Long-term potentiation and long-term depression in hippocampal CA1 neurons of mice lacking the IP(3) type 1 receptor.

To investigate the role in synaptic plasticity of Ca(2+) released from intracellular Ca(2+) stores, mice lacking the inositol 1,4,5-trisphosphate type 1 receptor were developed and the physiological properties, long-term potentiation, and long-term depression of their hippocampal CA1 neurons were examined. There were no significant differences in basic synaptic functions, such as membrane properties and the input/output relationship, between homozygote mutant and wild-type mice. Enhanced paired-pulse facilitation at interpulse intervals of less than 60 ms and enhanced post-tetanic potentiation were observed in the mutant mice, suggesting that the presynaptic mechanism was altered by the absence of the inositol 1,4,5-trisphosphate type 1 receptor. Long-term potentiation in the field-excitatory postsynaptic potentials induced by tetanus (100 Hz, 1 s) and the excitatory postsynaptic currents induced by paired stimulation in hippocampal CA1 pyramidal neurons under whole-cell clamp conditions were significantly greater in mutant mice than in wild-type mice. Homosynaptic long-term depression of CA1 synaptic responses induced by low-frequency stimulation (1 Hz, 500 pulses) was not significantly different, but heterosynaptic depression of the non-associated pathway induced by tetanus was blocked in the mutant mice. Both long-term potentiation and long-term depression in mutant mice were completely dependent on N-methyl-D-aspartate receptor activity. To rule out the possibility of an effect compensating for the lack of the inositol 1,4,5-trisphosphate type 1 receptor occurring during development, an anti-inositol 1,4,5-trisphosphate type 1 receptor monoclonal antibody that blocks receptor function was diffused into the wild-type cell through a patch pipette, and the effect of acute block of inositol 1,4,5-trisphosphate type 1 receptor on long-term potentiation was examined. Significant enhancement of long-term potentiation was observed compared with after control immunoglobulin G injection, suggesting that developmental redundancy was not responsible for the increase in long-term potentiation amplitude observed in the mutant mouse. The properties of channels that could be involved in long-term potentiation induction were examined using whole-cell recording. N-methyl-D-aspartate currents were significantly larger in mutant mice than in wild-type mice only between holding potentials of -60 and -80 mV. We conclude that inositol 1,4,5-trisphosphate type 1 receptor activity is not essential for the induction of synaptic plasticity in hippocampal CA1 neurons, but appears to negatively regulate long-term potentiation induction by mild modulation of channel activities.

Aberrant intracellular localization of RCAS1 is associated with tumor progression of gastric cancer.

A novel tumor-associated antigen, RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is expressed at a high frequency in human uterine and ovarian cancer cells as well as in other mammalian cancer cells. We investigated a relationship between RCAS1 expression and clinicopathological features in gastric cancer. Immunohistochemically, RCAS1 was detected in 98.4% of gastric carcinomas. However, its expression was also observed in non-cancerous gastric epithelial cells including gastric adenomas (100%), gastric ulcers (66.7%) and normal gastric epithelia (100%). Striking difference was observed in the pattern of RCAS1 expression between benign and malignant cells. In cases of normal gastric mucosae, gastric ulcers and gastric adenomas, RCAS1 was localized only in the perinuclear region of the mucosal epithelial cells (PN pattern), while, in most of gastric cancers (83.9%), it was detected diffusely in the cytoplasm and cell membranes of the tumor cells (DC pattern). In semi-quantitative RT-PCR analysis, RCAS1 mRNA levels in gastric adenocarcinoma tissues were significantly higher than those in non-neoplastic tissues (p=0.038). The PN pattern of RCAS1 expression was more frequently observed in well differentiated adenocarcinoma (25%) than in moderately differentiated adenocarcinoma (0%) (p=0.01). In addition, it is noteworthy that DC pattern of RCAS1 expression was more frequently recognized in carcinomas which invaded beyond the submucosa (100%) compared to intramucosal carcinoma (67.7%) (p=0.0026). These findings suggest that altered intracellular distribution of RCAS1 is strictly associated with tumor progression of gastric cancer and is a useful marker for the diagnosis and prognosis in gastric cancer.

