- Email: [email protected]
Difference in the effects of the antidepressant tianeptine on dopaminergic metabolism in the prefrontal cortex and the nucleus accumbens of the rat. A voltammetric study
Life Sciences, Vol. 47, pp. 1083-1089 Printed in the U.S.A.
Pergamon Press
DIFFERENCE IN THE EFFECTS OF THE ANTIDEPRESSANT TIANEPTINE ON DOPAMINERGIC METABOLISM IN THE PREFRONTAL CORTEX AND THE NUCLEUS ACCUMBENS OF THE RAT. A VOLTAMMETRIC STUDY A. LOUILOT, E. MOCAER*, H. SIMON and M. LE MOAL
Laboratoire de Psychobiologic des Comportements Adaptatifs - INSERM U.259 Universit6 de Bordeaux II- Domaine de Carreire, Rue Camille Saint-Sa~ns 33077 Bordeaux Cedex, France. *Institut de Recherches Internationales Servier (I.R.I.S.) - 27 rue du Pont - B.P. 126 - 92202 NeuiUy Cedex (Received in final form July 23, 1990)
SUMMARY The effects of the new tricyclic antidepressant tianeptine were investigated on dopaminergic (DAergic) metabohsm in the anteromedian prefrontal cortex and the nucleus accumbens of the rat. DAergic metabolism was assessed by the measurement of DOPAC, the main presynaptic metabolite of dopamine, using in vivo voltammetry in rats ventilated with halothane (0.50.75% in air). Acute treatment with tianeptine (10 mg/kg, 20 mg/kg) only increased significantly DOPAC levels in the anteromedian prefrontal cortex. After chron{c treatment with tianeptine (15 days, 2 times/day) the increases in DOPAC levels in this structure were altered and less pronounced with the 20 mg/kg dose. Previous studies led to suggest that both acute and chronic effects on DAergic terminals in the anteromedian prefrontal cortex may be involved in the therapeutic action of this new antidepressant. Tianeptine (S1574) is a new tricyclic antidepressant drug (1, 2) which has been shown to have activity in experimental tests used for the selection of classical antidepressants (3). The neurochemical effects of this compound appear to differ from those described for classical tricyclic antidepressants. A principle action is an enhancement of serotonin uptake in cortex and hippocampus after acute or chronic treatment with no effect on spontaneous serotonin release (4). Noradrenergic and dopaminergic transmissions, do not appear to be affected by tianeptine. Striatal uptake or release ofdopamine (DA) are not affected by acute or chronic treatment of this drug which also lacks affinity for DAbinding sites (4). However, it is difficult to ascertain the effect of tianeptine on DAergic neurons from results obtained at the striatal level alone since the DAergic mesencephalic neurons are grouped in different subunits depending on their location in the ventral mesencephalon a n d their projections areas (5, 6). The pharmacological reactivity of the DAergic mesencephalic subunits can be differentiatedat the terminal level in both the nucleus accumbens (ACC) and the anteromedian prefrontal cortex (PFC) (7, 8, 9, 10). In the present study, the effects of tianeptine on DAergic neurons were investigated by the measurement of the 3,4-dihydroxyphenylacetic acid (DOPAC), the main presynaptic DA metabolite in the ACC and the PFC. DOPAC levels were assessed by in vivo differential pulse voltammetry (DPV) using electrochemically pretreated carbon fibres electrodes which has been shown to be a reliable and powerful technique to study the kinetic of drugs effects on DAergic metabolism (8, 9, 10, 11, 12, 13, 14, 15). The effects of acute treatment of tianeptine on DAergic metabolism were studied in both the ACC and the PFC, and the effects of chronic treatment only in the PFC since acute treatment was found to be without significant effect in the ACC. 0024-3205/90 $3.00 + .00 Copyright (c) 1990 Pergamon Press plc
1084
Tianeptine Effects on DAergic Metabolism
Vol. 47, No. 13, 1990
METHODS
Electrochemistry A classical three-electrode system was used. DPV coupled with electrochemically pretreated carbon fiber microelectrodes (8 #m diameter, 500/~m length) was employed. Microelectrode preparation and electrochemical treatment procedures have been reported elsewhere (16, 17). The reference electrode was a AgCl-coated silver wire obtained from a Teflon-coated silver wire and prepared as previously described (18). The auxilliary electrode was a platinum wire. The commercially available voltammetric apparatus Biopulse (Tacussel, Villeurbanne, France) was set up with the following parameters for the detection of the DOPAC peak: scan rate, 10 mV/s; voltage range, -100 mV, + 150 mV; pulse modulation amplitude 50 mV; pulse modulation duration 48 ms; modulation period 200 ms. DOPAC peak was recorded every 2 rain at +50 mV/reference electrode. DOPAC peak height was calculated as previously described (15). Tianeptine and saline were injected at the end of the control period of 20 rain during which the signal varied less than 10%. For each experiment the mean of the 10 peaks measured during the control period was calculated and represented the 100% value of the DOPAC peak height. The responses of the carbon fiber microelectrodes were calibrated before and after the experiments in solutions containing different concentrations of DOPAC. Animals and surgery Male Sprague-Dawley rats (Iffa-Credo, L),on, France) weighing 360-380 g were used. Animals were housedat 22°C, and maintained on a 13-11 h light-dark cycle (light on at 7.00 A.M.). Animals were tracheotomized under halothane anaesthesia, intubated with a tracheal cannula, artificially ventilated with halothane (0.5-0.75% in air) after injection of d-tubocurarine (10 mg/kg i.p.), and placed in a stereotaxic frame with the incisor bar 3 mm below the interaural line. All stereotaxic pressure points and incision margins were locally anesthetized with lidocaine (xylocaine). Body temperature was monitored and maintained constant (37°C) by a thermostatically controlled blanket. The carbon fiber microelectrodes were implanted in the PFC or the ACC. The following stereotaxic coordinates were used: PFC: + 12.5 mm anterior to the interaural line (AP); 0.75 mm lateral to the midline (L); 4 mm below the cortical surface(V); ACC: + 10.6 mm (AP); 1,5 mm (L); 7 mm (V) according to the atlas of Paxinos et Watson (19). In some cases, the recording sites were visualized as previously described (6). DruGs v
Tianeptine (S1574, Servier, France) and the solvant (NaC1 0.9%) were injected i.p. in a volume of 1 ml/kg. For chronic treatment, tianeptine (10 mg/kg and 20 mg/kg) and saline were administered twice per day during 15 days. For chronic treatment followed by a wash-out the procedure was the same as for chronic treated animals excepted that treatment was withdrawn 72 h before the experiment. Data analvsis and statisti¢~ Results were expressed as percentages (mean _+ S.E.M.). For each structure, results obtained after acute treatment were submitted to "a two-factor analysis of variance (ANOVA) with doses (tianeptine 10 mg/kg, 20 mg/k~, and NaC1 0.9%)being the independent factor, and time the repeated measure. In relation to the significance of this analysis, effects of chronic treatment of tianeptine and chronic treatment+wash-out on DAergic neurons were only investigated in the PFC. Changes in DOPAC levels in this structure after chronic treatment and chronic treatment +wash-out were submitted to the ANOVA.
