Disinhibition of nucleus accumbens neurons by the dopamine D2 receptor agonist LY-141865: prevented by 6-OHDA pretreatment

Intravenous administration of LY-141865, a specific dopamine (DA) D2 receptor agonist, caused a biphasic increase/decrease in the firing rate of cells in the rat nucleus accumbens (NAc). 6-Hydroxydopamine injected directly into the medial forebrain bundle, through which the ascending DA fibers pass, prevented the initial rate increase of NAc neurons produced by low doses of LY-141865. In contrast, pretreatment of rats with 5,7-dihydroxytryptamine did not alter the biphasic response of NAc neurons to LY-141865. These results, together with previous findings that D2 autoreceptors are much sensitive to DA and DA agonists, strongly support the hypothesis that the initial rate-increase caused by low doses of LY-141865 is the result of disinhibition.

Chronic treatment with high doses of haloperidol fails to decrease the time course for the development of depolarization inactivation of midbrain dopamine neurons

Using extracellular single unit recording techniques, we investigated the effects produced by chronic treatment with high doses of haloperidol (CHAL, 5 mg/kg/day, s.c.) on midbrain dopamine (DA) neuronal activity. This regimen of HAL treatment produced a time-dependent reduction in the number of spontaneously active DA neurons. Additionally, this dose regimen induced an irregular firing pattern in many of the remaining active DA neurons in both the ventral tegmental area (A10) and substantia nigra pars compacta (A9) regions. These effects were comparable to those obtained previously in rats treated chronically with lower doses of HAL (0.5 mg/kg/day, s.c.). However, there was a greater decrease in the number of spontaneously active DA cells detected in rats treated with high doses of HAL for three weeks compared to those receiving the low doses. On the other hand, higher doses of apomorphine (200 micrograms/kg, i.v.) were required to reverse both the reduction of DA activity and irregular discharge pattern in rats treated chronically with high doses of HAL. In conclusion, the results of the present study substantiate the view that CHAL-induced depolarization inactivation (DI) of DA neurons is a time-dependent process and chronic treatment with high doses of HAL did not shorten the time course required for the development of DI on the majority of midbrain DA neurons.

Possible involvement of the A20-A21 peptide bond in the expression of the biological activity of insulin. 3. [21-Desasparagine,20-cysteine ethylamide-A]insulin and [21-desasparagine,20-cysteine 2,2,2-trifluoroethylamide-A]insulin

We have synthesized [21-desasparagine,20-cysteine ethylamide-A]insulin and [21-desasparagine,20-cysteine 2,2,2-trifluoroethylamide-A]insulin, which differ from natural insulin in that the C-terminal amino residue of the A chain, asparagine, has been removed and the resulting free carboxyl group of the A20 cysteine residue has been converted to an ethylamide and a trifluoroethylamide group, respectively. [21-Desasparagine,20-cysteine ethylamide-A]insulin displayed equivalent potency in receptor binding and biological activity, ca. 12% and ca. 14%, respectively, relative to bovine insulin. In contrast, [21-desasparagine,20-cysteine 2,2,2-trifluoroethylamide-A]insulin displayed a divergence in these properties, ca. 13% in receptor binding and ca. 6% in biological activity. This disparity is ascribed to a difference in the electronic state of the A20-A21 amide bond in these two analogues. A model is proposed to account for the observation of divergence between receptor binding and biological activity in a number of synthetic insulin analogues and naturally occurring insulins. In this model, changes in the electronic state and/or the orientation of the A20-A21 amide bond can modulate biological activity independently of receptor binding affinity. The A20-A21 amide bond is thus considered as an important element in the "message region" of insulin.

Possible involvement of the A20-A21 peptide bond in the expression of the biological activity of insulin. 1. [21-Desasparagine,20-cysteinamide-A]insulin and [21-desasparagine,20-cysteine isopropylamide-A]insulin

The C-terminal region of the A chain of insulin has been shown to play a significant role in the expression of the biological activity of the hormone. To further delineate the contribution of this segment, we have synthesized [21-desasparagine,20-cysteinamide-A]insulin and [21-desasparagine,20-cysteine isopropylamide-A]insulin, in which the C-terminal amino acid residue of the A chain of insulin, asparagine, has been removed and the resulting free carboxyl group of the A20 cysteine residue has been converted to an amide and an isopropylamide, respectively. Both insulin analogues display biological activity, 14-15% for the unsubstituted amide analogue and 20-22% for the isopropylamide analogue, both relative to bovine insulin. In contrast, a [21-desasparagine-A]insulin analogue has been reported to display less than 4% of the activity of the natural hormone [Carpenter, F. (1966) Am. J. Med. 40, 750-758]. The implications of these findings are discussed, and we conclude that the A20-A21 amide bond plays a significant role in the expression of the biological activity of insulin.

