- Email: [email protected]
Effects of L-DOPA and L-5-HTP on the visual evoked response
Physiology & Behavior, Vol. 25, pp. 317-320. Pergamon Press and Brain Research Publ., 1980. Printed in the U.S.A.
Effects of L-DOPA and L-5-HTP on the Visual Evoked Response IWAO KADOBAYASHI, MASAHIKO MORI, KUNIO TANAKA AKITERU TOYOSHIMA 1 AND NOBUKATSU KATO
Department of Psychiatry, Kyoto Prefrectural University of Medicine Kawaramachi-hirokoji, Kamigyo-ku, Kyoto, Japan R e c e i v e d 16 F e b r u a r y 1979 KADOBAYASHI, I., M. MORI, K. TANAKA, A. TOYOSHIMA AND N. KATO. Effects o f L-DOPA and L-5-HTP on the visual evoked response. PHYSIOL. BEHAV. 25(2) 317-320, 1980.--Small doses (10 and 20 mg/kg) of L-DOPA
inhibited the amplitude of the visual evoked response (VER), while large doses (40 and 80 mg/kg) enhanced it. Though low doses (12.5 and 25 mg/kg) of L-5-HTP caused a slight increase in amplitude of the VER, the simultaneous administration of 12.5 mg/kg of L-5-HTP and 10 mg/kg of L-DOPA produced a marked enhancement. The peak latency was prolonged after the injection of any doses of L-DOPA, L-5-HTP, or both. L-DOPA
L-5-HTP
Amplitude
Inhibition
WE studied modification of visual signals by electrical stimulation of the substantia nigra or the striatum, and suggested that it occurred as a result of nigro-striatal system modulation of reticular activity [12, 13, 14, 15, 16]. Recent histocbemical experiments [1, 9, 21] have revealed that the neostriatum receives not only dopaminergic but also serotoninergic fibers. The functional interaction between dopamine and serotonin [10] has received attention. So a question arises how the visual signals would change if dopamine, serotonin, or both increase in the brain. As it has been well known that brain dopamine increases after the administration of L-3,4-dihydroxyphenylalanine (L-DOPA) [4, 6, 22], and serotonin does after the injection of L5-hydroxytryptophan (L-5-HTP) [3,7], an attempt was made to study effects of the administration of either L-DOPA or L-5-HTP and both on the visual evoked response (VER). METHOD
The experiments were performed on 55 adult mongrel cats. The animals were anesthetized with ether during tracheotomy and mounted on a stereotaxic frame. The cat was immobilized by gallamine triethiodide (Flaxedil) and artificially respired. Throughout the experiment all pressure points and wound margins were inf'dtrated with 2% procaine. The cat remained in a semi-dark room and recording was begun several hours after tracheotomy. The left pupil was dilated with atropine, while the right eye was shaded with a thick vinyl wrapper. A silver ball electrode was located in the fight primary visual area (lateral gyrus), with reference to the frontal sinus. A 9-channel E E G machine or an oscilloscope with a time constant of 0.3 sec was used for amplification. Sixty flashes at the rate of 0.5 Hz were presented
Enhancement
Latnecy
Prolongation
from a xenon flash lamp facing the eye at a distance of 80 cm. After responses to flashes were stored on FM tape, samples of them were added on a computer, excluding those when artifacts or high voltage basic activity appeared. At first three control records were obtained before the administration of the drug. The injection of the drug was followed by recordings every 5 min for the first 40 min, and then every 10 min for the following 80 min. The 55 cats were divided into 11 groups. To each group of 5 cats one of the following was given intraperitoneally in aqueous solution: (1) 10 mg/kg of L-DOPA; (2) 20 mg/kg of L-DOPA; (3) 40 mg/kg of L-DOPA; (5) 80 mg/kg of L-DOPA; (5) 12.5 mg/kg of L-5-HTP; (6) 25 mg/kg of L-5-HTP; (7) 50 mg/kg of L-5-HTP; (8) 100 mg/kg of L-5-HTP; (9) 10 mg/kg of L-DOPA and 12.5 mg/kg of L-5-HTP; (10) 40 mg/kg of L-DOPA and 12.5 mg/kg of L-5-HTP; (11) 10 mg/kg of L-DOPA and 50 mg/kg of L-5-HTP. Measurements were made of amplitude (in microvolts) from peak of the primary positive component to that of the succeeding negative component in the cats which were in good condition (Fig. 1). The latency (in milliseconds) was also measured from flash stimulus to peak of the positive component and to that of the negative component. RESULTS
Effects of L-DOPA Changes in amplitude of the VER were observed after the administration of L-DOPA. There were statistically significant differences between the mean amplitudes after the administration of L-DOPA, F(11,143)=14.93, p<0.001. The analysis of variance indicates statistically significant differences between the means after the administration of 10
1Present address: Department of Psychology, Ottemon-Gakuin University, Ibaraki, Japan.
