Long glutamine tracts cause nuclear localization of a novel form of huntingtin in medium spiny striatal neurons in HdhQ92 and HdhQ111 knock-in mice

Huntington's disease (HD) is caused by an expanded N-terminal glutamine tract that endows huntingtin with a striatal-selective structural property ultimately toxic to medium spiny neurons. In precise genetic models of juvenile HD, HdhQ92 and HdhQ111 knock-in mice, long polyglutamine segments change huntingtin's physical properties, producing HD-like in vivo correlates in the striatum, including nuclear localization of a version of the full-length protein predominant in medium spiny neurons, and subsequent formation of N-terminal inclusions and insoluble aggregate. These changes show glutamine length dependence and dominant inheritance with recruitment of wild-type protein, critical features of the altered HD property that strongly implicate them in the HD disease process and that suggest alternative pathogenic scenarios: the effect of the glutamine tract may act by altering interaction with a critical cellular constituent or by depleting a form of huntingtin essential to medium spiny striatal neurons.

Huntington aggregates may not predict neuronal death in Huntington's disease

The mechanism by which polyglutamine expansion in Huntington's disease (HD) results in selective neuronal degeneration remains unclear. We previously reported that the immunohistochemical distribution of N-terminal huntingtin in HD does not correspond to the severity of neuropathology, such that significantly greater numbers of huntingtin aggregates are present within the cortex than in the striatum. We now show a dissociation between huntingtin aggregation and the selective pattern of striatal neuron loss observed in HD. Aggregate formation was predominantly observed in spared interneurons, with few or no aggregates found within vulnerable spiny striatal neurons. Multiple perikaryal aggregates were present in almost all cortical NADPH-diaphorase neurons and in approximately 50% of the spared NADPH-diaphorase striatal neurons from early grade HD cases. In severe grade HD patients, aggregates were more prominent as nuclear inclusions in NADPH-diaphorase neurons, with less perikaryal and neuropil aggregation. In contrast, nuclear or perikaryal huntingtin aggregates were present in less than 4% of the vulnerable calbindin striatal neurons in all HD cases. These findings support the hypothesis that polyglutamine aggregation may not be a predictor of cell loss. Rather than a harbinger of neuronal death, mutant huntingtin aggregation may be a cytoprotective mechanism against polyglutamine-induced neurotoxicity.

The early cellular pathology of Huntington's disease

Huntington's disease (HD) is an inherited neurodegenerative disorder that affects about one in 10,000 individuals in North America. The genetic defect responsible for the disease is an expansion of a CAG repeat that encodes a polyglutamine tract in the expressed protein, huntingtin. The disease is characterized by involuntary movements, cognitive impairment, and emotional disturbance. Despite the widespread expression of huntingtin, the brains of HD patients show selective neuronal loss in the striatum and the deep layers of the cerebral cortex. Recent studies have shown that polyglutamine expansion causes huntingtin to aggregate, to accumulate in the nucleus, and to interact abnormally with other proteins. Several cellular and animal models for HD have revealed that intranuclear accumulation of mutant huntingtin and the formation of neuropil aggregates precede neurological symptoms and neurodegeneration. Intranuclear huntingtin may affect nuclear function and the expression of genes important for neuronal function, whereas neuropil aggregates may interfere with neuritic transport and function. These early pathological events, which occur in the absence of neurodegeneration, may contribute to the neurological symptoms of HD and ultimately lead to neuronal cell death.

[Melatonin decreases the release of amino acid transmitters in hypoxic rat cortical slice]

To study the effect of melatonin on changes in amino acid release following hypoxic stimulation, a RP-HPLC fluorometric method was used to measure the content of amino acids in the culture medium of rat brain slices. Hypoxic condition was instituted by a gas of 91.6% N2 and 8.4% O2. The results showed that the contents of amino acids, including aspartate, glutamate, glutamine, glycine, taurine and GABA, in the medium were significantly increased to 240.4%, 334.3%, 200.6%, 210.4%, 168.6% and 263.9%, respectively (P < 0.01 vs control) by 30 min hypoxic incubation. Melatonin can significantly reduce the increase of aspartate and glutamate, to 55.1% and 57.0% of the hypoxic group.

