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Long-term effects of 5,7-dihydroxytryptamine on brain monoamines
Pergamon Press
Life Sciences Vol. 14, pp . 909-919, 1974. Printed in Great Britain
LONG-TERM EFFECTS OF 5,7-DIHYDROXYTRYPTAMINE ON BRAIN MONOAMINES Jacob H . Jacoby, Loy D . Lytle, and Mark F . Nelson Department of Nutrition and Food Science Massachusetts Institute of Technology Cambridge, Massachusetts 02139 (Received 19 December 1973; in final form 21 January 1974) Sommar 5,7-dihydroxytryptamine (75 and 150 Ug) was injected intraventricularly to adult male rats ; animals were killed at various times after the injection and brains were examined for changes in the concentration of tryptophan, serotonin, 5-hydroxyindole acetic acid, norepinephrine and dopamine . Brain 5-hydroxyindoleamines were markedly depleted at all time periods examined, even after the administration of a tryptophan load (50 mg/kg) . A small but significant decline in brain norepinephrine but not dopamine was also noted after the administration of the dihydroxytryptamine . Two dihydroxylated indoleamines, 5,6-dihydroxytryptamine (5,6-DHT) and 5,7-dihydroxytryptamine (5,7-DHT) have been shown to produce a relatively specific depletion of brain serotonin (5HT) after intraventricular
(iv)
injection (1, 2) .
A single 75 ug dose
of 5,6-DHT reduces 5HT concentrations in several brain regions to 40-608 of control values for 10-30 days
(1) .
Tryptophan hydroxyl-
ase activity is also markedly reduced during this time period (3) . Injection of 5,7-DHT decreases brain tryptophan hydroxylase activity (4) and appears to produce long lasting reductions in the fluorescence intensity of serotonin-containing brain neurons (2) . Low doses of 5,7-DHT reduce the fluorescence intensity of catecholamine neurons for 24-48 hrj higher doses exert a more pronounced and longer lasting effect (2) . This report shows that following the iv injection of 5,7-DHT, there are persistent, dose-related reductions in the whole brain
Vol . 14, No . 5
5, 7-DHT end Brain Monoamiaes
910
concentrations of 5HT and 5-hydroxyindole acetic acid (SHIAA) . This treatment also causes a small, long-lasting reduction in brain norepinephrine (NE), but not dopamine (DA) . Materials and Methods Male Sprague-Dawley albino rats
(150-200 g, Charles River
Laboratories, Wilmington, Mass .) were exposed to light (Vita-Lite, Duro-Test Mfg . Co ., North Bergen, N .J .) from 9 AM to 9 PM daily and fed ad Zibitum with Biq Red Rat Chow and water .
Animals were
injected unilaterally into the left lateral ventricle under light ether anesthesia with one dose of 5,7-DHT (provided by Dr . A . Manian, Psychopharmacology unit, NIMI3, Bethesda, Md .) uq free base, in a volume of 15 ul)
1-ascorbic acid in 0 .98 saline) . or 60 days after the injection .
(75 or 150
or the vehicle (1 mg/ml
Animals were killed 1, 10, 30, Hlood from the cervical wound was
collected in heparinized tubes and centrifuged ; plasma was frozen and later assayed for tryptophan (5) . bissected midsagitally, and frozen .
Brains were quickly removed, One half of each brain,
alternating from left to right for each successive sample
(to
insure an equal representation of both sides), was homogenized in 0 .4 N HClOy and an aliquot of the homogenate was assayed for the concentration of brain tryptophan (5) .
The remaining portion of
the homogenate was centrifuged and the 35,000 adsorbed onto alumina colums (6) .
X
g supernatant was
DA in the acetic acid eluate
was estimated fluorimetrically by the method of Carlsaon and Waldeck (7) ; NE was assayed by the method of Von Euler and Lishajko (B) .
Overall recoveries for these compounds were approximately 808 ;
all data were corrected for these recoveries .
The other .half of
the brain was assayed for 5HT and 5HIAA by the method of Curzon and Green (9) .
No difference in any parameters measured were
5, 7-DHT end &~in Honoemines
Vol. 14, No . 5
noted for left vs right brain halves . in a second experiment, animals were pretreated with 150 uq of 5,7-DHT (iv) or vehicle .
Ten days later, the animals were
fasted overnight (18 hr), then injected with either 50 mg/kg 1-tryptophan (40 mg/ml of 1-tryptophan in warm 0 .98 saline, pH 9) or the vehicle .
