Candidate tumor suppressor RIZ is frequently involved in colorectal carcinogenesis

The distal portion of chromosome 1p is one of the most commonly affected regions in human cancer. In this study of hereditary and sporadic colorectal cancer, a region of frequent deletion was identified at 32.2 centimorgans from 1ptel. Deletion breakpoints clustered in the vicinity of or inside the gene RIZ, which encodes a retinoblastoma protein-interacting zinc finger protein. Sequence analysis revealed frequent frameshift mutations of the RIZ gene. The mutations consisted of 1- or 2-bp deletions of a coding (A)(8) or (A)(9) tract and were confined to microsatellite-unstable colorectal tumors, being present in 9 of 24 (37.5%) primary tumors and in 6 of 11 (54.5%) cell lines; in 2 cell lines the mutation was homozygous/hemizygous. The mutations apparently were selected clonally in tumorigenesis, because similar poly(A) tracts in other genes were not affected. Two alternative products of the gene exist, RIZ1, which contains a PR (PRDI-BF1-RIZ1) domain implicated in tumor suppressor function, and RIZ2, which is lacking this motif. Furthermore, the C-terminal region, which contains the poly(A) tracts, includes a PR-binding motif, possibly mediating interactions with other proteins or with RIZ itself (oligomerization). Four of eleven microsatellite-unstable colorectal cancer cell lines, three of which had frameshifts, showed reduced or absent mRNA expression of RIZ1. In a cell line that is homozygous/hemizygous for the typical frameshift mutation, immunoblotting showed truncated RIZ protein, whereas adenovirus-mediated RIZ1 expression caused G(2)/M arrest and apoptosis. We propose that RIZ is a target of the observed 1p alterations, with impairment of the PR domain-mediated function through either frameshift mutation or genomic deletion.

A novel DNA element mediates transcription of Nkx2.1 by Sp1 and Sp3 in pulmonary epithelial cells

NKX2.1 is a member of the NK2 family of homeodomain-containing transcription factors whose targeted disruption in mouse results in the absence of thyroid tissue and a severely abnormal lung phenotype. Little is known regarding the mechanisms that control tissue and temporal specificity of Nkx2.1 gene expression. The Nkx2.1 gene has been cloned from a number of species and it is composed of three exons and two introns. Two distinct DNA domains located 5' of exon I and within intron I have been found to exhibit promoter activity in lung and thyroid cells. In the current study we used deletional analysis of the 5' flanking region of exon I and identified a 300 bp TATA-less region that exhibits significant promoter activity in H441 cells. The DNA sequence of this region contains multiple palindromes, composed of G/C-rich elements. DNase I footprinting demonstrates that this promoter region interacts with nuclear factors present in H441 cells. In particular electrophoretic mobility shift assay using antibodies against the Sp family members show that both Sp1 and Sp3 as well as an as yet unknown H441-specific factor interact with the palindromic structure within this promoter region. Co-transfection studies show that this promoter region responds to Sp1 and Sp3 and mutations therein result in a significantly diminished response to these transcriptional factors. Therefore, we have identified a novel DNA structure on the Nkx2.1 gene which participates in transcription of this gene in pulmonary epithelial cells by Sp1 and Sp3 transcription factors.

[Pot experiment on effect of clipping at seedling stage on spring wheat]

Pot experiment on the compensatory effects of spring wheat(Triticum aestivum) at different clipping intensities (simulating herbivory) at seedling stage (three leaves) was conducted in semiarid region of Gansu Province. Under two conditions of 60% and 90% of field water-holding capacity, spring wheat growth was stimulated by clipping at seedling stage, resulting in overcompensation in biological and economic yields, and with more compensation for heavy clipping than light clipping. The overcompensation of the spring wheat was at the cost of more water consumption.

