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Quinolinic acid: effects on brain catecholamine and c-AMP content during L-dopa and reserpine administration
Exp Toxic Pathol 1992; 44: 66-69 Gustav Fischer Verlag Jena
I) Medical Centre of Postgraduate Education, Department of Cell Pathophysiology, Laboratory of Histochemistry, Warsaw, Poland
2) Medical Academy, Department of Neurology, Bialystok, Poland
Quinolinic acid: effects on brain catecholamine and c-AMP content during L-dopa and reserpine administration *) M. BESKID1) and L. FINKIEWICZ-MuRAWIEJSKA 2 ) With 3 figures Received: June 5, 1990; Accepted: July 12, 1990 Address for correspondence: Prof. M. BESKID, M. D., Medical Centre of Postgraduate Education, Department of Cell Pathophysiology, Laboratory of Histochemistry, ul. Marymoncka 99, 0 I - 8 I 3 Warsaw, Poland Key words: quinolinic acid; catecholamine; c-AMP; brain; L-dopa; reserpine
Summary
Biochemical incestigations
The catecholamine content in rat brain tissue was determined following the administration of quinolinic acid alone or combined either with L-dopa and decarboxylase inhibitor or reserpine. Quinolinic acid alone decreased the levels of dopamine and noradrenaline, as well as those of c-AMP, and increased those of adrenaline. Treatment with L-dopa/ decarboxylase inhibitor reversed the suppressing'dfect of quinolinic acid on dopamine, but not on noradrenaline. Reserpine alone depleted the contents of dopamine, noradrenaline and adrenaline. It could be concluded from the effects of quinolinic acid and reserpine given together that quinolinic acid suppresses the depletion of amines induced by reserpine. It has been demonstrated that quinolinic acid leads to injuries of nerve-cell bodies in pars compacta of the substantia nigra and in the striatum.
The content of dopamine, noradrenaline and adrenaline in whole brain tissue was measured fluorimetrically according to BRODIE (1966), CHANG (1964) and UDENFRIEND (1962), c-AMP levels were determined according to BROWN et al. (1971). Protein was determined by the method of LOWRY et al. (1951). The following experiments were carried out: Group I received daily 60 mM of quinolinic acid for 8 days. The drug was administered to ether anesthetized rats through intracardiac injection. Group II received daily 100 mg/kg L-dopa with 10 mg/kg carbidopa once every 24h for 8 days. The drugs were administered by gastric tube. Group III received daily quinolinic acid intracardially, and Ldopa with carbidopa by gastric tube for 8 days. Group IV received daily 60 mM of quinolinic acid intracardially for 8 days. The last day of the experiment 30 min before the animals were sacrificed a single injection of reserpine (0.5 mg/ kg) was added. Group V received 30 min before sacrificing a single injection of reserpine alone (0.5 mg/kg). Group VI consisted of 14 untreated (control) animals. Obtained data in control and experimental conditions were analyzed statistically. The differences between mean values were analyzed by using the t-test, and by 2 X 2 factorial comparisons (Buss 1967).
Quinolinic acid is a natural metabolite of tryptophan, normally occurring in the liver, kidney and brain (Wolfensberger et al. 1983; MORONI et al. 1984). This compound exhibits convulsant and neuron excitant properties (STONE et al. 1987). It induces a selective pattern of neuronal degeneration both at the site of intracerebral injection (SCHW ARCZ et al. 1983; STONE et al. 1987) and after general (intracardiac) administration (BESKID and MARKIEWICZ 1988). The ability of quinolinic acid to produce neurotoxicity was greater in the striatum than in other parts of the brain. This prompted us to study catecholamine and c-AMP levels in rat brain tissue following quinolinic acid and L-dopa administration, as well as the influence of reserpine on quinolinic acid action.
Materials and Methods Experiments were carried out in male albino rats weighing 200-220 g, kept on pellet diet ad libitum. Each experimental group consisted of 7 animals.
*) This work was supported by the grant CPBP 06-20.11. 3.2.
