Behavioral Consequences of Delta-Opioid Receptor Activation in the Periaqueductal Gray of Morphine Tolerant Rats

<table>No change in
nociception following deltorphin microinjection into the vPAG in rats treated
with continuous morphine. Rats implanted with morphine pellets 3 days prior to
this test had higher baseline hot-plate latency than rats implanted with
placebo pellets indicating that tolerance to the antinociceptive effects was not complete. 
Microinjection of deltorphin into the vPAG caused an increase in hot-plate
latency in rats with placebo pellets (<i>N</i>  =  5), but did not increase the hot-plate
latency for rats with morphine pellets (<i>N</i>  =  5) above the baseline latency. That
is, there was no additional antinociception by injecting deltorphin into the
vPAG of rats receiving morphine.</table>

Neural Plasticity

fig4

Figure 4

Figure 4: Behavioral Consequences of Delta-Opioid Receptor Activation in the Periaqueductal Gray of Morphine Tolerant Rats 