C o p y r i g h t © 1980 Brain R e s e a r c h Publications Inc.--0031-9384/80/080317-04502.00/0
KADOBAYASHI ET AL.
318
N 20O
4:0
)180 [~ 160
Z
~ 140 P
120 0 100
FIG. 1. Visual evoked response (VER) in the primary visual cortex. P: positive component. N: negative component. Measurements were made of amplitude from peak of the positive component to that of the negative component. Flashes were given at the beginning of the sweep. The latency was measured from flash to peak of the positive component and to that of the negative component. Triangle indicates flash stimulus. Negativity upwards. Calibration: 100 ~V, 100 msec.
8O 60 40 20 O
mg/kg, F(11,33)=6.84, p<0.001, 40 mg/kg, F(11,44)= 18.90, p<0.001, and 80 mg/kg, F(11,33)=45.33, p<0.001. Changes in amplitude depended on the dose. There were statistically significant differences between the dosages, F(3,12)=8.01, p<0.01. Small doses produced reduction but large doses resulted in enhancement. Figure 2 shows recovery curves of the amplitude of the VER. Ordinate indicates the amplitude after the administration of L-DOPA as percentage of that of the control response, and abscissa does time in min after the injection of the drug. The numerals on the curve represent the dose of mg/kg, and the vertical lines do standard errors. As seen in this Figure, a marked reduction in amplitude occurred after the administration of 10 mg/kg of L-DOPA and reached a peak 30 min after. After the injection of 20 mg/kg a slight decrease was visible, lasting for a longer time. Forty mg/kg induced a marked enhancement of the VER, which reached a peak 30 min after the injection. Soon after the administration of 80 mg/kg an increase in amplitude appeared and reached a maximum 15 min after, going down slowly thereafter. The peak latencies of the positive and negative components of the VER lengthened together after the administration of L-DOPA. There were statistically significant differences between the means of the latencies of the positive and negative components after the administration of L-DOPA (positive component: F(11,143)=2.92, p<0.01, negative component: F(11,143)=5.39, p <0.001.
15
30
50
70
90 110 MIN
FIG. 2. Recovery curves of the amplitude of the VER after the administration of L-DOPA. Ordinate: amplitude of the VER after the injection of the drug as percentage of that of the control response. Abscissa: time in minutes after the intraperitoneal injection of the drug. The numbers on the curve indicate the dose of the drug, and the vertical lines the standard errors. The same graph is used in Figs. 3 and 4.
200 180 I~ ~ 160
)0
O 140
~ 120 0 100 o~
80 60
Effects of L-5-HTP L-5-HTP also changed the amplitude of the VER. There were statistically significant differences between the means of the amplitudes after the administration of L-5-HTP, F(11,132)=6.00, p<0.001. The change in amplitude induced by L-5-HTP was in general an increase, but not so remarkable (Fig. 3). Twelve and five tenths mg/kg of L-5-HTP produced a slight enhancement of the VER. The first peak appeared 30 min after the injection and the second one did 80 min after. Twenty-five mg/kg resulted in a moderate enhancement. Two peaks of the recovery curve were seen 30
1 40 20 0
15
30
50
70
90 110 MIN
FIG. 3. Recovery curves of the amplitude of the VER after the administration of L-5-HTP.
L - D O P A A N D L-5-HTP ON T H E VER
319 curve represent the dose of the drugs; the former indicates the dose of L-DOPA and the latter does that of L-5-HTP. As seen in this Figure, a marked increase in amplitude appeared after the administration of 10 mg/kg of L-DOPA and 12.5 mg/kg of L-5-HTP. A peak could be seen 30 min after the injection and a marked increase continued from 1 hour to 2 hours after. Though an increase in amplitude was also observed after the administration of 40 mg/kg of L-DOPA and 12.5 mg/kg of L-5-HTP, it was less than that seen after the injection of 10 mg/kg of L-DOPA and 12.5 mg/kg of L5-HTP. The least increase occurred after the administration of 10 mg/kg of L-DOPA and 50 mg/kg of L-5-HTP. The latencies of the positive and negative components lengthened together after the administration of L-DOPA and L-5-HTP. There were statistically significant differences between the means of the latencies of the positive and negative components after the administration of L-DOPA and L-5-HTP (positive component: F(11,110)=7.28, p<0.001, negative component: F(11,110) = 5.13, p <0.001).
