以口腔黏膜刺激试验检测碳化硅种植材料的生物安全性★

目的：寻找一种陶瓷材料替代金属材料成为种植体核心材料。以口腔黏膜刺激试验作为二级试验，观察碳化硅种植材料的生物安全性。 方法：实验于2007-03/06在沈阳药科大学药理实验室完成。选择雄性家兔25只，双侧颊黏膜无病变。将碳化硅种植材料制成直径为5 mm，厚度为1 mm圆片，阴性对照为牙胶材料，阳性对照为工业用聚氯乙烯。用医用无创伤缝合线将试件固定于家兔口腔双侧颊黏膜上，一侧为阳性对照物，另一侧为碳化硅试件和阴性对照物。术后2周观察动物有无全身不良反应，另外每日观察圆片接触局部的黏膜反应，有无色泽异常、充血、糜烂、渗出等异常现象。2周后麻醉后处死动物，取与试件直接接触部位颊黏膜全层组织，行苏木精-伊红染色观察其组织学改变。 结果：纳入动物25只，均进入结果分析。①大体观察：碳化硅试样圆片固定良好，局部黏膜表面完整清晰，无异常反应如充血、出血、糜烂、溃疡等，与阴性对照无明显差异；阳性对照工业用聚氯乙烯圆片与家兔的颊黏膜表面出现了一定程度的充血、水肿。②组织学观察：碳化硅试件组和阴性对照组的黏膜被覆复层鳞状上皮，表面角化，未见上皮钉突伸长、黏膜表面过度角化、棘层增生等异常变化，基底膜完整，下方毛囊丰富，固有层纤维细胞组织致密，未见炎细胞，黏膜下层肌肉丰富。阳性对照组被覆复层鳞状上皮，紧接基底膜区可见炎细胞散在浸润，肌纤维旁、腺体内均可见炎细胞散在浸润，中性粒细胞为主、少量嗜酸细胞浆细胞，腺胞萎缩消失，导管增生扩张，局部中性粒细胞灶性浸润，血管内可见中性粒细胞，毛囊周围有中性粒细胞包绕浸润。 结论：碳化硅种植材料对实验动物颊黏膜无不良刺激反应。     

组织工程化口腔黏膜构建的研究现状

背景：口腔黏膜组织工程期待能解决自体黏膜修复组织来源不足的难题。 目的：综述组织工程化口腔黏膜的种子细胞的来源及选择、各种常见支架材料的优缺点及相关生长因子的研究进展。 方法：由第一作者以“tissue engineering of oral mucosa, seed cells, scaffold material, growth factor”为检索词,检索PubMed数据库及Elsevier数据库2000-01/2011-12有关文章。 结果与结论：几种常见的口腔黏膜组织工程种子细胞在研究中都有较好的增殖或分化能力,脂肪干细胞与其他种子细胞相比具有更明显的优势,可作为一种较理想的种子细胞;各种常见的支架材料都有各自的优缺点,可以采用多种方式改善其性能;将一些关键的细胞因子运用到口腔黏膜组织工程中,能促进移植物血管化,加快伤口愈合过程。口腔黏膜组织工程将是在临床上能解决异体移植免疫排斥及传播疾病和自体黏膜修复组织来源不足等问题一种安全有效的修复方法。     

脱细胞膀胱黏膜下层支架材料的生物学评价

背景：脱细胞膀胱黏膜下层是一种天然的细胞外基质生物材料,主要由Ⅰ、Ⅲ型纤维胶原蛋白构成,是一种理想的生物支架材料。 目的：脱细胞猪膀胱组织作为组织工程支架材料的生物学评价。 方法：取适量健康猪膀胱置于PBS 和叠氮钠的混合溶液,浸泡过夜,刮去膀胱黏膜层。用低渗、-80 ℃反复冻融、DNase和RNase混合液消化和NaOH裂解连续方法制备脱细胞膀胱黏膜下层。通过观察其组织学结构特征、DNA残留、细胞毒性、细胞黏附效果及皮下炎症反应等来综合评价脱细胞膀胱黏膜下层的生物相容性。 结果与结论：正常猪的膀胱经改进的脱细胞方法处理后,绝大部分细胞组分被去处,细胞外基质结构保持完好。细胞毒性试验结果显示脱细胞膀胱黏膜下层细胞毒性为1级,DNA提取结果中未见有DNA残留,细胞黏附结果显示猪平滑肌细胞能在脱细胞支架上较好的贴附生长,SD大鼠皮下植入试验显示无明显的炎症反应。结果证实所制备的脱细胞膀胱黏膜下层结构保存完好,有良好的组织相容性,可能成为组织工程修复的替代材料。 关键词：脱细胞膀胱黏膜下层;生物相容性;组织工程膀胱;猪;细胞毒性;DNA残留 doi:10.3969/j.issn.1673-8225.2010.08.009     

