Journal of Neuroscience, Vol 14, 6472-6480, Copyright © 1994 by Society for Neuroscience
NMDA receptor blockade rescues Clarke's and red nucleus neurons after spinal hemisection
CA Sanner, TJ Cunningham and ME Goldberger
Department of Neurology, Washington University School of Medicine, St. Louis, Missouri 63110.
Hemisection of the adult rat spinal cord at T9 transects the ascending
ipsilateral axons of Clarke's nucleus (CN) neurons and the descending
contralateral axons of red nucleus (RN) neurons. Eight weeks following
axotomy, 30% of CN neurons and 22% of RN neurons die. Since both nuclei
receive glutamatergic input, we wished to examine the possibility that
glutamatergic excitotoxicity contributes to axotomy-induced neuronal death
in these nuclei. To test this we studied the effects of administration of
the NMDA receptor antagonist MK-801 on cell survival after axotomy. When 1
mg/kg body weight MK-801 is administered subcutaneously every day for 1-8
weeks to hemisected rats, cell death is prevented. Treatment with 0.5 mg/kg
body weight MK-801 over the same time periods results in only partial
rescue of axotomized neurons. Paradoxically, when 1 mg/kg MK-801
administration is restricted to the first week of an 8 week survival
period, cell death in both the RN and CN is greatly exaggerated over the
cell loss found in saline-treated animals. Withdrawal of 1 mg/kg MK-801
after 1 week of administration induces the loss of 92% of CN neurons, which
is 63% greater than that occurring after axotomy alone. If, however, 1
mg/kg MK-801 is withdrawn after 2 weeks post-axotomy in the RN and 3 weeks
postaxotomy in CN, all axotomized neurons survive. This rescue is found at
6 months postsurgery, the longest survival period studied, and therefore
appears to be permanent. These results suggest that glutamatergic afferent
input contributes significantly to the death of axotomized red nucleus and
Clarke's nucleus neurons via NMDA receptors located on these neurons.