2B.Vollmayr,F.A.Henn/Brain Rearch Protocols8(2001)1–7
ible4/86computer with controlling and recording soft-(4)Clean conditioning chambers thoroughly,using ware.waterfirst,wipe dry and clean with70%ethanol thereafter. Operant conditioning chambers:with inside dimensions
of25330321.5cm(small)or48.5330321.5cm(large). 4.3.Test
Thefloor is constructed of steel rods6mm in diameter and
20mm spaced apart.On one side of the chambers is a(1)Twenty-four hours after shock exposure carefully lever of35335mm and a12W white signal light40mm place animals in conditioning chambers with lever and above the lever only on testing days.Walls were initially signal light.Again,avoid prior transport or handling.The constructed of clear Plexiglas to permit obrvation during experimental room is dimly lit.
the experiment.This was later changed to walls of steel(2)Deliver pulsating current with a pha duration of allowing electrification and thus minimizing animals200ms and an intensity of0.8mA.Apply15shocks avoiding current.The front wall in the new and rec-lasting60s each with a
n inter-trial time of24s.Current is ommended boxes is made of Plexiglas with an overlying accompanied by a light clue clo to the lever to facilitate electrified grid to permit obrvation.detection of the lever and discrimination to the inescapable Shock generator:delivering scrambled pulsating shocks shock ssion.Animals can stop a trial by pressing the of0.8mA intensity and choosable pha-duration to the lever.The animals have to relea the lever briefly before gridfloor and the walls.If the generator cannot deliver the they can stop the next trial by a press.
current between any of the rods becau of the animals Again,carefully obrve the rat’s reactions to the position,this is audible by clicking of the relay in the current.If animals em relaxed while they get shock shock generator.arch for the reasons described above.Additionally
exclude standing on the lever or sitting on one rod and
holding on the lever.
4.Detailed procedure(3)The computer records the time to terminate shock
for each animal and each trial.
4.1.Animals
•For failure pattern(FP)failure to terminate shock Male Sprague–Dawley rats weighing200to240g results in a failed trial.
(Janvier,France).Animals were houd in plastic cages•For deficit pattern(DP)failure to terminate shock 38320359cm,four animals per cage in a room main-within thefirst20s results in a failed trial.
tained at a constant temperature of228C and12-h light–•More than10failures are accepted as‘learned help-dark circle(lights on ).Food lessness’(LH),less thanfive failures are considered and water were provided ad libitum.Animals were treated‘not learned helplessness’(NLH).
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in accordance with the European Communities Council
Directive of24November1986,and the procedures were(4)Place animals back to their home cages. approved by Regierungspraesidium Karlsruhe.(5)Clean conditioning chambers thoroughly between
ssions as described above.
4.2.Inescapable shock
(1)Place animals in conditioning chambers without 5.Results
lever or signal light.Avoid transport or handling of
animals prior to shock exposure.Animals are picked up 5.1.Avoiding of current as an artifact
with support of their abdomen and thorax,not by their tail.
The experimental room is dimly lit.During inescapable shock as well as during the test (2)Deliver a40min ssion of0.8mA inescapable procedure many animals avoided current,mostly by sitting shock,consisting of single shocks and inter-shock times on a single rod and leaning against the walls of the testing ranging from5to15s randomized by the computer.Total chamber.Animals sitting like this appeared passive and shock duration is20min.Choo a high pha duration during the test helpless,becau they had no reason to (e.g.,200ms)for pulsations of current.press the bar to terminate the current.Due to necessary Obrve rats carefully during shock exposure.If they long current exposure in the learned helplessness em not to experience stress exclude short circuits by paradigm,animals learned to avoid during shock exposure. fecal boluss or urine bridges between rods,high input In experiment1avoidance was detected for thefirst time. resistance of animals due to fur,or failure to apply current During shock exposure and test ssion animals avoiding becau the animal touches only surfaces of the same shock were gently pushed to a position where they again
potential(e Troubleshooting for details).received current.Twenty rats with shock exposure were (3)Mark animals and place them back in their home compared to20rats without shock exposure.Rats without cages.shock exposure avoided the shock during the test on
B.Vollmayr,F.A.Henn/Brain Rearch Protocols8(2001)1–73 average1.05times(n520),after inescapable shock the helpless animals with a constant fraction of learned rats avoided significantly more,on average 6.35times helpless animals after inescapable shock at the same (n520),Mann–Whitney U-test:P,0.001.parameters and examined the influence of chamber size In the small chambers all animals learned rapidly to and pha duration of the current pulsations on the validity terminate shock by bar press,there were almost no helpless of the test results.Table1shows that in small boxes there animals even after inescapable shock(Fig.1A).Fig.1B are a considerable fraction of spontaneously helpless rats shows an estimation of the test result if tho animals and shock exposure does not induce additional helpless-avoiding shock had not been detected.Animals avoiding ness.This is due to spontaneous,not goal directed contact shock would have remained in their position for at least with the bar.A longer pha duration of current pulsations one trial and thus would not have presd the bar.had the advantage of more helpless rats,but there was no Therefore,for Fig.1B a failure was counted for each trial specific induction of helplessness by shock
exposure. during which the animal avoided the shock without Testing in large boxes with long pha durations yielded pressing the bar.This resulted in clear paration of the no spontaneously helpless rats and,after inescapable shock two groups,inescapable shock now emed to induce more a significant and specific induction of learned helplessness helpless behavior,a fally positive result becau it truly(one-sided Mann–Whitney:0.016,one-sided Chi-square: only induced avoidance.Current avoiding behavior there-0.004).Therefore large boxes and a long pha duration of fore has to be minimized,for example by electrified walls,current pulsations were chon as the best parameters. for improvement of validity.
