Brain Research 892 (2001) 336–343www.elsevier.com/ locate /bres

Research report

Facilitated stimulus-response associative learning and long-termmemory in mice lacking the NTAN1 amidase of the N-end rule

pathwaya a c a,b ,*Seth A. Balogh , Cary S. McDowell , Yong Tae Kwon , Victor H. Denenberg

aBiobehavioral Sciences Graduate Degree Program, University of Connecticut, 3107 Horsebarn Hill Road, Storrs, CT 06269-4154, USAbDepartment of Psychology, University of Connecticut, Storrs, CT 06269-4154, USAcDivision of Biology, California Institute of Technology, Pasadena, CA 91125, USA

Accepted 21 November 2000

Abstract

The N-end rule relates the in vivo half-life of a protein to the identity of its N-terminal residue. Inactivation of the NTAN1 geneencoding the asparagine-specific N-terminal amidase in mice results in impaired spatial memory [26]. The studies described here weredesigned to further characterize the effects upon learning and memory of inactivating the NTAN1 gene. NTAN1-deficient mice werefound to be better than wild-type mice on black–white and horizontal–vertical discrimination learning. They were also better at 8-weekMorris maze retention testing when a reversal trial was not included in the testing procedures. In all three tasks NTAN1-deficient miceappeared to use a strong win–stay strategy. It is concluded that inactivating the asparagine-specific branch of the N-end rule pathway inmice results in impaired spatial learning with concomitant compensatory restructuring of the nervous system in favor of non-spatial(stimulus-response) learning. 2001 Elsevier Science B.V. All rights reserved.

Theme: Neural basis of behavior

Topic: Learning and memory: systems and functions

Keywords: Non-spatial learning; Ubiquitin-mediated protein degradation; N-end rule pathway; NTAN1 amidase; Long-term retention; Spatial learning

1. Introduction directly by UBR1/E3a, the E3 component of the N-endrule pathway [25] through its type 1 and type 2 substrate-

The ubiquitin–proteolytic pathway regulates numerous binding sites [28]. Target proteins are subsequently pro-cellular processes including signal transduction, cell cycle cessively degraded by the 26S proteasome.progression, DNA repair, apoptosis, antigen processing, Although protein degradation via this system is neces-and gene expression [21]. The N-end rule pathway, one sary for several critical cellular processes, its relationshipsubset of the ubiquitin pathway, relates the in vivo half-life to cognition has received little attention. This is in markedof a protein to the identity of its N-terminal residue [4]. contrast to the extensive investigations of the neuro-The N-end rule is organized hierarchically. In mice, the behavioral consequences of protein synthesis, resulting inN-terminal asparagine and glutamine are deamidated into the conclusion that protein synthesis and the systems thataspartate and glutamate by NTAN1 and NTAQ1, respec- accomplish this are necessary for the formation of certaintively [20,26]. N-terminal aspartate and glutamate are then types of memories [1,10,15]. In particular, both short- andconjugated with arginine by ATE1 [27]. N-terminal ar- intermediate-term memory systems are protein indepen-ginine and other primary destabilizing residues are bound dent, whereas long-term memory systems are dependent

upon the production of new proteins [5,16,17,19,29–31].The dearth of knowledge regarding the relationship be-tween the degradation or removal of intracellular, short-*Corresponding author. Tel.: 11-860-486-3826; fax: 11-860-486-lived regulatory proteins and cognition is beginning to3827.

E-mail address: dberg@uconnvm.uconn.edu (V.H. Denenberg). change because gene targeting (in mice) via homologous

0006-8993/01/$ – see front matter 2001 Elsevier Science B.V. All rights reserved.PI I : S0006-8993( 00 )03268-6

S.A. Balogh et al. / Brain Research 892 (2001) 336 –343 337

recombination now makes it possible to relate gene 19–218C), with a gray stem. In Experiment 1 the twofunctioning with cognition. alleys were painted black or white; in Experiment 2 the

