Detection of the 5-HT1A receptor and 5-HT1A receptor mRNA in the rat bowel and pancreas: comparison with 5-HT1P receptors.
We tested the hypothesis that the rat bowel and pancreas contain 5-HT1A receptors. 3H-8-hydroxy-2-(di-n-propylamino)tetralin (3H-8-OH-DPAT) was used as a radioligand. Binding of 3H-8-OH-DPAT to membranes derived from the myenteric plexus and the pancreas was investigated by rapid filtration. Alternatively, radioautography was employed to locate 3H-8-OH-DPAT binding sites in frozen sections of unfixed bowel or pancreas. An excess of 5-HT (10 microM) was used to define nonspecific binding. Saturable, high affinity binding of 3H-8-OH-DPAT to enteric (Kd = 2.8 +/- 1.1 nM; Bmax = 83.8 +/- 4.3 fmol/mg protein) and pancreatic (Kd = 6.6 +/- 1.3 nM; Bmax = 44 +/- 2.2 fmol/mg protein) membranes was found. The binding of 3H-8-OH-DPAT to enteric and pancreatic membranes was inhibited by 8-OH-DPAT, NAN-190, and spiperone. In contrast, the binding of 3H-8-OH-DPAT to enteric and pancreatic membranes was not inhibited by 5-carboxyamidotryptamine, or by a variety of compounds known to bind to other subtypes of 5-HT receptor. Digoxigenin-labeled oligonucleotides were found to detect mRNA encoding the 5-HT1A receptor in a subset of neurons in myenteric and submucosal ganglia. In contrast, 5-HT1A mRNA was not found in the pancreas. Radioautography revealed that the highest density of 3H-8-OH-DPAT binding sites was found in the stomach. These sites were especially numerous in the lamina propria adjacent to gastric glands, and in myenteric ganglia. Pancreatic 5-HT1A receptors were located on nerves, lymphoid tissue (especially the capsule of nodes), and on cells scattered in the pancreatic parenchyma. The concentration of 3H-8-OH-DPAT binding sites in the rat bowel and pancreas was less than that of 3H-5-HT binding sites; however, the distribution of 3H-8-OH-DPAT binding sites was similar to that of sites that bind 3H-5-HT. It is concluded that the rat gut and its extension in the pancreas contains 5-HT1A receptors. Many, if not all, of the nerve cells and processes that express 5-HT1A receptors express 5-HT1P receptors as well. The function of these receptors in the physiology of the entero-pancreatic innervation remains to be determined.
Kirchgessner
A L
AL
Department of Anatomy and Cell Biology, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Liu
M T
MT
Howard
M J
MJ
Gershon
M D
MD
D017371:8-Hydroxy-2-(di-n-propylamino)tetralin / Q000378:metabolism; D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D005260:Female; D006168:Guinea Pigs; D017403:In Situ Hybridization; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D008566:Membranes / Q000378:metabolism; D010179:Pancreas / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011985:Receptors, Serotonin / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D014018:Tissue Distribution; D014316:Tritium
D012333:RNA, Messenger; D011985:Receptors, Serotonin; D014316:Tritium; D017371:8-Hydroxy-2-(di-n-propylamino)tetralin