Information storage in the brain is a temporally graded process involving different memory types or phases. It has been assumed for over a century that one or more short-term memory (STM) processes are involved in processing new information while long-term memory (LTM) is being formed. Because brain-derived neutrophic factor (BDNF) modulates both short-term synaptic function and activity-dependent synaptic plasticity in the adult hippocampus, we examined the role of BDNF in STM and LTM formation of a hippocampal-dependent one-trial fear-motivated learning task in rats. Using a competitive RT-PCR quantitation method, we found that inhibitory avoidance training is associated with a rapid and transient increase in BDNF mRNA expression in the hippocampus. Bilateral infusions of function-blocking anti-BDNF antibody into the CA, region of the dorsal hippocampus decreased extracellular signal-regulated kinase 2 (ERK2) activation and impaired STM retention scores. Inhibition of ERK1/2 activation by PD098059 produced similar effects. In contrast, intrahippocampal administration of recombinant human BDNF increased ERK1/2 activation and facilitated STM. The infusion of anti-BDNF antibody impaired LTM when given 15 min before or 1 and 4 hr after training, but not at 0 or 6 hr posttraining, indicating that two hippocampal BDNF-sensitive time windows are critical for LTM formation. At the same time points, PD098059 produced no LTM deficits. Thus, our results indicate that endogenous BDNF is required for both STM and LTM formation of an inhibitory avoidance learning. Additionally, they suggest that this requirement involves ERK1/2-dependent and -independent mechanisms.

It has been recently demonstrated that ubiquitin-proteasome-mediated proteolysis is required for long-term synaptic facilitation in Aplysia. Here we show that the hippocampal blockade of this proteolytic pathway is also required for the formation of long-term memory in the rat. Bilateral infusion of lactacystin, a specific proteasome inhibitor, to the CA1 region caused full retrograde amnesia for a one-trial inhibitory avoidance learning when given 1, 4 or 7h, but not 10 h, after training. Proteasome inhibitor I produced similar effects. In addition, inhibitory avoidance training resulted in an increased ubiquitination and 26S proteasome proteolytic activity and a decrease in the levels of IkappaB, a substrate of the ubiquitin-proteasome cascade, in hippocampus 4 h after training. Together, these findings indicate that the ubiquitin-proteasome cascade is crucial for the establishment of LTM in the behaving animal.

Nature © Macmillan Publishers Ltd 19988 T he formation of long-term memory takes several hours 1-3 , during which time memories rely on short-term systems 1,2,4,5 . For over 100 years 1 , the main unanswered question of memory research has been whether short-term memory is a necessary step towards long-term memory 4,5 , or whether they are separate processes 1,2 . Here we report four treatments that block shortterm memory while leaving long-term memory intact, showing that these memory systems are separate to some degree.The treatments we used here all alter longterm memory when infused into the CA1 subregion of the hippocampus or the entorhinal cortex of rats that have been trained to perform certain behaviours 6-8 . These treatments were the glutamate AMPA (Ȋ-amino-3hydroxy-5-methyl-4-isoxazole propionic acid) receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 0.5 Ȗg), the GABA A (ȍ-aminobutyric acid type A) receptor agonist muscimol (MUS, 0.5Ȗg), the serotonin 1A receptor agonist 8-hydroxy-2-(di-npropylamino) tetralin (DPAT, 2.5 Ȗg) and the serotonin 1A receptor antagonist 1-(2methoxyphenyl)-4-(4-(2-phthalimido)) butylpiperazine (NAN, 2.5 Ȗg).We implanted 30-gauge guides bilaterally 1 mm above the dorsal CA1 region of the hippocampus (A ǁ4.3, L DŽ4.0, V 3.4) or 1 mm above the surface of the entorhinal cortex (A ǁ7.0, L DŽ5.0, V 8.4) of Wistar rats (240-300 g) under deep thionembutal anaesthesia; stereotaxic coordinates are given in millimetres according to ref. 9. After recovery, the rats were placed on a platform that was 25 cm high and 7 cm wide. This platform faced a 43 ǂ25 cm grid of stainless steel bars, spaced 1.0 cm apart and of 0.1 cm in width. The platform was used for inhibitory avoidance training. We measured how quickly the rats stepped down onto the grid with all four paws. Once on the grid, the rats received a scrambled electric shock to their paws of 0.3 mA for 1 second. They immediately received bilateral infusions of 0.5 Ȗl saline, a vehicle (20% dimethylsulphoxide) or a drug. MUS and DPAT were dissolved in saline, and CNQX and NAN were dissolved in the vehicle. Infusion cannulae protruded 1.0 mm beyond the guides. Infusion procedures and verification of cannula placement were performed as described 6-8 .There were two main experiments. In the first, animals were tested twice to see whether they had retained the memory of the electric shock: once at 1.5 hours after training, to measure short-term memory, and once at 24 hours after training, to measure longterm memory (Fig. 1a, b). In the second experiment, we tested the animals 1.5, 3.0 and 4.5 hours after training (Fig. 1c, d). Test sessions for both experiments were as above, except that the foot-shock was omitted (so we were measuring how long it took for rats to step down to the grid, and we used this time as a measurement of their memory of the shock). We stopped measuring the time taken to step down to the grid after 180 seconds 6-8 . This required the use of nonparametric statistics 7,8 .When given into the CA1 subregion of t...

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Pentylenetetrazole (PTZ) is a common convulsant agent used in animal models to investigate the mechanisms of seizures. Although adult zebrafish have been recently used to study epileptic seizures, a thorough characterization of the PTZ-induced seizures in this animal model is missing. The goal of this study was to perform a detailed temporal behavior profile characterization of PTZ-induced seizure in adult zebrafish. The behavioral profile during 20 min of PTZ immersion (5, 7.5, 10, and 15 mM) was characterized by stages defined as scores: (0) short swim, (1) increased swimming activity and high frequency of opercular movement, (2) erratic movements, (3) circular movements, (4) clonic seizure-like behavior, (5) fall to the bottom of the tank and tonic seizure-like behavior, (6) death. Animals exposed to distinct PTZ concentrations presented different seizure profiles, intensities and latencies to reach all scores. Only animals immersed into 15 mM PTZ showed an increased time to return to the normal behavior (score 0), after exposure. Total mortality rate at 10 and 15 mM were 33% and 50%, respectively. Considering all behavioral parameters, 5, 7.5, 10, and 15 mM PTZ, induced seizures with low, intermediate, and high severity, respectively. Pretreatment with diazepam (DZP) significantly attenuated seizure severity. Finally, the brain PTZ levels in adult zebrafish immersed into the chemoconvulsant solution at 5 and 10 mM were comparable to those described for the rodent model, with a peak after a 20-min of exposure. The PTZ brain levels observed after 2.5-min PTZ exposure and after 60-min removal from exposure were similar. Altogether, our results showed a detailed temporal behavioral characterization of a PTZ epileptic seizure model in adult zebrafish. These behavioral analyses and the simple method for PTZ quantification could be considered as important tools for future investigations and translational research.