Functional interconnections between CA3 and the dentate gyrus revealed by current source density analysis

Area of Science:

• Neuroscience
• Neurophysiology

Background:

• The hippocampus, particularly the CA3 region and dentate gyrus (DG), plays a crucial role in memory formation and processing.
• Understanding the intricate physiological interactions between hippocampal subfields is essential for deciphering neural circuit function.

Purpose of the Study:

• To quantitatively investigate the physiological interactions between the CA3 region and the dentate gyrus (DG) in vivo.
• To elucidate the pathways and mechanisms underlying excitatory feedback from CA3 to DG.

Main Methods:

• Field potential recording and current source density (CSD) analysis in urethane-anesthetized rats.
• Pharmacological manipulations using non-N-methyl-D-aspartate and GABA(A) receptor antagonists.
• Stimulation of CA3b and perforant path with varying timing and intensity.

Main Results:

• CA3b stimulation induced short-latency antidromic spikes in DG and CA3c, with excitation in the DG's inner molecular layer (IML) likely from CA3 or hilar projections.
• Non-N-methyl-D-aspartate receptors mediated IML and CA3c dendritic excitations, while GABA(A) receptor blockade unmasked CA3b-evoked bursts.
• A late excitation in the DG's middle molecular layer (MML) was observed after CA3 stimulation, originating from the medial entorhinal cortex.

Conclusions:

• CA3 provides an early excitatory feedback to the DG via recurrent collaterals or hilar interneurons.
• A late excitatory feedback pathway from CA3 to DG exists, mediated by the medial entorhinal cortex.
• CSD analysis in vivo provides a quantitative method to study hippocampal network interactions.