Mxi1 mutations in human neurofibrosarcomas

Mxi1 is thought to negatively regulate Myc function and may therefore be a potential tumor suppressor gene. Little effort has yet been made to find alterations involving this gene in human solid tumors. We screened 31 human gastric cancers, 7 esophageal cancers, 85 bone and soft tissue tumors of various types, including 4 neurofibrosarcomas. We also examined 29 human tumor cell lines consisting of 12 esophageal cancers, 7 glioma/glioblastomas and 10 others for Mxi1 mutations in exons 1, 2, 4 (HLH domain), 5 and 6. Polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and subsequent sequencing revealed three distinct polymorphisms in the intron-exon boundary upstream from exon 6. We discovered a missense mutation, GCA to GTA (Ala 54 Val), in exon 2 in a neurofibrosarcoma patient (case 1), two missense mutations, AAA to CAA (Lys 118 Gln) and GAA to GGA (Glu 154 Gly) in exon 5 of another neurofibrosarcoma patient (case 2), and 3 amino acid substitutions, GTG to GCG (Val 179 Ala), GTT to GCT (Val 181 Ala) and TTC to CTC (Phe 186 Leu), in a third neurofibrosarcoma patient (case 3). In case 3, loss of heterozygosity was also demonstrated by informative (TTC)3/(TTC)2 polymorphism. Our data demonstrate that mutations occur in the Mxi1 gene in neurofibrosarcoma. Missense mutations in the functional domain of Mxi1 in these cases may be involved in the pathogenesis of neurofibrosarcoma.

Cellular defects and altered gene expression in PC12 cells stably expressing mutant huntingtin

Expanded polyglutamine tracts cause huntingtin and other proteins to accumulate and aggregate in neuronal nuclei. Whether the intranuclear aggregation or localization of a polyglutamine protein initiates cellular pathology remains controversial. We established stably transfected pheochromocytoma PC12 cells that express the N-terminal fragment of huntingtin containing 20 (20Q) or 150 (150Q) glutamine residues. The 150Q protein is predominantly present in the nuclei, whereas the 20Q protein is distributed throughout the cytoplasm. Electron microscopic examination confirmed that most of the 150Q protein is diffuse in the nucleus with very few microscopic aggregates observed. Compared with parental PC12 cells and cells expressing 20Q, cells expressing 150Q display abnormal morphology, lack normal neurite development, die more rapidly, and are more susceptible to apoptotic stimulation. The extent of these cellular defects in 150Q cells is correlated with the expression level of the 150Q protein. Differential display PCR and expression studies show that cells expressing 150Q have altered expression of multiple genes, including those that are important for neurite outgrowth. Our study suggests that mutant huntingtin in the nucleus is able to induce multiple cellular defects by interfering with gene expression even in the absence of aggregation.

Ultrastructural localization and progressive formation of neuropil aggregates in Huntington's disease transgenic mice

How aggregates of polyglutamine proteins are involved in the neurological symptoms of glutamine repeat diseases is unknown. We show that huntingtin aggregates are present in the neuronal processes of transgenic mice that express exon 1 of the Huntington's disease (HD) gene. Unlike aggregates in the nucleus, these neuropil aggregates are usually smaller and are not ubiquitinated. Electron microscopy reveals many neuropil aggregates in axons and axon terminals. Huntingtin aggregates in the axon terminal are co-localized with some synaptic vesicles, implying that they may affect synaptic transmission and neuronal communication. The formation of neuropil aggregates is highly correlated with the development of neurological symptoms. The present study raises the possibility that neuropil aggregates may cause a dysfunction in neuronal communication and con-tribute to the neurological symptoms of HD.