Animals were killed one hour after the injection
and brain andlasma tryptophan, and brain SHT, SHIAA, NE and DA were determined as described . Results Brain levels of SHT, SHIAA, NE and DA did not differ significantly in the vehicle-injected control groups over the 60 day time course of the experiment (Table 1) .
By contrast, both the 75 uq
and 150 yg dose of 5,7-DfiT significantly reduced brain levels of 5HT and SHIAA at all time periods examined .
Maximal decreases in
the concentrations of these amines were attained by 10 and 30 days after injection of either dose (Fig . 1) ; significant increases in the levels of these indoleaminea were found to occur after the 30day time point.
In contrast to the large decreases in brain 5HT
and SHIAA, relatively small but significant declines in brain levels of NE were found after all time periods following the injection of the drug (Fig . 2) .
Concentrations of brain DA, and plasma
and brain tryptophan, were unaffected by either dose (Table 1) . The administration of 150 ug 5,7-DHT was followed, in approximately 508 of the animals, by severe tonic-clonic convulsions . The subsequent survival of convulsive animals was facilitated by brief ether anesthesia .
These observations suggest that the
150 Uq dose of 5,7-DHT is close to the toxic limitations of this compound .
Following administration of either dose, acute hypo-
thermia was detected for as long as 24 hr following injection
912
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5, 7-DHT aad Hcaia Ilonoamiaes
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914
Vol. 14, No . 5
5, 7-DHT and Brain Monoamines
In addition, the animals were hyper-
(unpublished observation) .
reactive to external handling .
A marked, nondose-related reduc-
tion in the occurrence of postdecapitation convulsions was also observed . In the second experiment, rats pretreated with 150 yg of 28
VEHICLE
130 ftq 5,7-DHT
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TREATMENT FIG. 3
Animals (n ~ 8 per group) were given a single intraventricular injection of 5,7-DHT (150 ug free base) or vehicle . Ten days later, animals were fasted overnight and then injected with either 1-tryptophan (50 mg/kg) or vehicle intraperitoneally one hour prior to decapitation . Brain and plasma tryptophan and brain 5HT and SHIAA were determined (all values are mean t 5 .8 .) .
915
5, 7-DHT end Brain èlonoemines
Vol . 14, No . 5
5,7-DHT followed by the injection of tryptophan 10 days later, showed decreases in brain 5HT and SHIAA similar to those described in the first experiment (Fig . 3) .
Again, brain and plasma levels
of tryptophan were unchanged by the 5,7-DHT .
The intraperitoneal
administration of tryptophan significantly increased the plasma and brain concentrations of this compound one hour after injection in a similar magnitude in both the vehicle and the 5,7-DHT pretreated groups .
The tryptophan injections significantly elevated
the concentrations of both brain 5HT and 5HIAA in the vehicle pretreated group .
However, only 5HT, and not 5HIAA, was increased in
the 5,7-DHT pretreated group, although the percent increase in 5HT with respect to each control group was approximately the same in both groups
(i .e ., 278 increase in the vehicle pretreated group
and 578 in the 5,7-DHT pretreated group)
(Fig . 3) .
Even after
injection of the tryptophan load to 5,7-DHT pretreated animals, the total level of 5-hydroxyindoles remained greatly reduced when compared to saline pretreated animals not receiving tryptophan (0 .44 ug/g in 5,7-DHT pretreated, tryptophan injected animals va 1 .11 ug/g in saline pretreated, vehicle injected controls) . Discussion These data demonstrate that 5,7-DHT is a potent depleting agent capable of inducing severe and long lasting reductions in brain 5HT and SHIAA without affecting brain tryptophan levels . The decrease in brain 5HT is accompanied by a marked reduction in the accumslation of 5-hydroxyindoles following the exogenous administration of tryptophan .
Concomitant with this depletion in
indoleamines is a less marked depletion of brain NE but not DA . 5,7-DHT appears to affect 5HT containing neurons of the brain in a manner very similar and analogous to the effects of 6-hydroxy-
Vol. 14, No . 5
5, 7-DHT end Brain Monoamines
916
dopamine on brain catecholamine containing neurons (10-13) . Following injection of this compound (75 ug), brain 5HT is reduced to 40$ of control values at 10 to 30 days postinjection .
