The role of Schwann cells, T cells and Mycobacterium leprae in the immunopathogenesis of nerve damage in leprosy

Damage to peripheral nerves is the major complication of reversal (type I) reactions in leprosy. The underlying mechanism of nerve damage remains largely unresolved; however, an important role for type-1 T cells has been suggested. Mycobacterium leprae has a remarkable tropism for the Schwann cells that surround peripheral axons. Because reversal reactions in leprosy are often accompanied by severe and irreversible nerve destruction, and are associated with increased cellular immune reactivity against M. leprae, a likely immunopathogenic mechanism of damage to Schwann cells and peripheral nerves in leprosy is that infected Schwann cells process and present antigens of M. leprae to antigen-specific, inflammatory, type-1 T cells, and that these T cells subsequently damage and lyse infected Schwann cells. Previous animal studies with CD8+ T cells revealed evidence for the existence of such a mechanism. A similar role has been suggested for CD4+ T cells. These latter cells may be more important in causing nerve damage in vivo, given the predilection of M. leprae for Schwann cells, and the dominant role of CD4+, serine esterase+ Th1 cells in the lesions of leprosy. Antagonism of the molecular interactions among M. leprae, Schwann cells and inflammatory T cells may therefore provide a rational strategy for prevention of damage of Schwann cell and nerves in leprosy.

Novel mechanisms in the immunopathogenesis of leprosy nerve damage: the role of Schwann cells, T cells and Mycobacterium leprae

The major complication of reversal (or type 1) reactions in leprosy is peripheral nerve damage. The pathogenesis of nerve damage remains largely unresolved. In situ analyses suggest an important role for type 1 T cells. Mycobacterium leprae is known to have a remarkable tropism for Schwann cells that surround peripheral axons. Reversal reactions in leprosy are often accompanied by severe and irreversible nerve destruction and are associated with increased cellular immune reactivity against M. leprae. Thus, a likely immunopathogenic mechanism of Schwann cell and nerve damage in leprosy is that infected Schwann cells process and present antigens of M. Leprae to antigen-specific, inflammatory type 1 T cells and that these T cells subsequently damage and lyse infected Schwann cells. Previous studies using rodent CD8+ T cells and Schwann cells have revealed evidence for the existence of such a mechanism. Recently, a similar role has been suggested for human CD4+ T cells. These cells may be more important in causing leprosy nerve damage in vivo, given the predilection of M. leprae for Schwann cells and the dominant role of CD4+ serine esterase+ Th1 cells in leprosy lesions. Antagonism of molecular interactions between M. leprae, Schwann cells and inflammatory T cells may therefore provide a rational strategy to prevent Schwann cell and nerve damage in leprosy.

A comparison of the physicochemical and biological properties of mirtazapine and mianserin

Although the chemical structures of the antidepressants mirtazapine and mianserin are closely related there are considerable differences in their biological properties. To find an explanation of this, various physicochemical properties of mirtazapine and mianserin were measured or calculated. Isosteric replacement of CH in mianserin by N in mirtazapine has profound effects on physicochemical properties. The charge distributions as indicated by NMR and calculated by semi-empirical quantum mechanics differ, not only for the changed aromatic A-ring (as expected), but also in other regions of the molecule. The N5 atom in particular, which is conjugated to the changed aromatic ring, is less negatively charged in mirtazapine than in mianserin. Consequently the oxidation potential of mirtazapine is significantly higher than that of mianserin. Another result of this difference in charge distribution is that the (calculated) dipole-moment vectors of the compounds are oriented roughly perpendicular to each other. The dipole moment of mirtazapine is, moreover, three times larger than that of mianserin; mirtazapine is, therefore, more polar than mianserin and this is reflected in a lower retention index. Finally, the basicity of mirtazapine, expressed as the pKa value, is slightly but significantly lower than that of mianserin. The observed differences between the physicochemical properties of mirtazapine and mianserin result in different interactions of these two antidepressants with macromolecules, such as receptors, transporters and metabolizing enzymes; this might explain the differences observed in pharmacological activity and metabolic and kinetic behaviour, that is, the reduced affinity for the alpha 1-adrenoceptor and negligible noradrenaline reuptake of mirtazapine compared with mianserin.

The alpha 2-adrenoceptor antagonist Org 3770 enhances serotonin transmission in vivo

The antidepressant properties of Org 3770 (1,2,3,4,10,14b-hexahydro-2-methylpyrazino[2,1-a]pyrido[2,3- c][2]benzazepine) may be mediated via blockade of auto and hetero alpha 2-adrenoceptors. On-line microdialysis studies in freely moving rats showed Org 3770 (2 mg/kg s.c.) to increase hippocampal 5-HT (5-hydroxytryptamine) and dihydroxyphenyl acetic acid (DOPAC)--a measure of noradrenergic activity--by approximately 80%. The increase in DOPAC is probably caused by blockade of alpha 2-autoreceptors on noradrenergic terminals. Indirect alpha 1-adrenoceptor-mediated enhancement of 5-HT cell firing and direct blockade of inhibitory alpha 2-heteroreceptors located on 5-HT terminals are held responsible for the increase in extracellular 5-HT.