The likely transformation of papillary thyroid carcinoma into anaplastic carcinoma during postoperative radioactive iodine-131 therapy: report of a case.

We report herein a case of papillary carcinoma which appeared to transform into anaplastic carcinoma during postoperative radioactive iodine-131 (131I) therapy. A 67-year-old man who was diagnosed as having papillary thyroid carcinoma with bilateral neck lymph node involvement and multiple lung metastases underwent total thyroidectomy prior to 131I therapy. Immediately after a second course of 131I therapy, the patient complained of right neck pain and swelling, and a biopsy of the swollen neck lymph node was taken. Histologic examination of this biopsy specimen revealed anaplastic carcinoma. With p53 immunohistochemical staining, both the primary tumor and the biopsy specimen were positive. We speculate that first, some DNA damage in tumor cells was induced by the initial 131I therapy, but neither DNA repair nor cell apoptosis occurred because the p53 gene was already mutated; then further DNA damage was induced by the second 131I therapy, leading to anaplastic transformation.

Requirement of transfer-messenger RNA for the growth of Bacillus subtilis under stresses.

BACKGROUND: Bacterial transfer-messenger RNA (tmRNA, 10Sa RNA) is involved in a trans-translation reaction which contributes to the degradation of incompletely synthesized peptides and to the recycling of stalled ribosomes. However, its physiological role in the cell remains elusive. In this study, an efficient system for controlling the expression of the gene for tmRNA (ssrA), as well as a tmRNA gene-defective strain (ssrA:cat), were constructed in Bacillus subtilis. The effects of tmRNA on the growth of the cells were investigated under various physiological culture conditions using these strains. RESULTS: The cells were viable in the absence of ssrA expression under the usual culture conditions. However, the growth rate of cells without tmRNA expression, relative to that of the expressed cells, decreased with elevating temperature (> 45 degrees C), and at 52 degrees C, the highest temperature for growth of the wild-type, cells grew depending on the expression level of tmRNA. Furthermore, the transcription level of the ssrA from the authentic promoter at a high temperature (51 degrees C) was about 10-fold higher than that at a lower temperature (37 degrees C). tmRNA-dependent growth and an increase in tmRNA amount were also observed in cells under other stresses, such as high concentrations of ethanol or cadmium chloride. It is also shown that alanylated tmRNA rather than tmRNA-mediated proteolysis is required for growth at high temperature. CONCLUSION: The expression of tmRNA gene (ssrA) is required for the efficient growth of B. subtilis under several strong stresses. The transcription of ssrA increases under several stressful conditions, suggesting that it is a stress-response gene. Alanyl-tmRNA, probably via its ability of recycling stalled ribosomes via trans-translation, is involved in the stress tolerance of bacteria.

Effects of adenosine receptors on the synaptic and EPSP-spike components of long-term potentiation and depotentiation in the guinea-pig hippocampus.

1. Long-term potentiation (LTP) of synaptic efficacy comprises two components: a synaptic component consisting of increased field excitatory postsynaptic potentials (EPSPs), and a component consisting of a larger population spike amplitude for a given EPSP size (E-S potentiation). In hippocampal CA1 neurons, delivery of three weak bursts (5 pulses at 100 Hz, 20 min intervals) induced LTP in both the EPSP and E-S components. In the same cells, reversal of LTP (depotentiation, DP) in the field EPSP and the E-S component was achieved by delivering three trains of low-frequency stimuli (LFS; 200 pulses at 1 Hz, 20 min intervals). 2. The effects of adenosine A1 and A2 receptor antagonists on the synaptic and E-S components of LTP and DP in CA1 neurons were studied by perfusing guinea-pig hippocampal slices with either 8-cyclopentyltheophylline (8-CPT) or CP-66713. 3. When bursts or LFS were applied to CA1 inputs in the presence of the A1 receptor antagonist 8-CPT, the field EPSP was enhanced in LTP and attenuated in DP, while the E-S relationship was not significantly affected in either LTP or DP. 4. When similar experiments were performed using the A2 receptor antagonist CP-66713, the field EPSP was blocked in LTP, but facilitated in DP, while E-S potentiation was enhanced during both LTP and DP. 5. The results show that A1 and A2 adenosine receptors modulate both the synaptic and E-S components of the induction and reversal of LTP. Based on these results, we discuss the key issue of the contribution of these receptors to the dynamics of neuronal plasticity modification in hippocampal CA1 neurons.

