Transient expression of NADPH-diaphorase/nitric oxide synthase in the paratenial nucleus of the rat thalamus

Abstract

The distribution pattern of nitric oxide synthesizing neurons was studied in the paratenial nucleus throughout the rat development using the NADPH-diaphorase (ND) histochemical method and nitric oxide synthase (NOS) immunocytochemistry. The onset of ND/NOS activity in the paratenial nucleus was detected in the postnatal life day 1. Until the postnatal stage 4, a quick increase in the number and staining intensity of the ND/NOS positive neurons was observed. From postnatal day 4 to postnatal day 6, these variations continued slowly, whereas an increase in the neuronal size was evident. In these stages, densely packed ND/NOS-labeled neurons were observed. From stages 6 to 10, the ND/NOS-positive elements demonstrated similar number, size, and staining intensity. These cells had medium size, variable morphology and showed reaction product in the cell bodies and, at most, their proximal dendrites. After postnatal day 10, a quick decrease in the staining intensity and in the number of ND/NOS-labeled elements was detected, although no changes were observed in their morphological characteristics. Postnatal day 15 was the last developmental stage studied in which ND/NOS-positive elements were observed. Finally, the paratenial nucleus did not present ND/NOS-positive elements in adult animals. This transient expression of the ND/NOS-activity suggests a role of nitric oxide in the reorganization of the paratenial nucleus during the first postnatal fortnight.