Comparison of motor performance, brain biochemistry and histology of two A30P α-synuclein transgenic mouse strains

Three point mutations in the SNCA gene encoding α-synuclein (aSyn) have been associated with autosomal dominant forms of Parkinson's disease. To better understand the role of the A30P mutant aSyn, we compared two transgenic mouse strains: a knock-in mouse with an introduced A30P point mutation in the wild-type (WT) gene (Snca(tm(A30P))) and a transgenic (Tg) mouse overexpressing the human A30P aSyn gene under the prion promoter [tg(Prnp-SNCA A30P)]. The brain aSyn load, motor performance, brain dopamine (DA) and sensitivity to 6-hydroxydopamine (6-OHDA) were studied in these mice. aSyn was evidently accumulating with age in all mice, particularly in tg(Prnp-SNCA A30P) Tg mice. There were no robust changes in basal locomotor activities of the mice of either line at 6 months, but after 1 year, tg(Prnp-SNCA A30P) Tg mice developed severe problems with vertical movements. However, the younger Tg mice had a reduced locomotor response to 1mg/kg of d-amphetamine. Snca(tm(A30P)) mice with the targeted mutation (Tm) were slightly hyperactive at all ages. Less 6-OHDA was required in tg(Prnp-SNCA A30P) Tg (1 μg) than in WT (3μg) mice for an ipsilateral rotational bias by d-amphetamine. That was not seen with the Snca(tm(A30P)) strain. A small dose of 6-OHDA (0.33 μg) led to contralateral rotations and elevated striatal DA in Tg/Tm mice of both lines but otherwise 6-OHDA-induced striatal DA depletion was similar in all mice, indicating no A30P-aSyn-related toxin sensitivity. 3,4-Dihydroxyphenylacetic acid/DA-ratio was elevated in tg(Prnp-SNCA A30P) mice, suggesting an enhanced DA turnover. This ratio and homovanillic acid/DA-ratio were declined in Snca(tm(A30P)) mice. Our results demonstrate that the two differently constructed A30P-aSyn mouse strains have distinct behavioral and biochemical characteristics, some of which are opposite. Since the two lines with the same background were not identically produced, the deviations found may be partially caused by factors other than aSyn-related genetic differences.

A prolyl oligopeptidase inhibitor, KYP-2047, reduces α-synuclein protein levels and aggregates in cellular and animal models of Parkinson's disease

BACKGROUND AND PURPOSE

The aggregation of α-synuclein is connected to the pathology of Parkinson's disease and prolyl oligopeptidase (PREP) accelerates the aggregation of α-synuclein in vitro. The aim of this study was to investigate the effects of a PREP inhibitor, KYP-2047, on α-synuclein aggregation in cell lines overexpressing wild-type or A30P/A53T mutant human α-syn and in the brains of two A30P α-synuclein transgenic mouse strains.

EXPERIMENTAL APPROACH

Cells were exposed to oxidative stress and then incubated with the PREP inhibitor during or after the stress. Wild-type or transgenic mice were treated for 5 days with KYP-2047 (2 × 3 mg·kg(-1) a day). Besides immunohistochemistry and thioflavin S staining, soluble and insoluble α-synuclein protein levels were measured by Western blot. α-synuclein mRNA levels were quantified by PCR. The colocalization of PREP and α-synuclein,and the effect of KYP-2047 on cell viability were also investigated.

KEY RESULTS

In cell lines, oxidative stress induced a robust aggregation of α-synuclein,and low concentrations of KYP-2047 significantly reduced the number of cells with α-synuclein inclusions while abolishing the colocalization of α-synuclein and PREP. KYP-2047 significantly reduced the amount of aggregated α-synuclein,and it had beneficial effects on cell viability. In the transgenic mice, a 5-day treatment with the PREP inhibitor reduced the amount of α-synuclein immunoreactivity and soluble α-synuclein protein in the brain.

CONCLUSIONS AND IMPLICATIONS

The results suggest that the PREP may play a role in brain accumulation and aggregation of α-synuclein, while KYP-2047 seems to effectively prevent these processes.

Prolyl oligopeptidase induces angiogenesis both in vitro and in vivo in a novel regulatory manner

BACKGROUND AND PURPOSE A serine protease, prolyl oligopeptidase (POP) has been reported to be involved in the release of the pro-angiogenic tetrapeptide acetyl-N-Ser-Asp-Lys-Pro (Ac-SDKP) from its precursor, 43-mer thymosin β4 (Tβ4). Recently, it was shown that both POP activity and the levels of Ac-SDKP are increased in malignant tumours. The aim of this study was to clarify the release of Ac-SDKP, and test if POP and a POP inhibitor, 4-phenyl-butanoyl-L-prolyl-2(S)-cyanopyrrolidine (KYP-2047), can affect angiogenesis. EXPERIMENTAL APPROACH We used HPLC for bioanalytical and an enzyme immunoassay for pharmacological analysis. Angiogenesis of human umbilical vein endothelial cells was assessed in vitro using a 'tube formation' assay and in vivo using a Matrigel plug assay (BD Biosciences, San Jose, CA, USA) in adult male rats. Moreover, co-localization of POP and blood vessels was studied. KEY RESULTS We showed the sequential hydrolysis of Tβ4: the first-step hydrolysis by proteases to <30-mer peptides is followed by an action of POP. Unexpectedly, POP inhibited the first hydrolysis step, revealing a novel regulation system. POP with Tβ4 significantly induced, while KYP-2047 effectively prevented, angiogenesis in both models compared with Tβ4 addition itself. POP and endothelial cells were abundantly co-localized in vivo. CONCLUSIONS AND IMPLICATIONS We have now revealed that POP is a second-step enzyme in the release of Ac-SDKP from Tβ4, and it has novel autoregulatory effect in the first step. Our results also advocate a role for Ac-SDKP in angiogenesis, and suggest that POP has a pro-angiogenic role via the release of Ac-SDKP from its precursor Tβ4 and POP inhibitors can block this action.

Epithelial transport and deamidation of gliadin peptides: a role for coeliac disease patient immunoglobulin A

In coeliac disease, the intake of dietary gluten induces small-bowel mucosal damage and the production of immunoglobulin (Ig)A class autoantibodies against transglutaminase 2 (TG2). We examined the effect of coeliac patient IgA on the apical-to-basal passage of gluten-derived gliadin peptides p31-43 and p57-68 in intestinal epithelial cells. We demonstrate that coeliac IgA enhances the passage of gliadin peptides, which could be abolished by inhibition of TG2 enzymatic activity. Moreover, we also found that both the apical and the basal cell culture media containing the immunogenic gliadin peptides were able to induce the proliferation of deamidation-dependent coeliac patient-derived T cells even in the absence of exogenous TG2. Our results suggest that coeliac patient IgA could play a role in the transepithelial passage of gliadin peptides, a process during which they might be deamidated.

Inhibitors of catechol-O-methyltransferase sensitize mice to pain

BACKGROUND AND PURPOSE

Catechol-O-methyltransferase (COMT) inhibitors are used in Parkinson's disease in which pain is an important symptom. COMT polymorphisms modulate pain and opioid analgesia in humans. In rats, COMT inhibitors have been shown to be pro-nociceptive in acute pain models, but also to attenuate allodynia and hyperalgesia in a model of diabetic neuropathy. Here, we have assessed the effects of acute and repeated administrations of COMT inhibitors on mechanical, thermal and carrageenan-induced nociception in male mice.

EXPERIMENTAL APPROACH

We used single and repeated administration of a peripherally restricted, short-acting (nitecapone) and also a centrally acting (3,5-dinitrocatechol, OR-486) COMT inhibitor. We also tested CGP 28014, an indirect inhibitor of COMT enzyme. Effects of OR-486 on thermal nociception were also studied in COMT deficient mice. Effects on spinal pathways were assessed in rats given intrathecal nitecapone.

