Biochemical characterization of a thrombin inhibitor from the bloodsucking bug Dipetalogaster maximus

From the bloodsucking bug Dipetalogaster maximus, a protein with anticoagulant activity was isolated and biochemically characterized. The isolated protein, named dipetalogastin, possesses an average molecular mass of 11.8 kD. Its N-terminal sequence shows homology to rhodniin, a thrombin inhibitor isolated from the bug Rhodnius prolixus. The in vitro anticoagulant activity of dipetalogastin occurs via the inhibition of thrombin. The anticoagulant and thrombin inhibitory potency of dipetalogastin is comparable to that of recombinant hirudin. Its specific thrombin inhibitory activity is 9,300 antithrombin units/mg protein. Dipetalogastin forms only 1:1 molar complexes with thrombin. It is a tight-binding inhibitor of thrombin possessing a dissociation constant of 125 fM. It does not inhibit factor Xa or alpha-chymotrypsin and only weakly inhibits trypsin.

Plasma levels of interleukin-6, interleukin-10, and interleukin-1 receptor antagonist in depression: comparison between the acute state and after remission

There is now some evidence that major depression is accompanied by an immune response with an increased production of pro-inflammatory cytokines. The aim of the present study was to examine serum level of cytokines: interleukin-6 (IL-6), which is considered pro-inflammatory one and anti-inflammatory cytokines: interleukin 10 (IL-10), and interleukin-1 receptor antagonist (IL-1Ra) in acute clinical state of depression and after 6-week antidepressant treatment. Serum IL-6, IL-10, IL-1Ra levels were higher in the subjects with major depression than in normal controls although these results were not statistically significant. The mean score according to the Hamilton Depression Rating Scale (HDRS) in the patients significantly decreased during the 6 weeks of the study, demonstrating an overall improvement. Successful antidepressant treatment had no significant effect on serum level of this cytokines.

Meizothrombin, an intermediate of prothrombin activation, stimulates human glioblastoma cells by interaction with PAR-1-type thrombin receptors

Thrombin induces well-characterized effects on normal and neoplastic brain cells by interaction with protease-activated receptor (PAR)-type thrombin receptors. However, nothing is known about the function of intermediate enzymes of prothrombin activation recently shown to evoke PAR-1-mediated signaling in smooth muscle cells. Therefore, we investigated the effect of recombinant human meizothrombin (rMT), one of thrombin's catalytically active precursor enzymes in the prothrombin cleavage cascade, on calcium mobilization in human SNB-19 glioblastoma cells. By using reverse-transcription polymerase chain reaction, immunofluorescence studies with a monoclonal anti-PAR-1 antibody and calcium measurements, SNB-19 cells were shown to express functional PAR-1-type thrombin receptors. PAR-1 is not only a receptor for thrombin in SNB-19 cells but was also activated by rMT very effectively. Under the conditions used in our experiments, SNB-19 cells stimulated with thrombin after rMT challenge were unable to elicit a new calcium response and vice versa. In addition, both rMT and thrombin induced no further calcium signal after that observed with the PAR-1-activating peptide SFLLRN. Therefore, rMT and thrombin seem to activate calcium signaling by similar mechanisms including PAR-1. Our results demonstrate rMT as a potent activator of PAR-1-type thrombin receptors in SNB-19 glioblastoma cells, suggesting a function of catalytically active thrombin precursor enzymes in cells of glial origin.

Noradrenergic lesion antagonizes desipramine-induced adaptation of NMDA receptors

Repeated administration of the tricyclic antidepressant, desipramine, for 28 days to mice effected a decrease in the potency of glycine to displace [3H]5,7-dichlorokynurenic acid (5,7-DCKA) in mouse cortical homogenates. Pre-treatment with the noradrenergic neurotoxin DSP-4, while having no effect alone, attenuated the desipramine-induced effect. The present findings support a norepinephrine-dependent adaptation of the NMDA receptor complex in vivo following chronic desipramine treatment. The inter-relationship of norepinephrine and glutamate transmission may provide insight into the mechanism underlying the action of antidepressant drugs.

Hirudin treatment in a breastfeeding woman

We report on a breastfeeding woman with deep venous thrombosis treated with hirudin because of heparin-induced thrombocytopenia, in whom hirudin was not detectable in human breastmilk.