Vol. 47, No. 13, 1990
Tianeptlne Effects on DAergic Metabolism
1085
Administration of tianeptine (10 mg/kg, 20 mg/kg, acute treatment) was followed by a small increase in the DOPAC peak recorded in the ACC (Fig. 1). The maximal increases (respective to the corresponding control values) were about 15% for the 10 mg/kg dose and about 20% for the 20 mg/kg dose, and were reached respectively 20 min and 90 rain after the injection. These changes were not statistically significant F(2, 19) = 2.84 P = 0.082 N.S.
NUCLEUS ACCUMBENS ACUTE TREATMENT
NaCI 0.9 % n=7 0--.o TIANEPTINE (lOmg/kg) n=8 II--II TIANEPTINE ( 2 0 m g / k g ) n=7
175
150
<~ 125
~<
lOO
t
75 1"
I
-2o
I
-lO
I
o
I
lo
I
20
I
30
I
40
I
so
I
eo
I
ro
I
8o
t
9o
TIME (MIN)
FIG.1. Time-courses of the DOPAC peak height measured from DP voltammograms recorded from the nucleus accumbens of rats treated with tianeptine (10 mg/kg, 20 mg/kg) or saline injected intraperitoneally. Animals were in acute preparation vendiated with halothane (0.5%-0.75% m air). For each experiment the results were expressed as the percentage (mean _+ SEM) of the mean pre-injection value calculated by averaging the 10 absolute values of the peak heights obtained during the control period (20 rain pre-injection period). The DOPAC peak was recorded every 2 rain between -100 mV and + 150 mV vs the reference electrode. The arrow indicates the time of the injection. The injection of tianeptine (10 mg/kg, 20 mg/kg, acute treatment) was followed by an increase in the DOPAC peak recorded in the PFC (Fig. 2A) with a greater increase after administration of the 20 mg/kg dose. The maximal values reached were about 30% and 45% (compared to the respective control values) for the 10 mg/kg and 20 mg/kg doses respectively..The dose-response was statistically significant F(2, 12) = 6.68 P <
1086
Tianeptine Effects on DAergic Metabolism
Vol. 47, No. 13, 1990
0.01. Comparison of the different groups gave the following results: NaCI 0.9% / 10 mg/kg, F(1, 8) = 4.23 P = 0.072 N.S.; NaC1 0.9% / 20 mg/kg, F(1, 8) = 35.4 P < 0.001; 10 mg/kg / 20 mg/kg, F(1, 8) = 1.22 P = 0.3 N.S. After chronic treatment the administration of tianeptine (10 mg/kg, 20 mg/kg) was followed by an increase of the DOPAC peak recorded in the P F C (Fig. 2B). The maximal values reached after administration of the 10 mg/kg and 20 mg/kg doses were about 30% and 20% respectively (compared to control values). The dose-response on chronically treated animals was statistically significant F(2, 12) = 4.55 P < 0.05. Comparison of the different groups gave the following results: NaCI 0.9% / 10 mg/kg, F(1, 8) = 8 P < 0.05; NaC1 0 . 9 % / 2 0 mg/kg, F(I, 8) = 8.25 P < 0.05; 10 mg/kg / 20 mg/kg, F(1, 8) = 0.63 P = 0.76 N.S. After chronic treatment followed by a wash-out (72 h), the DOPACpeak in the PFC was only increased after administration of the 10 mg/kg dose (Fi~g. 2C). The maximal increase was about 20% (versus control levels). The dose-response m chronically treated animals submitted to a wash-out was statistically significant F(2, 12) = 4.15 P < 0.05; NaC1 0.9% / 10 mg/kg, F(1, 8) = 7.07 P < 0.05; NaC1 0.9% / 20 mg/kg, F(1, 8) = 0.02 P = 1 N.S.; 10 mg/kg / 20 mg/kg, F(1, 8) = 5.16 P < 0.05. A
B
PREF~(T~. ~ ACUT~ TRF.ATMf34T
F~IF.F'RO~ OOm'F.X TIRF.ATMINT
e.° o-o TIA(NI~OTIN~ (lOmglk0)nm° TIANEPTllq£ (20ntG/kg ) rim° NII¢I o.e I
NJCI 0.0 Sl, n - S O.--O l IA'~IEP+'rIIE (I0 mg]kll)n - 5 TIA/VlPTINI ( ~ m l l / k g ) n . 5 H
t
|I
t o-~,
-"
6
~
TIME 1~1)
~
•
~o
t~Mli
(MIN)
~)
Jo ~
~
¢ &
TREATMENT*WAIIH CUT 17[
*:~-,o
,
TIAN~PTINI[(lOmilJk0) ~ $ TIANEpT~ ~l"lq~/kg) ~ S
,<, ~ ,,o ~, ,t,, ,,o FIG.2.