Dopamine D1 and D2 receptors in the caudate nucleus of spontaneously hypertensive rats and normotensive Wistar-Kyoto rats

A series of studies was carried out to characterize the binding properties of dopamine D1 and D2 receptors in membrane homogenates of the caudate nucleus of spontaneously hypertensive rats (SHR). Binding in SHR was studied at the age of 4 weeks when the rats were still in the prehypertensive phase, and at the age of 8 weeks, during the phase in which blood pressure is increasing dramatically; age-matched normotensive Wistar-Kyoto rats (WKY) were used as controls. Binding to dopamine D1 receptors was studied using [3H]SCH 23390. Antagonist binding of dopamine D2 receptors was performed with [3H]spiperone. At both ages no differences were found between SHR and WKY in affinity (Kd) or concentration (Bmax) of dopamine D1 and D2 receptors. Binding to the high affinity state of the dopamine D2 receptor was measured using the agonist [3H]N-n-propylnorapomorphine (NPA). No differences in Bmax or Kd were found between SHR and WKY at both ages studied, indicating that the ratio between dopamine D2 receptors in the high and in the low affinity state is not altered in spontaneous hypertension. Although the results do not reveal differences in affinities or concentrations of dopamine D1 or D2 receptors in the caudate nucleus between SHR and WKY, a role in the development of hypertension for the here described lack of receptor up-regulation in connection with our previous observation of lower release of dopamine in the caudate nucleus of SHR, cannot be excluded.

Characterization of the inhibitory effect of adrenocorticotropin/melanocyte-stimulating hormone-like peptides on the binding of dopamine receptor ligands to the dopamine D2 receptor in vitro

Adrenocorticotropin (ACTH)-(1-24) decreased the binding of the dopamine D2 agonist [3H]N-n-propylnorapomorphine [3H](NPA) to the dopamine D2 receptor in rat striatal membranes in vitro. The association and dissociation of [3H]NPA to the dopamine D2 receptor was inhibited by ACTH-(1-24), suggesting an apparent competitive interaction between ACTH-(1-24) and the binding of [3H]NPA. ACTH-(1-24) was able to inhibit the binding of the dopamine D2 receptor antagonist [3H]spiperone to the dopamine D2 receptor, both in the high- and the low-affinity state. These observations suggest a G-protein-independent mechanism of action. The inhibitory effect of ACTH-(1-24) and ACTH-(7-16)-NH2 was diminished after the addition of polylysine chains, presumably via a blockade of the attachment sites for ACTH-(1-24) on the dopamine D2 receptor. The effect of ACTH-(1-24) on membrane fluidity and on the inhibition of the binding of [3H]NPA to the dopamine D2 receptor appeared to be unrelated because lowering the incubation temperature from 25 degrees C to 4 degrees C, which causes a strong decrease of membrane fluidity, did not diminish the effect of ACTH-(1-24) on the binding of [3H]NPA to the dopamine D2 receptor. Furthermore, in both young and old rats, whose membranes are reported to differ in lipid composition and membrane fluidity, ACTH-(1-24) inhibited the binding of [3H]NPA to the dopamine D2 receptor to nearly the same extent.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of the potential antipsychotic ORG 5222 on local cerebral glucose utilization in freely moving rats

The effects of administration of different doses of the potential antipsychotic Org 5222 (0.01 and 0.1 mg/kg i.v.) upon local cerebral glucose utilization (LCGU) in 102 anatomically discrete brain regions of freely moving male Wistar rats were studied with the quantitative autoradiographic [14C]2-deoxyglucose technique. Glucose utilization was significantly changed after treatment with 0.01 and 0.1 mg/kg i.v. Org 5222 in two and four brain areas, respectively. Treatment with 0.01 mg/kg Org 5222 significantly reduced LCGU in the basal thalamus (the ventral posterior medial (VPM) and lateral (VPL) nuclei). After administration of 0.1 mg/kg Org 5222, significant reductions were seen in the basal thalamus (VPL and VPM) and the medio dorsal thalamic nuclei. A highly significant elevation in LCGU was observed in the lateral nucleus of the habenula. The results show that Org 5222 selectively reduced LCGU in thalamic structures and had no or minimal effect on limbic, cortical and nigrostriatal structures, suggesting that Org 5222 may have antipsychotic potential, without inducing cognitive and extrapyramidal side-effects.

