Neurokinin-1 and neurokinin-3 receptors are expressed in vagal efferent neurons that innervate different parts of the gastro-intestinal tract.

Vagal efferent neurons innervating the digestive tract are mainly contained in the dorsal motor nucleus of the vagus. Previous studies have suggested that neurokinins and their neurokinin-1 and neurokinin-3 receptors are involved in the parasympathetic control of digestive functions. The purpose of the present study was to analyze the distribution of neurokinin-1 and neurokinin-3 receptors amongst vagal efferent neurons innervating the stomach, the duodenum, the ileum and the cecum. The immunocytochemical detection of neurokinin-1 and neurokinin-3 receptors was combined with the immunocytochemical detection of retrogradely transported cholera toxin-B subunit, previously injected in the gut wall. Neurokinin-1 and neurokinin-3 receptors were present in 19+/-7% and 8+/-3% of retrogradely labeled neurons innervating the stomach. Almost half of the labeled neurons innervating the duodenum (46+/-7%) expressed neurokinin-1 receptors but less than 0.5% contained neurokinin-3 receptors. None of the retrogradely labeled vagal efferent neurons innervating the ileum and the cecum were immunoreactive for neurokinin-1 and neurokinin-3 receptors. We conclude that neurokinin-1 and neurokinin-3 receptors are located on vagal efferent neurons which innervate the stomach and that neurokinin-1 receptors are common, whereas neurokinin-3 receptors are rare on neurons projecting to the duodenum. Additionally, the distal part of the rat small intestine is innervated by vagal efferent neurons that do not express neurokinins receptors on their membrane. This suggests that neurokinins may influence the parasympathetic control of different regions of the gastro-intestinal tract in specific ways.