2OO
~ 180 ~ 160 0140
~
120 100
80 60 40 20 0
DISCUSSION
15
30
50
70
90 110 MIN
FIG. 4. Recovery curves of the amplitude of the VER after the simultaneous administration of L-DOPA and L-5-HTP. The numbers on the curve represent the dose of the drug; the former indicates L-DOPA, and the latter does L-5-HTP.
and 90 min after the injection. Soon after the administration of 50 mg/kg a reduction in amplitude was observed. It reached a minimum 15 min later. Then the amplitude recovered and changed into an increase 25 min after the injection. A small peak appeared 30 min after and a big one did 70 min later. One hundred mg/kg caused a marked enhancement of the VER. A big peak was seen 30 min after the administration and the following one appeared 70 rain after. The latencies of the positive and negative components were prolonged together after the injection of L-5-HTP. There were statistically significant differences between the means of the latencies of the positive and negative components after the administration of L-5-HTP (positive component: F(11,132)=6.67, p<0.001, negative component: F(11,132)= 13.54, p<0.001). Effects o f L-DOPA and L-5-HTP Three different dose combinations of L-DOPA and L-5-HTP were given. There were statistically significant differences between the means of the amplitudes after the administration of L-DOPA and L-5-HTP, F(11,110) =3.12, p<0.001. The analysis of variance indicates statistically significant differences between the mean amplitudes after the administration of L-DOPA 10 mg/kg and L-5-HTP 12.5 mg/kg, F(11,33)=3.04, p<0.01, L-DOPA 40 mg/kg and L-5-HTP 12.5 mg/kg, F(11,44)=7.38, p<0.001. There were statistically significant differences between the dosage combinations, F(2,9)= 11.25, p <0.01. Though the combination of small doses of L-DOPA and L-5-HTP resulted in a marked increase in amplitude of the VER, effects of other combinations were not so remarkable. Figure 4 shows recovery curves of the amplitude of the VER after the simultaneous administration of L-DOPA and L-5-HTP. Numbers on the
In this study it was observed that small doses (10 and 20 mg/kg) of L-DOPA induced inhibition of the VER, while large doses (40 and 80 mg/kg) resulted in enhancement. Our previous studies [13,15] revealed that electrical stimulation of the nigro-striatal system produced enhancement of the VER in cats anesthetized lightly with hexobarbital. Though no direct pathway from the nigro-striatal system to the visual system has been found, there are fibers from the substantia nigra to the reticular formation. So stimulation of the nigrostriatal system could change the activity of the reticular formation. This may cause enhancement of the VER. Sabelli et al. [19] reported that 20 and 50 mg/kg of L-DOPA induced a slight decrease in amplitude of the fast component of the VER of rabbits but an increase in amplitude of the slow negative component. They also described that peak latency of the slow negative wave was not changed by any doses of L-DOPA. But in our experiments prolongation of the peak latencies of both positive and negative components could be seen. This discrepancy may be due to the difference of experimental animals and methods. They used rabbits, red flashes, and chronically implanted electrodes. It is well known that the nigro-striatal pathways contain dopamine [1,9] and the administration of L-DOPA increases the level of dopamine in the brain [4, 6, 22]. But it has been reported that the concentration of brain serotonin decrease markedly in proportion to the dose of L-DOPA administered [6]. So changes in the metabolism of not only dopamine but also serotonin and other neurotransmitters after the administration of L-DOPA must be taken into consideration for explaining the findings described above. After the administration of L-5-HTP, enhancement of the VER was also found, except for a period soon after the injection of 50 mg/kg. The change was not so remarkable as that seen after the administration of 10 and 40 mg/kg of L-DOPA. The latenncies, too, were prolonged after the injection of L-5-HTP. It has been reported that brain serotonin levels increase after the injection of L-5-HTP [3,7]. Moreover, brain norepinephrine showed a significant decrease after the administration of L-5-HTP, while dopamine remained at normal control levels [7]. Though serotonin has been thought to be critical for the initiation and maintenance of slow wave sleep [11], a recent study [18] shows that depletion of brain serotonin fails to disrupt sleep. Morphologi-
320
KADOBAYASHI ET AL.
cally serotoninergic efferents terminate in the lateral geniculate body, superior colliculus, m e s e n c e p h a l i c reticular formation, and neostriatum [1, 2, 9]. So one can speculate that the serotoninergic system plays a role in the signal processing mechanism. But it must be taken into consideration that in high concentrations serotonin enter catecholaminergic n e r v e endings in addition to serotoninergic neurons [17,20]. The simultaneous administration of 10 mg/kg of L - D O P A and 12.5 mg/kg of L-5-HTP p r o d u c e d a marked and longlasting e n h a n c e m e n t of the V E R , in contrast with a manifest inhibition after the injection of 10 mg/kg of L - D O P A alone. Other combinations of a higher dose of either of the two drugs resulted in a less increase in amplitude. It is difficult to explain these p h e n o m e n a . One possibility is that changes in the metabolism and storage of norepinephrine and o t h e r
neurotransmitters in addition to dopamine and serotonin would occur after the simultaneous administration of L - D O P A and L-5-HTP. The other is that the e n z y m e , aromatic acid decarboxylase, which decarboxylases L - D O P A and L - 5 - H T P may be related to the p h e n o m e n a . Morphologically the neostriatum receives both dopaminergic and serotoninergic fibers [1,9]. M o r e o v e r , the raphe nuclei send projections to the substantia nigra [2,5]. Therefore, the functional interaction between dopaminergic and serotoninergic systems is important. Jacobs [10] reported the interaction of the two neurotransmitters, d o p a m i n e and serotonin, in behavioral syndromes. So the interaction in the signal process may also occur. Of course further studies are necessary to solve this complicated mechanism.