5.3.Analysis according to failure pattern or deficit
5.2.Influence of chamber size and pha duration of pattern:influence on nsitivity and specificity
current pulsations on validity
For analysis of test results we ud a modified version of Helpless behavior should not occur spontaneously and the recently introduced failure pattern criterion[10]and should be induced only by uncontrollable stress.Otherwi classified animals as helpless when they failed to escape in we could not decide in the individual animal between true more than10out of15trials.As an alternative a
deficit learned helplessness,that is interference of the experience pattern criterion is often ud,which classifies animals as of helplessness with learning[9],or a poor test result due helpless if they escape only slowly(after20s)in more to a primary cognitive deficit or a general inactivity.We than10out of15trials.We compared the nsitivity(ratio: therefore aimed for the minimum number of spontaneously LH animals after shock/all animals expod to shock)and
Fig.1.Avoidance of current leads to fally helpless rats.Experiments were performed in small chambers with a pha duration of200ms during inescapable shock exposure and test.(A)Twenty animals without shock exposure(open squares)were compared with20animals24h after shock exposure (clod squares).When animals avoided current during test they were gently pushed to a position where they again received current.Animals were classified as learned helpless(LH)if they had.10failures to stop a trial.Under given parameters there were almost no LH animals with or without inescapable shock.(B)Recalculation of the experimental test results if avoidance of current had not been detected:every time an animal showed current-avoiding behavior this trial was counted as a failure becau by avoiding current the animal had no need to terminate the trial by bar press.Under the conditions inescapable shock emed to induce a considerable excess of failures and thus helpless-like behavior,becau animals with shock exposure showed more current avoidance during test(average6.35)than animals without shock exposure(average1.05).
4B.Vollmayr,F.A.Henn/Brain Rearch Protocols8(2001)1–7
Table1
Influence of chamber size and pha duration of current pulsations on validity of learned helplessness
Pha duration Chamber size Percentage of helpless rats Percentage of helpless rats
without shock exposure24h after shock exposure
(n)(n)
70ms Small10%5%
(20)(20)
200ms Small20%25%
(20)(20)
200ms Large0%15%**
(37)(172)
**One-sided Chi-square,P50.004.
specificity(ratio:LH animals after shock/LH animals 5.4.Reliability of testing
without and after shock)of helplessness induction under
analysis with both patterns.Fig.2shows the failure The learned helplessness model has often been criticized histograms of37animals without shock exposure and172for a lack of reproducibility[4,10].When reproducibility is animals after inescapable shock according to failure pattern tested intra-individually by repeated testing,some animals (A)and deficit pattern(B).According to failure pattern improve their testing results due to learning during multi-learned helplessness was induced with a nsitivity of0.15ple tests;in others the performance decreas from test to and a specificity of1.According to deficit pattern nsitivi-test most probably becau each testing with many failures ty was0.30but specificity was only0.89.Since high has the effect of uncontrollable stress on the animal.The specificity was considered most important,the cut-off effects interfere with the true test reliability.We therefore criterion for learned helplessness was moved for deficit tested the interindividual reproducibility.With the chon pattern analysis.With a cut-off criterion of more than12parameters learned helplessness testing was highly re-slow escapes specificity of learned helplessness according producible.Eight groups of20animals were trained and to deficit pattern was1,but nsitivity was only0.09.We tested.There were two helpless rats infive groups,three therefore prefer analysis according to failure pattern be-helpless rats in one group andfive helpless r
ats in two cau of the better relation of nsitivity and specifiups,which gave a mean of14.466.8%(mean6S.D.)