Effect of the mono- and tetra-sialogangliosides, GM1 and GQ1b, on long-term potentiation in the CA1 hippocampal neurons of the guinea pig.

Effects of the mono- and tetra-sialogangliosides, GM1 and GQ1b, on long-term potentiation (LTP) were investigated in the CA1 neurons of guinea-pig hippocampal slices. The magnitude of LTP induced by a strong tetanus (100 Hz, 100 pulses) was not significantly affected by application of either ganglioside. In contrast, when LTP was induced by a weak tetanus (100 Hz, 4 pulses), a significantly greater LTP was induced in the presence of either ganglioside. Similarly, when slices were incubated in low-Ca2+ (1.0-1.1 mM) medium for more than 2 h, the LTP was usually small or absent, but showed a significant increase in amplitude of population spike (A-PS) when the slices were incubated with either GM1 or GQ1b (4-5 microg/ml). In addition, the application of GQ1b (4 microg/ml) reversed the blocking effect of an NMDA-receptor antagonist, APP-5 (10 microM), on the induction of LTP and resulted in forming LTP. Based on these findings, we conclude that GM1 and GQ1b exert positive modulatory effects on the induction of LTP in hippocampal CA1 neurons and suggest that GM1 and GQ1b may participate in the induction of LTP as donors of Ca2+ ions.

Properties of calcium spikes revealed during GABAA receptor antagonism in hippocampal CA1 neurons from guinea pigs.

Properties of calcium spikes revealed during GABAA receptor antagonism in hippocampal CA1 neurons from guinea pigs. J. Neurophysiol. 78: 2269-2279, 1997. Intracellular electrical responses and changes in intracellular calcium concentration ([Ca2+]i) in response to activation of synaptic inputs and to DC injections were recorded simultaneously from CA1 pyramidal neurons (n = 42) in guinea pig hippocampal slices. In the presence of the gamma-aminobutyric acid-A (GABAA) receptor antagonists, bicuculline (mu M) and picrotoxin (10 mu M, broad (>20 ms) all-or-none spikes were induced by activation of synaptic inputs (20 pulses, 30 Hz) and were accompanied by a simultaneous rapid and large rise in [Ca2+]i (34 of 34 cells). By contrast, direct depolarizing current (0.7 nA, 1 s) induced spikes having short duration, during which time the spike firing pattern was observed not to be significantly affected. When Na+ channels were blocked by QX-314 applied intracellularly through the recording microelectrode in the presence of GABAA receptor antagonists, broad spikes were frequently generated by activation of synaptic inputs (32 of 33 cells). These broad spikes were blocked by Cd2+ (200 mu M) or in Ca2+-free medium (6 of 6 cells) but were resistant to either tetrodotoxin (TTX; 1 micro M; 6 of 6 cells) or QX-314, whereas short-duration spikes were blocked by both TTX and QX-314. Based on these findings we conclude that broad and short-duration spikes are Ca2+ and Na+ spikes, respectively. To investigate the properties of the Ca2+ spikes, antagonists of a voltage-operated Ca2+ channel were applied to the evoked responses. Nifedipine (30 mu M), a L-type Ca2+ channel blocker, suppressed the generation of Ca2+ spikes, whereas Ni2+ (100 mu M), the T- and R-type Ca2+ channel blocker, and omega-agatoxin-IVA (omega-Aga-IVA, 60 nM), a P-type Ca2+ channel blocker, had little effect on the generation of Ca2+ spikes. Nifedipine suppressed the rise in [Ca2+]i induced by synaptic inputs up to 26% of the control in the soma and 18-32% in the dendrites (n = 5), respectively, whereas Ni2+ suppressed the rise by 12-27% (n = 5) in both soma and dendrites. omega-Aga-IVA showed little effect (less than a 10% change; n = 7). These results suggest that the GABAA inhibitory system tonically suppresses dendritic Ca2+ spikes, and the L-type Ca2+ channel plays a major role in the generation of Ca2+ spikes and in Ca2+ influx.