REFERENCES 1. Andrn, N.-E., A. Dahlstrrm, K. Fuxe, K. Larsson, L. Olson and U. Ungerstedt. Ascending monoamine neurons to the telencephalon and diencephalon. Aeta physiol, stand. 67: 313-326, 1966. 2. Bobillier, P., S. Seguin, F. Petitjean, D. Salvert, M. Touret and M. Jouvet. The raphe nuclei of the cat brain stem: A topographical atlas of their efferent projections as revealed by autoradiography. Brain Res. 113: 44%486, 1976. 3. Bogdanski, D. F., H. Weissbach and S. Udenfriend. Pharmacological studies with the serotonin precursor, 5-hydroxytryptophan. J. Pharmac. exp. Ther. 122: 182-191, 1958. 4. Carlsson, A., M. Lindqvist, T. Magnusson and B. Waldeck. On the presence of 3-hydroxytyramine in brain. Science 127: 471, 1958. 5. Dray, A., T. J. Gonye, N. R. Oakley and T. Tanner. Evidence for the existence of a raphe projection to the substantia nigra in rat. Brain Res. 113: 45-57, 1976. 6. Everett, G. M. and J. W. Borcherding. L-DOPA: Effect on concentrations of dopamine, norepinephrine, and serotonin in brains of mice. Science 168: 84%850, 1970. 7. Everett, G. M. Effect of 5-hydroxytryptophan on brain levels of dopamine, norepinephrine, and serotonin in mice. In: Advances in Biochemical Psychopharmacology, Vol. 10, Serotonin: New Vistas. Histoehemistrv and Pharmacology, edited by E. Costa, G. L. Gessa and M. Sandier. New York: Raven Press, 1974, pp. 261-262. 8. Frazer, A. and J. L. Stinnett. Distribution and metabolism of norepinephrine and serotonin in the central nervous system. In: Biological Psychiatry, edited by J. Mendels. New York: John Wiley and Sons, 1973, pp. 35-64. 9. Fuxe, K. Evidence for the existence of monoamine neurons in the central nervous system. IV. The distribution of monoamine terminals in the central nervous system. Aeta physiol, seand. Suppl. 247, 64: 37-85, 1965. 10. Jacobs, B. L. Evidence for the functional interaction of two central neurotransmitters. Psychopharmaeologia 39: 81-86, 1974. 11. Jouvet, M. Biogenic amines and the states of sleep. Science 163: 32-41, 1969.
12. Kadobayashi, I. and G. Ukida. Effects of lenticular stimulation on unitary responses of the lateral geniculate body to light. Expl. Neurol. 33: 518-527, 1971. 13. Kadobayashi, I. Effects of lenticular stimulation on unitary and mass response of the visual cortex to light. Pfliigers Arch. ges. Physiol. 332: 10-20, 1972. 14. Kadobayashi, 1. Effects of caudate stimulation on unitary responses of the lateral geniculate body to light. Expl Neurol. 37: 463~,68, 1972. 15. Kadobayashi, 1. and M. Nakamura. Modification of visual, auditory, and somatosensory evoked responses in cortical primary receiving areas by nigral stimulation. Experientia 30: 260-262, 1974. 16. Kadobayashi, 1. Modification of visual signals by nigral stimulation. Experientia 32: 1547-1548, 1976. 17. Lichtensteigen, W., U. Mutzner and H. Langemann. Uptake of 5-hydroxytryptamine and 5-hydroxytryptophan by neurons of the central nervous system normally containing catecholamines. J. Neurochem. 14: 489--497, 1967. 18. Ross, C. A., M. E. Trulson and B. L. Jacobs. Depletion of brain serotonin following intraventricular, 5,7-dihydroxytryptamine fails to disrupt sleep in the rat. Brain Res. 114: 517-523, 1976. 19. SabeUi, H. C., W. J. Giardina, S. B. Myles and A. J. Vazquez. The effects of DOPA on the visual-evoked potentials in rabbit and mouse motor behavior following inhibition of dopamine-/3hydroxylase. Arzneimittel-Forsch. 24: 333-337, 1974. 20. Shaskin, E. G. and S. H. Snyder. Kinetics of serotonin uptake into slices from different regions of rat brain. J. Pharmae. exp. Ther. 175: 404-418, 1970. 21. Ternaux, J. P., F. Hrry, S. Bourgoin, J. Adrien, J. Glowinski and M. Hamon. The topographical distribution of serotoninergic terminals in the neostriatum of the rat and the caudate nucleus of the cat. Brain Res. 121: 311-326, 1977. 22. Thut, P. D. and R. H. Rech. Effects of L-DOPA on the EEG and brain amines of unrestrained rats. Expl Neurol. 35: 13-29, 1972. 23. Winer, B. J. Statistical Principles in Experimental Design. New York: McGraw-Hill, 1971.