KEY RESULTS

After single administration, both nitecapone and OR-486 reduced mechanical nociceptive thresholds and thermal nociceptive latencies (hot plate test) at 2 and 3 h, regardless of their brain penetration. These effects were still present after chronic treatment with COMT inhibitors for 5 days. Intraplantar injection of carrageenan reduced nociceptive latencies and both COMT inhibitors potentiated this reduction without modifying inflammation. CGP 28014 shortened paw flick latencies. OR-486 did not modify hot plate times in Comt gene deficient mice. Intrathecal nitecapone modified neither thermal nor mechanical nociception.

CONCLUSIONS AND IMPLICATIONS

Pro-nociceptive effects of COMT inhibitors were confirmed. The pro-nociceptive effects were primarily mediated via mechanisms acting outside the brain and spinal cord. COMT protein was required for these actions.

Degradation of coeliac disease-inducing rye secalin by germinating cereal enzymes: diminishing toxic effects in intestinal epithelial cells

Currently the only treatment for coeliac disease is a lifelong gluten-free diet excluding food products containing wheat, rye and barley. There is, however, only scarce evidence as to harmful effects of rye in coeliac disease. To confirm the assumption that rye should be excluded from the coeliac patient's diet, we now sought to establish whether rye secalin activates toxic reactions in vitro in intestinal epithelial cell models as extensively as wheat gliadin. Further, we investigated the efficacy of germinating cereal enzymes from oat, wheat and barley to hydrolyse secalin into short fragments and whether secalin-induced harmful effects can be reduced by such pretreatment. In the current study, secalin elicited toxic reactions in intestinal Caco-2 epithelial cells similarly to gliadin: it induced epithelial cell layer permeability, tight junctional protein occludin and ZO-1 distortion and actin reorganization. In high-performance liquid chromatography and mass spectroscopy (HPLC-MS), germinating barley enzymes provided the most efficient degradation of secalin and gliadin peptides and was thus selected for further in vitro analysis. After germinating barley enzyme pretreatment, all toxic reactions induced by secalin were ameliorated. We conclude that germinating enzymes from barley are particularly efficient in the degradation of rye secalin. In future, these enzymes might be utilized as a novel medical treatment for coeliac disease or in food processing in order to develop high-quality coeliac-safe food products.

Importance of membrane-bound catechol-O-methyltransferase in L-DOPA metabolism: a pharmacokinetic study in two types of Comt gene modified mice

BACKGROUND AND PURPOSE

Catechol-O-methyltransferase (COMT) metabolizes compounds containing catechol structures and has two forms: soluble (S-COMT) and membrane-bound (MB-COMT). Here we report the generation of a mouse line that expresses MB-COMT but not S-COMT. We compared the effects of deleting S-COMT only or both COMT forms on the pharmacokinetics of oral L-DOPA.

EXPERIMENTAL APPROACH

L-DOPA (10 mg kg(-1)) and carbidopa (30 mg kg(-1)) were given to mice by gastric tube, and samples were taken at various times. HPLC was used to measure L-DOPA in plasma and tissue samples, and dopamine and its metabolites in brain. Immunohistochemistry and Western blotting were used to characterize the distribution of COMT protein isoforms.

KEY RESULTS

Lack of S-COMT did not affect the levels of L-DOPA in plasma or peripheral tissues, whereas in the full COMT-knock-out mice, these levels were increased. The levels of 3-O-methyldopa were significantly decreased in the S-COMT-deficient mice. In the brain, L-DOPA levels were not significantly increased, and dopamine was increased only in females. The total COMT activity in the S-COMT-deficient mice was 22-47% of that in the wild-type mice. In peripheral tissues, female mice had lower COMT activity than the males.

CONCLUSIONS AND IMPLICATIONS

In S-COMT-deficient mice, MB-COMT in the liver and the duodenum is able to O-methylate about one-half of exogenous L-DOPA. Sexual dimorphism and activity of the two COMT isoforms seems to be tissue specific and more prominent in peripheral tissues than in the brain.

Expression and traffic of cellular prolyl oligopeptidase are regulated during cerebellar granule cell differentiation, maturation, and aging

Prolyl oligopeptidase (POP) is an endopeptidase which cleaves short proline-containing neuropeptides, and it is involved in memory and learning. POP also has an intercellular function mediated through the inositol pathway, and has been involved in cell death. POP has been early considered as a housekeeping enzyme, but the recent research indicates that POP expression is regulated across tissues and intracellularly. In the brain, POP is exclusively expressed in neurons and most abundantly in pyramidal neurons of cerebral cortex, in the CA1 field neurons of hippocampus and in cerebellar Purkinje's cells. Intracellularly, POP is mainly present in the cytoplasm and some in intracellular membranes, like rough endoplasmic reticulum and Golgi apparatus. In this paper, we systematically studied the levels of expression of POP along the life of cerebellar granule cells (CGC) in culture and the distribution of POP within different intracellular compartments. We used the tight-binding inhibitor JTP-4819 covalently coupled with fluorescein (FJTP) as a tool to study the changes on expression and localization of POP protein. Our results indicate that POP activity levels are regulated during the life of the neurons. POP was found mainly in cytoplasm and neuronal projections, but at an early developmental phase significant amounts were found also in nuclei. Along the life of the neurons, POP activity fluctuated in 7-day cycles. In young neurons, the cytosolic POP activity was low but increased by maturation so that the activity peak coincided with full differentiation. Over aging, cytoplasmic POP was concentrated around nucleus, but the activity decreased with time. POP was also present in vesicles across the neuron. No major changes were seen in the nuclear or membrane bound POP over aging until activity disappeared upon neuronal death. This is the first time when POP was found in the nuclei of human neuronal cells.

On the role of prolyl oligopeptidase in health and disease

Prolyl oligopeptidase (POP) is a serine peptidase which digests small peptide-like hormones, neuroactive peptides, and various cellular factors. Therefore, this peptidase has been implicated in many physiological processes as well as in some psychiatric disorders, most probably through interference in inositol cycle. Intense research has been performed to elucidate, on the one hand, the basic structure, ligand binding, and kinetic properties of POP, and on the other, the pharmacology of its inhibitors. There is fairly strong evidence of in vivo importance of POP on substance P, arginine vasopressin, thyroliberin and gonadoliberin metabolism. However, information about the biological relevance of POP is not yet conclusive. Evidence regarding the physiological role of POP is lacking, which is surprising considering that peptidase inhibitors have been exploited for drug development, some of which are currently in clinical trials as memory enhancers for the aged and in a variety of neurological disorders. Here we review the recent progress on POP research and evaluate the relevance of the peptidase in the metabolism of various neuropeptides. The recognition of novel forms and relatives of POP may improve our understanding of how this family of proteins functions in normal and in neuropathological conditions.

Increased p53 levels without caspase-3 activity and change of cell viability in 6-hydroxydopamine-treated CV1-P cells

The effect of 6-hydroxydopamine (6-OHDA) on the level of p53 protein, the activity of caspase-3 and the nuclear morphology-based assessment of cell viability were compared in the nonneuronal CV1-P fibroblast and neuronal SH-SY5Y neuroblastoma cells. The level of p53 protein was increased in the low-dose range (<100 micromol/L) in both cell types, particularly in fibroblasts. In the neuroblastoma cells, a moderate p53 increase paralleled the elevated caspase-3 activity and apoptotic cell behavior. Interestingly, in the fibroblasts at the low 6-OHDA concentrations, p53 remained high during the whole experiment, and there was neither significant caspase-3 activity nor cell death. In the high-dose range (>100 micromol/L), the increase of p53 was reduced and the cell death was predominantly necrotic as judged from the nuclear morphology in both fibroblasts and neuroblastoma cells. Also, the caspase-3 activity was reduced in SH-SY5Y cells. In contrast to some earlier reports, we have shown that the actual 6-OHDA sensitivity of nonneuronal cells may be equal or even higher than that in neuronal cells if the enhancement of p53 levels is used as a criterion for the response. However, the 6-OHDA toxicity was clearly higher in the neuronal than in fibroblast cells.

