HLA-A2.1-restricted T cells react to SEREX-defined tumor antigen CML66L and are suppressed by CD4+CD25+ regulatory T cells

The question of whether T cell responses to SEREX-defined tumor antigens are under regulation of naturally occurring CD4+CD25+ regulatory T cells (nTreg cells) has not been answered. To address this issue, we first identified an HLA-A2.1-restricted T cell antigen epitope of SEREX-identified tumor antigen CML66L, 66Pa. The HLA-A2.1/66Pa peptide complex in vitro stimulated the in vivo-primed T cells as shown by increased T cell proliferation, higher secretion of the T cell cytokine interferon-gamma (IFN-gamma), increased production of intracellular IFN-gamma in CD8+ T cells, and higher T cell-mediated cytotoxicities of CML66L+ human tumor cells. This suggests that CML66L elicits T cell immune responses. We also developed a novel internal reference epitope for identification of T cell epitopes by construction of chimeric CML66L containing myeloid antigen proteinase 3 epitope Pr1 as a control. Finally, we found that nTreg cells regulates T cell responses to 66Pa, and that depletion of nTreg cells via a pro-apoptotic protein Bax-dependent mechanism enhances polyclonal T cell responses to 66Pa. These findings provide new insights into the T cell participation in SEREX-defined anti-tumor immune responses and novel direction in enhancement of anti-leukemia immunotherapy by modulation of homeostasis of nTreg cells.

Processing sites are different in the generation of HLA-A2.1-restricted, T cell reactive tumor antigen epitopes and viral epitopes

In order to improve the processing efficiency of T cell tumor antigen epitopes, this bioinformatic study compares proteolytic sites in the generation of 47 experimentally identified HLA-A2.1-restricted immunodominant tumor antigen epitopes to those of 52 documented HLA-A2.1-restricted immunodominant viral antigen epitopes. Our results show that the amino acid frequencies in the C-terminal cleavage sites of the tumor antigen epitopes, as well as several positions within the 10 amino acid (aa) flanking regions, are significantly different from those of the viral antigen epitopes. In the 9 amino acid epitope region, frequencies differed somewhat in the secondary-anchored amino acid residues on E3 (the third aa of the epitope), E4, E6, E7 and E8; however, frequencies in the primary-anchored positions, on E2 and E9, for binding in the HLA-A2.1 groove, remained almost identical. The most frequently occurring amino acid pairs in both N-terminal and C-terminal cleavage sites in the generation of tumor antigen epitopes were different from those of the viral antigen epitopes. Our findings demonstrate for the first time that these two groups of epitopes may be cleaved by distinct sets of proteasomes and peptidases or similar enzymes with lower efficiencies for tumor epitopes. In the future, in order to more effectively generate tumor antigen epitopes, targeted activation of the immunoproteasomes and peptidases that mediate the cleavage of viral epitopes could be achieved, thus enhancing our potential for antigen-specific tumor immunotherapy.

Acidotoxicity in brain ischaemia

Intracellular calcium toxicity remains the central feature in the pathophysiology of ischaemic cell death in brain. Glutamate-gated channels have been thought to be the major sites of ischaemia-induced toxic calcium entry, but the failure of glutamate antagonists in clinical trials has suggested that glutamate-independent mechanisms of calcium entry during ischaemia must exist and may prove central to ischaemic injury. We have shown that ASICs (acid-sensing ion channels) in brain are glutamate-independent vehicles of calcium flux and transport calcium in greater measure in the setting of the two major neurochemical components of ischaemia: acidosis and substrate depletion. Pharmacological blockade of ASICs markedly attenuates stroke injury with a robust therapeutic time window of 5 h following stroke onset. Here, we describe this new mechanism of calcium toxicity in brain ischaemia and offer a potential new therapy for stroke.