Effects of L-DOPA and L-5-HTP on the Visual Evoked Response IWAO KADOBAYASHI, MASAHIKO MORI, KUNIO TANAKA AKITERU TOYOSHIMA 1 AND NOBUKATSU KATO
Department of Psychiatry, Kyoto Prefrectural University of Medicine Kawaramachi-hirokoji, Kamigyo-ku, Kyoto, Japan R e c e i v e d 16 F e b r u a r y 1979 KADOBAYASHI, I., M. MORI, K. TANAKA, A. TOYOSHIMA AND N. KATO. Effects o f L-DOPA and L-5-HTP on the visual evoked response. PHYSIOL. BEHAV. 25(2) 317-320, 1980.--Small doses (10 and 20 mg/kg) of L-DOPA
inhibited the amplitude of the visual evoked response (VER), while large doses (40 and 80 mg/kg) enhanced it. Though low doses (12.5 and 25 mg/kg) of L-5-HTP caused a slight increase in amplitude of the VER, the simultaneous administration of 12.5 mg/kg of L-5-HTP and 10 mg/kg of L-DOPA produced a marked enhancement. The peak latency was prolonged after the injection of any doses of L-DOPA, L-5-HTP, or both. L-DOPA
L-5-HTP
Amplitude
Inhibition
WE studied modification of visual signals by electrical stimulation of the substantia nigra or the striatum, and suggested that it occurred as a result of nigro-striatal system modulation of reticular activity [12, 13, 14, 15, 16]. Recent histocbemical experiments [1, 9, 21] have revealed that the neostriatum receives not only dopaminergic but also serotoninergic fibers. The functional interaction between dopamine and serotonin [10] has received attention. So a question arises how the visual signals would change if dopamine, serotonin, or both increase in the brain. As it has been well known that brain dopamine increases after the administration of L-3,4-dihydroxyphenylalanine (L-DOPA) [4, 6, 22], and serotonin does after the injection of L5-hydroxytryptophan (L-5-HTP) [3,7], an attempt was made to study effects of the administration of either L-DOPA or L-5-HTP and both on the visual evoked response (VER). METHOD
The experiments were performed on 55 adult mongrel cats. The animals were anesthetized with ether during tracheotomy and mounted on a stereotaxic frame. The cat was immobilized by gallamine triethiodide (Flaxedil) and artificially respired. Throughout the experiment all pressure points and wound margins were inf'dtrated with 2% procaine. The cat remained in a semi-dark room and recording was begun several hours after tracheotomy. The left pupil was dilated with atropine, while the right eye was shaded with a thick vinyl wrapper. A silver ball electrode was located in the fight primary visual area (lateral gyrus), with reference to the frontal sinus. A 9-channel E E G machine or an oscilloscope with a time constant of 0.3 sec was used for amplification. Sixty flashes at the rate of 0.5 Hz were presented
Enhancement
Latnecy
Prolongation
from a xenon flash lamp facing the eye at a distance of 80 cm. After responses to flashes were stored on FM tape, samples of them were added on a computer, excluding those when artifacts or high voltage basic activity appeared. At first three control records were obtained before the administration of the drug. The injection of the drug was followed by recordings every 5 min for the first 40 min, and then every 10 min for the following 80 min. The 55 cats were divided into 11 groups. To each group of 5 cats one of the following was given intraperitoneally in aqueous solution: (1) 10 mg/kg of L-DOPA; (2) 20 mg/kg of L-DOPA; (3) 40 mg/kg of L-DOPA; (5) 80 mg/kg of L-DOPA; (5) 12.5 mg/kg of L-5-HTP; (6) 25 mg/kg of L-5-HTP; (7) 50 mg/kg of L-5-HTP; (8) 100 mg/kg of L-5-HTP; (9) 10 mg/kg of L-DOPA and 12.5 mg/kg of L-5-HTP; (10) 40 mg/kg of L-DOPA and 12.5 mg/kg of L-5-HTP; (11) 10 mg/kg of L-DOPA and 50 mg/kg of L-5-HTP. Measurements were made of amplitude (in microvolts) from peak of the primary positive component to that of the succeeding negative component in the cats which were in good condition (Fig. 1). The latency (in milliseconds) was also measured from flash stimulus to peak of the positive component and to that of the negative component. RESULTS
Effects of L-DOPA Changes in amplitude of the VER were observed after the administration of L-DOPA. There were statistically significant differences between the mean amplitudes after the administration of L-DOPA, F(11,143)=14.93, p<0.001. The analysis of variance indicates statistically significant differences between the means after the administration of 10
1Present address: Department of Psychology, Ottemon-Gakuin University, Ibaraki, Japan.
C o p y r i g h t © 1980 Brain R e s e a r c h Publications Inc.--0031-9384/80/080317-04502.00/0
KADOBAYASHI ET AL.
