Post-ischaemic Alteration of Excitatory Amino Acid Transport Sites in the Gerbil Hippocampus

Sodium-dependent [³H]d -aspartate binding as a marker of excitatory amino acid transport sites in the gerbil hippocampus was evaluated by quantitative receptor autoradiography 1 h to 7 days after transient cerebral ischaemia for 10 min. Sodium-dependent [³H]d -aspartate binding in the hippocampal CA1 and CA3 sectors significantly increased in the early post-ischaemic stage. After 7 days, a conspicuous elevation of sodium-dependent [³H]d -aspartate-binding was observed in the hippocampal CA1 sector and dentate gyrus. However, no significant change in the binding was found in the hippocampal CA3 sector. A histological study revealed that transient ischaemia caused severe neuronal damage in the hippocampal CA1 sector and mild damage in the hippocampal CA3 sector. However, no ischaemic neuronal damage was observed in the dentate gyrus. An immunohistochemical study also showed that numerous reactive astrocytes were evident in the hippocampus, particularly in the hippocampal CA1 sector, 7 days after ischaemia. These results demonstrate that transient cerebral ischaemia can cause marked elevation in excitatory amino-acid transport sites in the hippocampus. Furthermore, our results suggest that the post-ischaemic increase in excitatory amino acid transport sites might reflect expression of reactive astrocytes. These findings are of interest in relation to the mechanisms of ischaemic hippocampal damage.     

Long-term changes in gerbil brain neurotransmitter receptors following transient cerebral ischaemia.

1. Receptor autoradiographic and histological techniques were used to investigate long-term changes in the gerbil brain following transient cerebral ischaemia. 2. Transient ischaemia was induced for 3 min and 10 min, and the animals were allowed to survive for 8 months. 3. Histological examination revealed that 3 min ischaemia caused neuronal damage and mild shrinkage only in the hippocampal CA1 sector. Ten minutes of ischaemia produced severe neuronal damage in the striatum and the hippocampal CA1 and CA3 sectors. Considerable shrinkage was seen in the hippocampus; the dentate gyrus, however, was not damaged. 4. Three minutes of ischaemia produced changes in the binding of [3H]-quinuclidinylbenzilate ([3H]-QNB), [3H]-muscimol, and [3H]-MK-801 in various brain regions, as determined autoradiographically. In contrast, [3H]-cyclohexladenosine ([3H]-CHA) and [3H]-PN200-110 ([3H]-isradipine) binding in the brain was unaltered. 5. Ten minutes of ischaemia resulted in a major loss of neurotransmitter receptors, especially in the hippocampus. The substantia nigra showed a significant reduction in [3H]-CHA binding, whereas the striatum, which was morphologically damaged, showed no significant changes in any of the neurotransmitter receptors examined. 6. The results demonstrated that long-term survival after transient cerebral ischaemia produced alterations in neurotransmitter receptors, especially in the hippocampal formation, where considerable shrinkage was noted. These results also suggest that the hippocampal damage was not static, but progressive.     

Age-related Changes in [3H]Nimodipine and [3H]Rolipram Binding in the Rat Brain

Ageing is associated with changes in neurotransmission which might be correlated with abnormal calcium metabolism. Because there is evidence that nimodipine can enhance the learning abilities of ageing animals and rolipram can enhance the excitability of neurons, providing a functional basis for cognition-enhancing activity, age-related alterations in the binding of voltage-dependent L-type calcium channels and calcium/calmodulin-independent cyclic adenosine monophosphate-selective phosphodiesterase (cyclic-AMP PDE) were studied in 3-week- and 6-, 12-, 18- and 24-month-old Fisher 344 rats by use of receptor autoradiography. [³H]Nimodipine and [³H]rolipram were used to label the voltage-dependent L-type calcium channels and calcium/calmodulin-independent cyclic-AMP PDE, respectively. [³H]Nimodipine binding showed no obvious change in all brain areas of 12- and 18-month-old rats, as compared with 6-month-old animals. In 24-month-old rats, however, [³H]nimodipine binding increased significantly in the striatum and hippocampal CA3 sector. In contrast, [³H]rolipram binding showed no significant change in most brain areas during ageing, except for a transient change only in the hippocampal CA1 sector of 12-month-old animals. [³H]Nimodipine and [³H]rolipram binding showed a significant increase in some brain areas of 3-week-old rats compared with 6-month-old animals. The results indicate that in rats voltage-dependent L-type calcium channels are more susceptible to ageing processes than calcium/calmodulin-independent cyclic-AMP PDE. Our data also demonstrate that voltage-dependent L-type calcium channels and calcium/calmodulin-independent cyclic-AMP PDE might play roles in developmental processes. These findings might help further elucidation of the relationship between age-related neurological deficits and behavioural pharmacology including cognitive function.     