Fig.2.Analysis according to failure pattern(FP)yields a better specificity than analysis according to deficit pattern(DP).Experiments were performed in large chambers with a pha duration of200ms during inescapable shock exposure and test.Thirty-ven animals without shock exposure(open squares) were compared to172animals after shock exposure(clod squares).Note the two different y-axis scales.(A)According to FP animals were classified as learned helpless(LH),if they failed.10times to stop a test trial.Specificity of this criterion(ratio:LH animals after shock/LH animals without and after shock)was1,nsitivity(ratio:LH animals after shock/animals expod to shock)was0.15.(B)According to DP animals were classified LH if they had .10escapes slower than20s.Specificity with this criterion was0.89and nsitivity was0.3.
B.Vollmayr,F.A.Henn/Brain Rearch Protocols8(2001)1–75 learned helpless animals per group.According to ANOV A
this variation is within statistically expected limits.
Testing results were determined according to failure
pattern(FP)which was reported to be more reliable when
ud with a sufficiently difficult shuttle box test[10].We
tested whether deficit pattern(DP)also was less reproduc-
好高骛远的近义词
ible when a bar press was ud to test for learned
helplessness.DP identifies more helpless animals becau
the criterion for a failure is more strict.When the experi-
ment from above was rated according to DP there was one
group with three,four,six,ven,eight and10helpless
Fig. 3.Learning during inescapable shock ssion does not predict animals,respectively,and two groups withfive helpless
number of failures during test.One hundred and venty-two animals animals each,which gave a mean of30613.5%were expod to inescapable shock and subquently tested.Current
(mean6S.D.)learned helpless animals per group.Thus,we avoiding behavior during shock exposure was counted and ud as a did notfind differences in reproducibility between FP and
measure for learning.Each symbol reprents one or more animals.There
was a weak but significant inver correlation to the performance during DP in our tting.
test(Spearman’s rho:20.257;P50.001)indicating that animals learning
well were less helpless.This effect was due to the nine most-persistent 5.5.Correlation between learning during inescapable animals which continued to avoid throughout the shock exposure and
shock ssion and learning during testing thereby achieved highest avoidance values.The animals thus had
learned to avoid current and were extremely persistent.It was assumed
that this persistency protected them from becoming helpless.If the According to Seligman and Maier,experience of hel-
animals were excluded from analysis there was no correlation(Spear-plessness interferes with the learning of a task,in our ca
man’s rho:20.098;P50.21)indicating that cognitive performance to press the bar for terminating current[13].Since we during shock exposure does not predict the outcome in the learned
apply mild current,not all animals displayed the deficit.helplessness test.
How can we be sure,that we do not simply lect animals
with poor cognitive capabilities but tho with cognitive
deficits due to uncontrollable stress?We ud the fact,that
围场坝上
during thefirst ries of experiments the conditioning 6.Discussion
boxes allowed the animal to avoid the current which had to
be stopped by the experimenter.Repeated avoidance meant 6.1.Troubleshooting
that the animal had learned how to terminate the current
briefly;therefore the number of current avoidances during
6.1.1.Categorization
the shock exposure ssion was ud to asss the pre-test
Helpless behavior can be assd with a continuous cognitive function and was correlated with the number of
创新产品,the latency to press a lever or cross a door) failed trials during testing.The result is shown in Fig.3.
[13],with a discrete ,the number of failures There was a weak but significant inver correlation
to escape)[3,13]or with a categorical variable if one between current avoidance during shock exposure and
choos a cut-off criterion for helpless behavior[3,11].We failures during testing,indicating that animals learning
opted for categorization becau of the need to identify well during shock exposure did better during learned
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individual animals with learned helplessness for sub-helplessness testing(Spearman’s rho:20.257;P50.001).
quent neurobiologic studies and compared them with This effect was due to nine animals(5%of the group)
animals displaying most pronounced not helpless behavior. avoiding current extremely often.The animals exhibited
Thus we did not have to rely on the comparison of animal not only good learning but also extremely persistent
groups which have only slight differences in behavior and behavior:while most of the animals would give up
therefore make it difficult or impossible tofind subtle arching for escape after about two thirds of the inescap-二话不说是成语吗
molecular differences underlying helpless behavior.But able shock ssion,the animals continued to avoid
categorization also has requirements:there must be a current throughout the trial.Thus,it is not surprising that
considerable inter-individual variance of behavior to allow the persistence of the animals was correlated with
tting of cut-off points between groups of animals with resistance to shock exposure effects and the animals did
well-defined behavior.This is given in our paradigm due to better during testing.Excluding the nine animals from
the mild current during inescapable shock and testing[7,8]. analysis led to the disappearance of the correlation(Spear-
man’s rho:20.098;P50.21).This indicates that learned
helplessness testing does not identify animals with primary 6.1.2.Almost all animals are helpless,even without cognitive deficits but rather lects for cognitive deficits inescapable shock
induced by uncontrollable stress,which may be an equiva-If a large proportion of the rats is helpless even without lent to the human cognitive deficits during depression.inescapable shock,animals most probably avoid current.