Isolation and characterization of the moxJ, moxG, moxI, and moxR genes of Paracoccus denitrificans: inactivation of moxJ, moxG, and moxR and the resultant effect on methylotrophic growth

By using the moxF gene encoding the large fragment of methanol dehydrogenase as a probe, a downstream linked chromosomal fragment was isolated from a genomic bank of Paracoccus denitrificans. The nucleotide sequence of the fragment was determined and revealed the 3' part of moxF, four additional open reading frames, and the 5' part of a sixth one. The organization and deduced amino acid sequences of the first three frames downstream from moxF were found to be largely homologous to the moxJ, moxG, and moxI gene products of Methylobacterium extorquens AM1. Directly downstream from these three genes, a new mox gene was identified. The gene is designated moxR. By using the suicide vector pGRPd1, the moxJ, moxG, and moxR genes were inactivated by the insertion of a kanamycin resistance gene. Subsequently, suicide vector pRVS1 was used to replace the marker genes in moxJ and moxG for unmarked deletions made in vitro. As a result, the three insertion strains as well as the two unmarked mutant strains were unable to grow on methanol, even in the presence of pyrroloquinoline quinone. Growth on succinate and on methylamine was not affected. In all five mutant strains, synthesis of the large subunit of methanol dehydrogenase and of inducible cytochrome c553i was observed. The moxJ and moxG insertion mutant strains were unable to synthesize both the cytochrome c551i and the small subunit of methanol dehydrogenase, and this lack of synthesis was attended by the loss of methanol dehydrogenase activity. The moxJ deletion mutant strain partly synthesized the latter two proteins, cytochrome c551i. Partial synthesis of the small subunit of methanol dehydrogenase observed with the latter strain was attended by a corresponding extent of methanol dehydrogenase activity. The moxR insertion mutant strain was shown to synthesize cytochrome c551i as well as the large and small subunits of methanol dehydrogenase, but no methanol dehydrogenase activity was observed. The results show that periplasmic cytochrome c551i is the moxG gene product and the natural electron acceptor of methanol dehydrogenase in P. denitrificans. In contrast to earlier suggestions, this cytochrome was found to be different from membrane-bound cytochrome c552. In addition, it is demonstrated that moxI encodes the small subunit of methanol dehydrogenase. It is suggested that MoxJ is involved in the assemblage of active methanol dehydrogenase in the periplasm and, in addition, that MoxR is involved in the regulation of formation of active methanol dehydrogenase.

cGMP formation and phosphoinositide turnover in rat brain slices are mediated by pharmacologically distinct muscarinic acetylcholine receptors

The cGMP response and the accumulation of inositol monophosphate (IP) induced by carbachol were compared in slices of different rat brain structures. Basal cGMP and the responses of cGMP to carbachol appeared dependent on the concentration of added Ca2+, suggesting that distinct Ca(2+)-mediated and Ca(2+)-sensitive muscarinic receptor-mediated mechanisms stimulate guanylate cyclase. Regional responses of cGMP to carbachol or to direct stimulation of guanylate cyclase with sodium nitroprusside were markedly distinct, indicating that a major proportion of guanylate cyclase in the cortex, an intermediate proportion in other forebrain regions, and only a minor proportion in the brainstem is sensitive to muscarinic receptor stimulation. The regional patterns of IP and cGMP responses to carbachol were different in the forebrain. Maximal IP accumulation was found in the cortex, whereas cGMP responses were highest in the hippocampus. Moreover, IP and cGMP formation in the hippocampus were differently antagonized by atropine, 4-diphenylacetoxy-N-methyl piperidine methiodide (4-DAMP), the M2-receptor subtype-preferring antagonist AF-DX 116 and the M1-selective antagonist pirenzepine. These data support the notion that the IP formation induced by carbachol in the forebrain predominantly is mediated by muscarinic receptors of the M1 subtype, and indicate the involvement of muscarinic receptors of the M3 subtype in the carbachol-induced cGMP formation.

ACTH/MSH-like peptides inhibit the binding of dopaminergic ligands to the dopamine D2 receptor in vitro

