Brain research bulletin
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Brain research bulletin · Apr 1999
The effect of morphine on responses of nucleus ventroposterolateralis neurons to colorectal distension in the rat.
In 71 halothane-anesthetized rats, we characterized the responses of single neurons in the nucleus ventroposterolateralis (VPL) of the thalamus to a noxious visceral stimulus (colorectal balloon distension; CRD) and studied the effects of intravenous morphine on these responses using standard extracellular microelectrode recording techniques. One hundred nine neurons were isolated on the basis of spontaneous activity. Sixty-four (59%) responded to CRD, of which 52 (81 %) had excitatory and 12 (19%) had inhibitory responses. ⋯ Naloxone (0.4 mg/ kg, i.v.) reversed the effects of morphine. Morphine and naloxone had no significant 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 aspects of nociception.