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Biphasic actions of L-Dopa on the release of endogenous dopamine and norepinephrine via presynaptic regulatory mechanisms in rat striatal and hypothalamic slices
S150
26 Neurotransmitters V
Presynaptic mechanism
VERAPAMIL AND DILTIAZEM A N T A G O N I Z E THE F A C I L I T A T O R Y THE SYNAPTIC T R A N S M I S S I O N
EFFECT OF A M I N O P Y R I D I N E
ON
K O I C H ~ O TAKASHIMA , MITSUHIKO MATSUMOTO , KAZUHIKO SASAKI , and WILLIAM K. RIKER-X ist Department of Physi~logy, School of Medicine, Iwate Medical University, Morioka 020, JAPAN. Department of Pharmacology, L221, Oregon Health Sciences University, Portland OR 97201, U.S.A. The a m i n o p y r i d i n e s release.
facilitate
This f a c i l i t a t o r y
from an increase
volley normally
sympathetic
ganglion.
by increasing
release
in calcium influx at the p r e s y n a p t i c
presynaptic
produces
synaptic t r a n s m i s s i o n
effect on transmitter
terminals.
induces a single p o s t s y n a p t i c
However,
the a p p l i c a t i o n
spike
This f a c i l i t a t o r y
in response
and intracellular
compound action potential
whereas
the first spike
(CAP)
in the presence of 1 mM 3-AP.
Similarly,
inhibited
SBR and the same c o n c e n t r a t i o n
of diltiazem barely
verapamil
The results thus demonstrate
and diltiazem antagonize
the C a 2 + - d e p e n d e n t
3-AP-enhanced
The
was markedly recorded on the
was barely inhibited by the same c o n c e n t r a t i o n
verapamil
presence of 1 mM 3-AP.
(3-AP) to the
spike discharges.
(SBR) recorded on the compound action potential
inhibited by 160 uM verapamil,
The single
effect of 3-AP was confirmed by both
recordings of compound action potentials second spike
to result
in the bullfrog
of 1 mM 3-aminopyridine
the second or third spike firings p o s t s y n a p t i c a l l y
same stimulation.
transmitter
is considered
of
65 uM diltiazem markedly inhibited CAP in the
that calcium entry blockers,
t r a n s m i s s i o n and further confirm
effect of aminopyridines.
BIPHASIC A C T I O N S OF L-DOPA ON THE RELEASE OF ENDOGENOUS DOPAMINE AND NOREPINEPHRINE V I A PRESYNAPTIC REGULATORY MECHANISMS IN RAT S T R I A T A L AND H Y P O T H A L A M I C SLICES YOSHIO GOSHIMA*, T A K A O KUBO* and YOSHIMI MISU, D e p a r t m e n t o f Pharmacology, Yokohama C i t y U n i v e r s i t y School o f Medicine, Yokohama 232, Japan We i n v e s t i g a t e d the actions o f L-dopa on the e l e c t r i c a l f i el d s t i m u l a t i o n - e v o k e d release o f e n d o g e n o u s dopamine ( D A ) from r a t s t r i a t a l slices and o f DA and n o r e p i n e p h r i n e (NE) from h y p o t h a l a m i c slices. The slices ( 0 . 7 mm) were s u p e r f u s e d in an over, flow manner with K r e b s medium, and s t i m u l a t i o n s ( 5 H z , 2 msec, 30 mA, 3 min) were p e r f o r m e d 30 ( S o ) , 60 ( S J and 90 (S2) min a f t e r the s t a r t o f s u p e r f u s i o n . L-Dopa was a p p l i e d 15 min b e f o r e S2 f o r 27 min and the e f f e c t s were estimated by S21Sl release r a t i o . Cocaine 20 pM, a n e u r o n a l u p t a k e i n h i b i t o r , and p - b r o m o b e n z y l o x y a m i n e (NSD-1055) 10 ~M, a d o p a - d e c a r b o x y l a s e i n h i b i t o r , or the a n t a g o n i s t s used were u s u a l l y a p p l i e d at the s t a r t o f s u p e r f u s i o n and were p r e s e n t t h r o u g h o u t the e x p e r i m e n t s . DA and NE w e r e measured by H P L C - E C D . In the p r e s e n c e o f cocaine and NSD-1055, a c o n c e n t r a t i o n - r e l e a s e - r e l a t i o n s h i p o f L-dopa f o r DA and NE showed a b i p h a s i c p a t t e r n , r e s p e c t i v e l y , in b o t h slices. L-Dopa 10 and 100 nM i n c r e a s e d s t r i a t a l DA and h y p o t h a l a m i c NE in a d o s e - d e p e n d e n t manner and the increases were a n t a g