Inhibition of distal lung morphogenesis in Nkx2.1(-/-) embryos

In vitro and in vivo results are consistent with a critical role for NKX2.1, an epithelial homeodomain transcription factor in lung morphogenesis. Nkx2.1 null mutant embryos die at birth due to respiratory insufficiency caused by profoundly abnormal lungs. However, the precise role of NKX2.1 in the multistep process of lung structural morphogenesis and differentiation of various pulmonary cell types remains unknown. In the current study, we tested the hypothesis that the mutant lungs do not undergo branching morphogenesis beyond the formation of the mainstem bronchi and therefore consist solely of dilated tracheobronchial structures. To test this hypothesis, we determined the spatial and temporal expression pattern of a number of extracellular matrix (ECM) proteins and their cellular receptors, including alpha-integrins, laminin, and collagen type IV. Although laminin is expressed in the mutant Nkx2.1(-/-) lungs, expression of alpha-integrins and collagen type IV is significantly reduced or absent. In addition, examination of regionally specific expression of differentially spliced Vegf (vascular endothelial growth factor) transcripts, clearly indicates that the epithelial phenotype of the Nkx2.1(-/-) lungs is similar to the tracheobronchial epithelium. In contrast to wild-type lungs in which both Vegf1 and Vegf3 are developmentally expressed, Nkx2.1(-/-) lungs are characterized by predominant expression of Vegf1 and reduced or absent Vegf3. A similar pattern of Vegf expression is also observed in isolated tracheo-bronchial tissue. The sum of these findings suggest that at least two separate pathways may exist in embryonic lung morphogenesis: proximal lung morphogenesis is Nkx2.1 independent, while distal lung morphogenesis appears to be strictly dependent on the wild-type activity of Nkx2.1.

Chronic blockade of brain "ouabain" prevents sympathetic hyper-reactivity and impairment of acute baroreflex resetting in rats with congestive heart failure

In rats with congestive heart failure (CHF) post myocardial infarction (MI) acute blockade of brain "ouabain" reverses sympathetic hyperactivity and chronic blockade prevents the desensitization of baroreflex function. This study was conducted to determine: i) if chronic blockade of brain "ouabain" maintains normal sympathetic reactivity; and ii) if acute baroreflex resetting (another parameter of baroreflex function) also becomes impaired, and if so, does brain "ouabain" contribute to impairment in acute baroreflex resetting. CHF post MI was induced by acute coronary artery ligation in Wistar rats. Animals were treated with 200 microg x day(-1) i.c.v. or i.v. Fab fragments (which bind brain "ouabain" with high affinity), or treated with 200 microg x day(-1) i.c.v. gamma-globulins (control group). The length of treatment was 0.5-8 weeks or 4-8 weeks post MI. At 8 weeks mean arterial pressure (MAP), central venous pressure (CVP), heart rate (HR), and renal sympathetic nerve activity (RSNA) were recorded in concious rats at rest and in response to: i) air-jet stress, ii) i.c.v. guanabenz (an alpha2-adrenoceptor agonist), and iii) a 30 min i.v. infusion of nitroprusside (NP). Excitatory responses to air stress and inhibitory responses to guanabenz of MAP, HR, and RSNA were significantly enhanced in rats with CHF versus the sham-operated treated group. This enhancement was prevented in the CHF group treated with i.c.v., but not i.v., Fab. Nitroprusside induced a sustained decrease in MAP (approximately 25 mmHg) and a transient decrease in CVP. Heart rate and RSNA increased significantly within 1 min of beginning the infusion. The peak increases as well as the product of changes in MAP-HR and RSNA-HR were significantly smaller in rats with CHF treated with gamma-globulins versus sham rats and versus CHF rats treated with i.c.v. Fab. In sham-operated rats and CHF rats treated with i.c.v. Fab, RSNA and HR began to decrease within 3-4 min of beginning the NP infusion and had returned to baseline by 20 min. In contrast, RSNA and HR remained increased throughout the infusion in the CHF rats treated with gamma-globulins. These data indicate that in rats with CHF acute resetting of the arterial baroreflex in response to a lower BP becomes impaired, and chronic blockade of brain "ouabain" prevents both this change in baroreflex resetting as well as sympathetic hyperactivity.

Characterization of a novel member of the DOK family that binds and modulates Abl signaling

A novel member of the p62(dok) family of proteins, termed DOKL, is described. DOKL contains features of intracellular signaling molecules, including an N-terminal PH (pleckstrin homology) domain, a central PTB (phosphotyrosine binding) domain, and a C-terminal domain with multiple potential tyrosine phosphorylation sites and proline-rich regions, which might serve as docking sites for SH2- and SH3-containing proteins. The DOKL gene is predominantly expressed in bone marrow, spleen, and lung, although low-level expression of the RNA can also be detected in other tissues. DOKL and p62(dok) bind through their PTB domains to the Abelson tyrosine kinase in a kinase-dependent manner in both yeast and mammalian cells. DOKL is phosphorylated by the Abl tyrosine kinase in vivo. In contrast to p62(dok), DOKL lacks YxxP motifs in the C terminus and does not bind to Ras GTPase-activating protein (RasGAP) upon phosphorylation. Overexpression of DOKL, but not p62(dok), suppresses v-Abl-induced mitogen-activated protein (MAP) kinase activation but has no effect on constitutively activated Ras- and epidermal growth factor-induced MAP kinase activation. The inhibitory effect requires the PTB domain of DOKL. Finally, overexpression of DOKL in NIH 3T3 cells inhibits the transforming activity of v-Abl. These results suggest that DOKL may modulate Abl function.