For example, Kwon et al. [26] recently reported on the alleys contained either horizontal or vertical black andinactivation of the asparagine branch of the N-end rule white stripes [6,35]. A computer program for tracking andpathway in mice by disruption of the NTAN1 gene which scoring animals has been described previously [11].encodes the asparagine-specific N-terminal amidase. Each animal was randomly assigned a positive stimulusNTAN1-deficient mice were fertile, outwardly normal, but (black or white alley, horizontal or vertical stripes). Aless active and inferior to wild-type mice during the different semi-random sequence was used each day toacquisition and retention of the Lashley III maze. The specify the left–right location of the positive stimulus. Thegenotypes did not differ during original Morris maze stimuli also occurred equally often on the left and the right.learning; however, the mutant mice subsequently spent Thus, the animal could not use spatial information to solvemore time and swam a longer distance to locate a hidden the problem and had, instead, to learn to associate aescape platform when retested 8 weeks later. Although specific stimulus with reinforcement.neither NTAN1 mutant nor wild-type mice were able to The mouse was placed into the water at the stem endlearn the spatial or non-spatial versions of an eight-arm and allowed 60 s to find the escape ladder. After arriving atradial maze [22], the mutant animals made more errors on the ladder, the mouse was removed and put into its homethe spatial version, suggesting that they were not utilizing cage under a heat lamp where it remained until allspatial information as effectively as wild-types. Kwon et members of the squad had been tested. It was then givenal. [26] concluded that NTAN1-deficient mice have im- its second trial. Ten trials were given per day for 5 dayspaired spatial memory. Similar deficits in spatial process- (Experiment 1) or 10 days (Experiment 2). The measure ofing have been noted in other mutant mice lacking a protein learning was the number of correct choices a mouse madeinvolved in the ubiquitin-mediated proteolytic system [24]. (swimming down the stem of the T and choosing theThe current experiments were undertaken to further in- correct arm without entering the incorrect arm) divided byvestigate the effects of inactivation of NTAN1 amidase on the total number of choices it made (percent correctlearning and memory in mice. choices). In Experiment 2, Group 1 mice were tested at 9

and 10 weeks of age and given 5 days of retesting at week16; while Group 2 mice were tested when 11–12 weeks

2. Experiments 1 and 2: two-choice discrimination old and retested at 21 weeks of age.learning

2.3. Statistical analysesTwo-choice discrimination learning was chosen because

it is known to be a reliable test of non-spatial ability that The Experiment 1 data were evaluated using a repeatedmice can learn [35]. measures analysis of variance procedure with Genotype as

the independent classification and Days of testing as the2.1. Subjects repeated measure. In Experiment 2, Group and Sex served

as additional independent classifications.2 /2129-strain wild-type and congenic NTAN1 mice

used in this study were offspring of homozygous breeding 2.4. Black–white discrimination results2 /2 2 /2pairs (1 /1X1 /1 and NTAN1 3NTAN1 matings,

2 /2respectively), reared at the University Connecticut’s De- One NTAN1 mouse was removed from the analysesvelopmental Psychobiology Laboratory. Their production due to aberrant behavioral data (i.e. scores deviating ashas been described in detail previously [26]. At weaning much as four S.D.’s from the mean).mice were housed individually and maintained on a 12-h Fig. 1 shows that both genotypes increased their correctlight–dark cycle (lights on at 0600 h) with food and water choices over days [F 514.15, P,0.0001], with the(1,60)

2 /2ad lib. Experiment 1 consisted of 18, 10-week old, male NTAN1 mice having significantly higher scores2 /2mice (ten NTAN1 and eight wild-type) tested in black– [F 513.03, P,0.01].(1,15)

white brightness discrimination. Experiment 2 consisted oftwo independent replications (Group 1 and Group 2) 2.5. Horizontal–vertical discrimination resultsconducted approximately 4 weeks apart with a total of 30

2 /2NTAN1 and 29 wild-type mice (approximately equal 2.5.1. Original learningnumbers of males and females) tested in horizontal–verti- Fig. 2 shows the percent of daily correct responses overcal discrimination. the 10 days of testing and the 5 days of retesting. Neither

Group nor Sex was significant as a main effect or in any2.2. Procedure interaction. The Genotype3Days interaction was signifi-

cant [F 52.22, P,0.02]. Trend analyses found the(9, 459)

The apparatus was a two-arm swimming T-maze (water two genotypes did not differ in their linear slopes but did

338 S.A. Balogh et al. / Brain Research 892 (2001) 336 –343

2.5.2. RetentionThe groups did not differ in their long-term retention, in

part because both genotypes had excellent memories;averaging |85% correct on the first day of retesting.

