Reflex inhibition of vagally-induced jejunal contractions by capsaicin

$129 I N H I B I T I O N O F V A G A L L Y - I N D U C E D J E J U N A L C O N T R A C T I O N S BY CAPSAICIN. TOSHIAKI NEYAf AND M A S A T O S H I MIZUTANI* r Department of Physioloqy, Okayama University Medical School t 2-5-I S h i k a t a - c h o r O k a y a m a 7001 Japan. We studied w h e t h e r capsaicin, which stimulates e x t r i n s i c p e p t i d e r g i c sensory neurons, caused reflex effect on jejunal m o t i l i t y in dogs. A n i m a l s were anesthetized w i t h k e t a m i n e h y d r o c h l o r i d e (12.5mg/kg,i.m.) and i.v. infusion of 5% urethane-Ringer solution. M o t i l i t y of jejunal segments separated from e a c h other was recorded. Drugs were a d m i n i s t e r e d on each segment through m e s e n t e r i c artery. C h o l i n e r g i c c o n t r a c t i o n s of one s e g m e n t (effector segment) induced by u n i l a t e r a l vagus s t i m u l a t i o n (10Hz, Ims) were inhibited by c a p s a i c i n (10-100pM, 0.07-0.14mi /min) on the o t h e r s e g m e n t (receptor segment). The inhibitory action of c a p s a i c i n was a b o l i s h e d by sympathectomy, s p i n a l i z a t i o n (C6), p h e n t o l a m i n e (lmM, 0.07 ml/min) and y o h i m b i n e (ImM, 0.07ml/min) a d m i n i s t e r e d on e f f e c t o r segment, but not by decerebration, p r a z o s i n (10pM, 0.07ml/min) or p r o p r a n o l o l (lmM, 0.03ml /min). Vagally-induced contractions were also inhibited by d i s t e n s i o n of r e c e p t o r segment. This effect was a b o l i s h e d by d e s e n s i t i z a t i o n to c a p s a i c i n of the r e c e p t o r segment. Single unit d i s c h a r g e of m e s e n t e r i c and splanchnic nerve a f f e r e n t was i n c r e a s e d by d i s t e n s i o n and capsaicin. S y m p a t h e t i c nerve efferent was also excited by c a p s a i c i n a d m i n i s t e r e d on r e c e p t o r segment. The results suggest that p e p t i d e r g i c sensory neurons sensitive to c a p s a i c i n are involved in a f f e r e n t limb of i n t e s t i n o - i n t e s t i n a l inhibitory reflex m e d i a t e d via brain stem.

REFLEX

TRANSIENT EXPRESSION OF SOMATOSTATIN mRNA IN THE COCHLEAR NUCLEI OF THE VERY YOUNG RAT. MIWAKO SEKITANI ~, SADAO SHIOSAKA, HIROMICHI K U R I Y A M A ~ YUKITSUKA KUDOU ~, AND MASAYA TOHYAMA, 2nd Department of Anatomy, and Department of Neuroanatom¥, Biomedical Research Center, Osaka University Medical School. We used i m m u n o c y t o c h e m i c a l methods to investigate the early development of somatostatin immunoreactive neurons in the rat dorsal (DCN) and ventral (VCN) cochlear nuclei, and found that these increase in number until a few days after birth, but then decrease drastically. By in situ hybridization histochemistry we observed the post-transcriptional somatostatin producing system during postnatal development. Antisense synthetic oligonucleotide was endolabeled with S-ATP and TdT and used as the probe. The largest numbers of neurons containing h y b r i d i z a t i o n signal were observed on postnatal day 2 in both nuclei. The h y b r i d i z a t i o n signal slightly decreased at days 7-9. After this, the signal dramatically diminished and autoradiographic grains in a labeled cell became quite few in the adult, though the number of labeled cells did not change much. The transient expression and following decrease of somatostatin seems to be caused mainly by change in the somatostatin producing system, not by cell death of somatostatinergic neurons.