318
N 20O
4:0
)180 [~ 160
Z
~ 140 P
120 0 100
FIG. 1. Visual evoked response (VER) in the primary visual cortex. P: positive component. N: negative component. Measurements were made of amplitude from peak of the positive component to that of the negative component. Flashes were given at the beginning of the sweep. The latency was measured from flash to peak of the positive component and to that of the negative component. Triangle indicates flash stimulus. Negativity upwards. Calibration: 100 ~V, 100 msec.
8O 60 40 20 O
mg/kg, F(11,33)=6.84, p<0.001, 40 mg/kg, F(11,44)= 18.90, p<0.001, and 80 mg/kg, F(11,33)=45.33, p<0.001. Changes in amplitude depended on the dose. There were statistically significant differences between the dosages, F(3,12)=8.01, p<0.01. Small doses produced reduction but large doses resulted in enhancement. Figure 2 shows recovery curves of the amplitude of the VER. Ordinate indicates the amplitude after the administration of L-DOPA as percentage of that of the control response, and abscissa does time in min after the injection of the drug. The numerals on the curve represent the dose of mg/kg, and the vertical lines do standard errors. As seen in this Figure, a marked reduction in amplitude occurred after the administration of 10 mg/kg of L-DOPA and reached a peak 30 min after. After the injection of 20 mg/kg a slight decrease was visible, lasting for a longer time. Forty mg/kg induced a marked enhancement of the VER, which reached a peak 30 min after the injection. Soon after the administration of 80 mg/kg an increase in amplitude appeared and reached a maximum 15 min after, going down slowly thereafter. The peak latencies of the positive and negative components of the VER lengthened together after the administration of L-DOPA. There were statistically significant differences between the means of the latencies of the positive and negative components after the administration of L-DOPA (positive component: F(11,143)=2.92, p<0.01, negative component: F(11,143)=5.39, p <0.001.
15
30
50
70
90 110 MIN
FIG. 2. Recovery curves of the amplitude of the VER after the administration of L-DOPA. Ordinate: amplitude of the VER after the injection of the drug as percentage of that of the control response. Abscissa: time in minutes after the intraperitoneal injection of the drug. The numbers on the curve indicate the dose of the drug, and the vertical lines the standard errors. The same graph is used in Figs. 3 and 4.
200 180 I~ ~ 160
)0
O 140
~ 120 0 100 o~
80 60
Effects of L-5-HTP L-5-HTP also changed the amplitude of the VER. There were statistically significant differences between the means of the amplitudes after the administration of L-5-HTP, F(11,132)=6.00, p<0.001. The change in amplitude induced by L-5-HTP was in general an increase, but not so remarkable (Fig. 3). Twelve and five tenths mg/kg of L-5-HTP produced a slight enhancement of the VER. The first peak appeared 30 min after the injection and the second one did 80 min after. Twenty-five mg/kg resulted in a moderate enhancement. Two peaks of the recovery curve were seen 30
1 40 20 0
15
30
50
70
90 110 MIN
FIG. 3. Recovery curves of the amplitude of the VER after the administration of L-5-HTP.
L - D O P A A N D L-5-HTP ON T H E VER
319 curve represent the dose of the drugs; the former indicates the dose of L-DOPA and the latter does that of L-5-HTP. As seen in this Figure, a marked increase in amplitude appeared after the administration of 10 mg/kg of L-DOPA and 12.5 mg/kg of L-5-HTP. A peak could be seen 30 min after the injection and a marked increase continued from 1 hour to 2 hours after. Though an increase in amplitude was also observed after the administration of 40 mg/kg of L-DOPA and 12.5 mg/kg of L-5-HTP, it was less than that seen after the injection of 10 mg/kg of L-DOPA and 12.5 mg/kg of L5-HTP. The least increase occurred after the administration of 10 mg/kg of L-DOPA and 50 mg/kg of L-5-HTP. The latencies of the positive and negative components lengthened together after the administration of L-DOPA and L-5-HTP. There were statistically significant differences between the means of the latencies of the positive and negative components after the administration of L-DOPA and L-5-HTP (positive component: F(11,110)=7.28, p<0.001, negative component: F(11,110) = 5.13, p <0.001).