Brain "ouabain" and angiotensin II contribute to cardiac dysfunction after myocardial infarction

In chronic heart failure (CHF), sympathetic activity increases in parallel with the impairment of left ventricle (LV) function, and sympathetic hyperactivity has been postulated to contribute to the progression of heart failure. In the brain, compounds with ouabain-like activity ("ouabain," for brevity) and the renin-angiotensin system contribute to sympathetic hyperactivity in rats with CHF after myocardial infarction (MI). In the present studies, we assessed whether, in rats, chronic blockade of brain "ouabain" or the brain renin-angiotensin system inhibits the post-MI LV dysfunction. In rats, an MI was induced by acute coronary artery ligation. At either 0.5 or 4 wk post-MI, chronic treatment with Fab fragments for blocking brain "ouabain" or with losartan for blocking brain AT(1) receptors was started and continued until 8 wk post-MI using osmotic minipumps connected to intracerebroventricular cannulas. At 8 wk post-MI, in conscious rats, LV pressures were measured at rest and in response to volume and pressure overload, followed by LV passive pressure-volume curves in vitro. At 8 wk post-MI, control MI rats exhibited clear increases in LV end-diastolic pressure (LVEDP) at rest and in response to pressure and volume overload. LV pressure-volume curves in vitro showed a marked shift to the right. Intravenous administration of the Fab fragments or losartan at rates used for central blockade did not affect these parameters. In contrast, chronic central blockade with either Fab fragments or losartan significantly lowered LVEDP at rest (only in 0.5- to 8-wk groups) and particularly in response to pressure or volume overload. LV dilation, as assessed from LV pressure-volume curves, was also significantly inhibited. These results indicate that chronic blockade of brain "ouabain" or brain AT(1) receptors substantially inhibits development of LV dilation and dysfunction in rats post-MI.

Comparison of heteroduplex analysis, direct sequencing, and enzyme mismatch cleavage for detecting mutations in a large gene, FBN1

Analysis of large genes for mutations of clinical relevance is complicated by intragenic heterogeneity, sensitivity, and cost of the methods available, and in the case of many conditions, specificity of the genetic alterations detected. We examined the FBN1 gene for mutations in people who had Marfan syndrome using three methods: single-chain polymorphism analysis (SSCP) with heteroduplex (HA) analysis, enzyme-mediated cleavage (EMC) of heteroduplexes, and direct sequencing. We also used these methods to search for mutations in the P53 gene in patients with hepatocellular carcinoma. The results showed that EMC was most efficient for detecting mutations. However, the cost favored SSCP with heteroduplex analysis, provided conditions did not need to be optimized to detect a mutation. Until more cost-effective and sensitive methods are developed to detect unknown mutations in large genes, diagnosis of many genetic disorders will depend on the willingness of an investigator who is studying a particular disorder to perform clinical molecular testing and have the laboratory accredited.

[A new explanation for shadow bands on denaturing PAGE for products of STRS--the difference between sense and antisense strands in electrophoresis]

OBJECTIVE

To explore the mechanism of shadow bands on denaturing PAGE for PCR products of STR sequences and try to eliminate them.

METHODS

PCR and asymmetric PCR were employed. The amplified fragments were separated on denaturing PAGE and visualized by silver stain.

RESULTS

By asymmetric PCR, half of shadow bands of dinucleotide repeats were eliminated and there was only one band for each allele for tetranucleotide sequence. A different migration between the sense strand and antisense strand was identified.

CONCLUSION

The difference between sense and antisense strands in electrophoresis is one of the causes in shadow bands, and these shadow bands can be eliminated by asymmetric PCR partly or totally.