Stimulative activity of Drynaria fortunei (Kunze) J. Sm. extracts and two of its flavonoids on the proliferation of osteoblastic like cells

The osteoblastic activity of extracts of Drynaria fortunei (Kunze) J. Sm. rhizome was assayed in the UMR106 cell line cultured in vitro. An ethanol extract and its fractions were added to the cell culture at different concentrations. Osteoblastic proliferation stimulating activity was determined using the MTT method. The ethanol extract, and its ethyl acetate and n-butanol fractions exhibited stimulating activity. Two active constituents were isolated from n-butanol fraction by bioassay-directed isolation, and identified as naringin and neoeriocitrin. The latter is reported for the first time from this herbal medicine.

Alternative splicing factor ASF/SF2 is down regulated in inflamed muscle

BACKGROUND

In our recent studies, alternative splicing has been shown to have a major role in inflammation and autoimmune muscle diseases.

AIM

To examine the novel hypothesis that the expression of an essential alternative splicing factor, alternative splicing factor 2 (ASF/SF2), is modulated in muscle inflammation.

METHODS

ASF/SF2 expression in muscle biopsy samples from eight patients with inflammatory myopathy and six non-myositic controls was determined by using western blot with anti-ASF/SF2 antibodies. To further elucidate the mechanism of reduced ASF/SF2 expression in inflamed muscle, differentiated C2C12 myotubes were stimulated with proinflammatory cytokine tumour necrosis factor alpha (TNFalpha), followed by western blot analysis of ASF/SF2 expression.

RESULTS

ASF/SF2 expression in the muscle biopsy samples from patients with inflammatory myopathy was found to be lower (mean of relative densitometric units 41.1 (2SD 20.7)) than that of the non-myositic controls (mean of relative densitometric units 76.7 (39.6); p<0.05). In addition to this, ASF/SF2 expression was seen to be significantly down regulated (sevenfold) in C2C12 myotubes compared with expression variations in the beta-actin control (0.62-fold; mean 1.22 (0.40); p<0.05).

CONCLUSION

Collectively, it is shown, for the first time, that alternative splicing factor ASF/SF2 is down regulated in autoimmune inflammatory myositis-potentially via a TNFalpha-mediated pathway. The development of (1) novel autoantigen isoform microarrays for disease diagnosis and prognosis; (2) novel autoantigen-tolerising treatments for autoimmune diseases; and (3) novel splicing-redirection treatments can be facilitated by the ongoing study of alternative splicing of autoantigen transcripts.

Natural Occurrence of Chilli veinal mottle virus on Capsicum chinense in China

An outbreak of a viral disease on chili pepper (Capsicum chinense Jacp. cv. Yellow Lantern) occurred in Hainan Province, China during 2003 and 2004. The disease was prevalent in five chili-producing counties surveyed. Leaves of infected plants initially displayed symptoms of dark green banding along veins and later became distorted with striking mosaic. Infected plants had reduced flower numbers and fruit set, resulting in a significant yield loss. The causative virus was characterized and identified as Chilli veinal mottle virus (ChiVMV) (3). An isolate of the virus was obtained via three single lesion passages through Chenopodium amaranticolor and was shown to reproduce the same symptoms on inoculated C. chinense cv. Yellow Lantern. Negative staining of crude extracts of the infected tissue and subsequent electron microscopy revealed flexuous rods of 12 to 13 × 750 nm, typical of a potyvirus. Pinwheel-like inclusion bodies were abundant in thin sections of infected leaves. Purified virus preparations contained one major protein of 32.8 kDa and one minor protein of 28 kDa when fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Both of these protein bands were excised and subsequently analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Multiple peptide fragments from both proteins were identified as arising from ChiVMV capsid protein (CP) (1,2). Therefore, the 32.8-kDa protein is the full-length ChiVMV CP and the 28-kDa protein is presumably a degradation product of the CP. The combined biological and molecular data provided strong evidence that the viral disease on C. chinense was caused by ChiVMV. To our knowledge, this is the first report of ChiVMV infection on C. chinense in China and the first report of C. amaranticolor as an experimental host for ChiVMV. References: (1) P. Chiemsombat et al. Arch. Virol. 143:1855, 1998. (2). J. Joseph and H. S. Savithri. Arch. Virol. 144:1679, 1999. (3) P. Siriwong et al. Plant Pathol. 44:718, 1995.

