Functional deficiency of MHC class i enhances LTP and abolishes LTD in the nucleus accumbens of mice

Major histocompatibility complex class I (MHCI) molecules were recently identified as novel regulators of synaptic plasticity. These molecules are expressed in various brain areas, especially in regions undergoing activity-dependent synaptic plasticity, but their role in the nucleus accumbens (NAc) is unknown. In this study, we investigated the effects of genetic disruption of MHCI function, through deletion of β2-microblobulin, which causes lack of cell surface expression of MHCI. First, we confirmed that MHCI molecules are expressed in the NAc core in wild-type mice. Second, we performed electrophysiological recordings with NAc core slices from wild-type and β2-microglobulin knock-out mice lacking cell surface expression of MHCI. We found that low frequency stimulation induced long-term depression in wild-type but not knock-out mice, whereas high frequency stimulation induced long-term potentiation in both genotypes, with a larger magnitude in knock-out mice. Furthermore, we demonstrated that knock-out mice showed more persistent behavioral sensitization to cocaine, which is a NAc-related behavior. Using this model, we analyzed the density of total AMPA receptors and their subunits GluR1 and GluR2 in the NAc core, by SDS-digested freeze-fracture replica labeling. After repeated cocaine exposure, the density of GluR1 was increased, but there was no change in total AMPA receptors and GluR2 levels in wildtype mice. In contrast, following repeated cocaine exposure, increased densities of total AMPA receptors, GluR1 and GluR2 were observed in knock-out mice. These results indicate that functional deficiency of MHCI enhances synaptic potentiation, induced by electrical and pharmacological stimulation

Iodine-125 Seed Implantation (Permanent Brachytherapy) for Clinically Localized Prostate Cancer

From January 2004 to March 2007, 308 patients with clinically localized prostate cancer were treated using iodine-125 (125I) seed implantation (permanent brachytherapy) at Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences. We evaluated the treatment’s effi cacy and morbidity in 300 prostate cancer patients who were followed up for more than 1 month after brachytherapy. Based on the National Comprehensive Cancer Network (NCCN) guidelines, patients with a prostate volume of less than 40 ml in transrectal ultrasound imaging were classifi ed as low or intermediate risk. The median patient age was 67 years (range 50 to 79 years), the median prostate-specific antigen (PSA) value before biopsy was 6.95 ng/ml (range 1.13 to 24.7 ng/ml), and the median prostate volume was 24.33 ml (range 9.3 to 41.76 ml). The median follow-up was 18 months (range 1 to 36 months) and the PSA levels decreased in almost all patients after brachytherapy. Although 194 of 300 patients (64.7%) complained of diffi culty in urination, pollakisuria/urgency, miction pain, and/or urinary incontinence, all of which might be associated with radiation prostatitis during the fi rst month after brachytherapy, these symptoms gradually improved. 125I seed implantation brachytherapy is safe and eff ective for localized prostate cancer within short-term follow up.</p

MHCI molecules are expressed in the nucleus accumbens core in WT mice.

<p>Staining for MHCI with OX-18 antibody (upper-left), Neurogranin (upper-center) and the merged image (upper-right) are shown. Lower images represent negative controls without OX-18. Scale bar represents 50 µm.</p

Comparison of the fEPSP slopes.

<p>A) Comparison between WT mice and β2m^−/− mice after high frequency stimulation (HFS) at 100 Hz. HFS induced LTP in both groups (WT: 125.8±4.5%, n = 9/N = 5, T = 1, p<0.01; β2m^−/−: 141.8±5.7%, n = 11/N = 6, T = 0, p<0.001; Signed rank test), whereas LTP was enhanced in the β2m^−/− group (t(18) = 2.107, p<0.05; Student’s t-test). B) Comparison between WT and β2m^−/− mice after low frequency stimulation (LFS) at 10 Hz. LFS induced LTD in WT mice (79.2±5.9%, n = 9/N = 6, T = 1, p<0.05), whereas it was ineffective in β2m^−/− mice (103.2±7.3%, n = 9/N = 6, T = 18, p = 0.65). At 45–50 min after LFS, the fEPSP slope in β2m^−/− mice was significantly higher than in WT mice (t(16) = 2.548, p<0.05). C) Comparison between WT and β2m^−/− mice after 1 Hz stimulation. Neither LTP nor LTD was induced by this stimulation (WT: 103.4±7.1%, n = 7/N = 6, T = 9, p = 0.47; β2m^−/−: 100.7±5.7%, n = 7/N = 6, T = 12, p = 0.81). There was no significant difference in the fEPSP slope at 45–50 min after 1 Hz/15 min stimulation between genotypes (t(12) = 0.302, p = 0.768). D) Comparison of paired pulse ratios (PPRs). (Left) PPRs in WT and β2m^−/− mice at 30, 50 and 100 ms inter stimulus interval (ISI). There was no significant difference in the PPRs of WT (ISI 30 ms: 117.9±2.4%; ISI 50 ms: 124.5±2.6%; ISI100 ms: 111.7±1.0%) (n = 9/N = 5) and β2m^−/− (ISI 30 ms: 116.8±1.9%; ISI 50 ms: 123.2±2.3%; ISI 100 ms: 111.5±0.8%) (n = 9/N = 5) mice, in all tested ISIs (ISI 30 ms: t(16) = 0.349, p = 0.731; ISI 50 ms: t(16) = 0.355, p = 0.727; ISI 100 ms: t(16) = 0.164, p = 0.872). (Right) Representative traces of fEPSPs at 50 ms inter stimulus interval (blue: WT; red: β2m^−/−). Vertical scale bars represent 100 µV, and horizontal scale bars represent 10 ms. *p<0.05. n = slices/N = animals.</p

Comparison of AMPA receptor densities.