This
reduction is comparable to the 40-60$ depletion of 5HT noted in several brain areas after injection of 5,6-DHT (1) .
A higher dose
of 5,7-DHT (150 ug) reduces brain 5HT and SHIAA to even lower concentratipns (30$ of control values) without further affecting brain NE and DA concentrations .
This latter dose is beyond the tolerable
dose of 5,6-DHT (1) ; hence, 5,7-DHT may be used to attain even greater reductions in brain SHT and SHIAA than can be produced with the 5,6-DHT congener . In contrast to 5,6-DHT, 5,7-D1iT appears to produce small, but persistent, nondoae-related effects on brain NE .
Brain DA, how-
ever, appears to be relatively unaffected by doses of 5,7-DHT that decrease the levels of brain NE .
In contrast,
5,6-DHT produces
relatively small, transient depletions of both NE and DA in brain (1) . 5,7-DHT does not appear to decrease the level of brain 5-hydroxyindoles by altering concentrations of brain or plasma tryptophan,
Even at doses that decrease the level of NE, plasma
and brain levels of this amino acid were unaltered .
Although
under normal conditions the concentration of tryptophan in brain may physiologically regulate the levels of brain 5HT and SHIAA, (14) the mechanism by which 5,7-DHT alters brain 5HT appears to be different. Recent studies utilizing histochemical fluorescence nicrographs have demonstrated that both 5,6- and 5,7-DI3T produce extensive damage to the axonal and terminal apparatus of 5HT-containinq neurone (1,2,15) and van decrease the capacity of these neurons to take up this amine (16) .
917
5, 7-DHT end Brain Monoemiaes
Vol. 14, No . 5 Baumgarten et al .
(4) reported that the injection of 5,7-DHT
drastically reduces the tryptophan hydroxylase activity in selected brain regions that contain relatively large innervations from 5HT containing neurons .
It is unclear at present whether the reduc-
tions in tryptophan hydroxylase activity reflect less concentrations of this enzyme per surviving neuron or whether the dihydroxyindoleamines directly affect the overall enzyme activity .
Our
findings show that the peroent increase in 5HT is similar in both 5,7-DHT and saline pretreated animals given tryptophan, while the total concentration of 5-hydroxyindoleamines in 5,7-DHT pretreated animals is markedly reduced .
These data suggest that 5,7-DHT
apparently reduces the number of intact neurons, but that these surviving neurons may be able to function normally . Brain levels of 5HT and SHIAA show evidence of recovery 30 to 60 days following 5,7-DHT injection .
Recent findings suggest that
many brain neurons containing monoamines may regenerate and re sprout following either surgically (17) or chemically (18) induced lesions ; hence, the increase in 5HT and SHIAA levels noted in this study between 30 and 60 days following injection may reflect a regrowth or resprouting of 5HT containing neurons .
Alternatively,
the small increase in brain 5HT levels may indicate that the synthetic capacity of surviving 5HT containing neurons may increase following injection, or that a further loss in the ability to metabolize 5HT has occurred (i .e ., MAO activity may have been impaired) .
However, since the recovery pattern of SHIAA between
the 30th and 60th postinjection day parallels that of 5HT, this latter possibility seems unlikely . In contrast to adults injected with 5,7-DST, neonates administered doses up to 50 ug on the day of birth show little or no recovery, and 5HT levels, which ai~e drastically reduced, remain
Vol . 14, No . 5
5, 7~DHT aad Brain èlonoemiaea
918
essentially unchanged until at least 60 days of age (unpublished observation) . 5,7-DHT appears to be able to induce a more severe depletion of brain 5HT and 5HIAA than 5,6-DHT, but also induces a longer lasting depletion of brain NE . Acknowledgments These studies were supported by grants IF AM-14228 and NS-10459 .
Dr . Jacoby holds a USPHS Postdoctoral Fellowship
(1-702NS54909-1) .
The authors wish to thank Dr . Richard J .
Wurtman for his helpful comments and Mr . Ken Cottman for technical assistance . References 1.
H.G . BAUMGARTEN, A. IiJORRLUND, L . LACHENMAYER, A. NOBIN and U. STENEVI, Acta Physiol . Scand . , Supp . 373, 1-16
2.
(1971) .
H.G . BAUMGARTEN and L. LACHENMAYER, Z . Zellforsch , 135,
399-
414 (1972) . 3.
S .J . VICTOR, H .G . BAUMGARTEN and W. LOVENBERG, Fed . Proc . , 32, 564 (1973) .