Effects of aqueous extracts of Halimeda incrassata (Ellis) Lamouroux and Bryothamnion triquetrum (S.G.Gmelim) Howe on hydrogen peroxide and methyl mercury-induced oxidative stress in GT1-7 mouse hypothalamic immortalized cells

The current investigation focuses attention on the neuroprotective and antioxidant properties of aqueous extracts from Halimeda incrassata (Hi) and Bryothamniom triquetrum (Bt) in the mouse immortalized hypothalamic GT1-7 cell line. Under basal oxidative conditions, Hi extract reduces intracellular reactive oxygen species production, as assessed by 2',7'-dichlorofluorescein fluorescence, while Bt extract does not contribute to basal ROS generation. Both extracts, at concentrations higher than 0.20 mg/ml, exert protection against hydrogen peroxide-mediated cell death, although only Hi extract can additionally prevent hydrogen peroxide-induced ROS production. The two seaweed aqueous extracts, at concentrations higher than 0.05 mg/ml, also display protection against neuronal death induced by methyl mercury chloride, as well as against methyl mercury chloride-mediated ROS generation. None of the extracts increase GSH intracellular pools, in basal conditions, after depleting its levels with either hydrogen peroxide or methyl mercury chloride. Some comments on the probable targets of the neuroprotection exerted by these two extracts are included in this paper.

Cholecystokinin2 receptor-deficient mice display altered function of brain dopaminergic system

RATIONALE

Cholecystokinin (CCK) has been shown to coexist and interact with dopamine in the regulation of behaviour. Two different CCK receptors (CCK1 and CCK2) have an opposite influence on the activity of dopamine neurons. Stimulation of CCK2 receptors decreases the release of dopamine and that receptor could mediate the neuroleptic-like effect of CCK.

OBJECTIVE

To investigate the activity of the dopaminergic system in pharmacological experiments on CCK2 receptor (CCK2R)-deficient mice.

METHODS

We used age- and sex-matched littermates in all our experiments. To evaluate the behavioural differences, we performed the rotarod test and measured the locomotor activity of animals using computer-connected photoelectric motility boxes. Amphetamine and apomorphine, two dopaminergic drugs with different pharmacodynamic properties, were used to influence the activity of the dopaminergic system in the brain. Neurochemical differences related to the different genotype were analysed by means of high-performance liquid chromatography and radioligand binding studies.

RESULTS

Motor co-ordination was significantly impaired in the rotarod test of CCK2R receptor-deficient mice. Moreover, the locomotor activity of heterozygous (+/-) and homozygous (-/-) CCK2R receptor-deficient mice was somewhat reduced. A low dose of apomorphine (0.1 mg/kg), an unselective agonist of dopamine receptors, suppressed locomotor activity significantly more in homozygous (-/-) and heterozygous (+/-) mutant mice than in their wild-type (+/+) littermates. Amphetamine (3-6 mg/kg), increasing release of dopamine from the presynaptic terminals, caused a dose-dependent motor stimulation in wild-type (+/+) mice. In heterozygous (+/-) and homozygous (-/-) mice, a lower dose of amphetamine (3 mg/kg) did not alter the locomotor activity, whereas the higher dose of (6 mg/kg) induced a significantly stronger increase in locomotor activity in homozygous (-/-) mice than in their heterozygous (+/-) and wild-type (+/+) littermates. Despite the changes in the action of apomorphine and amphetamine in homozygous (-/-) mice, we did not find any significant differences in the concentration of dopamine and their metabolites in the striatum or cortex. However, the density of dopamine D2 receptors was significantly increased in the striatum of homozygous (-/-) animals compared with wild-type (+/+) mice.

CONCLUSIONS

The targeted mutation of the CCK2 receptor gene induced gene dose-dependent changes in the activity of the dopaminergic system. The sensitivity of presynaptic dopamine receptors was increased in heterozygous (+/-) and homozygous (-/-) animals, whereas the increase in sensitivity of postsynaptic dopamine receptors was apparent only in homozygous (-/-) mice.

Synthesis and in-vitro/in-vivo evaluation of orally administered entacapone prodrugs

Entacapone is a new inhibitor of catechol-O-methyltransferase (COMT) that is used as an adjunct to L-dopa therapy in the treatment of Parkinson's disease. The bioavailability of orally administered entacapone is, however, relatively low (29-46%). In this study we have prepared more lipophilic acyl and acyloxyacyl esters, an acyloxy alkyl ether and an alkyloxycarbonyl ester of entacapone, and we have evaluated them as potential prodrugs to enhance the oral bioavailability of entacapone. All the derivatives fulfilled prodrug criteria and released entacapone in human serum in-vitro. The oral bioavailability of monopivaloyl (1a) and dipivaloyl (1b) esters of entacapone were investigated further in rats. The lipophilicity of 1b was high (log Papp 4.0 at pH 7.4) but its oral bioavailability was low (F = 0.6%), most probably due to its low aqueous solubility. The monopivaloyl ester of entacapone (1a) had a higher lipophilicity (log Papp 0.80) than entacapone (log Papp 0.18) at pH 7.4 while maintaining an aqueous solubility equal to entacapone. However, oral bioavailability was not increased when compared with the parent drug entacapone (F = 7.0% and 10.4%, respectively).

Efficient transfection of novel bovine papillomavirus 1 expression plasmids

A series of novel bovine papillomavirus type 1 (BPV-1)-based expression plasmids was constructed and characterized in vitro as a starting point for the development of an in vivo gene therapeutic method. The order of transfection efficiency for different pBPVlacZ plasmids was pCGalBPV > pTKBPV > pSRalphaBPV in CV1-P cells. In the absence of selection pressure, the expression of pCGalBPVlacZ and pTKBPVlacZ was associated with long-term maintenance. In a comparison of pBPVlacZ with pSVlacZ, expression was maintained up to 12-17 and 8-12 days, respectively. The transfection of pBPVlacZ plasmids was efficient in secondary and primary, dividing and nondividing, neural and nonneural, and human cells and, furthermore, independent of the cell cycle as seen in growing as well as resting cells. All these characteristics are likely to be relevant for in vivo conditions, under which the percentage of proliferating cells could be quite low. In conclusion, the pBPV plasmids were efficiently delivered and expressed in different host cells, and therefore their performance in gene therapy is worth testing.

Catecholamine metabolism in the brain by membrane-bound and soluble catechol-o-methyltransferase (COMT) estimated by enzyme kinetic values

A kinetic model was constructed to reevaluate the catecholamine metabolism in hypothetical brain homogenates. Earlier published kinetic values of recombinant membrane-bound (MB-) COMT and soluble (S-) COMT were combined with data suggesting that MB-COMT represents 70% and 30% of total COMT protein in human and rat brain, respectively. In the rat brain model L-DOPA and 3,4-dihydroxybenzoic acid were O-methylated mainly via S-COMT, while dopamine and noradrenaline, at low concentrations, were O-methylated slightly more by MB-COMT. In the human brain model dopamine and noradrenaline were metabolized primarily by MB-COMT. The ratio of meta (3-methoxy) over para (4-methoxy) product formation from 3,4-dihydroxybenzoic acid was higher for MB-COMT than S-COMT. It is suggested that MB-COMT clearly predominates the O-methylation of dopamine and noradrenaline also in vivo. Additionally, meta/para ratios could support the enrichment of either isoform of COMT in a homogenate sample.