Mutations altering the moloney murine leukemia virus p12 Gag protein affect virion production and early events of the virus life cycle

The p12 Gag protein of Moloney murine leukemia virus is a small polypeptide of unknown function, containing two proline-rich motifs. To determine its role in replication, we introduced a series of deletion and alanine-scanning substitution mutations throughout the p12 coding region of a proviral DNA, and characterized the phenotypes of the resulting mutant viruses. Complete deletion of p12 and mutations affecting the PPPY motif caused substantial reduction in the yield of virions and a modest reduction in Gag processing. Proteolytic cleavage of the R-peptide from the cytoplasmic tail of the envelope protein TM was abolished in these mutants, suggesting that the PPPY motif is crucial for the viral protease to access the TM tail. The resulting virions were non-infectious, and unable to initiate DNA synthesis in infected cells. Mutants with alterations in both the N- and C-terminal portions of p12 exhibited a distinct phenotype. The production of virions and processing of Gag, Pol and Env precursors were normal. The viruses were able to direct synthesis of linear viral DNA, but there was almost no detectable circular DNAs or LTR-LTR junction. These data suggest that p12 plays a critical role in the early events of the virus life cycle.

Morphine applied to the thalamic nucleus submedius produces a naloxone reversible antinociceptive effect in the rat

Our previous studies have indicated that the thalamic nucleus submedius (Sm) is involved in nociceptive modulation and plays an important role in an endogenous analgesic system (a feedback loop) consisting of spinal cord - Sm - ventrolateral orbital cortex (VLO) - periaqueductal gray (PAG) - spinal cord. To further investigate the neurotransmitter and receptor mechanisms in this nociceptive modulatory pathway, we tested the effects of microinjection of morphine and naloxone into the Sm on the rat tail flick (TF) reflex. A unilateral microinjection of morphine (8.0 mM, 0.5 microl) into the Sm significantly depressed the TF reflex, whereas a unilateral microinjection of naloxone (5.0 mM, 0.5 microl) into the Sm facilitated the TF reflex. Five minutes after morphine application into Sm, injection of naloxone in this nucleus markedly reversed the inhibition evoked by applying morphine in Sm. These findings suggest that the endogenous opioid peptides may be involved in the antinociceptive effects evoked by activation of the Sm-VLO-PAG pathway which depressed the nociceptive inputs at the spinal level via the brainstem descending inhibitory system, and exert a tonic descending influence.

Blockade of AT(1) receptors and Na(+)/H(+) exchanger and LV dysfunction after myocardial infarction in rats

Mechanical stretch, ANG II, and alpha(1)-receptor stimulation may contribute to cardiac remodeling after myocardial infarction (MI). Each of these mechanisms involves different signaling pathways for the cellular hypertrophic response. All three also activate the Na(+)/H(+) exchanger. In the present study we evaluated the hypothesis that activation of the Na(+)/H(+) exchanger is involved in parallel with other signaling mechanisms for ANG II. Three days before coronary artery ligation, rats were randomly allocated to no treatment or treatment with amiloride, losartan, or amiloride and losartan in combination. Four weeks after coronary artery ligation, left ventricular (LV) function was assessed from in vivo resting cardiac pressures, hemodynamic responses to cardiac volume and pressure load, and cardiac remodeling by in vitro pressure-volume curves and LV and right ventricle (RV) weight. Amiloride and losartan given alone to a similar extent attenuated the shift of the pressure-volume curve to the right. This effect was significantly more pronounced with amiloride and losartan in combination. Each drug alone to a minor extent improved LV responses to pressure and volume load. However, with amiloride and losartan in combination, close-to-normal responses to pressure and volume load were observed. Losartan and amiloride alone had only a small effect on development of RV hypertrophy after MI but in combination completely prevented the RV hypertrophy. Amiloride and losartan appear to be complementary in prevention of cardiac remodeling and LV dysfunction after MI. This finding suggests that, besides ANG II, other mechanisms activating the Na(+)/H(+) exchanger contribute to cardiac remodeling after MI.

