Organization of neuronal clusters in the mesencephalic trigeminal nucleus of the rat: Fluorescent tracing of temporalis and masseteric primary afferents

The organization of neuronal clusters in the rat mesencephalic trigeminal nucleus (Mes V) was analysed using fluorescent tracing techniques. Simultaneous injections of fluorescent compounds (True blue and Diamidino yellow) were made unilaterally in the masseter and temporalis muscle, or in the masseteric and temporalis nerve. Examination of labeled neurons in frozen brainstem sections showed that (1) the arrangement of temporalis and masseteric primary afferent neurons in the mesencephalic trigeminal nucleus is not somatotopic; (2) primary afferent neurons of both muscles are located at all rostrocaudal levels; and (3) clustering of temporalis, of temporalis and masseteric, and of masseretic afferent neurons occurs at all levels throughout the nucleus.