The two-receptor system PAR-1/PAR-4 mediates alpha-thrombin-induced [Ca(2+)](i) mobilization in human astrocytoma cells

The proteinase-activated receptor 1 (PAR-1) was characterized as a functional receptor for thrombin in cells from different brain tumor entities. Whether PAR-1 alone accounts for thrombin-induced effects in human cancer cells, or whether other PAR contribute is unknown. We established primary cultures from two neurosurgically removed human astrocytomas and investigated intracellular signaling roles of PAR-1 and PAR-4 by estimating the effect of alpha-thrombin and PAR-activating peptides on [Ca(2+)](i) mobilization in single astrocytoma cells. alpha-Thrombin or the PAR-1-activating peptide SFLLRN induced a transient calcium mobilization. This suggests the involvement of PAR-1 in alpha-thrombin-induced calcium signaling in human astrocytoma cells. In addition, a second, PAR-4-dependent, mechanism exists. This was deduced from the findings that a further calcium signal could be observed in human astrocytoma cells stimulated with alpha-thrombin after SFLLRN and the PAR-4-activating peptide GYPGQV also induced a calcium response. In addition, the observation that trypsin, known to activate both PAR-2 and PAR-4, but not the specifically PAR-2-activating peptide SLIGRL induced calcium signaling is a further indication of functional PAR-4-type thrombin receptors in human astrocytoma cells. This is the first report demonstrating a signaling role for a dual thrombin receptor system in human tumor cells.

HELLP syndrome with haemaglobin vasospasm

The syndrome of haemolysis, elevated liver enzymes and low platelets (HELLP syndrome) is a life threatening, severe complication of pre-eclampsia with typical laboratory findings. An unusual case of a 36-year-old woman with HELLP syndrome and the initial complication of intracerebral haemorrhage is presented. The diagnosis of HELLP syndrome was confirmed by elevated liver enzymes, low platelets, increased total bilirubin and increased lactate dehydrogenase. The intracranial haematoma was removed with good neurological recovery ensuing. However, this case was complicated by cerebral vasospasm on the eleventh day, confirmed by cerebral angiography and computer tomographic findings. The patient died from brain swelling. Possible vasospam should be considered during the treatment of patients with HELLP syndrome.

Alterations in serum and brain trace element levels after antidepressant treatment. Part II. Copper

We have studied the effect of chronic treatment with imipramine, citalopram, and electroconvulsive shock (ECS) on serum and brain copper levels in rats. Chronic treatment with citalopram and imipramine (but not ECS) significantly (approx 14%) decreased the serum copper level. Chronic treatment with both drugs did not alter the brain copper level. However, chronic ECS induced a significant increase (by 36%) in the copper level in the hippocampus and also in the cerebellum (by 16%). In contrast to the zinc, where both pharmacologic and ECS treatment increased its hippocampal concentration, these two antidepressant therapy (drugs versus ECS) differ in their effect on brain copper level. These findings suggest that the mechanism by which copper is involved in ECS differs from that of any involvement in the action of the drugs studied.

Dipetalogastin, a potent thrombin inhibitor from the blood-sucking insect. Dipetalogaster maximus cDNA cloning, expression and characterization

A cDNA coding for the thrombin inhibitor dipetalogastin has been isolated from a stomach library of Dipetalogaster maximus, a blood-sucking insect. The open reading frame of the cloned inhibitor cDNA codes for a protein of 344 amino-acid residues. Sequence analysis reveals the existence of three repeated homologous main regions, indicating that the inhibitor consists of three domains. Each domain shows a double-headed structure with an internal sequence homology like rhodniin, the thrombin inhibitor from the blood-sucking insect Rhodnius prolixus. Peptide sequence comparisons of the deduced amino-acid sequence exhibit a high homology of the domains I and II to the natural inhibitor dipetalogastin from the stomach content of D. maximus and to rhodniin, respectively. Significant sequence similarities to Kazal-type inhibitors, like the conserved sequence CGXDXXTYXNXC and several cysteine residues, indicate that the thrombin inhibitor from D. maximus is a further blood-sucking insect which belongs to the Kazal-type family (besides rhodniin). A biologically active recombinant protein corresponding to domain II of the dipetalogastin cDNA was expressed in Escherichia coli. The isolated recombinant dipetalogastin with a molecular mass of 12.91 kDa has proved to be a specific thrombin inhibitor similar to its natural counterpart as well as rhodniin and hirudin. The Ki value of the recombinant dipetalogastin was determined to be 49.3 +/- 22.28 fM.

