Abstract
BackgroundThe hippocampus is a functionally heterogeneous brain structure and specializations of the intrinsic neuronal network may crucially support the functional segregation along the longitudinal axis of the hippocampus. Short-term synaptic plasticity plays fundamental roles in information processing and may be importantly involved in diversifying the properties of local neuronal network along the hippocampus long axis. Therefore, we aimed to examine the properties of the cornu ammonis 1 (CA1) synapses along the entire dorsoventral axis of the rat hippocampus using field excitatory postsynaptic potentials from transverse rat hippocampal slices and a frequency stimulation paradigm.ResultsApplying a ten-pulse stimulus train at frequencies from 0.1 to 100 Hz to the Schaffer collaterals we found a gradually diversified pattern of frequency-dependent synaptic effects along the dorsoventral hippocampus axis. The first conditioned response was facilitated along the whole hippocampus for stimulus frequencies 10–40 Hz. However, steady-state responses or averaged responses generally ranged from maximum synaptic facilitation in the most dorsal segment of the hippocampus to maximum synaptic depression in the most ventral segment of the hippocampus. In particular, dorsal synapses facilitated for stimulus frequency up to 50 Hz while they depressed at higher frequencies (75–100 Hz). Facilitation at dorsal synapses was maximal at stimulus frequency of 20 Hz. On the contrary, the most ventral synapses showed depression regardless of the stimulus frequency, only displaying a transient facilitation at the beginning of 10–50 Hz stimulation. Importantly, the synapses in the medial hippocampus displayed a transitory behavior. Finally, as a whole the hippocampal synapses maximally facilitated at 20 Hz and increasingly depressed at 50–100 Hz.ConclusionThe short-term synaptic dynamics change gradually along the hippocampal long axis in a frequency-dependent fashion conveying distinct properties of information processing to successive segments of the structure, thereby crucially supporting functional segregation along the dorsoventral axis of the hippocampus.
Highlights
The hippocampus is a functionally heterogeneous brain structure and specializations of the intrinsic neuronal network may crucially support the functional segregation along the longitudinal axis of the hippocampus
Short‐term synaptic plasticity along the whole hippocampus dorsoventral axis We recorded field excitatory postsynaptic potentials (fEPSP) from one hundred seventeen slices prepared from the hippocampi of ten rats
Stimulation applied at frequencies 1–40 Hz induced synaptic facilitation that was higher at the dorsal segment of the hippocampus and declined gradually along the dorsoventral axis eventually turning into synaptic depression at most ventral parts; stimulation at 0.1 Hz did not produce any Position Slices Rats
Summary
The hippocampus is a functionally heterogeneous brain structure and specializations of the intrinsic neuronal network may crucially support the functional segregation along the longitudinal axis of the hippocampus. Short-term synaptic plasticity plays fundamental roles in information processing and may be importantly involved in diversifying the properties of local neuronal network along the hippocampus long axis. The hippocampus is an elongated functionally heterogeneous brain structure in which different functions have been ascribed to discrete segments along its longitudinal axis [1,2,3] The ability of synapses to undergo lasting changes in their effectiveness [9, 10] is thought to play fundamental roles in brain functions and behavior [11, 12] and is importantly involved in information processing in the hippocampus [13]. In addition to long-term plasticity, hippocampal synapses display a large variety of short-term plasticity phenomena [21], which constitute transient forms of activitydependent variations of the synaptic efficacy [22,23,24]
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