The Journal of Neuroscience, June 1, 1998, 18(11):4393-4402
Activation of Coeruleospinal Noradrenergic Inhibitory Controls
during Withdrawal from Morphine in the Rat
Dana S.
Rohde2, 3 and
Allan I.
Basbaum1, 2, 3
Program in Biomedical Sciences, Departments of
1 Anatomy and 2 Physiology and
3 W. M. Keck Foundation Center for Integrative
Neuroscience, University of California at San Francisco, San Francisco,
California 94143
We previously reported that withdrawal from morphine induces
the expression of Fos, a marker of neuronal activity, in spinal cord
neurons, particularly in laminae I and II of the superficial dorsal
horn, and that the magnitude of Fos expression is increased in rats
with a midthoracic spinal transection. We suggested that loss of
withdrawal-associated increases in descending inhibitory controls that
arise in the brainstem underlie the increased Fos expression after
spinal transection. Here, we addressed the origin of the supraspinal
inhibition. We injected rats intracerebroventricularly with saline or
anti-dopamine-
-hydroxylase-saporin, a toxin that destroys
noradrenergic neurons of the locus coeruleus. Eleven days later, we
implanted rats with morphine or placebo pellets, and after 4 d, we
precipitated withdrawal with naltrexone. One hour later, the rats were
killed, their brains and spinal cords were removed, and transverse
sections of the brains and spinal cords were immunoreacted with an
antibody to Fos.
In placebo-pelleted rats, the toxin injection did not alter behavior
and did not induce expression of the Fos protein. However, compared
with saline-injected withdrawing rats, the toxin-treated rats that
underwent withdrawal demonstrated an intense withdrawal behavior rarely
seen in the absence of toxin, namely forepaw fluttering. The rats also
had significantly increased Fos-like immunoreactivity in all laminae of
the cervical cord and in laminae I and II and the ventral horn of the
lumbar cord. No differences were recorded in the sacral cord. We
conclude that the effects of spinal transection in rats that withdraw
from morphine in part reflect a loss of coeruleospinal noradrenergic
inhibitory controls.
Key words:
descending inhibition; Fos; locus coeruleus; morphine
withdrawal; saporin; spinal cord; tolerance
Copyright © 1998 Society for Neuroscience 0270-6474/98/18114393-10$05.00/0