Immobility accompanies the antinociception mediated by the rostral ventromedial medulla of the rat.
The rostral ventromedial medulla (RVM) is part of a descending pain modulatory system that runs from the periaqueductal gray (PAG) to the spinal cord. The objective of the present study was to determine whether the antinociception mediated by the RVM is associated with locomotor changes as has been reported for the PAG [42]. Kainate (4, 20, or 40 pmol), morphine (1, 5, or 10 microg), or saline (0.2 or 0. 5 microl) was injected into the RVM and locomotion and nociception assessed. Microinjections of kainate and morphine that produced antinociception almost invariably inhibited locomotor activity. In some rats this immobility consisted of no movements when placed in the center of the open field chamber. These data are consistent with the immobility and antinociception produced by activation of the ventrolateral PAG and indicate that the descending ventrolateral PAG/RVM system integrates a behavioral response of which antinociception is only one component.
Department of Psychology, Washington State University, 14204 NE Salmon Creek Ave. Vancouver, WA 98686, USA. morgan@vancouver.wsu.edu
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D000700:Analgesics / Q000494:pharmacology*; D000818:Animals; D007103:Immobilization / Q000502:physiology*; D007608:Kainic Acid / Q000008:administration & dosage; D008297:Male; D008526:Medulla Oblongata / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D008845:Microinjections; D009020:Morphine / Q000008:administration & dosage; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000502:physiology; D010147:Pain Measurement / Q000187:drug effects; D010487:Periaqueductal Gray / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects
D000700:Analgesics; D009020:Morphine; D007608:Kainic Acid