The Basic Properties Of The Rat EC Superficial Layers Main Neurons

Memory can be divided into non-hippocampus and hippocampus-dependent memory,in which hippocampal loop plays a crucial role. The entorhinal cortex (EC) has beenconsidered to be the hippocampal input and output relay station working as a bidirectionaltransmission of information gateway between higher cortical areas and the hippocampus.Stellate and pyramidal neurons are the principal neurons in the superficial layers of the EC.Sensory information from various cortical areas converges onto neurons in the superficiallayers (layers II/III) of the EC, which then project directly to all subregions of thehippocampus. The EC is one of the structures essential for the spatial learning and memory.Due to the key position in cortico-hippocampal circuits, it plays an active role in interfacingspatial information between the neocortex and the hippocampus. Therefore,in the presentstudy, we systematically investigated the basic electrophysiological properties of ECsuperficial pyramidal neurons and stellate neurons, which might help us to understand theirroles in the process of space learning and memory.These studies will lay a good foundationto investigate the neural mechanism underlying the narcotic drugs-induced impairment inlearning and memory in the central nervous system.In the present study, we performed Golgi staining and in vitro brain slice patch-clamprecording to illustrate the morphological and electrophysiological properties of pyramidalneurons and stellate neurons in the superficial layers of the EC.Firstly, we observed themorphological characteristics of pyramidal neurons and stellate neurons in the superficiallayers of the EC with the help of Infrared interference contrast (IR-DIC) microscope. Onthis basis, we studied the inner cells composition and fiber connections in the EC by theGolgi silver staining. Finally, by performing the patch-clamp whole-cell recording, weanalyzed the basic electrophysiological properties of pyramidal neurons and stellateneurons in the superficial layers of the EC. These results indicated that the two types ofprincipal neurons in the EC exhibited prominent difference in their morphology andelectrophysiological prosperities. Stellate neurons have a polygonal soma with multiple thick sparsely primary dendrites radiating out from the cell body, but lack a clearlydominant dendrite. Pyramidal neurons have a pyramidal soma with one thick apicaldendrite that runs to the surface of the cortex. The size of the pyramidal neurons isremarkably smaller than stellate neurons.In vitro whole-cell patch clamp recording, we found stellate and pyramidal neuronshave similar resting membrane potential, while the pyramidal neurons have higher neuronalexcitability in response to depolarizing current stimuli. This difference might result fromthe stellate and pyramidal neurons expressing distinct high-voltage activation calciumchannel density. This finding might also partially explain why the pyramidal neurons arepreferentially degenerated in the epileptic patients. Compared to the pyramidal neurons,stellate neurons exhibited bigger depolarizing voltage sags in response to hyperpolarizingcurrent pulses and had larger hyperpolarization activated currents in voltage-clamprecordings.This electrophysiological difference is attributed to stellate neurons expressing ahigh level of HCN channels at their somata, while in pyramidal neurons HCN channels aremainly expressed at the distal dendrites.