Repeated tandem translocations in a clone and subclones of B16-F10 murine melanoma

In one clone and three subclones isolated from the F10 line of the B16 mouse melanoma, a family of extraordinarily long marker chromosomes was found. Banding analyses showed that these long markers represented repeated tandem translocations. Most of these markers exhibited only two or three C-bands. Immunofluorescence staining using antikinetochore serum revealed that these markers had either two active kinetochores or one active and one inactive kinetochore. The original clone and one of the subclones were highly unstable with respect to the composition of the markers and to the ability for retaining the markers. The other two subclones were found to be relatively stable. Because all three subclones were derivatives of one clone, which was unstable, our data suggest that stable genomes can be generated from unstable progenitors.

Spontaneous mutation rates in cloned murine tumors do not correlate with metastatic potential, whereas the prevalence of karyotypic abnormalities in the parental tumors does

We tested the hypothesis that highly malignant cell lines are genomically more unstable than their less malignant counterparts, and that this instability is more pronounced in clones than in cell lines. We compared MDAY-D2 to its non-metastatic variant, D36W25, with regard to (1) the rate of development of ouabain resistance within parallel clones and (2) the prevalence of G-banded karyotypic abnormalities. We detected no significant difference between the spontaneous mutation rates for ouabain resistance. However, the MDAY-D2 cell line possessed both a higher prevalence and greater diversity of chromosomal abnormalities. One possible explanation for these seemingly inconsistent results is that genomic instability may remain essentially constant throughout tumor progression, whereas an accumulation of genetic changes may be responsible for the observed increased prevalence of abnormalities and the development of selective survival advantages during progression.

Rate of generation of major karyotypic abnormalities in relationship to the metastatic potential of B16 murine melanoma

To test the hypothesis that genetic instability correlates with malignant potential, we compared the rate of generation of marker chromosomal abnormalities in clones of B16 F1 and B16 F10 murine melanoma. These rates were estimated through an adaptation of fluctuation analysis of Luria and Delbruck (S. E. Luria and M. Delbruck, Genetics, 28: 491-511, 1943). The highly metastatic F10 line showed the same degree of marker chromosomal instability as the poorly metastatic F1 line (0.01 variants/cell/generation). When subclones of a karyotypically unstable F10 clone were compared with those of a more stable F10 clone, both groups caused the same number of pulmonary metastases, thus demonstrating a further lack of correlation of malignant potential with the level of genomic instability. Since measurements based on marker chromosomes may not truly reflect all of the changes detectable by G-banding, we also analyzed the G-banded karyotypes of the cell lines and their clones (chromatid or chromosomal breaks were not considered in this study). The F10 clones possessed an additional copy of chromosome 1 and also a significantly higher prevalence of the translocation t(9,12) when compared with the F1 clones. Rather than general rates of major karyotypic change determining tumor progression, we suggest the importance of other genetic or epigenetic mechanisms, particularly subtle nonrandom genetic or molecular changes, as the determining factors for malignant potential.

Differential effects of acute clozapine and haloperidol on the activity of ventral tegmental (A10) and nigrostriatal (A9) dopamine neurons