Electrically-evoked inhibitory effects of the nucleus submedius on the jaw-opening reflex are mediated by ventrolateral orbital cortex and periaqueductal gray matter in the rat

In previous studies we have shown that electrical stimulation of the nucleus submedius inhibits the rat radiant heat-induced tail flick reflex, and that this antinociceptive effect is mediated by the ventrolateral orbital cortex and periaqueductal gray. The aim of the present study was to examine whether electrical stimulation of the nucleus submedius could inhibit the rat jaw-opening reflex, and to determine whether electrolytic lesions of the ventrolateral orbital cortex or the periaqueductal gray could attenuate the nucleus submedius-evoked inhibition. Experiments were performed on pentobarbital-anesthetized rats. The jaw-opening reflex elicited by electrical stimulation of the tooth pulp or the facial skin was monitored by recording the evoked digastric electromyogram. Conditioning stimulation was delivered unilaterally to the nucleus submedius 90 ms prior to each test stimulus to the tooth pulp. After that, electrolytic lesions were made in ventrolateral orbital cortex or periaqueductal gray, and the effect of nucleus submedius stimulation on the jaw-opening reflex was re-examined. Unilateral electrical stimulation of nucleus submedius was found to significantly depress the jaw-opening reflex (mean threshold of 28.0+/-1.4 microA, n = 48), and the magnitude of inhibition increased linearly when the stimulus intensity was increased from 20 to 70 microA, resulting in depression of the digastric electromyogram amplitude from 18.4+/-5.4% to 74.0+/-4.9% of the control (P < 0.01, n = 37). The onset of inhibition occured 60 ms after the beginning of nucleus submedius stimulation and lasted about 100 ms, as determined by varying the conditioning-test time interval. Furthermore, ipsilateral lesions of the ventrolateral orbital cortex or bilateral lesions of the lateral or ventrolateral parts of periaqueductal gray eliminated the nucleus submedius-evoked inhibition of the jaw-opening reflex. These data suggest that the nucleus submedius plays an important role in modulation of orofacial nociception, and provide further support for a hypothesis that the antinociceptive effect of nucleus submedius stimulation is mediated by ventrolateral orbital cortex and activation of a descending inhibitory system in the periaqueductal gray.

Zinc exposure in Chinese foundry workers

BACKGROUND

Inhalational exposure to zinc oxide fumes is associated with metal fume fever, a self-limited but very uncomfortable condition closely resembling influenza. Very little is known regarding the toxicokinetics of inhaled zinc, making the interpretation of zinc measurements in serum and urine problematic.

METHODS

Twenty workers in a zinc foundry in Baiyin, Peoples' Republic of China, were investigated with serial examinations by a physician, chest radiographs, and spirometry. Exposure assessment consisted of the measurement of zinc in serum, urine, and personal air samples.

RESULTS

No cases of metal fume fever were observed during the study period despite exposures to as high as 36.3 mg/m3 over less than 4 hr. In addition, no radiographic or functional changes were noted. Serum zinc levels of all workers were within the reference range and did not correlate with external exposure measurements. However, elevations were noted in urinary zinc levels, which showed a significant association (Spearman's correlation coefficient = 0.47, P = 0.04) between exposure to zinc and urine zinc.

CONCLUSIONS

These results provide exposure measurements for zinc at which workers demonstrate tolerance to the development of metal fume fever. Furthermore, they suggest that urine may be the preferred biological medium for the assessment of zinc exposure.

[X-ray diffraction spectrum of heroin]

In this paper, practical measured X-ray diffraction spectra of heroin and opium are given and the parameters of each diffraction peak of the heroin are listed. The heroin belongs to orthorhombic crystal system; the basic vectors of the primitive cell are: a = 8.003, b = 14.373, c = 16.092 x 10(-10) m. As compared with the standard spectra of pure heroin and sucrose, the main doped additive checked by us, is sugar affirmatively.

A Drosophila doublesex-related gene, terra, is involved in somitogenesis in vertebrates

The Drosophila doublesex (dsx) gene encodes a transcription factor that mediates sex determination. We describe the characterization of a novel zebrafish zinc-finger gene, terra, which contains a DNA binding domain similar to that of the Drosophila dsx gene. However, unlike dsx, terra is transiently expressed in the presomitic mesoderm and newly formed somites. Expression of terra in presomitic mesoderm is restricted to cells that lack expression of MyoD. In vivo, terra expression is reduced by hedgehog but enhanced by BMP signals. Overexpression of terra induces rapid apoptosis both in vitro and in vivo, suggesting that a tight regulation of terra expression is required during embryogenesis. Terra has both human and mouse homologs and is specifically expressed in mouse somites. Taken together, our findings suggest that terra is a highly conserved protein that plays specific roles in early somitogenesis of vertebrates.