66
Exp Toxic Pathol 44 (1992) 2
Results As presented in table 1, quinolinic acid produced decreases of dopamine and noradrenaline and an increase of adrenaline in the rat brain. Administration of L-dopa with decarboxylase inhibitor reversed the effect of quinolinic acid on dopamine, but not on the noradrenaline content. Reserpine alone led to a decrease of both dopamine and noradrenaline, as well as of adrenaline content. Reserpine adding to quinolinic acid resulted in abolishing the depleting action of reserpine (cL table 2).
Table 1. Concentrations of catecholamines ([lg! g tissue) in whole rat brain.
C Q LD Q + LD R Q+R
Dopamine
Noradrenaline
Adrenaline
x 1.02± 0.03 x 0.83 ± O.03xx x 1.34 ± 0.13 x x 1.75 ± 0.10xxx x 0.61 ±O.Ol xxx x 0.70±0.02 xxx
x 0.44±0.01 x 0.36 ± 0.01 x x 0.44±0.01 x 0.42±0.02 x 0.24 ± O.OOxxx x 0.36 ± 0.01 x
x 0.05 ± 0.01 x O.IO±O.Olx x 0.04±0.01 x 0.03±0.01 x 0.06±0.01
C control; Q quinolinic acid; LD L-dopa!decarboxylase inhibitor; R reserpine; xp<0.05; xxp
Table 2. Orthogonal factor analysis (mean effects and values of F-function). Dopamine
Noradrenaline
Adrenaline
mean effect
F
mean effect
mean effect
3.65 104xxx 27.4xxx
3.85 0.024 -0.103 71 xxx 0.100 67 xxx
-0.050 Q -0.267 R Q+R 0.137
F
F
0.023 7.95 xx -0.075 7.09 x -0.020 0.20
Q quinolinic acid; R reserpine; for explanation of symbols see table 1.
Table 3. c-AMP-Ievel in rat brain follwing quinolinic acid administration (pmol! mg protein). C Q
17.7 ± 1.48 14.4 ± 0.50 x
C control; Q quinolinic acid; for explanation of symbols see table 1.
As presented in table 3, quinolinic acid produced a decrease of c-AMP-Ievels in rat brain as compared with controls. Histological investigations Serial sections of substantia nigra and striatum were collected and stained with haematoxyline and eosine, and for Nissl staining with cresyl violet. Each group consisted of 6 animals. It was found that administration of quinolinic acid alone, and quinolinic acid with reserpine led to damage of the nervecell body and to tissue changes. The characteristic feature was the presence of degenerated neurons and tissue spongiosis. The degenerated nerve-cell bodies selectively developed in pars compacta of the substantia nigra. In the substantia nigra the damaged neurons were more numerous, whereas in the striatum they were less numerousand dispersed. No signs of significant nerve-cell body and tissue injuries were seen after quinolinic acid with L-dopa and carbidopa administration.
Discussion The presented results indicate that quinolinic acid administered intracardially produced decrease in the brain content of both dopamine and noradrenaline. It seems that the dopamine decrease is causally related to the presence of the degenerative nerve-cell bodies in the pars compacta of the substantia nigra and in the striatum. This cOlTesponds to the ability of quinolinic acid to produce more pronounced effects in the striatum than in other parts of the brain (SCHW ARCZ et a1. 1983; STONE et a1. 1987). The mapping of the monoamine calTying neuronal path originates in the pars compacta of the substantia nigra where the cell bodies are located. Their fibres enter the neostriatum and fOlTl1 nerve telTl1inals, where dopamine is stored in the synaptic vesicles and granules (HILLARP et al. 1966; BAK 1967; HASSLER et al. 1980). The existence of other dopamine-calTying neuronal paths should be pointed out. This path is considered a part of the limbic system. Another dopamine path occurs in the tuberoinfundibulum region, and in the retina. The distribution of the noradrenaline-calTying neuronal system is considerably more widespread than the dopamine-cauying one. The hypothalamus and lower brainstem are particularly well supplied by the fOlTl1er. A more detailed study of local monoamine distribution possibly explains the high amounts of dopamine detected in regions containing only little noradrenaline (HORNYKIEWICZ 1966; GLOWINSKI and BALDESSARIMI 1966; IVERSEN 1967). It seems to be interesting to note that quinolinic acid administration produced an increase of the adrenaline brain content. The adrenaline content of peripheral tissues is, however, more variable than that of noradrenaline. Most tissues contain small amounts of adrenaline ranging fOlTl1 2 to 15 % of the total catecholamine content (IVERSEN 1967). The circulating adrenaline released from adrenal medulla may stimulate the presynaptic Betaz receptors (CORR et al. 1986), which facilitates the noradrenaline release (ADLER-GRASCHINSKY and LANGER 