Effects of systemic bicuculline or morphine on formalin-evoked pain-related behaviour and c-Fos expression in trigeminal nuclei after formalin injection into the lip or tongue in rats.
This study examined differences in nociceptive responses between lip and tongue. Formalin-induced pain-related behaviour and c-Fos expression in the trigeminal caudal nucleus (Vc) with/without systemic preadministration of a gamma-aminobutyric acid (GABA) type A receptor antagonist, bicuculline (2 mg/kg, i.p., 10 min before formalin injection) or a micro-opioid receptor agonist, morphine (3 mg/kg, i.p., 10 min before formalin injection) have been studied. Formalin injection into the upper lip induced an immediate pain-related behaviour, mostly face-rubbing behaviour, for 15 min (phase 1, mean +/- SEM/5 min, 81.2 +/- 30.1), followed by a more increased activity for 15 min (phase 2, 205.4 +/- 43.6) and a decline to baseline for next 15 min (phase 3, 63.9 +/- 28.0). Formalin injection into the tongue induced similar amount of pain-related behaviour at phase 1 (67.9 +/- 16.7), followed by similar activity at phase 2 (48.6 +/- 6.2), and lesser behaviour at phase 3 (20.4 +/- 7.6). The behaviour at phase 2 decreased following preadministration of bicuculline or morphine when formalin was injected into the lip (b, 62.5 +/- 14.5; m, 95.8 +/- 10.0) but not into the tongue (b, 31.0 +/- 9.2; m, 77.4 +/- 27.0). A considerable numbers of c-Fos-immunoreactive (IR) cells were induced in the caudal and inter-medio-lateral center of superficial layers of the Vc (VcI/II; mean +/- SEM/section = 225.8 +/- 12.9) and magnocellular zone of the Vc (VcIII/IV; 67.1 +/- 4.7) 2 h after formalin injection into the lip. Much smaller numbers of c-Fos-IR cells were induced in the rostral and dorso-medial one-fourth of the VcI/II (72.6 +/- 3.7) and VcIII/IV (55.6 +/- 6.6) after formalin injection into the tongue. Following preadministration with systemic bicuculline or morphine, the formalin-induced c-Fos-IR cells were decreased more in the VcI/II when formalin was injected into the lip (VcI/II, 102.4 +/- 8.0; VcIII/IV, 32.8 +/- 1.4) than into the tongue (VcI/II, 49.5 +/- 8.1; VcIII/IV, 31.7 +/- 5.3). These results show that the lip is more sensitive to formalin-induced noxious stimulation and regulated more through GABA(A) and micro-opioid receptors than the tongue.
Sugiyo
S
S
Department of Oral Anatomy and Neurobiology, Osaka University Graduate School of Dentistry, Suita, Osaka, Japan.
Uehashi
D
D
Satoh
F
F
Abe
T
T
Yonehara
N
N
Kobayashi
M
M
Takemura
Motohide
M
D000700:Analgesics / Q000008:administration & dosage*; D000701:Analgesics, Opioid / Q000008:administration & dosage; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D001640:Bicuculline / Q000008:administration & dosage*; D005557:Formaldehyde; D018756:GABA Antagonists / Q000008:administration & dosage; D015870:Gene Expression / Q000187:drug effects; D016762:Genes, fos; D008046:Lip / Q000294:innervation; D008297:Male; D009020:Morphine / Q000008:administration & dosage*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D010146:Pain / Q000139:chemically induced / Q000188:drug therapy*; D010147:Pain Measurement; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014059:Tongue / Q000294:innervation; D012668:Trigeminal Ganglion / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014278:Trigeminal Nuclei / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
D000700:Analgesics; D000701:Analgesics, Opioid; D018756:GABA Antagonists; D016760:Proto-Oncogene Proteins c-fos; D005557:Formaldehyde; D009020:Morphine; D001640:Bicuculline