4.
H.G . BAUMGARTEN, S .J . VICTOR and W. LOVENBERG, J. Neurochem . , 21, 251-253 (1973) .
5.
W.D . DENCKLA and H .K . DEWEY, J . Lab . Clin . Med . , 69, 160-169 (1967) .
6.
A.H . ANTON and D .F . SAYRE, J . Pharmacol . Exp . Ther . , 138, 360375 (1962) .
7.
A. CARLSSON and B . WALDECK, Acta Physiol . Scand . , 44, 293-298 (1958) .
8.
U.S . VON EDLER and F . LISHAJRO, Acta Physiol . Scand . , 51, 348 356 (1961) .
Vol. 14, No . 5
9.
5,7-DHT end Brain Noeoeminea
919
G . CURZON and A .R . GREEN, Br . J. Pharmacol ., 39, 653-655 (1970) .
10 .
N .J . URETSKY and L.L . IVERSEN, Nature
(London) , 221, 557-559
(1969) . 11 .
W.P . BURKARD, M. JALFRE and J. BLUM, Experientia (Basel) , 25, 1295-1296 (1969) .
12 .
G. HARTHOLINI, J .G . RICHARDS and A. PLETSCHER, Experientia (Basel) ,
13 .
26, 142-144 (1970) .
G.R . BREESE and T.D . TRAYLOR, J . Pharmacol . Exp . Ther . , 174, 413-420 (1970) .
14 .
J .D . FERNSTROM and R.J . WURTMAN, Science , 178, 414-416 (1972) .
15 .
H.G . BAUMGARTEN, L . LACHENMAYER and H .G . SCBIASSBERGER, Z . Zellforach, 125, 553-569 (1972) .
16 .
A.S . HORN, H .G . BAUMGARTEN and H .G . SCHLOSSBERGSR, J . Neurochen, 21, 233-236 (1973) .
17 .
R. RATZMAN, A. BJORRLUND, C . OWMAN, U . STENEVI and R .A . WEST, Brain Res . , 25, 579-596 (1971) .
18 .
A. HJORRLUND, A . NOBIN and U. STENEVI, Brain Res . , 50, 214220 (1973) .
Life Sciences Vol. 14, pp . 909-919, 1974. Printed in Great Britain
LONG-TERM EFFECTS OF 5,7-DIHYDROXYTRYPTAMINE ON BRAIN MONOAMINES Jacob H . Jacoby, Loy D . Lytle, and Mark F . Nelson Department of Nutrition and Food Science Massachusetts Institute of Technology Cambridge, Massachusetts 02139 (Received 19 December 1973; in final form 21 January 1974) Sommar 5,7-dihydroxytryptamine (75 and 150 Ug) was injected intraventricularly to adult male rats ; animals were killed at various times after the injection and brains were examined for changes in the concentration of tryptophan, serotonin, 5-hydroxyindole acetic acid, norepinephrine and dopamine . Brain 5-hydroxyindoleamines were markedly depleted at all time periods examined, even after the administration of a tryptophan load (50 mg/kg) . A small but significant decline in brain norepinephrine but not dopamine was also noted after the administration of the dihydroxytryptamine . Two dihydroxylated indoleamines, 5,6-dihydroxytryptamine (5,6-DHT) and 5,7-dihydroxytryptamine (5,7-DHT) have been shown to produce a relatively specific depletion of brain serotonin (5HT) after intraventricular
(iv)
injection (1, 2) .
A single 75 ug dose
of 5,6-DHT reduces 5HT concentrations in several brain regions to 40-608 of control values for 10-30 days
(1) .
Tryptophan hydroxyl-
ase activity is also markedly reduced during this time period (3) . Injection of 5,7-DHT decreases brain tryptophan hydroxylase activity (4) and appears to produce long lasting reductions in the fluorescence intensity of serotonin-containing brain neurons (2) . Low doses of 5,7-DHT reduce the fluorescence intensity of catecholamine neurons for 24-48 hrj higher doses exert a more pronounced and longer lasting effect (2) . This report shows that following the iv injection of 5,7-DHT, there are persistent, dose-related reductions in the whole brain
Vol . 14, No . 5
5, 7-DHT end Brain Monoamiaes
910
concentrations of 5HT and 5-hydroxyindole acetic acid (SHIAA) . This treatment also causes a small, long-lasting reduction in brain norepinephrine (NE), but not dopamine (DA) . Materials and Methods Male Sprague-Dawley albino rats
(150-200 g, Charles River
Laboratories, Wilmington, Mass .) were exposed to light (Vita-Lite, Duro-Test Mfg . Co ., North Bergen, N .J .) from 9 AM to 9 PM daily and fed ad Zibitum with Biq Red Rat Chow and water .
