Induction of NADPH-diaphorase/nitric oxide synthase in the brainstem trigeminal system resulting from cerebellar lesions

Recent evidence indicates that NADPH-diaphorase (NADPH-d) and nitric oxide synthase (NOS) can be induced in cerebellar afferent neurons following mechanical, thermal, or chemical damage to the cerebellar cortex (Saxon and Beitz [1994] Neuroreport 5:809-812). The present study reports on the induction of NADPH-d/NOS in neurons of the brainstem trigeminal complex (BVC). Three groups of rats were used: Group I received a unilateral glass micropipette lesion into the vermal/paravermal region of the cerebellar cortex, group II received a concurrent injection of fluoro-gold along with the pipette lesion, and in group III the cerebellar cortex on one side was aspirated. Following survival times of 7-120 days, animals were processed for NADPH-d histochemistry. All three groups showed projection-specific induction of NADPH-d in different regions of the brainstem trigeminal complex. Induced neurons were distributed throughout the ipsilateral subnucleus interpolaris, principal trigeminal nucleus, and intertrigeminal nucleus. Subnucleus oralis contained a small number of induced neurons localized to the ipsilateral dorsomedial portion of the subnucleus. Projection-specific induction was confirmed by the presence of neurons double-labeled for NADPH-d and Fluoro- Gold. Although the functional consequences of NADPH-d/NOS induction remain to be elucidated, the induction of these enzymes in precerebellar neurons suggests that nitric oxide may play a role in the neuronal response to target specific lesions.