2.6. Comment

2 /2These data show quite clearly that NTAN1 mice aresuperior to wild-type mice at two-choice discriminationlearning.

3. Experiment 3: Morris maze re-analysis

Kwon et al. tested the two genotypes for 5 days on thehidden platform Morris water maze (four trials per day).On Day 6 they moved the platform to the diagonallyopposite quadrant for 1 day (four trials) of testing; this iscalled ‘reversal learning.’ Seven to 8 weeks later duringretention testing, the mice again received 5 days of testing(four trials /day) with the platform back in its originallocation. Kwon et al. found no Genotype difference inFig. 1. Percent correct choices (mean6S.E.M.) made in a non-spatial

2 /2black–white T-maze for NTAN1 and wild-type mice. Insert shows a original or reversal learning. However, on the first day of2 /2three-quarter side-view of maze. NTAN1 mice made a significantly retention testing they found that the wild-type mice took

higher percent correct choices over days.significantly less time and traveled a lesser distance to getto the platform. The distance curves for these effects (not

in their quadratics [F 55.82, P,0.05], with the presented in Kwon et al.) are shown in Fig. 3. The time(1, 459)2 /2NTAN1 mice achieving 90% correct by the sixth day curves are very similar and are not shown.

of testing, whereas the wild-type group took 9 days to Since mice lacking NTAN1 had poorer performance onreach this level. the first retest day (the purest measure of long-term recall),

2 /2Fig. 2. Percent correct choices (mean6S.E.M.) in horizontal–vertical T-maze for NTAN1 and wild-type mice during original learning and 8-week2 /2retention testing. Insert shows a three-quarter side-view of maze. A significant Genotype3Days Quadratic trend revealed that NTAN1 mice acquired

this non-spatial maze at a significantly faster rate than wild-type mice.

S.A. Balogh et al. / Brain Research 892 (2001) 336 –343 339

2 /2Fig. 3. Distance (mean6S.E.M.) traveled by NTAN1 and wild-typemice to locate the hidden platform in the Morris water maze. Maze inserts

2 /2show platform locations. NTAN1 mice did not differ from wild-typemice during original or Day 6 reversal learning. Compared to wild-typemice, however, they swam a significantly longer distance to locate thehidden platform on Day 1 of retention testing.

the conclusion drawn was that NTAN1 plays a role in2 /2spatial memory. However, NTAN1 mice did learn

something because their retention scores matched those ofthe wild-type mice by the second retention day. Two linesof evidence suggest that the reversal learning experience

2 /2may have had an adverse effect upon the NTAN1 mice.First, the hidden platform had been moved to the diagonal-ly opposite quadrant for reversal learning, but had beenplaced back in its original quadrant for the retentiontesting. Second, the discrimination learning experiment

2 /2found NTAN1 mice to be better at S-R associative2 /2learning than wild-type mice. If the NTAN1 mice were

guided by their latest memory of the location of theplatform, this could have had a negative effect upon theirretention scores. Therefore, detailed analyses of the quad-rant choices for both genotypes were performed.

3.1. Reversal learning

Since reversal learning is defined by shifting the hiddenplatform from one quadrant to another, we examined thepercent of time the two genotypes spent in each of the fourquadrants on (a) Day 5, the last day of original learning,(b) Day 6, when the platform was shifted to the diagonal Fig. 4. Distribution of time across Morris water maze quadrants for eachquadrant, and (c) the first day of retention, 7–8 weeks later, genotype during (A) original learning, (B) Day 6 reversal, and (C) Day 1when the platform was in the same location as during retention. Maze inserts show different quadrants (T5target, O5opposite,

R5right, and L5left). Both genotypes spent the highest percent of theiroriginal learning. Fig. 4 shows the distribution of timetime in the target quadrant on Day 5 of original learning. Unlikespent in the four quadrants on each of those days.

