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Crus cerebri lesions abolish amphetamine-induced ascorbate release in the rat neostriatum
Brain Research, 370 (1986) 393-396
393
Elsevier BRE 21486
Crus cerebri lesions abolish amphetamine-induced ascorbate release in the rat neostriatum ROBERT L. WILSON I, KATSUO KAMATA2, JAMES C. BIGELOW l, GEORGE V. REBEC 2and R. MARK WIGHTMANl,
1Departmentof Chemistry and 2Departmentof Psychology, Indiana University, Bloomington, IN 47405 (U.S.A.) (Accepted December 17th, 1985)
Key words: amphetamine - - ascorbic acid - - crus cerebri - - in vivo voltammetry - - neostriatum - - picrotoxin - - substantia nigra
An increase in the concentration of ascorbate in the extracellular fluid of the rat striatum following systemic amphetamine administration previously has been demonstrated with the use of in vivo electrochemistry, push-pull cannula and in vivo dialysis. In this report, the effect of infusions of amphetamine into the substantia nigra on extrallular ascorbate levels in the striatum is further investigated by in vivo electrochemistry. Electrolytic lesions in the crus cerebri of the striatonigral pathway abolish this effect. Furthermore, these lesions abolish the effect of systemic amphetamine in the striatum ipsilateral to the lesion but not on the contralateral side. This phenomenon is independent of neostriatal dopamine or 7-aminobutyric acid since levels were shown to be unchanged relative to the intact side. These results lend further support to the hypothesis that ascorbate secretion in the striatum after amphetamine is mediated in the central nervous system, and indicate that a pathway that courses through the crus cerebri is necessary for this release.
Several investigators have shown that systemic administration of a m p h e t a m i n e causes an increase in the extracellular concentration of ascorbate in the
neostriatal ascorbate since this effect persists after a near total destruction of dopamine afferents to the neostriatum 4. However, the substantia nigra is
neostriatum of the rat. This was first shown with the use of electrochemically modified carbon fiber microvoltammetric electrodes9, t0 and confirmed by other voltammetric techniques4, 5, dialysis and p u s h - p u l l perfusion 7,11.15A6. Recent experimental evidence in-
known to receive n e u r o n a l feedback from the neostriatum, and this pathway exerts a strong influence on nigral activity2. Therefore, it is conceivable that the amphetamine-induced release of ascorbate in the neostriatum is controlled, at least in part, by this
dicates that this effect of a m p h e t a m i n e on ascorbate release is not mediated in the neostriatum. In fact, direct infusions of a m p h e t a m i n e into this site reduce
feedback pathway. To test this hypothesis, we de-
extracellular levels of ascorbate. However, when infused into the substantia nigra, a m p h e t a m i n e increases the extracellular fluid concentration of ascorbate in the neostriatum 17. The amphetamine-induced rise in neostriatal ascorbate may have important functional consequences since ascorbate has been shown to modulate n e u r o n a l activity in the neostriatum8 and to attenuate the behavioral response to amphetamine, which is d e p e n d e n t on the integrity of neostriatal neurons 14. It is unlikely that the dopaminergic projection from the substantia nigra to the neostriatum is responsible for the a m p h e t a m i n e - i n d u c e d increase in
stroyed the feedback system with crus cerebri lesions and used voltammetric techniques to measure extracellular ascorbate in the neostriatum after systemic or intranigral injections of amphetamine. Electrolytic lesions were made in the crus cerebri of male, S p r a g u e - D a w l e y rats (ca. 350 g) that were anesthetized with chloral hydrate. A burr hole was drilled in the skull 4.1 m m anterior and 2.4 m m lateral to lambda 12 and an insulated bipolar electrode was lowered into the crus cerebri (8.0 mm ventral from the dura). A 2.0 m A current (DC) was applied for 15 s. The electrode was removed, the wound was closed and the animal was injected (i.m.) with 100,000 units of Bicilin (Wyeth) and allowed to recover for a m i n i m u m of 5 days before subsequent ex-