1975; YAMAGUCHI et al. 1977). It follows from our experiments that this neurotoxic effect of quinolinic acid could be reversed by L-dopa! decarboxy lase inhibitor treatment. In this case neither in the substantia nigra nor in the striatum tissues degenerated fOlTl1s of the nerve-cell bodies were observed. This was accompanied with the elevation of dopamine, but not of noradrenaline content. A positive effect of L-dopa on the nigro-striatal dopamine system has been demonstrated in human parkinsonism (HORNYKIEWICZ 1966; CARLSSON 1972; GARNETT et al. 1980), as well as in experimentally induced extrapyramidal disorders!CARLSSON 1972; HASSLER et al. 1980). The marked elevation of dopamine content as a result of combined L-dopa! decarboxylase inhibitor action was also observed when either MAO or catechol-O-methyl transferase (COMT) inhibitors were used. This might suggest that quinolinic acid inhibits the catecholamine degradation rather than its synthesis. It may be added that following oral or parenteral administration of L-dopa, a considerable portion of it was decarboxylated in peripheral tissue. Hence the pretreatment with dopa decarboxylase inhibitor facilitates the passage of L-dopa. Under nOlTl1al conditions the presence of a specific balTier mechanism in the capillaries of the central nervous system, including the optic tract and retina, was demonstrated (BERTLER et al. 1966). L-dopa, but not D-dopa or dopamine, readily penetrates into capillary walls where decarboxylase and MAO are present. Exp Toxic Pathol 44 (1992) 2
67
Detailed experiments demonstrated that only 20 % of L-dopa that entered the endothelial cells was available to the nerve-cell bodies (GARNETT et al. 1980). Oui experiments show that quinolinic acid has the ability to inhibit the depleting action of reserpine on brain amines. Reserpine when added prior to quinolinic acid, produces much smaller depleting effects than when reserpine alone is applied. It can be suggested that quinolinic acid inhibits the release of amines from the brain, as demonstrated by orthogonal factor analysis. Reserpine depletes the brain of its dopamine, noradrenaline and 5-hydroxytryptamine content (HORNYKIEWICZ 1966; CARLSSON 1966). The intracellular storage granules were found to be the site of reserpine action (CARLSSON 1966). The ability of these granules to incorporate amines is blocked by reserpine, leading to depletion and further transmission failure. The active transport mechanism for amines, located in the cell membrane, is resistant to reserpine action (CARLSSON 1966; POTTER 1966; SCHUMANN 1966; STJARNE 1966). Numerous studies on intact cells have suggested that a rise in the intracellular calcium ion concentration triggers the secretion of amines, but the intracellular Mg/ ATP is essential in supporting this secretion (POTTER 1966; SCHUMANN 1966; Knight 1986). Quinolinic acid can affect the calcium ion concentration within the cells. As was demonstrated quinolinic acid has a potent modulatory effect on the calcium ion channel, producing both negative and positive inotropic heart responses with an enhancement of the coronary flow (BESKID, in press). Moreover, quinolinic acid has the ability to increase calcium influx, and can form complexes with calcium ions (BESKID et al., in press). The binding of calcium by quinolinic acid was low, but dose-dependent. Since the complex may accumulate within the cells, it may produce excess of calcium within the cell, thus leading to their damage. A similar effect was observed with kainic acid (COYLE 1987). On the other hand, the calcium ion-dependent sensitivity of the secretory process can be increased by 12-0-tetradenaoylphorbol-13-acetate (TPA) (KNIGHT 1986). It is known that phorbol esters can substitute diacylglycerol and directly stimulate the phospholipase activity (WEINSTEIN 1981). It is worth adding that phospholipase activity is mediated by c-AMP-dependent phosphorylation (McDONALD et al. 1984). Hence, the decrease of c-AMP-Ievel in brain tissue after quinolinic acid treatment may be the cause of amine transmission failure. It may be added that quinolinic acid produces the drop of c-AMP-Ievel also in the rat heart tissue (BESKID, unpublished data). In conclusion, it may be inferred that quinolinic acid possessing the ability to modulate calcium ion concentration within the cell (BESKID et aI., in press) and inducing a decrease of c-AMPlevel, can lead to failure in dopamine transmission and to further injury of the nerve-cell body.