Coumarins from Cnidium monnieri (L.) and their proliferation stimulating activity on osteoblast-like UMR106 cells

The proliferation of various fractions of alcoholic extracts from fruits of Cnidium monnieri (L.) Cuss (umbelifera) were screened using the osteoblast-like UMR106 cells in vitro. The chloroform fraction from the crude extract was found to have the most stimulating activity. Three coumarins (osthole, bergapten and imperatorin) were isolated from this fraction by activity-guided assay, and their effects on osteoblastic proliferation were investigated. Osthole, a major pharmacologically active constituent, significantly promoted the cells' activity. Bergapten and imperatorin were less effective than osthole. These results suggested Cnidium monnieri (L.) Cuss extracts might have potential activity against osteoporosis, and its chloroform fraction might contain active constituents stimulating osteoblasts.

Follicle-stimulating hormone (FSH) induced internalization of porcine FSH receptor in cultured porcine granulosa cells and Chinese hamster ovary cells transfected with recombinant porcine FSH receptor cDNA

In order to study the fate of human follicle-stimulating hormone (FSH) when hormone binds to its receptor, a quick biochemical method that can differentiate between the surface-bound and internalized hormone was used to determine the internalization induced by FSH in cultured both porcine granulosa cells and Chinese hamster ovary (CHO) cells expressing recombinant porcine FSH receptor. The results showed that FSH was slowly internalized, and the internalized radioactivity (acid resistant) reached a peak 10-12 h after addition of 125I-hFSH. It was suggested that FSHR do not get internalized rapidly under physiological circumstances precisely because the appropriate sequences are absent.

Osteoblastic differentiation bioassay and its application to investigating the activity of fractions and compounds from Psoralea corylifolia L

A cell differentiation bioassay measuring alkaline phosphatase activity was developed using osteoblast-like UMR 106 cell line as a model. The effect of fractions and compounds of Psoralea corylifolia L. extract on osteoblastic differentiation was investigated. The fractions or compounds were co-cultured with cells for 48 h, the cellular ALP activity was then measured. The crude ethanol extract of Psoralea corylifolia L. increased ALP activity by 39.5% at a concentration of 0.1 mg/ml, and the activity was concentrated in the ethyl acetate fraction, which produced a maximum ALP activity increase of 38.2%. A significant activity was observed for a flavonoid, corylin, providing 30.0% increment in ALP. These effects suggest that Psoralea corylifolia L. extract, its ethyl acetate fraction and corylin would stimulate bone formation.

Mismatch repair deficiency and CpG island hypermethylation in sporadic colon adenocarcinomas

Many studies have documented CpG island hypermethylation in human colon adenocarcinomas. Several of these reports have additionally found such CpG island hypermethylation to be more extensive in tumors with a mismatch-repair deficiency, as revealed by microsatellite instability (MSI+). Because the source of samples used in these prior studies may not have been representative of the general population, we have reinvestigated this issue using samples from a population-based study. A total of 15 MSI+ tumors were identified, and they were compared with 47 MSI- tumors that were similar in distribution by age, sex, and race. Microdissected tumor and normal adjacent mucosal DNA samples from each patient were subjected to a quantitative DNA methylation analysis at 13 separate CpG dinucleotides located in five CpG islands in four different genes [APC, ESR1 (ER), CDKN2A (p16; promoter and exon 2), and MLH1]. Four of five CpG islands showed a statistically significantly increased level of methylation in tumor tissue compared with adjacent normal mucosa. In contrast to previous studies, we did not find any statistically significant correlations between MSI status and methylation levels of any of the CpG islands other than MLH1. Furthermore, we observed a positive correlation between MLH1 methylation and CDKN2A methylation (P = 0.03), whereas no association was noted between MSI positivity and CDKN2A methylation (P = 0.95). The latter results suggest a possible defect in the protection against CpG island hypermethylation shared between CDKN2A and MLH1 and do not support the notion of a functional association between CDKN2A methylation and the phenotype of mismatch repair deficiency.

