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Role of Aβ and Aδ afferent nerve fibers in the suppressive effects on the tail flick reflex in rat
$170 ROLE OF A@ AND A6 A F F E R E N T F L I C K !:IEFLEX IN R A T
NERVE
AiKO M A T S U I , M A S A Y O S H I T S U R U O K A DeFal~tment of P h y s i o l o g y , S h o w a Sh~na~awa-ku, T o k v o 142, J a p a n
FIBERS
II! THE
SUP°f{ESSIVE
~n ~" ,o O~.I THE T A I L E_~Eoff<~
and £ O I C H I R O [.(ATSUI U n i v e r s i t y S c h o o l of Dentlstr,,,
I-5-8
Hatanodai,
The s u p p r e s s i v e e f f e c t s o£ A@ and A6 a f f e r e n t n e r v e i m p u l s e s on the tail f l i c k muscle activity were investigated. ~ats w e r e a n e s t h e t i z e d w ~ t h an i n i t i a l dose of' ~0 m ~ / k s of t h i a m y l a l sodium, and a m a i n t e n a n c e dose of ~ m £ / k s was ~ i v e n to m a i n t a i n light a n e s t h e s i a . The ~ n t e s r a t e d electrom~'osram (EM@) of the tai] f l i c k m u s c l e (M. e x t e n s o r c a u d a e m e d i a l i s ) e l i c i t e d by n o x i o u s heat s t i m u l a t i o n to the tail skin was u s e d as an i n d i c a t o r of the s u p p r e s s i v e e f f e c t by s e l e c t i v e s t i m u l a t i o n of A@ and A6 n e r v e fibers. U s i n £ a p a i r of n e e d l e e l e c t r o d e s , e l e c t r i c a l s t i m u l a t i o n was a p p l i e d to the Z u s a n l i point and n e a r b y . B;~ m o n i t o r i n g c o m p o u n d a c t i o n p o t e n t i a l s r e c o r d e d from the c o m m o n <'eronea! nerve, we c o u l d d i s t i n g u i s h the A@ and the A6 a c t i o n r~otentJals j u d £ i n s from the c o n d u c t i o n v e l o c i t y . On the m e r i d i a n point, a b o u t 5 m m d i s t a l from the c a ~ i t u l u m f i b u l a e , t h e r e was a c e r t a f n a r e a w h i c h had a relative!?7 low t h r e s h o l d ]ntensit),' (T) for elicitinf< the AB a c t i o n r~otentJal. W h e n the s t i m u l u s i n t e n s i t y was less th-~n 7 times of T, onl~! the ;~ a c t i o n p o t e n t i a l was o b s e r v e d , rn the m e d i a ] F~ide a b o u t 5 mm from the c ~ p i t u l u m fitulae, there ,J~s a c e r t a i n area in w h i c h o n l y the A~ ~ c t i o n p o t e n t i a l wa~ e l i c i t e d bj~, e l e c t r i c a l s t i m u l a t i o n w i t h i n 3 times of T. W h e n A[% a f f e r e n t n e r v e s t ~ m u ! a t i o n was ~iven for 30 rain at v a r i o u s f r e q u e n c i e s from 2 to 10O IIz, the ma~iritude of E~,I~ d e c r e a s e d to 6S 5 ( m a x i m u m (~ffect d u r i n ¢ 30 rain) at 2 Hz, and to ~lli ,~ at _]00 l=z. B~ ,~6. a f f e r e n t r~erve stimulat~or~ For_ ~,O rain at 2 }{z, the m u s c l e a c t i v i t y d e c r e a s e d to 5~ ~'.. A S t e r the c e s s a t i o n of e l e c t r i c a ] s t i m u l a t i o n , thes~ s u ~ : r e s s i v e e f f e c t s l a s t e d f'cr 20 to on m i n in b o ~ h ):<~ses These effects w e r e not a n t a < o n i z e d b)~ n a l o x o n e (1 ml./ks, 20 m~E/ks, i.F. '.,. , n the o t h e r hslnd, An n e r v e s t i m u l a t i o n of the l[oku [~o!nt l o c a t e d .~t the d i f f e r e ~ t d e r m a t o m e s from the Z u s a n ! i , also o r o d u c o d the sur}nression ,of the m u s c l e act.]vit~/. H o w e v e r , the s u ! p r e s s J w ~ e f f e c t s of the ]!oku s t i m u l a t i o n w e ? e <]nt<]~onized ~;~.,rr~]oxone (I mT/kK)