Brain prolyl oligopeptidase activity is associated with neuronal damage rather than beta-amyloid accumulation

Prolyl oligopeptidase (POP) have been suggested to participate in the pathogenesis of Alzheimer's disease (AD). In this study the activity of POP is evaluated in AD patients and in transgenic mice with substantial deposits of beta-amyloid (Abeta). In AD cases, the POP activity displayed a significant negative correlation with the scores of senile/neuritic plaques and neurofibrillary tangles but not with Abeta-load. The transgenic mice with high levels of Abeta did not have altered POP activity compared to wild type mice. Based on our results, the low POP activity in AD seems to be associated with neuronal degeneration rather than to Abeta accumulation.

Effect of intracerebral 6-nitronoradrenaline, an endogenous catechol-O-methyltransferase (COMT) inhibitor, on striatal dopamine metabolism in anaesthetised rats

6-Nitronoradrenaline, a bioactive compound recently identified in the brain, is known to inhibit catechol-O-methyltransferase. To study its effect on dopamine metabolism, it was administered into rat striatum via a microdialysis probe. Other nitrated catechols (6-nitrodopamine, 6-nitro-DOPAC and 5-nitro-HVA) were studied for comparison. Tolcapone, a selective catechol-O-methyltransferase inhibitor, was used as a positive reference compound. Both 6-nitronoradrenaline and tolcapone increased striatal extracellular dopamine levels during the perfusion (at 100 microM concentration but not at 10 microM) and decreased the efflux of homovanillic acid. Tolcapone, but not other nitrated catechols, increased 3,4-dihydroxyphenylacetic acid efflux. None of the compounds inhibited MAO-B activity at 100 microM or lower. At 1 mM, 6-nitrodopamine inhibited MAO-B by 60%. Compared to tolcapone, other nitrated catechols were very weak COMT inhibitors in vitro. Neither tolcapone nor 6-nitronoradrenaline modified the metabolism of L-dopa which was given peripherally. In binding studies, both 6-nitronoradrenaline and other nitrocatechols failed to affect the dopamine transporter even at high micromolar concentrations. In conclusion, exogenous 6-nitronoradrenaline can act as a COMT inhibitor in the striatum and elevate striatal dopamine levels without inhibiting dopamine reuptake. Whether endogenous 6-nitronoradrenaline can be formed also in vivo in the striatum and act as a regulator of dopaminergic tone remains to be determined.

The role of dopamine-metabolizing enzymes in the regulation of renal sodium excretion in the rat

The intrarenal natriuretic hormone dopamine (DA) is metabolized by catechol-O-methyltransferase (COMT) and monoamine oxidase (MAO). We have previously shown that inhibition of COMT by entacapone results in a potent D1-like receptor-mediated natriuretic response. The present study was performed using anaesthetized rats to compare the importance of MAO and COMT in DA-mediated natriuresis by use of the MAO inhibitor phenelzine. Urinary sodium and DA excretion remained unchanged after MAO inhibition, while excretion of the main metabolite dihydroxyphenylacetic acid (DOPAC) decreased by 55%. The response was unaltered if 5-hydroxytryptamine receptors (5-HT1A) were blocked during MAO inhibition. We also investigated the specific renal activities of MAO and COMT in rat renal cortex during DA-influenced natriuresis. Specific COMT activity in the renal cortex was reduced by 13% after isotonic sodium loading (5% of body mass) whereas renal MAO-A and MAO-B activities remained unaltered. Furthermore, preliminary data obtained from spontaneously hypertensive rats, whose basal urinary DA excretion is higher than that of normotensive Wistar-Kyoto rats, show a tendency for renal COMT activity to be lower. It is concluded that MAOinhibition by phenelzine does not alter sodium excretion. Furthermore, specific renal cortical COMT activity is reduced during partly D1-like receptor-mediated natriuresis, whereas MAO activity remains unchanged. The results suggest that MAO is less important than COMT in regulating DA-mediated natriuresis in the rat kidney.

Modulation of histamine H3 receptors in the brain of 6-hydroxydopamine-lesioned rats

Parkinson's disease is a major neurological disorder that primarily affects the nigral dopaminergic cells. Nigral histamine innervation is altered in human postmortem Parkinson's disease brains. However, it is not known if the altered innervation is a consequence of dopamine deficiency. The aim of the present study was to investigate possible changes in the H3 receptor system in a well-characterized model of Parkinson's disease--the 6-hydroxydopamine (6-OHDA) lesioned rats. Histamine immunohistochemistry showed a minor increase of the fibre density index but we did not find any robust increase of histaminergic innervation in the ipsilateral substantia nigra on the lesioned side. In situ hybridization showed equal histidine decarboxylase mRNA expression on both sides in the posterior hypothalamus. H3 receptors were labelled with N-alpha-[3H]-methyl histamine dihydrochloride ([3H] NAMH). Upregulation of binding to H3 receptors was found in the substantia nigra and ventral aspects of striatum on the ipsilateral side. An increase of GTP-gamma-[35S] binding after H3 agonist activation was found in the striatum and substantia nigra on the lesioned side. In situ hybridization of H3 receptor mRNA demonstrated region-specific mRNA expression and an increase of H3 receptor mRNA in ipsilateral striatum. Thus, the histaminergic system is involved in the pathological process after 6-OHDA lesion of the rat brain at least through H3 receptor. On the later stages of the neurotoxic damage, less H3 receptors became functionally active. Increased H3 receptor mRNA expression and binding may, for example, modulate GABAergic neuronal activity in dopamine-depleted striatum.

An acute i.c.v. infusion of leptin has no effect on hypothalamic histamine and tele-methylhistamine contents in Wistar rats

The actions of intracerebroventricularly (i.c.v.) infused leptin on food intake, body weight and hypothalamic contents of histamine and tele-methylhistamine, the main histamine metabolite in the mammalian brain, were studied in male Wistar rats. The effect of the histamine H(1) receptor blockade on leptin-induced anorexia was also examined. It was found that leptin at the dose of 10 microg i.c.v. reduced 24-h food intake by 48% as compared with the controls (P<0.01). This leptin dose reduced feeding during 2-4 consecutive days. In spite of the marked changes in food consumption and body weight gain, leptin did not alter the hypothalamic contents of histamine and tele-methylhistamine. Furthermore, the blockade of histamine H(1) receptors by mepyramine did not attenuate the effect of leptin on feeding and body weight. The findings indicate that centrally administered leptin suppresses feeding and promotes weight loss through mechanisms that do not require the direct participation of the brain histaminergic neuron system.

Activation of 5-HT2A receptors impairs response control of rats in a five-choice serial reaction time task

The present experiments investigated the effects of agents acting at serotonin (5-HT)-2 receptors on the performance of rats in a choice serial reaction time (5-CSRT) task in order to examine the role of 5-HT2 receptors in the modulation of attention and response control. The results indicate that DOI, [(+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride; 0.05, 0.1 and 0.2 mg/kg, subcutaneously], a 5-HT(2A/2C) agonist, slightly impaired the choice accuracy of the well performing rats and markedly increased their premature responding. DOI (0.05 and 0.1 mg/kg) had no effect on the latency to collect earned food pellets or to respond correctly, indicating that these lower doses of DOI did not reduce motivation for the food reward in this task. The selective effect of a low dose of DOI (0.1 mg/kg) on premature responding was completely blocked by ketanserin (0.2 mg/kg), a 5-HT2A antagonist, and ritanserin (0.3 mg/kg), a 5-HT(2A/2C) antagonist, but only partially blocked by a high dose of SER082 (1.0 mg/kg), a 5-HT2C antagonist. In contrast to DOI, mCPP, [1-(3-phenyl)piperazine; 0.05 and 0.15 mg/kg], a 5-HT2C agonist, had no effect on choice accuracy or premature responding, but it reduced behavioral activity and/or arousal as indicated by the decreased number of trials completed and increased the probability of omissions. SER082 (1.0 mg/kg) blocked the effects of mCPP on performance. These data suggest that the overactivation of 5-HT2A receptors impairs response control in a 5-CSRT task, whereas the overactivation of 5-HT2C receptors can affect behavioral activity and/or arousal state of the animals for this food rewarded task.