Persistent increase in striatal dopamine stimulated adenylate cyclase activity persists for more than 6 months but disappears after 1 year following withdrawal from 18 months cis-flupenthixol intake

Administration of cis-flupenthixol to rats for 18 months enhanced apomorphine-induced stereotyped behaviour, increased the number of specific [³H]spiperone binding sites in striatum and potentiated striatal dopamine stimulated cyclic AMP formation, but did not alter specific [³H]piflutixol binding. Following withdrawal of cis-flupenthixol intake, apomorphine-induced stereotypy returned to control values after 1 month and B_max for [³H]spiperone binding returned to normal after 3 months. In contrast, the increased dopamine stimulated adenylate cyclase activity remained elevated 6 months after drug removal, but was normal 1 year after drug withdrawal.     

Characterization and radioautography of [3H] LSD binding by rat brain slices in vitro: The effect of 5-hydroxytryptamine

Binding of D-[³H] lysergic acid diethylamide (LSD) to rat coronal brain slices and its blockade by 5-hydroxytryptamine (5-HT) had characteristics similar to those of brain homogenates in respect of K_D, kinetics and reversibility of binding. Radioautography was done on slices that had been incubated in 6 nM [³H] LSD and on adjacent slices incubated in the same concentration of tritiated LSD plus 10^?5 M of 5-HT. Choroid plexus showed densest labeling of [³H] LSD. In neuropil, dense labeling occurred within parts of the hippocampal formation except for fields CA2 and CA3 which were sparsely labeled. All layers of the cortex except the posterior cingulate gyrus were labeled by LSD. 5-HT blocked labeling of choroid plexus, hippocampal formation, septum, pons, medulla and parts of cortex but only reduced labeling of most other structures. LSD binding sites may relate to some of its pharmacological effects.     

从远志中分离鉴定出一种多巴胺受体活性化合物

从中药远志中提出一种多巴胺受体的配基,四氢非州防己胺。此化合物在体外可抑制[³H]SCH23390和[³H]螺哌隆与大鼠纹状体膜的结合,IC₅₀值分别为0.75±0.08μmol·L^-1和0.92±0.10μmol·L^-1。它在体外还能抑制[³H]哌唑嗪和大鼠脑皮质细胞膜结合(IC₅₀值为46μmol·L^-1),但不能改变[³H]QNB及[³H]muscimol对膜的结合。Scatchandplot分析显示此化合物对[³H]SCH23390和[³H]螺哌隆与膜结合的抑制作用是通过竞争性与非竞争性混合机制而实现的。     

Unusual binding of [3H] MDL 72222 in guinea pig hippocampus

[³H] MDL 72222 labeled a non-homogeneous population of sites in guinea pig hippocampal membranes (K_d1 = 1 nM; K_d2 = 60 nM). The binding was not sodium dependent. Competition studies with a variety of characterizing agents showed displacement of [³H] MDL 72222 binding by 5-HT uptake inhibitors. [³H] MDL 72222 binding was not effectively displaced by established 5-HT₃ antagonists. MDL 72222, fluoxetine, fluvoxamine and citalopram competitively inhibited the uptake of [³H] 5-HT into guinea pig hippocampal synaptosomes with K_i values of 1.97, 0.02, 0.023, 0.049 μM, respectively. The results demonstrate that [³H] MDL 72222 labels a non-homogeneous population of sites in guinea pig brain, as well as inhibiting 5-HT uptake into synaptosomal preparations.     

Autoradiographic analysis of dopamine D1 receptors in the gerbil brain following transient cerebral ischemia.