References ADLER-GRASCHINSKY, E., LANGER, S.Z.: Possible role of a betaadrenoceptor in the regulation of noradrenaline release by nerve stimulation through a positive feedback mechanism. Br. J. Pharmacal. 1975; 53: 43-50. BAK, 1. J.: The ultrastructure of the substantia nigra and caudate nucleus of the mouse and the cellular localization of catecholamines. Exp. Brain Res. 1967; 3: 40-57.
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Exp Toxic Pathol 44 (1992) 2
BERTLER, A., FALCK, B .. OWMAN, CH., ROSENGRENN, E.: The localization of monoaminergic blood-brain barrier mechanism. Pharmacal. Rev. 1966; 18: 396-385. BESKID, M.: Quinolinic acid as calcium channel modulator in isolated rat heart preparations. Exp. Pathol. 1990; 39: 31-36. MARKIEWICZ, D.: Morphological changes in the brain of rats after intracardiac and intraperitoneal administration of quinolinic acid. Neuropat. Pol. 1988; 26: 61-68. FINKIEWICZ-MuRAWIEJSKA, L., OBMINSKJ. Z., WOLSKA, B.: Quinolinic acid: a modulator. of heart calcium channel in the rat and a binder of calcium ions. Exp. Pathol. 1991; 41: 110- I 14. - - - Quinolinic acid: effect on 45Ca content in perfused rat heart preparations, and calcium ion binding propelty in Krebs-Henseleit medium and blood serum. Exp. Pathol. 1991; 42: 175-178. BLISS, C. I.: Statistics in biology. Ed. McGraw-Hili 1976; 1: 249. BRODIE, B. B., COMER, M. A., COSTA, E., DIABAC, A.: The role of brain 5 HT in the mechanism of central action of reserpine. J. Phannacol. Exp. Ther. 1966; 152: 340-346. BROWN, B. L., ALBANO, J. D. M., PEKINS, R. P., SGHERZI, A. M., TAMPION, W.: A simple and sensitive saturation assay method for the measurement of adenosine 3,5-cyclic monophosphate. Biochem. J. 1971; 121: 561-562. CARLSSON, A.: Pharmacological depletion of catecholamine stores. Pharmacal. Rev. 1966; 18: 541-549. - Biochemical and pharmacological spects of parkinsonism. Acta neurolog. scand. 1972; suppl. 51: I 1-42. CHANG, C. c.: A sensitive method for spectrophotofluorometric assay of catecholamines. Intern. J. Pharmacal. 1964; 3: 643-u46. CORR, P. B., YAMADA, K. A., WITKOWSKI, F. X.: Mechanism controlling cardiac autonomic function and their relation to arrythmogenesis. In: The heart and cardiovascular system (Eds. FOZZARD, H. A. et al.). Raven Press, New York 1986; pp. 1343-1403. COYLE, J. T.: Kainic acid: insights into excitatory mechanism causing selective neuronal degeneration. In: Selective neuronal death. Ciba Found. symp. 126. Wiley Intersci. Publ., Chichester 1987; pp. 186-198. GARNETT, E. S., FIRNAU , G., NAHMIAS, C.: (18 F) fIuoro dopa for the measurement of intracerebral dopamine metabolism in man. In: Parkinson's disease. Current progress, problems