Reduced vagal sensory innervation of the small intestinal myenteric plexus following capsaicin treatment of adult rats

To determine whether capsaicin treatment damages small intestinal vagal sensory nerve endings, we made intra-nodose injections of wheat-germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) to label peripheral and central vagal endings in control and capsaicin-treated rats. Labeled intraganglionic laminar endings (IGLEs), characteristic of vagal sensory endings of the myenteric plexus, were counted. In controls IGLEs were numerous in the duodenum, less numerous in the jejunum and scarce in the ileum. In capsaicin-treated rats, IGLEs were significantly diminished in all areas of the small intestine. Capsaicin also reduced WGA-HRP activity in the medial and commissural nucleus of the solitary tract. Systemic capsaicin produces a longlasting loss of vagal IGLEs in the small intestinal myenteric plexus. Such loss is consistent with capsaicin-induced impairment of intestinal reflexes and controls of food intake. (C) 1997 Elsevier Science Ireland Ltd.