1. We studied the postischemic time-course of dopamine D1 receptors in selectively vulnerable areas in the gerbil using receptor autoradiography. 2. [3H]SCH 23390 was used to label dopamine D1 receptors and transient cerebral ischemia was induced for 10 min. 3. [3H]SCH 23390 binding showed no significant alteration in selectively vulnerable areas at an early stage (1-24 hr) of recirculation. Thereafter, [3H]SCH 23390 binding showed a significant reduction in most selectively vulnerable areas 48 hr or 7 days of recirculation. The ventromedial striatum and dentate gyrus which were resistant to ischemia also exhibited a significant reduction in [3H]SCH 23390 binding. 4. Especially, marked reduction was noted in the dorsolateral striatum. However, this reduction in the dorsolateral striatum was not seen early in the recirculation prior to morphological neuronal damage. 5. The result suggests that transient cerebral ischemia can cause a severe reduction in dopamine D1 receptors in most selectively vulnerable areas. Furthermore, they suggest that dopamine D1 transmission is not always responsible for the evolution of ischemic brain damage. 6. These findings are discussed in relation to the mechanism of ischemic brain damage.     

Regional in vivo binding of [3H]N-propylnorapomorphine in the mouse brain. Evidence for labelling of central dopamine receptors

Tain vein injections of [³H]N-propylnorapomorphine ([³H]NPA) in male mice resulted in a dose-related accumulation of radioactivity in the following brain regions: striatum (max), olfactory tubercle and cerebellum (min). The specific binding was saturable with increasing concentrations of the drug and stereospecifically displaced by (+)butaclamol. Dopamine agonists (apomorphine, NPA and bromocriptine) and antagonists (spiperone, haloperidol, (+)butaclamol and l-sulpiride) all caused dose-dependent prevention of [³H]NPA binding. Mianserin, phenoxybenzamine and propranolol did not prevent the in vivo [³H]NPA binding suggesting that [³H]NPA binds specifically to dopamine receptors in the striatum and the olfactory tubercle of the mouse.     

Serotonin-sensitive adenylate cyclase and [3H]serotonin binding sites in the CNS of the rat—II: Respective regional and subcellular distributions and ontogenetic developments

The 5-HT receptor linked to adenylate cyclase and the high affinity binding site of [³H]5-HT were compared on the basis of their localization and ontogenetic changes in the CNS of the rat. Subcellular fractionation of cerebral tissues from newborn rats showed a good correlation between the distributions of 5-HT-sensitive cyclase and [³H]5-HT binding sites, with the mitochondrial fraction exhibiting the highest specific adenylate cyclase activity and density of binding sites. There was also a good correlation between the regional distributions of the cyclase and the binding in the CNS of newborn rats. However, when the regional distribution of [³H]5-HT binding in newborns was compared to that of adults, no correlation was found, showing that large changes were occurring during ontogenesis. In the cortex and hippocampus, there was little change in the amount of 5-HT-sensitive adenylate cyclase during development whereas [³H]5-HT binding increased approximately 7-fold from birth to adulthood. Only in the striatum was there a positive correlation between the changes in the cyclase and the binding. The injection of kainic acid into the striatum of 10-day-old rats produced large decreases in both DA-and 5-HT-sensitive adenylate cyclase activities. The specific binding of [³H]5-HT was also reduced in the injected striatum but to a smaller extent. Therefore, the 5-HT-sensitive adenylate cyclase but not the [³H]5-HT-high affinity binding site appeared to be preferentially associated with neurons destroyed by kainic acid, i.e. neurons intrinsic to the striatum. The findings that the 5-HT-sensitive adenylate cyclase and the [³H]5-HT binding sites can develop independently and are localized, at least partly, on different types of cells provide additional evidence for the existence of multiple types of 5-HT receptors in the CNS of the rat.     

Binding of adenosine receptor ligands to brain of adenosine receptor knock-out mice: evidence that CGS 21680 binds to A1 receptors in hippocampus

