Hippocampal CA 1 pyramidal neurons in brain slices provide an ideal model system for studying drug effects on synaptic transmission. Intact synaptic pathways and interneuron circuits can be preserved in thin slices (0.4 to 0.5 mm) of brain tissue which remain viable and physiologically stable.

Brain slice circuitry for the CA1 area is shown below, note the trisynaptic pathway (pp to DG, mf to CA3 and sc to CA1) and synaptic circuit loop (pp to CA1 directly, and indirectly via DG and CA3):


Hippocampal Slice

Synaptic circuits in the hippocampus are known to process signals related to sensory/motor integration and planning - Bland, learning and memory formation - Buzsaki, and form an important hub within the Brain's Limbic System.  

In the illustration above, projection neurons and main synaptic pathways are shown in black, inhibitory interneuron colors represent cells that function in concert (red) vs  cells that belong to different inhibitory classes.  By activating the appropriate interneuron class, an input can selectively control large groups of projection cells.  Thus interneurons can gate or index groups of projection neurons, like CA1 pyramidal cells, so that subpopulations of CA1 cells can be synchronously active during theta and/or gamma frequency EEG oscillations.  EEG synchronization provides timing specificity for circuit level memory formation, such as LTP - Nicoll, and spike timing-dependent plasticity - Poo.

Abbreviations: CA1 - cornu ammonis region # 1 of the hippocampal formation; STIM - stimulating electrode used to activate excitatory and inhibitory inputs to CA1 neurons; RECORD - recording electrode to measure pyramidal neuron response to stimulation; a/c - association/commissural input pathways from
septum, hypothalamus and contralateral hippocampus; alv - alveus, CA1 output axons to cortex; sc - Schaffer collateral pathway from CA3 neurons; mf - mossy fiber pathway from dentate gyrus (DG) granule neurons; pp - perforant path axons from entorhinal cortex; fim - fimbria pathway to and from midbrain and other regions.

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