Sources of inputs to longitudinal muscle motor neurons and ascending interneurons in the guinea-pig small intestine.
Light- and electron-microscopic studies were used to investigate connections between specific subgroups of neurons in the myenteric plexus of the guinea-pig small intestine. Inputs to two classes of calretinin-immunoreactive (IR) nerve cells, longitudinal muscle motor neurons and ascending interneurons, were examined. Inputs from calbindin-IR primary sensory neurons and from three classes of descending interneurons were studied. Electron-microscopic analysis showed that calbindin-IR axons formed two types of inputs, synapses and close contacts, on calretinin-IR neurons. About 40% of inputs to the longitudinal muscle motor neurons and 70% to ascending interneurons were calbindin-IR. Approximately 50% of longitudinal muscle motor neurons were surrounded by bombesin-IR dense pericellular baskets and 40% by closely apposed varicosities. At the electron-microscope level, the bombesin-IR varicosities were found to form synapses and close contacts with the motor neurons. Dense pericellular baskets with bombesin-IR surrounded 36% of all ascending interneurons, and a further 17% had closely apposed varicosities. Somatostatin- and 5-HT-IR descending interneurons provided no dense pericellular baskets to calretinin-IR nerve cells. Thus, calretinin-IR, longitudinal muscle motor neurons and ascending interneurons receive direct synaptic inputs from intrinsic primary sensory neurons and from non-cholinergic, bombesin-IR, descending interneurons.
Pompolo
S
S
Department of Anatomy and Cell Biology, University of Melbourne, Victoria, Australia.
Furness
J B
JB
D000818:Animals; D001839:Bombesin / Q000032:analysis; D064032:Calbindin 2; D002450:Cell Communication; D005260:Female; D006168:Guinea Pigs; D007150:Immunohistochemistry; D007395:Interneurons / Q000502:physiology* / Q000648:ultrastructure; D007421:Intestine, Small / Q000294:innervation* / Q000502:physiology; D008297:Male; D008854:Microscopy, Electron; D009046:Motor Neurons / Q000502:physiology* / Q000648:ultrastructure; D064030:S100 Calcium Binding Protein G / Q000032:analysis; D012701:Serotonin / Q000032:analysis; D013004:Somatostatin / Q000032:analysis
D064032:Calbindin 2; D064030:S100 Calcium Binding Protein G; D012701:Serotonin; D013004:Somatostatin; D001839:Bombesin