Inhibition of caspase-1 slows disease progression in a mouse model of Huntington's disease

Huntington's disease is an autosomal-dominant progressive neurodegenerative disorder resulting in specific neuronal loss and dysfunction in the striatum and cortex. The disease is universally fatal, with a mean survival following onset of 15-20 years and, at present, there is no effective treatment. The mutation in patients with Huntington's disease is an expanded CAG/polyglutamine repeat in huntingtin, a protein of unknown function with a relative molecular mass of 350,000 (M(r) 350K). The length of the CAG/polyglutamine repeat is inversely correlated with the age of disease onset. The molecular pathways mediating the neuropathology of Huntington's disease are poorly understood. Transgenic mice expressing exon 1 of the human huntingtin gene with an expanded CAG/polyglutamine repeat develop a progressive syndrome with many of the characteristics of human Huntington's disease. Here we demonstrate evidence of caspase-1 activation in the brains of mice and humans with the disease. In this transgenic mouse model of Huntington's disease, expression of a dominant-negative caspase-1 mutant extends survival and delays the appearance of neuronal inclusions, neurotransmitter receptor alterations and onset of symptoms, indicating that caspase-1 is important in the pathogenesis of the disease. In addition, we demonstrate that intracerebroventricular administration of a caspase inhibitor delays disease progression and mortality in the mouse model of Huntington's disease.

Protective effect of melatonin on injuried cerebral neurons is associated with bcl-2 protein over-expression

AIM

To study the protective effect of melatonin against neuronal injury and the possible roles of alteration in the expression of bcl-2 and bax following brain ischemia.

METHODS

Brain ischemia was induced by left middle cerebral artery occlusion (MCAO) for 60 min in rats. Brain damage was evaluated by the infarct area and the neuronal cell counting. The expression of bcl-2 and bax was analyzed by immunohistochemical method.

RESULTS

Melatonin decreased the infarct area and prevented the neuronal death after 24-h reperfusion following 1-h MCAO. Melatonin given before the ischemia enhanced the expression of bcl-2 in the penumbra area and had no significant effect on the expression of bax.

CONCLUSION

Melatonin effectively attenuated ischemic brain injury and increased the expression of neuronal bcl-2 in the ischemic brain, indicating that the protective effect of melatonin was associated with up-regulation of bcl-2 in ischemia-induced neuronal death.

[The use of subdermal vascularized thin flap in the repair of the burned scar on neck]

OBJECTIVE

To evaluate the clinical efficacy of thin flap with subdermal vascular network of the neck-pectoral region on repair of the contracture of the burn scar on the neck.

METHODS

From March 1990 to May 1998, 21 cases of deformity of neck due to burn scar were repaired with the thin flap ranging from 8 cm x 5 cm to 14 cm x 8 cm, and all of the cases were followed up for 6 to 42 months.

RESULTS

Except partial necrosis of the distal end of the flap in 1 case, the flaps in the other 20 cases all survived and presented a satisfactory appearance and function.

CONCLUSION

The thin flap with subdermal vascular network in neck-pectoral region may provide a large area of flap, and could be easily transferred. It's an ideal flap for the repair of skin defect on the neck.

A YAC mouse model for Huntington's disease with full-length mutant huntingtin, cytoplasmic toxicity, and selective striatal neurodegeneration

We have produced yeast artificial chromosome (YAC) transgenic mice expressing normal (YAC18) and mutant (YAC46 and YAC72) huntingtin (htt) in a developmental and tissue-specific manner identical to that observed in Huntington's disease (HD). YAC46 and YAC72 mice show early electrophysiological abnormalities, indicating cytoplasmic dysfunction prior to observed nuclear inclusions or neurodegeneration. By 12 months of age, YAC72 mice have a selective degeneration of medium spiny neurons in the lateral striatum associated with the translocation of N-terminal htt fragments to the nucleus. Neurodegeneration can be present in the absence of macro- or microaggregates, clearly showing that aggregates are not essential to initiation of neuronal death. These mice demonstrate that initial neuronal cytoplasmic toxicity is followed by cleavage of htt, nuclear translocation of htt N-terminal fragments, and selective neurodegeneration.

