15. 11. 1970

1227

Specialia

Ling,N--~(6eniogl.)

Reflex

g

B

2l

Mean control

Z_

Condifione~ resoonse ConditioneO by stimulation of

~,nterior ~igastric n.

Fig. 1. Effect of electrical stimulation of trigeminal proprioceptive afferents on reflexes to the protruder of the tongue (genioglossus). Reflexes were elicited by single test stimuli to the lingual nerve (A, B) or the glossopharyngeal nerve (C), and recorded from the proximal portion of the severed hypoglossal branch to the ipsilateral genioglossus muscle, The computer-determined 'mean control' reflexes are shown in the upper part of the figure. If conditioning stimulation to fpsilateral trigeminal proprioeeptive atferents in the anterior digastric nerve (A, C) or the masseteric nerve (B) preceded the test stimulus by the optimal conditioning-testinterval of 15 msec, the reflexes were considerably depressed ('conditioned responses'; lower part of figure). Each tracing was computed from 50 individual responses. Time calibration: 5 msec.

_ing.N~ E(6eniogl.) ~(Geni0gl.)

5

Masseteric nerve

Anterior digastric n.

100 80

~'60 mS6C

40

IEZ

Fig. 2. Time course of reflex inhibition showing the effect of electrical stimulation of trigeminal proprioceptive afferents on reflexes to the genioglossus. Reflexes were elicited by single test stimuli to the lingual nerve and recorded from the hypoglossal branch to the ipsilateral genioglossus. Conditioning stimulation was applied to the ipsilateral anterior digastric nerve. Each point on the curve was computed from 50 individual responses. The smaller inset illustrates the remarkable duration of the inhibitory phase (400 msec or longer).

z0 P

I

10

I

Z'0

J

?'0

4'0ms ec

conditioninginterval a f f e r e n t activities in p r o p r i o c e p t i v e fibers are responsible, for t h e o b s e r v e d i n h i b i t o r y effect. This v i e w is s u p p o r t e d b y t h e f a c t t h a t n a t u r a l s t i m u l a t i o n of p r o p r i o c e p t o r s in t h e m a s s e t e r or a n t e r i o r digastric muscle p r o d u c e d identical effects as did electrical s t i m u l a t i o n of t h e n e r v e s of t h e s e muscles 3. T h e r e m a r k a b l e d u r a t i o n of t h e t i m e course of reflex d e p r e s s i o n suggest t h e i n v o l v e m e n t of a p r e s y n a p t i e i n h i b i t o r y m e c h a n i s m . T h e r e is e x p e r i m e n t a l e v i d e n c e t h a t such a m e c h a n i s m e x e r t s its influence o n t h e c e n t r a l e n d i n g s of p r i m a r y s e n s o r y n e u r o n s in cranial nerves. ~AUERLAND and THIEL]~ 3 d e m o n s t r a t e d t h a t a c t i v a t i o n of t r i g e m i n a l p r o p r i o c e p t i v e a f f e r e n t s leads to p r e s y n a p t i c d e p o l a r i z a t i o n of lingual a n d g l o s s o p h a r y n geal n e r v e t e r m i n a l s . P r o p r i o c e p t o r s in t h e m a s s e t e r (jaw closer) a n d a n t e r i o r d i g a s t r i c muscle (jaw opener) are a c t i v a t e d d u r i n g m a s t i cation. A f f e r e n t activities f r o m b o t h muscles p r o d u c e one a n d t h e s a m e effect: a r e m a r k a b l e a n d long-lasting r e d u c t i o n of t h e reflex a c t i v i t y to t h e p r o t r u d e r of t h e t o n g u e , i.e. a decrease in p r o t r u s i v e t o n g u e action. This p h e n o m e n o n c o n s t i t u t e s a v e r y effective p r o t e c t i v e m e c h a n i s m for t h e a n t e r i o r p o r t i o n of t h e t o n g u e d u r i n g masticatory activity. It appears that this protective mechanism already commences during the opening phase of t h e month~.

Zusammen/assung. Die R e f l e x a k t i v i t X t des P r o t r u d o r s der Zunge (M. genioglossus) w u r d e d u r c h die A k t i v i e r u n g p r o p r i o z e p t i s c h e r a f f e r e n t e r F a s e r n i m N. t r i g e m i n u s bedeutend herabgesetzt. Polysynaptische Reflexe zum M. genioglossus w u r d e n e n t w e d e r d u r c h R e i z u n g des N. lingualis oder des N. g l o s s o p h a r y n g i c u s ausgel6st. B e d i n g e n d e elektrische R e i z u n g der N e r v e n v e r s c h i e d e n e r K a u m u s k e l n i n d u z i e r t e eine bis zu 500 msec a n d a u e r n d e H e m m u n g dieser Reflexe. E . K . SAUI~RLAND a n d N . M I Z U N O

Departments o/Anatomy and Oral Medicine and the Brain Research Institute, Center/or Health Sciences, University o/ Cali/ornia at Los A ngeles, Los Angeles (Cali/ornia 90024, USA), 29 April 7970.

