Central afferent connections and origin of efferent projections of the facial nerve in the chicken (Gallus gallus domesticus).

The central afferent connections and origin of efferent projections of the facial nerve in the adult domestic chicken were studied by anterograde and retrograde transport of horseradish peroxidase from the geniculate ganglion. Ipsilateral afferent projections were traced caudal to the level of entrance of the facial nerve and into tractus solitarius (TS), located dorsomedial to the spinal trigeminal nuclear complex. At several rostrocaudal levels in the medulla, fibers exited from TS and terminated in n. sensorius N. facialis (SVII), and nn. ventrolateralis anterior (Vla) and intermedius anterior (Ia) solitarii. Some axons were followed to n. presulcalis anterior (Pas) solitarii. A separate component terminated in subnucleus interpolaris (ip) of n. descendens nervi trigemini or its medially adjacent reticular formation either by exiting from TS or coursing caudally through the trigeminal complex from entering facial rootlets. Another diffuse component of facial axons ascended dorsally and rostrally from the level of entrance of the facial nerve; these projections dissipated in the pons--some on the dorsomedial border of n. principalis N. trigemini (PrV). Ipsilateral efferent projections were traced through the main genu of the facial nerve to retrogradely labelled somata of pars dorsalis (FMd), pars intermedia (FMi), and pars ventralis (FMv) of n. motorius nervi facialis. A separate group of smaller, multipolar, and spindle-shaped cells (8-25 microns) wedged between n. olivaris superioris (OS) and the caudal end of FMv, rostrally, and extending caudally in ventrolateral medulla were labelled. These small cells contrast with the larger (21-45 microns), oval, round, and multipolar somata of FMv and may correspond, in part, to a parasympathetic n. salivatorius (Sal).