Study of the mechanical properties of Nd:YVO4 crystal by use of laser interferometry and finite-element analysis

A hybrid method that combines experimental and numerical approaches for determining the material properties of Nd:YVO4 is reported. In the experimental investigations a laser interferometer is proposed for measuring the physical deformation of lasing materials at the end-pump surface. By matching with the measured end bulging, we have implemented a numerical solution with finite-element analyses to determine the Poisson ratio and Young's modulus of the crystal. The accuracy interval of the evaluated Poisson ratio of 0.33 and Young's modulus of 133 GPa is discussed numerically. Based on the mechanical properties obtained, the end effect is separated from thermal effects, and it shows that the end effect results in an approximate equal thermal lensing effect compared with the index parts for end-pumped Nd:YVO4 lasers.

Does the autoantibody immunodominant region on thyroid peroxidase include amino acid residues 742-771?

Identification of the thyroid peroxidase (TPO) amino acid residues that comprise the autoantibody immunodominant region is an important goal that has proven difficult because of the conformational nature of the epitopes involved. Recent data suggest that the immunodominant region has been located. Thus, by autoantibody recognition of tryptic fragments of native TPO, as well as of conformational portions of TPO expressed as cell-free translates, the autoantibody immunodominant region appears to include amino acid residues 742-771, near the C terminus of the ectodomain. To evaluate this deduction, we expressed as cell-free translates the full TPO ectodomain, as well as TPO truncated after residues 741 and 771. The epitopic integrity of these molecules was first confirmed by immunoprecipitation by patient sera containing TPO autoantibodies. However, autoantibody recognition could involve a minority of TPO autoantibodies with the individual sera, not fulfilling the strict criteria for immunodominance. In order to obtain definitive data, we performed immunoprecipitations on these TPO variants with four recombinant human monoclonal autoantibodies that define the immunodominant region. All four monoclonal autoantibodies immunoprecipitated TPO 1-741 to the same extent as they did TPO 1-771 and the full TPO ectodomain, indicating that the immunodominant region comprises (at least in large part) amino acid residues upstream of residue 741.

Clinical characteristics of transmitted transfusion virus infection in children

Clinical characteristics of transmitted transfusion virus (TTV) infection and its pathogenicity in children were evaluated. Serum TTV DNA from 118 children (mean age: 7.8 +/- 2.8 years) was detected by nested PCR. The product of PCR was cloned and sequenced. The positive rate for serum TTV-DNA in 20 healthy children, 9 cases of acute hepatitis, 51 cases of chronic hepatitis, 24 cases of nephritis or nephrotic syndrome and 14 cases of hypoplastic anemia or acute leukemia was 20%, 11%, 29%, 42% and 21% respectively, but there was no significant difference in TTV-DNA frequency among them (P > 0.05). Of the 16 patients receiving immunosuppressive agent for a long time, 7 (44%) were positive for TTV-DNA, and of the 17 cases not receiving immunosuppressive agent, 5 (29%) were positive with the difference being not significant (P > 0.05). Essential characteristics were pathogen-carrier or asymptomatic infection in children with TTV infection. Long-term employment of immunosuppressive agent did not increase the incidence in TTV infection. There was still high prevalence in TTV infection in healthy children not receiving blood product, suggesting the possibility of non hematogenous transmitted transfusion in TTV transmission.