o n i z e d by l - p r o p r a n o l o l 100 nM, a B - r e c e p t o r a n t a g o n i s t , in b o t h slices. In h y p o t h a l a m i c slices, L-dopa I ~M decreased NE release and t e n d e d to d e c r e a s e DA rel ease, and the decreases were a n t a g o n i z e d by s - s u l p i r i d e 10riM, a D 2 - r e c e p t o r antagoni~st. In s t r i a t a l slices, L-dopa I ~M p r o d u c e d no m o d i f i c a t i o n s o f DA release u n d e r usual e x p e r i m e n t a l c o n d i t i o n s , b u t d e c r e a s e d DA release when N S D - | 0 5 5 was a p p l i e d 15 rain b e f o r e S~. T h i s decrease was a n t a g o n i z e d b y s - s u l p i r i d e I nM a p p l i e d s i m u l t a n e o u s l y w i t h the a p p l i c a t i o n o f L-dopa 15 rain b e f o r e S2. An i m p o r t a n t f i n d i n g is t h a t in the absence o f cocaine and NSD-1055, L-dopa 30 nM i n c r e a s e d DA release w i t h o u t accompanying increases in the s p o n t a n e o u s release and accumulation o f DA in s t r i a t a l slices. T h e minimum c o n c e n t r a t i o n o f L-dopa r e q u i r e d to increase the s p o n t a n e o u s release o f DA from s t r i a t a l slices was 100 nM, and the c o n c e n t r a t i o n necess a r y to cause the accumulation o f DA was h i g h e r t h a n 10 ~M in the absence o f cocaine and NSD-1055, In c o n c l u s i o n , micromolar c o n c e n t r a t i o n s o f L-dopa i n h i b i t the release o f e n d o g e n o u s DA and NE v i a p r e s y n a p t i c i n h i b i t o r y D A - r e c e p t o r s , and the lower c o n c e n t r a t i o n s increase the release o f DA and NE v i a a p r o p r a n o l o l - s e n s i t i v e p r o c e s s o f p r e s y n a p t i c f a c i l i t a t o r y ~ - a d r e n o c e p t o r s in r a t s t r i a t u m and h y p o t h a l a m u s . U n d e r these e x p e r i m e n t a l c o n d i t i o n s , the p r i m a r y action o f L-dopa in r a t s t r i a t u m a p p e a r s to increase the release o f DA, r a t h e r than the s y n t h e s i s and accumulation o f DA.
26 Neurotransmitters V
Presynaptic mechanism
VERAPAMIL AND DILTIAZEM A N T A G O N I Z E THE F A C I L I T A T O R Y THE SYNAPTIC T R A N S M I S S I O N
EFFECT OF A M I N O P Y R I D I N E
ON
K O I C H ~ O TAKASHIMA , MITSUHIKO MATSUMOTO , KAZUHIKO SASAKI , and WILLIAM K. RIKER-X ist Department of Physi~logy, School of Medicine, Iwate Medical University, Morioka 020, JAPAN. Department of Pharmacology, L221, Oregon Health Sciences University, Portland OR 97201, U.S.A. The a m i n o p y r i d i n e s release.
facilitate
This f a c i l i t a t o r y
from an increase
volley normally
sympathetic
ganglion.
by increasing
release
in calcium influx at the p r e s y n a p t i c
presynaptic
produces
synaptic t r a n s m i s s i o n
effect on transmitter
terminals.
induces a single p o s t s y n a p t i c
However,
the a p p l i c a t i o n
spike
This f a c i l i t a t o r y
in response
and intracellular
compound action potential
whereas
the first spike
(CAP)
in the presence of 1 mM 3-AP.
Similarly,
inhibited
SBR and the same c o n c e n t r a t i o n
of diltiazem barely
verapamil
The results thus demonstrate
and diltiazem antagonize
the C a 2 + - d e p e n d e n t
3-AP-enhanced
The
was markedly recorded on the
was barely inhibited by the same c o n c e n t r a t i o n
verapamil
presence of 1 mM 3-AP.
(3-AP) to the
spike discharges.
(SBR) recorded on the compound action potential
inhibited by 160 uM verapamil,
The single
effect of 3-AP was confirmed by both
recordings of compound action potentials second spike
to result
in the bullfrog
of 1 mM 3-aminopyridine
the second or third spike firings p o s t s y n a p t i c a l l y
same stimulation.
transmitter
is considered
of
65 uM diltiazem markedly inhibited CAP in the
that calcium entry blockers,
t r a n s m i s s i o n and further confirm
effect of aminopyridines.