3 E. K. SAUERLANDand H. THIELE, Expl Neural. 28, in press (1970). This research was supported by grants No. NS 06819-04 and No. MH 10083 from the United States Public Health Service. The authors are indebted to the UCLA Brain Research Institute for the use of the computer facilities. Dr. Mizuno's present address : Department of Anatomy, School of Dentistry, Hiroshima University, I-tiroshima City, Japan.

Exercise, Blood Lactate and Food Intake I n m a n a n d o t h e r a n i m a l s b o u t s of exercise are followed b y a p e r i o d of h y p o p h a g i a w h i c h is s u c c e e d e d b y t h e r e s t o r a t i o n of e n e r g y b a l a n c e w i t h i n 1 to 2 d a y s ~, 2. D u r i n g exercize blood c o n c e n t r a t i o n s of l a c t a t e increase f r o m a n o r m a l of 0.5-1.0 m M up to 15 m M 3, a n d we h a v e s h o w n

t h a t a 30-min i.v. i n j e c t i o n of L-lactate (1.3-1.5 mmoles/kg) into m o n k e y s , c a u s i n g a m a x i m u m blood l a c t a t e concent r a t i o n of 2.5 mM, d e c r e a s e d t h e i r food i n t a k e a b o u t 40% d u r i n g s u b s e q u e n t feeding ~. Since t h e l a c t a t e levels q u i c k l y r e t u r n e d to normal, t h e h y p o p h a g i a a p p e a r s to be a

1228

Specialia

r e s i d u a l effect. The p r e s e n t s t u d y was d e s i g n e d t o t e s t t h e possible influence of exercise a n d / o r l a c t a t e on t h e m e t a b o l i s m of t h e m e d i a l h y p o t h a l a m u s as a possible e x p l a n a t i o n for t h e s u s t a i n e d d e p r e s s i o n of food intake. W e t h e o r i z e d t h a t a n increase in b l o o d l a c t a t e levels p r o d u c e d b y severe exercize or i n j e c t i o n of l a c t a t e causes t h e release of a f a c t o r w h i c h increases t h e glucose m e t a b o lism r a t e a n d a c t i v i t y of t h e v e n t r o m e d i a l area of t h e h y p o t h a l a m u s (VMH) for several hours. T h e a c t i o n of gold thioglucose (GTG) in p r o d u c i n g lesions in t h e V M H is closely r e l a t e d to t h e r a t e of glucose m e t a b o l i s m 5, 6. Mice m a d e d i a b e t i c w i t h alloxan do n o t d e v e l o p V M H lesions a f t e r GTG injections unless also g i y e n insulin 7, a n d insulin-insensitive b u t h y p e r g l y c e m i c a n d h y p e r i n s u l i n e m i c o b o b B a r H a r b o r mice are m u c h less sensitive t o t h e V M I t effect of GTG 5. C o n s e q u e n t l y , to m e a s u r e t h e r a t e of glucose m e t a b o l i s m , a histological d e t e r m i n a t i o n of t h e lesioning effect of GTG on t h e V M H of mice was m a d e . To t e s t t h e effect of exercize on m e d i a l h y p o t h a l a m i c m e t a b o l i s m , a l l o x a n - d i a b e t i c mice (65 m g / k g i.v.) were r u n on a t r e a d m i l l a t r a t e s of 12 to 16 m / m i n for 60 rain. Group 2 was r u n 15 min, i n j e c t e d i.p. w i t h 0.8 m g / g GTG, a n d r u n a n o t h e r 45 min. T h r e e groups of mice, 3, 4, a n d 5,

EXPERIENTIA 26/11

were t r a i n e d b y r u n n i n g 60 m i n for 5 t o 7 days. On t h e last d a y of t r a i n i n g G r o u p 3 was i n j e c t e d w i t h GTG a f t e r 15 rain of t h e 60-rain exercize p e r i o d ; Groups 4 a n d 5 were i n j e c t e d 2 a n d 4 h a f t e r exercize, respectively. All m i c e were s h o w n to h a v e glucosuria a n d h y p e r g l y c e m i a . T h e b r a i n s were r e m o v e d 1 to 3 d a y s a f t e r GTG i n j e c t i o n for histological p r e p a r a t i o n 5. As s h o w n in t h e Table, exercize increased t h e f r e q u e n c y of lesions f r o m 0 to 60% in u n t r a i n e d d i a b e t i c mice. T h e

