Inhibitory effects of somatostatin on the substantia gelatinosa neurons of trigeminal subnucleus caudalis via somatostatin type 2 receptors in juvenile mice.
The substantia gelatinosa (SG) of the trigeminal subnucleus caudalis (Vc) receives many thin-myelinated Adelta-fiber and unmyelinated C primary afferent fibers and has been implicated in the processing of nociceptive information. Somatostatin (SST) is a neuromodulator in the brain and spinal cord. A number of studies have demonstrated that SST can play a key role in pain modulation at the spinal cord level. However, there is little information available on functional SST receptor expression in the SG neurons of the Vc in mice. This study examined the direct membrane effects of SST and SST receptor type 2 agonist, seglitide (SEG) on the SG neurons of Vc in gramicidin perforated current clamp mode. In addition, SSTR2 mRNA expression was detected on the SG neurons using single cell RT-PCR in juvenile mice. Most SG neurons (37/68, 54%) were hyperpolarized after a bath application of SST. When SST was applied in stages, the second responses (83% of the first response) were less intense than those after the first application suggesting that SSTRs are desensitized by repeated application. The SST-induced hyperpolarizing response was maintained in the presence of TTX (Na(+) channel blocker), AP-5 (NMDA receptor antagonist), CNQX (non-NMDA glutamate receptor antagonist), picrotoxin (GABA(A) receptor antagonist) and strychnine (glycine receptor antagonist), respectively, suggesting that SST has direct effects on the postsynaptic SG neurons. SSTR2 mRNA was detected in 11 out of 28 (39%) SG neurons tested. The SST-induced hyperpolarizing effects were mimicked by SEG, a SSTR2 agonist. These results suggest that functional SSTR2 receptors are expressed on the SG neurons of Vc in juvenile mice and can be a potential target for modulating orofacial pain.
Department of Oral Physiology and Institute of Oral Bioscience, School of Dentistry, Chonbuk National University, Jeonju, 561-756, Republic of Korea.
Hua
H
Yin
Kyung Eun
KE
Lee
Seon Ah
SA
Park
Janardhan P
JP
Bhattarai
Bong Jik
BJ
Suh
Jae Gyu
JG
Jeon
Byung Gook
BG
Kim
Soo Joung
SJ
Park
Seong Kyu
SK
Han
D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D012333:RNA, Messenger / Q000378:metabolism; D017481:Receptors, Somatostatin / Q000819:agonists / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013004:Somatostatin / Q000378:metabolism*; D013376:Substantia Gelatinosa / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D014275:Trigeminal Caudal Nucleus / Q000187:drug effects / Q000502:physiology*
D012333:RNA, Messenger; D017481:Receptors, Somatostatin; C492049:Sstr2 protein, mouse; D013004:Somatostatin