The influence of developmental period of aluminum exposure on synaptic plasticity in the adult rat dentate gyrus in vivo.

Previous studies from our group have demonstrated that chronic aluminum exposure from parturition throughout life impairs both long-term potentiation (LTP) and long-term depression (LTD) of the excitatory postsynaptic potential (EPSP) slope and reduces the population spike (PS) amplitude in the rat dentate gyrus in vivo. The present study sought to extend these findings by evaluating the developmental periods critical for aluminum-induced impairment of synaptic plasticity. Rats were exposed to aluminum (gestational, lactational and postlactational) through drinking 0.3% aluminum chloride in water over different developmental intervals: (1) prenatal exposure; (2) beginning from birth and terminating at weaning; (3) beginning at weaning throughout life; (4) beginning at birth and continuing throughout life. As adults (postnatal day 80-100), field potentials were measured in the dentate gyrus of hippocampus in response to stimulation applied to the lateral perforant path. The results showed: (1) Prenatal aluminum exposure had no effect on the magnitude of LTP as measured by the EPSP slope and LTD as measured for the PS amplitude, while it had a small effect on the magnitude of LTP as measured for the PS amplitude and LTD as measured by the EPSP slope. (2) Lactational, postlactational and throughout life exposure to aluminum impaired both LTP and LTD of the EPSP slope and PS amplitude, except that LTD of PS amplitude was not significantly changed in animals postlactationally exposed. (3) Aluminum exposure from parturition throughout life caused the greatest impairment of the range of synaptic plasticity, while prenatal aluminum exposure caused the least. From these results we conclude that the lactational period was the most susceptible to aluminum-induced impairment of synaptic plasticity and that chronic aluminum exposure from parturition throughout life is extremely disruptive to synaptic plasticity and should be avoided.