Extracellular single-unit recording techniques were used to evaluate the effects of acute intravenous (i.v.) clozapine (CLOZ) and haloperidol (HAL) on the activity of dopamine (DA) neurons of the ventral tegmental area (VTA or A10) and the substantia nigra pars compacta (SNC or A9). CLOZ increased the firing rate of A10 but not A9 cells, and drove 9/23 (39%) of A10 cells into an apparent depolarization blockade. HAL, on the other hand, produced a rate elevation and, at higher doses, depolarization inactivation in both subpopulations of DA neurons. Cell firing was restored in inactivated cells with i.v. apomorphine (APO) or iontophoretic GABA. CLOZ always fully reversed APO-induced suppression of A10 DA activity, but in many cases only partially reversed suppression of A9 DA neurons. Scopolamine did not mimic the effects of CLOZ on A10 neurons, and it also failed to block the activating effect of HAL on A9 units, indicating that the selective action of CLOZ cannot be interpreted simply by its anticholinergic properties. After hemi-transections of the diencephalon, which severed the medial forebrain bundle and other feedback pathways to the DA somata, CLOZ was still ineffective in altering A9 DA activity. This suggests that the lack of effect on CLOZ on A9 cells is not due to the inhibitory influence of forebrain feedback pathways. This hemi-transection also left intact the activation of A10 neurons produced by HAL and CLOZ, but it did prevent the excitatory action of HAL on most A9 neurons sampled. This indicates that forebrain feedback pathways are less critical in mediating the action of APDs on A10 DA neurons. Finally, iontophoretic application of CLOZ and HAL into the vicinity of DA cell bodies blocked the rate-reducing effects of locally applied DA, but not those of GABA. This suggests that both APDs block somatodendritic DA autoreceptors. However, HAL was considerably more potent than CLOZ in producing this blockade. It is suggested that the different pharmacological and clinical properties of HAL and CLOZ may be partially explained by a differential mode of action on the A10 and A9 subpopulations of DA cells. The data also provide pharmacological evidence that these 2 groups of DA cells are regulated by different mechanisms.

Effects of acute thioridazine, metoclopramide and SCH 23390 on the basal activity of A9 and A10 dopamine cells

Extracellular single-unit recording techniques were employed to examine the effects of various dopamine (DA) antagonists on the basal activity of spontaneously active DA cells. Metoclopramide and thioridazine were both effective in reversing apomorphine-induced suppression of A9 and A10 DA cells. SCH 23390 produced only a partial reversal of this suppression. When the antagonists were given without any pretreatment, thioridazine preferentially increased the firing rate of A10 DA cells, and was relatively ineffective in altering A9 activity. Metoclopramide, on the other hand, increased the activity of most A9 DA cells, but was less effective in doing so with A10 cells. SCH 23390 did not significantly affect the basal activity of either cell subpopulation. These data support the hypothesis that the so-called 'atypical' antipsychotic drugs act preferentially on the A10 DA system. Taken together with previous results, they also suggest that the acute effects of DA antagonists on DA cell subpopulations coincide with their chronic effects.

Failure of subchronic lisuride to modify A10 dopamine autoreceptors' sensitivity

The concept that prolonged treatment with dopamine (DA) mimetics results in a subsensitivity of DA autoreceptors generally is accepted. However, the present study indicates that the administration of a rather specific DA-D2 agonist, lisuride hydrogen maleate (LIS), for one week (200 micrograms/kg/daily) failed to modify the sensitivity of DA autoreceptors of A10 neurons. Indeed, by using extracellular single unit recording in chloral hydrate-anesthetized rats, we observed that neither intravenous apomorphine nor microiontophoresis of DA changed their firing rate-depressant potency when it was estimated at 1 or 3 days after the last LIS injection. A possible interpretation of the results is that the subchronic stimulation of DA-D2 receptors activates an unknown compensatory mechanism which avoids the changes in their sensitivity. Alternatively, the possibility that LIS may also possess antagonistic properties for DA receptors, which might balance the D2 receptors activation, is discussed.

Clonal origin of metastasis in B16 murine melanoma: a cytogenetic study

A cell line isolated from the B16 melanoma and carried in continuous culture for 8 years (the parent line) exhibited great heterogeneity in terms of marker chromosome content. A lung metastasis from a C57BL/6 mouse inoculated im with cells of this line showed karyotypic homogeneity. Inoculation iv of cells from the parent line produced numerous tumor foci in various organs. Cytogenetic analyses of 18 such lesions led to the following conclusions: Cells from each metastatic colony exhibited relatively homogeneous karyotypic characteristics, indicating that metastases are of clonal origin; many parental cells with different marker chromosomes had metastatic potential; and some genomes maintained homogeneity longer than others.