Correspondence: G.V. Rebec, Department of Psychology, Indiana University, Bloomington, IN 47405, U.S.A. 0006-8993/86/$03.50 © 1986 Elsevier Science Publishers B.V. (Biomedical Division)
394 periments. Fig. 1 illustrates the largest extent of tissue destroyed by the lesion. Note that despite damage to the crus cerebri, the medial forebrain bundle, which contains ascending d o p a m i n e fibers, remains intact. In some animals, p o s t m o r t o m analyses of neostriatal d o p a m i n e and 7-aminobutyric acid ( G A B A ) were made. Assays e m p l o y e d the technique of liquid c h r o m a t o g r a p h y with electrochemical detection 3,13. Neither d o p a m i n e (0.080 + 0.009 ktmol/gram) nor G A B A (2.5 + 0.3/,tmol/gram tissue) levels were altered significantly from control values (n = 4, P > 0.05). On the day of experimentation, the rat was anesthetized with ether and placed in a stereotaxic instrument. Burr holes were drilled through the skull bilaterally over each neostriatum (2.0 mm anterior and 2.5 mm lateral to bregma) and unilaterally over the substantia nigra (2.8 mm anterior and 1.8 mm lateral to lambda). A n intravenous catheter was i m p l a n t e d
in the left or right femoral vein and the dura was carefully removed. Local anesthetics were applied to all surgical (procaine) and stereotaxic (lidocaine) contact points. The ether was withdrawn and 2.0 mg/kg D-tubocurarine chloride (Lilly) was administered to relax all skeletal muscles. Positive-pressure artificial respiration was maintained by a rubber cone fitted snugly over the snout and attached to a rodent respirator. A n end-tidal carbon dioxide content of 4.0 _+ 0.5% was maintained throughout the experiment as described previously6. Carbon fiber microelectrodes 17 were lowered 4.5 m m below the cortical surface into each neostriatum. Electrochemical techniques were identical to those described previously 17. An A p p l e I1+ c o m p u t e r was used to generate the waveforms and store the sampled current. C h r o n o a m p e r o m e t r i c potential pulses from - 0 . 2 to 0.7 V of 92 ms duration were applied at 10 s intervals. Staircase v o l t a m m e t r y e m p l o y e d 40 steps (25 mV/step) of 66.7 ms duration from - 0 . 2 to 0.8 V. A saturated calomel electrode, placed in contact with cerebrospinal fluid at the surface of the brain through a saline bridge, was used as a reference. A m p h e t a m i n e was infused into the substantia nigra by means of a stainless steel infusion cannula (30 gauge) lowered 7.6 mm ventral to the dura. Histological verification of the cannula placement was accomplished upon completion of each experiment. In each case, the infusion cannula was found to be in the ventral substantia nigra zona compacta, an area in which amphetamine is known to induce ascorbate release in CRUS CEREBRI LESION 400
, . . ~.., -.'.,...v.... ~ ~.......,~......... ~ .
7
INTACT
"..
300
-..
--:. '..~..
i (pA) 200 LESION ,.,:o,.......'"~ 2" .,..-.".';. .'" ;"" "'''L "~''"" "'" v ' ' ' '''" " "'~'''''':'~ ' ' ' ' '''''''" "'~.""; : ' " "
,ooi
I
/
I
I
0
20
40
60
TIME(min)
Fig. 1. Representation of the greatest extent of the electrolytic lesion (2 mA-DC current for 15 s) of the crus cerebri. The lesion projected anteriorly and posteriorly ca. 950 gm from the cross-hatched region shown here. This figure was drawn from K6nig and Klippe112.
Fig. 2. Representative response obtained with systemic (i.v.) administration of 2.5 mg/kg o-amphetamine to an animal with a unilateral lesion of the crus cerebri. Both responses represent the oxidation current obtained at 0.6 V vs a saturated calomel electrode.
