Age-dependent modulation of short-term neuronal dynamics in the dorsal and ventral rat hippocampus

Brain aging is associated with alterations in the behavioral capacity to process information, due to mechanisms that are still largely unclear. Short-term neuronal activity dynamics are basic properties of local brain networks profoundly involved in neural information processing. In this study, we investigated the properties of short-term changes in excitatory synaptic transmission and neuronal excitation in the CA1 field of dorsal and ventral hippocampal slices from young adult and old rats. We found that short-term synaptic plasticity (i.e. short-term dynamics of input to CA1 circuit) does not significantly differ between young and old dorsal or ventral hippocampus. However, short-term dynamics of hippocampal output differ markedly between young and old rats. Notably, age-dependent alterations in short-term neuronal dynamics were detected mainly in the dorsal hippocampus. Thus, the dorsal hippocampus of young rats can detect and facilitate transmission of 1-30 Hz input and depress transmission of higher-frequency input. In contrast, the old dorsal hippocampus appears unable to transmit information in a frequency-dependent discriminatory manner. Furthermore, the amplification of steady-state output at frequencies < 40 Hz is considerably lower in the old than the young dorsal hippocampus. The old ventral hippocampus did not show major alterations in short-term processing of neural information, though under conditions of intense afferent activation, neuronal output of the ventral hippocampus is depressed at steady-state more in old than in young rats. These results suggest that aging is accompanied by alterations in neural information processing mainly in the dorsal hippocampus, which displays a narrower dynamic range of frequency-dependent transient changes in neuronal activity in old compared with young adult rats. These alterations in short-term dynamics may relate to deficits in processing ongoing activity seen in old individuals.