口腔钛合金种植体的临床应用

背景：钛合金质量较轻、密度低,具有抗电化学腐蚀、良好的生物相容性、低弹性模量和高强度等优异性能,已被广泛应用于口腔医学。 目的：总结近年来口腔生物材料钛合金种植体的临床应用进展。 方法：由作者应用计算机检索1998-01/2010-10维普数据库中与口腔生物材料钛合金种植体有关的文献,检索关键词为“钛合金,种植,生物相容性”。 结果与结论：目前的研究大多数集中于钛合金种植体的生物相容性研究。国内外学者们正在努力寻求更加理想的钛合金种植体表面结构来提高种植体的骨结合能力,此对种植体骨性结合界面形成也极其重要。钛合金种植体的表面处理对提高种植成功率起着重要作用,不同处理方法都有其优点,但共同的特点是形成粗糙表面,使其具有更好的生物活性与骨结合能力。因此寻找一种能兼具各方面优点,更好促进骨结合的表面处理方法,已成为近年来口腔种植学研究的热点。     

咽部冷刺激联合口腔营养管对脑卒中吞咽障碍患者的康复效果观察

目的观察咽部冷刺激联合口腔营养管对脑卒中吞咽障碍患者的康复效果。方法 110例脑卒中吞咽障碍患者随机分为2组,每组55例,2组均采用咽部冷刺激进行康复干预,观察组在此基础上采用口腔营养管间歇置管进食,对照组使用常规鼻胃管留置补充营养。治疗前及治疗14d后对吞咽功能进行评估。结果治疗2周后观察组洼田饮水试验评分明显低于对照组,差异有统计学意义(P0.05);观察组总有效率明显高于对照组,差异有统计学意义(P0.05)。结论咽部冷刺激联合口腔营养管能明显改善脑卒中后吞咽障碍患者的吞咽功能,提高康复效果,缩短住院周期,显著降低误吸性肺炎等并发症的发生率,值得临床推广应用。     

壳多糖-胶原凝胶构建组织工程口腔黏膜固有层

背景：有研究探讨了以胶原/壳聚糖聚合物为支架材料构建组织工程人工皮肤的可行性。 目的：拟探讨以壳多糖-胶原凝胶支架材料与口腔黏膜成纤维细胞在体外构建人工固有层的可行性。 方法：口腔黏膜成纤维细胞取自成年鼠颊部、牙龈或腭部。以2×DMEM培养液、胎牛血清、胶原溶液、壳多糖等或2×DMEM培养液、胎牛血清、胶原溶液等按一定比例配置成凝胶溶液,将大鼠口腔黏膜成纤维细胞与上述凝胶溶液迅速混合制成口腔黏膜人工固有层,动态观察细胞生长状况和凝胶收缩情况。 结果与结论：胶原-口腔黏膜成纤维细胞复合物、壳多糖-胶原-口腔黏膜成纤维细胞复合物体外培养1 d,口腔黏膜成纤维细胞在支架材料中生长良好,细胞呈长梭形,排列无一定方向。随时间推移,口腔黏膜成纤维细胞逐渐增多,凝胶颜色变浅,厚度变薄,分别于2,3 d后发生收缩。结果证实,口腔黏膜成纤维细胞可在壳多糖-胶原凝胶形成的三维空间结构生长并分泌基质,形成类似黏膜固有层的致密结缔组织。壳多糖-胶原凝胶是构建组织工程化口腔黏膜固有层的合适材料。 关键词：口腔黏膜成纤维细胞;胶原;凝胶;壳多糖;组织工程 doi:10.3969/j.issn.1673-8225.2010.25.016     