395 both neostriata in intact animals 17. However, in lesioned animals, a dose of 2 pl of 10 pg/pl D-amphetamine infused ipsilateral to the lesion did not induce ascorbate release in either neostriatum (n = 6). The effect of systemic amphetamine on ascorbate release in the neostriata of animals with an unilateral lesion of the crus cerebri was also examined. Crus cerebri lesions eliminate the release of ascorbate on the lesioned side as a result of systemic (i.v.) administration. However, the increase in ascorbate that is observed on the non-lesioned side is statistically identical to that obtained in intact animals (n -- 4, P > 0.05). Fig. 2 illustrates the response of a typical animal for each neostriatum after the intravenous administration of 2.5 mg/kg D-amphetamine. A possible mechanism for the elimination of ascorbate release following crus cerebri lesions is the removal of G A B A e r g i c colaterals. G A B A induces release of ascorbate from neostriatal tissue in vitro and this effect is blocked by picrotoxinl. Therefore picrotoxin (1 mg/kg) was administered to intact animals that were anesthetized with chloral hydrate (400 mg/kg). Picrotoxin did not change extracellular ascorbate concentrations and was unable to inhibit the increase of extracellular ascorbate caused by systemic amphetamine (2.5 mg/kg, n = 3, P > 0.05 compared to control). Taken together these data provide additional evidence for a central mechanism that mediates release of ascorbate in the neostriatum after amphetamine
This research was supported by the National Institutes of Health (PHS RO1 NS 15841, R . M . W . ) and National Science Foundation (NSF BNS 84-16303, G.V.R.). The technical assistance of Doris Batson in the histological verifications of electrode placement is appreciated.
1 Bigelow, J.C., Brown, D.S. and Wightman, R.M. y-Aminobutyric acid stimulates the release of endogenous ascorbic acid from rat striatal tissue, J. Neurochem., 42 (1984) 412-419. 2 Bunney, B.S. and Aghajanian, G.K., D-Amphetamine-induced inhibition of central dopaminergic neurons: mediation by a striato-nigral feedback pathway, Science, 192 (1976) 391-393. 3 Caudill, W.L., Bigelow, J.C. and Wightman, R.M., Comparison of release of endogenous dop.amine and 7-aminobutyric acid from rat caudate synaptosomes, Neurochem. Res., 10 (1985) 319-331. 4 Dayton, M.A., Ewing, A.G. and Wightman, R.M., Evaluation of amphetamine-induced in vivo electrochemical response, Eur. J. PharmacoL, 75 (1981) 141-144. 5 Ewing, A.G., Wightman, R.M. and Dayton, M.A., In vivo voltammetry with electrodes that discriminate between dopamine and ascorbate, Brain Research, 249 (1982) 361-370. 6 Ewing, A.G., Alloway, K.D., Curtis, S.D., Dayton, M.A., Wightman, R.M. and Rebec, G.V., Simultaneous electro-
chemical and unit recording measurements: characterization of the effect of D-amphetamine and ascorbic acid on neostriatal neurons, Brain Research, 261 (1983) 101-108. 7 Fillenz, M. and Grunewald, R.A., Changes in brain ascorbate after amphetamine monitored with voltammetry and push-pull perfusion in unanesthetized animals, J. Physiol. (London), 339 (1982) 160P. 8 Gardiner, T.W., Armstrong-James, M., Caan, J.W., Wightman, R.M. and Rebec, G.V., Modulation of neostriatal activity by iontophoresis of ascorbic acid, Brain Research, 344 (1985) 181-185. 9 Gonon, F., Buda, M., Cespuglio, R., Jouvet, M. and Pujol, J.F., In vivo electrochemical detection in the neostriatum of anesthetized rats: dopamine or DOPAC? Nature (London), 286 (1980) 902-904. 10 Gonon, F.G., Buda, M., Cespuglio, R., Jouvet, M. and Pujol, J.F., Voltammetry in the striatum of chronic freely moving rats: detection of catechols and ascorbate, Brain Research, 223 (1981) 69-80. 11 Justice, J.B., Wages, S.A., Michael, A.C., Blakely, R.D. and Neill, D.B., Interpretations of voltammetry in the stri-
administration. Furthermore, this effect appears to be mediated by projections coursing through the crus cerebri. Unilateral lesions of the crus cerebri eliminate the effect of nigral infusions of amphetamine on ascorbate in both neostriata. Moreover, the response in the neostriatum to systemic amphetamine is abolished on the side ipsilateral to the crus cerebri lesion, which suggests that the crus cerebri contains a major pathway that controls extracellular ascorbate. However, in vivo evidence for a direct link with G A B A receptors is not apparent in these experiments. Lesions that eliminate the nigral actions of amphetamine on the release of ascorbate in the ipsilateral caudate do not effect G A B A levels in the neostriatum. Furthermore, the amphetamine-induced release of ascorbate is unaffected by picrotoxin, a blocker of the G A B A receptor. Thus, while it appears that G A B A is not a major affector of amphetamine-induced ascorbate release, it is increasingly clear that specific activation of some, as yet unknown, neuronal circuit, as a result of amphetamine challenge, is responsible for the increase of ascorbate in neostriatal extracellular fluid.