The effects of D-alpha-aminoadipic acid on long-term potentiation in the hippocampus of the rat in vitro.

Many studies on long-term potentiation (LTP) in hippocampal region CA1 focus on receptor-mediated events that are often presumed to be linked to postsynaptic processes. Whereas it is now well-known that LTP consists of multiple components involving increases in postsynaptic responsiveness as well as enhanced presynaptic release of transmitter, little specific information has accrued on the nature of the presynaptic receptor-linked events. In the course of a series of experiments examining the actions of several antagonists of N-methyl-D-aspartate (NMDA) receptors on LTP, we made certain observations that suggested the role of a novel type of amino acid receptor which possibly was located presynaptically and that seemed to contribute to the induction of LTP. LTP evoked in region CA1 following high frequency stimulation (HFS) of the Schaffer collateral-commissural pathway measured 20-30 min after HFS always was attenuated incompletely when induced during administration of DalphaAA at doses ranging from 50 mu M to as high as 1000 mu M, whereas 2-amino-5-phosphonopropionate (AP5), at a concentration of 30 mu M, always abolished the process completely. 6,7-Dinitroquinoxaline-2,3-dione (DNQX) (10 mu M) administered alone also did not block LTP completely unless delivered in combination with DalphaAA. These non-AP5-like effects of DalphaAA could not be attributed to incomplete antagonism of postsynaptic NMDA receptors, since DalphaAA (200 mu M) completely and reversibly blocked the membrane depolarising effects of NMDA, as assessed through intracellular recording. Furthermore, the pharmacologically isolated NMDA-receptor-mediated component of the low-frequency, stimulus-evoked synaptic response was always abolished reversibly by DalphaAA (200 mu M). The most parsimonious explanation of these data is that a receptor which is only activated during HFS, is sensitive to the antagonising actions of AP5 and possibly also to DNQX but not to DalphaAA, and which could conceivably exist on terminals of the Schaffer collateral-commissural fibres, makes a significant contribution to LTP.

Masked long-term potentiation in kitten visual cortex in vitro.

In slices from the visual cortex of kittens maintained in vitro, long-term potentiation of synaptic transmission following high frequency stimuli (10 Hz, 2 min) delivered at low to medium stimulus intensities (80 to 200 microA), is accompanied by changes of certain electrophysiological measures recorded intracellularly, such as long-lasting depolarization of membrane potential and decreased threshold to elicitation of an action potential. These parameters have never before been shown to be altered following high frequency stimulation in other systems widely used in studying synaptic plasticity, such as in hippocampal neurons. Another important difference between results from these two systems is that the amplitude of the excitatory post-synaptic potential is enhanced after high frequency stimulation in hippocampal neurons, whereas in striate cortex from young kittens, we observed a decrease. We demonstrate here that this decrease can be reversed to show enhancement from the original amplitude, upon clamp of membrane potential back to the voltage observed prior to stimulation. Thus, what appears to be "long-term depression" of synaptic transmission, as recorded extracellularly and represented by diminished flow of synaptic current, can be reversed by stepping membrane voltage back to the pre-high frequency stimulation level, to produce responses that then become consistent with long-term potentiation.