FOS— IMMUNOREACTIVE NEURONS 
FIGURE 6. Correlation between noxious stimulus-evoked “pain" behavior 
and spinal cord FLI. The mean area-under-the-curve (AUC) 
scores for behavior (abscissa) are plotted against the overall 
mean FLI values (i.e., the mean sum of the superficial-f-nucleus 
proprius+neck+ventral FLI; ordinate) for each of the six 
intracerebroventricular (ICV) drug treatments used (0.006, 
0.02, 0.06, 0.20, 0.60 pgDAMGO (D-Ala 2 , NMe—Phe 4 , Gly-OL 5 - 
enkephalin) or saline; n=3 per group). The expression of pain 
behavior was significantly correlated with the number of neurons 
expressing FLI (Pearson’s r=0.84, p<0.001). 
SOURCE: Reprinted with permission from Neuroscience 42, Gogas, 
K.R.; Presley, R.W.; Levine, J.D.; and Basbaum, A.I. The 
antinociceptive action of supraspinal opioids results from an 
increase in descending, inhibitory control: Correlation of 
nociceptive behavior and c-fos expression, 1991, Pergamon 
Press, pic. 
That the number of Fos-immunoreactive neurons in individual regions of the 
cord can be quantified further allows the differential regulation by morphine of 
the activity of neurons in functionally distinct areas of the cord to be determined 
(figure 7). Importantly, the dose-response curve for the effects of morphine 
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