396 atum based on chromatography of striatal dialysate, J. Liq. Chromatol., 6 (1983) 1873-1896. 12 Konig, J.F.R. and Klippel, R.A., The Rat Brain Stereotaxic Atlas, Krieger Pub. Co., 1963. 13 Kuhr, W.G., Ewing, A.G., Caudill, W.L. and Wightman, R.M., Monitoring the stimulated release of dopamine with in vivo voltammetry. I: Characterization of the response observed in the caudate nucleus of the rat, J. Neurochem., 43 (1984) 560-569. 14 Rebec, G.V., Centore, L.M., White, L.K. and Alloway, K.D., Ascorbic acid and the behavioral response to haloperidol: implications for the action of antipsychotic drugs, Science, 227 (1985) 438-440.
15 Salamone, J.D., Leigh, S.H., Neill, D.B. and Justice, J.B,, Extracellular ascorbic acid increases in striatum following systemic amphetamine, Pharm. Biochem. Behav., 20 (1984) 609-612. 16 Wightman, R.M., Brown, D.S., Kuhr, W.G. and Wilson, R.L., The molecular specificity of in vivo electrochemical measurements. In J. Justice (Ed.), In Vivo Voltammetry, in press. 17 Wilson, R.L. and Wightman, R.M., Systemic and nigral application of amphetamine both cause an increase in extracellular concentration of ascorbate in the caudate nucleus of the rat, Brain Research, 339 (1985) 219-226.
393
Elsevier BRE 21486
Crus cerebri lesions abolish amphetamine-induced ascorbate release in the rat neostriatum ROBERT L. WILSON I, KATSUO KAMATA2, JAMES C. BIGELOW l, GEORGE V. REBEC 2and R. MARK WIGHTMANl,
1Departmentof Chemistry and 2Departmentof Psychology, Indiana University, Bloomington, IN 47405 (U.S.A.) (Accepted December 17th, 1985)
Key words: amphetamine - - ascorbic acid - - crus cerebri - - in vivo voltammetry - - neostriatum - - picrotoxin - - substantia nigra
An increase in the concentration of ascorbate in the extracellular fluid of the rat striatum following systemic amphetamine administration previously has been demonstrated with the use of in vivo electrochemistry, push-pull cannula and in vivo dialysis. In this report, the effect of infusions of amphetamine into the substantia nigra on extrallular ascorbate levels in the striatum is further investigated by in vivo electrochemistry. Electrolytic lesions in the crus cerebri of the striatonigral pathway abolish this effect. Furthermore, these lesions abolish the effect of systemic amphetamine in the striatum ipsilateral to the lesion but not on the contralateral side. This phenomenon is independent of neostriatal dopamine or 7-aminobutyric acid since levels were shown to be unchanged relative to the intact side. These results lend further support to the hypothesis that ascorbate secretion in the striatum after amphetamine is mediated in the central nervous system, and indicate that a pathway that courses through the crus cerebri is necessary for this release.