6B.Vollmayr,F.A.Henn/Brain Rearch Protocols8(2001)1–7
孕早期腰疼While doing so they have no reason to perform the desired without having learned the paradigm.In this ca the task and they appear helpless.Avoiding animals appear current intensity should be decread until some animals more relaxed than helpless animals suffering from current,become helpless.
but differences are sometimes subtle.Rats avoid current by
different ways:sitting on rods connected in ries and thus
having the same potential all the time;sitting on only one 6.2.Alternative and support protocols
苹果自带浏览器打不开网页rod and holding with forepaws on not electrified walls;
touching electrified rods only with fur by putting paws There are other methods to apply inescapable
stress. between rods;climbing the walls along small protrusions Well established is the u of tail shock to induce learned or holes or sitting on lever or hurdle.Boxes for shock helplessness behavioral deficits[2,5].Tail shocks allow exposure and testing boxes have to be built to prevent excellent control over the applied current and avoidance of the possibilities.A warning signal from the shock current is almost impossible,but it requires an immobiliza-generator whenever it cannot apply current helps to detect tion of the animal and the effects of immobilization stress avoidance of current.superimpo tho of uncontrollable or controllable stress If avoidance is excluded,the pha duration of current of shocks.
pulsations or current intensity may not be sufficient and Secondly,some protocols u a triadic design with should be incread in increments.Control experiments yoked controls and stress-naive animals.This design without shock exposure are needed to determine the provides the capability of evaluating the importance of specificity of helplessness induction with a given pha controllability of stress but pos problems of lection(of duration and d learners in the controllable stress group)[2].We are Occasionally a fecal bolus will connect two rods,interested in factors that determine vulnerability to learned thereby short-circuiting the shock generator.Under that helplessness and u animals that received inescapable condition the animal is expod only to mini
mal current,if shock but did not acquire helplessness as a control group any.If not detected immediately,the animals have to be with identical stress exposure.Since learned helplessness excluded from the experiment.Spacing of rods can be lasts for more than a week but acute stress effects in the incread but should not be too far,becau this increas non-helpless group taper off in a few days,this protocol the possibility for the animal to contact only one rod.also allows evaluation of long-lasting molecular changes
during learned helplessness as a model for human depres-
sion.
6.1.3.Too few animals are helpless Learned helplessness can also be assd with shuttle If after inescapable shock too few animals are helpless boxes[5].While this ems to be particularly suited for the test may be too easy.As early as1973failures to mice[1]which do not readily acquire the bar press,it may induce helplessness were reported to be due to tasks that be too easy for rats.In this ca a hurdle between the are too rapidly acquired like a shuttle box escape respon compartments can make the task more difficult and thereby [9].Selecting a more difficult task like a bar press increas the reproducibility[10].
increas the number of animals in which learned helpless-
ness can be induced and also increas the specificity of
the induction[12].We therefore lected a bar press
paradigm.While sometimes FR3bar press respons are7.Quick procedures
ud[12]we found it sufficiently difficult to require a
short relea of the bar after one trial before stopping the7.1.Inescapable shock
next trial with a new bar press.If a difficult task like the
bar press is ud and there is little induction of helpless-A40min ssion of0.8mA inescapable shock,consist-ness after inescapable shock,the boxes may be too small ing of single shocks and inter-shock times ranging from5 with animals hitting the bar incidentally too often.As to15s randomized by the computer.Total shock duration: Musty et al.pointed out,reproducibility can be incread20min.Pulsation of current with a pha-duration of200 by a more difficult test[10];possibly this is due to a ms.
decrea of incidentally correct respons and thereby
incread specificity of correct respons.
A cond possibility if not enough helpless animals are7.2.Testing
obtained may be current too inten or the pulsations are
too slow.If the current is experienced as really painful by Twenty-four hours after inescapable shock:15trials the rats they become very active,and no rat will give up with0.8mA pulsating current lasting60s each with an and tolerate the current helplessly.By jumping and run-inter-trial time of24s.Current is accompanied by a light ning around very actively the rats hit the bar incidentally clue.Animals can stop a trial by pressing the lever.
