Diffuse distribution of sulforhodamine-labeled neurons during serotonin-evoked locomotion in the neonatal rat thoracolumbar spinal cord

Citation
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
Citations number
62
Categorie Soggetti
Neurosciences & Behavoir
Journal title
JOURNAL OF COMPARATIVE NEUROLOGY
ISSN journal
00219967 → ACNP
Volume
423
Issue
4
Year of publication
2000
Pages
590 - 602
Database
ISI
SICI code
0021-9967(20000807)423:4<590:DDOSND>2.0.ZU;2-1
Abstract
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.