In vitro study of r-hirudin permeability through membranes of different haemodialysers

BACKGROUND

After introducing the specific thrombin inhibitor recombinant hirudin (r-hirudin) into clinical practice in cases of heparin-induced thrombocytopenia (HIT, type II) the possibility of its use as an anticoagulant during haemodialysis treatment in HIT II patients is being discussed more frequently. On the one hand, the efficient, safe and routine use of r-hirudin during haemodialyses, including the maintenance of a therapeutic blood level, presupposes that no r-hirudin will leave the circulation by passing through the dialyser membrane. On the other hand, it is important to have dialysers whose permeability to r-hirudin allows its efficient removal from the human body because, to date, no antidote is commercially available in cases of dangerously high blood concentrations of r-hirudin.

METHODS

An in vitro circulation model was used to study the r-hirudin permeability of some low- and high-flux dialysers. As r-hirudin-containing vehicles, both albumin-containing saline solution and bovine blood were circulated in the blood space of the system for 2 h. Transmembrane r-hirudin passage was tested by measuring r-hirudin concentration both in the blood and dialysate space fluids using the ecarin clotting time (ECT).

RESULTS

Low-flux dialysers with membranes made from polysulfone or regenerated cellulose proved to be almost impermeable to r-hirudin. In contrast, other low-flux membranes were partly permeable to r-hirudin (e.g. Hemophan) or even almost completely permeable (e.g. cellulose acetate). All high-flux dialysers tested were permeable to r-hirudin.

CONCLUSIONS

Only low-flux dialysers with polysulfone or regenerated cellulose membranes proved to be suitable for r-hirudin use in routine haemodialysis therapy. Other low-flux, and all high-flux, capillaries are permeable to r-hirudin and offer the possibility of lowering toxic r-hirudin concentrations after overdosing.

Is serum copper a "trait marker" of unipolar depression? A preliminary clinical study

Depression is not a homogenous illness and is diagnosed in only one in three persons suffering from this disorder. Besides psychological-psychiatric diagnostic methods (e.g. Hamilton's, Beck's rating scales), some biochemical measures have been introduced as markers of depression. However, the sensitivity of even the best characterized dexamethasone suppression test is as low as 40-50%. A search for better markers is continuously in progress. In the present study, we investigated alterations in serum copper concentrations in depressive patients before, during and after antidepressant treatment and compared these values with the concentrations in healthy volunteers. The serum copper concentration in depression is significantly higher (by 21%) than in the control. However, effective antidepressant treatments (which reduced symptoms by ca. 50% measured by Hamilton Depression Rating Scale) did not affect (did not normalize) this increased copper concentration. The present data indicate that serum copper is a "trait marker" (remains constant regardless of successful treatment) of unipolar depression.

Heterozygous prothrombin gene mutation: a new risk factor for early renal allograft thrombosis

BACKGROUND

Underlying thrombophilic disorders increase the risk of early allograft loss after renal transplantation. We report three cases of early graft thrombosis in two carriers of a recently discovered prothrombotic variation of the prothrombin gene.

CASE REPORTS

The first patient, an adolescent girl, developed multiple thrombotic shunt occlusions after the initiation of hemodialysis until continuous cumarin anticoagulation was instituted. During living-related kidney transplantation, peracute thrombosis of the renal arteries and veins occurred during surgery despite excellent intraoperative conditions and continuous low-dose heparinization. A few hours after reperfusion of the organ by immediate thrombectomy and intrarenal fibrinolysis, an irreversible rethrombosis occurred. A detailed evaluation of the coagulation system showed highly elevated prothrombin protein activity and concentrations. A heterozygous G-->A transition at position 20210 of the prothrombin gene was identified. Hemodialysis was resumed using recombinant hirudin, a direct and selective thrombin inhibitor, as an anticoagulant. The second patient, a girl with end-stage renal failure due to atypical hemolytic uremic syndrome, lost two cadaver kidney allografts, each time by massive thrombosis a few days after transplantation. In this patient also, elevated prothrombin activity and concentrations were present and a heterozygous G-->A transition at position 2210 of the prothrombin gene was detected.

