CENTRAL PROJECTIONS AND SOMATOTOPIC ORGANIZATION OF TRIGEMINAL PRIMARY AFFERENTS IN PIGEON (COLUMBA-LIVIA)

Injections of cholera toxin B-chain conjugated to horseradish peroxida se into individual peripheral branches of the trigeminal nerve or into the trigeminal ganglion showed that an ascending trigeminal tract (TT A) terminated in distinct ventral and dorsal divisions of the principa l sensory nucleus (PrVv and PrVd, respectively), and a descending trac t (TTD) terminated within pars oralis, pars interpolaris, and pars cau dalis divisions of the nucleus of TTD (nTTD) and within the dorsal hor n of the first six cervical spinal segments. In PrVd, mandibular, opht halmic, and maxillary projections were predominantly located dorsally, ventrally, and medially, respectively. In nTTD, mandibular projection s lay dorsomedially, ophthalmic projections lay ventrolaterally, and m axillary projections lay in between. At caudal medullary and spinal le vels, mandibular projections were situated medially, ophthalmic projec tions were situated laterally, and maxillary projections were situated centrally. The terminations within the dorsal horn were most dense in laminae III and IV and were best dense in lamina II, with laminae III -TV also receiving topographically organised contralateral projections . Extratrigeminal projections were mainly to the external cuneate nucl eus by way of a lateral descending trigeminal tract (ITTD; Dubbeldam a nd Karten [1978] J. Comp. Neurol. 180:661-678) and to the region of th e tract of Lissauer and lamina I of the dorsal horn. Other projections were to a region medial to the apex of pars interpolaris, to the nucl ei ventrolateralis anterior (Via) and presulcalis anterior (Pas) of th e solitary complex, and sparsely to the lateral reticular formation (p lexus of Horsley) ventral to TTD. No projections were seen to the trig eminal motor nuclei or to the cerebellum. (C) 1996 Wiley-Liss, Inc.