Central gustatory paths in the crucian carp,carassius carassius

The central fiber connections of the gustatory system (VII, IX, and X nerves) in the crucian carp were examined by the Fink-Heimer method and its modification. The sensory and recurrence roots of the VII enter the brainstem separately and terminate in the ipsilateral half of the facial lobe (L-VII). Afferent fibers of the IX terminate in the glossopharyngeal lobe (L-IX). Most afferent fibers of the X terminate in the sensory layer of the vagal lobe (L-X), in which degenerating terminals occur in some laminae. Some vagal afferents project bilaterally to the commissural nucleus of Cajal. The cutaneous component of the X projects to the nucleus of the spinal trigeminal tract (SpV) and the medial funicular nucleus (nFM). Ascending secondary fibers from the L-VII project bilaterally to the secondary gustatory nucleus (nGS) in the isthmus region. Descending secondary fibers from the L-VII turn caudally in the SpV. These fibers terminate mostly in the nucleus of the SpV and sparsely in the nFM. The L-IX and L-X give rise to the long and short secondary paths. The long path projects as the ascending secondary tract to the ipsilateral nGS. The short path includes secondary fibers projecting to the motor layer of the L-X and the medullary reticular formation. Tertiary gustatory fibers arising in the nGS project ipsilaterally to two diencephalic nuclei: the nucleus glomerulosus and the nucleus diffusus lobi inferioris.