Time-courses of the DOPAC peak height measured from DP voltammograms recorded from the prefrontal cortex of rats treated with tianeptine (10 mg/kg, 20 mg/kg) or saline. A) Effect of acute treatment. B) Effect of chronic treatment (15 days, 2 injections/day). C) Effect of chronic treatment (15 days, 2 injections/ day) followed by a wash-out (72h). For comments, see legend of Fig.1.
Vol. 47, No. 13, 1990
Tlaneptine Effects on DAerglc Metabolism
1087
DISCUSSION
The aim of the present study was to investigate the effect of the new tricyclic antidepressant tianeptine on DAergic metabolism at the level of the PFC and ACC using. DPV. The results obtained with acute treatment showed that this drug only had a sigmficant effect on DAergic terminals in the PFC whereas in the ACC stanstically non-significant increases in DOPAC levels were obtained. In PFC, DOPAC levels were significantly increased for the two doses used with a greater effect for the higher dose (20mg/kg). For both structures DOPAC levels raised earlier at the lower dose (10 mg/kg). I n this context, it is interesting to notice that tianeptine induced different psychopharmacological responses following administration of the 10 mg/kg and the 20 mg/kg doses (3}.. The differential neurochemical effects of tianeptine depending on doses may contribute to the distinct behavioral expressions. The difference between the results obtained with the acute treatment of tianeptine in the PFC and the ACC could have several interpretations. It might be the result of a different distribution of the antidepressant in the two brain areas and/or to a different sensitivity of the two DAergic projections to the drug. Another possibility is that tianeptine primarily acts on non-DAergic pathways that modulate the two DAergic projections differently. A primary non-DAergic action of tianeptine is consistent with the delayed increases in DOPAC levels observed in both stuctures after administration of the higher dose. With respect to the results obtained in the PFC after acute administration of tianeptine, the amplitude of the increase in DOPAC levels was comparable to that obtained with neuroleptics (10), whose effects on DAergic metabolism is assumed to be due to DA receptor blockade (20, 21). However, it has recently been shown at the ACC level that DAergic metabolism is markedly enhanced by buspirone (11), an anxiolytic drug which does not act directly on DAergic neurons (12). Thus, a similar, but different indirect action may explain the effects of tianeptine on DAergic neurons reachin~g the PFC. The fact that DOPAC levels, which reflect both DA release and DA synthesis (12, 20), may be increased by an indirect action of tianeptine, is consistent with recent results showing that tianeptine enhanced the firing rate of ventral tegmental area neurons and that the inhibitory effect of apomorphine was not modified by tianeptine (Dresse, submitted for publication). Since the main neurochemical effect of tianeptine at the cortical level is an increase in serotonin (5-HT) uptake (4, 22), the effects of tianeptine on DAer~ic neurons could be linked to its effects on 5-HT neurons. An inhibitory modulating action of 5-HT neurons on DAergic transmission has been shown at the striatal level(23). Since tianeptine does not modify 5-HT uptake in the mesencephalon (4) an interaction between 5HT neurons and DAergic terminals may be involved in the tianeptine action on DAergic metabolism in the PFC. However, an indirect action of tianeptine related to other neurotransmitters cannot be excluded. With respect to the ACC, taking into account the hypothesis of an indirect effect of tianeptine on DAergic neurons secondary to an action on the 5-HT transmission, the results obtained in the present study could mdicate that tianeptine is not as efficient on 5-HT transmission in this structure. In this context, it is important to notice that ACC and dorsal striatum receive 5-HT projections originatin~ from the same raphe nucleus (24). Thus the small non-significant chan~e on DAerglc metabolism observed in the ACC after acute treatment of tianeptine is consistent with results showing a lack of effect of tianeptine on dorsal striatalDAergic terminals as demonstrated on different parameters of the DAergic transmission (4). Furthermore it has been observed that tianeptine does not modify the firing rate of raphe dorsalis serotonergic neurons (25). However as indicated previously for the P F C an indirect action of tianeptine not related to 5-HT neurons could also be envisaged. In other respects, the similarity of tianeptine effects in the two parts of the striatum emphasizes the particular neurochemical profile of this new tricyclic coumpound. Thus, other tricyclic antidepressants such as amineptine, amitriptyline or imipramine with little effect on DAergic transmission in the dorsal strmtum have been reported to increase
1088
Tianeptlne Effects on DAerglc Metabolism
Vol. 47, No. 13, 1990
significantly DAergic transmission in the ACC (26, 27). In these eases the primary action of the antidepressants seem to be an inhibition of DA uptake. In our study, the effects of the chronic administration of tianeptine were investigated only in the PFC. Chronic treatment of tianeptine was followed by a significant increase of DAergic metabolism in the PFC at both doses used. However, this increase was less than that obtained after acute administration of the drug and a larger effect was observed with the lower dose. In addition, chronic administration of the higher dose had less effect than acute administration of the same dose. This phenomenon was even more obvious when chronic treatment was followed by a washout period. In this situation, the increase in DAergic metabolism was only observed with the lower dose. Thus, from results obtained in the two latter experiments, it appears that chronic administration of tianeptine altered the response of DAergic neurons innervating the PFC. In this context, it should be noticed that repeated treatment with neuroleptics do not modify the increase in DAergic metabolism in the PFC (28, 29). Thus the diminution in the increase in DAergic metabolism observed in the PFC after chronic administration of tianeptine may be related as the acute response to a primary non-DAergic action of the antidepressant. In conclusion, the results obtained in the present study show that tianeptine increases preferentially DAergic metabolism in the PFC. Previous data reported in the literature suggest that both acute and chronic effects of tianeptine on DAergic terminals may be related to a primary action of the antidepressant on nondopaminergic neurons. Inhibition of 5-HTtransmission by an enhancement of 5-HT uptake may be involved in the increase in DAergic metabolism and need to be further investigated. Thus this interregulation may be direct and efficient presynaptically at the DAerglc terminals level. However less direct mechanims or mechanisms involving other neurotransmitters may also be envisaged. In other respects tianeptine was reported to facilitate active wakefulness in the rat, social interactions in the monkey (3) and focalized attention in the cat (30). Behavioral experiments realized after selective lesions of DAergic terminals suggest that DA neurons exert a permissive action on the normal functionning of the structures they innervate (eg. 31, 32). Experimental and clinical studies dealing with ablation and stimulation of the PFC led to consider that this cortical re~ion play a crucial role in social behavior and attentive processes (33, 34). Thus the mcrease in DAergic activity in the PFC following acute and chronic administration of tianeptine may contribute to the particular therapeutic effect and the rapid onset of this new tricyclic antidepressant. ACKNOWLEDGMENTS The authors wish to thank Ms. M. Kharouby for the carbon fiber microelectrodes fabrication REFERENCES 1. R. DEFRANCE, C. MAREY and A. KAMOUN, Clin. Neuropharmacol. ll(suppl. .70 S 74 (1988). 2. H. LOO, R. MALKA, R. DEFRANCE, D. BARRUCAND, J.Y. BENARD, H.NIOX-RIVIERE, A. RAAB, A. SARDA, G. VACHONFRANCE and A. KAMOUN, Neuropsychobiology. 19 79-85 (1988). 3. J.C. POIGNANT, in Biological Psychiatry (C. Perris, G. Struwe and B. Jansson, eds) 4. ~P 573-578 Elsevier, Amsterdam, ~1981). MENNINI, E. MOCAER and S. GARATTINI, Naunyn-Schmiedeberg's Arch. Pharmacol. 336 478-482 (1987). 5. A. BJORKLUND and O. LINDVALL, in Handbook of Phvsioloav. The Nervous System IV (V.B. Mountcastle, F.E. Bloom and S.R. Geiger, eds) Aiiaerican Physiol. Society, 677-700 (1986). 6. L.W. SWANSON, Brain Res. Bull. 9 321-353 (1982).