Methylated DNA-binding protein from human placenta recognizes specific methylated sites on several prokaryotic DNAs

Methylated DNA-binding protein (MDBP) from human placenta recognizes specific DNA sequences containing 5-methylcytosine (m5C) residues. Comparisons of binding of various prokaryotic DNAs to MDBP indicate that m5CpG is present in the recognition sites for this protein but is only part of the recognition sequence. Specific binding to MDBP was observed for bacteriophage XP12 DNA, which naturally contains approximately 1/3 of its residues as m5C, and for Micrococcus luteus DNA, M13mp8 replicative form (RF) DNA, and pBR322 when these three DNAs were methylated at CpG sites by human DNA methyltransferase. Five DNA regions binding to MDBP have been localized by DNase I footprinting or restriction mapping in methylated pBR322 and M13mp8 RF DNAs. A comparison of their sequences reveals a common 5'-m5CGRm5CG-3' element or closely related sequence in which one of the m5C residues may be replaced by a T. In addition to this motif, one upstream and one downstream m5CpG as well as other common residues over an approximately 20-bp long region may be recognized by MDBP.

Modulation of cholecystokinin release from posterior nucleus accumbens by D-2 dopamine receptor

The effect of specific D-2 dopamine (DA) receptor agonists and antagonists on potassium (55 mM)-evoked release of cholecystokinin-like immunoreactivity (CCK-LI) was studied in tissue slices of the rat posterior nucleus accumbens (NAc). Incubating the tissue slices in 100 nM or 1 microM of LY-141865, a specific D-2 DA receptor agonist, reduced the release of CCK-LI as indicated by a significant decrease in the S2/S1 ratio. Addition of 10 microM of (-)-sulpiride, a specific D-2 DA receptor antagonist, blocked the inhibitory effect of 100 nM of LY-141865 on the release of CCK-LI. In contrast, 10 microM of the specific D-1 DA receptor antagonist SCH 23390 was unable to attenuate the decrease in release of CCK-LI caused by 100 nM of LY-141865. Furthermore, the active isomer of LY-141865, LY-171555 at 0.1 to 50 nM, also decreased the release of CCK-LI from the tissue slices, while the inactive isomer, LY-181990 at 1 nM, did not affect CCK-LI release. The inhibitory effect of LY-171555 on the release of CCK-LI was lost when its concentration was increased to 100 nM, thus revealing a biphasic effect of D-2 DA receptor stimulation on the release of CCK-LI. These results demonstrate that stimulation of D-2 DA receptor can modulate the release of CCK from in vitro slices of the rat posterior NAc.

Effect of site-specific DNA methylation and mutagenesis on recognition by methylated DNA-binding protein from human placenta

Methylated DNA-binding protein (MDBP) from human placenta is the first protein shown to bind specifically to certain DNA sequences only when they are methylated at cytosine residues. Among the sites recognized by MDBP is pB site 1, a pBR322-derived sequence which has a high affinity for MDBP when methylated at all CpG positions. We have substituted pB site 1 with 5-methyl-cytosine (m5C) residues at one to three of its CpG dinucleotides on one strand by the use of m5C-containing oligonucleotides. MDBP binds best when all three CpG dinucleotides in the region 5'-ATCGTCACGGCGAT-3' are methylated. Even more binding is obtained when both strands are methylated. Alteration of various residues in this binding site by oligonucleotide-directed mutagenesis decreased the binding. However, two mutations which increased the dyad symmetry of part of the binding site yielded ligands with a higher affinity for MDBP.

[Combination therapy of advanced choriocarcinoma--an analysis of 60 patients]

From Jan. 1973 to Dec. 1984, 60 patients with advanced choriocarcinoma were treated in our hospital. 34 of them were stage IIIB and 26 stage IV. There were 36 patients with lobulated pulmonary metastases and 13 with brain metastases. The 4-drug chemotherapy (methotrexate or fluorouracil, kengsengmycin, vincristine and nitrogen mustard) was used as the main treatment, supplemented by surgery or irradiation. In those with lobulated pulmonary metastatic foci and lesions in the brain, the 4-drug chemotherapy was used before, during or after split course irradiation. Generally, radiation with a total dose of 4,000 rad (2,000 rad/12 D, interval of 4 weeks, 2,000 rad/12 D) was given after 3-4 courses of chemotherapy. The 1, 3 and 5 year survival rates were 85.7%, 78.6% and 79.4%, respectively. Lobulated pulmonary lesions as treated with 4-drug chemotherapy plus split course irradiation gave a 3 year survival rate of 88.0% (22/25). 7 of 8 with brain metastases treated by the same modality gave complete remission. 5 have survived for more than 3 years. In this series, the combination therapy of advanced choriocarcinoma, role of irradiation for this tumor and individualization in treatment are discussed. The authors believe that the 4-drug chemotherapy for advanced choriocarcinoma is superior to the other regiment and, when combined with split course irradiation is very effective in lobulated pulmonary and brain metastases.

