Effect Of Age-dependent Balance Of Excitatory And Inhibitory Input On LTD In The CA1 Region Of Rat Hippocampus

Hippocampus is an important brain region in the central nervous system which is closely related to many kinds of brain functions such as learning and memory. Some psychological disorders such as Alzheimer, Parkinson, schizophrenia, drug addiction are associated with the hippocampal malfunction. The dynamic balance of excitatory and inhibitory efficacy in the brain underlies the normal function, which are also the therapeutic target of psychological disorders. Thus, it is important to study the balance of excitation and inhibition in hippocampus for understanding the information processing in the brain and developing the new ways to teat mental diseases.Glutamate and gamma aminobutyric acid are the major excitatory and inhibitory neurotransmitters in the brain respectively. The homestasis of neural network excitability is determined by these two inputs. The outcome of a neuron is decided by the temporal and spatial input of glutamergic input and GABAergic input. The precisely modulated balance contributes significantly to the information processing.Synaptic plasticity putatively underlies learning and memory. Glutamergic and GABAergic systems both express synaptic plasticity with different induction and expression mechanism. Thus it is possible that the induction of synaptic plasticity would result in the change of balance between excitatory and inhibitory input. Protein expression is age dependent in both excitatory and inhibitory system in the brain. Even in the same age, the same stimuli induced different form of synaptic plasticity in excitatory and inhibitory systems, which suggest the change of balance in the neuronal network. But it is still not clear how these change of balance influence subsequent synaptic plasticity in development.Long term depression (LTD), one form of synaptic plasticity, not only involves in learning and memory, but also involves in several kinds of brain disorders.In this study, we tested the effects of dis-balance on the induction and maitainence of LTD in Schaffer collateral pathway in rat hippocampal CA1 area by blockade of GABAA receptor with picrotoxin.The major results were as follows:(1)The amplitude of LTD in rat hippocampal CA1 area had the features of age dependency. The amplitude of LTD in adult rats was higher than those in new born and young rats.(2)Picrotoxin applied after LFS did not affect LTD maintainence in the three age groups, whereas Picrotoxin applied before LFS blocked the induction of LTD in adult rats.(3)In this experiment, LTD was not dependent on NMDA receptors in all three age groups.We found the effect of the changed balance between excitatory and inhibitory input on LTD was age dependent, which suggested that unsynchronized excitatory and inhibitory system during development process might regulate synaptic plasticity, learning and memory.