Vol. 47, No. 13, 1990
Tianeptlne Effects on DAerglc Metabolism
1089
7. B.H.C. WESTERINK, B. LF-JEUNE, J. KORF and H.M. VAN PRAAG, Europ. J. Pharmacol. 42 179-190 (1977). 8. A. LOUILOT, M. BUDA, F. GONON, H. SIMON, M. LE MOAL and J.F. PUJO~ Neuroscience 14 775-782 (1985). 9. A. LOUILOT, F. GONON, M. BUDA, H. SIMON, M. LE MOAL and J.F. PUJOL, Brain Res. 335 253-263 (1985). 10. A. SERRANO, M. D'ANGIO and B. SCATTON, Brain Res. 378 191-196 (1986). 11. A. LOUILOT, M. LE MOAL and H. SIMON, Life Sci. 39 685-692 (1986). 12. A. LOUILOT, M. LE MOAL and H. SIMON, Life Sci. 40 2017-2024 (1987). 13. M. BUDA, F. GONON, R. CESPUGLIO, M. JOUVET and J.F. PUJOL, Eur. J. Pharmacol. 73 61-68 (1981). 14. F. GONON, M. BUDA, R. CESPUGLIO, M. JOUVET and J.F. PUJOL, Nature 136 902-904 (1980). 15. F. GONON, M. BUDA, R. CESPUGLIO, M. JOUVET and J.F. PUJOL., Brain Res. 223 69-80 (1981). 16. J.L. PONCHON, R. CESPUGLIO, F. GONON, M. JOUVET and J.F. PUJOL., Analyt. Chem. 51 1483-1486 (1979). 17. F. GONON, C. FOMBARLET, M. BUDA and J.F. P U J O L Analyt. Chem. 53 1386-1389 (1981). 18. T. SHARP, N.T. MAIDMENT, M.P. BRAZELL, T. ZETTERSTROM, U. UNGERSTEDT, G.W. BENNETT and C.A. MARSDEN, Neuroscience 12 12131221 (1984). 19. G. PAXINOS and G. WATSON, The rat brain in st¢re0taxic coordinates, Academic Press, New York, (1982). 20. B.H.C. WESTERINK, in The Neurobiolo~v of Dooamine (A. Horn, J. Korf and B.H.C. Westerink, eds), pp 255-291 Acaderrtiic Press~ London, (1979). 21. B.A. Mc MILLEN and C.C. Mc DONALD, Neuropharmacol. 22 273-278 22. G. KATO and A.F. WEITSCH, Clinical Neuropharmacol. 11 (suppl.2) $43 (1988). 23. M.G. DE SIMONI, R. GIGLIO, G. DAL TOSO, W. KOSTOWSKI and S. ALGERI, Europ. J. Pharmacol. 110 289-291 (1985). 24. H. W. M. STEINBUSCH and R. NIEUWENHUYS, in Chemical Neuroanatomv (P.C. Emson, ed), pp 131-207 Raven Press, New York, (1983). 25. A. DRESSE, J. SCUVEE-MOREAU. Clin. Neuropharmacol. 11 sunni 2. $51-$58 (1988). -26. M.G. DE SIMONI, G. DAL TOSO, S. ALGERY and F. PONZIO, Europ. J. Pharmacol. 123 433-439 (1986). 27. J. MAJ and K. WEDZONY, J. Pharm. Pharmacol. 37 362-366 (1985). 28. B. SCATFON, J. GLOWINSKI and L. JULOU, Brain Res. 109 184-189 (1976). 29. B. SCAq'TON, Europ. J. Pharmacol. 46 363-369 (1977). 30. P. DELAGRANGE, J.J. BOUYER, M.F. MONTARON, C. DURAND, E. MOCAER and A. ROUGEUL, Psychopharmacology ~ P 275 (1988). 31. A. LOUILOT, K. TAGHZOUTI, J.M. DEMINIERE, H.SIMON and M. LE MOAL, in Neurotransmitters Interactions in the Basal Ganglia (M. Sandler, C. Feuerstein, B. Scatton, eds) pp 193-204 Raven Press, New York, (1987). 32. A. LOUILOT, K. TAGHZOUTI, H. SIMON and M. LE MOAL, Brain Behav. Evol. 33 157-161 (1989). 33. B. KOL--B,Brain Res. Rev. 8 65-98 (1984). 34. J.M. FUSTER, The prefrontal cortex, Raven Press, New York, (1989).