2 /2wild-type mice, NTAN1 mice spent the majority of their time in theOn Day 5, both groups spent approximately 40% of their target quadrant during Day 6 reversal training. As a result, they also spent

time in the target quadrant, and the remainder of their time a greater amount of their time in the opposite quadrant during Day 1 ofwas randomly distributed among the other three quadrants. retention testing, which resulted in the significant ‘impairments’ observed.

The only significant effect is due to quadrants (P,0.0001).On Day 6, the two genotypes spent the plurality of their

time in the new target quadrant, followed by time in the spent a significantly greater percentage of their time in theprior target quadrant, with time in the two remaining new target quadrant than the prior target quadrant [F 5(1,26)

2 /2quadrants randomly distributed. The NTAN1 mice 14.38, P,0.001], while the wild-type animals did not

340 S.A. Balogh et al. / Brain Research 892 (2001) 336 –343

differ in their time distribution [F ,1.0]. This prefer- in diameter and placed 23 cm from the outer wall of the(1,25)

ence for the new target quadrant over the old by the maze. Before trial 1, on the first day only, each mouse was2 /2NTAN1 mice was carried forward into retention test- placed on the platform for 10 s. At the end of each trial,

ing, as discussed below. each mouse remained on the platform for 10 s, before itwas placed back into its heated home cage. After all mice

3.2. Retention in a squad (four to five mice) had completed trial 1, thenext trial was given.

An analysis of the percent time spent in each quadrant Starting when 16 weeks old, each mouse was given fouron the first retention day found a significant Genotype3 trials (45 s maximum per trial) a day, one from each of theQuadrants interaction [F 53.25, P,0.03]. The pro- four positions, with the order determined semi-randomly,(3,153)

files of the two genotypes is shown in the bottom part of for 5 days. Eight weeks later they were given fiveFig. 3. The wild-type mice spent approximately 38% of additional days of testing. The platform remained in thetheir time in the target quadrant. For the wild-type mice the same fixed position throughout testing and retesting. Anpercent time spent in each quadrant on Day 5 of original animal’s path was traced on an electronic digitizing tabletlearning was compared to the same profile on Day 1 of containing a template of the maze. A computer programretention for the wild-type mice. The profiles were virtual- obtained, for each trial, the time to reach the platform, thely identical [F ,1.0]. distance traveled, speed, percent time in each quadrant and(3,75)

2 /2In contrast, the NTAN1 mice spent almost as much percent time in each of the three annuli [12].time in the quadrant where the target had been on Day 6 asthey did in the quadrant now containing the hiddenplatform. A comparison of their quadrant distribution time 4.3. Resultson Day 5 of original learning was significantly differentfrom their quadrant distribution time on the first day of Fig. 5 shows the distance curves of learning and 8-weekretention testing [F 56.21, P,0.0008]. retention for the two genotypes. Time data are similar and(3,78)

are not presented. The groups did not differ in original2 /23.3. Comment learning. When retested 8 weeks later, NTAN1 mice

swam a significantly shorter distance to the platform overThe quadrant analyses above strongly suggested that the days [F 55.78, P,0.03]. They also tended to take less(1,20)

2 /2poorer retention performance by NTAN1 mice was due time than wild-type mice to locate the platform [F 5(1,20)

to the introduction of the reversal learning. 3.49, P,0.07].An analysis of the quadrant distributions on the fifth day

of original learning found that the wild-type and2 /24. Experiment 4: Morris maze learning and retention NTAN1 mice spent 41 and 44% of their time in the

without reversal learning target quadrant, respectively, with their time in the otherthree quadrants randomly distributed. On the first day of

In this experiment the original Morris maze experiment retention testing, the corresponding values were 45 andwas repeated except that the reversal learning procedurewas eliminated. Since the two genotypes did not differ intheir original Morris maze learning, we expected to obtainthe same findings in the new experiment and, therefore,predicted that the two groups would not differ in theirlong-term retention.