Cholecystokinin-induced anxiety in rats: relevance of pre-experimental stress and seasonal variations

OBJECTIVE

To examine the influence of pre-experimental stress on the anxiogenic-like action of caerulein, an agonist of cholecystokinin (CCK) receptors. Differences in the anxiety levels of rats in summer and winter, and the role of CCK in these behavioural alterations, were also examined.

DESIGN

Prospective animal study.

INTERVENTIONS

Male Wistar rats were injected with the CCK agonist caerulein, or the CCK antagonists L-365,260 or devazepide, after being exposed to pre-experimental stress (handling and isolation).

OUTCOME MEASURES

Performance in the plus-maze model of anxiety; serum levels of prolactin, thyrotropin and growth hormone; brain density and affinity of dopamine D2, serotonin 5-HT2 and CCK receptors.

RESULTS

Caerulein (5 micrograms/kg, subcutaneous injection) caused the strongest action in animals brought to the experimental room immediately before the experiment and kept in isolation after the administration of caerulein. Caerulein did not cause any reduction of exploratory activity in rats made familiar with the experimental room and kept in the home-cage after the injection of the CCK agonist. The anti-exploratory action of caerulein in stressed rats was reversed by the CCK antagonist L-365,260 (100 micrograms/kg, intraperitoneal injection), demonstrating the involvement of the CCKB receptor subtype. In addition, seasonal fluctuations occur in the exploratory activity of rats; such activity was much lower in July than in November. The rats displaying the reduced exploratory activity had an increased number of CCK receptors in the frontal cortex and hippocampus. Simultaneously, the density of serotonin 5-HT2 receptors in the frontal cortex, but not that of dopamine D2 receptors in the striatum, was elevated. The blood level of growth hormone was also higher in July.

CONCLUSIONS

The anti-exploratory action of caerulein appears to be dependent on the pre-experimental stress of rats. Moreover, the seasonal variations of exploratory behaviour of rats are evident in the plus-maze model of anxiety. The reduced exploratory activity in summer appears to be related to the elevated density of CCK and 5-HT2 receptors in the brain.

Apomorphine-induced behavioural sensitization in rats: individual differences, role of dopamine and NMDA receptors

Apomorphine-induced behavioural sensitization was studied in male Wistar rats. The acute administration of apomorphine (0.5 mg/kg s.c.), a dopamine agonist, did not affect the locomotor activity of rats, but it caused stereotyped behaviour characterized by repeated gnawing, licking and sniffing. A significant increase in the locomotor activity became evident after repeated treatments with apomorphine (0.5 mg/kg twice daily for 14 days). However, there were marked individual differences in the sensitization of rats to apomorphine. One third of animals did not react with increased locomotor activity even after the 2-week administration of apomorphine, whereas the other one third needed only a few injections to display increased behavioural response to apomorphine. The behavioural response of the remaining one third of rats was between weak and strong responders. Simultaneously, the stereotyped behaviour occurred earlier and its intensity tended to be lower after repeated treatment with apomorphine. Nevertheless, the established changes of stereotyped behaviour did not correlate with the increase of locomotor activity. The administration of amphetamine (2.5 mg/kg, s.c.), an indirect dopamine agonist, but not a non-competitive NMDA antagonist dizocilpine (0.25 mg/kg i.p.), tended to cause a similar response profile with apomorphine in sensitized rats. The ED50 values of the dopamine antagonists blocking apomorphine-induced increase in the locomotor activity were the following: 0.09 mg/kg for raclopride (dopamine D2 antagonist), 0.023 mg/kg for SCH 23390 (dopamine D1 antagonist), 6.42 mg/kg for clozapine (dopamine D4 antagonist). This supports the involvement of D1 and D1 receptors in the expression of apomorphine-induced behavioural sensitization. The concomitant administration of dizocilpine (0.5 mg/kg), SCH 23390 (0.05 mg/kg), raclopride (0.1 mg/kg) and clozapine (20 mg/kg) with apomorphine (0.5 mg/kg twice daily for 2 weeks) antagonized the development of behavioural sensitization to apomorphine. Accordingly, at least three different molecular targets, namely dopamine D1 and D2, and NMDA receptors, are involved in the development of apomorphine-induced behavioural sensitization.

Microdialysis studies on the action of tolcapone on pharmacologically-elevated extracellular dopamine levels in conscious rats

To elucidate the importance of catechol-O-methyltransferase, we performed striatal microdialysis studies in conscious rats given tolcapone, an inhibitor of catechol-O-methyltransferase, together with four compounds each of which elevates the extracellular dopamine content through a different mechanism. Tolcapone itself did not alter dopamine levels in the striatal microdialysis fluid but increased DOPAC and decreased homovanillic acid levels. However, tolcapone pretreatment (30 mg/kg) multiplied the already high dopamine levels after levodopa, and less so the moderately elevated dopamine levels after GBR-12909 (at 20 mg/kg) alone, but the minor (insignificant) dopamine-elevating effects of haloperidol and (+)-U232 were not altered. In all cases, a tolcapone pretreatment decreased homovanillic acid levels and elevated DOPAC levels. In further combination studies, GBR-12909 did not alter significantly the effects of levodopa/carbidopa on dopamine, DOPAC and homovanillic acid levels. In these rats, tolcapone enhanced the effect of GBR-12909 on extracellular dopamine but not on DOPAC. In conclusion, when levodopa and carbidopa are given together, COMT inhibition becomes extremely meaningful, and dopamine levels are multiplied by tolcapone. Otherwise, tolcapone is able to further elevate extracellular dopamine levels only when dopamine turnover is normal or low but not when it is high. Overall, the role of COMT in the elimination of synaptic dopamine remains minor compared to the dominance of the reuptake process.

Effects of repeated low dose administration and withdrawal of haloperidol on sexual behaviour of male rats

Neuroleptics are known to cause anhedonia and attenuate sexual behaviour at therapeutic doses in humans. These effects are assumed to result from the dopamine antagonism of the drugs. It has been observed that a mixed dopamine D1/D2 antagonist, haloperidol, may cause a reduction in the number of intromissions required to achieve ejaculation. On the other hand, dopamine antagonists are considered unable to modify sexual behaviour once the copulatory sequence is initiated. In this study, male rats received low doses of haloperidol (30 or 60 microg/kg) before the investigation of sexual behaviour in five consecutive days and the mating test was repeated after withdrawal periods of four and five days. Haloperidol dose-dependently reduced intromission frequency, and this effect was maintained for four days after withdrawal. Ejaculation latency was reduced in all groups, including controls. The results indicate that at low doses haloperidol dose-dependently reduces intromission frequency, and the effect of a repeated dosage may persist several days after cessation of medication.