1 j. A. F. STEVENSON, B. M. Box, V. FILEKI and J. K. BEATON, Am. J. Physiol. 27, 118 (1966). 20. B. EDHOL~I, J. G. FLETCHER, E. M. WIDDOWSON and R. A. McCANCE, Br. J. Nutr. 9, 286 (1955). 8 A. DECosTER, H. DENOLIN, R. MESSIN, S. DEGRE and P. VANDERMOTEN, Biochemistry o/ Exercize, in Medicine and Sport (Ed. J. POORTMANS;S. Karger, NewYork 1969), vol. 3, p. 15. C. A. BAILE and W. ZINN, Fedn Proc. 29, 657 (1970). 5 C. A. BAILE, M. G. HERRERA and J. MAYER, Am. J. Physiol. 278, 857 (1970). 6 H. J. LIKUSKI,A. F. DEBONSand R. J. CEOIJTIER,Am. J. Physiol. 212, 669 (1967). 7 A. F. DEBONS, I. KRIMSKY, A. FROI~I and R. J. CEOUTIER,Am. J. Physiol. 217, 1114 (1969).

Photomicrographs of the hypothalamus of diabetic mice injected i.p. with 0.8 mg/g body weight of goldthioglueose. A) Showing no lesion, is from a mouse in Group 1. and B) showing severe bilateral lesions is from a mouse in Group 9.

15.11. 1970

Specialia

size of t h e lesions v a r i e d f r o m s m a l l t o c o m p l e t e V M H a b l a t i o n . T h e low incidence of lesions in G r o u p 3 m a y b e r e l a t e d to a n i n c r e a s e d a b i l i t y t o m e t a b o l i z e t h e l a c t a t e due t o t r a i n i n g . I n t h e F i g u r e are p h o t o m i c r o g r a p h s of t h e V M H of t h e b r a i n of d i a b e t i c mice, one exercized a n d t h e o t h e r n o t exercized. I t sbould be n o t e d t h a t n o n e of t h e u n e x e r c i z e d mice (Group 1) d e v e l o p e d VMI-I lesions following GTG injection, while 15 of 24 n o r m a l mice given doses of o n l y 0.3 m g / g b o d y w e i g h t d e v e l o p e d lesions. I n a second e x p e r i m e n t u n t r a i n e d d i a b e t i c mice (Group 6) w e r e i n j e c t e d i.p. w i t h 2.5 ~zmoles/g of N a l a c t a t e (pH = 7.34) a n d 30 rain l a t e r w i t h 0.8 m g / g GTG. G r o u p s 7, 8, 9 a n d 10 were t r a i n e d as d e s c r i b e d a b o v e a n d on t h e d a y following t h e t r a i n i n g p e r i o d were first i n j e c t e d w i t h 2.5 a m o l e s / g of N a l a c t a t e a n d t h e n 0.8 m g / g GTG 0.5, 2, 4 a n d 8 h later, r e s p e c t i v e l y . T h e s e mice also d e v e l o p e d lesions in t h e V M H , evei1 u p t o 8 h a f t e r l a c t a t e i n j e c t i o n (Table). S o d i u m p r o p i o n a t e , 2.5 ~moles/g (pH = 7.34), was n o t effective in m e d i a t i n g t h e GTG lesions of t h e VMt-I of d i a b e t i c mice. The results of t h e a b o v e e x p e r i m e n t are e v i d e n c e t h a t t h e m e t a b o l i s m of t h e V M H of t h e d i a b e t i c mice following exercize or i n j e c t i o n of l a c t a t e was c h a n g e d in a n l a n n e r similar to t h a t of a d i a b e t i c m o u s e g i v e n insulin. A l t h o u g h

The effect of exercize or lactate on the lesioning of the ventromediaI hypothalamus by goldthioglucose (GTG) in mice made diabetic with alloxan Group

1 2 3 4 5 6 7 8 9 10

n

9 5 11 5 5 , 5 5 5 5 5

Blood glucose Condi- GTGinjection time Lesions (mg/100 ml) 9 tion After After (%) exercize lactate'~ (min) (mill) 398-4- 91 514:~ 33 4 7 7 ~ 37 534~: 98 531~ 27 411-4- 50 4874- 55 4 3 7 • 55 3 9 7 ~ = 20 558•

Uc U Ta T T U T T T T

Ne 0 0 120 240 30 30 120 240 480

0 60 18 60 0 40 40 40 80 40

Day of injection, b 2.5 [xmoles]gbody weight, oUntrained. a Trained. e Not exereized or injected with lactate.