4.1. Subjects

2 /2Twelve wild-type and 12 NTAN1 mice, with equalnumbers of males and females, were used. They weregiven five trials of water escape training in 1 day at 15weeks [7]. The genotypes did not differ on this measureand the data will not be presented.

2 /2Fig. 5. Distance (mean6S.E.M.) traveled by NTAN1 and wild-typemice to locate the hidden Morris maze platform during original learning4.2. Morris water mazeand 8-week retention testing when Day 6 reversal was excluded. Mazeinsert shows the location of the platform throughout testing. When Day 6

Mice were placed into a large circular black tub (d5 reversal learning was removed, the genotypes did not differ significantly2 /2123) of water (19–218C) from any of four locations (N, S, during original learning. NTAN1 mice subsequently swam a sig-

E, W) and had to find a submerged escape platform 23 cm nificantly shorter distance to the platform during 8-week retention testing.

S.A. Balogh et al. / Brain Research 892 (2001) 336 –343 341

39% in the target quadrant, not significantly different fromDay 5 of original learning.

4.4. Comment

The original Morris maze learning in this study essen-tially replicated Kwon et al. [26]: the genotypes did notdiffer; they had asymptotes around 13–15 s by the fifthday of testing, and they spent approximately 40% of theirtime in the target quadrant on Day 5. The surprising

2 /2finding was that the NTAN1 mice had superior long-term retention scores, in marked distinction to the poorer

2 /2performance reported in Kwon et al. when 1 day of Fig. 6. Distance (mean6S.E.M.) traveled by NTAN1 and wild-typemice to locate hidden Morris maze platform when a one trial /per dayreversal training was interposed between original learningtesting regime was undertaken. The maze insert shows location ofand retesting.platform throughout testing. The distance traveled by the two genotypesdid not differ under these testing conditions.

5. Experiment 5: Single trial Morris maze testing5.3. Comment

2 /2Kwon et al. had found that NTAN1 mice werepoorer than wild-type control mice on original learning of The results are unequivocal. Whether given one dailythe Lashley maze and also on Day 1 of retention testing. trial (this study) or four daily trials ([26]; Study 3 above),The latter finding is the same as obtained on the Morris both genotypes are able to learn the Morris maze and domaze when the mice were given 1 day of reversal learning not differ in their learning.training. The Lashley maze can be learned by use ofextra-maze cues, like the Morris maze, but can also belearned by using intra-maze cues to memorize the pathway

6. Discussionto the goal. We have found that rodents prefer to use theextra-maze cues [9,18,23]. One major procedural differ-

2 /2NTAN1 mice learned brightness and pattern dis-ence between the two mazes is that animals are given onlycriminations more rapidly than wild-type mice. They alsoone trial per session in the Lashley III maze, whereas theyhad poorer long-term retention of the spatial Morris mazereceive four trials per session in the Morris maze. Thus,when reversal learning testing intervened between originalshort-term memory cannot be utilized in Lashley III mazelearning and retention testing. In contrast, when there waslearning but can in learning the Morris maze. To investi-

2 /2no reversal learning testing, NTAN1 mice had superiorgate this possibility, mice were given a single daily trial onlong-term retention. These findings, in combination withthe Morris maze.data reported by Kwon et al. [26], lead to the conclusion

2 /2that NTAN1 mice use non-spatial stimulus-response5.1. Procedure(S-R) associative processes as their primary learning

2 /2 mechanism with much less reliance upon spatial processes.Twenty wild-type and 20 NTAN1 mice, with equalThe evidence supporting this thesis is presented below.numbers of males and females, were used. At 11 weeks

In discrimination learning all spatial cues are eliminatedthey were given 1 day of water escape learning. Theby pairing reinforcement with a positive stimulus thatgenotypes did not differ on this measure and the data willoccurs equally often on the right and left in a semi-randomnot be reported.manner. Consequently, a mouse can only learn by attend-Starting at 12 weeks the mice were given one dailying to the intra-maze cues (i.e. black and white alleys orswim test in the Morris maze for eight consecutive days.horizontal and vertical stripes), and by learning to associateOver the 8 days, using a semi-random schedule, each

2 /2escape from the water with one of them. NTAN1 miceanimal was started twice from each of the four startdo this more effectively than wild-type mice.locations.