2OO
~ 180 ~ 160 0140
~
120 100
80 60 40 20 0
DISCUSSION
15
30
50
70
90 110 MIN
FIG. 4. Recovery curves of the amplitude of the VER after the simultaneous administration of L-DOPA and L-5-HTP. The numbers on the curve represent the dose of the drug; the former indicates L-DOPA, and the latter does L-5-HTP.
and 90 min after the injection. Soon after the administration of 50 mg/kg a reduction in amplitude was observed. It reached a minimum 15 min later. Then the amplitude recovered and changed into an increase 25 min after the injection. A small peak appeared 30 min after and a big one did 70 min later. One hundred mg/kg caused a marked enhancement of the VER. A big peak was seen 30 min after the administration and the following one appeared 70 rain after. The latencies of the positive and negative components were prolonged together after the injection of L-5-HTP. There were statistically significant differences between the means of the latencies of the positive and negative components after the administration of L-5-HTP (positive component: F(11,132)=6.67, p<0.001, negative component: F(11,132)= 13.54, p<0.001). Effects o f L-DOPA and L-5-HTP Three different dose combinations of L-DOPA and L-5-HTP were given. There were statistically significant differences between the means of the amplitudes after the administration of L-DOPA and L-5-HTP, F(11,110) =3.12, p<0.001. The analysis of variance indicates statistically significant differences between the mean amplitudes after the administration of L-DOPA 10 mg/kg and L-5-HTP 12.5 mg/kg, F(11,33)=3.04, p<0.01, L-DOPA 40 mg/kg and L-5-HTP 12.5 mg/kg, F(11,44)=7.38, p<0.001. There were statistically significant differences between the dosage combinations, F(2,9)= 11.25, p <0.01. Though the combination of small doses of L-DOPA and L-5-HTP resulted in a marked increase in amplitude of the VER, effects of other combinations were not so remarkable. Figure 4 shows recovery curves of the amplitude of the VER after the simultaneous administration of L-DOPA and L-5-HTP. Numbers on the
In this study it was observed that small doses (10 and 20 mg/kg) of L-DOPA induced inhibition of the VER, while large doses (40 and 80 mg/kg) resulted in enhancement. Our previous studies [13,15] revealed that electrical stimulation of the nigro-striatal system produced enhancement of the VER in cats anesthetized lightly with hexobarbital. Though no direct pathway from the nigro-striatal system to the visual system has been found, there are fibers from the substantia nigra to the reticular formation. So stimulation of the nigrostriatal system could change the activity of the reticular formation. This may cause enhancement of the VER. Sabelli et al. [19] reported that 20 and 50 mg/kg of L-DOPA induced a slight decrease in amplitude of the fast component of the VER of rabbits but an increase in amplitude of the slow negative component. They also described that peak latency of the slow negative wave was not changed by any doses of L-DOPA. But in our experiments prolongation of the peak latencies of both positive and negative components could be seen. This discrepancy may be due to the difference of experimental animals and methods. They used rabbits, red flashes, and chronically implanted electrodes. It is well known that the nigro-striatal pathways contain dopamine [1,9] and the administration of L-DOPA increases the level of dopamine in the brain [4, 6, 22]. But it has been reported that the concentration of brain serotonin decrease markedly in proportion to the dose of L-DOPA administered [6]. So changes in the metabolism of not only dopamine but also serotonin and other neurotransmitters after the administration of L-DOPA must be taken into consideration for explaining the findings described above. After the administration of L-5-HTP, enhancement of the VER was also found, except for a period soon after the injection of 50 mg/kg. The change was not so remarkable as that seen after the administration of 10 and 40 mg/kg of L-DOPA. The latenncies, too, were prolonged after the injection of L-5-HTP. It has been reported that brain serotonin levels increase after the injection of L-5-HTP [3,7]. Moreover, brain norepinephrine showed a significant decrease after the administration of L-5-HTP, while dopamine remained at normal control levels [7]. Though serotonin has been thought to be critical for the initiation and maintenance of slow wave sleep [11], a recent study [18] shows that depletion of brain serotonin fails to disrupt sleep. Morphologi-
320
KADOBAYASHI ET AL.
cally serotoninergic efferents terminate in the lateral geniculate body, superior colliculus, m e s e n c e p h a l i c reticular formation, and neostriatum [1, 2, 9]. So one can speculate that the serotoninergic system plays a role in the signal processing mechanism. But it must be taken into consideration that in high concentrations serotonin enter catecholaminergic n e r v e endings in addition to serotoninergic neurons [17,20]. The simultaneous administration of 10 mg/kg of L - D O P A and 12.5 mg/kg of L-5-HTP p r o d u c e d a marked and longlasting e n h a n c e m e n t of the V E R , in contrast with a manifest inhibition after the injection of 10 mg/kg of L - D O P A alone. Other combinations of a higher dose of either of the two drugs resulted in a less increase in amplitude. It is difficult to explain these p h e n o m e n a . One possibility is that changes in the metabolism and storage of norepinephrine and o t h e r
neurotransmitters in addition to dopamine and serotonin would occur after the simultaneous administration of L - D O P A and L-5-HTP. The other is that the e n z y m e , aromatic acid decarboxylase, which decarboxylases L - D O P A and L - 5 - H T P may be related to the p h e n o m e n a . Morphologically the neostriatum receives both dopaminergic and serotoninergic fibers [1,9]. M o r e o v e r , the raphe nuclei send projections to the substantia nigra [2,5]. Therefore, the functional interaction between dopaminergic and serotoninergic systems is important. Jacobs [10] reported the interaction of the two neurotransmitters, d o p a m i n e and serotonin, in behavioral syndromes. So the interaction in the signal process may also occur. Of course further studies are necessary to solve this complicated mechanism.