1229

we h a v e no e v i d e n c e t h a t t h e r e is a r e l a t i o n s h i p t o t h e s e e x p e r i m e n t s , it is i n t e r e s t i n g t h a t a f a c t o r released b y muscle d u r i n g exercize has insulin-like a c t i v i t y on glucose m e t a b o l i s m on v a r i o u s tissues i n c l u d i n g t h e b r a i n (8, 9, 10). I t is especially r e l e v a n t t h a t s u c h a f a c t o r h a s b e e n f o u n d in t h e u r i n e of t r a i n e d r a t s up t o 12 h a f t e r t h e session of exercizeS. I t m a y be t h a t t h i s f a c t o r or one w i t h similar p r o p e r t i e s is released b y i n c r e a s e d p l a s m a levels of l a c t a t e a n d h a s insulin-like a c t i v i t y on t h e V M H w h i c h increases t h e m e t a b o l i c a n d p r e s u m a b l y t h e firing rate. Since it is a l o n g - a c t i n g factor, it m a y cause a sust a i n e d h y p o p h a g i a t h r o u g h t h e s u p p r e s s i o n of t h e l a t e r a l h y p o t h a l a m i c area a c t i v i t y b y t h e i n c r e a s e d V M H activity. T h e i m p o r t a n c e of exercize in t h e t r e a t m e n t of d i a b e t e s has long b e e n s t r e s s e d n . Our e x p e r i m e n t s suggest t h a t , in a d d i t i o n to t h e i m p r o v e m e n t of glucose u t i l i z a t i o n generally observed, exercize m a y also be beneficial in c o n t r o l l i n g t h e d e v e l o p m e n t of o b e s i t y n o t only b y increasing e n e r g y e x p e n d i t u r e b u t also b y p r e v e n t i n g excessive food i n t a k e 12

Zusammen/assung. E r h 6 h t e L a c t a t m e n g e n i m P l a s m a k 6 n n e n w/ihrend k 6 r p e r l i c h e r A n s t r e n g u n g die F r e i s e t z n n g eines Stoffes v e r u r s a c h e n , welcher, ~hnlich wie Insulin, i m m i t t l e r e n H y p o t h a l a m u s w i r k t . D i e s e r Stoff k 6 n n t e a u c h a n der A u s l 6 s u n g der H y p o p h a g i e , welche n a c h k 6 r p e r l i c h e r A n s t r e n g u n g a u f t r i t t , b e t e i l i g t sein. C. A. BAILE, W. ZINN a n d CAROL McLAuGHLIN

Department o/ Nutrition, Harvard School o/Public Health, Boston (Massachusetts 02775, USA), 3 July 7970.

s M. G. GOLDSTEIN, Excerpta reed. Found. 8g, 308 (1965). 9 R. R. CANDELAand J. L. R. CANDELA,Proc. Soc. exp. Biol. )/led. 7I0, 803 (1962). 10 E. HAvlvi and H. E. WERTHEI~ER, J. Physiol. 172, 342 (1964). 11 2E. P. JosLIN, H. F. ROOT, P. WHITE, A. MARKLEand C. C. BAILEY, The Treatmento] Diabetes Mellitus (Lea and Febiger, Philadelphia 1949), p. 357. 12 This work was supported, in part, by grantS-in-aid from the National Institute of Neurological Diseases and Blindness No. NB-01941, National Institute of Arthritis and Metabolic Diseases No. AM-02911 and the Fund for Research and Teaching, Department of Nutrition, Harvard School of Public Health.

Physiologic and Pharmacologic Responses of Mammalian Vascular Smooth Muscles Durin~ Electric Field Stimulation Previous studies I-~ have shown that brief pulses of 60 Hz alternating current field stimulation (AC) cause contraction of various types of isolated smooth muscle. A portion of the response in vascular smooth muscle appears to be due to the release of endogenous catecholamines, principally norepinephrine I, 5. We will demonstrate that essentially steady-state levels of contraction can be achieved during continuous AC stimulation, and that voltage-response curves can thus be generated. These curves are depressed by 'direct' smooth muscle relaxants, by an alpha-adrenergic blocking agent, and

b y u l t r a - v i o l e t r a d i a t i o n , w h i c h is k n o w n t o r e d u c e a c t i v e t o n e 6. E v i d e n c e will b e p r e s e n t e d t h a t t h e nonc a t e c h o l a m i n e m e d i a t e d p o r t i o n of t h e AC r e s p o n s e is due t o s t i m u l a t i o n of t h e e x c i t a b l e m e m b r a n e , a n d p e r h a p s t o direct a c t i v a t i o n of t h e e x c i t a t i o n - c o n t r a c t i o n c o u p l i n g mechanisms. Materials and methods. Spiral s t r i p s of a o r t a f r o m r a b b i t s killed b y cervical concussion w e r e s u s p e n d e d u n d e r a t e n s i o n of a p p r o x i m a t e l y 3 g in a c o n s t a n t t e m p e r a t u r e b a t h , a c c o r d i n g to e s t a b l i s h e d m e t h o d o l o g y L T h e b a t h i n g m e d i u m was K r e b s b i c a r b o n a t e solution