The adenosine receptor agonist 2-[p-(2-carboxyethyl)phenylethylamino]-5-N-ethylcarboxamidoadenosine (CGS 21680) is generally considered to be a selective adenosine A_2A receptor ligand. However, the compound has previously been shown to exhibit binding characteristics that are not compatible with adenosine A_2A receptor binding, at least in brain regions other than the striatum. We have examined binding of [³H]CGS 21680 and of antagonist radioligands with high selectivity for adenosine A₁ or A_2A receptors to hippocampus and striatum of mice lacking either adenosine A₁ (A1R^(–/–)) or A_2A (A2AR^(–/–)) receptors. Both receptor autoradiography and membrane binding techniques were used for this purpose and gave similar results. There were no significant changes in the binding of the A₁ receptor antagonist [³H]DPCPX in mice lacking A_2A receptors, or in the binding of the A_2A receptor antagonists [³H]SCH 58261 and [³H]ZM 241385 in mice lacking A₁ receptors. Furthermore, [³H]CGS 21680 binding in striatum was abolished in the A2AR^(–/–), and essentially unaffected in striatum from mice lacking A₁ receptors. In hippocampus, however, binding of [³H]CGS 21680 remained in the A2AR^(–/–), whereas binding was virtually abolished in the A1R^(–/–). There were no adaptive alterations in A_2A receptor expression in this region in A1R^(–/–) mice. Thus, most of the [³H]CGS 21680 binding in hippocampus is dependent on the presence of adenosine A₁ receptors, but not on A_2A receptors, indicating a novel binding site or novel binding mode.     

Tetanic stimulation-induced changes in [3H]glutamate binding and uptake in rat hippocampus

Tetanus-induced (400 Hz, 200 pulses) long-lasting potentiation of the stratum radiatum-evoked CA1 population spike in hippocampal slices is not accompanied by any change in Na+-independent [3H]glutamate binding sites. Homosynaptic depression that occurs subsequent to either a low frequency tetanus (20 Hz, 600 pulses) or a transient exposure to Cl(-)-free (containing NO3-) medium is associated with an elevation in the amino acid binding. [3H]Glutamate uptake into slices was decreased following a high frequency (400 Hz, 200 pulses) tetanus but in the majority of cases was increased following a low frequency (20 Hz, 600 pulses) tetanus to stratum radiatum. When the high frequency tetanus was given in the absence of extracellular Ca2+, there was a further reduction in [3H]glutamate uptake.     

Sodium dependent [3H]cocaine binding associated with dopamine uptake sites in the rat striatum and human putamen decrease after dopaminergic denervation and in Parkinsons disease

Summary The binding of radiolabelled cocaine, an inhibitor of dopamine uptake, to the post-mortem human putamen was studied and compared to that in the rat striatum. Saturation analysis of [³H]cocaine binding to the human putamen revealed the presence of a high affinity component of binding with a K _d of 0.21 mol/l and a B _max of 1.47 pmol/mg protein. In addition a low affinity component (K _d=26.4 mol/l) was demonstrated, having a B _max of 42.2 pmol/mg protein. Also in the rat striatum [³H]cocaine binding was both of high affinity (K _d=0.36 mol/l, B _max=5.56 pmol/mg protein) and low affinity (K _d=25.9 mol/l, B _max=35.6 pmol/mg protein). A pharmacological characterisation of high affinity [³H]cocaine binding to rat striatal membranes clearly indicates an association with the neuronal dopamine transporter. The IC₅₀ values of 8 selected drugs for inhibition of [³H]cocaine binding in the rat striatum were highly significantly correlated with their potency to inhibit [³H]dopamine uptake into slices of the rat striatum. [³H]Cocaine binding was stereospecifically inhibited by (+)nomifensine and (+)diclofensine which were 50–80-fold more active than their respective (-)isomers. Drugs with dopamine releasing activity were more potent at inhibiting [³H]dopamine uptake than at competing for the high affinity site of [³H]cocaine binding. A highly significant correlation was found between IC₅₀ values for [³H]cocaine binding in the rat striatum and the human putamen. Further evidence in support of an association of [³H]cocaine binding in the rat striatum with the dopamine transporter was obtained from lesion studies. Thus, intranigral 6-hydroxydopamine administration produced a marked (67%) decrease in striatal [³H]cocaine binding. Also in the human putamen high affinity [³H]cocaine binding sites appear localized on dopaminergic nerve terminals as evidenced by a prominent decrease in binding in the putamen obtained from subjects with Parkinsons disease. It is concluded that [³H]cocaine may be a useful ligand to examine the dopamine transporter in the rat striatum and the human putamen. Therefore it offers a new and valuable approach in the study of drug effects and neuropsychiatric diseases.Preliminary results on some parts of this study have appeared previously in abstract form (Langer et al. 1984a) or as a rapid communication (Pimoule et al. 1983)     

Kainic acid lesions of striatum and decortication reduce specific [3H]sulpiride binding in rats,so D-2 receptors exist post-synaptically on corticostriate afferents and striatal neurons

