Anatomical and neurochemical features of the extrinsic and intrinsic innervation of the striated muscle in the porcine esophagus: evidence for regional and species differences

Abstract

Studies of the intrinsic and extrinsic innervation patterns of esophageal motor endplates (MEPs) are mainly confined to small rodents. Therefore, an immunocytochemical, denervation and tracing study was conducted on the pig, an experimental model in which the distribution of the striated esophageal muscle portion more closely resembles the human situation. The purpose of this study was to analyze the origin and neurochemical content of the nerve fibers participating in the myoneural synapse. Fifteen 6-week-old domestic pigs were studied by immunohistochemistry combined with a-bungarotoxin labeling to define the co-innervation patterns of nitrergic and peptidergic nerve terminals in MEPs. Some animals were subjected to unilateral infra-or supranodose vagotomy to determine the origin of the nerve terminals in MEPs. Special attention was paid to the interregional differences in terms of co-innervation rates, and these findings were compared with literature data on small mammals. Double stainings revealed that most of the nNOS-immunoreactive (ir) terminals in MEPs co-stained for VIP, GAL and NPY, but not for PACAP and L-ENK. PACAP-and L-ENK-ir terminals were coarser than nNOS-ir terminals, and largely co-localized VAChT. High percentages of MEPs at the cervical level were contacted by PACAP-(~94%) and L-ENK-ir (~78%) terminals, but the proportion of both decreased in the rostrocaudal direction. Vagotomy significantly reduced their presence in MEPs at the thoracic and abdominal levels, while nNOS-ir terminals observed in approximately 30% of the MEPs were unaffected by vagotomy. Immunostainings on brainstem cryosections after retrograde tracing from the cervical esophagus showed that a large number of FB-positive cells in the nucleus ambiguus were PACAP-ir (~72%). C-kit-positive interstitial cells of Cajal were seen adjacent to the striated muscle fibers, apparently without direct relationship to MEPs. Similar to mouse esophagus, intrinsic nitrergic fibers were found to run close to, or even spiral around, these interstitial cells, an association that might point to a role as specialized spindle proprioceptors. In conclusion, the cholinergic terminals -part of which coexpress PACAP and/or L-ENK -that innervate MEPs in the porcine esophagus have a vagal origin, whereas the nNOS/VIP/GAL/NPY-ir fibers co-innervating these MEPs are intrinsic in nature. The regional differences observed along the esophageal length pertain to the neurochemical content of the vagal motor innervation of the MEPs.

Interstitial cells of Cajal and electrical activity of smooth muscle in porcine ileum

“…The distribution observed concurs with ultrastructural studies in the pig where ICC have been described at the level of the myenteric plexus and deep muscular plexus in the ileum (Jiménez et al 1999) and the deep muscular plexus in the duodenum (Henry et al 1998). In the only other study to use Kit-immunohistochemistry in the porcine gastrointestinal tract, Kit-immunoreactive ICC were observed in the striated muscle region of the cervical and thoracic oesophagus (Wu et al 2003). The cells in that study were spindle-shaped with bipolar tapering processes similar to the bipolar intramuscular ICC observed in the present study.…”

On the origin of rhythmic contractile activity of the esophagus in early achalasia, a clinical case study

“…Zhang and Diamant noted that rhythmic esophageal contractions were not common when the UES did not show them (Zhang and Diamant, 1994). This does not exclude ICC from playing a role in the origin of the rhythmicity since ICC occur in the human striated muscle of the esophagus (Faussone-Pellegrini and Cortesini, 1986) as well as in the mouse (Rumessen et al, 2001) and pig (Wu et al, 2003). Furthermore, when cell clusters were isolated from the rat esophagus, rhythmic contractions developed, dependent on the presence of ICC (Ludlow et al, 2013).…”

“…In addition, the ICC in the striated muscle of the mouse appear to be uniquely associated with intrinsic inhibitory nerves, primarily nitrergic nerves (Rumessen et al, 2001; Wu et al, 2003). Paterson showed that balloon distention in the opossum esophagus generates myogenic contractions that increase in amplitude after TTX administration, indicating physiologically that the musculature is under tonic inhibitory control (Muinuddin and Paterson, 2001).…”

Fall in density, but not number of myenteric neurons and circular muscle nerve fibres in guinea‐pig colon with ageing

“…There are also strain differences in rats in the extent to which nitrergic neurons are protected. 7,31 nNOS gene expression, nNOS synthesis and catalytic activity decreased in the myenteric plexus of aged rats. 16 There was an age-dependent reduction in AChrelease in the rat colon myenteric plexus between 4-to 8-month and 22-to 28-month-old rats.…”