Background: A single infusion of ketamine has rapid antidepressant properties, although the drawback is a lack of sustained effect. A previous study showed a rapid enhancement (within 2 hours) in ventral tegmental area (VTA) dopamine (DA) neuron population and locus coeruleus (LC) norepinephrine (NE) firing and bursting activity following a single ketamine administration. The current study investigated whether these changes are present 24 hours after a single administration and if they are maintained with repeated administration. Additionally, we examined dorsal raphe nucleus (DRN) serotonin (5-HT) neurons to assess the effects of single and repeated ketamine administration on these neurons. Methods: Ketamine (10 mg/kg, i.p.) was administered to male Sprague Dawley rats once or repeatedly (3 times/week) for 2 weeks. After single and repeated administration of ketamine, electrophysiological recordings were done in the VTA, LC and DRN in anesthetized rats, 24 hrs, 3 or 7 days post-administration. Spike frequency, bursting, and for VTA neurons, spontaneously active neurons/trajectory were assessed. Results: In the VTA, LC and DRN, 24 hrs after ketamine was injected acutely there was no significant difference between controls and treated animals in all parameters assessed. However, after repeated administration, there was an increase in bursting and number of spontaneously discharging neurons per tract of VTA DA neurons as well as an increase in frequency of discharge of LC NE neurons. While the increased number of spontaneously discharging neurons per tract had dissipated after 3 days, the enhanced bursting was still present but dissipated after 7 days. As for LC NE neurons, the increased frequency of discharge was no longer present after 3 days. No significant differences in the firing of DRN 5-HT neurons were observed between controls and treated animals even after ketamine was administered repeatedly. Conclusion: These results indicate that repeated but not acute administration of ketamine maintained the increase in population activity of DA neurons and firing activity of NE neurons.

Ungefär 20% av befolkningen uppfyller kriterier för läs- och skrivsvårigheter. För att kunna hjälpa elever som uppvisar svårigheter av denna typ behövs reliabla och valida testinstrument. LäSt är ett normerat svenskt lästest som är väl använt på nationell basis i syfte att mäta barns förmåga till ordavkodning. Avkodning innefattar en koppling mellan enskilda bokstäver och ord till deras korrekta språkljud vid uttal, och utgör således en central teknisk del av läsning. Evidens finns för att olika typer av psykologiska test, däribland lästest, uppvisar en igenkänningseffekt varigenom elevers prestation på dessa test ökar till följd av upprepad administrering. Syftet med den aktuella studien är att undersöka huruvida LäSt uppvisar en igenkänningseffekt vid upprepad administrering till ett urval av elever i årskurs 4 och 6.  Sammanlagt deltog 92 elever från 4 skolor i Sverige. De genomförde LäSt vid tre separata tillfällen under ett tidsintervall på 8 veckor. Testning 1 skedde vid vecka 1, testning 2 skedde vid vecka 2, och testning 3 skedde vid vecka 8.  En signifikant igenkänningseffekt hittades som tyder på att elevers resultat på LäSt förbättrades över tid. Det fanns ingen skillnad i igenkänning mellan pojkar och flickor, elever i årskurs 4 och årskurs 6, eller enspråkiga och flerspråkiga elever. En signifikant skillnad i igenkänning fanns mellan de elever som hade allra lägst avkodningsförmåga (poor decoders)och de elever som hade en mycket hög avkodningsförmåga (good decoders). Poor decoders uppvisade en starkare igenkänning på deltestet ord än good decoders. Ingen sådan effekt fanns för deltestet non-ord.  Dessa resultat indikerar att elevers prestation på LäSt kan förbättras över tid till följd av igenkänning av testmaterialet. Detta påverkar hur man bör tolka individers resultatutveckling vid upprepad testning och hur ofta det är lämpligt att använda LäSt på en och samma elev. Dessa resultat och deras implikationer diskuteras i relation till tidigare forskning. / Approximately 20% of the population suffer from a reading- or writing disability. In order to aid students with such disabilities reliable and valid reading tests are warranted. LäSt is a Swedish standardised reading test currently well-used nationally to measure children’s ability to decode words. Decoding encompasses the making of connections between single letters and words and their correct sounds, and therefore constitutes a central technical aspect of reading. There is evidence to show that some common psychological tests, including reading tests, display a retest-effect, whereby individual’s results increase over time as a result of repeated test administration. The aim of the current study is to investigate whether such a retest-effect is pronounced when LäSt is repeatedly administered to a sample of students in year 4 and 6.  In sum, 92 students from 4 different schools in Sweden took part in the study. They completed LäSt at three separate times during a time interval of 8 weeks. Testing 1 was completed in the first week, testing 2 was completed in the second week, and testing 3 was completed in the eight week.  A significant retest-effect was found indicating that students’ results on LäSt increased with each administration. There was no difference in retest-effect between boys and girls, students in year 4 and year 6, or monolingual and multilingual students. A significant difference emerged between students who had a very low word decoding ability (poor decoders) and those who had a very high word decoding ability (good decoders). Poor decoders showcased a stronger retest-effect on the sub-test Words than good decoders. No such effect was found for the sub-test Non-words.  The current results indicate that repeated testing with LäSt yields improved results over time due to familiarity. These findings have implications for how one should interpret students’ test scores over time, as well as how often LäSt should be administered. The findings and their implications are further discussed in relation to previous research.