The synaptic relationship between vasoactive intestinal polypeptide (VIP)-like immunoreactive neurons and their axon terminals in the rat small intestine: light and electron microscopic study

The present study demonstrates synaptic contacts between vasoactive intestinal polypeptide (VIP)-like immunoreactive neurons and immunoreactive axon terminals in the submucous and myenteric plexuses of the rat small intestine. Our observations suggest that VIP afferents directly affect the VIP neurons in the small intestine via synapses.     

VIP nerve fibres around peripheral blood vessels

By immunocytochemistry nerve fibres containing vasoactive intestinal polypeptide (VIP) were demonstrated around many peripheral blood vessels in the cat. Such nerve fibres were particularly numerous around arteries in the upper respiratory, gastrointestinal and genito-urinary tracts. They were less numerous around large arteries and veins and seemed to be absent from blood vessels in the liver, spleen and kidney. VIP nerve fibres were few around blood vessels in skeletal muscle and absent in coronary arteries. Administration of VIP in vitro relaxed all arteries tested provided they had been given an increased tone, for instance by preincubation with PGF_2α. It is likely that VIP in vascular nerve fibres may participate in the regulation of systemic and local blood flow.     

STIMULATION OF SODIUM AND WATER SECRETION WITHOUT INHIBITION OF GLUCOSE ABSORPTION IN THE RAT JEJUNUM BY VASOACTIVE INTESTINAL PEPTIDE (VIP)

1. Infusion of vasoactive intestinal peptide (VIP) into the arterial blood supply of the small intestine in anaesthetized rats did not alter either the perfusion pressure in the superior mesenteric artery or the active absorption of glucose from the jejunum, but did produce a large net secretion of Na⁺ and water into the lumen of the jejunum. 2. The results are compared to the effects of prostaglandin E₁ which stimulates Na⁺ and water secretion and inhibits glucose active absorption in the rat jejunum.     

Self-association and solubility of peptides.

Self-associated species of the protected C-terminal tetrapeptide segment of porcine vasoactive intestinal peptide and related short sequences in methylene chloride have been disrupted by adding increasing amounts of dimethylsulphoxide. This structural transition has been monitored following the disappearance of the amide I carbonyl stretching band assigned to strongly intermolecularly hydrogen-bonded molecules (1655–1633 cm^-1) in the infrared absorption spectra. A scale for the propensity of the various peptides to aggregate has been established. Substitution of the asparagine residue by a β-tert.-butylaspartic acid residue in the tripeptide drastically reduces the extent of self-association. The increasing tendency to aggregate shown by these peptides is paralleled by a decrease in their solubility. The impact of these results on the strategy of synthesis of porcine vasoactive intestinal peptide is briefly outlined.     

Antidipsogenic action of vasoactive intestinal peptide in the rat

The effect of vasoactive intestinal peptide (VIP) on the intake of water was studied in the rat. Intracerebroventricular administration of vasoactive intestinal peptide strongly inhibited drinking in rats deprived of water, but peripheral administration had no effect, indicating that the site of action was central. Drinking induced by angiotensin II was also markedly blocked by simultaneous administration of vasoactive intestinal peptide. The results indicate that in the rat, vasoactive intestinal peptide may play a role in the control of intake of water as a neuropeptide thirst inhibitor.     

The simultaneous presence of neuroepithelial cells and neuroepithelial bodies in the respiratory gas bladder of the longnose gar, Lepisosteus osseus, and the spotted gar, L. oculatus

Anatomical and functional studies on the autonomic innervation as well as the location of airway receptors in the air-bladder of lepisosteids are very fragmentary. These water-breathing fishes share in common with the bichirs the presence of a glottis (not a ductus pneumaticus) opening into the esophagus. In contrast to a high concentration of neuroepithelial cells (NECs) contained in the furrowed epithelium in the lung of Polypterus, these cells are scattered as solitary cells in the glottal epithelium, and grouped to form neuroepithelial bodies (NEBs) in the mucociliated epithelium investing the main trabeculae in the air-bladder of Lepisosteus osseus and L. oculatus. The present immunohistochemical studies also demonstrated the presence of nerve fibers in the trabecular striated musculature and a possible relation to NEBs in these species, and identified immunoreactive elements of this innervation. Tyrosine hydroxylase (TH), choline acetyltransferase (ChAT), 5-HT and neuropeptide immunoreactivities were detected in the intramural nerve fibers. 5-HT and VIP immunopositive nerve fibers are apparently associated with NEBs. TH, VIP and SP immunoreactivities are also present in nerve fibers coursing in the radially arranged striated muscle surrounding the glottis and its submucosa. 5-HT positive neurons are also found in submucosal and the muscle layers of the glottis. The physiological function of the adrenergic and inhibitory innervation of the striated muscle as well as the neurochemical coding and morphology of the innervation of the NEBs are not known. Future studies are needed to provide evidence for these receptors with the capacity of chemoreceptors and/or mechanoreceptors.     

Neural structures and mechanisms involved in scene recognition: a review and interpretation

Since the discovery in 1996 that a region within caudal parahippocampal cortex subserves learning and recall of topographical information, numerous studies aimed at elucidating the structures and pathways involved in scene recognition have been published. Neuroimaging studies, in particular, have revealed the locations and identities of some of the principal cortical structures that mediate these faculties. In the present study the detailed organization of the system is examined, based on a meta-analysis of neuroimaging studies of scene processing in human subjects, combined with reviews of the results of lesions on this type of processing, single neuron studies, and available hodological data in non-human primates. A cortical hierarchy of structures that mediate scene recognition is established based on these data, and an attempt is made to determine the function of the individual components of the system.