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Sandkhler and his colleagues have shown that subpopulations of these spinal neurons, with different ascending projections to the brain, may become sensitized under pathological conditions. To be more specific, neurons in lamina I of spinal dorsal horn that express the neurokinin 1 receptor for substance P mediate this abnormal pain sensitivity. The cellular mechanisms of these sensitizations resemble those in hippocampus known to be important for cognitive learning and memory. Depending upon the kind of underlying pathology, different spinal neurons become sensitized so that different parts of the CNS "memorize" different aspects of chronic pain.

Results were obtained from more than seven hundred spinal nerve cells in an "in vitro" spinal cord-dorsal root slice preparation from rats. Prior to recordings, animals received an injection of a retrograde tracer into different brain areas. Three days later, spinal neurons with a projection to the injection site were labeled and could thereby be identified in the slice preparation. It is the first time this approach was used in such a spinal cord preparation.

Then a dorsal root was stimulated electrically and C-fiber-evoked responses were recorded from spinal projection neurons. C-fibers are known to transmit pain-related information from the periphery to the spinal cord. After a few control responses, dorsal roots were stimulated with different stimulation patterns which can also be observed in C-fibers during inflammation or nerve injury. After these stimuli, the responses of well-defined subgroups of spinal dorsal horn neurons were much enhanced (up to 300 % above control levels), indicating that pain-related information was amplified strongly.

Depending upon the type and pattern of dorsal root stimulation, different sub
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Contact: Dawn McCoy
dawn@sfn.org
202-462-6688
Society for Neuroscience
10-Nov-2003