NEONATAL IONIZING RADIATION: EFFECTS ON SHORT- AND LONG-TERM HIPPOCAMPAL-RELATED MEMORY

L. G. CÁCERES; L. R. GUELMAN

San Diego., CA, USA

Congreso; 37th Annual Meeting of the Society for Neuroscience (SFN); 2007

Society for Neuroscience (SFN)

Neonatal ionizing radiation: effects on short- and long-term hippocampal-related memory L. G. Cáceres and L. R. Guelman 1ª Cátedra de Farmacología, Facultad de Medicina, UBA and CONICET, Buenos Aires, Argentina. Email: lguelman@fmed.uba.ar   Developing Central Nervous System (CNS) is vulnerable to ionizing radiation damage, being hippocampus (HIP) sensitive to it. The aim of the present work was to test if this radiosensitivity can affect short and long term hippocampal memory. Neonatal rats were X-irradiated (5 Gy) in their cephalic ends up to 48hs of postnatal life and the Passive Avoidance test (PA) was used at 30 postnatal day. The animals were separated in three groups, depending on the time of testing: 1h (G1), 24hs (G2) and both (G3). 24 hs after the habituation period, animals were exposed to a 2 sec, 1,2 mA electric footshock and returned to their home cages. At 1 h and/or 24 hs after the shock, animals were re-exposed to the apparatus to test the retention of the memory. Only the irradiated animals from G2 showed an impairment in PA test, with minor latency to enter the dark compartment than control animals (rate T2/T1: C= 44.5 ± 7.74; Rx= 2.94 ± 0.64, p< 0.05). No differences between irradiated and control animals of G1 and G3 groups were observed in the T2/T1 rate. Interestingly, the irradiated animals from G3 (exposed both at 1 and 24hs after training and tested for retention at 24 hs) improved their performance when compared with the irradiated animals from G2 (exposed and tested for retention only at 24hs after training) (rate T2/T1: Rx (G2)= 2.94 ± 0.64; Rx (G3) = 28.26 ± 11.83, p< 0.05). These data suggest that: (1) ionizing radiation damage induces an impairment in the retention of the long-term memory (group G2), while retention tested 1 h after training (short-term memory, group G1) was unaltered (2) in addition, since no differences between irradiated and control animals latencies at the training phase were found, it would be suggested that no alterations in the acquisition phase were induced  by ionizing radiation exposure, and (3) long-term memory can be improved if the animals are exposed to the context both at 1 and 24 hs after training. This additional exposure would facilitate the retention performed 24hs later, attenuating the performance-impairing effect of ionizing radiations, and would reinforce long-term memory that could have been debilitated due to radiation damage.