Ultrastructure of striated muscle fibers in the middle third of the human esophagus

Striated muscle fibers and .their spatial relationship to smooth muscle cells have been studied in the middle third of human esophagus. Biopsies were obtained from 3 patients during surgery. In both the circular and longitudinal layers, the muscle coat of this transition zone was composed of fascicles of uniform dimensioi~ (100-200 pm of diameter); some of these bundles were made up of striated muscle fibers, others were pure bundles of smooth muscle cells and some were of the mixed type. Striated muscle fibers represented three different types, which were considered as intermediate, with certain structural features characteristic of the fast fiber type. Of these, the most frequently-found fibers were most similar to the fast fiber type. Satellite cells were numerous; in mixed fascicles they were gradually replaced by smooth muscle cells. The gap between striated muscle fiber and smooth muscle cells was more than 200 nm wide. It contained the respective basal laminae and a delicate layer of amorphous conective tissue. No specialized junctions were formed between consecutive striated muscle fibers, or between striated muscle fibers and smooth muscle cells. Interstitial cells of Cajal were never situated as close to striated muscle fibers as to smooth muscle cells

NK1 receptor expression in the interstitial cells of Cajal and neurons and tachykinins distribution in rat ileum during development

The origin and function of the interstitial cells of Cajal (ICCs) that are located at the level of the deep muscular plexus (DMP) have not been completely identified. It has been recently reported that these cells express neurokinin-1 (NK1) receptors to which substance P (SP) shows the highest affinity. Studies during pre- and postnatal life have demonstrated that ICCs are identifiable in the rat ileum soon after birth and already show adult features at 7 days of postnatal life. Several neurotransmitters have been identified at the DMP which appear at specific times during development. We have studied the expression of NK1 receptors by ICCs and enteric neurons and the timing of the appearance of SP in the DMP, myenteric plexus (MP) and submucous plexus (SMP) of rat ileum during development. Rats, aged from 18 days of fetal life to adulthood, were used. NK1 receptors and SP were identified by using NK1 polyclonal antibodies and tachykinin (SP/TK) polyclonal antibodies, respectively. NK1-immunoreactivity (IR) was detected in the ICCs immediately after birth and reached maximal intensity at 7 days. From birth, SP/TK-IR fibers originated from short excitatory neurons at the MP and reached the DMP at 1 week of postnatal life. NK1- and SP/TK-IR appeared in the MP neurons in the fetus and in the SMP neurons at weaning. The present study demonstrates that by the first days of postnatal life, the NK1-IR might be used as a marker of the ICCs at the DMP and suggests that these cells may participate in the actions exerted by tachykinins on muscle cells

Fine structure of the recptors at the myotendinous junction of human extraocular muscles

The myotendinous junction of the human extraocular muscles was studied by electron microscopy. Some peculiar receptorial structures have been found in the majority of the samples examined. These structures are very small and consist of 1) the terminal portion of one muscle fibre, 2) the tendon into which it inserts and y), within the tendon, a rich nerve arborization, whose branches are always very close to the rnuscle component. Only one discontinuous layer, made up of tlat cells. which lack a basa1 lamina and often show pinocytotic vesicles, encapsules every musculo-tendinous complex. The tendinous component consists of amorphous ground substance of different electron density. of collagen and elastic fibres and is divided in compartments by ramified cells, which make an inner capsular-like covering to the nerve fibres. Three types of afferent nerve endings can be identified. One type is usually more frequent than the others, possesses a large number of neurotubules and neurofilaments and few mitochondria and is always surrounded by a Schwann cell which forms finger-like processes penetrating into the axoplasm. The second type is only partially enveloped by the Schwann cell. The axoplasm is devoid of neurotubules and contains few neurofilarnents, several mitochondria and groups of small clear vesicles placed in the areas uncovered by the glial sheath. The third one is completely surrounded by the Schwann cell, but is devoid of neurotubules and neurofilaments and full of mitochondria. These rnorphological features correspond well with the probable role of these receptorial structures, which is to ensure very exact and precise ocular movements

Structural organization of enteric

The organization of the Enteric Nervous System (ENS) was studied in the human colon. Fragments of the whole colonic wall were either routinely processed or Zinc-Iodide Osmium impregnated. Single-layer preparations were also obtained from some of the Zinc-Iodide Osmium-impregnated specimens. The results showed some differences in the organization of human colonic ENS from that of other mammals. In fact, the human submucous plexus was made up of three interconnected ganglionated networks arranged along three different planes. With respect to the myenteric plexus, its ganglia were large sized and irregularly shaped. Moreover, during the microdissection of the colonic wall, we found the absence of a cleavage plane between the circular and longitudinal muscle layers; on the other hand the cleavage plane between mucosa and submucosa was not immediately below the muscularis mucosae, but slightly deeper, since the innermost part of the submucosa remained adhering to overlying layers

Interstitital cells of Cajal in the human stomach: distribution and relationship with enteric innervation

Interstitial cells of Cajal (ICC) are distributed throughout the gastrointestinal muscle coat with a region-specific location, and are considered to be pacemaker and/or mediators of neurotransmission. Little is known about their shape, size, distribution and relationships with excitatory and inhibitory nerves in human stomach. With this aim, we labeled the ICC, using c-Kit immunohistochemistry, followed by a quantitative analysis to evaluate the distribution and area occupied by these cells in the circular and longitudinal muscle layers and at the myenteric plexus level in the human fundus, corpus and antrum. Furthermore, by NADPH-d histochemistry and substance P (SP) immunohistochemistry, we labeled and quantified nitric oxide (NO)-producing and SP-containing nerves and evidenced their relationships with the ICC in these three gastric regions. In the fundus, the ICC appeared as bipolar cells and in the corpus and antrum they mainly appeared as multipolar cells, with highly ramified processes. The networks formed by ICC differed in the three gastric regions. The ICC number was significantly higher and cell area smaller in the fundus compared to the corpus and antrum. The area occupied by the ICC was significantly higher at the myenteric plexus level compared with circular and longitudinal muscle layers. Everywhere, NADPH-d-positive nerves were more numerous than SP-positive ones. Both kinds of fibers were closely apposed to the ICC in the corpus and antrum. In conclusion, in the human stomach, the ICC have region-specific shape, size and distribution and in the corpus and antrum have close contact with both inhibitory and excitatory nerves. Presumably, as suggested for laboratory mammals, these differences are in relationship with the motor activities peculiar to each gastric area