<p>A) A raw electron micrograph image of SDS-FRL replica immunolabeled with pan-AMPA antibody (left), and an analyzed image (right). A representative replica from a wild type mouse treated with saline (WT-Sal) is shown. The blue area indicates intra-membrane particle clusters and the black dots indicate immunogold particles. B) Densities of pan-AMPA, GluR1, and GluR2 in WT-Sal mice and β2m mice treated with saline (β2m^−/−-Sal). The densities normalized to WT in each receptor were: pan-AMPA: β2m^−/−-Sal, 110.0±8.5%; GluR1: β2m^−/−-Sal, 92.9±7.8%; GluR2: β2m^−/−-Sal, 95.4±1.5%, n = 6 [for each receptor 6 replicas from three animals, 30 synapses per replica]. C) Comparison of pan-AMPA, GluR1 and GluR2 densities between WT-Sal mice and wild type mice treated with cocaine (WT-Coc). The densities normalized to saline group in each receptor were: pan-AMPA: WT-Coc, 119.4±8.3%; GluR1: WT–Coc, 135.3±8.9%; GluR2: WT–Coc, 105.6±9.6%, n = 6 [for each receptor six replicas from three animals, 30 synapses per replica]. D) Comparison of pan-AMPA, GluR1 and GluR2 densities between β2m^−/−-Sal mice and β2m^−/− mice treated with cocaine (β2m^−/−-Coc). The densities normalized to saline group in each receptor were: pan-AMPA: β2m^−/−-Coc, 130.9±10.0%; GluR1: β2m^−/−-Coc, 117.5±5.8%; GluR2: β2m^−/−-Coc, 119.7±6.2%, n = 6 [for each receptor six replicas from three animals, 30 synapses per replica]. E) Representative electron micrographs of the replicas from WT-Sal and WT-Coc mice. The blue area indicates intra-membrane particle clusters and the black dots indicate immunogold particles. F) Representative electron micrographs of the replicas from β2m^−/−-Sal and β2m^−/−-Coc mice. The red area indicates intra-membrane particle clusters and the black dots indicate immunogold particles. Scale bars represent 200 nm. *p<0.05.</p

Behavioral sensitization elicited by repeated cocaine exposure.

<p>After three days of saline injections, WT and β2m^−/− mice were divided into groups that received daily injections of saline or cocaine (20 mg/kg) for 7 days. These groups were composed of WT mice treated with saline (WT-Sal) (n = 6) or cocaine (WT-Coc) (n = 6) and β2m^−/− mice treated with saline (β2m^−/−-Sal) (n = 6) or cocaine (β2m^−/−-Coc) (n = 6). Mice of both genotypes showed increased locomotor activity following cocaine but not saline injections. Analysis was conducted over a 8-day period from day 3 to day 10 in WT-Coc and β2m^−/−-Coc groups. Two-way ANOVA with repeated measures revealed significant interactions of day × genotype (F(7, 70) = 2.892, p<0.05), a main effect of day (F(7, 70) = 42.285, P<0.001) and genotype (F(1, 10) = 5.027, p<0.05). Bonferroni post-hoc test revealed significant differences at day 7, day 9 and day 10. Furthermore, the β2m^−/−-Coc group displayed a larger response to a challenge dose of cocaine after withdrawal (Day 24) than the WT-Coc group. Two-way ANOVA revealed a main effect of genotype (F(1, 20) = 19.674, p<0.001) and treatment (F(1, 20) = 121,488, p<0.001), and a significant interaction of genotype × treatment (F(1, 20) = 13.138, p<0.01). A significant difference was observed between genotypes treated with cocaine (p<0.001, Bonferroni post-hoc test). *p<0.05 β2m^−/−-Coc versus WT-Coc; ***p<0.001 β2m^−/−-Coc versus WT-Coc.</p

Functional Deficiency of MHC Class I Enhances LTP and Abolishes LTD in the Nucleus Accumbens of Mice

Major histocompatibility complex class I (MHCI) molecules were recently identified as novel regulators of synaptic plasticity. These molecules are expressed in various brain areas, especially in regions undergoing activity-dependent synaptic plasticity, but their role in the nucleus accumbens (NAc) is unknown. In this study, we investigated the effects of genetic disruption of MHCI function, through deletion of β2-microblobulin, which causes lack of cell surface expression of MHCI. First, we confirmed that MHCI molecules are expressed in the NAc core in wild-type mice. Second, we performed electrophysiological recordings with NAc core slices from wild-type and β2-microglobulin knock-out mice lacking cell surface expression of MHCI. We found that low frequency stimulation induced long-term depression in wild-type but not knock-out mice, whereas high frequency stimulation induced long-term potentiation in both genotypes, with a larger magnitude in knock-out mice. Furthermore, we demonstrated that knock-out mice showed more persistent behavioral sensitization to cocaine, which is a NAc-related behavior. Using this model, we analyzed the density of total AMPA receptors and their subunits GluR1 and GluR2 in the NAc core, by SDS-digested freeze-fracture replica labeling. After repeated cocaine exposure, the density of GluR1 was increased, but there was no change in total AMPA receptors and GluR2 levels in wild-type mice. In contrast, following repeated cocaine exposure, increased densities of total AMPA receptors, GluR1 and GluR2 were observed in knock-out mice. These results indicate that functional deficiency of MHCI enhances synaptic potentiation, induced by electrical and pharmacological stimulation