and management (Eds. RINNE, U. K. et al.). Elsevier North Holland Biomed. Press 1980; pp. 186-191. GLOWINSKI, J., BALDESSARINI, R. J.: Metabolism of norepinephrine in the central nervous system. Pharmacal. Rev. 1966: 18: 1201-1238. HASSLER, R., NITSCH, c., LEE, H. L.: The role of the eight putative transmitters in the nine types of synapses in rat caudate putamen. In: Parkinson's disease. Current progress, problems and management (Eds. RINNE, U. K. et al.). Elsevier North Holland Biomed. Press 1980; pp. 186-191. HILLARP, N. A., Fuxe, K., DAHLSTROM, A.: Demonstration and mapping of central neurons containing dopamine, noradrenaline, and 5-hydroxytryptamine and their reactions to psychopharrnaca. Pharmacal. Rev. 1966; 18: 727-741. HORNYKJEWICZ, 0.: Dopamine (3hydroxytyramine) and brain function. Pharmacal. Rev. 1966; 18925-964. IVERSEN, L. L.: The uptake and storage of noradrenaline in sympathetic nerves. Ed. Univ. Press, Cambridge 1967. LOWRY, J. O. H., ROSENBROUGH, N. J., FARR, A. L.: Protein measurement with phenol reagent. J. BioI. Chern. 1951; 193: 265. McDONALD, J. M., GRAVES, C. B., CHRISTENSEN, B. L.: Calcium and the adipocyte. In: Calcium and cell function (Ed. Cheung, W. Y.). Academic Press, Inc., New York 1984; 209-277. MORONI, F., LOMBARDI, G., CARLA, V., MONET!, G.: The excitotoxin quinolinic acid is present and unevenly distributed in the rat brain. Brain Res. 1984; 295: 352-355. POTTER, L. T.: Storage of norepinephrine in sympathetic nerves. Pharmacal. Rev. 1966; 18: 439-451.
SCHUMANN, H. J.: Medullary particles. Pharmacol Rev.
1966; 18:
433-43.8. SCHWARCZ, R., WHETSELL , W.O., JR. , MANGANO , R. M.: Quinolinic acid: an endogenous metabolite that produces axon-sparing lesions in rat brain. Science (Wash.) 1983; 219: 316-318. STJ ARNE, L.: Storage particles in noradrenaline tissues. Pharmacol. Rev. 1966; 18: 425-432. STONE , T. W., CONNICK, J. H., WINN , P. , HASTINGS, M. H., ENGLISH, M. : Endogenous excitotoxic agents. In: Selective neuronal death. Ciba Found. symp . 126. Wiley Intersci. Pub I. Chichester 1987 ; pp.
UDENFRIEND, S.: Fluorescence assay in biology and medicine. Academic Press , New York 1962. WEINSTEIN, I. B.: Current concepts and controversies in chemical carcinogenesis. J. Supramol. Struct. Cell Biochem. 1981; 17: 99-120. WOLFENSBERGER, A., AMSLER, H., CUENOD, M., FOSTER, A. C., WHETSELL, W., SCHWARCZ, R.: Identification of quinolinic acid in rat and human brain tissue. Neurosci. Lett . 1983; 41: 247-254. YAMAGUCHI, N., DECHAMPLAIN, J. , NADEAU, R. A.: Regulation of norepinephrine release from cardiac sympathetic fibres in the dog by presynaptic alpha- and beta-receptors. Circ. Res. 1977; 41: 108-117.
204-214.
