The Journal of Neuroscience, December 1, 1999, 19(23):10397-10403
Developmental Tuning in a Spinal Nociceptive System: Effects of
Neonatal Spinalization
Anders
Levinsson,
Xiao-Ling
Luo,
Hans
Holmberg, and
Jens
Schouenborg
Department of Physiological Sciences, Section for Neurophysiology,
Lund University, S-223 62 Lund, Sweden
Recent studies indicate a modular organization of the nociceptive
withdrawal reflex system. Each module has a characteristic receptive
field, closely matching the withdrawal movement caused by its effector
muscle. In the rat, the strength of the sensory input to each module is
tuned during the first postnatal weeks, i.e., erroneous spinal
connections are depressed, and adequate connections are strengthened.
To clarify if this tuning is dependent on supraspinal structures, the
effect of a complete neonatal spinal cord transection on the postnatal
tuning of withdrawal reflexes was studied. The nociceptive receptive
fields of single hindlimb muscles and compound withdrawal reflexes were
examined in decerebrate unanesthetized and awake rats, respectively.
Noxious thermal CO2 laser stimulation was used to evoke
reflex responses. Neonatal spinal cord transection resulted in a
disrupted reflex organization in the adult rat, resembling that
previously found in neonatal rats. The receptive fields of single
hindlimb muscles exhibited abnormal distribution of sensitivity not
matching the withdrawal action of the effector muscles. Likewise, the
composite nocifensive movements, as documented in the awake rat, often
resulted in erroneous movements toward the stimulus. It is concluded
that withdrawal reflexes do not become functionally adapted in rats
spinalized at birth. These findings suggest a critical role for
supraspinal systems in the postnatal tuning of spinal nociceptive systems.
Key words:
pain; plasticity; sensorimotor integration; spasticity; brainstem control; rat
Copyright © 1999 Society for Neuroscience 0270-6474/99/192310397-07$05.00/0
Previous Article | Next Article