Animals were
injected unilaterally into the left lateral ventricle under light ether anesthesia with one dose of 5,7-DHT (provided by Dr . A . Manian, Psychopharmacology unit, NIMI3, Bethesda, Md .) uq free base, in a volume of 15 ul)
1-ascorbic acid in 0 .98 saline) . or 60 days after the injection .
(75 or 150
or the vehicle (1 mg/ml
Animals were killed 1, 10, 30, Hlood from the cervical wound was
collected in heparinized tubes and centrifuged ; plasma was frozen and later assayed for tryptophan (5) . bissected midsagitally, and frozen .
Brains were quickly removed, One half of each brain,
alternating from left to right for each successive sample
(to
insure an equal representation of both sides), was homogenized in 0 .4 N HClOy and an aliquot of the homogenate was assayed for the concentration of brain tryptophan (5) .
The remaining portion of
the homogenate was centrifuged and the 35,000 adsorbed onto alumina colums (6) .
X
g supernatant was
DA in the acetic acid eluate
was estimated fluorimetrically by the method of Carlsaon and Waldeck (7) ; NE was assayed by the method of Von Euler and Lishajko (B) .
Overall recoveries for these compounds were approximately 808 ;
all data were corrected for these recoveries .
The other .half of
the brain was assayed for 5HT and 5HIAA by the method of Curzon and Green (9) .
No difference in any parameters measured were
5, 7-DHT end &~in Honoemines
Vol. 14, No . 5
noted for left vs right brain halves . in a second experiment, animals were pretreated with 150 uq of 5,7-DHT (iv) or vehicle .
Ten days later, the animals were
fasted overnight (18 hr), then injected with either 50 mg/kg 1-tryptophan (40 mg/ml of 1-tryptophan in warm 0 .98 saline, pH 9) or the vehicle .
Animals were killed one hour after the injection
and brain andlasma tryptophan, and brain SHT, SHIAA, NE and DA were determined as described . Results Brain levels of SHT, SHIAA, NE and DA did not differ significantly in the vehicle-injected control groups over the 60 day time course of the experiment (Table 1) .
By contrast, both the 75 uq
and 150 yg dose of 5,7-DfiT significantly reduced brain levels of 5HT and SHIAA at all time periods examined .
Maximal decreases in
the concentrations of these amines were attained by 10 and 30 days after injection of either dose (Fig . 1) ; significant increases in the levels of these indoleaminea were found to occur after the 30day time point.
In contrast to the large decreases in brain 5HT
and SHIAA, relatively small but significant declines in brain levels of NE were found after all time periods following the injection of the drug (Fig . 2) .
Concentrations of brain DA, and plasma
and brain tryptophan, were unaffected by either dose (Table 1) . The administration of 150 ug 5,7-DHT was followed, in approximately 508 of the animals, by severe tonic-clonic convulsions . The subsequent survival of convulsive animals was facilitated by brief ether anesthesia .
These observations suggest that the
150 Uq dose of 5,7-DHT is close to the toxic limitations of this compound .
Following administration of either dose, acute hypo-
thermia was detected for as long as 24 hr following injection
912
S, 7-DHT and Braie Yonoaomes
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914
Vol. 14, No . 5
5, 7-DHT and Brain Monoamines
In addition, the animals were hyper-
(unpublished observation) .
reactive to external handling .
A marked, nondose-related reduc-
tion in the occurrence of postdecapitation convulsions was also observed . In the second experiment, rats pretreated with 150 yg of 28
VEHICLE
130 ftq 5,7-DHT
26
.r, .
22 18
__
20 15
10
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0.9
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TREATMENT FIG. 3
Animals (n ~ 8 per group) were given a single intraventricular injection of 5,7-DHT (150 ug free base) or vehicle . Ten days later, animals were fasted overnight and then injected with either 1-tryptophan (50 mg/kg) or vehicle intraperitoneally one hour prior to decapitation . Brain and plasma tryptophan and brain 5HT and SHIAA were determined (all values are mean t 5 .8 .) .