Exp Toxic Pathol 44 (1992) 2
69
I) Medical Centre of Postgraduate Education, Department of Cell Pathophysiology, Laboratory of Histochemistry, Warsaw, Poland
2) Medical Academy, Department of Neurology, Bialystok, Poland
Quinolinic acid: effects on brain catecholamine and c-AMP content during L-dopa and reserpine administration *) M. BESKID1) and L. FINKIEWICZ-MuRAWIEJSKA 2 ) With 3 figures Received: June 5, 1990; Accepted: July 12, 1990 Address for correspondence: Prof. M. BESKID, M. D., Medical Centre of Postgraduate Education, Department of Cell Pathophysiology, Laboratory of Histochemistry, ul. Marymoncka 99, 0 I - 8 I 3 Warsaw, Poland Key words: quinolinic acid; catecholamine; c-AMP; brain; L-dopa; reserpine
Summary
Biochemical incestigations
The catecholamine content in rat brain tissue was determined following the administration of quinolinic acid alone or combined either with L-dopa and decarboxylase inhibitor or reserpine. Quinolinic acid alone decreased the levels of dopamine and noradrenaline, as well as those of c-AMP, and increased those of adrenaline. Treatment with L-dopa/ decarboxylase inhibitor reversed the suppressing'dfect of quinolinic acid on dopamine, but not on noradrenaline. Reserpine alone depleted the contents of dopamine, noradrenaline and adrenaline. It could be concluded from the effects of quinolinic acid and reserpine given together that quinolinic acid suppresses the depletion of amines induced by reserpine. It has been demonstrated that quinolinic acid leads to injuries of nerve-cell bodies in pars compacta of the substantia nigra and in the striatum.
The content of dopamine, noradrenaline and adrenaline in whole brain tissue was measured fluorimetrically according to BRODIE (1966), CHANG (1964) and UDENFRIEND (1962), c-AMP levels were determined according to BROWN et al. (1971). Protein was determined by the method of LOWRY et al. (1951). The following experiments were carried out: Group I received daily 60 mM of quinolinic acid for 8 days. The drug was administered to ether anesthetized rats through intracardiac injection. Group II received daily 100 mg/kg L-dopa with 10 mg/kg carbidopa once every 24h for 8 days. The drugs were administered by gastric tube. Group III received daily quinolinic acid intracardially, and Ldopa with carbidopa by gastric tube for 8 days. Group IV received daily 60 mM of quinolinic acid intracardially for 8 days. The last day of the experiment 30 min before the animals were sacrificed a single injection of reserpine (0.5 mg/ kg) was added. Group V received 30 min before sacrificing a single injection of reserpine alone (0.5 mg/kg). Group VI consisted of 14 untreated (control) animals. Obtained data in control and experimental conditions were analyzed statistically. The differences between mean values were analyzed by using the t-test, and by 2 X 2 factorial comparisons (Buss 1967).
Quinolinic acid is a natural metabolite of tryptophan, normally occurring in the liver, kidney and brain (Wolfensberger et al. 1983; MORONI et al. 1984). This compound exhibits convulsant and neuron excitant properties (STONE et al. 1987). It induces a selective pattern of neuronal degeneration both at the site of intracerebral injection (SCHW ARCZ et al. 1983; STONE et al. 1987) and after general (intracardiac) administration (BESKID and MARKIEWICZ 1988). The ability of quinolinic acid to produce neurotoxicity was greater in the striatum than in other parts of the brain. This prompted us to study catecholamine and c-AMP levels in rat brain tissue following quinolinic acid and L-dopa administration, as well as the influence of reserpine on quinolinic acid action.
Materials and Methods Experiments were carried out in male albino rats weighing 200-220 g, kept on pellet diet ad libitum. Each experimental group consisted of 7 animals.
*) This work was supported by the grant CPBP 06-20.11. 3.2.
66
Exp Toxic Pathol 44 (1992) 2
Results As presented in table 1, quinolinic acid produced decreases of dopamine and noradrenaline and an increase of adrenaline in the rat brain. Administration of L-dopa with decarboxylase inhibitor reversed the effect of quinolinic acid on dopamine, but not on the noradrenaline content. Reserpine alone led to a decrease of both dopamine and noradrenaline, as well as of adrenaline content. Reserpine adding to quinolinic acid resulted in abolishing the depleting action of reserpine (cL table 2).
Table 1. Concentrations of catecholamines ([lg! g tissue) in whole rat brain.
