CENTRAL TERMINATIONS OF LOW-THRESHOLD MECHANORECEPTIVE AFFERENTS IN THE TRIGEMINAL NUCLEI INTERPOLARIS AND CAUDALIS OF THE CAT

Previous studies indicate that vibrissa, nonvibrissa, guard hair, hair y skin, and periodontal ligament afferents give rise to morphologicall y distinct terminal arbors in the trigeminal nuclei principalis (Vpi a nd oralis (Vo) in the cat. The present study describes the extent to w hich morphological and functional relationships exist in the nuclei in terpolaris (Vi) and caudalis (Vc). Twenty-two fibers were physiologica lly characterized and stained by intra-axonal HRP injection techniques . The fast adapting (FA) vibrissa (VF) afferents gave rise to compact and circumscribed arbors in Vi and Vc. These tended to be larger in Vc than in Vi. The slowly adapting (SA) vibrissa (VSI afferents in Vi an d Vc had more widespread and larger arbors than those of the VF affere nts. The VS arbors in Vc tended to be larger and less circular than th ose in Vi. Guard hair (GH) afferents gave rise to circumscribed arbors in both nuclei, but those in Vc tended to have larger and more circul ar arbors than those in Vi. Down hair (DH) afferents gave rise to smal l, circumscribed arbors or a few distinct patches of boutons within a small area in Vi; arbors in Vc were less extensive and ''stringy.'' Un like other afferents, DH arbors were larger in Vi than in Vc, but smal ler than those of GH afferents in either nuclei. The SA hairy skin (SS ) afferents had arbors that were widespread with a few distinct patche s of boutons; the arbors in Vc were larger than those in Vi. The arbor s of SS afferents were smaller than those of VS and GH afferents in bo th nuclei. Like GH afferents, FA periodontal ligament (PF) afferents g ave rise to large and circumscribed arbors in Vi, although the arbors in Vc were smaller and less dense. The present study demonstrated sign ificant functional and morphological relationships for primary afferen ts in Vi and Vc, thus suggesting that sensory information from each of the distinct fiber or functional classes is processed in a characteri stic manner in the individual nuclei. (C) 1994 Wiley-Liss, Inc.