Pavlov’s dogs - COnnecting REpositoriesThen, on the last day of my visit, Elena asked if I might like a private tour of Pavlov’s home — Apartment #11, 7th Line on Vasilievsky

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Eleven years ago, I began ascientific mission with a trip toRussia, to find the names ofPavlov’s dogs. My intention was toname Drosophila memory mutantsafter the dogs. At the time,however, two major impedimentslay in the way of this high-mindedobjective. I didn’t have manymemory mutants and I could findthe name of but one of Pavlov’sdogs, Bierka. My mission was tochange all that. So in the Spring of1992, I braved a trip to the PavlovInstitute in Koltushi, a small villageoutside of St. Petersburg, torummage through the last placethat Pavlov worked. My efforts toidentify the dogs failed, and I wasready to accept that their nameswould remain forever anonymous,when a soft-spoken, lonely womanin an obscure museumnonchalantly handed me 40photographs of Pavlov’s dogs,names and all! Now, more than tenyears later, we have completed alarge-scale behavioral screen,identifying 60 new memorymutants [1]. Mission complete.Meet some of the namesakes of‘Pavlov’s flies’.

So what’s in a name?Drosophologists have a tradition ofchristening new mutants with funand creative names. And, why not?Finding the mutants in the firstplace usually involves apromethean struggle againsttedium, boredom and insecurity.Often, the new names aredescriptive — like stuck,dissatisfaction, cuckold or dongiovanni to describe mutants withdefective courtship behavior.Sometimes, labs develop themesaround which to name mutants.One of my favorites concerns theoriginal set of learning mutants.This effort began in Seymour

Benzer’s lab at Cal Tech in theearly 1970s. His graduate student,Bill Harris, and an upstart newpostdoctoral student, W.G. ‘Chip’Quinn, published in 1974 the firstvalid claim for learning inDrosophila by showing that fliescould learn to avoid an odor whenpunished with footshock [2,3]. TheBenzer lab then began a chemicalmutagenesis to look for X-linkedlearning mutants, resulting in thediscovery by Duncan Byers ofdunce [4], the first experimentallyinduced learning-defective animalin history. That effort got Quinn ajob at Princeton University, wherehe continued the behavioralscreen, successfully generatingadditional mutants (see [5]). Quinndecided to play on the word dunceand gave these mutants names likedingy, daffy, dumbo, etc. When hementioned these names in a grantproposal to NIH, however,someone there objected to “thederogatory terms used to definelearning disabled animals”. Quinnretaliated by renaming the mutantsafter vegetables — rutabaga,radish, turnip, cabbage, zucchini,ochre. Great sport! And, as JeffHall once quipped, “You can’tdynamite an interesting name outof nematologist”.

So, does the name Pavlov ring abell? Most of us know from collegethat Pavlov (1849–1936) was thefamous Russian ‘psychologist’ whodevised a simple, elegantexperimental paradigm with whichto study learning. For severalrepetitions, Pavlov would ring a belljust before giving food to a hungrydog. Before long, he noticed, thedog started salivating whenever itheard the bell. Pavlov interpretedthis as indicating that the dog hadlearned to ‘associate’ the bell tonewith food reward and, thus, the

concept of associative learningwas born [6].

While these studies weretremendously influential in their day— see the writings of the Americanbehaviorist John Watson, forinstance — their true impact hasbecome apparent only now. Inessence, Pavlov distilled thecomplexity of learned behaviordown to one elemental component— a change in behavior producedby the association of two stimuli intime (bell and food, for instance).As such, the particular behavioralresponse was no longer important,making the proceduregeneralizable to other species andtasks. With complete experimentalcontrol over presentations of thetwo stimuli, moreover, thefunctional properties of thiselemental association could bequantified in detail. Throughout therest of the 1900s, behavioralproperties of Pavlovian learningwere quantified and comparedacross the animal kingdom,revealing a ‘functional homology’ranging from insects (Drosophila,bee, cockroach) to mollusks(Aplysia, Hermissenda) tomammals (rodent, chick, primate,human).

How is this possible, given thegreat diversity and complexity ofbehavioral tasks and underlyingneural circuitries observed in thiswide range of species? The answermust be that the behavioralproperties of Pavlovian learningreflect the cellular plasticity ofunderlying neurons. Neurons ininsects function much the sameway as neurons in mammals, forinstance, and accumulatingmolecular biological evidencesuggests a staggering level ofevolutionary conservation. So nowwe can see that Pavlov’sconceptualization of an elementalform of associative learningprovided an experimental ‘window’to link behavioral plasticity withneuronal plasticity.

I began studying Pavlovianlearning as an undergraduate in

A pilgrimage to the last working place of the behavioral psychologistIvan Pavlov in Russia led to the discovery of a photograph album full ofpictures of the original ‘Pavlov’s dogs’. Tim Tully explains how hemade this remarkable discovery, and how the photos have inspired thenaming of many new mutant fruitflies with defective memoryphenotypes.