Pergamon Press
DIFFERENCE IN THE EFFECTS OF THE ANTIDEPRESSANT TIANEPTINE ON DOPAMINERGIC METABOLISM IN THE PREFRONTAL CORTEX AND THE NUCLEUS ACCUMBENS OF THE RAT. A VOLTAMMETRIC STUDY A. LOUILOT, E. MOCAER*, H. SIMON and M. LE MOAL
Laboratoire de Psychobiologic des Comportements Adaptatifs - INSERM U.259 Universit6 de Bordeaux II- Domaine de Carreire, Rue Camille Saint-Sa~ns 33077 Bordeaux Cedex, France. *Institut de Recherches Internationales Servier (I.R.I.S.) - 27 rue du Pont - B.P. 126 - 92202 NeuiUy Cedex (Received in final form July 23, 1990)
SUMMARY The effects of the new tricyclic antidepressant tianeptine were investigated on dopaminergic (DAergic) metabohsm in the anteromedian prefrontal cortex and the nucleus accumbens of the rat. DAergic metabolism was assessed by the measurement of DOPAC, the main presynaptic metabolite of dopamine, using in vivo voltammetry in rats ventilated with halothane (0.50.75% in air). Acute treatment with tianeptine (10 mg/kg, 20 mg/kg) only increased significantly DOPAC levels in the anteromedian prefrontal cortex. After chron{c treatment with tianeptine (15 days, 2 times/day) the increases in DOPAC levels in this structure were altered and less pronounced with the 20 mg/kg dose. Previous studies led to suggest that both acute and chronic effects on DAergic terminals in the anteromedian prefrontal cortex may be involved in the therapeutic action of this new antidepressant. Tianeptine (S1574) is a new tricyclic antidepressant drug (1, 2) which has been shown to have activity in experimental tests used for the selection of classical antidepressants (3). The neurochemical effects of this compound appear to differ from those described for classical tricyclic antidepressants. A principle action is an enhancement of serotonin uptake in cortex and hippocampus after acute or chronic treatment with no effect on spontaneous serotonin release (4). Noradrenergic and dopaminergic transmissions, do not appear to be affected by tianeptine. Striatal uptake or release ofdopamine (DA) are not affected by acute or chronic treatment of this drug which also lacks affinity for DAbinding sites (4). However, it is difficult to ascertain the effect of tianeptine on DAergic neurons from results obtained at the striatal level alone since the DAergic mesencephalic neurons are grouped in different subunits depending on their location in the ventral mesencephalon a n d their projections areas (5, 6). The pharmacological reactivity of the DAergic mesencephalic subunits can be differentiatedat the terminal level in both the nucleus accumbens (ACC) and the anteromedian prefrontal cortex (PFC) (7, 8, 9, 10). In the present study, the effects of tianeptine on DAergic neurons were investigated by the measurement of the 3,4-dihydroxyphenylacetic acid (DOPAC), the main presynaptic DA metabolite in the ACC and the PFC. DOPAC levels were assessed by in vivo differential pulse voltammetry (DPV) using electrochemically pretreated carbon fibres electrodes which has been shown to be a reliable and powerful technique to study the kinetic of drugs effects on DAergic metabolism (8, 9, 10, 11, 12, 13, 14, 15). The effects of acute treatment of tianeptine on DAergic metabolism were studied in both the ACC and the PFC, and the effects of chronic treatment only in the PFC since acute treatment was found to be without significant effect in the ACC. 0024-3205/90 $3.00 + .00 Copyright (c) 1990 Pergamon Press plc
1084
Tianeptine Effects on DAergic Metabolism
Vol. 47, No. 13, 1990
METHODS
Electrochemistry A classical three-electrode system was used. DPV coupled with electrochemically pretreated carbon fiber microelectrodes (8 #m diameter, 500/~m length) was employed. Microelectrode preparation and electrochemical treatment procedures have been reported elsewhere (16, 17). The reference electrode was a AgCl-coated silver wire obtained from a Teflon-coated silver wire and prepared as previously described (18). The auxilliary electrode was a platinum wire. The commercially available voltammetric apparatus Biopulse (Tacussel, Villeurbanne, France) was set up with the following parameters for the detection of the DOPAC peak: scan rate, 10 mV/s; voltage range, -100 mV, + 150 mV; pulse modulation amplitude 50 mV; pulse modulation duration 48 ms; modulation period 200 ms. DOPAC peak was recorded every 2 rain at +50 mV/reference electrode. DOPAC peak height was calculated as previously described (15). Tianeptine and saline were injected at the end of the control period of 20 rain during which the signal varied less than 10%. For each experiment the mean of the 10 peaks measured during the control period was calculated and represented the 100% value of the DOPAC peak height. The responses of the carbon fiber microelectrodes were calibrated before and after the experiments in solutions containing different concentrations of DOPAC. Animals and surgery Male Sprague-Dawley rats (Iffa-Credo, L),on, France) weighing 360-380 g were used. Animals were housedat 22°C, and maintained on a 13-11 h light-dark cycle (light on at 7.00 A.M.). Animals were tracheotomized under halothane anaesthesia, intubated with a tracheal cannula, artificially ventilated with halothane (0.5-0.75% in air) after injection of d-tubocurarine (10 mg/kg i.p.), and placed in a stereotaxic frame with the incisor bar 3 mm below the interaural line. All stereotaxic pressure points and incision margins were locally anesthetized with lidocaine (xylocaine). Body temperature was monitored and maintained constant (37°C) by a thermostatically controlled blanket. The carbon fiber microelectrodes were implanted in the PFC or the ACC. The following stereotaxic coordinates were used: PFC: + 12.5 mm anterior to the interaural line (AP); 0.75 mm lateral to the midline (L); 4 mm below the cortical surface(V); ACC: + 10.6 mm (AP); 1,5 mm (L); 7 mm (V) according to the atlas of Paxinos et Watson (19). In some cases, the recording sites were visualized as previously described (6). DruGs v
Tianeptine (S1574, Servier, France) and the solvant (NaC1 0.9%) were injected i.p. in a volume of 1 ml/kg. For chronic treatment, tianeptine (10 mg/kg and 20 mg/kg) and saline were administered twice per day during 15 days. For chronic treatment followed by a wash-out the procedure was the same as for chronic treated animals excepted that treatment was withdrawn 72 h before the experiment. Data analvsis and statisti¢~ Results were expressed as percentages (mean _+ S.E.M.). For each structure, results obtained after acute treatment were submitted to "a two-factor analysis of variance (ANOVA) with doses (tianeptine 10 mg/kg, 20 mg/k~, and NaC1 0.9%)being the independent factor, and time the repeated measure. In relation to the significance of this analysis, effects of chronic treatment of tianeptine and chronic treatment+wash-out on DAergic neurons were only investigated in the PFC. Changes in DOPAC levels in this structure after chronic treatment and chronic treatment +wash-out were submitted to the ANOVA.