THE EFFECTS OF STIMULATION OF THE THALAMIC PARAFASCICULAR NUCLEUS ON NOCICEPTIVE NEURONS IN THE PERIAQUEDUCTAL GRAY SHUJI SAKATA, FUMIO SHIMA AND MOTOHIRO KATO : Department of Neurophysiology, I n s t i t u t e , Faculty of Medicine, Kyushu University 60, Fukuoka 812, Japan
Neurological
We studied the effects of e l e c t r i c a l stimulation of the parafascicular nucleus (Pf) of the thalamus and peripheral noxious stimuli on the a c t i v i t i e s of neurons in the periaqueductal gray (PAG), in order to investigate the mechanism of the analgesic e f f e c t of Pf stimulation. Single unit e x t r a c e l l u l a r responses to these stimuli were recorded in PAG in rats under l i g h t halothane anesthesia. Bipolar stimulating electrodes were placed in Pf and Nucleus raphe magnus (NRM). PAG neurons projecting to NRM were i d e n t i f i e d by antidromic stimulation. Pf stimulation caused excitatory responses in 43 out of 90 units (45%), and i n h i b i t o r y ones in 30 (33%). Noxious stimuli produced excitatory responses in 60 out of 130 units (46%) and inhibitory in 30 (23%). Of 60 units which responded to both stimuli, 49 (75%) responded in the same manner. Eighteen of the PAG neurons were i d e n t i f i e d as projecting d i r e c t l y to the NRM: Excitatory responses were obtained in 7 out of I I units (64%) for Pf stimulation, and 7 out of I0 (70%) for noxious s t i m u l i . The predominantly excitatory e f f e c t of Pf stimulation on PAG neurons suggests that the descending pain control system plays an important role in the analgesic mechanism of Pf stimulation. Also, the predominantly excitatory effect of noxious stimuli suggests the presence of a negative feed-back mechanism on pain mediation at the midbrain l e v e l .
NERVE
AiKO M A T S U I , M A S A Y O S H I T S U R U O K A DeFal~tment of P h y s i o l o g y , S h o w a Sh~na~awa-ku, T o k v o 142, J a p a n
FIBERS
II! THE
SUP°f{ESSIVE
~n ~" ,o O~.I THE T A I L E_~Eoff<~
and £ O I C H I R O [.(ATSUI U n i v e r s i t y S c h o o l of Dentlstr,,,
I-5-8
Hatanodai,
The s u p p r e s s i v e e f f e c t s o£ A@ and A6 a f f e r e n t n e r v e i m p u l s e s on the tail f l i c k muscle activity were investigated. ~ats w e r e a n e s t h e t i z e d w ~ t h an i n i t i a l dose of' ~0 m ~ / k s of t h i a m y l a l sodium, and a m a i n t e n a n c e dose of ~ m £ / k s was ~ i v e n to m a i n t a i n light a n e s t h e s i a . The ~ n t e s r a t e d electrom~'osram (EM@) of the tai] f l i c k m u s c l e (M. e x t e n s o r c a u d a e m e d i a l i s ) e l i c i t e d by n o x i o u s heat s t i m u l a t i o n to the tail skin was u s e d as an i n d i c a t o r of the s u p p r e s s i v e e f f e c t by s e l e c t i v e s t i m u l a t i o n of A@ and A6 n e r v e fibers. U s i n £ a p a i r of n e e d l e e l e c t r o d e s , e l e c t r i c a l s t i m u l a t i o n was a p p l i e d to the Z u s a n l i point and n e a r b y . B;~ m o n i t o r i n g c o m p o u n d a c t i o n p o t e n t i a l s r e c o r d e d from the c o m m o n <'eronea! nerve, we c o u l d d i s t i n g u i s h the A@ and the A6 a c t i o n r~otentJals j u d £ i n s from the c o n d u c t i o n v e l o c i t y . On the m e r i d i a n point, a b o u t 5 m m d i s t a l from the c a ~ i t u l u m f i b u l a e , t h e