CONCLUSIONS

The prothrombin gene mutation is a new risk factor for thrombotic complications both on hemodialysis and after renal transplantation. It may be useful to screen for this disorder in the pretransplant thrombophilia work-up.

The activity of rat brain nitric oxide synthase following chronic antidepressant treatment

Nitric oxide synthase (NOS) is an enzyme involved in the activation of the glutamate/NMDA receptor-induced cascade of events. In this study we investigated the NOS activity in different rat brain regions after chronic electroconvulsive, imipramine and citalopram treatments. Chronic electroconvulsive treatment significantly increased the NOS activity (by 49%) in the cerebral cortex. However, chronic treatment with imipramine or citalopram did not alter the activity of NOS in all examined brain regions (cortex, hippocampus or cerebellum). The increased NOS activity after electroconvulsive but not pharmacologic (imipramine or citalopram) treatment may well reflect the differences between the adaptive changes of the NMDA receptor complex induced by these treatments.

R-hirudin as anticoagulant in regular hemodialysis therapy: finding of therapeutic R-hirudin blood/plasma concentrations and respective dosages

Recently heparin-induced thrombocytopenia type II has been diagnosed more frequently and does not exclude hemodialysis patients. Up to now, recombinant hirudin is the only available anticoagulant showing no immunologic cross reactions with heparin. However, the use of r-hirudin in hemodialysis patients with different degrees of residual renal functions is impossible using standard dosages because elimination of r-hirudin varies depending on the degree of residual renal function. Therefore the first study was carried out using consecutive r-hirudin anticoagulated hemodialyses to determine the appropriate dose of r-hirudin. Ten hemodialysis patients with creatinine clearance values ranging between 0 and 13 mL/min/1.73m2 were anticoagulated with r-hirudin. An initial bolus of 0.1 mg/kg bwt before the first hemodialysis, resulted in an average r-hirudin blood concentration of 305 ng/mL at the end of treatment. The dose for each of the following four hemodialyses was adjusted individually to reach the minimum therapeutic r-hirudin blood concentration. At the end of these treatments the mean blood r-hirudin concentration was 422 ng/mL. The necessary mean doses ranged between 0.008 and 0.125 mg/kg bwt correlating to the creatinine clearance values of the patients. All hemodialyses of the study were effective and safe. Bleeding times determined during r-hirudin anticoagulation were significantly lower than control values measured 2 days after a heparin administration. The study proved that r-hirudin may be an efficient and safe heparin alternative as a hemodialysis anticoagulant when the individual's residual renal function is noted for dosage and dose adjustment and is controlled by drug monitoring using the ecarin clotting time.

Presence of the proteinase-activated receptor-2 (PAR-2) in human brain tumor cells--trypsin- and SLIGRL-induced calcium response in primary cultured meningiomas

This study focused on proteinase-activated receptor-2 (PAR-2) in primary cultured human meningioma cells. Stimulation of these cells with the serine proteinase trypsin resulted in a dose-dependent transient calcium response. Since the specific PAR-2 agonist peptide SLIGRL also induced [Ca2+]i mobilization in human meningioma cells and successive application of SLIGRL and trypsin elicited no new calcium signal we conclude that trypsin-induced calcium signaling is mediated by PAR-2 in human meningioma cells. To our knowledge, this is the first report describing functional PAR-2-type receptors in human brain tumor cells.