[Characteristics of high frequency 249 codon mutation of p53 gene in hepatocellular carcinoma in prevalent area of China]

OBJECTIVE

To study the characteristic features of an unique hotspot missense mutation of the 249 codon of p53 gene demonstrated in human hepato-cellular carcinoma(HCC) in a region of high(Qidong) and low (Beijing) exposure to both hepatitis B virus (HBV) and aflatoxin B1 (AFB1) in China.

METHODS

Surgical samples from 97 HCC from Qidong and 22 from Beijing, China, collected in 1994 through 1997, were studied. The 249 codon mutation of p53 gene was detected by PCR followed by HaeIII RFLP analysis and DNA sequencing. Intracellular p53 protein level was determined by immunohistochemical staining.

RESULTS

High mutation rate of 249 codon of p53 gene was consistently found in recent years, with an average of 53.6% (52/97). No such mutation was identified in 22 Beijing HCC collected in the same time period. The genotype of p53 249 codon mutants which showed heterozygous profile was identified to be homozygous in nature following tumor tissue enrichment. Of 21 HCC shown to have 249 codon mutation, 20 exhibited high intranuclear accumulation of p53 protein. p53 protein staining was negative in the surrounding noncancerous hepatic tissue.

CONCLUSION

The high frequency of homozygous mutation of the 249 codon of p53 gene accompanied with p53 protein accumulation provides important enlightenment in the understanding of hepatocarcinogenesis and clinical application of gene therapy and/or immunotherapy for HCC.

Inhibitory effects of 5-hydroxytryptamine microinjection into thalamic nucleus submedius on rat tail flick reflex are mediated by 5-HT2 receptors

Our previous findings indicated that electrical or chemical activation of the thalamic nucleus submedius (Sm) produced significant antinociceptive effects and that these effect were blocked by lesion or depression of the ventrolateral orbital cortex (VLO) or the periaqueductal gray (PAG) suggesting a role of the Sm in modulation of nociception. To further investigate the neurotransmitter mechanism involved in this nociceptive modulatory pathway, we tested the effects of microinjection of 5-hydroxytryptamine (5-HT, 50 mM, 0.5 microl) into Sm on the tail flick (TF) reflex. The results show that a unilateral microinjection of 5-HT into Sm significantly depresses the TF reflex; and that this effect is repeatable and dose-dependent. Furthermore, microinjection of 5-HT2 receptor antagonist cyproheptadine (CPT, 0.3 mM, 0.5 microl) into the same Sm site reverses this 5-HT-evoked inhibition of TF reflex. These results suggest that 5-HT application to the Sm may activate Sm neurons through the 5-HT2 receptors leading to activation of the brainstem descending inhibitory system via the VLO and depression of the nociceptive information at the spinal level.

Positive and negative cis-acting elements are required for hematopoietic expression of zebrafish GATA-1

GATA-1 is a transcription factor required for development of erythroid cells. The expression of GATA-1 is tightly restricted to the hematopoietic lineage. Using transgene constructs containing zebrafish GATA-1 genomic sequences and the green fluorescent protein (GFP) reporter gene, we previously showed that a 5.6-kb enhancer/promoter fragment is sufficient to direct erythroid-specific expression of the GFP. In this study, we used enhancer/promoter fragments containing various deletion and point mutations to further characterize the cis-acting elements controlling tissue-specific GATA-1 expression. We report here the identification of distinct cis-acting elements that cooperate to confer on GATA-1 its hematopoietic expression pattern. A CACCC box, located 142 bp upstream of the translation start codon, is critical for the initiation of GATA-1 expression. A distal double GATA element is required for maintaining and enhancing the hematopoietic expression of GATA-1. The erythroid-specific activity of the GATA-1 promoter is also enhanced by a 49-bp sequence element located 218 bp upstream of the CACCC element and a CCAAT box adjacent to the double GATA motif. Finally, the hematopoietic specificity of the GATA-1 promoter is secured by a negative cis-acting element that inhibits expression in the notochord.

