NADPH-diaphorase in the spinal trigeminal nucleus oralis and rostral solitary tract nucleus of rats.

NADPH-diaphorase histochemical staining demonstrated a distinct neural group that might synthesize nitric oxide in the lower brainstem of rats. The NADPH-diaphorase stain revealed a Golgi-like network in the dorsomedial spinal trigeminal nucleus oralis and rostrolateral solitary tract nucleus, whereas this network was more dense in the latter nucleus. The distribution of NADPH-diaphorase-positive neurons in these areas overlapped with parts of central terminations from the chorda tympani nerve, as demonstrated with transganglionic transport of wheatgerm agglutinin conjugated horseradish peroxidase. The number of NADPH-diaphorase-positive neurons changed after chorda tympani nerve lesion relative to the contralateral side. The control value (%) was 106.0 +/- 4.9 (mean +/- S.E.M.). One hour after the nerve lesion, the value increased to 115.2 +/- 9.1 (P > 0.05). It then decreased to 83.9 +/- 5.2 two days after the lesion (P < 0.05), and remained at this reduced level for one or two weeks, 83.2 +/- 3.0 (P < 0.01) and 83.7 +/- 2.3 (P < 0.01), respectively. This statistically significant reduction recovered to control level 103.4 +/- 2.9 four weeks after the lesion. These results show that NADPH-diaphorase-positive neurons in the lower brainstem could be regulated trans-synaptically by primary afferents, possibly gustatory inputs.