ACTH-(1-24) decreased the binding of the dopamine D2 receptor agonist, [3H]N-propylnorapomorphine ([3H]NPA), to rat striatal membranes in a concentration-dependent manner, with a Ki of 5 x 10(-7) M. Saturation curves for [3H]NPA binding in the presence of increasing concentrations of ACTH-(1-24) were performed. Scatchard analysis in the presence of ACTH-(1-24) revealed an increased dissociation constant (Kd), while the binding capacity (Bmax) was not affected by the peptide, suggesting an apparent competitive interaction between ACTH-(1-24) and [3H]NPA. ACTH-(1-24) also reduced the binding of the dopamine D2 receptor antagonist [3H]spiperone to striatal membranes, with a Ki of 10(-6) M. Much higher concentrations of ACTH-(1-24), up to 10(-4) M, were needed for the displacement of appropriate radiolabelled ligands from dopamine D1 receptors, serotonin 5-HT1A, serotonin 5-HT1B, muscarinic M1 acetylcholine and histamine H1 receptors. ACTH-(1-24) also inhibited the binding of [3H]spiperone to dopamine D2 receptors in membranes of the pituitary gland, the septum and the substantia nigra. ACTH-(1-39) and most ACTH fragments and analogs were less potent than ACTH-(1-24) in displacing [3H]NPA from the dopamine D2 receptor in striatal membranes. In general there was a relationship between displacing potency and chain length. ACTH-(7-16)-NH2 and benzyloxycarbonyl-ACTH-(8-16)-NH2, however, were more potent than ACTH-(1-24) in reducing the binding of [3H]NPA to dopamine D2 receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurochemical studies with the potential antipsychotic compound trans-5-Chloro-2-methyl-2,3,3a,12b-tetrahydro-1H- dibenz[2,3:6,7]oxepino[4,5-c]pyrrolidine maleate

trans-5-Chloro-2-methyl-2,3,3a,12b-tetrahydro-1H-dibenz [2,3:6,7]oxepino[4,5-c]pyrrolidine maleate (Org 5222) has dopamine D2 antagonistic and negligible anticholinergic properties of the classical neuroleptic haloperidol. In addition it combines the strong antiserotonergic and antihistaminergic properties of chlorpromazine and clozapine with the potent dopamine D-1 antagonistic properties of Sch 23390 (R-(+)-delta-chloro-2,3,4,5-tetrahydro-3-methyl-5- phenyl-1H-3-benazepin-7-ol(Z)-2-buteneoate). This in conjunction to its behavioural properties, warrants clinical testing in psychotic patients.

The neuropeptide, Org 5878 (desenkephalin-gamma-endorphin, DE gamma E), affects local cerebral glucose utilization in freely moving rats

The effect of the antipsychotic peptide, Org 5878 (desenkephalin-gamma-endorphin, beta-endorphin-(6-17), on local cerebral glucose utilization was studied in freely moving male Wistar rats. Org 5878 (20 micrograms/kg, i.v.) or saline were given acutely and local cerebral glucose utilization was measured in 116 brain structures. Glucose uptake was not altered by Org 5878 in most brain areas, including areas of the nigrostriatal system, the cortex and the thalamus. However, significant reductions in glucose uptake were observed in the ventral tegmental area, the diagonal band complex, the hippocampus, the amygdala, the interpeduncular nucleus, the reticular nucleus of the thalamus and the cerebellum. These results indicate that the nigrostriatal and cortico-thalamic systems remain unaffected but the activity of the mesolimbic ventral tegmental area and of major target areas of cholinergic basal forebrain structures is selectively reduced following Org 5878 administration. It is concluded that the effect of Org 5878 on local cerebral glucose utilization is distinct from and more selective than that of antipsychotics currently used in the clinic.

Local cerebral glucose uptake in anatomically defined structures of freely moving rats

Two limitations of the classical [14C]2-deoxyglucose (DG) method are the severe stress to which the restrained animals are exposed, and the difficulties with the anatomical analysis of the autoradiograms. The present study describes modifications which circumvent these limitations. Firstly, rats are provided with two chronic indwelling cannulas to allow blood sampling under unrestrained conditions. Absence of stress is demonstrated by low plasma corticosterone levels in the cannulated rats at the start of the experiment. The second modification concerns the image analysis system. The image of the autoradiogram is superimposed on the image of the identical histologically stained section in order to improve the accuracy of the structure identification. This approach enables the operator to delineate the anatomical brain structure in the histologically stained section and quantify the glucose uptake in the autoradiogram generated from this section. The reproducibility of the present quantitative measuring system is illustrated by glucose uptake measurements in different laminar zones of the various fields in the dorsal hippocampal formation. It is concluded that the present technical improvements of the classically applied [14C]2-deoxyglucose technique provide favourable conditions for the quantitative study on cerebral glucose uptake in normally behaving animals.

Stimulation of D2-dopamine receptors in rat neostriatum inhibits the release of acetylcholine and dopamine but does not affect the release of gamma-aminobutyric acid, glutamate or serotonin

D1-dopamine receptor stimulation did not affect the K+-induced release of [3H]GABA, [3H]glutamate, [3H]serotonin, [3H]dopamine and [14C]acetylcholine from slices of rat neostriatum. D2-dopamine receptor stimulation did not change the release of [3H]GABA, [3H]glutamate and [3H]serotonin, but inhibited the release of both [3H]dopamine and [14C]acetylcholine; this inhibition was antagonized by (-)-sulpiride. The release-inhibiting dopamine autoreceptors and the post synaptic dopamine receptors mediating the inhibition of acetylcholine release appear to be pharmacologically similar and can be classified as D2-receptors.