C Q LD Q + LD R Q+R
Dopamine
Noradrenaline
Adrenaline
x 1.02± 0.03 x 0.83 ± O.03xx x 1.34 ± 0.13 x x 1.75 ± 0.10xxx x 0.61 ±O.Ol xxx x 0.70±0.02 xxx
x 0.44±0.01 x 0.36 ± 0.01 x x 0.44±0.01 x 0.42±0.02 x 0.24 ± O.OOxxx x 0.36 ± 0.01 x
x 0.05 ± 0.01 x O.IO±O.Olx x 0.04±0.01 x 0.03±0.01 x 0.06±0.01
C control; Q quinolinic acid; LD L-dopa!decarboxylase inhibitor; R reserpine; xp<0.05; xxp
Table 2. Orthogonal factor analysis (mean effects and values of F-function). Dopamine
Noradrenaline
Adrenaline
mean effect
F
mean effect
mean effect
3.65 104xxx 27.4xxx
3.85 0.024 -0.103 71 xxx 0.100 67 xxx
-0.050 Q -0.267 R Q+R 0.137
F
F
0.023 7.95 xx -0.075 7.09 x -0.020 0.20
Q quinolinic acid; R reserpine; for explanation of symbols see table 1.
Table 3. c-AMP-Ievel in rat brain follwing quinolinic acid administration (pmol! mg protein). C Q
17.7 ± 1.48 14.4 ± 0.50 x
C control; Q quinolinic acid; for explanation of symbols see table 1.
As presented in table 3, quinolinic acid produced a decrease of c-AMP-Ievels in rat brain as compared with controls. Histological investigations Serial sections of substantia nigra and striatum were collected and stained with haematoxyline and eosine, and for Nissl staining with cresyl violet. Each group consisted of 6 animals. It was found that administration of quinolinic acid alone, and quinolinic acid with reserpine led to damage of the nervecell body and to tissue changes. The characteristic feature was the presence of degenerated neurons and tissue spongiosis. The degenerated nerve-cell bodies selectively developed in pars compacta of the substantia nigra. In the substantia nigra the damaged neurons were more numerous, whereas in the striatum they were less numerousand dispersed. No signs of significant nerve-cell body and tissue injuries were seen after quinolinic acid with L-dopa and carbidopa administration.
Discussion The presented results indicate that quinolinic acid administered intracardially produced decrease in the brain content of both dopamine and noradrenaline. It seems that the dopamine decrease is causally related to the presence of the degenerative nerve-cell bodies in the pars compacta of the substantia nigra and in the striatum. This cOlTesponds to the ability of quinolinic acid to produce more pronounced effects in the striatum than in other parts of the brain (SCHW ARCZ et a1. 1983; STONE et a1. 1987). The mapping of the monoamine calTying neuronal path originates in the pars compacta of the substantia nigra where the cell bodies are located. Their fibres enter the neostriatum and fOlTl1 nerve telTl1inals, where dopamine is stored in the synaptic vesicles and granules (HILLARP et al. 1966; BAK 1967; HASSLER et al. 1980). The existence of other dopamine-calTying neuronal paths should be pointed out. This path is considered a part of the limbic system. Another dopamine path occurs in the tuberoinfundibulum region, and in the retina. The distribution of the noradrenaline-calTying neuronal system is considerably more widespread than the dopamine-cauying one. The hypothalamus and lower brainstem are particularly well supplied by the fOlTl1er. A more detailed study of local monoamine distribution possibly explains the high amounts of dopamine detected in regions containing only little noradrenaline (HORNYKIEWICZ 1966; GLOWINSKI and BALDESSARIMI 1966; IVERSEN 1967). It seems to be interesting to note that quinolinic acid administration produced an increase of the adrenaline brain content. The adrenaline content of peripheral tissues is, however, more variable than that of noradrenaline. Most tissues contain small amounts of adrenaline ranging fOlTl1 2 to 15 % of the total catecholamine content (IVERSEN 1967). The circulating adrenaline released from adrenal medulla may stimulate the presynaptic Betaz receptors (CORR et al. 1986), which facilitates the noradrenaline release (ADLER-GRASCHINSKY and LANGER 1975; YAMAGUCHI et al. 1977). It follows from our experiments that this neurotoxic effect of quinolinic acid could be reversed by L-dopa! decarboxy lase inhibitor treatment. In this case neither in the substantia nigra nor in the striatum tissues degenerated fOlTl1s of the nerve-cell bodies were observed. This was accompanied