Electrophysiological evidence for locus coeruleus norepinephrine autoreceptor subsensitivity following subchronic administration of D-amphetamine

The effect produced by subchronic administration of D-amphetamine (D-AMP) on the sensitivity of norepinephrine (NE) autoreceptors in the rat locus coeruleus (LC) was studied by means of single unit recording and microiontophoretic techniques. Twice daily i.p. administration of 5 mg/kg D-AMP for one week markedly reduced the ability of i.v. D-AMP and microiontophoretic application of clonidine to suppress the firing of LC NE neurons, suggesting strongly that NE autoreceptors became subsensitive. In addition, the firing pattern of NE neurons became 'disorganized' following subchronic AMP treatment.

Effects of tiaspirone (BMY-13859) and a chemical congener (BMY-13980) on A9 and A10 dopamine neurons in the rat

Two new potential antipsychotic drugs, BMY-13980 and BMY-13859 were compared for the ability to influence the electrophysiological activity of dopaminergic neurons in the substantia nigra zona compacta (A9 DA cells) and ventral tegmental area (A10 DA cells) in the brain of the rat. Both drugs reversed the rate-suppressant effects of the DA agonist apomorphine on DA cells in A10 to a greater extent than DA cells in A9; BMY-13980 was particularly selective in this regard. These results indicate that both drugs may exert DA antagonist effects which are suggestive of antipsychotic potential. In other experiments, the effects of chronic (28 days) treatment with BMY-13980 and BMY-13859 on the neuronal activity of DA were evaluated. Both compounds caused a significant decrease in the number of spontaneously active DA neurons in A10 recorded per electrode track, an effect previously demonstrated to be associated with antipsychotic efficacy. The drug BMY-13859, but not BMY-13980, also significantly decreased the number of spontaneously active DA cells/track in A9, an effect which may predict the liability of potential antipsychotic drugs for causing extrapyramidal motor dysfunction, including tardive dyskinesia. Thus, these experiments indicate that both BMY-13980 and BMY-13859 exert effects which may predict potential antipsychotic efficacy in clinical trials and that BMY-13980 may be less likely to cause extrapyramidal side effects.

Does cholecystokinin potentiate dopamine action in the nucleus accumbens?

Extracellular single unit recording and microiontophoretic techniques were used to determine whether sulfated cholecystokinin octapeptide (CCK-8S) potentiates the inhibitory action of dopamine (DA) on neurons in the nucleus accumbens of rats. The results show that CCK-8S attenuated, rather than enhanced the action of DA. The interaction between CCK-8S and DA does not appear to be specific because similar antagonizing actions between CCK-8S and serotonin were observed. In addition to opposing the inhibitory effects of DA and serotonin, CCK-8S potentiated the activation of glutamate. It is concluded that CCK-8S and DA exerted their actions independently via depolarizing and hyperpolarizing the neuronal membrane of the NAc neurons, respectively.

Acute and subchronic effects of Rimcazole (BW 234U), a potential antipsychotic drug, on A9 and A10 dopamine neurons in the rat

The effects of acute and subchronic Rimcazole administration on A9 and A10 dopamine (DA) neurons were examined using extracellular single cell recording techniques. Intravenous injections of Rimcazole did not prevent or reverse the inhibition of firing rates of DA cells produced by DA agonist apomorphine (APO). Single intraperitoneal injection of Rimcazole decreased the number of spontaneously active DA cells in A10, but not in A9; it had no effect on the firing rate of DA neurons in either A9 or A10. Following prolonged administration of Rimcazole, 25 mg/kg/day for 28 days, there was a significant increase in the number of spontaneously active A10 DA neurons, but not A9 DA cells. The firing rate of both A9 and A10 DA cells decreased significantly following prolonged Rimcazole administration; however, the firing pattern of these cells did not change. In addition, chronic Rimcazole did not affect the ID50 of APO for DA neurons. These results suggest that Rimcazole has an indirect effect on DA neurons with a relative selectivity for A10 DA cells; it does not exhibit pharmacological profiles of previously reported antipsychotic drugs.