Vol. 47, No. 13, 1990
Tianeptlne Effects on DAergic Metabolism
1085
Administration of tianeptine (10 mg/kg, 20 mg/kg, acute treatment) was followed by a small increase in the DOPAC peak recorded in the ACC (Fig. 1). The maximal increases (respective to the corresponding control values) were about 15% for the 10 mg/kg dose and about 20% for the 20 mg/kg dose, and were reached respectively 20 min and 90 rain after the injection. These changes were not statistically significant F(2, 19) = 2.84 P = 0.082 N.S.
NUCLEUS ACCUMBENS ACUTE TREATMENT
NaCI 0.9 % n=7 0--.o TIANEPTINE (lOmg/kg) n=8 II--II TIANEPTINE ( 2 0 m g / k g ) n=7
175
150
<~ 125
~<
lOO
t
75 1"
I
-2o
I
-lO
I
o
I
lo
I
20
I
30
I
40
I
so
I
eo
I
ro
I
8o
t
9o
TIME (MIN)
FIG.1. Time-courses of the DOPAC peak height measured from DP voltammograms recorded from the nucleus accumbens of rats treated with tianeptine (10 mg/kg, 20 mg/kg) or saline injected intraperitoneally. Animals were in acute preparation vendiated with halothane (0.5%-0.75% m air). For each experiment the results were expressed as the percentage (mean _+ SEM) of the mean pre-injection value calculated by averaging the 10 absolute values of the peak heights obtained during the control period (20 rain pre-injection period). The DOPAC peak was recorded every 2 rain between -100 mV and + 150 mV vs the reference electrode. The arrow indicates the time of the injection. The injection of tianeptine (10 mg/kg, 20 mg/kg, acute treatment) was followed by an increase in the DOPAC peak recorded in the PFC (Fig. 2A) with a greater increase after administration of the 20 mg/kg dose. The maximal values reached were about 30% and 45% (compared to the respective control values) for the 10 mg/kg and 20 mg/kg doses respectively..The dose-response was statistically significant F(2, 12) = 6.68 P <
1086
Tianeptine Effects on DAergic Metabolism
Vol. 47, No. 13, 1990
0.01. Comparison of the different groups gave the following results: NaCI 0.9% / 10 mg/kg, F(1, 8) = 4.23 P = 0.072 N.S.; NaC1 0.9% / 20 mg/kg, F(1, 8) = 35.4 P < 0.001; 10 mg/kg / 20 mg/kg, F(1, 8) = 1.22 P = 0.3 N.S. After chronic treatment the administration of tianeptine (10 mg/kg, 20 mg/kg) was followed by an increase of the DOPAC peak recorded in the P F C (Fig. 2B). The maximal values reached after administration of the 10 mg/kg and 20 mg/kg doses were about 30% and 20% respectively (compared to control values). The dose-response on chronically treated animals was statistically significant F(2, 12) = 4.55 P < 0.05. Comparison of the different groups gave the following results: NaCI 0.9% / 10 mg/kg, F(1, 8) = 8 P < 0.05; NaC1 0 . 9 % / 2 0 mg/kg, F(I, 8) = 8.25 P < 0.05; 10 mg/kg / 20 mg/kg, F(1, 8) = 0.63 P = 0.76 N.S. After chronic treatment followed by a wash-out (72 h), the DOPACpeak in the PFC was only increased after administration of the 10 mg/kg dose (Fi~g. 2C). The maximal increase was about 20% (versus control levels). The dose-response m chronically treated animals submitted to a wash-out was statistically significant F(2, 12) = 4.15 P < 0.05; NaC1 0.9% / 10 mg/kg, F(1, 8) = 7.07 P < 0.05; NaC1 0.9% / 20 mg/kg, F(1, 8) = 0.02 P = 1 N.S.; 10 mg/kg / 20 mg/kg, F(1, 8) = 5.16 P < 0.05. A
B
PREF~(T~. ~ ACUT~ TRF.ATMf34T
F~IF.F'RO~ OOm'F.X TIRF.ATMINT
e.° o-o TIA(NI~OTIN~ (lOmglk0)nm° TIANEPTllq£ (20ntG/kg ) rim° NII¢I o.e I
NJCI 0.0 Sl, n - S O.--O l IA'~IEP+'rIIE (I0 mg]kll)n - 5 TIA/VlPTINI ( ~ m l l / k g ) n . 5 H
t
|I
t o-~,
-"
6
~
TIME 1~1)
~
•
~o
t~Mli
(MIN)
~)
Jo ~
~
¢ &
TREATMENT*WAIIH CUT 17[
*:~-,o
,
TIAN~PTINI[(lOmilJk0) ~ $ TIANEpT~ ~l"lq~/kg) ~ S
,<, ~ ,,o ~, ,t,, ,,o FIG.2.
Time-courses of the DOPAC peak height measured from DP voltammograms recorded from the prefrontal cortex of rats treated with tianeptine (10 mg/kg, 20 mg/kg) or saline. A) Effect of acute treatment. B) Effect of chronic treatment (15 days, 2 injections/day). C) Effect of chronic treatment (15 days, 2 injections/ day) followed by a wash-out (72h). For comments, see legend of Fig.1.