915
5, 7-DHT end Brain èlonoemines
Vol . 14, No . 5
5,7-DHT followed by the injection of tryptophan 10 days later, showed decreases in brain 5HT and SHIAA similar to those described in the first experiment (Fig . 3) .
Again, brain and plasma levels
of tryptophan were unchanged by the 5,7-DHT .
The intraperitoneal
administration of tryptophan significantly increased the plasma and brain concentrations of this compound one hour after injection in a similar magnitude in both the vehicle and the 5,7-DHT pretreated groups .
The tryptophan injections significantly elevated
the concentrations of both brain 5HT and 5HIAA in the vehicle pretreated group .
However, only 5HT, and not 5HIAA, was increased in
the 5,7-DHT pretreated group, although the percent increase in 5HT with respect to each control group was approximately the same in both groups
(i .e ., 278 increase in the vehicle pretreated group
and 578 in the 5,7-DHT pretreated group)
(Fig . 3) .
Even after
injection of the tryptophan load to 5,7-DHT pretreated animals, the total level of 5-hydroxyindoles remained greatly reduced when compared to saline pretreated animals not receiving tryptophan (0 .44 ug/g in 5,7-DHT pretreated, tryptophan injected animals va 1 .11 ug/g in saline pretreated, vehicle injected controls) . Discussion These data demonstrate that 5,7-DHT is a potent depleting agent capable of inducing severe and long lasting reductions in brain 5HT and SHIAA without affecting brain tryptophan levels . The decrease in brain 5HT is accompanied by a marked reduction in the accumslation of 5-hydroxyindoles following the exogenous administration of tryptophan .
Concomitant with this depletion in
indoleamines is a less marked depletion of brain NE but not DA . 5,7-DHT appears to affect 5HT containing neurons of the brain in a manner very similar and analogous to the effects of 6-hydroxy-
Vol. 14, No . 5
5, 7-DHT end Brain Monoamines
916
dopamine on brain catecholamine containing neurons (10-13) . Following injection of this compound (75 ug), brain 5HT is reduced to 40$ of control values at 10 to 30 days postinjection .
This
reduction is comparable to the 40-60$ depletion of 5HT noted in several brain areas after injection of 5,6-DHT (1) .
A higher dose
of 5,7-DHT (150 ug) reduces brain 5HT and SHIAA to even lower concentratipns (30$ of control values) without further affecting brain NE and DA concentrations .
This latter dose is beyond the tolerable
dose of 5,6-DHT (1) ; hence, 5,7-DHT may be used to attain even greater reductions in brain SHT and SHIAA than can be produced with the 5,6-DHT congener . In contrast to 5,6-DHT, 5,7-D1iT appears to produce small, but persistent, nondoae-related effects on brain NE .
Brain DA, how-
ever, appears to be relatively unaffected by doses of 5,7-DHT that decrease the levels of brain NE .
In contrast,
5,6-DHT produces
relatively small, transient depletions of both NE and DA in brain (1) . 5,7-DHT does not appear to decrease the level of brain 5-hydroxyindoles by altering concentrations of brain or plasma tryptophan,
Even at doses that decrease the level of NE, plasma
and brain levels of this amino acid were unaltered .
Although
under normal conditions the concentration of tryptophan in brain may physiologically regulate the levels of brain 5HT and SHIAA, (14) the mechanism by which 5,7-DHT alters brain 5HT appears to be different. Recent studies utilizing histochemical fluorescence nicrographs have demonstrated that both 5,6- and 5,7-DI3T produce extensive damage to the axonal and terminal apparatus of 5HT-containinq neurone (1,2,15) and van decrease the capacity of these neurons to take up this amine (16) .
917
5, 7-DHT end Brain Monoemiaes
Vol. 14, No . 5 Baumgarten et al .
(4) reported that the injection of 5,7-DHT
drastically reduces the tryptophan hydroxylase activity in selected brain regions that contain relatively large innervations from 5HT containing neurons .
It is unclear at present whether the reduc-
tions in tryptophan hydroxylase activity reflect less concentrations of this enzyme per surviving neuron or whether the dihydroxyindoleamines directly affect the overall enzyme activity .
Our
findings show that the peroent increase in 5HT is similar in both 5,7-DHT and saline pretreated animals given tryptophan, while the total concentration of 5-hydroxyindoleamines in 5,7-DHT pretreated animals is markedly reduced .
