Facial and oral representations within the trigeminal nucleus caudalis in cats

$145 FACIAL AND ORAL REPRESENTATIONS WITHIN THE TRIGEMINAL NUCLEUS CAUDALIS IN CATS SETSUKO SUEMUNE*, TOSHIKAZU NISHIMORI*, Y.C. CHEN*, I.D. NASUTION*, TAKASHI OKAMOTO*, MASAYUKI SERA* and YOSHIO SHIGENAGA, Department of Oral Anatomy, Hiroshima University School of Dentistry, Kasumi I-2-3, Minami-ku, Hiroshima 734, Japan. The central projections of afferent fibers from the cornea(C), and frontal(f), infraorbital(io), zygomatic(z), palatine(p), superior alveolar(as), auriculotemporal(at), mylohyoid(my), mental(m), buccal(b), lingual(l) and inferior alveolar(ai) nerves were investigated by the method of transganglionic transport of horseradish peroxidase. The receptive fields of the oral structures innervated by (I), (p) and (as) nerves were represented in laminae I and II of the most rostral part of the nucleus caudalis, arranged with dorsomedial to ventrolateral order, respectively. The projections of facial and other oral structural (ai and b) receptive fields were organized with the 'onion-skin' pattern; oral(ai) and perioral regions(io, m) were represented rostrally, while more posterior portions of the mouth(ai, b) and face(m, f, c, z, my and at) were represented at successively more caudal levels; and furthermore, the ventrodorsal bands of the face corresponding to the 'onion-skin' were represented in the mediolateral dimensions of the nucleus. This organization is uniform over the laminae of I-IV in the caudalis. These results show that the so-called 'onion-skin' organization described by D~jerine is applicable to a rostrocaudal axis of the nucleus caudalis, especially in laminae I and II. T O O T H PULP THALAMUS

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T O S H I K A T S U Y O K O T A , N A T S U K O Y A M A * and YASUO NISHIKAWA*, D e p a r t m e n t of P h y s i o l o g y , M e d i a c a l C o l l e g e of Shiga, Seta, 520-21, J a p a n

Otsu

N e u r o n s r e s p o n s i v e to e l e c t r i c a l s t i m u l a t i o n of c a n i n e t o o t h p u l p a f f e r e n t s w e r e s t u d i e d in u r e t h a n e - c h l o r a l o s e anesthetized cats. P r e v i o u s l y , we h a v e f o u n d t r i g e m i n a l n o c i c e p t i v e s p e c i f i c (NS) and w i d e d y n a m i c r a n g e (WDR) n e u r o n s w i t h i n the s h e l l r e g i o n of the c a u d a l V P M proper. NS n e u r o n s w e r e f o u n d in the c a u d a l t h i r d of the V P M p r o p e r , w h e r e a s W D R n e u r o n s w e r e e n c o u n t e r e d in a n a r r o w zone just r o s t r a l to the NS region. In the p r e s e n t experiments, two c l a s s e s of t o o t h p u l p n e u r o n s w e r e f o u n d w i t h i n t h e s e two r e g i o n s . One c l a s s c o n s i s t e d of t o o t h p u l p s p e c i f i c n e u r o n s . T h e y w e r e f o u n d in the m e d i a l p a r t of the NS region. A n o t h e r c l a s s c o n s i s t e d of w i d e d y n a m i c r a n g e n e u r o n s r e s p o n s i v e to t o o t h p u l p s t i m u l a t i o n . T h e y w e r e f o u n d w i t h i n the m e d i a l h a l f of the W D R zone. T o o t h p u l p n e u r o n s w i t h i n the d o r s a l s h e l l r e g i o n r e s p o n d e d to s t i m u l a t i o n of the c o n t r a l a t e r a l m a x i l l a r y c a n i n e , w h e r e a s t o o t h p u l p n e u r o n s w i t h i n the v e n t r a l s h e l l r e g i o n resp o n d e d to s t i m u l a t i o n of the c o n t r a l a t e r a l m a n d i b u l a r canine. Some of t h e m r e s p o n d e d to b o t h m a x i l l a r y and m a n d i b u l a r c a n i n e s . E l e c t r i c a l s t m u l a t i o n of the s o m a t o s e n s o r y cortex antidromically a c t i v a t e d t h e s e two c l a s s e s of t o o t h p u l p n e u r o n s . C o o l i n g of the d o r s o l a t e r a l p a r t of the m e d u l l a o b l o n g a t a c a u d a l to the o b e x reversibly blocked their tooth pulp evoked responses. Trigeminal t r a c t o t o m y n e a r the level of the o b e x i r r e v e r s i b l y a b o l i s h e d t h e s e r e s p o n s e s . It is s u g g e s t e d t h a t i m p u l s e s f r o m the t o o t h p u l p to the V P M are r e l a y e d t h r o u g h the c a u d a l m e d u l l a o b l o n g a t a .