Open Access(640) The Effect of Morphine on Responses of Nucleus Ventroposterolateralis (VPL) Neurons to Colorectal Distension in the Rat
Publication year - 2000
Publication title -
pain medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.893
H-Index - 97
eISSN - 1526-4637
pISSN - 1526-2375
DOI - 10.1046/j.1526-4637.2000.000024-39.x
Subject(s) - nociception , medicine , morphine , distension , (+) naloxone , noxious stimulus , inhibitory postsynaptic potential , receptive field , excitatory postsynaptic potential , visceral pain , anesthesia , nociceptor , electrophysiology , opioid , endocrinology , neuroscience , psychology , receptor
In 61 halothane‐anesthetized rats, we characterized the responses of single VPL neurons to a noxious visceral stimulus (colorectal balloon distension, CRD), and studied the effects of intravenous morphine sulfate(Mor) on these responses using standard extracellular microelectrode recording techniques. Ninety‐four neurons were isolated. Fifty‐three (56%) responded to CRD, of which 43 (81%) had excitatory and 10 (19%) had inhibitory responses. Neurons showed graded responses to graded CRD pressures (20 to 100 mmHg). Responses to noxious (pinch, heat) and innocuous (brush, tap) cutaneous stimuli were studied in 44 CRD‐responsive neurons. Forty of these neurons (91%) had cutaneous receptive fields, of which 39 (98%) were small and contralateral and 1 (2%) was large and bilateral. Ninety‐five percent of these neurons had wide dynamic range responses, 5% were nociceptive‐specific. Cumulative doses of Mor (0.125, 0.25, 0.5, 1, and 2 mg/kg) produced dose‐dependent attenuation of neuronal activity. Naloxone (0.4 mg/kg IV) reversed the effects of Mor. Mor and Naloxone had no effects on spontaneous activity. These data support the involvement of VPL neurons in visceral nociception and are consistent with a role of VPL in sensory‐discriminative aspect of nociception.