BIPHASIC A C T I O N S OF L-DOPA ON THE RELEASE OF ENDOGENOUS DOPAMINE AND NOREPINEPHRINE V I A PRESYNAPTIC REGULATORY MECHANISMS IN RAT S T R I A T A L AND H Y P O T H A L A M I C SLICES YOSHIO GOSHIMA*, T A K A O KUBO* and YOSHIMI MISU, D e p a r t m e n t o f Pharmacology, Yokohama C i t y U n i v e r s i t y School o f Medicine, Yokohama 232, Japan We i n v e s t i g a t e d the actions o f L-dopa on the e l e c t r i c a l f i el d s t i m u l a t i o n - e v o k e d release o f e n d o g e n o u s dopamine ( D A ) from r a t s t r i a t a l slices and o f DA and n o r e p i n e p h r i n e (NE) from h y p o t h a l a m i c slices. The slices ( 0 . 7 mm) were s u p e r f u s e d in an over, flow manner with K r e b s medium, and s t i m u l a t i o n s ( 5 H z , 2 msec, 30 mA, 3 min) were p e r f o r m e d 30 ( S o ) , 60 ( S J and 90 (S2) min a f t e r the s t a r t o f s u p e r f u s i o n . L-Dopa was a p p l i e d 15 min b e f o r e S2 f o r 27 min and the e f f e c t s were estimated by S21Sl release r a t i o . Cocaine 20 pM, a n e u r o n a l u p t a k e i n h i b i t o r , and p - b r o m o b e n z y l o x y a m i n e (NSD-1055) 10 ~M, a d o p a - d e c a r b o x y l a s e i n h i b i t o r , or the a n t a g o n i s t s used were u s u a l l y a p p l i e d at the s t a r t o f s u p e r f u s i o n and were p r e s e n t t h r o u g h o u t the e x p e r i m e n t s . DA and NE w e r e measured by H P L C - E C D . In the p r e s e n c e o f cocaine and NSD-1055, a c o n c e n t r a t i o n - r e l e a s e - r e l a t i o n s h i p o f L-dopa f o r DA and NE showed a b i p h a s i c p a t t e r n , r e s p e c t i v e l y , in b o t h slices. L-Dopa 10 and 100 nM i n c r e a s e d s t r i a t a l DA and h y p o t h a l a m i c NE in a d o s e - d e p e n d e n t manner and the increases were a n t a g o n i z e d by l - p r o p r a n o l o l 100 nM, a B - r e c e p t o r a n t a g o n i s t , in b o t h slices. In h y p o t h a l a m i c slices, L-dopa I ~M decreased NE release and t e n d e d to d e c r e a s e DA rel ease, and the decreases were a n t a g o n i z e d by s - s u l p i r i d e 10riM, a D 2 - r e c e p t o r antagoni~st. In s t r i a t a l slices, L-dopa I ~M p r o d u c e d no m o d i f i c a t i o n s o f DA release u n d e r usual e x p e r i m e n t a l c o n d i t i o n s , b u t d e c r e a s e d DA release when N S D - | 0 5 5 was a p p l i e d 15 rain b e f o r e S~. T h i s decrease was a n t a g o n i z e d b y s - s u l p i r i d e I nM a p p l i e d s i m u l t a n e o u s l y w i t h the a p p l i c a t i o n o f L-dopa 15 rain b e f o r e S2. An i m p o r t a n t f i n d i n g is t h a t in the absence o f cocaine and NSD-1055, L-dopa 30 nM i n c r e a s e d DA release w i t h o u t accompanying increases in the s p o n t a n e o u s release and accumulation o f DA in s t r i a t a l slices. T h e minimum c o n c e n t r a t i o n o f L-dopa r e q u i r e d to increase the s p o n t a n e o u s release o f DA from s t r i a t a l slices was 100 nM, and the c o n c e n t r a t i o n necess a r y to cause the accumulation o f DA was h i g h e r t h a n 10 ~M in the absence o f cocaine and NSD-1055, In c o n c l u s i o n , micromolar c o n c e n t r a t i o n s o f L-dopa i n h i b i t the release o f e n d o g e n o u s DA and NE v i a p r e s y n a p t i c i n h i b i t o r y D A - r e c e p t o r s , and the lower c o n c e n t r a t i o n s increase the release o f DA and NE v i a a p r o p r a n o l o l - s e n s i t i v e p r o c e s s o f p r e s y n a p t i c f a c i l i t a t o r y ~ - a d r e n o c e p t o r s in r a t s t r i a t u m and h y p o t h a l a m u s . U n d e r these e x p e r i m e n t a l c o n d i t i o n s , the p r i m a r y action o f L-dopa in r a t s t r i a t u m a p p e a r s to increase the release o f DA, r a t h e r than the s y n t h e s i s and accumulation o f DA.