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up study to examine the long-term effects in terms of othercrucial time-related indicators such as education placementfactors. The study shaws the importance of a child's earlyenvironment and preschool experience. Some of ourchildren in Singapore are more vulnerable to being at riskof failure sooner or more easily than their peers when theyjoin PI, for example children who come from non-Englishspeaking backgrounds or low SES. These at-risk groupsrequire more nurturing and stimulating environments in theearly years to develop optimally. To this end, the findingsseem to indicate that there is a need to judge the study onthe basis of its success in narrowingthe gap among chiIdrenof different backgrounds. The research study providesevidence that pupils from the low SES and non-Englishspeaking pupils in the experimental groups have better gainsfor Phase 1 of the research study. From this perspective, theinterventions of the new curriculum delivered by trainedteachers have made an impact on the preschool pupils.Team Members: Carolyn Tan-Niam and MOE officers fromPsychological Assessment & Research Branch, and Researchand Evaluation Services.This was an MOE PSE project, in collaboration with NIE.Howdoes the Snakehead, Channa Asisfica,Survive During Aerial Exposure?IntroductionSome teleostean fish actively lead an amphibious life (e.g.mudskippers) while others occasionally get trapped inpuddles of water (e.g. marble goby) or in the intertidal zonein their natural habitats. Without the buoyancy of water,gills would collapse and lamellaewould coalesce, Branchialammonia excretion would be inefficient when no externalwater current is available to irrigate the gills during aerialexposure. Consequently, endogenously produd ammoniawouldaccumulate and thesefish must deal withtheproblemof ammonia intoxication in the absence of water.Three different major nitrogenous products are found toaccumulatein the tissues of some tropical teleostean fishesduring aerial exposure. These are alanine, glutamine andurea. The weather loach and the mangrove killifishaccumulateboth alanineandglutamine, although to a lowerextent than the mudskipper and the sleeper, respectively,when expod to terrestrialconditions. These two fish havethe unique capability of excreting ammonia throughvolatilizing NH, during aerial exposure.Urea productiondoes not appear to be a common strategyadoptedby teleosts to detoxify endogenous ammonia duringaerial exposure, probably because it is energy expensive.GIutamine formation is also energy dependentand appearsto be adopted mainly by fishes that remain completelyquiescent on land. On the contrary, alanine formationthrough partial amino acid catabolism would lead to theproduction of ATP without releasing ammonia. Hence, itcannot be regarded as an ammonia-detoxifyingmechanism,but rather a way to use certainamino acidsas energy sourceswithout leading to ammonia accumulation in the body.Channa ajafica andother snakeheadsare valuedfreshwaterfood fish in Southern China and Far East Asia. Theycommand very high prices of between S$10 and S$20 perkilogramwhen fresh. There, peoplebelievetheconsumptionof this fish aids the recovery of injuries (especially for postsurgicalpatients). Channa asiatica is apredaceousfish thatresides in slow-flowing streams and in crevices nearriverbanks. In its natural habitat, it may encounterbouts ofaerial exposure during the dry seasons. While "walking"fish Ii ke Anabas sp. and Clariag sp. have been frequentlyreported upon, "walkingsnakeheads" are less we1 l known.However snakeheads can move a considerabledistance onall kinds of surfacesby squirmingand skipping. However,unIike mudskippers, C. asiatica is incapable of using itspectoral fins to move actively on land, and does not exhibitany feeding, territorialor courtship behaviour while out ofthe water. When trapped in puddles of water, it would tryto struggleback to water through eel-likebody movements,which may last several minutes. After strugglingfor a whilewithout any luck of getting back to water, it would turnmotionless and remainquiescent, with only occasional eellikemovements, for an extended period.From these information, we hypothesized that asiaticawas capable of undergoing partial amino acid catabolismleading to the formation of alanine to reduce the rate ofammonia accumulation in its tissues during aerial exposure.Objective and researchThis study was undertakento investigate the effects of aerialexposure on the snakehead Channa asiatica, which is anobligatory air-breather.Experiments were thus performed to study the effects ofaerial exposure on (1)the concentration of free amino acids(FAAs) in the muscle, Iiver and blood plasma, (2) theammonia and urea excreted by, and accumulated in thevarious tissues, (3) the activities of alanine aminotransferase(ALT), glutam ine synthetase and gl utamate dehydrogenase(CDH) and (4) the activities of the ornithine-urea cycleenzymes.Results and discussionResults obtained showed that aerial exposure significantlydecreased the rates of ammonia excretion by C. asiatica.Upon re-submergence, the rates returned to the initialC.