Sites of elimination and pharmacokinetics of recombinant [131I]lepirudin in baboons

Lepirudin has a short half-life, and only 50-60% of the intravenously administered dose is excreted by the kidneys. The fate of the remainder is unknown. We designed a study to determine the fate of this lepirudin. In each of six baboons, [131I]lepirudin was given intravenously as a bolus or infused over 30 min, 24 h apart. The in vivo redistribution of [131I]lepirudin was determined and quantified by scintillation camera imaging. In all studies, the half-life of [131I]lepirudin, as determined from the disappearance of radioactivity, was 21 +/- 3 min. The half-life determined from the disappearance of lepirudin, measured by the Ecarin Clotting Time (ECT) method, was similar at 23 +/- 8 min. Results obtained with the labeled lepirudin are therefore comparable with those obtained using the plasma concentration of lepirudin. When lepirudin was administered as a bolus, the half-life was 18 +/- 4 min, and lepirudin was cleared from the plasma at a rate of 42 +/- 12 mL/min and by the kidneys at 23 +/- 2 mL/min. Following infusion over 30 min, the half-life and total and renal clearances were not significantly different. In both studies, between 50 and 60% of the administered lepirudin was excreted by the kidney. Studies on sacrificed baboons showed that appreciable amounts of lepirudin were present in the bile, indicating the liver as a contributor to the elimination of lepirudin.

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-10,1 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 Bmax 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.

Evidence for proteinase-activated receptor-2 (PAR-2)-mediated mitogenesis in coronary artery smooth muscle cells

1. This study investigates, whether in addition to the thrombin receptor (PAR-1), the proteinase-activated receptor-2 (PAR-2) is present in vascular smooth muscle cells (SMC) and mediates mitogenesis. PAR-2 is activated by low concentrations of trypsin and the synthetic peptide SLIGRL. 2. Stimulation of bovine coronary artery SMC by trypsin (2 nM) caused a 3 fold increase in DNLA-synthesis. A similar effect was observed with 10 nM thrombin. Trypsin-induced mitogenesis was inhibited by soybean trypsin inhibitor, indicating that the proteolytic activity of the enzyme was required for its mitogenic effect. 3. The specific PAR-2-activating peptide SLIGRL or the PAR1-activating peptide SFFLRN did not elicit mitogenesis. 4. When the SMC were exposed to SLIGRL (40 nM), a homologous desensitization of cytosolic Ca2+ mobilization was found after subsequent stimulation with trypsin (40 nM) but not thrombin (15 nM). 5. Trypsin (2 nM) as well as SLIGRL (100 microm) activated the nuclear factor KB (NFkappaB) with a maximum response 2 h after stimulation of the SMC. This suggests that both agonists acted via a common receptor, PAR-2. Maximum activation of NFkappaB by thrombin (10 nM) was detected after 4-5 h. 6. These data suggest that PAR-2 is present in coronary SMC and mediates a mitogenic response. Activation of NFkappaB via either PAR-1 or PAR-2 does not predict mitogenesis.

PAR 1-type thrombin receptors are involved in thrombin-induced calcium signaling in human meningioma cells

Thrombin is known to play a role as regulator in tumor spreading and tumor growth. Proteinase-activated receptor 1 (PAR 1)-type thrombin receptors were identified in different cancer cells including human glioblastoma cells. Thus a function of PAR 1 in brain tumors may be suggested. In this study, the presence of PAR 1-type thrombin receptors was investigated in primary cell cultures established from operated human meningiomas from two 59- and 79-year-old women. Characterization of PAR 1 on binding level was performed using immunofluorescence studies with the monoclonal anti-PAR 1 antibody Mab 61-1 directed against a domain in the NH2-terminus of PAR 1. These binding sites constitute functional thrombin receptors that are involved in thrombin-induced signaling in human meningioma cells as demonstrated by investigation of alpha-thrombin- and PAR 1-activating hexapeptide (TRAP-6)-induced [Ca2+]i mobilization. To our knowledge, this is the first report demonstrating thrombin-induced intracellular signaling in human meningioma cells mediated by the PAR 1-type thrombin receptor.

Dural arteriovenous malformation in the anterior cranial fossa

Two cases of dural arteriovenous malformation (AVM) at the base of the anterior cranial fossa are described. In both cases an intracerebral hematoma following the rupture of the AVM was the first indication of the disease. In one case, the malformation was supplied both by the anterior ethmoidal artery and frontopolar artery draining into the superior sagittal sinus. In the second case, the right anterior ethmoidal artery with draining veins into the superior sagittal sinus and sphenoparietal sinus was the feeding vessel. Surgical evacuation of the hematoma and excision of the malformation was performed on both patients. The typical clinical signs and radiological findings are described. A review of the pertinent literature is given.

