REDUCED VAGAL SENSORY INNERVATION OF THE SMALL-INTESTINAL MYENTERIC PLEXUS FOLLOWING CAPSAICIN TREATMENT OF ADULT RATS

To determine whether capsaicin treatment damages small intestinal vaga l sensory nerve endings, we made intra-nodose injections of wheat-germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) to label periph eral and central vagal endings in control and capsaicin-treated rats. Labeled intraganglionic laminar endings (IGLEs), characteristic of vag al 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 significant ly diminished in all areas of the small intestine. Capsaicin also redu ced WGA-HRP activity in the medial and commissural nucleus of the soli tary tract. Systemic capsaicin produces a longlasting loss of vagal IG LEs 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.