Unilateral kainic acid lesions of rat striatum reduced specific striatal [³H]spiperone and [³H]sulpiride binding sites (Bmax) by 52 and 67% respectively compared with the intact side. The dissociation constant (K_D) for [³H]spiperone binding was unchanged but that for [³H]]sulpiride binding was reduced. Specific striatal [³H]spiperone and [³H]sulpiride binding was reduced by 22 and 37% respectively in unilateral decorticate animals, but there was no change in K_D. Unilateral 6-hydroxydopamine lesions of the medial forebrain bundle caused no change in striatal [³H]spiperone binding sites or K_D value, but produced a 27% increase in [³H]sulpiride binding sites with no change in K_D. These data support the hypothesis of D-2 receptors located on cortico-striate glutamate fibres, but also indicate the presence of both D-1 and D-2 receptors on the cell bodies of striatal neurons.     

Multiple [3H]-nemonapride binding sites in calf brain

[³H]-Nemonapride has been the ligand of choice to label D₄ dopamine receptors. Its specificity was questioned when it was discovered that sigma (σ) sites were also labeled by [³H]-nemonapride. To further characterize the binding of [³H]-nemonapride, three areas of calf brain (striatum, frontal cortex and cerebellum) were examined. In all three areas, [³H]-nemonapride labeled multiple sites. Dopaminergic and σ sites were the most prominent. The σ binding profile was σ-1 like with a K_i binding profile as follows (in order of decreasing potency): haloperidol, PPAP, pentazocine, DTG, U-50488, R(+)-3-PPP. Experiments using sulpiride and pentazocine to block striatal dopaminergic and σ sites, respectively, revealed additional, not previously characterized binding sites for [³H]-nemonapride. One component which was present in striatum but not in frontal cortex or cerebellum, had affinity for some neuroleptics and WB-4101, but not for typical serotonergic agents. Thus, [³H]-nemonapride has no selectivity for dopamine receptors unless stringent experimental conditions are met. Received: 19 September 1996 / Accepted: 12 March 1997     

In vivo [3H]spiperone binding to the rat hippocampal formation: Involvement of dopamine receptors

The existence of DA receptors in the rat hippocampus was demonstrated with an in vivo [³H]spiperone radio-receptor assay. Kinetic studies revealed that maximum binding of [³H]spiperone in hippocampus was much smaller than in striatum and frontal cortex but much higher than in cerebellum. In inhibition studies of [³H]spiperone binding, all neuroleptics tested were active in hippocampus as well as in striatum. In contrast, 5HT antagonists were definetely less potent in these two brain regions than in frontal cortex. Finally, even when 5HT receptors were blocked, dipropyl-ATN and haloperidol remained fully effective in hippocampus, striatum, but also in frontal cortex although to a lesser degree. From these results it was concluded that [³H]spiperone binds mainly to DA receptors in hippocampus as well as in striamtum, whereas both 5HT and DA receptors are present in frontal cortex.     

Chronic haloperidol and clozapine administration increases the number of cortical NMDA receptors in rats

The aim of the present study was to examine the influence of 3-month administration of haloperidol (1 mg/kg per day) and clozapine (30 mg/kg per day) in drinking water on cortical NMDA (N-methyl-d-aspartate) receptors in rats. On day 5 of withdrawal, the animals were killed and their brains were removed. The binding of [³H]MK-801 ([³H](5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine) and [³H]CGP 39653 ([³H]d,l-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic acid) to NMDA receptors in different cortical areas, as well as the binding of [³H]spiperone to dopamine D₂ receptors in the striatum, were analysed by quantitative autoradiography. Haloperidol increased the binding of [³H]CGP 39653 in frontal, insular and parietal cortices. Clozapine increased the binding of [³H]CGP 39653 in insular and parietal cortices. Haloperidol, but not clozapine, increased the binding of [³H]spiperone in the striatum. None of the neuroleptics influenced the binding of [³H]MK-801 to cortical NMDA receptors. An additional assay revealed an increase in the B _max value, with no significant changes in the K _D of [³H]CGP 39653 binding in parieto-insular cortical homo-genates as a result of haloperidol and clozapine administration. The present results suggest that long-term treatments with haloperidol and clozapine increase the number of NMDA receptors in different cortical regions. Received: 15 September 1998 / Accepted: 25 January 1999     