Effect of tolcapone, a catechol-O-methyltransferase inhibitor, on striatal dopaminergic transmission during blockade of dopamine uptake

To examine the mechanisms of tolcapone in the central nervous system (CNS), we analyzed alterations in parameters of striatal dopamine transmission induced by this drug (30 mg/kg) co-administered with the selective dopamine uptake inhibitor, GBR 12909 (10 mg/kg). Using microdialysis in freely moving rats, it was determined that combined administration of tolcapone with GBR 12909 resulted in a further increase of dopamine levels over that obtained without the catechol-O-methyltransferase inhibitor, while tolcapone alone failed to change dopamine levels. Fast-scan cyclic voltammetric monitoring of electrically evoked dopamine did not show any changes in dopamine release after the combination of the drugs, but there was a pronounced decrease in the rate of dopamine clearance after GBR 12909 alone and when co-administered with tolcapone. These data indicate that in rat striatum, a tolcapone-induced increase in extracellular dopamine is not observed because of the presence of uptake. These results also support the hypothesis that under normal conditions, uptake, rather than metabolism, control extracellular levels of dopamine.

Synthesis and in vitro pharmacology of a series of new chiral histamine H3-receptor ligands: 2-(R and S)-Amino-3-(1H-imidazol-4(5)-yl)propyl ether derivatives

To investigate stereospecificity and the mechanism of activation of the histamine H3-receptor, a series of 2-(R and S)-amino-3-(1H-imidazol-4(5)-yl)propyl ether derivatives were synthesized. In these compounds, the structures of the well-known antagonist iodoproxyfan and the full agonists R- or S-(alpha)-methylhistamine were combined in one molecule. The obtained "hybrid" molecules were tested for H3-receptor affinity on rat cerebral cortex. Some selected compounds were further screened for H3-receptor functional activity with GTPgamma[35S] autoradiography studies using rat brain tissue sections. The affinity of all the synthesized compounds (-log Ki = 5.9-7.9) was lower than that found for iodoproxyfan or two of its analogues; however, the compounds showed stereospecificity. The S-configuration of the series of 2-amino-3-(1H-imidazol-4(5)-yl)propyl ether derivatives, which resembles the stereochemistry of R-(alpha)-methylhistamine, was more favorable. Incorporation of an amino group in the propyl chain of iodoproxyfan and analogues did not alter the antagonistic behavior for compounds with an aromatic side chain. However, when also the aromatic moiety was replaced by a cyclohexyl group, the compounds behaved as agonists. This indicates that an interaction between the side chain amino group and the H3-receptor protein is involved in H3-receptor activation. The 2-(S)-amino-3-(1H-imidazol-4(5)-yl)propyl cyclohexylmethyl ether (23) has H3-receptor agonistic properties with high affinity for the histamine H3-receptor (-log Ki = 7.9 +/- 0.2) and might serve as a useful tool for further studies concerning drug design and receptor-ligand interactions.

Hypothalamic histamine, growth rate, plasma prolactin and growth hormone levels in rats with long-term portacaval anastomosis

OBJECTIVE AND DESIGN

Histamine can modulate feeding behaviour and hormone release; therefore we examined the hypothalamic histamine system, the growth pattern and the serum levels of prolactin and growth hormone in rats with portacaval anastomosis (PCA).

MATERIAL

The growth rate of 30 PCA- and 30 sham-operated male Han:Wistar rats was monitored for 6 months. Thirteen sham and 9 PCA rats were used for biochemical studies.

METHODS

Histamine was assayed by HPLC, tele-methylhistamine by GC-MS, prolactin and growth hormone by RIA. Student's t-test was used to compare the groups.

RESULTS

Six months after surgery, the PCA rats exhibited marked growth retardation (weight gain of 20 g vs. 140 g for the sham rats; p < 0.001), increased plasma levels of prolactin (9.7 +/- 2.4 vs. 3.6 +/- 0.6; p<0.01) and unaltered growth hormone levels (6.2 +/- 0.5 vs. 8.1 +/- 1.0). A six-fold elevation of histamine concentration (29.5 +/- 3.9 vs. 4.8 +/- 0.4; p<0.001) and a two-fold increase of tele-methylhistamine levels (1.8 +/- 0.1 vs. 0.8 +/- 0.02; p<0.001) were found in hypothalamus.

CONCLUSION

We suggest that increased histaminergic activity in the hypothalamus may be involved in the development of growth retardation and in the enhanced basal secretion of prolactin in male rats with long-term PCA.

No change of brain extracellular catecholamine levels after acute catechol-O-methyltransferase inhibition: a microdialysis study in anaesthetized rats

Catechol-O-methyltransferase inhibitors have been newly introduced as adjunct drugs to the levodopa/dopa decarboxylase inhibitor therapy in Parkinson's disease. When given alone, catechol-O-methyltransferase inhibitors seem to affect behaviour. We wanted to determine whether the concentrations of free amine would be increased by catechol-O-methyltransferase inhibition with tolcapone and underpin the positive behavioural effects. To this end, dopamine and noradrenaline levels were analyzed in the microdialysis perfusion fluid collected from several brain regions in chloral hydrate anaesthetized rats. We also analyzed the turnover rate of catecholamines in the brain after single doses of tolcapone and entacapone using the alpha-methyl-p-tyrosine method. On their own, tolcapone (at 10 or 30 mg/kg) did not elevate dopamine or noradrenaline levels in any brain region studied although the formation of catechol-O-methyltransferase-dependent metabolites was strongly reduced. Neither tolcapone nor entacapone (at 30 mg/kg) affected the turnover rate of catecholamines. It seems that catechol-O-methyltransferase inhibitors do not alter behaviour by elevating extracellular levels of free catecholamines levels but other explanations are needed.

L-Arginine abolishes the anxiolytic-like effect of diazepam in the elevated plus-maze test in rats

The involvement of nitrergic mechanisms in the behavioural effects of diazepam in rats was studied in the elevated plus-maze, open-field and rotarod tests. Administration of the nitric oxide (NO) precursor L-arginine (100 mg/kg, i.p.), assumed to increase the synthesis of NO, abolished the anxiolytic-like effect of diazepam (2 mg/kg, i.p.) in the elevated plus-maze, whereas the inactive enantiomer D-arginine (100 mg/kg) did not. Neither diazepam alone nor in combination with L- or D-arginine affected the exploratory activity of animals in the open field. Pretreatment with L-arginine (100 and 200 mg/kg) did not modify the motor impairment of rats after diazepam (3 mg/kg) in the rotarod test. Diazepam (2 mg/kg i.p.) did not inhibit the cortical or hippocampal cytosolic NO synthase activity measured ex vivo by [3H]L-arginine assay. Diazepam was similarly ineffective in in vitro studies at concentrations up to 10 microM. We conclude that a suppression of NO synthase activity may be important in the anxiolytic-like effect of benzodiazepines. However, diazepam does not inhibit NO synthase directly, but may affect NO synthase activity indirectly via some unknown mechanism.

Opioid antagonist naloxone potentiates anxiogenic-like action of cholecystokinin agonists in elevated plus-maze

This study investigated the interplay of cholecystokinin (CCK) and endogenous opioid peptides in the regulation of anxiety. The acute administration of non-selective CCK agonist caerulein (1 and 5 microg/kg) and a selective CCK(B) receptor agonist BOC-CCK-4 (1, 10 and 50 microg/kg) induced a dose-dependent anxiogenic-like action in the plus-maze model of anxiety. BOC-CCK-4 displayed a similar efficacy with caerulein, indicating that the described effect was mediated via CCK(B) receptor subtype. The opioid antagonist naloxone itself (0.5 mg/kg) did not change the exploratory activity of rats in the plus-maze. However, the combination of naloxone with the sub-effective doses of caerulein (1 microg/kg) and BOC-CCK-4 (1 microg/kg) induced a significant inhibition of exploratory behaviour in rats. Accordingly, CCK and endogenous opioid peptides have an antagonistic role in the exploratory model of anxiety in rats.