Several investigators have shown that systemic administration of a m p h e t a m i n e causes an increase in the extracellular concentration of ascorbate in the
neostriatal ascorbate since this effect persists after a near total destruction of dopamine afferents to the neostriatum 4. However, the substantia nigra is
neostriatum of the rat. This was first shown with the use of electrochemically modified carbon fiber microvoltammetric electrodes9, t0 and confirmed by other voltammetric techniques4, 5, dialysis and p u s h - p u l l perfusion 7,11.15A6. Recent experimental evidence in-
known to receive n e u r o n a l feedback from the neostriatum, and this pathway exerts a strong influence on nigral activity2. Therefore, it is conceivable that the amphetamine-induced release of ascorbate in the neostriatum is controlled, at least in part, by this
dicates that this effect of a m p h e t a m i n e on ascorbate release is not mediated in the neostriatum. In fact, direct infusions of a m p h e t a m i n e into this site reduce
feedback pathway. To test this hypothesis, we de-
extracellular levels of ascorbate. However, when infused into the substantia nigra, a m p h e t a m i n e increases the extracellular fluid concentration of ascorbate in the neostriatum 17. The amphetamine-induced rise in neostriatal ascorbate may have important functional consequences since ascorbate has been shown to modulate n e u r o n a l activity in the neostriatum8 and to attenuate the behavioral response to amphetamine, which is d e p e n d e n t on the integrity of neostriatal neurons 14. It is unlikely that the dopaminergic projection from the substantia nigra to the neostriatum is responsible for the a m p h e t a m i n e - i n d u c e d increase in
stroyed the feedback system with crus cerebri lesions and used voltammetric techniques to measure extracellular ascorbate in the neostriatum after systemic or intranigral injections of amphetamine. Electrolytic lesions were made in the crus cerebri of male, S p r a g u e - D a w l e y rats (ca. 350 g) that were anesthetized with chloral hydrate. A burr hole was drilled in the skull 4.1 m m anterior and 2.4 m m lateral to lambda 12 and an insulated bipolar electrode was lowered into the crus cerebri (8.0 mm ventral from the dura). A 2.0 m A current (DC) was applied for 15 s. The electrode was removed, the wound was closed and the animal was injected (i.m.) with 100,000 units of Bicilin (Wyeth) and allowed to recover for a m i n i m u m of 5 days before subsequent ex-
Correspondence: G.V. Rebec, Department of Psychology, Indiana University, Bloomington, IN 47405, U.S.A. 0006-8993/86/$03.50 © 1986 Elsevier Science Publishers B.V. (Biomedical Division)
394 periments. Fig. 1 illustrates the largest extent of tissue destroyed by the lesion. Note that despite damage to the crus cerebri, the medial forebrain bundle, which contains ascending d o p a m i n e fibers, remains intact. In some animals, p o s t m o r t o m analyses of neostriatal d o p a m i n e and 7-aminobutyric acid ( G A B A ) were made. Assays e m p l o y e d the technique of liquid c h r o m a t o g r a p h y with electrochemical detection 3,13. Neither d o p a m i n e (0.080 + 0.009 ktmol/gram) nor G A B A (2.5 + 0.3/,tmol/gram tissue) levels were altered significantly from control values (n = 4, P > 0.05). On the day of experimentation, the rat was anesthetized with ether and placed in a stereotaxic instrument. Burr holes were drilled through the skull bilaterally over each neostriatum (2.0 mm anterior and 2.5 mm lateral to bregma) and unilaterally over the substantia nigra (2.8 mm anterior and 1.8 mm lateral to lambda). A n intravenous catheter was i m p l a n t e d
in the left or right femoral vein and the dura was carefully removed. Local anesthetics were applied to all surgical (procaine) and stereotaxic (lidocaine) contact points. The ether was withdrawn and 2.0 mg/kg D-tubocurarine chloride (Lilly) was administered to relax all skeletal muscles. Positive-pressure artificial respiration was maintained by a rubber cone fitted snugly over the snout and attached to a rodent respirator. A n end-tidal carbon dioxide content of 4.0 _+ 0.5% was maintained throughout the experiment as described previously6. Carbon fiber microelectrodes 17 were lowered 4.5 m m below the cortical surface into each neostriatum. Electrochemical techniques were identical to those described previously 17. An A p p l e I1+ c o m p u t e r was used to generate the waveforms and store the sampled current. C h r o n o a m p e r o m e t r i c potential pulses from - 0 . 2 to 0.7 V of 92 ms duration were applied at 10 s intervals. Staircase v o l t a m m e t r y e m p l o y e d 40 steps (25 mV/step) of 66.7 ms duration from - 0 . 2 to 0.8 V. A saturated calomel electrode, placed in contact with cerebrospinal fluid at the surface of the brain through a saline bridge, was used as a reference. A m p h e t a m i n e was infused into the substantia nigra by means of a stainless steel infusion cannula (30 gauge) lowered 7.6 mm ventral to the dura. Histological verification of the cannula placement was accomplished upon completion of each experiment. In each case, the infusion cannula was found to be in the ventral substantia nigra zona compacta, an area in which amphetamine is known to induce ascorbate release in CRUS CEREBRI LESION 400
, . . ~.., -.'.,...v.... ~ ~.......,~......... ~ .