Vol. 47, No. 13, 1990
Tlaneptine Effects on DAerglc Metabolism
1087
DISCUSSION
The aim of the present study was to investigate the effect of the new tricyclic antidepressant tianeptine on DAergic metabolism at the level of the PFC and ACC using. DPV. The results obtained with acute treatment showed that this drug only had a sigmficant effect on DAergic terminals in the PFC whereas in the ACC stanstically non-significant increases in DOPAC levels were obtained. In PFC, DOPAC levels were significantly increased for the two doses used with a greater effect for the higher dose (20mg/kg). For both structures DOPAC levels raised earlier at the lower dose (10 mg/kg). I n this context, it is interesting to notice that tianeptine induced different psychopharmacological responses following administration of the 10 mg/kg and the 20 mg/kg doses (3}.. The differential neurochemical effects of tianeptine depending on doses may contribute to the distinct behavioral expressions. The difference between the results obtained with the acute treatment of tianeptine in the PFC and the ACC could have several interpretations. It might be the result of a different distribution of the antidepressant in the two brain areas and/or to a different sensitivity of the two DAergic projections to the drug. Another possibility is that tianeptine primarily acts on non-DAergic pathways that modulate the two DAergic projections differently. A primary non-DAergic action of tianeptine is consistent with the delayed increases in DOPAC levels observed in both stuctures after administration of the higher dose. With respect to the results obtained in the PFC after acute administration of tianeptine, the amplitude of the increase in DOPAC levels was comparable to that obtained with neuroleptics (10), whose effects on DAergic metabolism is assumed to be due to DA receptor blockade (20, 21). However, it has recently been shown at the ACC level that DAergic metabolism is markedly enhanced by buspirone (11), an anxiolytic drug which does not act directly on DAergic neurons (12). Thus, a similar, but different indirect action may explain the effects of tianeptine on DAergic neurons reachin~g the PFC. The fact that DOPAC levels, which reflect both DA release and DA synthesis (12, 20), may be increased by an indirect action of tianeptine, is consistent with recent results showing that tianeptine enhanced the firing rate of ventral tegmental area neurons and that the inhibitory effect of apomorphine was not modified by tianeptine (Dresse, submitted for publication). Since the main neurochemical effect of tianeptine at the cortical level is an increase in serotonin (5-HT) uptake (4, 22), the effects of tianeptine on DAer~ic neurons could be linked to its effects on 5-HT neurons. An inhibitory modulating action of 5-HT neurons on DAergic transmission has been shown at the striatal level(23). Since tianeptine does not modify 5-HT uptake in the mesencephalon (4) an interaction between 5HT neurons and DAergic terminals may be involved in the tianeptine action on DAergic metabolism in the PFC. However, an indirect action of tianeptine related to other neurotransmitters cannot be excluded. With respect to the ACC, taking into account the hypothesis of an indirect effect of tianeptine on DAergic neurons secondary to an action on the 5-HT transmission, the results obtained in the present study could mdicate that tianeptine is not as efficient on 5-HT transmission in this structure. In this context, it is important to notice that ACC and dorsal striatum receive 5-HT projections originatin~ from the same raphe nucleus (24). Thus the small non-significant chan~e on DAerglc metabolism observed in the ACC after acute treatment of tianeptine is consistent with results showing a lack of effect of tianeptine on dorsal striatalDAergic terminals as demonstrated on different parameters of the DAergic transmission (4). Furthermore it has been observed that tianeptine does not modify the firing rate of raphe dorsalis serotonergic neurons (25). However as indicated previously for the P F C an indirect action of tianeptine not related to 5-HT neurons could also be envisaged. In other respects, the similarity of tianeptine effects in the two parts of the striatum emphasizes the particular neurochemical profile of this new tricyclic coumpound. Thus, other tricyclic antidepressants such as amineptine, amitriptyline or imipramine with little effect on DAergic transmission in the dorsal strmtum have been reported to increase
1088
Tianeptlne Effects on DAerglc Metabolism
Vol. 47, No. 13, 1990
significantly DAergic transmission in the ACC (26, 27). In these eases the primary action of the antidepressants seem to be an inhibition of DA uptake. In our study, the effects of the chronic administration of tianeptine were investigated only in the PFC. Chronic treatment of tianeptine was followed by a significant increase of DAergic metabolism in the PFC at both doses used. However, this increase was less than that obtained after acute administration of the drug and a larger effect was observed with the lower dose. In addition, chronic administration of the higher dose had less effect than acute administration of the same dose. This phenomenon was even more obvious when chronic treatment was followed by a washout period. In this situation, the increase in DAergic metabolism was only observed with the lower dose. Thus, from results obtained in the two latter experiments, it appears that chronic administration of tianeptine altered the response of DAergic neurons innervating the PFC. In this context, it should be noticed that repeated treatment with neuroleptics do not modify the increase in DAergic metabolism in the PFC (28, 29). Thus the diminution in the increase in DAergic metabolism observed in the PFC after chronic administration of tianeptine may be related as the acute response to a primary non-DAergic action of the antidepressant. In conclusion, the results obtained in the present study show that tianeptine increases preferentially DAergic metabolism in the PFC. Previous data reported in the literature suggest that both acute and chronic effects of tianeptine on DAergic terminals may be related to a primary action of the antidepressant on nondopaminergic neurons. Inhibition of 5-HTtransmission by an enhancement of 5-HT uptake may be involved in the increase in DAergic metabolism and need to be further investigated. Thus this interregulation may be direct and efficient presynaptically at the DAerglc terminals level. However less direct mechanims or mechanisms involving other neurotransmitters may also be envisaged. In other respects tianeptine was reported to facilitate active wakefulness in the rat, social interactions in the monkey (3) and focalized attention in the cat (30). Behavioral experiments realized after selective lesions of DAergic terminals suggest that DA neurons exert a permissive action on the normal functionning of the structures they innervate (eg. 31, 32). Experimental and clinical studies dealing with ablation and stimulation of the PFC led to consider that this cortical re~ion play a crucial role in social behavior and attentive processes (33, 34). Thus the mcrease in DAergic activity in the PFC following acute and chronic administration of tianeptine may contribute to the particular therapeutic effect and the rapid onset of this new tricyclic antidepressant. ACKNOWLEDGMENTS The authors wish to thank Ms. M. Kharouby for the carbon fiber microelectrodes fabrication REFERENCES 1. R. DEFRANCE, C. MAREY and A. KAMOUN, Clin. Neuropharmacol. ll(suppl. .70 S 74 (1988). 2. H. LOO, R. MALKA, R. DEFRANCE, D. BARRUCAND, J.Y. BENARD, H.NIOX-RIVIERE, A. RAAB, A. SARDA, G. VACHONFRANCE and A. KAMOUN, Neuropsychobiology. 19 79-85 (1988). 3. J.C. POIGNANT, in Biological Psychiatry (C. Perris, G. Struwe and B. Jansson, eds) 4. ~P 573-578 Elsevier, Amsterdam, ~1981). MENNINI, E. MOCAER and S. GARATTINI, Naunyn-Schmiedeberg's Arch. Pharmacol. 336 478-482 (1987). 5. A. BJORKLUND and O. LINDVALL, in Handbook of Phvsioloav. The Nervous System IV (V.B. Mountcastle, F.E. Bloom and S.R. Geiger, eds) Aiiaerican Physiol. Society, 677-700 (1986). 6. L.W. SWANSON, Brain Res. Bull. 9 321-353 (1982).
