Studies on the avian gizzard: Auerbach's plexus

The gastric isthmus from D+ and D- broiler lines divergently selected for digestion efficiency shows histological and morphological differences

Previous results suggested that the gastric function plays a paramount role in digestive efficiency differences between D+ and D− broiler lines divergently selected for AME_n (more feed efficient and less feed efficient, respectively). In this paper we show an histological analysis of the gastric isthmus located between the proventriculus and the gizzard in the D+ and D− lines. Cross-sections were performed using a cryostat (Leica CM30505) and stained with a routine procedure using Mayer’s Hematoxylin and Eosin Stain. The surface and shape of the constitutive gastric isthmus tissues were quantified using the image analysis software Image J. The lumen occupied 11% of the whole D− isthmus cross-sectional area against 24% for D+ (P < 0.01). The mucosa relative area (cm²/total cross-sectional area) was higher in D− than in D+ [47% (D−) and 39% (D+), P < 0.01]. It was significantly more oval and more folded on the lumen side in D− than in D+ chickens; the muscle layer (muscularis mucosae) of the mucosa was relatively more developed in D− than in D+ (16 and 11% of the section, respectively; P < 0.01). A relationship between these observations and increased gastric motility reported in D− compared with D+ is discussed.

Relationship between appearance of GABA, fluorogenic monoamines and cytochrome oxidase activity during prenatal morphogenesis of chick myenteric plexus

The basic histology of the developing embryonic gut wall of the chick was examined on haematein and eosin-stained paraffin sections. In parallel with this, the ontogenic sequence of myenteric plexus formation was followed on whole mounts after NADH diaphorase histochemistry. The presence of nerve elements was verified also by electron microscopy. The appearance of enteric gamma-aminobutyric acid-containing neurons, as an example of an intrinsic inhibitory neuronal system, was studied by using an antiserum against the gamma-aminobutyric acid glutaraldehyde bovine serum albumin conjugate. The development of noradrenergic innervation as an extrinsic inhibitory supply was followed by means of a glyoxylic acid-induced fluorescence method. Cytochrome oxidase activity was detected histochemically. Three consecutive steps of the morphogenesis of the myenteric plexus were revealed; first the appearance of a cellular crest at the mesenteric border on embryonic day 9; second the migration and clustering of nerve cells between embryonic days 10 and 16; then the elongation of neurites on embryonic days 16 and 21. Immunoreactive and also fluorescent fibres were first detected on the 14th day of incubation, while immunopositive cell bodies appeared only after hatching. In the early stages the cytochrome oxidase activity was restricted to the perikarya, while at the end of embryonic development the activity also appeared in the ganglionic neuropile. On the basis of these observations, we concluded that there is a close time relation between the morphogenesis and the biochemical and functional maturation of the myenteric plexus.

On the nerve plexus of the chicken gizzard

The Auerbach's plexus of the gizzard was stained in toto in adult chicken and in young and newly-hatched chicks. The plexus lies immediately beneath the serosa and extends over 55% of the surface of the organ, covering its cranial and caudal poles and the two curvatures. The areas into which the plexus does not extend (i.e., most of the ventral and the dorsal surface) are those where the muscle is covered by the laminar tendon of the gizzard. The ganglia are large, often with hundred of neurons, and have short and broad connecting strands. They are surrounded by a capsule of connective tissue. The ganglion neurons are discoidal and in the adult they measure up to 50 microns in diameter, each being surrounded by a set of glial cells. A few small neurons persist in the adult; in the newly-hatched chick these are predominant, but some large neurons up to 25 microns in diameter are already present. The ultra-structural features of the ganglia of the Auerbach's plexus include the abundance of axo-somatic synapses, as well as numerous axo-dendritic synapses, the presence of intra-ganglionic bundles of collagen fibrils and blood vessels, the abundance of glial cells. In addition to the plexus beneath the serosa, the gizzard has many small intramuscular ganglia located throughout the musculature (which is exclusively circular). These ganglia do not have a connective tissue capsule and are made of small and tightly packed neurons.

The innervation of the hind gut of the domestic fowl

1. The intestinal nerve adjacent to the colon in the domestic fowl, contains motor fibres descending from the vagal and sympathetic thoracicolumbar outflows. 2. No electrophysiological or histological evidence for the existence of motor fibres ascending from the sacral part of the central nervous system could be obtained; ascending sensory fibres, however, were readily demonstrated.

The purinergic nerve hypothesis and insulin secretion

In adrenalectomized rats the effect of i.v. injection of glucose and ATP on insulin changes in external jugular vein was determined in normal and alloxan diabetic animals. In another set of experiments the direct effect of ATP on insulin secretion was investigated. Glucose and ATP were injected in the carotid artery and the blood samples were withdrawn from the portal vein. In these experiments there was immediate and excessive production of insulin release in the portal vein after ATP injection in the carotid artery. In alloxan diabetic rats, despite the high blood glucose levels, the plasma insulin was low and did not respond to glucose stimulation. ATP could increase the sensitivity of the diabetic rats to glucose. The possible role of purinergic nerves in insulin secretion is discussed. It is concluded that multiple innervation of the islets by purinergic, cholinergic and adrenergic nerves, regulate insulin secretion. It is suggested that: 1. Purinergic nerve stimulation is more specific for insulin secretion. 2. ATP is considered the principal transmitter released from purinergic nerves causing insulin secretion. 3. The insulin stimulatory effect normally produced by glucose is through purinergic nerves. 4. It could be possible that one of the causes of diabetes is a defect in the purinergic innervation of the islet cells thus the sensitivity of the islets to glucose is decreased.

Autonomic neuroeffector junctions--reflex vasodilatation of the skin

A general model of the autonomic neuroeffector junction is proposed. In this model, emphasis is placed on the muscle effector bundle with electrotonic coupling between individual cells via gap junctions (or nexuses) and en passage release of transmitter from autonomic nerve varicosities. This release results in transmission to effector cells across junctional clefts ranging from about 20 nm in the vas deferens and iris to as much as 2000 nm in some large arteries. The ultrastructural identification of different autonomic nerve types is described. Current theories on the synthesis, storage, release, and inactivation of transmitter during cholinergic, adrenergic, and purinergic transmission are summarized. Some speculations are made about the possible involvement of purinergic nerves in the innervation of vessels and mast cells in the skin, and whether this involvement results in a functional link between ATP, histamine, bradykinin, and prostaglandin in cutaneous vasodilatation. Another possibility considered as the basis for this reflex is the release of substance P from sensory (pain) nerve collaterals in the skin.