Distribution of GABA-immunoreactive premotor neurons projecting to the trigeminal motor nucleus in the rat.

The distribution of neuronal cell bodies with gamma-aminobutylic acid (GABA)-like immunoreactivity projecting to the trigeminal motor nucleus were examined in the rat brainstem by the retrograde transport of horseradish peroxidase (HRP) and immunofluorescence methods. After HRP injection into the unilateral trigeminal motor nucleus, retrogradely labeled neurons which showed GABA-like immunoreactivity were observed throughout the parvocellular reticular nucleus in the pons with ipsilateral predominance. A few neurons were encountered in the contralateral supratrigeminal nucleus, ipsilateral caudal pontine reticular nucleus. All labeled neuronal cell bodies were small or of medium size; no large cells were labeled. The results indicated that cell bodies of GABAergic premotor neurons projecting to the trigeminal motoneurons were mainly located in the bilateral parvocellular reticular nucleus of the pons.