小肠黏膜下层包绕丝素纤维复合韧带的生物力学测定

背景：基于仿生化思想,综合丝素蛋白纤维和小肠黏膜下层的优点,利用小肠黏膜下层分层包绕丝素蛋白纤维,拟构建良好生物活性和力学性能的复合韧带。 目的：检测小肠黏膜下层包绕丝素纤维复合韧带的生物力学特性。 设计、时间及地点：对比观察实验,于2008-03/06在华中科技大学附属协和医院骨科实验室完成。 材料：小肠取自封闭饲养的经过检疫的健康猪;蚕丝由湖北省德中茧丝有限公司惠赠。 方法：用裹有纱布的刀柄去除小肠的浆膜层和肌层,制备符合要求的小肠黏膜下层。分层包绕脱胶后的蚕丝丝素纤维。直径分别为4,5,6,7,8,9 mm,长度为15 cm。将复合韧带置于AGS-H多功能材料实验机的夹具中,固定后以10 mm/min的速度行拉断试验。 主要观察指标：检测复合韧带的最大载荷,刚度和最大拉伸长度力学指标。 结果：力学性能检测结果：复合韧带(以直径为7 mm为例)的最大载荷,刚度和最大拉伸长度分别达到(2 258±241) N, (309±16) N/mm和(43.0±1.5)%;而正常前交叉韧带的最大载荷,刚度和最大拉伸长度分别为2 195 N,306 N/mm和33%。复合韧带和正常前交叉韧带的力学性质差异无显著性意义(P > 0.05)。 结论：复合韧带力学性能优秀,满足韧带组织工程支架材料力学要求。     

氧化锆陶瓷材料的生物相容性

摘要 背景：已有大量研究表明,氧化锆陶瓷具有优良的生物学性能,但作为牙种植基台的研究在国内还鲜见报道,将其应用于种植牙基台上的生物学性能还需要进一步的验证。 目的：评价牙种植基台制作材料氧化锆陶瓷的生物相容性。 方法：将氧化锆陶瓷圆形试件固定在Wistar大鼠左颊黏膜表面,右侧用牙胶试件作为对照,使两组试件与颊黏膜紧密贴合但无压迫,术后2周应用大体观察和组织学方法观察口腔黏膜与氧化锆陶瓷材料的生物学反应;将氧化锆陶瓷棒形试件植入Wistar大鼠背部皮下组织内,于植入后1,2,4,8周应用大体观察和组织学方法动态观察皮肤组织与氧化锆陶瓷材料的生物学反应。 结果与结论：氧化锆陶瓷圆形试件固定后,大鼠颊黏膜局部组织未见异常,与对照组比较差异无显著性意义;氧化锆陶瓷棒形试件植入第1周可见局部组织轻微红肿,组织切片可见少量炎性细胞,2~8周红肿消退,组织切片见纤维包膜形成并逐渐变薄,到8周时包膜形成致密纤维,未见炎性细胞。提示氧化锆陶瓷材料与口腔黏膜、皮肤及皮下组织具有良好的生物相容性。 关键词：氧化锆陶瓷;口腔黏膜;皮肤组织;皮下组织;生物相容性;口腔生物材料 doi:10.3969/j.issn.1673-8225.2011.12.016     

国内期刊关于口腔材料研究成果文章发表的相关数据介绍

国内期刊关于口腔材料研究成果文章发表的相关数据介绍     

神经肌肉电刺激联合口腔感觉训练对重症病毒性脑炎合并吞咽障碍患儿的康复效果

目的 探讨神经肌肉电刺激（NMES）联合口腔感觉训练对重症病毒性脑炎（SVE）合并吞咽障碍患儿的康复效果、吞咽功能、神经功能、营养状况的影响。方法 选择河北省儿童医院2021-01—2023-03收治的SVE合并吞咽障碍患儿108例。随机数字表法分为口腔感觉训练组和NMES联合组各54例。2组患者均进行抗病毒、降颅内压、去高热、控制惊厥、保护脑神经等对症支持治疗。口腔感觉训练组给予口腔感觉运动训练,NMES联合组在口腔感觉训练基础上进行NMES康复治疗。比较2组患者康复效果、吞咽功能[吞咽障碍调查量表（DDS）]、神经功能指标[血清脑源性的神经营养因子（BDNF）、神经元特异性的烯醇化酶（NSE）水平]、营养状况[主观的综合性营养评分量表（SGA）]、生活质量[吞咽障碍特异性生存质量量表（SWAL-QOL）]。结果 康复治疗4周后,NMES联合组康复总有效率为92.59%,高于口腔感觉训练组的72.22%(P<0.05);NMES联合组口腔期、咽期、食管期DDS评分、SGA评分、SWAL-QOL评分、血清BDNF水平明显高于口腔感觉训练组,血清NSE水平低于口腔感觉训练组（P&l...     