Localization of [3H]gabapentin to a novel site in rat brain: autoradiographic studies

The autoradiographical distribution of [³H]gabapentin, the tritiated analogue of the novel anticonvulsant gabapentin (1-(aminomethyl)cyclohexaneacetic acid) was measured in rat brain. Binding to sections was uniformly inhibited by non-radioactive gabapentin and 3-isobutyl-γ-aminobutyric acid (3-isobutyl-GABA). Specific gabapentin binding sites were unevenly distributed throughout the brain with the highest level being found in the outer layers of the cerebral cortex (38 ± 7 fmol/mm²; n = 3) and the lowest amounts in the white matter. In the hippocampus, the distribution of the binding site paralleled the excitatory neuronal input with the highest levels of binding being measured in the outer layers of the dentate gyrus and in the dendritic regions of the CA1 pyramidal cell layer. The binding site appeared absent from the cell body region of granule and pyramidal cells. Lesions performed unilaterally in the striatum using quinolinic acid resulted in a marked loss of [³H]gabapentin binding sites as compared with sham-lesioned animals, suggesting the binding site was localized on neuronal cell bodies. These data complement and extend the results of experiments using [³H]gabapentin with homogenates of rat brain and show the discrete localization of this novel binding site in regions associated with excitatory amino acid input. The data do not support previous indications of an association of the gabapentin binding site and NMDA/glycine receptor complex.     

Radiolabeling of dopamine uptake sites in mouse striatum: comparison of binding sites for cocaine,mazindol, and GBR 12935

Summary This study addressed the possibility of a unique binding interaction between cocaine and the dopamine transporter as compared with other blockers of dopamine uptake. Cocaine binding sites in a fresh P₂ fraction of mouse striatum were labeled with [³H]CFT, a phenyltropane analog of cocaine also known as WIN 35,428, and compared with sites labeled with [³H]mazindol or [³H]GBR 12935. Under the conditions used, homogeneous binding was observed that was inhibited monophasically by cocaine, CFT, and mazindol; the same potencies were observed with the three radioligands. Saturation analysis in the presence and in the absence of unlabeled inhibitor (CFT, mazindol, cocaine) indicated a change in the K_d but not the B_max, consonant with a competitive mechanism. Tris-HCl reduced the affinity of each radioligand and unlabeled inhibitor without changing the B_max. N-Ethylmaleimide reduced the binding of all radioligands equally and cocaine offered protection. The dissociation rate of [³H]CFT and [³H]mazindol binding was not affected by the presence of mazindol and CFT, respectively. The B_max of [³H]CFT and [³H]mazindol binding was the same; the relatively higher value for [³H]GBR 12935 binding in analyses involving varying tritiated GBR 12935 only, was due primarily to an underestimation of the specific activity of [³H]GBR 12935. All results are in agreement with a one-site model in which cocaine, CFT, mazindol, and GBR 12935 share a common binding site in mouse striatum.     

Long-Term Alterations in Benzodiazepine,Muscarinic and α-Amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) Receptor Density Following Continuous Cocaine Administration

Abstract: Animal models of clinical phenomena, such as stimulant-induced psychosis have focused primarily on persisting alterations that develop in brain after chronic stimulant administration. The present study utilized autoradiographic measures to examine changes in the density of benzodiazepine ([³H] flunitrazepam), muscarinic ([³H] quinuclidinyl benzilate), and non-NMDA glutamatergic (³H α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid: AMPA) receptor binding in rats 21 days following two exposures to cocaine administered continuously for 5 days via subcutaneous pellets. A marked, selective increase in [³H] flunitrazepam binding in both the lateral and medial habenula nucleus was observed. Reduced [³H] quinuclidinyl benzilate binding was observed in various brain areas, including large decreases in the anterior cingulate cortex and ventral thalamus. A reduction in [³H]AMPA binding was observed in the ventral striatum and was suggested in the nucleus accumbens. [³H] Flunitrazepam binding was also examined 12 hr following a single 5 day cocaine exposure to determine if the long-term habenular changes were evident at acute withdrawal. No alterations in [³H] flunitrazepam binding were observed in the habenula or any other structure analyzed at this time point. The relation of these results to persisting alterations in mesocorticolimbic pathways and previous findings of cocaine-induced degeneration in lateral habenula circuitry is discussed.