Nuclear and neuropil aggregates in Huntington's disease: relationship to neuropathology

The data we report in this study concern the types, location, numbers, forms, and composition of microscopic huntingtin aggregates in brain tissues from humans with different grades of Huntington's disease (HD). We have developed a fusion protein antibody against the first 256 amino acids that preferentially recognizes aggregated huntingtin and labels many more aggregates in neuronal nuclei, perikarya, and processes in human brain than have been described previously. Using this antibody and human brain tissue ranging from presymptomatic to grade 4, we have compared the numbers and locations of nuclear and neuropil aggregates with the known patterns of neuronal death in HD. We show that neuropil aggregates are much more common than nuclear aggregates and can be present in large numbers before the onset of clinical symptoms. There are also many more aggregates in cortex than in striatum, where they are actually uncommon. Although the striatum is the most affected region in HD, only 1-4% of striatal neurons in all grades of HD have nuclear aggregates. Neuropil aggregates, which we have identified by electron microscopy to occur in dendrites and dendritic spines, could play a role in the known dendritic pathology that occurs in HD. Aggregates increase in size in advanced grades, suggesting that they may persist in neurons that are more likely to survive. Ubiquitination is apparent in only a subset of aggregates, suggesting that ubiquitin-mediated proteolysis of aggregates may be late or variable.

Effect of melatonin on production of hydroxyl radical and lactate dehydrogenase during hypoxia in rat cortical slices

AIM

To study the effect of melatonin on the production of hydroxyl radical (.OH) and lactate dehydrogenase (LDH) following hypoxia in cortical slice.

METHODS

Cortical slice was incubated with artificial cerebrospinal fluid (ACSF) in tube. Hypoxia was achieved by substituting 91.6% N2 and 8.4% O2. The salicylate trapping method was used to measure hydroxyl radicals generated. The content of LDH in medium after hypoxia was measured by International Federation of Clinic Chemistry (IFCC) method.

RESULTS

The contents of dihydroxybenzoic acid (DHBA) were increased significantly during hypoxia and reoxygenation in cortical slice. The production of DHBA in reoxygenation was decreased concentration-dependently by melatonin, but not during hypoxia 30 min. The release of LDH during hypoxia was steadily elevated and melatonin decreased the content of LDH after hypoxia.

CONCLUSION

Melatonin decreased the injury and production of .OH after hypoxia.

[Effect of noise on human mental performance]

OBJECTIVE

To investigate the effect of moderate noise on human thinking performance.

METHODS

During 2 h of exposure to 85, 90 dB(A), successive calculation, successive subtraction and determining figures according symbol were performed in 24 healthy young male subjects.

RESULTS

After l h exposure to noise of 85 dB(A), there were no significant changes in the accurate rate, correct number and total number of successive calculation, but the correct number and total number of successive subtraction decreased significantly as compared with control (P< 0.05). At 30 and 120 min exposure to noise of 90 dB(A), the mean reaction time prolonged, performance of reaction time decrease significantly (P<0.01) in the test of determining figures according symbol as compared with control; its total performance had a tendency of decrease, but was not significant. When the subjects were divided into two group according to their E score of EPQ, significantly different performance of accurate rate and different total performance were demonstrated in the test of determining figures according to symbol at 2 h of exposure under 90 dB(A) noise. The performance of extrovert was higher than that of introvert.

CONCLUSION

Moderate noise could affect performance of complex tasks with a higher workload and it had certain relationship with the personality of the subjects.

Association of HAP1 isoforms with a unique cytoplasmic structure

HAP1 is a neural protein and interacts with the Huntington's disease protein huntingtin. There are at least two HAP1 isoforms, HAP1-A and HAP1-B, which have different C-terminal amino acid sequences. Here we report that both HAP1 isoforms associate with a unique cytoplasmic structure in neurons of rat brain. The HAP1-immunoreactive structure appears as an inclusion that is an oval mass of electron-dense material, 0.5-3 microm in diameter, containing many curvilinear or ring-shaped segments, and often containing electron-lucent cores. This structure is very similar to those previously termed the stigmoid body, nematosome, or botrysome. Transfection of cell lines with cDNA encoding HAP1-A, but not HAP1-B, resulted in similar HAP1-immunoreactive inclusions in the cytoplasm, suggesting that HAP1-A is essential to the formation of this structure. Yeast two-hybrid and transfection studies show that both HAP1-A and HAP1-B can self-associate, implying that native HAP1 in the cytoplasmic inclusion may be a heteromultimer of HAP1-A and HAP1-B. Coexpression of HAP1-A and HAP1-B in human embryonic kidney 293 cells demonstrates that the ratio of the expressed HAP1-A to HAP1-B regulates the formation of HAP1-associated inclusions. We propose that HAP1 isoforms are involved in the formation of HAP1-immunoreactive inclusions in the neuronal cytoplasm.

The cellular and subcellular localization of huntingtin-associated protein 1 (HAP1): comparison with huntingtin in rat and human

The cellular and subcellular distribution of HAP1 was examined in rat brain by light and electron microscopic immunocytochemistry and subcellular fractionation. HAP1 localization was also determined in human postmortem tissue from control and Huntington's disease (HD) cases by light microscopic immunocytochemistry. At the cellular level, the heterogeneity of HAP1 expression was similar to that of huntingtin; however, HAP1 immunoreactivity was more widespread. The subcellular distribution of HAP1 was examined using immunogold electron microscopy. Like huntingtin, HAP1 is a cytoplasmic protein that associates with microtubules and many types of membranous organelles, including mitochondria, endoplasmic reticulum, tubulovesicles, endosomal and lysosomal organelles, and synaptic vesicles. A quantitative comparison of the organelle associations of HAP1 and huntingtin showed them to be almost identical. Within HAP1-immunoreactive neurons in rat and human brain, populations of large and small immunoreactive puncta were visible by light microscopy. The large puncta, which were especially evident in the ventral forebrain, were intensely HAP1 immunoreactive. Electron microscopic analysis revealed them to be a type of nucleolus-like body, which has been named a stigmoid body, that may play a role in protein synthesis. The small puncta, less intensely labeled, were primarily mitochondria. These results indicate that the localization of HAP1 and huntingtin is more similar than previously appreciated and provide further evidence that HAP1 and huntingtin have localizations consistent with roles in intracellular transport. Our data also suggest, however, that HAP1 is not present in the abnormal intranuclear and neuritic aggregates containing the N-terminal fragment of mutant huntingtin that are found in HD brains.

Effect of recombinant human bone morphogenetic protein-2 on fracture healing in a goat tibial fracture model

Bone morphogenetic proteins (BMPs) are considered to have important regulatory roles in skeletal embryogenesis and bone healing. Recombinant human BMPs (rhBMPs) have been shown to heal critical size defects and promote spinal fusion. We studied the effects of rhBMP-2 in an absorbable collagen sponge (ACS) on bone healing in a large animal tibial fracture model. Bilateral closed tibial fractures were created in 16 skeletally mature goats and reduced and stabilized using external fixation. In each animal, one tibia received the study device (0.86 mg of rhBMP-2/ACS or buffer/ACS), and the contralateral fracture served as control. The device was implanted as a folded onlay or wrapped circumferentially around the fracture. Six weeks following fracture, the animals were sacrificed and the tibiae harvested for torsional testing and histomorphologic evaluation. Radiographs indicated increased callus at 3 weeks in the rhBMP-2/ACS treated tibiae. At 6 weeks, the rhBMP-2/ACS wrapped fractures had superior radiographic healing scores compared with buffer groups and controls. The rhBMP-2/ACS produced a significant increase in torsional toughness (p = 0.02), and trends of increased torsional strength and stiffness (p = 0.09) compared with fracture controls. The device placed in a wrapped fashion around the fracture produced significantly tougher callus (p = 0.02) compared with the onlay application. Total callus new bone volume was significantly increased (p = 0.02) in the rhBMP-2/ACS fractures compared with buffer groups and controls regardless of the method of device application. The rhBMP-2/ACS did not alter the timing of onset of periosteal/endosteal callus formation compared with controls. Neither the mineral apposition rates nor bone formation rates were affected by rhBMP-2/ACS treatment. The increased callus volume associated with rhBMP-2 treatment produced only moderate increases in strength and stiffness.

A human HAP1 homologue. Cloning, expression, and interaction with huntingtin

Huntington's disease (HD) is caused by the expansion of a glutamine repeat in the protein huntingtin. The expanded glutamine repeat is thought to mediate a gain of function by causing huntingtin to abnormally interact with other proteins. We previously identified a rat huntingtin-associated protein (HAP1) that binds to huntingtin; HAP1 binds more tightly to huntingtin with an expanded glutamine repeat than to wild type huntingtin. Identification of the human homologue of HAP1 is necessary for investigation of the potential role of HAP1 in HD pathology. Here, we report the cloning of a human HAP1 homologue (hHAP) that shares 62% identity with rat HAP1 over its entire sequence and 82% amino acid identity in the putative huntingtin-binding region. The hHAP gene encodes a 4.1-kilobase transcript and a 75-kDa protein which are specifically expressed in human brain tissues. Its expression in Huntington's disease brains is reduced in parallel with a decreased expression of huntingtin. While two isoforms of rat HAP1 are expressed at similar levels in rat brain, only a single major form of hHAP is found in primate brains. In vitro binding, immunoprecipitation, and coexpression studies confirm the interaction of hHAP with huntingtin. The in vitro binding of hHAP to huntingtin is enhanced by lengthening the glutamine repeat. Despite similar binding properties of rat HAP1 and hHAP, differences in the sequences and expression of hHAP may contribute to a specific role for its interaction with huntingtin in humans.

Aggregation of N-terminal huntingtin is dependent on the length of its glutamine repeats

Huntington's disease (HD) is caused by expansion of a glutamine repeat in huntingtin. Mutant huntingtin contains 36-55 repeats in adult HD patients and >60 repeats in juvenile HD patients. An N-terminal fragment of mutant huntingtin forms aggregates in neuronal nuclei in the brains of transgenic mice and HD patients. Aggregation of expanded polyglutamine is thought to be a common pathological mechanism in HD and other glutamine repeat diseases. It is not clear how the length of the repeats is correlated with formation of protein aggregates. By expressing a series of huntingtin constructs encoding various glutamine repeats (23-150 units) in cultured cells we observed N-terminal fragments of huntingtin (amino acids 1-67 and 1-212), but not full-length huntingtins, with glutamine repeats >/=66 units formed protein aggregates. Huntingtin aggregation was not induced when the repeat was </=49 units and was markedly promoted by very long repeats >/=120 units. This study suggests that various N-terminal fragments of mutant huntingtin can form aggregates and that aggregation is prompted by lengthening the glutamine repeat.

Interaction of huntingtin-associated protein with dynactin P150Glued

Huntingtin is the protein product of the gene for Huntington's disease (HD) and carries a polyglutamine repeat that is expanded in HD (>36 units). Huntingtin-associated protein (HAP1) is a neuronal protein and binds to huntingtin in association with the polyglutamine repeat. Like huntingtin, HAP1 has been found to be a cytoplasmic protein associated with membranous organelles, suggesting the existence of a protein complex including HAP1, huntingtin, and other proteins. Using the yeast two-hybrid system, we found that HAP1 also binds to dynactin P150(Glued) (P150), an accessory protein for cytoplasmic dynein that participates in microtubule-dependent retrograde transport of membranous organelles. An in vitro binding assay showed that both huntingtin and P150 selectively bound to a glutathione transferase (GST)-HAP1 fusion protein. An immunoprecipitation assay demonstrated that P150 and huntingtin coprecipitated with HAP1 from rat brain cytosol. Western blot analysis revealed that HAP1 was enriched in rat brain microtubules and comigrated with P150 and huntingtin in sucrose gradients. Immunofluorescence showed that transfected HAP1 colocalized with P150 and huntingtin in human embryonic kidney (HEK) 293 cells. We propose that HAP1, P150, and huntingtin are present in a protein complex that may participate in dynein-dynactin-associated intracellular transport.

Intermittent on/off prostaglandin E2 and risedronate are equally anabolic as daily PGE2 alone treatment in cortical bone of ovariectomized rats

In this study, we evaluated the rat cortical bone changes after a two-cycle, 60-day each (ON/OFF/ON/OFF) treatment with either prostaglandin E2 (OVX/c-PGE2) alone or in combination with risedronate (OVX/c-PGE2+Ris), in comparison with daily treatment with PGE2 for 240 days (OVX/PGE2-240d) in ovariectomized (OVX) rats. At the end of the study, we found that: (1) the overall effectiveness of the treatment on bone mass in the tibial shaft indicates the following ranking: OVX/PGE2-240d = OVX/c-PGE2+Ris > OVX/c-PGE2 > OVX/c-Ris > or = OVX = aging; (2) the same bone mass and architecture were produced in the OVX/PGE2-240d and the OVX/c-PGE2+Ris groups, but the histomorphometric profiles differed in that the former exhibited a higher bone turnover and index of resorption; (3) OVX/c-PGE2+Ris treatment prevented endocortical bone loss and minimized trabecular bone loss during the OFF periods; and (4) the OVX/c-PGE2 alone treatment resulted in the accumulation of less total bone than OVX/PGE2-240d and OVX/c-PGE2+Ris because it could not maintain most of the new subendocortical and marrow trabecular bone generated earlier. In summary, both continuous daily PGE2 and two cycles ON/OFF combined PGE2 and Ris treatments result in more bone mass than two cycles ON/OFF PGE2 alone and Ris alone in estrogen-deficient rats. This study showed that the anabolic effects of PGE2 can be induced and maintained either by continuous administration or by cyclical PGE2+Ris.

Relationship of natural incidence and radiosensitivity for bone cancer in dogs

A comparison of the risk coefficients for 239Pu- or 226Ra-induced bone cancer in two canine breeds, one with a relatively low (beagle) and the other with a very high (St. Bernard) natural incidence, indicated only slightly higher risk in the giant breed. The differences in risk for skeletal malignancy in 239Pu and 226Ra dogs were nonsignificant (p > 0.05). Likewise, the values of the 239Pu:226Ra "toxicity ratios" for these respective breeds, using bone cancer as the endpoint, were not significantly different at the 0.05 level. The anatomical distribution of the radiation-induced bone tumors tended to be a function of both the bone mass and the skeletal distribution of the radionuclide, not the site of predilection for naturally occurring bone neoplasia. Although the etiology of the higher natural incidence of bone cancer in the St. Bernard was not determined, several possible factors, including a higher osteoblastic activity level in the St. Bernards, are presented. These data suggest that making extrapolations of radiation-induced bone cancer risk from animals to humans is valid.

Melatonin decreases production of hydroxyl radical during cerebral ischemia-reperfusion

AIM

To study the effect of melatonin on hydroxyl radical (.OH) contents during cerebral ischemia-reperfusion in rats.

METHODS

Ischemia was induced by occluding left lateral middle cerebral artery for 30 min following reperfusion. The salicylate trapping method coupled with ipsilateral striatal microdialysis for measurement of hydroxyl radicals generated during ischemia and reperfusion.

RESULTS

The contents of dihydroxybenzoic acid (DHBA) were increased at 15 min after ischemia and remained high for 30 min after reperfusion. Melatonin (4 mg.kg-1, sc, 30 min before ischemia) decreased the production of DHBA during ischemia for 16-30 min and reperfusion for 1-30 min.

CONCLUSION

Melatonin inhibits the production of hydroxyl radicals in rat brain during ischemia and reperfusion.