不同增稠载体过氧化脲漂白凝胶对口腔黏膜的刺激性☆

背景：牙齿漂白剂影响的部位主要是口腔黏膜及牙体硬组织，课题组前期已进行细胞毒性试验和短期全身毒性试验，参照国家标准YY/T0279-1995中规定的口腔黏膜刺激试验作进一步生物安全性评价。 目的：评价以Carbopol或PVP为增稠载体配制的10%过氧化脲漂白凝胶对口腔黏膜的刺激性，并与同类商品Opalescence漂白剂进行比较。 设计、时间及地点：材料学体外对照观察，于2005-10在解放军第四军医大学口腔医学院材料教研室完成。 材料：60~70 d龄的雄性金色仓鼠30只，颊囊无病变，由兰州生物制品研究所提供。以Carbopol或PVP为增稠载体的10%过氧化脲漂白凝胶由解放军第四军医大学口腔医学院材料教研室配制，进口漂白剂Opalescence为美国Ultradent公司产品。 方法：将直径5 mm的棉片分别浸透3种受试材料：以Carbopol为增稠载体配制的10%过氧化脲漂白凝胶、以PVP为增稠载体配制的10%过氧化脲漂白凝胶、以进口漂白剂Opalescence配制的10%过氧化脲漂白凝胶，每种受试材料取10只大鼠。同时选用新调和的熟石膏作为对照材料。用无创缝线将3种受试材料浸透的棉片随机固定于一侧颊黏膜极低处，将对照材料熟石膏固定于另一侧颊黏膜极低处，24 h后处死。 主要观察指标：大体观察结果，组织学评价。 结果：各组试样均固定良好。与对照组相比，试验组黏膜粗糙，局部轻微充血、肿胀，未见糜烂渗出及溃疡反应，反应程度为轻度。对照材料不具有口腔黏膜刺激性，而3种受试材料均具有口腔黏膜刺激性，组间比较无明显差异。与受试材料接触的颊黏膜上皮完整，角化层增厚；局部上皮细胞轻度增生，黏膜下结缔组织中有少量血管扩张、充血，少量炎性细胞浸润；细胞各层排列整齐，局部出现空泡变性。 结论：以Carbopol或PVP为增稠载体的10%过氧化脲漂白凝胶具有口腔黏膜刺激性，但与临床常用的Opalescence 10%漂白凝胶的刺激性无明显差别，并不会导致组织长期永久性改变。 关键词：口腔黏膜刺激试验；增稠载体；过氧化脲；漂白     

Peripheral gustatory processing of sweet stimuli by golden hamsters

Behaviors and taste-nerve responses to bitter stimuli are linked to compounds that bind T2 receptors expressed in one subset of taste-bud receptor cells (TRCs); and behavioral and neural responses to sweet stimuli are linked to chemical compounds that bind a T1 receptor expressed in a different TRC subset. Neural and behavioral responses to bitter-sweet mixtures, however, complicate the ostensible bitter and sweet labeled lines. In the golden hamster, Mesocricetus auratus, quinine hydrochloride, the bitter prototype, suppresses chorda tympani (CT) nerve responses to the sweet prototype: sucrose. This bitter-sweet inhibition was tested with concentration series of sucrose and dulcin, a hydrophobic synthetic sweetener that hamsters behaviorally cross-generalize with sucrose. Dulcin, sucrose and other sweeteners activate one subset of CT fibers: S neurons; whereas, quinine activates a separate subset of CT fibers: E neurons. Whole-nerve and S-neuron CT responses to a sweetener concentration series, mixed with 0, 1, 3 and 10 mM quinine, were measured for 0-2.5 s transient and/or 2.6-10 s steady-state response periods. Ten-sec total single-fiber records, aligned at response onset, were averaged for 100 ms bins to identify response oscillations. Quinine inhibition of dulcin and sucrose responses was identical. Each log molar increment in quinine resulted in equivalent declines in response to either sweetener. Furthermore, sucrose response decrements paralleled response increments in quinine-sensitive CT neurons to the same quinine increases. A 1.43 Hz bursting rhythm to the sweeteners was unchanged by quinine inhibition or decreases in sweetener concentration. Taste-bud processing, possibly between-cell inhibition and within-cell negative feedback, must modify signals initiated by T1 receptors before they are transmitted to the brain.     

