title: The effects of morphine on basal neuronal activities in the lateral and medial pain pathways.
abstract: Numerous studies indicate that morphine suppresses pain-evoked activities in both spinal and supraspinal regions. However, little is known about the effect of morphine on the basal brain activity in the absence of pain. The present study was designed to assess the effects of single-dose morphine on the spontaneous discharge of many simultaneously recorded single units, as well as their functional connections, in the lateral pain pathway, including the primary somatosensory cortex (SI) and ventral posterolateral thalamus (VPL), and medial pain pathway, including the anterior cingulate cortex (ACC) and medial dorsal thalamus (MD), in awake rats. Morphine (5mg/kg) was administered intraperitoneally before the recording. Naloxone plus morphine and normal saline injections were performed respectively as controls. The results showed that morphine administration produced significant changes in the spontaneous neuronal activity in more than one third of the total recorded neurons, with primary activation in the lateral pathway while both inhibition and activation in the medial pathway. Naloxone pretreatment completely blocked the effects induced by morphine. In addition, the correlated activities between and within both pain pathways was exclusively suppressed after morphine injection. These results suggest that morphine may play different roles in modulating neural activity in normal vs. pain states. Taken together, this is the first study investigating the morphine modulation of spontaneous neuronal activity within parallel pain pathways. It can be helpful for revealing neuronal population coding for the morphine action in the absence of pain, and shed light on the supraspinal mechanisms for preemptive analgesia.
authors: Key Laboratory of Mental Health, Institute of Psychology, Chinese Academy of Sciences, Beijing, China.
authors: Yuan-Lin
authors: YL
authors: Su
authors: Jin
authors: J
authors: Huang
authors: Ning
authors: N
authors: Wang
authors: Jin-Yan
authors: JY
authors: Wang
authors: Fei
authors: F
authors: Luo
mesh_terms: D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D055724:Electrophysiological Phenomena; D005625:Frontal Lobe / Q000187:drug effects* / Q000503:physiopathology; D006179:Gyrus Cinguli / Q000187:drug effects* / Q000503:physiopathology; D008297:Male; D009020:Morphine / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D010146:Pain / Q000503:physiopathology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013003:Somatosensory Cortex / Q000187:drug effects* / Q000503:physiopathology; D013788:Thalamus / Q000187:drug effects* / Q000503:physiopathology
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine