Proc. Natl. Acad. Sci. USAVol. 83, pp. 6203-6207, August 1986Neurobiology

Dopaminergic control of 125I-labeled neurotensin binding sitedensity in corticolimbic structures of the rat brain

(autoradiography/hetero-regulation/mesocorticolimbic dopaminergic neurons)

D. HERVE*, J. P. TASSIN*, J. M. STUDLER*, C. DANAt, P. KITABGIt, J. P. VINCENTt, J. GLOWINSKI*,AND W. ROSTENEt*College de France, Institut National de la Santd et de la Recherche Mddicale U 114, Chaire de Neuropharmacologie, 11 place Marcelin Berthelot, 75231 ParisCedex 05, France; tInstitut National de la Sante et de la Recherche Mddicale U 55, Hopital St. Antoine, 184 rue du Fg St. Antoine, 75771 Paris Cedex 12,France; and tCentre de Biochimie du Centre National de la Recherche Scientifique, Universitd de Nice, Parc Valrose, 06034 Nice Cedex, France

Communicated by Louis Sokoloff, April 21, 1986

ABSTRACT In the rat brain, destruction of dopaminergiccell groups by injections of 6-hydroxydopamine into the ventralmesencephalic tegmentum results in large decreases in thenumber of neurotensin binding sites in the mesencephalon andthe striatum. In contrast, these lesions produce an increase inthe number of 1251-labeled neurotensin binding sites in thelateral part of the prefrontal cortex despite a large decrease incortical dopamine levels. Increases; in the number of 125I-labeled neurotensin binding sites in this cortical area as well asin the entorhinal cortex, the nucleus accumbens, and thecentral part of the striatum were also obtained after chronicblockade of dopamine neurotransmission by a long-actingneuroleptic pipotiazine palmitic ester. We propose that dopa-mine inputs regulate the density of postsynaptic neurotensinbinding sites through cortical and subcortical dopamine recep-tors. Therefore, some of the clinical effects of neuroleptics inschizophrenic patients could be partly related to changes inneurotensin neurotransmission.

Neurotensin (NT) is a tridecapeptide that is unevenly dis-tributed in mammalian brain (1-4). High levels of NTimmunoreactivity have been found in some structures inner-vated by ascending dopaminergic neurons, such as thenucleus accumbens or the striatum, while relatively little NTimmunoreactivity was detected in others, such as theprefrontal cortex (5, 6). Histochemical studies have alsorevealed the occurrence ofNT immunoreactive fibers in theventral mesencephalic tegmentum (VMT) and in the zonacompacta and pars lateralis of the substantia nigra (SN)surrounding dopamine-containing cell bodies and theirdendrites (7). In addition, numerous neuronal perikarya ofthe VMT contain NT immunoreactivity: NT and dopaminecoexist in some VMT neurons (7) and the existence of a VMTNT projection to the median nucleus accumbens has beenalso described (8).There is some indication that NT stimulates the firing rate

of nigral dopaminergic cells (9), and several biochemical andbehavioral studies have suggested that intraventricularly orlocally injected NT can activate dopaminergic cells locatedeither in the VMT or in the SN (10-14). For example, in therat, the injection ofNT into the VMT produced concomitantincreases in the levels of dihydroxyphenylacetic acid in thenucleus accumbens and in locomotor activity (13). Moreover,one of the most striking features of the autoradiographicdistribution of [3H]NT binding sites was its similarity to thetopographic localization of dopaminergic cell bodies in theventral mesencephalon (15, 16). Lesion studies have con-firmed the presence of [3H]NT binding sites on mesencephal-ic dopaminergic neurons. Injection of 6-hydroxydopamine

into the VMT and the SN led to the destruction of theascending dopaminergic neurons and was associated with amarked decrease in [3H]NT binding in the mesencephalon(17, 18). In addition, a reduction of [3H]NT binding wasobserved in dopaminergic terminal areas such as the striatumand the olfactory tubercles (17).Although interactions between NT and dopaminergic neu-

rons are well-documented, there is no report about theinfluence of dopamine neurotransmission on the NT bindingsites located post-synaptically to the dopaminergic neurons.In the present study, two approaches were used to chroni-cally interrupt dopamine transmission: the first consisted ofthe destruction of ascending dopaminergic neurons by bilat-eral injections of 6-hydroxydopamine into the VMT, and thesecond took advantage of the property of a long-actingneuroleptic, the pipotiazine palmitic ester, to chronicallyblock dopamine receptors. Changes in NT binding sites wereexamined by using in vitro quantitative autoradiography of'25I-labeled [Tyr3]NT (1251-NT) binding (19, 20). Resultsobtained show that the blockade of dopamine transmissioninduces an increase in the 1251I-NT binding sites postsynapticto dopaminergic nerve terminals, especially in corticolimbicstructures.

METHODSAnimals and Surgery. Sprague-Dawley rats (250-300 g)

(Charles River, Elbeuf, France) were used. They were keptin stable conditions oftemperature (22°C) and humidity (65%)in a 12-hr light/dark cycle. Rats were anesthetized withketamine (130 mg/kg) and were fixed on a Kopf stereotaxicapparatus with incisor bars placed 3.4 mm above theinteraural line. Dopaminergic cell bodies were lesioned bybilateral microinjections of 1 ,ul of a solution containing6-hydroxydopamine (4 mg/ml), NaCl (9 mg/ml), and ascor-bic acid (0.2 mg/ml) adjusted to pH 4.5. Microinjectioncannulae were placed stereotaxically 4.3 mm posterior to and± 0.5 mm lateral to the Bregma and 8.7 mm under the surfaceof the skull. The 6-hydroxydopamine solution was deliveredslowly by a Hamilton syringe attached to a Braun-Melsungenpump (1 ,u per 3 min).

Long-Acting Neuroleptic Treatment. The long-acting neu-roleptic, pipotiazine palmitic ester, which has already beenused successfully to analyze the effects of long-term impreg-nation with neuroleptics on dopamine transmission (21), wasinjected subcutaneously 40, 20, and 5 days before sacrifice(Piportil L4; 32 mg/kg, expressed as weight of pipotiazine).The efficiency of the neuroleptic treatment was tested bymeasuring the locomotor activity of the animals according tothe method of LeMoal et al. (22). All the treated animals used

Abbreviations: NT, neurotensin; 125I-NT, 125I-labeled [Tyr3]NT; SN,substantia nigra; VMT, ventral mesencephalic tegmentum.

6203

The publication costs of this article were defrayed in part by page chargepayment. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Proc. Natl. Acad. Sci. USA 83 (1986)

in the present study exhibited a locomotor activity <40% ofthat of controls.

Estimation of Dopamine Levels. The efficiency of the6-hydroxydopamine lesions was tested by measuring dopa-mine levels according to the following procedure: animalswere stunned by a blow to the thorax and sacrificed bydecapitation. Microdiscs of tissue from the ventral tegmentalarea, medial and lateral SN, prefrontal cortex, nucleusaccumbens, and central and lateral striatum were dissectedout of frozen sections 500,m thick using 0.9-mm or 1.4-mm(prefrontal cortex) diameter cylindrical tubes. Tissue sam-ples were immersed in 110 ,ul of a 0.1 M perchloric acid/0.01M thioglycollic acid solution, sonicated, and centrifuged for20 min at 20,000 x g. Catechols were isolated from super-natants on alumina microcolumns and dopamine levels wereestimated by a radioenzymatic method derived from Gauchyet al. (23). In all structures examined, 6-hydroxydopamineinjections into the VMT decreased dopamine levels by > 85%except in the prefrontal cortex (80% decrease) and the lateralstriatum (74% decrease).In Vitro Autoradiography of '2MI-NT Binding Sites. 6-

Hydroxydopamine lesioned neuroleptic-treated, and controlrats were sacrificed by decapitation and their brains werefrozen rapidly on dry ice. Sections (20 Am thick) were cutwith a cryostat at different levels, determined by using theatlas of Paxinos and Watson (24), to include the prefrontalcortex, the anterior nucleus accumbens, the central striatum,and the mesencephalic dopaminergic cell bodies. Sectionswere mounted onto gelatin-coated glass slides and stored at-80'C until the day of the experiment. For each level, 8-10sections were incubated for 60 min at 40C in a solutioncontaining 0.1 nM 1251I-NT (2000 Ci/mmol; 1 Ci = 37 GBq),50 mM TrisHCl buffer (pH 7.5), 5 mM MgCl2, 0.2% bovineserum albumin, and 20 ,M bacitracin (19, 20). Nonspecificbinding was determined in parallel incubations, which in-cluded 500 nM unlabeled NT (20).