Behavioural and neuroendocrine adaptations to repeated stress during puberty in male golden hamsters

In adult animals, the consequences of stress are often severe and long lasting. Repeated subjugation in adult male golden hamsters inhibits aggression and increases submissive and avoidant behaviours. By contrast, subjugation during puberty enhances offensive aggression. The goals of this study were to characterize behavioural and neuroendocrine responses of naïve and repeatedly subjugated juveniles to social defeat and to assess potential recovery from social stress. From the onset of puberty on postnatal day 28 (P28) to mid puberty (P42), animals were either socially subjugated or placed in a clean and empty cage for 20 min daily. The subjugated and control groups were further divided into subgroups and sacrificed under basal conditions or after social defeat on P28, P35 (early puberty), P45 (mid puberty) and P70 (early adulthood). On P35 and P45, repeatedly subjugated juveniles showed a complete inhibition of olfactory investigation (i.e. risk assessment) towards aggressive adults. Repeatedly subjugated also animals had lower postdefeat cortisol levels than controls on P45. Interestingly, basal cortisol levels increased gradually during puberty but did not differ between treatment groups at any point. Repeated subjugation was also associated with increased tyrosine hydroxylase immunoreactivity (ir‐TH) within the extended medial amygdala. After a 4‐week recovery period, none of these variables differed between subjugated and control groups. In an additional experiment, subjugated adults also had increased ir‐TH in the medial extended amygdala, suggesting that these neurones are particularly responsive to social stress. In conclusion, puberty may be a developmental period characterized by behavioural and neuroendocrine plasticity in stress responsiveness. Furthermore, peri‐pubertal changes in stress hormones may explain why juvenile hamsters are more resilient to social stress than adults.     

Neural connections of the anterior hypothalamus and agonistic behavior in golden hamsters

In male golden hamsters, offensive aggression is regulated by an interaction between arginine-vasopressin and serotonin at the level of the anterior hypothalamus. The present studies were conducted to study a neural network underlying this interaction. The connections of the anterior hypothalamus were examined by retrograde and anterograde tracing in adult male hamsters. Several limbic areas were found to contain both types of tracing suggesting reciprocal connections with the anterior hypothalamus. Their functional significance relating to the consummation of aggression was tested by comparing neuronal activity (examined through quantification of c-Fos-immunolabeling) in two groups of animals. Experimental animals were sacrificed after attacking an intruder. Control animals were sacrificed after exposure to a woodblock carrying the odor of an intruder that elicited behaviors related to offensive aggression without its consummation. An increased density of Fos-immunoreactivity was found in experimental animals within the medial amygdaloid nucleus, ventrolateral hypothalamus, bed nucleus of the stria terminalis and dorsolateral part of the midbrain central gray. These data suggest that these areas are integrated in a neural network centered on the anterior hypothalamus and involved in the consummation of offensive aggression. Finally, c-Fos-immunoreactivity was combined with labeling of serotonin and vasopressin neurons to identify sub-populations particularly associated with offensive aggression. Vasopressin neurons in the nucleus circularis and medial division of the supraoptic nucleus showed increased neuronal activity in the fighters, supporting their role in the control of offensive aggression. Copyright (R) 2000 S. Karger AG, Basel     

On the conversion of high molecular weight urokinase to the low molecular weight form by plasmin

The conversion of high molecular weight urokinase (HMW-UK) to low molecular weight urokinase (LMW-UK) by plasmin $\text{in vitro}$ has been studied. The two forms of urokinase were separated by SDS-polyacrylamide gradient gel electrophoresis and active enzyme was extracted from 5 mm gel segments into isotonic saline and analyzed by the fibrin plate method. Electrophoretic separation of the two forms was complete, as indicated by comparison with the migration of purified standards and by the absence of lytic activity in extracts of intervening gel segments. HMW-UK was incubated with plasminogen and fibrinogen for various time intervals, after which enzymatic activity was inhibited with aprotinin and the samples subjected to electrophoresis. Conversion from HMW-UK to LMW-UK was apparent in the first sample at 2.5 minutes and continued for the 10 minute duration of the experiments. Similar experiments starting with LMW-UK showed no change in molecular weight. Incubation of HMW-UK without plasminogen resulted in no conversion to LMW-UK, indicating that plasmin was the active agent and that the reaction was not autocatalytic.     