Changes in cardiac ANG II postmyocardial infarction in rats: effects of nephrectomy and ACE inhibitors

We evaluated in rats the time course of changes in cardiac versus plasma ANG I and II postmyocardial infarction (MI) and the effects of nephrectomy and angiotensin-converting enzyme (ACE) inhibitors on the early changes post-MI. Acute coronary artery ligation was induced in conscious rats using the two-stage model, and plasma and cardiac tissue were obtained shortly (6 h, 1 and 3 days) and chronically (1, 4, and 8-9 wk) after MI. In an additional group of rats, bilateral nephrectomy was performed 18 h before the coronary artery ligation, and samples were obtained at 6 h post-MI. Furthermore, in two additional groups of rats, treatment with enalapril and quinapril was started 3 days before the ligation, and samples were obtained at 1 or 3 days post-MI. In these groups of rats, plasma and left ventricular (LV) (infarct and infarct free) ANG I and II were measured by RIA after separation on HPLC. In control rats, plasma ANG I and II showed a clear increase at 6 h post-MI but subsequently only minor increases were observed. In contrast, LV ANG II showed major increases at 6 h and 1 day post-MI, which had returned to normal by 3 days in the infarct-free LV and after 1(-2) wk in the infarct LV. LV ANG I showed a more gradual increase and remained elevated in the infarct up to 8-9 wk. Nephrectomy preceding the MI lowered ANG I and II in plasma but enhanced their increases in the heart at 6 h post-MI. Both ACE inhibitors decreased plasma ANG II associated with large increases in plasma ANG I. They also inhibited the increases in LV ANG II in both the infarct and infarct-free LV at 1 and 3 days post-MI with however no significant increase in LV ANG I. In conclusion, induction of a MI in conscious rats leads to rapid and marked, but only short-lived, increases in cardiac tissue ANG II in both the infarct and infarct-free parts of the LV. Pretreatment with ACE inhibitors, but not nephrectomy, blocks this increase. Local production appears to play a major role in the increases in cardiac ANG II post-MI.

Inhibitory effects of electrical stimulation of ventrolateral orbital cortex on the rat jaw-opening reflex

In previous studies, we have shown that electrically or chemically evoked activation of the ventrolateral orbital cortex (VLO) depresses the rat tail-flick (TF) reflex, and this antinociceptive effect is mediated by the periaqueductal gray (PAG). The aim of the present study was to examine whether electrical stimulation of the VLO could inhibit the rat jaw-opening reflex (JOR), and to determine whether electrolytic lesions of the PAG could attenuate this VLO-evoked inhibition. Unilateral electrical stimulation of the VLO significantly depressed the JOR elicited by tooth pulp or facial skin stimuli, with a mean threshold of 30.5+/-2.3 microA (n=22). Increasing stimulation intensities from 30 to 80 microA resulted in greater reduction of the dEMG amplitude from 22.9+/-5.0% to 69.7+/-3.7% of the baseline value (P<0.01, n=22). The inhibitory effect appeared 50 ms after the beginning of VLO stimulation and lasted about 150 ms, as determined by varying the conditioning-test (C-T) time interval. Unilateral lateral or ventrolateral lesions of the PAG produced only a small attenuation of the VLO-evoked inhibition of the JOR, but bilateral lesions eliminated this inhibition. These findings suggest that the VLO plays an important role in modulation of orofacial nociceptive inputs, and provide further support for the hypothesis that the antinociceptive effect of VLO is mediated by PAG leading to activation of a brainstem descending inhibitory system and depression of nociceptive inputs at the trigeminal level. The role played by VLO in pain modulation is discussed in association with the proposed endogenous analgesic system consisting of medullary cord-Sm-VLO-PAG-medullary cord.

Dietary-sodium-induced cardiac remodeling in spontaneously hypertensive rat versus Wistar-Kyoto rat

OBJECTIVE

To study the effects of short-term and long-term high sodium intake on cardiac mass and design in sodium-sensitive spontaneously hypertensive rats versus sodium-resistant Wistar-Kyoto rats.

METHODS

Young spontaneously hypertensive rats and Wistar-Kyoto rats were randomly allocated to control diet, 2 or 8% dietary sodium for 2-12 weeks and changes in resting hemodynamics, cardiac angiotensin II level, sympathetic activity and cardiac structure evaluated. Sympathetic activity was assessed by measuring levels of plasma catecholamines, responses of blood pressure to ganglionic blockade, and rates of cardiac turnover of norepinephrine.

