Investigation of the characteristics of behavioral sensitization in Drosophila melanogaster

Bihevioralna senzitizacija predstavlja neasocijativno učenje u kojem ponovljena administracija stimulansa rezultira progresivnim stepenastim povećanjem odgovora. Bihevioralna senzitizacija kod Drosophile može biti kratkotrajna, i trajati kraće od 30 minuta, ili dugotrajna, do dva dana. Pretpostavlja se da su u njihovoj podlozi različiti molekularni mehanizmi. Cilj rada je bio razvoj visokoprotočne metode za razvoj dugotrajne bihevioralne senzitizacije na psihostimulanse kokain i metamfetamin. Svi testovi provedeni su na mužjacima divljeg tipa (wt) Drosophile melanogaster, na soju Canton S, i mutantima period (per) i timeless (tim), od kojih je per prethodno povezan s razvojem bihevioralne senzitizacije na kokain, dok tim nije. Oralno administrirani metamfetamin kod mušica je izazivao toleranciju, bez obzira na doba dana administracije, koncentraciju ili dužinu trajanja administracije. Nasuprot tome, administracija volatiliziranog kokaina ili metamfetamina dovela je do brzog povećanja lokomotorne aktivnosti koja je bila dozno ovisna (75-1.25μl) i ovisna o dužini trajanja (1-7 minuta). Za administraciju volatiliziranog psihostimulansa razvili smo novu metodu gdje se regulacijom protoka zraka volatilizirana supstanca dostavlja individualnim mušicama u Drosophila Activity Monitoring System-u. Naredni eksperimenti će definirati uvjete za induciranje bihevioralne senzitizacije na kokain i metamfetamin u ovom visokoprotočnom sistemu. Razvijen je i postupak za izazivanje kratkotrajne bihevioralne senzitizacije na mehanički stres. Mušice su izložene početnom jakom mehaničkom stresu (startle, ST), a potom seriji slabijih senzitizirajućih podražaja (SS1-3). Mušice jače reagiraju na SS podražaje ukoliko su prethodno izložene ST, što je u skladu s prethodno publiciranim rezultatima. Per i tim mušice na ST i SS reagiraju poput wt što pokazuje po prvi puta da ti geni nisu uključeni u regulaciju kratkotrajne bihevioralne senzitizacije, i govore u prilog razlike u mehanizmima indukcije kratkotrajne i dugotrajne bihevioralne senzitizacije. Naši rezultati su u skladu s dvoprocesnom teorijom (dual-process theory) plastičnosti odgovora na ponovljenu stimulaciju, autora Groves i Thompson, 1970., koja govori da o jačini i trajanju podražaja ovisi razvoj senzitizacije ili habituacije. Oralna administracija (dugotrajan podražaj slabog intenziteta) izazvala je toleranciju, dok je mehanički stres (kratkotrajan podražaj jakog intenziteta) inducirao razvoj bihevioralne senzitizacije. Karakteristika podražaja dana putem volatiliziranog kokaina zadovoljava uvjete za razvoj bihevioralne senzitizacije što će se provoditi u narednim eksperimentima.Behavioral sensitization represents non-associative learning in which repeated administration of stimulus results in a progressive increase in response. Behavioral sensitization in Drosophila can be short-term (takes less than 30 minutes) or long-term (lasts up to two days). It is assumed that they rely on different molecular mechanisms. The aim of the study was the development of high-throughput method to develop long-term behavioral sensitization to psychostimulants cocaine and methamphetamine. All tests were performed on male wild type (wt) Drosophila melanogaster, of strain Canton S, and mutants period (per) and timeless (tim), of which is per previously associated with the development of behavioral sensitization, while tim is not. Oral administration of methamphetamine in flies induce tolerance, regardless of the day time, concentration or duration of administration. As opposed to that, the administration of volatilized cocaine or methamphetamine led to a rapid increase in locomotor activity which was dose dependent (75-1.25ěl) and time dependent (1 to 7 minute length). For administration of volatilized psychostimulants we have developed a new method where with regulation of airflow volatilized substance is delivered to individual flies in DAMS (Drosophila Activity Monitoring System). The next experiments will define requirements in this high-throughput system for induction of behavioral sensitization to cocaine and methamphetamine. Also, we developed a method for the induction of short-term bihevioral sensitization to mechanical stress. Flies were exposed to an initial strong mechanical stress (startle, ST), and then a series of weaker sensitizing stimulus (SS1-3). Flies are more responsive to the SS stimulus if they were previously treated with ST, which is in accordance with previously published results. On ST and SS per and tim flies react like wt which shows for the first time that these genes are not involved in the regulation of short-term bihevioral sensitization, and indicate the differences in the mechanisms of induction of short and long-term behavioral sensitization. Our results are in line with dual-process theory of plasticity response to repeated stimulation by Groves and Thompson 1970. which tells that development of sensitizaion or habituation depends on the strength and duration of the stimulus. Oral administration (long-terme stimulus od low intensity) caused tolerance, while the mechanical stress (short-term stimulus of high intensity) induced development of behavioraln sensitization. The characteristic of the stimulus given by volatilized cocaine satisfies conditions for the development of behavioral sensitzation which will be implemented in the next experiments