Different renal effects of two inhibitors of catechol-O-methylation in the rat: entacapone and CGP 28014

Dopamine is a natriuretic hormone that is abundantly synthesized in the kidney and is involved in sodium homeostasis. It is metabolized by monoamine oxidase (MAO) and catechol-O-methyl transferase (COMT) to form 3-methoxytyramine and dihydroxyphenylacetic acid (DOPAC) and finally homovanillic acid (HVA). In order to investigate whether dopamine metabolism is involved in renal sodium regulation, we tested the renal effects of the nitrocatechol entacapone (COMT inhibitor), in comparison with those of the pyridine derivative CGP 28014, in the anaesthetized rat. Entacapone injection resulted in a more than 5-fold increase in sodium excretion, while the renal excretion of dopamine only transiently increased by 20%. DOPAC excretion showed a more than 2-fold increase which persisted throughout the study. Pretreatment with the selective dopamine DA1-receptor antagonist SCH23390 reduced the entacapone-induced natriuretic response by 69%. Glomerular filtration rate (GFR) and mean arterial blood pressure (MAP) remained unchanged. Injection of CGP 28014 did not produce a natriuretic response; nevertheless, both dopamine and DOPAC excretion increased by 78% and more than 2-fold, respectively. GFR and MAP remained unchanged. In conclusion, COMT inhibition using entacapone results in a mainly DA1 receptor mediated natriuresis involving inhibition of tubular transport processes, supporting a role for dopamine metabolism in sodium homeostasis. Although CGP 28014 increases the renal excretion of both dopamine and DOPAC it does not affect renal sodium handling indicating a different mechanism of action.

Deramciclane, a putative anxiolytic drug, is a serotonin 5-HT2C receptor inverse agonist but fails to induce 5-HT2C receptor down-regulation

Deramciclane (EGIS-3886) is a novel anxiolytic agent that binds with high affinity to 5-HT2A/2C receptors. The interactions of deramciclane with the serotonin 5-HT2C receptor were characterized further using receptor phosphoinositide hydrolysis assays and receptor autoradiography. Deramciclane antagonized 5-HT2C receptor mediated 5-HT-stimulated phosphoinositide hydrolysis with an IC50 value of 168 nM. Deramciclane also decreased basal phosphoinositide hydrolysis by up to 33% (EC50 = 93 nM) in a physiological system in the choroid plexus, suggesting that deramciclane possesses inverse agonist properties at this receptor. Administration of single doses of 0.5 mg/kg and 10 mg/kg resulted in a maximal 5-HT2C receptor occupancy of up to 45% and 79%, respectively, in the choroid plexus. Chronic (14 days) treatment with 0.5 mg/kg or 10 mg/kg deramciclane did not alter [125I]DOI (agonist) or [3H]mesulergine (antagonist) binding to 5-HT2C receptors in the choroid plexus compared to saline-treated controls, as determined by quantitative receptor autoradiography. In comparison, the effects of deramciclane on 5-HT2A binding characteristics and receptor occupancy were also studied. Deramciclane treatment resulted in 5-HT2A receptor occupancy of up to 78%, but no significant effect of chronic treatment on 5-HT2A receptor agonist binding levels was found. In conclusion, these data indicate that deramciclane is a 5-HT2C receptor inverse agonist and occupies 5-HT2C receptors during treatment, and that chronic treatment with deramciclane does not lead to 5-HT2C receptor down-regulation.

Relation of exploratory behavior of rats in elevated plus-maze to brain receptor binding properties and serum growth hormone levels

Forty-five male Wistar rats were selected according to their behavior in the elevated plus-maze. They were separated as follows: animals with low exploratory activity ('anxious'), an 'intermediate' group and animals having high exploratory activity ('non-anxious'). Various receptor binding studies and hormonal assays were also performed in these selected rats. The affinity of 5-hydroxytryptamine 5-HT2A receptors in the frontal cortex was lower in the 'anxious' rats compared to home-cage controls and 'non-anxious' animals. Moreover, the number of cholecystokinin (CCK) receptors in the hippocampus was significantly elevated in the 'anxious' group compared to home-cage control animals. The blood levels of growth hormone (GH) were significantly lower in the 'non-anxious' rats compared to 'anxious' counterparts. In conclusion, it seems likely that the decreased exploratory activity of rats is related to the increased 5-hydroxytryptamine (5-HT) and CCK mediated neurotransmission in the brain. The different serum levels of GH in the selected rats probably reflect alterations in the activity of 5-HT and CCK.

Increase of catechol-O-methyltransferase activity in rat brain microglia after intrastriatal infusion of fluorocitrate, a glial toxin

Striatal catechol-O-methyltransferase (COMT), monoamine oxidase B (MAO-B; an astroglial enzyme), alkaline phosphodiesterase I (PDE; a microglia/macrophage marker) and tyrosine hydroxylase (TH; catecholaminergic neuron marker) activities were analyzed biochemically 1-3 days after infusion of fluorocitrate, an astrocyte damaging agent. Astrocytes, microglia and neurons were stained immunohistochemically with specific antibodies (against glial fibrillary acidic protein, OX-42 and TH, respectively) and with COMT antiserum. Three days after fluorocitrate infusion the activity of MAO-B was reduced, whereas COMT and PDE activities were increased. The elevation of COMT immunoreactivity co-localized to microglial cells, but not to astrocytes. In conclusion, this is the first report indicating that microglia contains COMT activity which may be increased in pathological conditions.

Effects of selective catechol-O-methyltransferase inhibitors on single-trial passive avoidance retention in male rats

The effects of new selective catechol-O-methyltransferase (COMT) inhibitors entacapone (mainly peripheral effect) and tolcapone (acting also in the brain) on normal and impaired cognitive functions were studied in aversively motivated inhibitory avoidance using a single-trial passive avoidance paradigm in young adult rats. Passive avoidance retention latency was shortened by either scopolamine (1.0 mg/kg) or bilateral lesions to nucleus basalis magnocellularis (NBM) caused by infusions of ethylcholine aziridinium (AF64A). Entacapone (30 mg/kg) administered once before training or before the retention test, 24 h after training, prevented the effect of scopolamine but did not alter extinction in these rats. However, entacapone (30 mg/kg) prolonged lag time when given during the extinction process to intact rats after training. Tolcapone administered once before training (10 mg/kg) counteracted the effect of scopolamine. It prolonged retention latency of the intact rats when given after training (10 mg/kg). Tolcapone (3 mg/kg) also prolonged lag time when given during extinction to rats bearing NBM lesions. The effect of scopolamine on extinction and retrieval was not prevented by tolcapone. Only entacapone improved memory storage. Collectively, the present results indicate that COMT inhibitors prolong retention latencies in a single-trial passive avoidance test assessed at several memory phases.

7-Nitroindazole, a nitric oxide synthase inhibitor, has anxiolytic-like properties in exploratory models of anxiety

The action of the novel nitric oxide synthase (NOS) inhibitor 7-nitroindazole (7-NI) was studied in different exploratory models of anxiety. In the rat plus-maze test, 7-NI potently increased time spent on open arms and percentage of open arm visits in a dose dependent manner with the minimal effective dose of 40 mg/kg. 7-NI caused an anxiolytic-like effect in the rat social interaction test. The minimal dose increasing social interaction time was 20 mg/kg. However, the drug also produced a clear sedative effect occurring even at smaller doses (10 mg/kg) in the open field test. 7-NI also showed an anxiolytic-like profile in the mouse light-dark compartment test and in the elevated plus-maze test, but the doses required were higher (80-120 mg/kg) than in rat models. Also, the sedative effect occurred at these doses in open field. We failed to demonstrate any effect of L-arginine either in the rat elevated plus-maze test or in the open field test at doses up to 600 mg/kg IP. These results indicate that there are no major interspecies differences between rats and mice in respect of action of 7-NI. The clear anxiolytic-like action of the nitric oxide synthase inhibitor in four different models shows that nitric oxide is involved in the process of anxiety and that NOS could be a new target in developing anxiolytic drugs.