RESULTS

High sodium intake for 4 weeks increased left ventricle weight of Wistar-Kyoto rats aged 4 weeks (by 11 and 25% for 2 and 8% NaCl diets, respectively). This hypertrophic response was temporary, however, had already diminished after 6 weeks, and was absent after 12 weeks of a high sodium intake. However, after prolonged exposure concentric remodeling occurred (i.e. left ventricle wall thickness : radius ratio increased with no change in left ventricle mass). High sodium intake did not affect resting blood pressure, cardiac index, cardiac angiotensin II level, and general sympathetic activity of Wistar-Kyoto rats. Short-term high sodium intake did not increase left ventricle mass of young spontaneously hypertensive rats, unless sodium intake was so high (8% NaCl) that blood pressure and general sympathetic activity increased, too. However, a prolonged moderate (2%) increase in sodium intake also caused concentric remodeling in spontaneously hypertensive rats without increasing left ventricle mass, blood pressure, cardiac index, and general and cardiac sympathetic activities.

CONCLUSIONS

The blood pressure in young Wistar-Kyoto rats is sodium-insensitive but the heart structure is sodium-sensitive and high dietary sodium intake causes an early hypertrophic response, and then concentric remodeling. In contrast, hypertrophic response appears to occur after the response of blood pressure in spontaneously hypertensive rats, whereas the remodeling is similar to that in Wistar-Kyoto rats.

[Responses of neurons in thalamic nucleus submedius to electrical stimulation of peroneal nerve and "zusanli" point in rats]

The experiments were performed on the anesthetized rats. Single unit was recorded extracellularlly from the thalamic nucleus submedius (Sm) with glass micropipettes. The responses of Sm neurons were examined to electrical stimulation of the peroneal nerve and "Zusanli" point. The results show that most (81%) of the neurons in Sm responded to electrical stimulation of the peroneal nerve with afferent C fiber excitation, and this response increased following increase of the stimulation intensity and pulse numbers. It was found that electrical stimulation of the "Zusanli" point could activate the Sm neuronal activities with higher intensity threshold compared to that of the peroneal nerve stimulation, and the response properties of Sm neurons to acupoint stimuli were similar to those to stimulation of peroneal nerve. These results provide support for the hypothesis that a negative feedback loop consisting of spinal cord-Sm-VLO-PAG-spinal cord responsible for nociceptive modulation is involved in acupuncture analgesia, especially in analgesia produced by electroacupuncture-evoked activation of the afferent C fibers.

[Effects of bilateral lesions of ventrolateral orbital cortex on the rat tail flick reflex inhibition evoked by electroacupuncture]

This study found that bilateral electrolytic lesions of the ventrolateral orbital cortex (VLO) markedly reduced the inhibitory effects of high intensity electroacupuncture (EA) at "Zusanli" point on tail flick reflex in lightly anesthetized rats, but did not influence the inhibitory effects of low intensity EA stimulation. The results show that the VLO is involved in acupuncture analgesia produced by activation of small afferent fibers with high intensity electroacupunture. Results of this study provide further support for a hypothesis that spinal cord-Sm-VLO-PAG-spinal cord may constitute a negative feedback loop of nociceptive modulation. The analgesic effects produced by high intensity electroacupuncture may be mediated by this loop leading to depression of the nociceptive inputs at the spinal cord level.

A region within murine chromosome 7F4, syntenic to the human 11q13 amplicon, is frequently amplified in 4NQO-induced oral cavity tumors

Our previous reports have shown that two thirds of 4-nitroquinoline-1-oxide (4NQO)-induced murine oral squamous cell carcinomas (SCC) have Hras1 mutations. Loss of heterozygosity (LOH) involving the distal portion of chromosome (Chr) 7 occurred in half of the tumors with Hras1 mutations. Here, we demonstrate that five of six tumors with LOH have 4-8-fold amplification involving the distal portion of Chr 7 (7F4). Ccnd1. Fgf4 and Fgf3, within the most telomeric region of Chr 7 (70.5 cM), are co-amplified. The region is syntenic to a previously identified human amplicon at 11q13. Only one out of eight tumors without LOH at Chr 7 had twofold amplification; the other seven had no detectable amplification. Significant amplification is restricted to the chromosome with the Hras1 mutation. Gene amplification occurred without overexpression since only one of five tumors with amplification and one of six tumors without Ccnd1 amplification expressed increased protein. Although amplification of 11q13 occurs rather frequently in human tumors, 4NQO-induced oral cavity tumors in inbred mice are the first example of a murine tumor with consistent amplification. Our observations are strikingly similar to human head and neck SCC where overexpression of genes within the 11q13 amplicon is inconsistently detected. The amplification of genes localized to human 11q13 and the syntenic region on murine Chr 7 during tumorigenesis suggests that similar structural elements are present which predispose these regions to amplification during malignant transformation.