Re-analysis of the Morris maze data [26] found that the2 /25.2. Results greater time and distance scores of NTAN1 mice on the

first retest day were associated with these mice spending aFig. 6 shows the distance learning curves for the two disproportionately large amount of their Day 1 retention

genotypes. The time curves are very similar and are not time in the Day 6 reversal learning quadrant. Moreover,2 /2shown. There was no difference between the two geno- when Day 6 reversal training was excluded, NTAN1

types. mice had superior long-term retention scores compared to

342 S.A. Balogh et al. / Brain Research 892 (2001) 336 –343

wild-type mice. These findings lead to the conclusion that, In summary, inactivating the NTAN1 gene in mice2 /2 revealed that this enzyme plays an important role in spatialin both experiments, NTAN1 mice remembered their

and non-spatial learning and memory. Equally as interest-most recent experience with the target location and spenting are the findings that decreased competence in spatialtime in that quadrant. Thus, they appear to be following alearning in NTAN1-deficient mice appears to be compen-win–stay rule both in the Morris maze and in discrimina-sated for by enhanced S-R associative learning and mem-tion learning. A non-spatial win–stay strategy ignores priorory capabilities. It is likely that other adaptive behaviors inconfigurational information and is not characteristic of athese animals are connected to these distinct learningspatial learning strategy [8].patterns. Thus, NTAN1-deficient mice may be useful inA third line of evidence supporting the S-R hypothesisstudying both spatial and non-spatial associative learningcomes from avoidance learning data presented in Kwon etmechanisms as well as helping to illuminate behavioral. The two genotypes were tested in a two-way shuttleboxpatterns which are adaptive for each learning phenotype.with retention testing 7 or 10 weeks later. If a mouse ran to

the other chamber after the CS (light) went on, but beforethe UCS (shock) occurred, this was classified as an

Referencesavoidance response. If the mouse received electric shockand crossed to the safe compartment before the shock

[1] T. Abel, P.V. Nguyen, M. Barad, T.A.S. Deuel, E.R. Kandel, R.terminated, this was called an escape response. If theBourtchouladze, Genetic demonstration of a role of PKA in the latemouse remained in the chamber for the entire shockphase of LTP and in hippocampus based long-term memory, Cell 88

interval, this was called a null response. Neither group (1997) 615–626.learned during the first 5 days of testing, nor during the 5 [2] S. Alyan, B.L. McNaughton, Hippocampectomized rats are capabledays of retention testing. However, learning did occur of homing by path integration, Behav. Neurosci. 113 (1999) 19–31.

[3] A. Amsel, Hippocampal function in the rat: cognitive mapping orbetween original learning and retesting. During original2 /2 vicarious trial and error?, Hippocampus 3 (1993) 251–256.learning NTAN1 mice had significantly more null

[4] A. Bachmair, D. Finley, A. Varshavsky, In vivo half-life of a proteinresponses and less escapes than wild-type mice. These is a function of its amino-terminal residue, Science 234 (1986)differences had disappeared by retesting because 179–186.

2 /2NTAN1 mice reduced their number of null responses [5] C.H. Bailey, D. Bartsch, E.R. Kandel, Toward a molecular definitionof long-term memory storage, Proc. Natl. Acad. Sci. USA 93 (1996)and increased their avoidance responses. Since shuttlebox13445–13452.conditioning involves non-spatial S-R learning mecha-

[6] S.A. Balogh, G.F. Sherman, L.A. Hyde, V.H. Denenberg, Effects ofnisms, the lack of differences between the genotypes neocortical ectopias upon the acquisition and retention of a non-during retesting, compared to the differences present spatial reference memory task in BXSB mice, Dev. Brain Res. 111during original learning, indicates more effective memory (1998) 291–293.