control values. Similar observations were made on the rates 12.6 pmol g-', in the muscle of C. asiatica after 48 h ofof urea excretionaerial exposure.There were significant increases in concentrations ofammonia in the muscle, liver and plasma after exposure toterrestrial conditions for 48 h. The urea level increasedslightiy after 12 h of aerial exposure and returned to normalvalue thereafter. Aerial exposure had no effect on the ureacontent in the liver. There was a significant increase in theurea concentration in the plasma of specimens exposed to24 or 48 h of terrestrial conditions, but the change wasminor compared to that for ammonia.No significant changes in the activities of the arnithine ureacycle enzymes were detected after aerial exposure. Thealanine level (3.7 pmol g-') in the muscle rose to 6.4 and12.6 pmol g-' after 24 h and 48 h of exposure to terrestrialconditions, respectively. There were significant changes tosome of the FAAs in the liver of specimens exposed toterrestrial conditions for 48 h. Aerial exposure induced onlyminor changes to some of the amino acids in the plasma ofC. asiatica.The accumulated alanine accounted for 70% of the deficitin ammonia excretion during that period. This would allowthe utilization of certain amino acids as energy sources and,at the same time, minimize ammonia accumulation.However, different from the mudskippers, the reduction innitrogenous excretion during 48 h of aerial exposure wascornpletety balanced by nitrogenous accumulation in thetissues. Hence, it is unlikely that the rates of proteolysisand amino acid cataho[ism were reduced during aerialexposure, as in the case of mudskippers. This implies thatC. asiaticacannot measure up to the mudskippers' capabilityof surviving on land.For details of this report please refer to: Chew, S F, IM YWong, Tam W L andY K Ip, The Snakehead Channa asjatjcnaccumulates alanine during aerial exposure, but is incapableof sustaining locomotory activities on land through partialamino acid catabolism. Journal of Experimental Biology,United Kingdom, 2003. 206 (5): 693-704.Activitiesof ALT in the cvtosolic and mitochondria1 fractions This sfudv was ~u~~orted bvthe Academic Research Fund.of the muscle and liver were unaffected by aerial exposure.However, there were significant decreases in the aminatingactivity of GDH from the muscle and liver of specimensexposed to terrestrial conditions, leading to significantdecreases in the aminati0n:deamination ratio. Malic enzymeis also present in the muscle of C. asiatica.From the results obtained, the first strategy adopted by thisfish to survive aerial exposure is to tolerate the build up ofammonia level in its body. However, in order to preventammonia from building up to an intolerable level, otherstrategies must be subsequently involved to maintain thenew steady state level of internal ammonia. It has beensuggested that fishes, like the mudskipper P. schlosseri,which are active on land with impeded excretion ofammonia would partially catabolize certain amino acids toalanine. This would allow amino acids to be used as anenergy source without pol luting the internal environment.Partial amino acid catabolism coupled with a reduction inamino acid catabolism in general constitutes the most costeffectiveway to minimize endogenous ammonia build-up.Alanine may be more suitable for accumulation because ithas less effects on kinetics of many enzymes than otheramino acids. Indeed, alanine increased 4-fold from 3.7 toSummary of the strategy utilised by C. asiafica during aeriaIexposureIFumarateAmination~b ~luirnatea-Ketog/utaratc+ NH,- + NADHDeamination'Jta-Ketoglutarate 4-Certain amino acidsDL~W...,~*-IIa-l(etoglutarate,no releaseofColorectal Diseased TissuesDetectionUsing LaserInduced Autofluorescence SpectroscopyIChia Teck Chee IColorectal cancer is currently the second leading cause of pathological stages of the disease during diagnosis.cancer mortality in Singapore after lung cancer for males However, most deaths can be prevented by eariydetection.and afterbreast cancer for females.The possibilityof survival Thus, further research and developmenton novel strategiesfrom colorectal cancer is closely related to the clinical and for early, noninvasiveor micro-invasivedetection can greatly
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