In saline-treated rats (A) there is dense labeling in laminae I and 
II as well as in the neck of the dorsal horn and the ventral horn. 
Pretreatment with 0.06 pg ICV DAMGO (B) produced 50-percent 
inhibition of overall FLI (i.e., superficial FLI+nucleus proprius 
FLI+neck FLI + ventral FLI). A quantitative analysis of the number 
of neurons expressing FLI in the superficial, nucleus proprius, 
neck, or ventral regions of the cord showed that this dose 
produced close to 50-percent inhibition in the neck and ventral 
regions but had minimal effect on the level of FLI in the superficial 
layers. Pretreatment with 0.60 ^g DAMGO (C) produced 
approximately 84-percent inhibition of the FLI in the neck and 
ventral regions but only 64-percent inhibition of the FLI in the 
superficial dorsal horn. The effects of 0.60 \ig DAMGO were 
completely reversed by naloxone (D). Calibration bars=250 pm; 
dc=dorsal column; lli=inner laminae II. 
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. 
potencies of ICV DAMGO were considered in different laminae (figure 10), it 
was found that there was approximately a fourfold difference in the estimated 
ED 50 values for the laminae V/VI or ventral horn vs. the superficial laminae; 
thus, at doses of 0.04 to 0.06 \iq ICV there was an approximate 50-percent 
decrease in both the behavioral response and the Fos expression in laminae 
V-X. By contrast, the dose-response curve for DAMGO-mediated inhibition of 
Fos immunoreactivity in the superficial cord was shallow. In fact, at the ED 50 
doses for inhibition of Fos expression in the neck and ventral regions of the 
cord, there was less than 10-percent inhibition of Fos in the superficial dorsal 
horn. 
These data are consistent with previous findings with systemic morphine 
(Presley et al. 1990), which also showed that complete behavioral analgesia 
could be produced without eliminating the Fos immunoreactivity in the 
superficial cord. On the other hand, our studies with both systemic and ICV 
morphine showed that a dose of morphine that produced approximately 
50 percent inhibition of Fos immunoreactivity in the neck and ventral cord 
produced a comparable suppression in the superficial dorsal horn Fos 
immunoreactivity. This contrasts with our findings using DAMGO in which 
doses that produced a 50-percent reduction in Fos immunoreactivity in the 
151 