Sections were washed four times for 2 min each in ice-cold50 mM TrisHCl buffer, dipped in distilled water, and driedunder a stream of cold air. Finally, they were opposed to 3HUltrofilm (LKB, Orsay, France) for 3 weeks at room tem-perature in the dark. Autoradiograms were analyzed quan-titatively with 125I standards using a densitometer (25, 26).Data are expressed as means ± SEM in fmol per mg ofprotein. Competition curves were obtained by incubatingbrain sections at the same anatomical levels with 0.1 nM125I-NT in the presence of increasing concentrations ofunlabeled NT. In each brain structure, optical densities forvarious concentrations of unlabeled NT were directly mea-sured on the film autoradiographs (25, 27). Values wereobtained by averaging six readings of different sections andconverted into fmol per mg of protein (26).

RESULTSEffects of VMT 6-Hydroxydopamine Lesions on 125I-NT

Binding. Six weeks following 6-hydroxydopamine lesions inthe VMT, very large decreases in 125I-NT binding wereobserved and quantified at the level of dopaminergic cellbodies (Fig. 1).

In forebrain areas innervated by dopaminergic neurons,the 6-hydroxydopamine lesions induced various effects on125I-NT binding (Fig. 2): although 125I-NT binding was re-duced in the central and lateral parts of the striatum, nosignificant modification was observed in the median part ofthe prefrontal cortex, the entorhinal cortex, and the nucleusaccumbens. Surprisingly, a significant increase in the densityof 1251-NT binding occurred in the lateral part ofthe prefrontalcortex just above the forceps minor (Fig. 3), an area knownto be innervated by dopaminergic fibers (28, 29).

Since slices were incubated with a single concentration of'25I-NT (0.1 nM) much lower than the Kd value (5 nM; ref.

0

c00

100-0aRc

z

Z 50-m

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Structures Containing DopaminergicCell Bodies and/or Dendrites

CENTRAL LATERALIN VT.A SNC SNC SNR

-17% -18%

-61% -70% -76% -59% -46%

TuT JT*

Eli Controls m 6-OHDA -VMT Lesioned

= Neuroleptic treated

FIG. 1. Effects of 6-hydroxydopamine (6-OHDA) injections intothe VMT and treatment by the long-acting neuroleptic pipotiazinepalmitic ester on the `25I-NT binding in structures containingdopaminergic cell bodies and/or dendrites. The interfascicular nu-cleus (IN) and the ventral tegmental area (VTA) correspond to themedioventral and lateral parts of the VMT, respectively. Eight to 10slide-mounted sections taken at the level of SN and VMT wereincubated in the presence of 0.1 nM '251-NT. After 3 weeks ofexposure, the autoradiograms of the sections were used to estimatethe optical density in the different structures. Using 125I standards,the measures were converted to fmol per mg of protein (26). Theresults are the mean ± SEM of 8-10 readings. The control valueswere 11.4 ± 0.6, 10.5 ± 0.4, 10.5 ± 0.5, 9.9 ± 0.4, and 5.4 ± 0.3 fmolper mg of protein in the interfascicular nucleus, ventral tegmentalarea, central SN compacta (SNC), lateral SN compacta, and SNreticulata (SNR), respectively. +, P < 0.05; *, P < 0.01 [significantlydifferent from control values (Student's t test)].

20), competition curves were also constructed to investigatewhether the modifications in binding observed in variousdopaminergic areas were due to a change in the numberand/or in the affinity of the binding sites (Fig. 4). The resultsobtained were in good agreement with those reported in Figs.1 and 2, with 125I-NT binding in lesioned animals beingincreased in the lateral prefrontal cortex, unaffected in thenucleus accumbens, and decreased in the lateral striatum andthe ventral tegmental area. In addition, comparison of theconcentrations ofNT required to decrease 125I-NT binding by50% in the lateral part of the prefrontal cortex revealed thatthere was no important difference in the apparent affinity ofNT binding sites between control and lesioned rats (Fig. 4),suggesting that the increase of 125I-NT binding is due to achange in the number of 125I-NT binding sites.A high density of 125I-NT binding sites was also seen in

several structures devoid of dopaminergic nerve terminals orcell bodies. Although a complete quantitative analysis of theeffect of the 6-hydroxydopamine lesions was not made in allthese brain structures, no modification in 125I-NT bindingcould be detected in those examined (Table 1).