Vol. 47, No. 13, 1990
Tianeptlne Effects on DAerglc Metabolism
1089
7. B.H.C. WESTERINK, B. LF-JEUNE, J. KORF and H.M. VAN PRAAG, Europ. J. Pharmacol. 42 179-190 (1977). 8. A. LOUILOT, M. BUDA, F. GONON, H. SIMON, M. LE MOAL and J.F. PUJO~ Neuroscience 14 775-782 (1985). 9. A. LOUILOT, F. GONON, M. BUDA, H. SIMON, M. LE MOAL and J.F. PUJOL, Brain Res. 335 253-263 (1985). 10. A. SERRANO, M. D'ANGIO and B. SCATTON, Brain Res. 378 191-196 (1986). 11. A. LOUILOT, M. LE MOAL and H. SIMON, Life Sci. 39 685-692 (1986). 12. A. LOUILOT, M. LE MOAL and H. SIMON, Life Sci. 40 2017-2024 (1987). 13. M. BUDA, F. GONON, R. CESPUGLIO, M. JOUVET and J.F. PUJOL, Eur. J. Pharmacol. 73 61-68 (1981). 14. F. GONON, M. BUDA, R. CESPUGLIO, M. JOUVET and J.F. PUJOL, Nature 136 902-904 (1980). 15. F. GONON, M. BUDA, R. CESPUGLIO, M. JOUVET and J.F. PUJOL., Brain Res. 223 69-80 (1981). 16. J.L. PONCHON, R. CESPUGLIO, F. GONON, M. JOUVET and J.F. PUJOL., Analyt. Chem. 51 1483-1486 (1979). 17. F. GONON, C. FOMBARLET, M. BUDA and J.F. P U J O L Analyt. Chem. 53 1386-1389 (1981). 18. T. SHARP, N.T. MAIDMENT, M.P. BRAZELL, T. ZETTERSTROM, U. UNGERSTEDT, G.W. BENNETT and C.A. MARSDEN, Neuroscience 12 12131221 (1984). 19. G. PAXINOS and G. WATSON, The rat brain in st¢re0taxic coordinates, Academic Press, New York, (1982). 20. B.H.C. WESTERINK, in The Neurobiolo~v of Dooamine (A. Horn, J. Korf and B.H.C. Westerink, eds), pp 255-291 Acaderrtiic Press~ London, (1979). 21. B.A. Mc MILLEN and C.C. Mc DONALD, Neuropharmacol. 22 273-278 22. G. KATO and A.F. WEITSCH, Clinical Neuropharmacol. 11 (suppl.2) $43 (1988). 23. M.G. DE SIMONI, R. GIGLIO, G. DAL TOSO, W. KOSTOWSKI and S. ALGERI, Europ. J. Pharmacol. 110 289-291 (1985). 24. H. W. M. STEINBUSCH and R. NIEUWENHUYS, in Chemical Neuroanatomv (P.C. Emson, ed), pp 131-207 Raven Press, New York, (1983). 25. A. DRESSE, J. SCUVEE-MOREAU. Clin. Neuropharmacol. 11 sunni 2. $51-$58 (1988). -26. M.G. DE SIMONI, G. DAL TOSO, S. ALGERY and F. PONZIO, Europ. J. Pharmacol. 123 433-439 (1986). 27. J. MAJ and K. WEDZONY, J. Pharm. Pharmacol. 37 362-366 (1985). 28. B. SCATFON, J. GLOWINSKI and L. JULOU, Brain Res. 109 184-189 (1976). 29. B. SCAq'TON, Europ. J. Pharmacol. 46 363-369 (1977). 30. P. DELAGRANGE, J.J. BOUYER, M.F. MONTARON, C. DURAND, E. MOCAER and A. ROUGEUL, Psychopharmacology ~ P 275 (1988). 31. A. LOUILOT, K. TAGHZOUTI, J.M. DEMINIERE, H.SIMON and M. LE MOAL, in Neurotransmitters Interactions in the Basal Ganglia (M. Sandler, C. Feuerstein, B. Scatton, eds) pp 193-204 Raven Press, New York, (1987). 32. A. LOUILOT, K. TAGHZOUTI, H. SIMON and M. LE MOAL, Brain Behav. Evol. 33 157-161 (1989). 33. B. KOL--B,Brain Res. Rev. 8 65-98 (1984). 34. J.M. FUSTER, The prefrontal cortex, Raven Press, New York, (1989).