Optimization of the hydrolysis of conjugated L-DOPA, dopamine and dihydroxyphenylacetic acid in human urine for assay by high-performance liquid chromatography with electrochemical detection

Conjugates of the catechol compounds, L-dihydroxyphenylalanine (L-DOPA), dopamine and dihydroxyphenylacetic acid in human urine were analysed using the isocratic ion-pair reversed-phase HPLC method with electrochemical detection. Acid hydrolysis, using 4 mol/l HCl for 60 min, was more effective than treatment with sulphatase for the generation of free catechols. Free (non-conjugated) catechols already present, as well as those produced by either of the hydrolysis procedures, were adsorbed onto aluminium oxide and extracted in acid solution. The repeatability of the technique for within and between-batch urine analysis was less than 2% and 8%, respectively. Free urinary dopamine (and dihydroxyphenylacetic acid) concentrations were much higher in the urine of patients treated with L-DOPA for Parkinson's disease than in healthy volunteers. At high dopamine (and dihydroxyphenylacetic acid) levels the conjugation capacity was apparently exceeded, since the overall percent conjugation of L-DOPA, dopamine and dihydroxyphenylacetic acid was decreased "concentration dependently" where the concentrations of free catechols were increased. Both in the control group and L-DOPA-treated groups, enzymatic hydrolysis was much less effective than acid hydrolysis in generating free catechols. This indicated that there were other, non-sulphated conjugates in the urine, accounting for between 66 and 100% of total conjugates.

Overflow of noradrenaline and dopamine in frontal cortex after [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine] (DSP-4) treatment: in vivo microdialysis study in anaesthetized rats

The changes in the extracellular concentration of endogenous noradrenaline and dopamine in the frontal cortex following pretreatment with noradrenergic neurotoxin DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine] were studied by in vivo microdialysis in rats anaesthetized with chloral hydrate. Noradrenaline and dopamine levels in frontal cortex were detected only when the uptake inhibitor, nomifensine (10 microM) was present in dialysis fluid. Under those conditions, the Na+ channel agonist veratridine and a depolarising concentration of potassium chloride (60 mM), applied locally through the microdialysis probe, increased the overflow of noradrenaline. Tetrodotoxin had an opposite effect. These results indicate that most of the noradrenaline probably arose from exocytotic release. Noradrenaline efflux in the frontal cortex of DSP-4 pretreated rats (52 +/- 6.1 fmol/sample) did not differ significantly from that of the control animals (69 +/- 4.9 fmol/sample). Dopamine efflux was not changed either (64 +/- 9.6 and 62 +/- 3.9 fmol/sample, respectively). The alpha 2-adrenoceptor antagonist, atipamezole (3 mg/kg i.p.), increased the overflow of noradrenaline in the frontal cortex of saline-treated rats by 100%, whereas in DSP-4 treated rats the increase was only around 30%. The overflow of dopamine was not changed under the conditions described. The effect of atipamezole in DSP-4 treated rats may be of smaller magnitude due to the diminished pool of releasable noradrenaline or due to a downregulation of presynaptic alpha 2-adrenoceptors in the frontal cortex. The perfusion of 60 mM KCl at the end of the experiment unexpectedly produced equivalent increases in noradrenaline and dopamine content in dialysates of both vehicle and DSP-4 treated rats. We conclude that the uptake inhibitor, nomifensine, and atipamezole, which had a stronger effect in vehicle-treated animals, reduced the effect of KCl-stimulation and masked the true difference in changes of noradrenaline efflux. Post-mortem tissue concentrations of noradrenaline 7 days after DSP-4 administration (50 mg/kg) were significantly reduced in the frontal cortex (54%), hippocampus (62.5%) and to lesser extent in the hypothalamus (27%) as compared to vehicle-treated rats. Dopamine and 3,4-dihydroxyphenylacetic acid concentrations were not changed confirming the efficacy and selectivity of the DSP-4 lesion. These results demonstrate that one week after DSP-4 treatment the extracellular levels of noradrenaline and dopamine as assessed by in vivo microdialysis are not changed in the frontal cortex, but atipamezole-stimulated release of noradrenaline is decreased in DSP-4 treated rats.

Catechol O-methyltransferase inhibitor tolcapone has minor influence on performance in experimental memory models in rats

Two catechol O-methyltransferase inhibitors, peripherally acting entacapone and also centrally acting tolcapone, were tested regarding their capacity to influence learning and memory in adult intact rats. Tolcapone was also studied in rats treated with scopolamine, in adult rats lesioned in the nuclei basalis magnocellularis, and in aged rats. Spatial working memory performance (radial-arm maze) of intact rats was facilitated following pretraining i.p. administration of tolcapone (10 mg/kg). Entacapone was ineffective at doses of 10 and 30 mg/kg. Senescent poor performers improved their accomplishment in the spatial memory task (linear-arm maze) under the influence of tolcapone. Scopolamine (1 mg/kg) impaired working memory performance. Bilateral lesions in the nucleus basalis magnocellularis reduced choline acetyltransferase activity in the frontal cortex by 26% and retarded the learning rate of spatial place task. Tolcapone was not able to counteract the performance deficits in these models. It is concluded that tolcapone can either slightly improve or impair the memory functions depending on task specific elements and performance factors.

Evidence for cholecystokininA receptors in bovine adrenal chromaffin cells

We have studied a possible role of cholecystokinin (CCK) in regulating adrenal medullary function. Caerulein (10(-10)-10(-7) M), a CCK receptor agonist, increased formation of inositol phosphates in primary cultured bovine adrenal medullary (BAM) chromaffin cells in a concentration-dependent manner. The effect of caerulein was antagonized by devazepide, a selective CCKA-receptor antagonist, but not by L-365.260, a selective CCKB-receptor antagonist. These results suggest that BAM cells possess functional CCK receptors of the CCKA-subtype. Stimulation of these receptors with caerulein activates a signal transduction pathway via phospholipase C. CCK may regulate catecholamine release in BAM cells.

Nitric oxide mediates caerulein-induced suppression of locomotor activity

Caerulein, a non-selective agonist of cholecystokinin (CCK) receptors, is shown to suppress locomotor activity in rodents via stimulation of CCK(A) receptors. In the present study we examined the possible involvement of nitric oxide (NO) in caerulein-induced hypolocomotion in rats. Caerulein (10 microg/kg) markedly decreased the horizontal and vertical components of locomotor activity in rats measured in dark motility boxes. Pretreatment with a nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME), at 5 mg/kg i.p., abolished the inhibiting action of caerulein on the horizontal activity, but did not affect the reduced frequency of rearing. The other doses of L-NAME (1, 10 and 20 mg/kg) were ineffective against caerulein. As L-NAME at this dose range does not stimulate locomotor activity, it is likely that NO is involved in the motor suppressant effect of systemically administered caerulein.

Minor effect of tolcapone, a catechol-O-methyltransferase inhibitor, on extracellular dopamine levels modified by amphetamine or pargyline: a microdialysis study in anaesthetized rats

In vivo microdialysis was used to examine the effects of tolcapone (30 mg/kg) on dopamine metabolism in amphetamine (5 mg/kg) and pargyline (75 mg/kg) treated rats. Amphetamine- or pargyline-induced decreases in the extracellular dihydroxyphenyl acetic acid (DOPAC) levels were counteracted by additional tolcapone. Tolcapone also decreased homovanillic acid effluxes below those caused by amphetamine or pargyline. However, dopamine effluxes were not further enhanced by additional tolcapone. These results show that central metabolism of dopamine can be modulated by catechol-O-methyltransferase (COMT) inhibition also without exogenous L-DOPA. However, extracellular dopamine levels are not easily increased.