Effects of Pipotiazine Palmitate Treatment on '25I-NT Bind-ing. The increase in 125I-NT binding observed in the lateralpart of the prefrontal cortex following destruction of theascending dopaminergic fibers suggested that the blockade ofdopamine transmission was responsible for the increase inthe number of NT binding sites. To test this hypothesisfurther, DA transmission was blocked chronically by along-acting neuroleptic, the pipotiazine palmitic ester.

Six weeks after the onset of the neuroleptic treatment(three injections), either no change or a small reduction in125I-NT binding occurred in the VMT and the SN (Fig. 1). On

6204 Neurobiology: Herve et al.

Proc. Natl. Acad. Sci. USA 83 (1986) 6205

Dopaminergic Terminal Fields

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the contrary, marked modifications of 1251-NT binding wereobserved in structures innervated by dopaminergic neurons(Fig. 2): indeed, 1251I-NT binding was increased in almost allthe structures examined, with the lateral striatum being theonly one in which no significant change was observed.Complementary binding experiments using membrane prep-arations demonstrated that pipotiazine palmitate treatmentproduced no change in the affinity of 125I-NT binding sites inthe prefrontal cortex, suggesting that the changes describedabove were due mainly to modifications in the number of125I-NT binding sites (data not shown).

Control

I________ FIG. 2. Effects of 6-hydroxydopamine (6-Lateral OHDA) injections into the VMT and treatment byStriatum the long-acting neuroleptic pipotiazine palmitic

ester on the "-'I-NT binding in structures inner--61% vated by dopaminergic terminals. The "1I-NT

binding in the lateral and median parts of theprefrontal cortex was estimated in the deep layersdorsal and medial, respectively, to the forceps

w, minor. The same experimental procedures wereused as in Fig. 1. The results are the mean

±SEM

of 8-10 determinations. The control values were4.8 ± 0.2,7.1 ± 0.4,3.0 ± 0.1,2.8 ± 0.2,3.8 ± 0.2,

* and 5.2 ± 0.2 fmol per mg of protein in the lateral0 and median parts of the prefrontal cortex, the

entorhinal cortex, the nucleus accumbens, and thecentral and lateral striatum, respectively. *, P <0.01 [significantly different from control values(Student's t test)].

Except in the nucleus of the diagonal band of Broca, whereslight reduction of 1251-NT binding was detected, no)dification of 125I-NT binding was seen in several structures-her devoid of dopaminergic innervation or poorly inner-ted by dopaminergic neurons (Table 1).

DISCUSSIONe present study was designed to investigate the influencedopamine neurotransmission on NT binding sites located)stsynaptically to dopaminergic neurons. To this end,iantitative autoradiographic analysis of 125I-NT binding in

6-OHDA lesionedA

B

FIG. 3. Examples of autoradiograms of '25I-NT binding sites in coronal brain sections of control and 6-hydroxydopamine (6-OHDA)-VMTlesioned rats. Slices were incubated with 0.1 nM '25I-NT and autoradiograms were used as negatives, so the highest density of 251I-NT bindingsites correspond to the brightest areas. Sections were located, respectively, at 4.2 mm (A) and 0.7 mm (B) anterior and 5.3 mm (C) posteriorto the bregma according to the atlas of Paxinos and Watson (24). (A) High densities of 125I-NT binding sites were observed in the deep layersof the prefrontal cortex. In the control brain, 125I-NT binding site density was higher in the median part of the prefrontal cortex (black arrows)than in the lateral part (white arrows), while in the 6-hydroxydopamine lesioned brain, 251I-NT binding was more evenly distributed. (B) A largedecrease of 125I-NT binding site density was observed in the striatum of the 6-hydroxydopamine lesioned animals, while the nucleus accumbensdid not seem to be affected. (C) The 6-hydroxydopamine injections into the VMT induced a large decrease of 125I-NT binding sites in the VMTand SN. Parallel immunohistochemical experiments have shown that, in SN of lesioned animals, 125I-NT binding sites were observed only inareas where dopaminergic cells were present.

Neurobiology: Herve et al.

