TRANSIENT NADPH-DIAPHORASE ACTIVITY IN MOTOR NUCLEI OF THE FETAL HUMAN BRAIN-STEM

NADPH-d activity is a marker for neurones which synthesize nitric oxid e (NO). In the present paper we study the NADPH-d activity in the huma n brain stem between 16 and 24 gestational weeks (GW). The adult distr ibution of NADPH-d containing neurones is established at 24 GW. Betwee n 19 and 21 GW, neurones of the facial, hypoglossal and ambiguus nucle i show transient NADPH-d positivity. Therefore, in the human brain ste m there are two chronological patterns of neuronal nitric oxide syntha se (NOS) expression, one that appears during prenatal development and persists during the whole life, and another one, present only at a pre cise foetal moment. The transient NADPH-d activity in motor nuclei sug gests that NO is involved in early regulatory processes of the human b rain development.