The aim of the present study was to examine changes in the level of neuronal nitric oxide synthase (nNOS) and parvalbumin (PV) in dorsal horn of the rat lumbar spinal cord segments (L2–L6) 7 and 14 days after thoracic spinal cord transection. Our data show that staining of control transverse spinal cord sections with nNOS antibody provided an intense labeling of small round or bipolar nNOS- immunoreactive (IR) cells bodies, fi bers and terminal like structures which were distributed throughout lamina II and formed a dense IR band. The large multipolar nNOS-IR cells with stellate or elongated cell bodies were occasionally seen in the deeper layers (laminae III–IV). A decreased density of fi berlike and the loss of somatic nNOS staining was found in dorsal horn layers after transection at both time points. A quantitative assessment of nNOS IR disclosed a strong decrease in the number of small neurons in superfi cial laminae (laminae I–III). In addition, an intense PV-IR band, consisting of terminal like structures in lamina II under normal conditions, was signifi cantly reduced due to spinal cord transection. The present study indicates a considerable decrease in the number of nNOS-IR neurons in superfi cial dorsal horn, where NO modulates the activity of inhibitory GABA-ergic interneurons. The changes in expression of both the calcium binding proteins in dorsal horn may modulate nociceptive transmission. Support: APVV grant 0314-06 and VEGA Grant 2/0015/08 from the SAS.
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