Paternal inheritance of chloroplast DNA in interspecific hybrids in the genus Larrea (Zygophyllaceae)

The mode of chloroplast DNA (cpDNA) inheritance was investigated in the genus Larrea (Zygophyllaceae) by polymerase chain reaction (PCR) amplification of cpDNA fragments using three pairs of chloroplast universal primers. A total of 20 F(1)s from interspecific crosses among five different taxa in the section Bifolium was examined. Twelve F(1)s were from six crosses between L. cuneifolia (4x) and L. divaricata (2x) (Peru or Argentina) or L. tridentata (2x or 4x). Eight F(1)s were from two sets of reciprocal crosses between L. divaricata (2x) (Argentina) and L. tridentata (2x). Length polymorphism was observed in all three regions of cpDNA that separated L. cuneifolia parents from L. divaricata and L. tridentata parents and in one of the three cpDNA regions that differentiated L. divaricata (Argentina) parents from L. tridentata (2x) parents. In each case, it was the paternal cpDNA marker that appeared in the F(1) individuals. This was further confirmed by restriction fragment length polymorphism (RFLP) analysis of the amplified cpDNA fragments. Larrea may be the fifth genus reported in angiosperms with a paternal bias in cpDNA transmission. Possible mechanisms that may result in paternal cpDNA inheritance were briefly reviewed. Based on the observed uniparental paternal inheritance of cpDNA, restriction analysis of the three cpDNA regions and previous cytogenetic studies, L. divaricata was probably the maternal progenitor of L. cuneifolia.

Enhanced calcium transients in glial cells in neonatal cerebellar cultures derived from S100B null mice

S100B is the major low-affinity Ca(2+)-binding protein in astrocytes. In order to study the role of S100B in the maintenance of Ca(2+) homeostasis, we generated S100B null mice by a targeted inactivation of the S100B gene. Absence of S100B expression was demonstrated by Northern and Western blotting for S100B mRNA and protein, respectively, and immunoperoxidase staining of sections of various brain regions. S100B null mice were viable, fertile, and exhibited no overt behavioral abnormalities up to 12 months of age. On the basis of light microscopy and immunohistochemical staining, there were no discernable alterations in the distribution and morphology of astrocytes or neurons in sections of adult brains of these mice. Astrocytes in cerebellar cultures derived from 6-day-old S100B null mice exhibited enhanced Ca(2+) transients in response to treatment with KCl or caffeine. On the other hand, granule neurons, in the same cultures, exhibited normal Ca(2+) transients in response to treatment with KCl, caffeine, or N-methyl-d-aspartate. These results demonstrate a specific decrease in Ca(2+)-handling capacity in astrocytes derived from S100B null mice and suggest that S100B plays a role in the maintenance of Ca(2+) homeostasis in astrocytes.

Long-term blockade of the expression of cocaine sensitization by ondansetron, a 5-HT(3) receptor antagonist

Intermittent cocaine administration induces sensitization (reverse tolerance) to its behavioral effects. The mechanism(s) mediating sensitization is not clear, however, previous research has implicated 5-HT(3) receptors in the expression of sensitization. The present experiment evaluated the ability of the 5-HT(3) receptor antagonist, ondansetron, administered during withdrawal from chronic intermittent cocaine administration, to block the expression of sensitization. Rats were pretreated for 14 days by daily subcutaneous injections of either 40 mg/kg cocaine or 0.9% saline. During the first 5 days of withdrawal from this pretreatment regimen, all rats received a daily subcutaneous injection of 0-1.0 mg/kg ondansetron. On days 7, 14 or 28 of withdrawal from the cocaine pretreatment, the rats received a 15.0-mg/kg cocaine challenge. Ambulatory behavior was automatically recorded for 60 min. Ondansetron had no significant effect on the subsequent behavioral response to cocaine in the saline control subjects. In contrast, daily injections of ondansetron blocked the expression of sensitization at all withdrawal times. We thus report that it is possible to permanently block the expression of sensitization once it has developed by administering a 5-HT(3) receptor antagonist.

