Distribution of substance P-like immunoreactivity in the enteric neurons of the large colon of normal and amitraz-treated ponies: an immunocytochemical study.

The research examines the distribution of a neurotransmitter called substance P in the large colon of normal ponies and those suffering from impaction colic triggered by amitraz. No changes in distribution or intensity of substance P were noticed when the colons of normal and amitraz-treated ponies were compared.

Substance P and its Role

• The study focuses on the neurotransmitter, substance P, which is believed to stimulate motor activity.
• It was observed in nerve fibres spread across all layers of bowel wall and nerve cell bodies in the enteric ganglia of a pony’s left dorsal colon.
• The substance P was noticeably more present in the cell bodies of the submucosal ganglia as compared to the myenteric ganglia.

Observations in Normal Ponies

• In normal ponies, internodal nerve strands of the myenteric plexus had an abundance of substance P.
• These strands formed networks around the neuronal cell bodies inside the ganglia.
• Nerve bundles rich in the substance diverged from the myenteric plexus towards the circular muscle of the tunica muscularis.
• However, in the longitudinal muscle, the presence of substance P was sparse, barring the thickened taenial band.
• In the submucosa, nerve fibres with substance P appeared to originate from ganglionic cell bodies.
• These immunoreactive fibres often condensed around arterial vessels in the submucosa.
• Fine nerve fascicles with substance P from the submucosal plexus also projected towards the muscularis mucosae and surrounded gland structures in the lamina propria.

Comparative Analysis

• Contact of substance P in the colon of a normal horse differs in some way from patterns found in large intestines of other mammals.
• There were no substantial differences in the distribution pattern or intensity of substance P reactivity when the colons of normal and amitraz-treated ponies were compared.