These data suggest that 5,7-DHT
apparently reduces the number of intact neurons, but that these surviving neurons may be able to function normally . Brain levels of 5HT and SHIAA show evidence of recovery 30 to 60 days following 5,7-DHT injection .
Recent findings suggest that
many brain neurons containing monoamines may regenerate and re sprout following either surgically (17) or chemically (18) induced lesions ; hence, the increase in 5HT and SHIAA levels noted in this study between 30 and 60 days following injection may reflect a regrowth or resprouting of 5HT containing neurons .
Alternatively,
the small increase in brain 5HT levels may indicate that the synthetic capacity of surviving 5HT containing neurons may increase following injection, or that a further loss in the ability to metabolize 5HT has occurred (i .e ., MAO activity may have been impaired) .
However, since the recovery pattern of SHIAA between
the 30th and 60th postinjection day parallels that of 5HT, this latter possibility seems unlikely . In contrast to adults injected with 5,7-DST, neonates administered doses up to 50 ug on the day of birth show little or no recovery, and 5HT levels, which ai~e drastically reduced, remain
Vol . 14, No . 5
5, 7~DHT aad Brain èlonoemiaea
918
essentially unchanged until at least 60 days of age (unpublished observation) . 5,7-DHT appears to be able to induce a more severe depletion of brain 5HT and 5HIAA than 5,6-DHT, but also induces a longer lasting depletion of brain NE . Acknowledgments These studies were supported by grants IF AM-14228 and NS-10459 .
Dr . Jacoby holds a USPHS Postdoctoral Fellowship
(1-702NS54909-1) .
The authors wish to thank Dr . Richard J .
Wurtman for his helpful comments and Mr . Ken Cottman for technical assistance . References 1.
H.G . BAUMGARTEN, A. IiJORRLUND, L . LACHENMAYER, A. NOBIN and U. STENEVI, Acta Physiol . Scand . , Supp . 373, 1-16
2.
(1971) .
H.G . BAUMGARTEN and L. LACHENMAYER, Z . Zellforsch , 135,
399-
414 (1972) . 3.
S .J . VICTOR, H .G . BAUMGARTEN and W. LOVENBERG, Fed . Proc . , 32, 564 (1973) .
4.
H.G . BAUMGARTEN, S .J . VICTOR and W. LOVENBERG, J. Neurochem . , 21, 251-253 (1973) .
5.
W.D . DENCKLA and H .K . DEWEY, J . Lab . Clin . Med . , 69, 160-169 (1967) .
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A.H . ANTON and D .F . SAYRE, J . Pharmacol . Exp . Ther . , 138, 360375 (1962) .
7.
A. CARLSSON and B . WALDECK, Acta Physiol . Scand . , 44, 293-298 (1958) .
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U.S . VON EDLER and F . LISHAJRO, Acta Physiol . Scand . , 51, 348 356 (1961) .
Vol. 14, No . 5
9.
5,7-DHT end Brain Noeoeminea
919
G . CURZON and A .R . GREEN, Br . J. Pharmacol ., 39, 653-655 (1970) .
10 .
N .J . URETSKY and L.L . IVERSEN, Nature
(London) , 221, 557-559
(1969) . 11 .
W.P . BURKARD, M. JALFRE and J. BLUM, Experientia (Basel) , 25, 1295-1296 (1969) .
12 .
G. HARTHOLINI, J .G . RICHARDS and A. PLETSCHER, Experientia (Basel) ,
13 .
26, 142-144 (1970) .
G.R . BREESE and T.D . TRAYLOR, J . Pharmacol . Exp . Ther . , 174, 413-420 (1970) .
14 .
J .D . FERNSTROM and R.J . WURTMAN, Science , 178, 414-416 (1972) .
15 .
H.G . BAUMGARTEN, L . LACHENMAYER and H .G . SCBIASSBERGER, Z . Zellforach, 125, 553-569 (1972) .
16 .
A.S . HORN, H .G . BAUMGARTEN and H .G . SCHLOSSBERGSR, J . Neurochen, 21, 233-236 (1973) .
17 .
R. RATZMAN, A. BJORRLUND, C . OWMAN, U . STENEVI and R .A . WEST, Brain Res . , 25, 579-596 (1971) .
18 .
A. HJORRLUND, A . NOBIN and U. STENEVI, Brain Res . , 50, 214220 (1973) .