Proc. Natl. Acad. Sci. USA 83 (1986)

NUCLEUS ACCUMBENS

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FIG. 4. Competition curves of 125I-NT binding by unlabeled NTin control and 6-hydroxydopamine (6-OHDA)-VMT lesioned rats.Brain sections were incubated with 0.1 nM 125I-NT in the presenceof increasing concentrations of unlabeled NT. Optical densities wereobtained for each brain region by averaging six readings of adjacentsections. SEM values for each point were always <6% of the mean.VTA corresponds to the ventral tegmental area. Nonspecific bindinghas not been subtracted. 0

dopaminergic-innervated areas of rat brain was performedfollowing 6-hydroxydopamine lesions of ascending dopamin-ergic neurons, or after treatment with a long-acting neuro-leptic, the pipotiazine palmitic ester. Both treatments inter-

Table 1. Effects of 6-hydroxydopamine injections into the VMTand treatment by the long-acting neuroleptic pipotiazine palmiticester on the 125I-NT binding in structure poorly innervated bydopaminergic fibers

1II-NT binding, fmol per mg of protein

6-Hydroxydopamine- Neuroleptic-Control VMT lesioned treated

Posteriorcingulatecortex 8.5 ± 0.3 7.8 ± 0.3 8.4 ± 0.3

Recessushippocampi 13.0 ± 0.6 14.4 ± 0.3 13.8 ± 0.5

Island ofCalleja 9.6 ± 0.6 10.8 ± 0.5 10.8 ± 0.4

Posteriorrhinalcortex 8.8 ± 0.2 8.7 ± 0.3 7.7 ± 0.3

Insularcortex 9.6 ± 0.2 9.7 ± 0.2 9.2 ± 0.3

Diagonalband ofBroca 10.4 ± 0.4 9.8 ± 0.3 7.1 ± 0.4*

Corticalnucleus ofamygdala 9.0 ± 0.6 10.9 ± 0.5 9.6 ± 0.4

Ventralhippocampus 6.1 ± 0.6 7.0 ± 0.6 7.3 ± 0.6

Optical densities were obtained from autoradiograms of sectionsincubated with 0.1 nM 1251-NT. Values are the means ± SEM of8-10determinations and are expressed in fmol per mg of protein.*P < 0.01 [significantly different from control values (Student's ttest)].

rupt dopamine transmission, but 6-hydroxydopamine lesionsdestroy NT binding sites located on dopaminergic neuronalcell bodies and fibers (presynaptic NT binding sites) whileneuroleptic treatment preserves them. As a consequence, ifpostsynaptic NT binding sites are regulated by dopaminergicinnervation, it is expected that 6-hydroxydopamine lesionswill modify the density of both pre- and postsynaptic NTbinding sites, while neuroleptic treatment will change onlypostsynaptic NT binding sites.For instance, our data in the SN and VMT show a marked

decrease in 125I-NT binding in 6-hydroxydopamine lesionedanimals and, in contrast, no change or a slight decrease inneuroleptic-treated animals. This indicates that a large pro-portion of NT binding sites are located on dopaminergicperikarya and dendrites in the SN and VMT, thus confirmingthe results of others (17, 18). This is also in good agreementwith the finding that the degeneration of cell bodies inParkinson disease is associated with an almost total disap-pearance ofNT binding sites in the SN (30, 31). However, thelack of effect of neuroleptic treatment on 125I-NT binding inthe SN is at variance with recent results of Uhl and Kuhar (32)who reported that [3H]NT binding was enhanced in the SN ofrats and humans after repeated treatment with neuroleptics.No explanation can yet be provided for this discrepancy, butour results clearly show that pipotiazine palmitate treatmentdoes not increase the number of NT binding sites located ondopaminergic neurons.At the level of subcortical dopaminergic terminal fields,

various situations arise. Similar to the SN and VMT, thelateral striatum shows a large decrease in 125I-NT bindingfollowing 6-hydroxydopamine lesions and no change afterneuroleptic treatment. These results indicate, in agreementwith others (17), that NT binding sites are not only located ondopaminergic perikarya and dendrites but also on dopamin-ergic nerve terminals in the nigrostriatal dopamine pathway.The existence ofa large proportion ofpresynaptic NT bindingsites in the striatum agrees well with biochemical evidencethat NT exerts a presynaptic control on the release of striataldopamine (33, 34). In the nucleus accumbens, unlike in thestriatum, a 6-hydroxydopamine lesion does not affect 125I-NTbinding, whereas neuroleptic treatment increases 125I-NTbinding. It therefore appears that a substantial population ofNT binding sites are located postsynaptically to dopamin-ergic nerve terminals in the nucleus accumbens and that thesesites are up-regulated when dopamine transmission is inter-rupted. The apparent lack of reduction of NT binding in thenucleus accumbens of6-hydroxydopamine lesioned rats, alsonoted by others (17), may be interpreted as resulting from theconjunction of a loss ofpresynaptic NT binding sites togetherwith the appearance of new postsynaptic NT binding sites.The existence ofboth pre- and postsynaptic NT binding sitesin the nucleus accumbens is compatible with behavioral andbiochemical data showing that, in this brain area, NT affectsdopamine transmission at pre- and postsynaptic levels (13,35, §).Of great interest are the data obtained at the level of