[7] G.W. Boehm, G.F. Sherman, B.J. Hoplight II, L.A. Hyde, N.S.consolidation of this type of information on the part of2 /2 Waters, D.M. Bradway, A.M. Galaburda, V.H. Denenberg, LearningNTAN1 mice.

and memory in the autoimmune BXSB mouse: effects of neocorticalThe present characterization of NTAN1-deficient mice ectopias and environmental enrichment, Brain Res. 726 (1996)

complements the conclusions drawn by Kwon et al. that 11–22.disrupting the NTAN1 gene affects spatial memory and [8] G. Boehm, G.F. Sherman, G.D. Rosen, A.M. Galaburda, V.H.

2 /2 Denenberg, Neocortical ectopias in BXSB mice: effects uponthat the NTAN1 mice are inferior to control mice inreference and working memory systems, Cereb. Cortex 6 (1996)spatial learning tasks. It extends these conclusions by696–700.

showing that mutant mice appear to have compensated for [9] D.A. Carroll, Sleep and wake states: Behavioral, developmental, andthis loss of spatial competence by developing enhanced pharmacological correlatess, Ph.D. dissertation, University of Con-associative learning mechanisms which they use to solve necticut, 1982.

[10] H.P. Davis, L.R. Squire, Protein synthesis and memory: a review,both spatial and non-spatial problems. This is not anPsychol. Bull. 96 (1984) 518–559.unlikely proposition since, even though the hippocampus

[11] V.H. Denenberg, N.W. Talgo, L.M. Schrott, G.H. Kenner, Anormally plays a central role in learning the hidden computer-aided procedure for measuring discrimination learning,platform Morris maze, research has shown that rats with Physiol. Behav. 47 (1990) 1031–1034.hippocampal damage can learn in this maze, sometimes [12] V.H. Denenberg, N.W. Talgo, N.S. Waters, G.H. Kenner, A com-

puter-aided procedure for measuring Morris maze performance,quite effectively [2,13,14,34,36]. Further, several research-Physiol. Behav. 47 (1990) 1027–1029.ers have proposed non-spatial associative mechanisms as

[13] H. Eichenbaum, Is the rodent hippocampus just for ‘place’?, Curr.mediators of Morris maze learning [3,32,33]. Opin. Neurobiol. 6 (1996) 187–195.

The argument given above assumes that S-R associative [14] H. Eichenbaum, C. Stewart, R.G. Morris, Hippocampal representa-2 /2learning was facilitated in the NTAN1 mice to compen- tion in place learning, J. Neurosci. 10 (1990) 3531–3542.

[15] E.M. Eisenstein, H.J. Altman, D.A. Barraco, R.A. Barraco, K.L.sate for decreased spatial processing. An alternative inter-Lovell, Brain protein synthesis and memory: the use of antibioticpretation, though less likely, is that prolonging the half-lifeprobes, Fed. Proc. 42 (1983) 3080–3085.

of asparagine-bearing substrate proteins by inactivating [16] J.F. Flood, E.L. Bennett, E. Orme, M.R. Rosenzweig, Relation ofNTAN1 serves to facilitate S-R learning processes which memory formation to controlled amounts of brain protein synthesis,then interfere with the effectiveness of spatial learning. Physiol. Behav. 15 (1975) 97–102.

S.A. Balogh et al. / Brain Research 892 (2001) 336 –343 343

[17] J.F. Flood, M.R. Rosenzweig, E.L. Bennett, A.E. Orme, The NTAN1p amidase and the asparagine branch of the N-End ruleinfluence of duration of protein synthesis inhibition on memory, pathway, Mol. Cell. Biol. 20 (2000) 4135–4148.Physiol. Behav. 10 (1973) 555–562. [27] Y.T. Kwon, A.S. Kashina, A. Varshavsky, Alternative splicing

[18] S.H. Freter, Differential learning strategies in the Lashley III maze results in differential expression, activity, and localization of the twoas a function of sex and early experience, Masters Thesis, University forms of arginyl–tRNA–protein transferase, a component of theof Connecticut, 1988. N-end rule pathway, Mol. Cell. Biol. 19 (1999) 182–193.

[19] M.E. Gibbs, K.T. Ng, Neuronal depolarization and the inhibition of [28] Y.T. Kwon, F. Levy, A. Varshavsky, Bivalent inhibitor of the N-endshort-term memory formation, Physiol. Behav. 23 (1979) 369–375. rule pathway, J. Biol. Chem. 274 (1999) 18135–18139.