Combined use of warfarin and adjusted subcutaneous heparin during pregnancy in patients with an artificial heart valve

Adjusted subcutaneous heparin was used for thromboembolism prophylaxis during 18 pregnancies in 16 women with an artificial heart valve. Oral warfarin was replaced by subcutaneous heparin as soon as pregnancy was confirmed. The dosage of heparin was adjusted to maintain a partial thromboplastin time at 1.5 times the control value and treatment was administered during the first trimester and the last 3 weeks of gestation. Warfarin was used between the 13th and 37th week. There were no maternal thromboembolic complications and none of the live-born infants showed congenital malformations, indicating that this regimen is effective. However, there were nine spontaneous abortions, including five that occurred in the first 12 weeks. The early abortions were probably related to warfarin exposure at the beginning of pregnancy. The preconception replacement of warfarin by heparin in these patients may be indicated.

DNA cytosine methylation and heat-induced deamination

The heat-induced conversion of 5-methylcytosine (m5C) residues to thymine residues and of cytosine to uracil residues in single-stranded DNA was studied. The calculated rates for deamination at 37 degrees C and pH 7.4 were approximately 9.5 X 10(-10) and 2.1 X 10(-10) sec-1, respectively. N4-Methyldeoxycytidine, which is in the DNA of certain thermophilic bacteria, was more heat-resistant than was deoxycytidine and much more than was 5-methyldeoxycytidine. Thermophilic bacteria which contain N4-methylcytosine rather than m5C in their genomes may thereby largely avoid heat-induced mutation due to deamination, which is incurred by the many organisms that contain m5C in their DNA.

Cholecystokinin octapeptides alter the release of endogenous dopamine from the rat nucleus accumbens in vitro

Sulfated cholecystokinin octapeptide (CCK-8S) has been reported to be extensively colocalized with dopamine in the posterior, but not the anterior, portion of the nucleus accumbens (NAc). The hypothesis tested in the present study was that CCK-8S alters the release of dopamine in this structure and the actions it produces are dependent on the extent of colocalization with dopamine. We observed in vitro that CCK-8S enhanced the resting release of dopamine from the posterior, but not anterior, NAc. It was also found that CCK-8S attenuated the release of dopamine induced by potassium-evoked depolarization in both regions of the NAc, although the concentration-release curves for the two areas differed. In the posterior NAc, a biphasic response was seen whereas, in the anterior NAc, there was a monophasic attenuation. Proglumide, a putative CCK-8S antagonist, was found to antagonize the action of a low concentration of CCK-8S on 40 mM K+-induced dopamine release from slices of the posterior, but not anterior, NAc. Unsulfated CCK-8 had mixed action on K+-evoked dopamine release, as it enhanced this form of release in the posterior NAc but attenuated it in the anterior NAc. Additionally, we found no effect of sulpiride on the actions of CCK-8S with respect to evoked release, suggesting that CCK-8S is not acting to alter dopamine autoreceptor function, as has recently been hypothesized. In summary, our results demonstrate that the observed effects of CCK-8S on dopamine release are dependent upon the region of the NAc studied, and there appear to be different subtypes of CCK-8S receptors present in the two regions.

The identification of some sources of afferent input to the rat nucleus basalis magnocellularis by retrograde transport of horseradish peroxidase

Neurons of the nucleus basalis magnocellularis (NBm) of the rat are contained within the ventromedial globus pallidus and adjacent internal capsule. Horseradish peroxidase injection limited to the ventromedial globus pallidus result in sparse neuronal labeling in a variety of brainstem, thalamic and hypothalamic nuclei, and the basal nuclei identified after NBm injections. Thus, these contiguous regions have comparable subcortical inputs. By contrast, only NBm injections yielded a large number of labeled neurons in layer V of NBm cholinergic neurons. in addition to the reciprocity observed between NBm and frontal cortex, the ventral tegmental area and NBm likewise appear to be reciprocally connected.