucosa was studied using an in vitro muscle tension measuring technique. Strips of the nasal mucosa were suspended in a Magnus tube filled with Krebs solution and aerated with 95% O2. Isometric changes in tension were detected on administration of various drugs under electric stimulation and recorded with a transducer. The relaxing reaction under electrical train pulse stimulation with pretreatment of blockers of the autonomic nerves was suppressed by nitric oxide synthase inhibitor (L-NAME) and antagonists to the receptors of sensory nerve transmitters (Spantide, hCGRP8-37). This result suggests that nitric oxide, substance P and CGRP may be mediators in the NANC inhibitory nerve system.

Gut hormones in gastric function

This chapter has focused on many of the gut hormones that regulate gastric function. Gastrin remains the principal, and only, gastric hormone controlling gastric acid secretion during the cephalic, gastric and intestinal phases of secretion. Several other hormones, including cholecystokinin, peptide YY and secretin, released from intestinal endocrine cells in response to food substrates, have significant inhibitory effects on gastric acid secretion. Many of these hormones, including enteroglucagon and glucagon-like peptide, may act through paracrine release of somatostatin, which in turn acts as the final mediator of acid inhibition. In addition, several peptides contained in nerves, including gastrin releasing peptide and vasoactive intestinal peptide, have been shown to regulate gastric acid secretion and motor function. With the creation of specific monoclonal antibodies for use in in vivo immunoneutralization studies, and the development of selective chemical antagonists for use in receptor blockade experiments, the specific contributions of the different gut hormones in the regulation of gastric function, can be assessed.

Evidence for vasoactive intestinal peptide as a mediator of non-adrenergic non-cholinergic neurotransmission in the trachea

1. The tracheal pouch, a surgical preparation designed to demonstrate non-adrenergic non-cholinergic inhibition, was prepared in chloralose/urethane-anaesthetized and positively ventilated guinea-pigs. The animals were given atropine and propranolol intraperitoneally to block cholinergic and adrenergic divisions of the autonomic innervation. The cervical vagi and sympathetic trunks were isolated bilaterally and cut cranially. 2. The relaxation responses of the pouch to graded concentrations of VIP (10(-11) M to 10(-6) M) were determined. Two consecutive dose-response curves at 20 min apart were determined in the control group. The VIP dose-response curves in the control group were reproducible and failed to show statistical significance upon paired Student's t-test. 3. [Ac-Tyr1,D-Phe2]-GRF(1-29)-amide, a VIP antagonist hereby referred to as antagonist-1 was tested for its ability to inhibit the VIP-induced pouch relaxation. Separate groups of animals were used for each concentration (10(-8) M, 10(-6) M or 10(-5) M) of the antagonist. VIP dose-response curves were determined before and after the pouch was incubated with the antagonist for 10 min. The second curve was determined after rinsing the pouch gently with saline and allowing 5 min for the pouch to stabilize. Statistical analysis showed that only 10(-5) M of the antagonist significantly blocked the VIP-induced tracheal pouch relaxation. 4. [4-C1-D-Phe6,Leu17]-VIP, another VIP antagonist hereby referred to as antagonist-2 was tested similarly for its ability to block the VIP-induced pouch relaxation. The significant blockade of the VIP-induced pouch relaxation was obtained with this antagonist at a concentration of 10(-6) M.(ABSTRACT TRUNCATED AT 250 WORDS)