DNA methylator and mismatch repair phenotypes are not mutually exclusive in colorectal cancer cell lines

A potential link between DNA repair and de novo methylation of exogenous sequences in colorectal cancer cell lines suggested that cells deficient in mismatch repair (MMR-) had an increased ability to silence the introduced virus promoter by DNA methylation due to the presence of a methylator phenotype (MET+) (Lengauer et al., 1997a). We explored this relationship in more detail and found that although there was a clear difference in the abilities of MMR+ cells to express the viral promoter compared to their MMR- counterparts, this difference was not consistently explained by levels of methylation in the viral promoter. Furthermore, we were unable to distinguish differences between the levels of methylation of six endogenous known CpG islands or 100 random DNA fragments containing CCGG sites within the cells. No consistent differences between the abilities of the cells to methylate the CpG island in exon 2 of the p16 gene were observed after transient demethylation by 5-aza-2'-deoxycytidine nor in the levels of expression of three human methyltransferase enzymes. Our results do not therefore support the existence of mutually exclusive DNA methylation (MET) and DNA repair (MMR) phenotypes. Oncogene (2000) 19, 943 - 952.

Distinct roles of synaptic and extrasynaptic NMDA receptors in excitotoxicity

Excitatory synaptic activity governs excitotoxicity and modulates the distribution of NMDA receptors (NMDARs) among synaptic and extrasynaptic sites of central neurons. We investigated whether NMDAR localization was functionally linked to excitotoxicity by perturbing F-actin, a cytoskeletal protein that participates in targeting synaptic NMDARs in dendritic spines. Depolymerizing F-actin did not affect NMDA-evoked whole-cell currents. However, the number of dendritic NMDAR clusters and the NMDAR-mediated component of miniature spontaneous EPSCs were reduced, whereas the number of AMPA receptor clusters and AMPA receptor-mediated component of EPSCs was unchanged. This selective perturbation of synaptically activated NMDARs had no effect on neuronal death or the accumulation of (45)Ca(2+) evoked by applying exogenous NMDA or L-glutamate, which reach both synaptic and extrasynaptic receptors. However, it increased survival and decreased (45)Ca(2+) accumulation in neurons exposed to oxygen glucose deprivation, which causes excitotoxicity by glutamate release at synapses. Thus, synaptically and extrasynaptically activated NMDARs are equally capable of excitotoxicity. However, their relative contributions vary with the location of extracellular excitotoxin accumulation, a factor governed by the mechanism of extracellular neurotransmitter accumulation, not the synaptic activation of NMDARs.

[High-level expression of Mycobacterium tuberculosis 16,000 antigen in E. coli]

OBJECTIVE

To gain the recombinant protein antigen 16,000 of Mycobacterium tuberculosis highly expressed in E. coli and study its immunological characteristics.

METHODS

DNA fragments code for the protein were obtained by PCR, then cloned into the pET plasmid vector to gain recombinant E. coli. Cells were cultured and induced to produce recombinant protein, whose molecular size and present form were analyzed by SDS-PAGE, and its immunological characteristics were analyzed by Western-blotting and ELISA technology.

RESULTS

The clone was analyzed at the nucleotide lever and shown the same DNA sequence coding for natural 16,000 protein. Analyzed by SDS-PAGE and Western-blotting, it was found to produce immunoreactive proteins with mobilities very similar to those of the 16,000 protein antigen, and the recombinant protein amounted to 40% of total cell proteins. ELISA results indicated that the purified recombinant protein could distinguish sera from tuberculosis patients with anti-PPD antibody and those from tuberculin positive contacts.

CONCLUSIONS

Recombinant 16,000 protein antigen highly expressed in the form of solution in E. coli was gained and this antigen was located in cell plasma. This recombinant protein showed specific immunogenicity.

