Receptors and transporter for serotonin in Merkel cell-nerve endings in the rat sinus hair follicle. An immunohistochemical study.
Serotonin (5-HT) has been a candidate for neurotransmitters in cutaneous type I mechanoreceptors (i.e., Merkel cell-nerve endings). Although recent electrophysiological studies have suggested the presence of the 5-HT2 and 3 receptors in the Merkel cell-nerve endings, the histological localization of these receptors are obscure. We thus immunohistochemically examined the presence of 5-HT1, 2, 3 receptors in Merkel cell-nerve endings in sinus hair follicles of the rat whisker pad. We also studied the immunohistochemical localization of the 5-HT transporter to confirm the site of 5-HT secretion. For this purpose, we used antibodies for the 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2C and 5-HT3 receptors, and for the 5-HT transporter, as well as antibodies for cytokeratin 20 (as a marker of Merkel cells) and neurofilament H (a marker of type I sensory nerve terminals). The immuno-stained sections were analyzed under a laser-scanning microscope. It was found that the sensory nerve terminals in the Merkel cell-nerve endings showed strong positive immunoreactions of 5-HT1A and 1B receptors but not 5-HT2A, 2C, and 3 receptors. Furthermore, both the Merkel cells and related axon terminals showed strong immunoreactions of the 5-HT transporter. These findings support the idea that 5-HT molecules are released from the Merkel cells during mechanical reception and indirectly regulate neural actions of sensory neurons via 5-HT1 receptors. The localization of the 5-HT transporter found in this study also suggests a possibility that axon terminals in the Merkel cell-nerve endings also release 5-HT.
Tachibana
Tamiko
T
Department of Oral Anatomy, Iwate Medical University School of Dentistry, Morioka Iwate 020-8505, Japan. tatamiko@iwate-med.ac.jp
Endoh
Makoto
M
Fujiwara
Naoki
N
Nawa
Tokio
T
D000818:Animals; D005260:Female; D018859:Hair Follicle / Q000166:cytology / Q000294:innervation / Q000378:metabolism*; D007150:Immunohistochemistry; D007381:Intermediate Filament Proteins / Q000378:metabolism; D053554:Keratin-20; D008297:Male; D008562:Membrane Glycoproteins / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D018862:Merkel Cells / Q000378:metabolism* / Q000648:ultrastructure; D018613:Microscopy, Confocal; D009411:Nerve Endings / Q000378:metabolism* / Q000648:ultrastructure; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D016900:Neurofilament Proteins / Q000378:metabolism; D017729:Presynaptic Terminals / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism; D050486:Serotonin Plasma Membrane Transport Proteins; D014738:Vibrissae / Q000166:cytology / Q000294:innervation / Q000378:metabolism
D007381:Intermediate Filament Proteins; D053554:Keratin-20; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D016900:Neurofilament Proteins; D011985:Receptors, Serotonin; D050486:Serotonin Plasma Membrane Transport Proteins; C493232:Slc6a4 protein, rat; C051774:neurofilament protein H; D012701:Serotonin