Glucocorticoids and the development of agonistic behaviour during puberty in male golden hamsters

During puberty, the agonistic behaviour of male golden hamsters undergoes a transition from play fighting to adult aggression. Repeated exposure to social stress early in puberty accelerates this transition. The present study investigated the possible role of glucocorticoids on the maturation of agonistic behaviour. First, we compared serum cortisol levels following a 20-min restraint stress during early puberty, mid-puberty or adulthood. Across puberty, animals exhibited a two-fold increase in post-restraint cortisol levels. We also compared corticotrophin-releasing hormone (CRH) immunoreactive fibres projecting to the median eminence between animals in early puberty and adulthood. The CRH fibre density was two-fold greater in adults compared to juveniles. Furthermore, we investigated the effects of stress hormones on the maturation of agonistic behaviour. Male hamsters were injected daily with dexamethasone, a corticosteroid receptor type II agonist (0, 10 or 40 microg/100 g), early in puberty from postnatal day 31 (P-31) to P-36. When paired with a smaller and younger intruder on P-37, attack frequency did not differ between groups. However, dexamethasone-treated animals showed a dose-dependent decrease in the percentage of play-fighting attacks and an increase in the percentage of adult attacks. In summary, puberty can be described as a period of increasing hypothalamic-pituitary-adrenal activity in male golden hamsters. Moreover, increasing glucocorticoid levels influence the maturation of agonistic behaviour. These data shed new light on the neuroendocrine mechanisms that regulate the maturation of social behaviours during puberty.     

Photoperiodic control of seasonal body weight cycles in hamsters

Syrian (Mesocricetus auratus) and Siberian (Phodopus sungorus sungorus) hamsters exhibit seasonal changes in body weight mainly by altering their carcass lipid stores. These seasonal changes are triggered largely by the photoperiod. Although both species exhibit gonadal regression when exposed to short photoperiods (“winterlike” daylength), they show opposite body weight changes. Syrian hamsters gain weight, but Siberian hamsters lose weight following short photoperiod exposure. Syrian hamsters prepare for overwintering by increasing energy stored as carcass lipid. In contrast, Siberian hamsters decrease their metabolic mass and therefore require lower energy intake for energy maintenance. In Syrian, and perhaps Siberian hamsters the short day-induced weight changes are exaggerated by high fat diets. Both species show photoperiod-induced changes in body weight without changing their food intake, suggesting a metabolic basis for these effects. In Syrian hamsters, the obesity is not secondary to gonadal regression, whereas in Siberian hamsters, the decrease in body weight is independent of the gonads for males but may be dependent upon the gonads in females. The pineal gland and its hormone, melatonin, are important transducers of photoperiodic signals in hamsters. This is certainly true for Siberian hamsters, in which pinealectomy blocks the short day-induced body weight loss. In contrast, pinealectomy has little effect on short day-induced weight gain in Syrian hamsters. Nevertheless, in both species, the body weight and gonadal changes induced by short day exposure are mimicked by systemic administration of melatonin in long day-housed animals. Thus, for these two hamster species, the same hormone, melatonin, produces opposite effects on body weight but does so by affecting the same carcass component. The target sites of action for the effects of melatonin on body weight change, energy metabolism, and reproductive status are not known. However, the suprachiasmatic and paraventricular nuclei of the hypothalamus are potentially important sites of action. The target site(s) and mechanism(s) of action for the pineal/melatonin-independent effect of photoperiod on body weight in Syrian hamsters are also unknown. This photoperiodic response is highly unusual among mammals in that it is not pineal-dependent. Studies of the mechanisms underlying these body weight changes in Syrian and Siberian hamsters may provide fundamental knowledge about how environmental influences affect obesity and they may also provide insight into the various strategies for overwintering shaped by natural selection. Further contributions in both fields of study may be made by comparative studies of Syrian and Siberian hamsters which gain and lose body weight, respectively, and Turkish hamsters which show no changes in body weight when exposed to short days.