Blockade of glutamate receptors and barbiturate anesthesia: increased sensitivity to pentobarbital-induced anesthesia despite reduced inhibition of AMPA receptors in GluR2 null mutant mice

BACKGROUND

Barbiturates enhance gamma-aminobutyric acid type A (GABA(A)) receptor function and also inhibit the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) subtype of glutamate receptor. The relative contribution of these actions to the behavioral properties of barbiturates is not certain. Because AMPA receptor complexes that lack the GluR2 subunit are relatively insensitive to pentobarbital inhibition, GluR2 null mutant mice provide a novel tool to investigate the importance of AMPA receptor inhibition to the anesthetic effects of barbiturates.

METHODS

GluR2 null allele (-/-), heterozygous (+/-), and wild-type (+/+) mice were injected with pentobarbital (30 and 35 mg/kg intraperitoneally). Sensitivity to anesthetics was assessed by measuring the latency to loss of righting reflex, sleep time, and the loss of corneal, pineal, and toe-pinch withdrawal reflexes. In addition, patch-clamp recordings of acutely dissociated CA1 hippocampal pyramidal neurons from (-/-) and (+/+) mice were undertaken to investigate the effects of barbiturates on kainate-activated AMPA receptors and GABA-activated GABA(A) receptors.

RESULTS

Behavioral tests indicate that sensitivity to pentobarbital was increased in (-/-) mice. In contrast, AMPA receptors from (-/-) neurons were less sensitive to inhibition by pentobarbital (concentrations that produced 50% of the maximal inhibition [IC50], 301 vs. 51 microM), thiopental (IC50, 153 vs. 34 microM), and phenobarbital (IC50, 930 vs. 205 microM) compared with wild-type controls, respectively. In addition, the potency of kainate was greater in (-/-) neurons, whereas no differences were observed for the potentiation of GABA(A) receptors by pentobarbital.

CONCLUSIONS

The GluR2 null mutant mice were more sensitive to pentobarbital anesthesia despite a reduced sensitivity of GluR2-deficient AMPA receptors to barbiturate blockade. Our results indicate that the inhibition of AMPA receptors does not correlate with the anesthetic effects of barbiturates in this animal model. We postulate that the increase in the sensitivity to anesthetics results from a global suppression of excitatory neurotransmission in GluR2-deficient mice.

The effects of continuous cocaine dose on the induction of behavioral tolerance and dopamine autoreceptor function

The current experiment evaluated the dose-dependent nature of the induction of behavioral tolerance, and changes in dopamine autoreceptor function, by continuously administering different doses of cocaine. For all experiments, rats were exposed to a 14-day pretreatment regimen involving the continuous administration of either 0, 5, 10, 20, or 40 mg/kg/day cocaine. All subjects were then withdrawn from the pretreatment regimen for 7 days. The subjects were placed in activity monitors, and ambulation measured. In experiment 1, the subjects were challenged with 0.0, 7.5, or 15.0 mg/kg i.p. cocaine on day 7 of withdrawal from the continuous cocaine administration regimen. The results indicated that all continuous cocaine doses induced significant tolerance to the 15.0 mg/kg cocaine challenge, relative to the control group. Furthermore, the 5.0 mg/kg/day group exhibited significantly less tolerance than the 40.0 mg/kg/day group. In experiment 2, the subjects were challenged with 0.0, 0.063, or 0.125 mg/kg quinpirole. The results indicated that the 0.063-mg/kg quinpirole challenge inhibited activity, while the 0.125 mg/kg quinpirole challenge enhanced behavior. The results further suggested that the inhibition of behavior was greater in the cocaine-pretreated subjects than in the saline control group. In experiment 3, the subjects were challenged with the same doses of quinpirole in combination with 15 mg/kg i.p. cocaine. The low quinpirole challenge dose inhibited cocaine-induced hyperactivity, while the higher challenge dose enhanced cocaine-induced hyperactivity. The results suggest that the induction of tolerance by continuous cocaine administration is dose-dependent. Continuous cocaine administration did induce dopamine autoreceptor supersensitivity. However, different continuous cocaine doses did not induce differential degrees of dopamine autoreceptor supersensitivity.