C. Cina et S. Hochman, Diffuse distribution of sulforhodamine-labeled neurons during serotonin-evoked locomotion in the neonatal rat thoracolumbar spinal cord, J COMP NEUR, 423(4), 2000, pp. 590-602
The fluorescent dye sulforhodamine-101 undergoes synaptic activity-dependen
t endocytotic uptake and consequent retrograde transport in presynaptic neu
rons. We used sulforhodamine to identify thoracolumbar spinal premotor neur
ons (T11-L6) activated during serotonin (5-HT) -induced hindlimb locomotor-
like activity in the in vitro neonatal rat spinal cord preparation. Sulforh
odamine labeling required locomotor-like activity because few neurons were
labeled unless bath applied 5-HT recruited the locomotor rhythm. In contras
t, N-methyl-D-aspartate (NMDA; 5 mu M) profoundly increased spinal neuronal
labeling irrespective of locomotor activity. The contribution of false-pos
itive activity labeling during locomotion induced by application of NMDA wi
th 5-HT (Kjaerulff et al. [1994] J Physiol (Lond). 478:265-273) necessitate
d the present re-mapping of sulforhodamine-tabeled neurons. During 5-HT-evo
ked locomotion, the sulforhodamine-labeled neurons were diffusely scattered
within the spinal cord with predominant labeling in lamina VII. Motor nucl
ei (lamina IX) and superficial laminae (I-II) were typically devoid of labe
led cells in the isolated spinal cord. However, unilateral labeling of moto
neurons was achieved when the ipsilateral hindlimb remained attached, sugge
sting that uptake in motoneurons requires an intact neuromuscular junction.
The rostrocaudal incidence and distribution of labeled neurons was uniform
in spinal segments L1-L5, with reduced numbers observed in thoracic and L6
spinal segments. Mean total cell labeling was less than 400 per spinal seg
ment, suggesting recruitment from a very small fraction of the neurons cont
ained within the spinal cord (calculated at < 0.1%). These results are cons
istent with the limited transfer of locomotor-related synaptic activity (Ra
astad et al. [1996] Neuron 17:729-738) and severe synaptic fatigue (Lev-Tov
and Pinco [1992] J Physiol. 447:149-169; Pinco and Lev-Tov [1993] J Neurop
hysiol. 70:1151-1158; Fleoter and Lev-Tov [1993] J Neurophysiol. 70:2241-22
50) observed in the neonatal rat spinal cord. J. Comp. Neurol. 422:590-602,
2000. (C) 2000 Wiley-Liss, Inc.