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Pavlov’s dogs

Jerry Hirsch’s laboratory at theUniversity of Illinois, where Iinvestigated whether circadianrhythm influenced conditioning ofthe proboscis extension reflex inblow flies. Though Hirsch is mostfamous for his studies of thegenetic bases of geotaxis [7,8], hewas trained by the Berkeleyexperimental psychologists,Tolman and Tryon, and primarilywas interested in the genetic basisof learning. I found Hirsch’sperspective on behavior-geneticsfascinating and decided to stay onfor graduate school, working onseveral aspects of associative andnonassociative learning in blowflies [9–11]. Full of Pavlov as a newpostdoctoral fellow in Quinn’slaboratory, I then focused ondeveloping a Pavlovian procedurefor the Drosophila odor–shockavoidance task. A new ‘teachingmachine’ and training protocolyielded robust initial learningscores with relatively long-lastingmemory retention in normal fliesand defective but detectablememory retention in the originalvegetable mutants [12,13]. Withthis Pavlovian task, my fledglingresearch group at BrandeisUniversity initiated a small-scalescreen for memory mutants in 1987

— and I started thinking aboutPavlov’s dogs.

Why his dogs? Well, obviously, Imust like dogs. Growing up inMidwest America, my brothers andI hunted with field dogs and wereconstantly amazed at the power ofselective breeding for retrievers,pointers and sniffers. While newlyenamored with behavior-geneticstudies in graduate school, Ibought a bassethound with theintention to begin my ownbreeding experiments forbehavioral traits. In a somewhattwisted form of scholarship, Inamed my puppy after W.F.R.Weldon, a famous turn-of-the-century British geneticist whostudied (among other things) theinheritance of coat color inbassethounds. To me, that had acertain conceptual ring to it, and itgave Weldon a certain stature.Weldon was still with me ten yearslater at Brandeis as I realized thatPavlov must have liked his dogsenough to name them. Thisseemed like an interesting piece ofscientific history, in spite of themore high-minded use I hadconcocted for the dogs’ names.

As mentioned above, my ownliterature search uncovered onlyBierka. So, I wrote my colleague,

Ivan Balaban, at the Institute ofHigher Nervous Activity in Moscowin 1988 to see if he could dig upany more ‘bones’ among Pavlov’soriginal papers. From PavlovianWednesdays. Isd. Akad. Nauk.,Moscow (1949) vII (protocols of1933–34years) Balaban uncovered21 names of Pavlov’s dogs. Two ofthe four memory mutants identifiedfrom the Brandeis screen werethen appropriately christened,nalyot and golovan [14,15]. Fourmemory mutants, however, werenot enough. For an emergent,behavioral process like memoryformation, many genes are likely tobe involved, clearly dictating moremutant screening and, accordingly,the likely need for more dognames.

I had just moved to Cold SpringHarbor Laboratory in the Fall of1991 with high hopes ofmarshalling the resources for alarge-scale mutant screen, when Iwas invited by Elena Savvateeva(now head of the Laboratory ofNeurogenetics) and NicholasKamyshev (now head of theLaboratory of ComparativeBehavioral Genetics) to lecture atthe Pavlov Institute in Koltushi. Iaccepted with relish, knowing thatsuch a trip may be my last chance

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Ten of the more photogenic of Pavlov's dogs. Krasavietz (upper left), Beck, Milkah, Ikar, Joy, Tungus, Arleekin, Ruslan, Toi andMurashka (bottom right). The rest of Pavlov's dogs and their corresponding Drosophila memory mutants can be found on the author'swebpage at www.cshl.org.

to find more of Pavlov’s dogs. Thetrip into the recently dissolvedSoviet Empire was a study incontrasts. While the physicalcondition of St. Petersburg waspitiful, my local colleagues wereexcited by the real prospects ofnew Western contacts. Travel wasslow and tiring; I drank the waterwithout thinking...

Elena and Nicholas werewonderful hosts. I stayed withElena and her mother, ProfessorDr. Valentina Ponomarenko, whothen was Head of Nicholas’Laboratory. After watching thetroubled look grow on my faceover the first few days, shepersonally boiled my drinkingwater ‘properly’. Valentinamothered me back to good healthand spirits. Elena introduced me toall their colleagues. She patientlyexplained my mission repeatedlyto the Director of the PavlovInstitute, Dr. Professor VladimirGovyrin, to the Director of Pavlov’sMuseum in Koltushi, Dr. ValeryBolondinsky, and to countlessother colleagues. I rummaged allday. Each night, Nicholas and hisichthyologist friend, VictorKryuchkov, helped me medicatemy daily pining for the lost dogs.The volume of warm collegialitygently helped me to accept thefact that my search had failed.