7
INTACT
"..
300
-..
--:. '..~..
i (pA) 200 LESION ,.,:o,.......'"~ 2" .,..-.".';. .'" ;"" "'''L "~''"" "'" v ' ' ' '''" " "'~'''''':'~ ' ' ' ' '''''''" "'~.""; : ' " "
,ooi
I
/
I
I
0
20
40
60
TIME(min)
Fig. 1. Representation of the greatest extent of the electrolytic lesion (2 mA-DC current for 15 s) of the crus cerebri. The lesion projected anteriorly and posteriorly ca. 950 gm from the cross-hatched region shown here. This figure was drawn from K6nig and Klippe112.
Fig. 2. Representative response obtained with systemic (i.v.) administration of 2.5 mg/kg o-amphetamine to an animal with a unilateral lesion of the crus cerebri. Both responses represent the oxidation current obtained at 0.6 V vs a saturated calomel electrode.
395 both neostriata in intact animals 17. However, in lesioned animals, a dose of 2 pl of 10 pg/pl D-amphetamine infused ipsilateral to the lesion did not induce ascorbate release in either neostriatum (n = 6). The effect of systemic amphetamine on ascorbate release in the neostriata of animals with an unilateral lesion of the crus cerebri was also examined. Crus cerebri lesions eliminate the release of ascorbate on the lesioned side as a result of systemic (i.v.) administration. However, the increase in ascorbate that is observed on the non-lesioned side is statistically identical to that obtained in intact animals (n -- 4, P > 0.05). Fig. 2 illustrates the response of a typical animal for each neostriatum after the intravenous administration of 2.5 mg/kg D-amphetamine. A possible mechanism for the elimination of ascorbate release following crus cerebri lesions is the removal of G A B A e r g i c colaterals. G A B A induces release of ascorbate from neostriatal tissue in vitro and this effect is blocked by picrotoxinl. Therefore picrotoxin (1 mg/kg) was administered to intact animals that were anesthetized with chloral hydrate (400 mg/kg). Picrotoxin did not change extracellular ascorbate concentrations and was unable to inhibit the increase of extracellular ascorbate caused by systemic amphetamine (2.5 mg/kg, n = 3, P > 0.05 compared to control). Taken together these data provide additional evidence for a central mechanism that mediates release of ascorbate in the neostriatum after amphetamine
This research was supported by the National Institutes of Health (PHS RO1 NS 15841, R . M . W . ) and National Science Foundation (NSF BNS 84-16303, G.V.R.). The technical assistance of Doris Batson in the histological verifications of electrode placement is appreciated.