cortical dopaminergic terminal fields. The distribution ofNTbinding sites in these brain areas following 6-hydroxydopa-mine lesion or neuroleptic treatment has not been previouslystudied. It is striking that '25I-NT binding is increased in theprefrontal and the entorhinal cortices following neuroleptictreatment. Furthermore, in 6-hydroxydopamine lesioned an-imals, NT binding is markedly increased in the lateralprefrontal cortex and slightly, although not significantly,increased in the median prefrontal cortex and in theentorhinal cortex. Our data favor the possibility that, in the

§Coquerel, A., Dubuc, I., Menard, J. F. & Constentin, J., 5thEuropean Winter Conference on Brain Research, March 11-16,1985, Vars, France, abstr.

6-

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6206 Neurobiology: Herve et al.

Proc. Natl. Acad. Sci. USA 83 (1986) 6207

lateral prefrontal cortex, the increase in NT binding resultedfrom an increased number of binding sites rather than from achange in affinity. It cannot be excluded that the 6-hydroxydopamine-induced increase in NT binding sites in thelateral prefrontal cortex might result from the destruction ofmixed NT/dopaminergic neurons. However, this is unlikelysince these neurons seem to be very sparse (8) and, in anycase, this hypothesis would not explain the effects of chronicblockade of dopamine receptors by the long-acting neuro-leptic. More likely, our results indicate that (i) in corticaldopaminergic terminal fields, there is an important propor-tion of postsynaptic NT binding sites, which is increased afterdopamine receptor blockade, and (ii) the destruction ofpresynaptic NT binding sites in 6-hydroxydopamine lesionedrats is more than compensated for by the appearance of newNT binding sites that results from dopamine transmissioninterruption, especially in the lateral prefrontal cortex.Our main conclusion is that dopaminergic neurons regulate

the density of NT binding sites on dopaminergic target cellsin several corticolimbic structures. Such a regulation ofreceptors by heterologous afferent fibers has already beenproposed by several authors. For instance, according toBrunello et al. (36), the desensitization of cortical f-adrener-gic receptors produced by chronic treatment with antidepres-sant drugs does not occur in the absence of serotonergicfibers. Similarly, the sensitivity of serotonin (5-HT1) recep-tors was modified by vasoactive intestinal peptide in arestricted zone of the hippocampus (37) and the density ofserotonin (5-HT2) receptors is increased when cortical slicesare incubated with isoproterenol (38). Finally, we haveshown that the development of D1 receptor supersensitivityin the prefrontal cortex, which occurred after denervation ofdopaminergic afferent fibers, was prevented by the absenceof noradrenergic fibers and that D1 receptor density in thenucleus accumbens was under the control of a corticonucleusaccumbens pathway that was probably glutamatergic(39-41).However, the influence of dopaminergic neurons on

postsynaptic 125I-NT binding sites could be indirect and couldinvolve local circuits. For instance, dopamine could mediateits effect through dopaminergic receptors located on NTneurons or nerve terminals. In this case, the increase in125I-NT binding would result from prolonged modifications ofNT release. Indeed, chronic treatments with neurolepticshave been shown to enhance NT levels in some cerebral areasinnervated by dopaminergic neurons in the rat brain and inthe cerebrospinal fluid of schizophrenic patients (42, 43). Inaddition, in a postmortem study, increased NT levels wereobserved in the prefrontal cortex (Brodman's area 32) ofschizophrenic patients (44). These observations, as well asthe heteroregulation of the density of corticolimbic I251-NTbinding sites by dopaminergic afferents described in thepresent study could suggest that some of the clinical effectsof neuroleptics seen in schizophrenic patients are partlymediated by changes in NT neurotransmission.

We thank Dr. C. Nemeroff for critical reading of the manuscript.This work has been supported in part by grants from Ministbre de laRecherche et de la Technologie (85.C.1139), Direction desRecherches ttudes et Techniques (83.084), and Rh6ne-PoulencSante.

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