[20] S. Grigoryev, A.E. Stewart, Y.T. Kwon, S.M. Arfin, R.A. Bradshaw, [29] K.T. Ng, M.E. Gibbs, S.F. Crowe, G.L. Sedman, F. Hua, W. Zhao,N.A. Jenkins, N.G. Copeland, A. Varshavsky, A mouse amidase B. O’Dowd, N. Rickard, C.L. Gibbs, E. Sykova et al., Molecularspecific for N-terminal asparagine. The gene, the enzyme, and their mechanisms of memory formation, Mol. Neurobiol. 5 (1991) 333–function in the N-end rule pathway, J. Biol. Chem. 271 (1996) 350.28521–28532. [30] K.T. Ng, B.S. O’Dowd, N.S. Rickard, S.R. Robinson, M.E. Gibbs,

[21] M. Hochstrasser, Ubiquitin, proteasomes, and the regulation of C. Rainey, W.Q. Zhao, G.L. Sedman, L. Hertz, Complex roles ofintracellular protein degradation, Curr. Opin. Cell Biol. 7 (1995) glutamate in the Gibbs–Ng model of one-trial aversive learning in215–223. the new-born chick, Neurosci. Biobehav. Rev. 21 (1997) 45–54.

[22] L.A. Hyde, B.J. Hoplight, V.H. Denenberg, Water version of the [31] Y. Tsukada, Molecular approaches to learning and memory, Jpn. J.radial-arm maze: learning in three inbred strains of mice, Brain Res. Phys. 38 (1988) 115–132.785 (1998) 236–244. [32] I.Q. Whishaw, Visits to starts, routes, and places by rats (Rattus

[23] L.A. Hyde, The effects of neocortical ectopias on learning and norvegicus) in swimming pool navigation tasks, J. Comp. Psychol.memory in the BXSB mouse; and massed and spaced learning in the 100 (1986) 422–431.NZB mouse, Ph.D. Dissertation, University of Connecticut, 1998. [33] I.Q. Whishaw, Latent learning in a swimming pool place task by

[24] Y.H. Jiang, D. Armstrong, U. Albrecht, C.M. Atkins, J.L. Noebels, rats: evidence for the use of associative and not cognitive mappingG. Eichele, J.D. Sweatt, A.L. Beaudet, Mutation of the Angelman processes, Q. J. Exp. Psychol. 43B (1991) 83–103.ubiquitin ligase in mice causes increased cytoplasmic p53 and [34] I.Q. Whishaw, J.C. Cassel, L.E. Jarrard, Rats with fimbria-fornixdeficits of contextual learning and long-term potentiation, Neuron 21 lesions display a place response in a swimming pool: a dissociation(1998) 799–811. between getting there and knowing where, J. Neurosci. 15 (1995)

[25] Y.T. Kwon, Y. Reiss, V.A. Fried, A. Hershko, J.K. Yoon, D.K. 5779–5788.Gonda, P. Sangan, N.G. Copeland, N.A. Jenkins, A.Varshavsky, The [35] R.E. Wimer, J.L. Fuller, Patterns of behavior, in: E.L. Green (Ed.),mouse and human genes encoding the recognition component of the Biology of the Laboratory Mouse, McGraw–Hill, New York, 1966,N-end rule pathway, Proc. Natl. Acad. Sci. USA 95 (1998) 7898– pp. 629–653.7903. [36] M.L. Woodruff, R.H. Baisden, A.J. Nonneman, Effects of trans-

[26] Y.T. Kwon, S.A. Balogh, I.V. Davydov, A.S. Kashina, J.K. Yoon, Y. plantation of fetal hippocampal or hindbrain tissue into the brains ofXie, A. Gaur, L. Hyde, V.H. Denenberg, A. Varshavsky, Altered adult rats with hippocampal lesions on water maze acquisition,activity, social behavior, and spatial memory in mice lacking the Behav. Neurosci. 106 (1992) 39–50.