1 Bigelow, J.C., Brown, D.S. and Wightman, R.M. y-Aminobutyric acid stimulates the release of endogenous ascorbic acid from rat striatal tissue, J. Neurochem., 42 (1984) 412-419. 2 Bunney, B.S. and Aghajanian, G.K., D-Amphetamine-induced inhibition of central dopaminergic neurons: mediation by a striato-nigral feedback pathway, Science, 192 (1976) 391-393. 3 Caudill, W.L., Bigelow, J.C. and Wightman, R.M., Comparison of release of endogenous dop.amine and 7-aminobutyric acid from rat caudate synaptosomes, Neurochem. Res., 10 (1985) 319-331. 4 Dayton, M.A., Ewing, A.G. and Wightman, R.M., Evaluation of amphetamine-induced in vivo electrochemical response, Eur. J. PharmacoL, 75 (1981) 141-144. 5 Ewing, A.G., Wightman, R.M. and Dayton, M.A., In vivo voltammetry with electrodes that discriminate between dopamine and ascorbate, Brain Research, 249 (1982) 361-370. 6 Ewing, A.G., Alloway, K.D., Curtis, S.D., Dayton, M.A., Wightman, R.M. and Rebec, G.V., Simultaneous electro-
chemical and unit recording measurements: characterization of the effect of D-amphetamine and ascorbic acid on neostriatal neurons, Brain Research, 261 (1983) 101-108. 7 Fillenz, M. and Grunewald, R.A., Changes in brain ascorbate after amphetamine monitored with voltammetry and push-pull perfusion in unanesthetized animals, J. Physiol. (London), 339 (1982) 160P. 8 Gardiner, T.W., Armstrong-James, M., Caan, J.W., Wightman, R.M. and Rebec, G.V., Modulation of neostriatal activity by iontophoresis of ascorbic acid, Brain Research, 344 (1985) 181-185. 9 Gonon, F., Buda, M., Cespuglio, R., Jouvet, M. and Pujol, J.F., In vivo electrochemical detection in the neostriatum of anesthetized rats: dopamine or DOPAC? Nature (London), 286 (1980) 902-904. 10 Gonon, F.G., Buda, M., Cespuglio, R., Jouvet, M. and Pujol, J.F., Voltammetry in the striatum of chronic freely moving rats: detection of catechols and ascorbate, Brain Research, 223 (1981) 69-80. 11 Justice, J.B., Wages, S.A., Michael, A.C., Blakely, R.D. and Neill, D.B., Interpretations of voltammetry in the stri-
administration. Furthermore, this effect appears to be mediated by projections coursing through the crus cerebri. Unilateral lesions of the crus cerebri eliminate the effect of nigral infusions of amphetamine on ascorbate in both neostriata. Moreover, the response in the neostriatum to systemic amphetamine is abolished on the side ipsilateral to the crus cerebri lesion, which suggests that the crus cerebri contains a major pathway that controls extracellular ascorbate. However, in vivo evidence for a direct link with G A B A receptors is not apparent in these experiments. Lesions that eliminate the nigral actions of amphetamine on the release of ascorbate in the ipsilateral caudate do not effect G A B A levels in the neostriatum. Furthermore, the amphetamine-induced release of ascorbate is unaffected by picrotoxin, a blocker of the G A B A receptor. Thus, while it appears that G A B A is not a major affector of amphetamine-induced ascorbate release, it is increasingly clear that specific activation of some, as yet unknown, neuronal circuit, as a result of amphetamine challenge, is responsible for the increase of ascorbate in neostriatal extracellular fluid.
396 atum based on chromatography of striatal dialysate, J. Liq. Chromatol., 6 (1983) 1873-1896. 12 Konig, J.F.R. and Klippel, R.A., The Rat Brain Stereotaxic Atlas, Krieger Pub. Co., 1963. 13 Kuhr, W.G., Ewing, A.G., Caudill, W.L. and Wightman, R.M., Monitoring the stimulated release of dopamine with in vivo voltammetry. I: Characterization of the response observed in the caudate nucleus of the rat, J. Neurochem., 43 (1984) 560-569. 14 Rebec, G.V., Centore, L.M., White, L.K. and Alloway, K.D., Ascorbic acid and the behavioral response to haloperidol: implications for the action of antipsychotic drugs, Science, 227 (1985) 438-440.
15 Salamone, J.D., Leigh, S.H., Neill, D.B. and Justice, J.B,, Extracellular ascorbic acid increases in striatum following systemic amphetamine, Pharm. Biochem. Behav., 20 (1984) 609-612. 16 Wightman, R.M., Brown, D.S., Kuhr, W.G. and Wilson, R.L., The molecular specificity of in vivo electrochemical measurements. In J. Justice (Ed.), In Vivo Voltammetry, in press. 17 Wilson, R.L. and Wightman, R.M., Systemic and nigral application of amphetamine both cause an increase in extracellular concentration of ascorbate in the caudate nucleus of the rat, Brain Research, 339 (1985) 219-226.