I resigned myself to sightseeingand spent three full days in theHermitage, easily the mostimpressive collection of art andsculpture I’ve seen. I saw theWinter Palace, the Summer Palaceand every other major piece of

architecture in St. Petersburg.Then, on the last day of my visit,Elena asked if I might like a privatetour of Pavlov’s home —Apartment #11, 7th Line onVasilievsky Island. I was tired oftouring and really didn’t want togo, but I had to be polite. To myeye, the place was run down. Thecurator, Dr. Nonna Volkova, was apleasant, attractive woman,however, and insisted withreligious fervor that everything —even the pen on his desk — hasbeen left exactly as the day Pavlovdied. Clearly, this place was notvisited often; Nonna moved slowlythrough those few rooms. Timecrawled. At some point during aspacey nod at a painting on thewall, I heard Elena explain mymission to Nonna. “Well”, shereplied, “if you want to hear aboutPavlov’s dogs, we can sit down tosome tea and biscuits after thetour!” Time stopped.

Eventually, we did sit down atthe kitchen table. Nonna made teaand laid out our biscuits. Then,without a word, she went to a hallcabinet, pulled out a photo albumand handed it to me. Inside werephotographs of Pavlov’s dogs.Forty of them, with Russian namesinscribed below! In response to myjaw-flapping silence, Nonnahappily remarked that Pavlov’sstudents gave him this photoalbum on his 83rd birthday. Icouldn’t believe what I was lookingat. I hugged Nonna more thanonce, explaining how these dogswould become a piece of scientifichistory. She was fascinated that Imight find Drosophila genesinvolved with Pavlovian memory.As I carefully snapped pictures,she came to understand that thesemotley dogs were a caninetreasure to me. Then, Nonna didsomething unforgettable. She letme wear Pavlov’s evening tophat— knowing perhaps that I wouldbe inspired to tell the storysomeday. I was.

References1. Dubnau, J., Chiang, A.-S., Grady, L.,

Barditch, J., Gossweiler, S., McNeil,J., Smith, P., Buldoc, F., Scott, R.,Certa, U. et al. (2003). Thestaufen/pumilio pathway is involvedin Drosophila long-term memory.Curr. Biol., this issue.

2. Quinn, W.G., Harris, W.A. andBenzer, S. (1974). Conditioned

behavior in Drosophilamelanogaster. Proc. Natl. Acad. Sci.U.S.A. 71, 707–712.

3. Tully, T. (1984). Drosophila learning:behavior and biochemistry. Behav.Genet. 14, 527–557.

4. Dudai, Y., Jan, Y.-N., Byers, D.,Quinn, W. and Benzer, S. (1976).dunce, a mutant of Drosophilamelanogaster deficient in learning.Proc. Natl. Acad. Sci. U.S.A. 73,1684–1688.

5. Quinn, W., Sziber, P.P. and Booker,R. (1979). The Drosophila memorymutant amnesiac. Nature 277,212–214.

6. Pavlov, I.P. (1927). Conditionedreflexes. (Dover, New York).

7. Toma, D.P., White, K.P., Hirsch, J.and Greenspan, R.J. (2002).Identification of genes involved inDrosophila melanogaster geotaxis,a complex behavioral trait. Nat.Genet. 31, 349–353.

8. Tully, T. (2003). Geotaxis: It’s not upor down but full-circle. TrendsGenet., in press.

9. Tully, T., Zawistowski, S.L. andHirsch, J. (1982). Behavior-geneticanalysis of Phormia regina: III. aphenotypic correlation between thecentral excitatory state (CES) andconditioning remains in replicatedF2 generations of hybrid crosses.Behav. Genet. 12, 181–191.

10. Tully, T. and Hirsch, J. (1983). Twononassociative components of theproboscis extension reflex in theblow fly, Phormia regina, which mayaffect measures of conditioning andof the central excitatory state.Behav. Neurosci. 97, 145–153.

11. McGuire, T.R. and Tully, T. (1987).Characterization of genes involvedwith classical conditioning thatproduces differences betweenbidirectionally selected strains ofthe blow fly Phormia regina. Behav.Genet. 17, 97–107.

12. Tully, T. and Quinn, W.G. (1985).Classical Conditioning and retentionin normal and mutant Drosophilamelanogaster. J. Comp. Physiol.157, 263–277.

13. Dubnau, J. and Tully, T. (1998).Gene discovery in Drosophila: newinsights for learning and memory.Annu. Rev. Neurosci. 21, 407–444.

14. DeZazzo, J., Sandstrom, D.,deBelle, S., Velinzon, K., Smith, P.,Grady, L., DelVecchio, M.,Ramaswami, M. and Tully, T. (2000).nalyot, a mutation of the Drosophilamyb-related Adf1 transcriptionfactor, disrupts synapse formationand olfactory memory. Neuron 27,145-158.

15. Tully, T., Bolwig, G., Christensen, J.,Connolly, J., DelVecchio, M.,DeZazzo, J., Dubnau, J., Pinto, S.,Regulski, M., Svedberg, B. et al.(1996). A return to geneticdissection of memory in Drosophila.Cold Spring Harb. Symp. Quant.Biol. 61, 207–218.

Cold Spring Harbor Laboratory, 1Bungtown Road, Cold Spring Harbor,New York 11724, USA.E-mail: [email protected]

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The author in Pavlov’s flat, wearing thefamous psychologist’s top hat. Thephoto on the table is of the man himself.