Innervation of interstitial cells of Cajal by vasoactive intestinal polypeptide containing nerves in canine colon

The hypothesis was tested, through structural and functional studies, that interstitial cells of Cajal receive and can respond to direct innervation from nerves containing the vasoactive intestinal polypeptide neuromediator. The submucosal network of interstitial cells of Cajal has been postulated to provide pacemaking activity for the circular muscle and to be involved in neurotransmission from noradrenergic, noncholinergic nerves for which vasoactive intestinal polypeptide is a putative mediator. The distribution of vasoactive intestinal polypeptide and substance P immunoreactive material in nerve profiles of the enteric nervous system of the canine colon was examined. In addition, electrophysiological studies were done on the interstitial cells bordering the submucosal side of the circular muscle layer after they were electrically isolated using heptanol. The vasoactive intestinal polypeptide immunoreactivity, located exclusively in nerve large granular vesicles, was found throughout the enteric nervous system (myenteric plexus, submucous plexus, and circular muscle – submucosa interface). The highest proportion (38% compared with 22–24%) of profiles of large granular vesicles with vasoactive intestinal polypeptide immunoreactivity was found in nerve profiles of the circular muscle – submucosa interface. In contrast, substance P immunoreactivity was found in nerve profiles of myenteric plexus (33% of large granular vesicles were positive) but not associated with submucosal interstitial cell nerve network. The vasoactive intestinal polypeptide hyperpolarized interstitial cells by 9 mV when electrically isolated by 1 mM heptanol and markedly reduced (about 50%) their input membrane resistance. We conclude that the distribution of vasoactive intestinal polypeptide immunoreactivity and its action are consistent with a postulated role of the interstitial cells as a major site of neurally mediated inhibition of colonic pacemaker activity.Key words: enteric nervous system, interstitial cells of Cajal, inhibitory junction potential, nonadrenergic noncholinergic nerves.

The Fine Structure of Intraepithelial Free Nerve Endings in the Canine Vocal Cord Mucosa

Innervation of the epithelium on the undersurface of the canine vocal cords was investigated by transmission electron microscopy. In the subepithelial lamina propria, nerve bundles containing unmyelinated fibers were observed. The nerve bundles, encircled by basal lamina, were enclosed by a thin connective tissue layer and by flattened flbroblast-like cells. With nerve bundles approaching the epithelium, the axons divided repeatedly and entered the epithelial layer. In the epithelial cells, nerve axons formed knob-like swellings that contained a small number of large granular vesicles and a large number of small agranular vesicles. A sensory function responsive to irritant chemical stimuli and to mechanical stimuli is presumed for these vesicle-containing nerve processes.

Occurrence of FMRF amide-like immunoreactive nerve fibers in guinea pig small intestine.

We investigated the distribution of FMRF amide-like immunoreactivity in the small intestine of the guinea pig. Immunoreactive nerve fibers were found mainly in the myenteric and submucous plexuses and in the inner circular muscle layer. The labeled processes contained variable proportions of small clear vesicles 30-40 nm in diameter and large granular vesicles 80-120 nm in diameter. The large granular vesicles showed heavy immunoreactivity. The antisera against FMRF amide crossreact with peptides belonging to the pancreatic polypeptide family; it has therefore been suggested that the FMRF amide immunoreactivity demonstrated in the small intestine is caused by a peptide that is biosynthetically related to, but not necessarily a member of, the pancreatic polypeptide family.

Ultrastructural demonstration of noradrenergic synapses in the rat central nervous system by dopamine-beta-hydroxylase immunocytochemistry.

Noradrenergic (NA) cell bodies and axonal processes were identified in the electron microscope by the immunocytochemical localization of the norepinephrine-synthesizing enzyme, dopamine-beta-hydroxylase (DBH). DBH immunoreactivity, visualized by the peroxidase-antiperoxidase method, was observed in the somata and proximal processes of locus coeruleus neurons and in the distal axons of several NA terminal fields. DBH immunoreactivity is distributed throughout the cytoplasm of the NA neuron, but demonstrates a selective association with endoplasmic reticulum, Golgi apparatus, mitochondrial outer membranes, large granular vesicles, and small, round synaptic vesicles. DBH-positive axonal profiles, typically interspersed between unlabeled dendrites, form two distinct populations: a) thin, unmyelinated intervaricose segments (ca. 0.28 micron) and b) spherical varicosities (ca. 1.00 micron). No DBH-positive varicosities were observed in contact with intracerebral capillaries. In order to determine whether or not NA axons typically form synaptic contacts, a quantitative analysis of selected areas of the diencephalon, cerebellum, and limbic cortex was carried out. More than half (58%) of all DBH-positive varicosities form axodendritic synapses characterized by specialized junctional appositions. The results suggest that NA neurons typically exert their influence on other neurons through highly restricted synaptic contacts.

The innervation of smooth muscle in the primary bronchus of the chicken

The innervation of the primary bronchus of the chicken was studied with in vitro pharmacological techniques and with the electron microscope. The primary response of the smooth muscle to field stimulation is relaxation of the muscle and this is not blocked by adrenergic blocking agents. Excitatory cholinergic innervation can be demonstrated when the muscle is partially relaxed. Examination of the ultrastructure of the muscle and nerves shows numerous axon profiles filled with large granular vesicles of the type associated with noradrenergic or purinergic neurotransmission. Agranular vesicles characteristic of cholinergic innervation are also seen but there is no evidence of adrenergic innervation to the smooth muscle. The smooth muscle ceils show connections of the nexus type. These findings indicate that the primary bronchus of the chicken has a dominant inhibitory system and this is nonadrenergic in type.

Comparative Ultrastructural Studies of the Pineal Gland of Rodents

Electron microscopic observations of mammalian pineal glands have mainly been made on rodents, especially rats. However, there is no comparative ultrastructural investigation of pineals of various rodent species. In the present experiments several species of rodents were used, but here will be described primarily the results obtained from the mouse and chinchilla pineal glands. Pineals were immersed in ice-cold buffered 6% paraformaldehyde and 2% OsO4 mixture (1: 1) for 5 hours and embedded in the plastic mixture recommended by Spurr. Pinealocytes, the major cell type in the organ, show similar fine structural features in both mouse and chinchilla. These cells have lobulated nuclei and similar cytoplasmic organelles except that mouse pinealocytes contain numerous large granular vesicles of 1200Å in mean diameter. Other types of parenchymal cells are quite different between these animals.

The innervation of the cat spleen

The use of histochemical methods shows that the main splenic artery has both a cholinergic and noradrenergic nerve supply, but only noradrenergic nerve fibres are found in the spleen. The innervation of the smooth muscle of the spleen is sparse. Electron-microscopy reveals the presence of large and small granular vesicles in terminal fibres, but only large granular vesicles in non-terminal axons. The way in which the innervation pattern may determine the characteristics of neurotransmission in the spleen is discussed.