with the elevation of dopamine, but not of noradrenaline content. A positive effect of L-dopa on the nigro-striatal dopamine system has been demonstrated in human parkinsonism (HORNYKIEWICZ 1966; CARLSSON 1972; GARNETT et al. 1980), as well as in experimentally induced extrapyramidal disorders!CARLSSON 1972; HASSLER et al. 1980). The marked elevation of dopamine content as a result of combined L-dopa! decarboxylase inhibitor action was also observed when either MAO or catechol-O-methyl transferase (COMT) inhibitors were used. This might suggest that quinolinic acid inhibits the catecholamine degradation rather than its synthesis. It may be added that following oral or parenteral administration of L-dopa, a considerable portion of it was decarboxylated in peripheral tissue. Hence the pretreatment with dopa decarboxylase inhibitor facilitates the passage of L-dopa. Under nOlTl1al conditions the presence of a specific balTier mechanism in the capillaries of the central nervous system, including the optic tract and retina, was demonstrated (BERTLER et al. 1966). L-dopa, but not D-dopa or dopamine, readily penetrates into capillary walls where decarboxylase and MAO are present. Exp Toxic Pathol 44 (1992) 2
67
Detailed experiments demonstrated that only 20 % of L-dopa that entered the endothelial cells was available to the nerve-cell bodies (GARNETT et al. 1980). Oui experiments show that quinolinic acid has the ability to inhibit the depleting action of reserpine on brain amines. Reserpine when added prior to quinolinic acid, produces much smaller depleting effects than when reserpine alone is applied. It can be suggested that quinolinic acid inhibits the release of amines from the brain, as demonstrated by orthogonal factor analysis. Reserpine depletes the brain of its dopamine, noradrenaline and 5-hydroxytryptamine content (HORNYKIEWICZ 1966; CARLSSON 1966). The intracellular storage granules were found to be the site of reserpine action (CARLSSON 1966). The ability of these granules to incorporate amines is blocked by reserpine, leading to depletion and further transmission failure. The active transport mechanism for amines, located in the cell membrane, is resistant to reserpine action (CARLSSON 1966; POTTER 1966; SCHUMANN 1966; STJARNE 1966). Numerous studies on intact cells have suggested that a rise in the intracellular calcium ion concentration triggers the secretion of amines, but the intracellular Mg/ ATP is essential in supporting this secretion (POTTER 1966; SCHUMANN 1966; Knight 1986). Quinolinic acid can affect the calcium ion concentration within the cells. As was demonstrated quinolinic acid has a potent modulatory effect on the calcium ion channel, producing both negative and positive inotropic heart responses with an enhancement of the coronary flow (BESKID, in press). Moreover, quinolinic acid has the ability to increase calcium influx, and can form complexes with calcium ions (BESKID et al., in press). The binding of calcium by quinolinic acid was low, but dose-dependent. Since the complex may accumulate within the cells, it may produce excess of calcium within the cell, thus leading to their damage. A similar effect was observed with kainic acid (COYLE 1987). On the other hand, the calcium ion-dependent sensitivity of the secretory process can be increased by 12-0-tetradenaoylphorbol-13-acetate (TPA) (KNIGHT 1986). It is known that phorbol esters can substitute diacylglycerol and directly stimulate the phospholipase activity (WEINSTEIN 1981). It is worth adding that phospholipase activity is mediated by c-AMP-dependent phosphorylation (McDONALD et al. 1984). Hence, the decrease of c-AMP-Ievel in brain tissue after quinolinic acid treatment may be the cause of amine transmission failure. It may be added that quinolinic acid produces the drop of c-AMP-Ievel also in the rat heart tissue (BESKID, unpublished data). In conclusion, it may be inferred that quinolinic acid possessing the ability to modulate calcium ion concentration within the cell (BESKID et aI., in press) and inducing a decrease of c-AMPlevel, can lead to failure in dopamine transmission and to further injury of the nerve-cell body.
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