r e was a c e r t a f n a r e a w h i c h had a relative!?7 low t h r e s h o l d ]ntensit),' (T) for elicitinf< the AB a c t i o n r~otentJal. W h e n the s t i m u l u s i n t e n s i t y was less th-~n 7 times of T, onl~! the ;~ a c t i o n p o t e n t i a l was o b s e r v e d , rn the m e d i a ] F~ide a b o u t 5 mm from the c ~ p i t u l u m fitulae, there ,J~s a c e r t a i n area in w h i c h o n l y the A~ ~ c t i o n p o t e n t i a l wa~ e l i c i t e d bj~, e l e c t r i c a l s t i m u l a t i o n w i t h i n 3 times of T. W h e n A[% a f f e r e n t n e r v e s t ~ m u ! a t i o n was ~iven for 30 rain at v a r i o u s f r e q u e n c i e s from 2 to 10O IIz, the ma~iritude of E~,I~ d e c r e a s e d to 6S 5 ( m a x i m u m (~ffect d u r i n ¢ 30 rain) at 2 Hz, and to ~lli ,~ at _]00 l=z. B~ ,~6. a f f e r e n t r~erve stimulat~or~ For_ ~,O rain at 2 }{z, the m u s c l e a c t i v i t y d e c r e a s e d to 5~ ~'.. A S t e r the c e s s a t i o n of e l e c t r i c a ] s t i m u l a t i o n , thes~ s u ~ : r e s s i v e e f f e c t s l a s t e d f'cr 20 to on m i n in b o ~ h ):<~ses These effects w e r e not a n t a < o n i z e d b)~ n a l o x o n e (1 ml./ks, 20 m~E/ks, i.F. '.,. , n the o t h e r hslnd, An n e r v e s t i m u l a t i o n of the l[oku [~o!nt l o c a t e d .~t the d i f f e r e ~ t d e r m a t o m e s from the Z u s a n ! i , also o r o d u c o d the sur}nression ,of the m u s c l e act.]vit~/. H o w e v e r , the s u ! p r e s s J w ~ e f f e c t s of the ]!oku s t i m u l a t i o n w e ? e <]nt<]~onized ~;~.,rr~]oxone (I mT/kK)
THE EFFECTS OF STIMULATION OF THE THALAMIC PARAFASCICULAR NUCLEUS ON NOCICEPTIVE NEURONS IN THE PERIAQUEDUCTAL GRAY SHUJI SAKATA, FUMIO SHIMA AND MOTOHIRO KATO : Department of Neurophysiology, I n s t i t u t e , Faculty of Medicine, Kyushu University 60, Fukuoka 812, Japan
Neurological
We studied the effects of e l e c t r i c a l stimulation of the parafascicular nucleus (Pf) of the thalamus and peripheral noxious stimuli on the a c t i v i t i e s of neurons in the periaqueductal gray (PAG), in order to investigate the mechanism of the analgesic e f f e c t of Pf stimulation. Single unit e x t r a c e l l u l a r responses to these stimuli were recorded in PAG in rats under l i g h t halothane anesthesia. Bipolar stimulating electrodes were placed in Pf and Nucleus raphe magnus (NRM). PAG neurons projecting to NRM were i d e n t i f i e d by antidromic stimulation. Pf stimulation caused excitatory responses in 43 out of 90 units (45%), and i n h i b i t o r y ones in 30 (33%). Noxious stimuli produced excitatory responses in 60 out of 130 units (46%) and inhibitory in 30 (23%). Of 60 units which responded to both stimuli, 49 (75%) responded in the same manner. Eighteen of the PAG neurons were i d e n t i f i e d as projecting d i r e c t l y to the NRM: Excitatory responses were obtained in 7 out of I I units (64%) for Pf stimulation, and 7 out of I0 (70%) for noxious s t i m u l i . The predominantly excitatory e f f e c t of Pf stimulation on PAG neurons suggests that the descending pain control system plays an important role in the analgesic mechanism of Pf stimulation. Also, the predominantly excitatory effect of noxious stimuli suggests the presence of a negative feed-back mechanism on pain mediation at the midbrain l e v e l .