Relationship between analgesia and cardiovascular changes induced by electrical stimulation of the mesencephalic periaqueductal gray matter in the rat.
Analgesia and cardiovascular changes produced by electrical stimulation of the midbrain periaqueductal gray matter were examined in the lightly pentobarbital-anesthetized rat. The current intensity required to elicit analgesia was first determined, using the tail-flick test, after which the effects on arterial pressure and heart rate were recorded from stimulating at the same intensity. Intensity thresholds for decreases and/or increases in arterial pressure were also ascertained at the same sites. Although stimulation at the analgesia threshold produced increases in arterial pressure at more than 60% of the sites within the periaqueductal gray, decreases, no change, and mixed responses were also observed. Below the periaqueductal gray, increases in arterial pressure occurred at analgesia threshold for more than 70% of the sites studied, and no cardiovascular changes were found for 20% of the sites. Above the periaqueductal gray, no change and mixed responses were the predominant effects at analgesia threshold. A correlation across sites within the periaqueductal gray was found between the threshold for stimulation-produced analgesia and the threshold for a change in arterial pressure. No reliable alterations in heart rate were observed at any stimulation site. These results are in agreement with the existence of a common midbrain substrate for both the regulation of pain inhibition and cardiovascular function. However, they indicate that analgesia resulting from stimulation of the periaqueductal gray matter does not necessarily occur concurrently with an increase in arterial pressure.
Depaulis
A
A
Department of Psychology, University of California, Los Angeles 90024.
Pechnick
R N
RN
Liebeskind
J C
JC
D000698:Analgesia; D000818:Animals; D001794:Blood Pressure; D004558:Electric Stimulation; D006339:Heart Rate; D008297:Male; D010487:Periaqueductal Gray / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains