The Journal of Neuroscience, November 15, 2002, 22(22):9972-9979
Propagation of Neuronal Activity along the
Neocortical-Perirhinal-Entorhinal Pathway in the Guinea Pig
Gerardo
Biella,
Laura
Uva, and
Marco
de Curtis
Department of Experimental Neurophysiology, Istituto Nazionale
Neurologico, 20133 Milan, Italy
The study of synaptic interactions within the parahippocampal
region is crucial to understand the integrative functions performed by
this region during memory information processing. Despite the extensive
anatomical studies, the intrinsic physiology of the parahippocampal
area has been poorly investigated. We describe here the organization
pattern of the synaptic network formed by the temporal neocortex, areas
36 and 35 of the perirhinal cortex (PRC) and the entorhinal cortex
(EC), in the in vitro isolated guinea-pig brain. Current
source density analysis of laminar field potential profiles was
performed with multichannel silicon probes positioned in different
parahippocampal subfields. Stimulation of the temporal neocortex
induced monosynaptic and polysynaptic potentials in areas 35 and 36, respectively. Area 36 stimulation evoked monosynaptic responses within
areas 36 and 35. Stimuli in area 35 induced responses that propagated
longitudinally along area 35 itself. No local field responses were
observed in the EC after stimulation of both neocortex and areas 35/36.
Despite the absence of a local extracellular response, intracellular
recordings demonstrated that subpopulations of superficial layer
neurons in medial and lateral EC showed polysynaptic EPSPs after
stimulation of area 35 and area 36.
The results demonstrate that the propagation of neuronal activity
across the rhinal sulcus in the direction from the PRC to the EC is
finely and diffusely distributed. In agreement with previous reports,
these findings suggest that the PRC-EC pathway is highly regulated by
inhibitory network interactions.
Key words:
current source density; entorhinal cortex; isolated
guinea pig brain preparation; parahippocampal region; perirhinal
cortex; neocortex
Copyright © 2002 Society for Neuroscience 0270-6474/02/22229972-08$05.00/0
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