Preoperative functional magnetic resonance imaging (fMRI) of the motor system in patients with tumours in the parietal lobe

Intracranial lesions may compromise structures critical for motor performance, and mapping of the cortex, especially of the motor hand area, is important to reduce postoperative morbidity. We investigated nine patients with parietal lobe tumours and used functional MRI sensitized to changes in blood oxygenation to define the different motor areas, especially the primary sensorimotor cortex, in relation to the localization of the tumour. Activation was determined by pixel-by-pixel correlation of the signal intensity time course with a reference waveform equivalent to the stimulus protocol. All subjects showed significant activation of the primary sensorimotor cortex while performing a finger opposition task with the affected and unaffected side. In five patients the finger opposition task additionally activated the ipsilateral sensorimotor cortex and the supplementary motor area (SMA). Extension and flexion of the foot, additionally performed in two patients, also activated the sensorimotor cortex, in one case within the perifocal oedema of the tumour. Tumour localization near the central sulcus induced displacement of the sensorimotor cortex as compared to the unaffected side in all patients with a relevant mass effect. The results of our study demonstrate that functional MRI at 1.5 T with a clinically used tomograph can reproducibly localize critical brain regions in patients with intracranial lesions.

Differential effects of EGF on repair of cellular functions after dichlorovinyl-L-cysteine-induced injury

This study examined the repair of renal proximal tubule cellular (RPTC) functions following sublethal injury induced by the nephrotoxicant S-(1,2-dichlorovinyl)-L-cysteine (DCVC). DCVC exposure resulted in 31% cell death and loss 24 h following the treatment. Monolayer confluence recovered through migration/spreading but not proliferation after 6 days. Basal, uncoupled, and ouabain-sensitive oxygen consumption (QO2) decreased 47, 76, and 62%, respectively, 24 h after DCVC exposure. Na+-K+-ATPase activity and Na+-dependent glucose uptake were inhibited 80 and 68%, respectively, 24 h after DCVC exposure. None of these functions recovered over time. Addition of epidermal growth factor (EGF) following DCVC exposure did not prevent decreases in basal, uncoupled, and ouabain-sensitive QO2 values and Na+-K+-ATPase activity but promoted their recovery over 4-6 days. In contrast, no recovery of Na+-dependent glucose uptake occurred in the presence of EGF. These data show that: 1) DCVC exposure decreases mitochondrial function, Na+-K+-ATPase activity, active Na+ transport, and Na+-dependent glucose uptake in sublethally injured RPTC; 2) DCVC-treated RPTC do not proliferate nor regain their physiological functions in this model; and 3) EGF promotes recovery of mitochondrial function and active Na+ transport but not Na+-dependent glucose uptake. These results suggest that cysteine conjugates may cause renal dysfunction, in part, by decreasing RPTC functions and inhibiting their repair.

Influence of long-lasting administration of neuroleptics on cortical NMDA receptors and phencyclidine-induced deficit in the sensorimotor gating in rats

The aim of this study was to examine the role of cortical NMDA receptors in the antipsychotic action of neuroleptics. Haloperidol (1 mg/kg/day) and clozapine (30 mg/kg/day) were administered to rats in drinking water. Autoradiographic and saturation binding analyses showed that a 3-month treatment with both haloperidol and clozapine increased the density of NMDA receptors labelled with [3H]CGP 39653 (a competitive antagonist) in the parietal and insular cortices. Haloperidol additionally increased the binding of that ligand in the frontal cortex. None of those neuroleptics influenced the binding of [3H]MK-801, an uncompetitive antagonist of NMDA receptors, in the frontal, parietal or insular cortices. A 6-week and a 3-month treatment with haloperidol antagonized the deficit of prepulse inhibition induced by phencyclidine (5 mg/kg s.c.). In contrast, short-term (4-day) administration of that neuroleptic was ineffective. The present study suggests that the increased density of cortical NMDA receptors, induced by long-term neuroleptic administration, may overcome the deficit of sensorimotor gating induced by phencyclidine. However, contribution of such an effect to the antipsychotic activity needs to be established.