title: Administration of somatostatin analog octreotide in the ventrolateral orbital cortex produces sex-related antinociceptive effects on acute and formalin-induced nociceptive behavior in rats.
abstract: The present study was designed to examine whether somatostatin analog octreotide (OCT) was involved in antinociception in the ventrolateral orbital cortex (VLO) and determine whether this effect had a sex difference between male and female rats. The radiant heat-evoked tail flick (TF) reflex was used as an index of acute nociceptive response in lightly anesthetized rats. The number of flinches evoked by formalin injection into the hindpaw was used to evaluate inflammatory persistent pain in conscious rats. Administration of OCT (2.0, 5.0 10.0 ng in 0.5 µl) into the VLO depressed the TF reflex in a dose-dependent manner only in female rats, but not male rats. Pretreatment with a nonselective somatostatin receptor antagonist cyclo-somatostatin (c-SOM) (25.0 µg in 0.5 µl) into the VLO antagonized 10.0 ng OCT-induced inhibition of the TF reflex in female rats. Similarly, application of high dose of OCT (10.0 ng in 0.5 µl) into the VLO depressed formalin-induced flinching response in the early and late phases only in female rats, and had no any effects in male rats. Pretreatment with c-SOM (25.0 µg in 0.5 µl) into the VLO totally antagonized the 10 ng OCT-induced inhibition of the flinches in both phases in female rats. Additionally, single administration of c-SOM into the VLO failed to alter tail reflex latencies and formalin-induced nociceptive behaviors in female rats. The results provide the first valuable evidence that somatostatin and its receptors are involved in antinociception in acute heat-evoked nociception and inflammatory persistent pain only in female rats, not male rats, in the VLO.
authors.affiliation: Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiaotong University School of Medicine, Xi'an, Shaanxi 710061, China. Electronic address: quchaoling@gmail.com.
authors.forename: Chao-Ling
authors.initials: CL
authors.lastname: Qu
authors.affiliation: Department of Forensic Medicine, Key Laboratory of Environment and Genes Related to Diseases of Ministry of Education, Xi'an Jiaotong University School of Medicine, Yanta Road West 76#, Xi'an, Shaanxi 710061, China.
authors.forename: Yong-Hui
authors.initials: YH
authors.lastname: Dang
authors.affiliation: Department of Physiology and Pathophysiology, Key Laboratory of Environment and Genes Related to Diseases, Ministry of Education, Xi'an Jiaotong University School of Medicine, Xi'an, Shaanxi 710061, China.
authors.forename: Jing-Shi
authors.initials: JS
authors.lastname: Tang
mesh_terms: D000818:Animals; D019540:Area Under Curve; D001522:Behavior, Animal / Q000187:drug effects; D005260:Female; D005557:Formaldehyde / Q000494:pharmacology*; D008297:Male; D008845:Microinjections; D059225:Nociception / Q000187:drug effects*; D015282:Octreotide / Q000008:administration & dosage* / Q000493:pharmacokinetics; D017397:Prefrontal Cortex / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012737:Sex Factors
chemical_list: D005557:Formaldehyde; D015282:Octreotide
keywords: Antinociception; Cyclo-somatostatin; Formalin test; Octreotide; Tail flick reflex; Ventrolateral orbital cortex