REFERENCES 1. Andrn, N.-E., A. Dahlstrrm, K. Fuxe, K. Larsson, L. Olson and U. Ungerstedt. Ascending monoamine neurons to the telencephalon and diencephalon. Aeta physiol, stand. 67: 313-326, 1966. 2. Bobillier, P., S. Seguin, F. Petitjean, D. Salvert, M. Touret and M. Jouvet. The raphe nuclei of the cat brain stem: A topographical atlas of their efferent projections as revealed by autoradiography. Brain Res. 113: 44%486, 1976. 3. Bogdanski, D. F., H. Weissbach and S. Udenfriend. Pharmacological studies with the serotonin precursor, 5-hydroxytryptophan. J. Pharmac. exp. Ther. 122: 182-191, 1958. 4. Carlsson, A., M. Lindqvist, T. Magnusson and B. Waldeck. On the presence of 3-hydroxytyramine in brain. Science 127: 471, 1958. 5. Dray, A., T. J. Gonye, N. R. Oakley and T. Tanner. Evidence for the existence of a raphe projection to the substantia nigra in rat. Brain Res. 113: 45-57, 1976. 6. Everett, G. M. and J. W. Borcherding. L-DOPA: Effect on concentrations of dopamine, norepinephrine, and serotonin in brains of mice. Science 168: 84%850, 1970. 7. Everett, G. M. Effect of 5-hydroxytryptophan on brain levels of dopamine, norepinephrine, and serotonin in mice. In: Advances in Biochemical Psychopharmacology, Vol. 10, Serotonin: New Vistas. Histoehemistrv and Pharmacology, edited by E. Costa, G. L. Gessa and M. Sandier. New York: Raven Press, 1974, pp. 261-262. 8. Frazer, A. and J. L. Stinnett. Distribution and metabolism of norepinephrine and serotonin in the central nervous system. In: Biological Psychiatry, edited by J. Mendels. New York: John Wiley and Sons, 1973, pp. 35-64. 9. Fuxe, K. Evidence for the existence of monoamine neurons in the central nervous system. IV. The distribution of monoamine terminals in the central nervous system. Aeta physiol, seand. Suppl. 247, 64: 37-85, 1965. 10. Jacobs, B. L. Evidence for the functional interaction of two central neurotransmitters. Psychopharmaeologia 39: 81-86, 1974. 11. Jouvet, M. Biogenic amines and the states of sleep. Science 163: 32-41, 1969.
12. Kadobayashi, I. and G. Ukida. Effects of lenticular stimulation on unitary responses of the lateral geniculate body to light. Expl. Neurol. 33: 518-527, 1971. 13. Kadobayashi, I. Effects of lenticular stimulation on unitary and mass response of the visual cortex to light. Pfliigers Arch. ges. Physiol. 332: 10-20, 1972. 14. Kadobayashi, 1. Effects of caudate stimulation on unitary responses of the lateral geniculate body to light. Expl Neurol. 37: 463~,68, 1972. 15. Kadobayashi, 1. and M. Nakamura. Modification of visual, auditory, and somatosensory evoked responses in cortical primary receiving areas by nigral stimulation. Experientia 30: 260-262, 1974. 16. Kadobayashi, 1. Modification of visual signals by nigral stimulation. Experientia 32: 1547-1548, 1976. 17. Lichtensteigen, W., U. Mutzner and H. Langemann. Uptake of 5-hydroxytryptamine and 5-hydroxytryptophan by neurons of the central nervous system normally containing catecholamines. J. Neurochem. 14: 489--497, 1967. 18. Ross, C. A., M. E. Trulson and B. L. Jacobs. Depletion of brain serotonin following intraventricular, 5,7-dihydroxytryptamine fails to disrupt sleep in the rat. Brain Res. 114: 517-523, 1976. 19. SabeUi, H. C., W. J. Giardina, S. B. Myles and A. J. Vazquez. The effects of DOPA on the visual-evoked potentials in rabbit and mouse motor behavior following inhibition of dopamine-/3hydroxylase. Arzneimittel-Forsch. 24: 333-337, 1974. 20. Shaskin, E. G. and S. H. Snyder. Kinetics of serotonin uptake into slices from different regions of rat brain. J. Pharmae. exp. Ther. 175: 404-418, 1970. 21. Ternaux, J. P., F. Hrry, S. Bourgoin, J. Adrien, J. Glowinski and M. Hamon. The topographical distribution of serotoninergic terminals in the neostriatum of the rat and the caudate nucleus of the cat. Brain Res. 121: 311-326, 1977. 22. Thut, P. D. and R. H. Rech. Effects of L-DOPA on the EEG and brain amines of unrestrained rats. Expl Neurol. 35: 13-29, 1972. 23. Winer, B. J. Statistical Principles in Experimental Design. New York: McGraw-Hill, 1971.