Feedforward inhibition regulates perirhinal transmission of neocortical inputs to the entorhinal cortex: Ultrastructural study in guinea pigs

Aline Pinto, Cesar Fuentes, Denis Paré

Research output: Contribution to journalArticle

38 Citations (Scopus)

Abstract

The rhinal cortices constitute the main route for impulse traffic to and from the hippocampus. Tracing studies have revealed that the perirhinal cortex forms strong reciprocal connections with the neo- and entorhinal cortex (EC). However, physiological investigations indicate that perirhinal transmission of neocortical and EC inputs occurs with a low probability. In search of an explanation for these contradictory findings, we have analyzed synaptic connections in this network by combining injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHAL) into the neocortex, area 36, or area 35 with γ-aminobutyric acid (GABA) immunocytochemistry and electron microscopic observations. Within area 36, neocortical axon terminals formed only asymmetric synapses, usually with GABA-negative spines (87%), and less frequently with GABA-immunopositive (GABA+) dendrites (13%). A similar synaptic distribution was observed within area 35 except that asymmetric synapses onto GABA+ dendrites were more frequent (23% of synapses). Examination of the projections from area 36 to area 35 and from both regions to the EC revealed an even higher incidence of asymmetric synapses onto GABA+ dendrites (35 and 32%, respectively) than what was observed in the neocortical projection to areas 36 and 35. Furthermore, some of the neocortical and perirhinal terminals containing PHAL and GABA immunolabeling formed symmetric synapses onto GABA-negative dendrites in their projection sites (neocortex to area 35, 16%; area 36 to 35, 7%; areas 36-35 to EC, 12%). Taken together, these findings suggest that impulse transmission through the rhinal circuit is subjected to strong inhibitory influences, reconciling anatomical and physiological data about this network.

Original languageEnglish (US)
Pages (from-to)722-734
Number of pages13
JournalJournal of Comparative Neurology
Volume495
Issue number6
DOIs
StatePublished - Apr 10 2006

Fingerprint

Entorhinal Cortex
gamma-Aminobutyric Acid
Guinea Pigs
Synapses
Dendrites
Neocortex
Nose
Aminobutyrates
Presynaptic Terminals
Hippocampus
Spine
Immunohistochemistry
Electrons
Injections
Incidence

All Science Journal Classification (ASJC) codes

  • Neuroscience(all)

Keywords

  • Electron microscopy
  • Entorhinal
  • GABA
  • Interneuron
  • Perirhinal
  • Tract-tracing

Cite this

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title = "Feedforward inhibition regulates perirhinal transmission of neocortical inputs to the entorhinal cortex: Ultrastructural study in guinea pigs",
abstract = "The rhinal cortices constitute the main route for impulse traffic to and from the hippocampus. Tracing studies have revealed that the perirhinal cortex forms strong reciprocal connections with the neo- and entorhinal cortex (EC). However, physiological investigations indicate that perirhinal transmission of neocortical and EC inputs occurs with a low probability. In search of an explanation for these contradictory findings, we have analyzed synaptic connections in this network by combining injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHAL) into the neocortex, area 36, or area 35 with γ-aminobutyric acid (GABA) immunocytochemistry and electron microscopic observations. Within area 36, neocortical axon terminals formed only asymmetric synapses, usually with GABA-negative spines (87{\%}), and less frequently with GABA-immunopositive (GABA+) dendrites (13{\%}). A similar synaptic distribution was observed within area 35 except that asymmetric synapses onto GABA+ dendrites were more frequent (23{\%} of synapses). Examination of the projections from area 36 to area 35 and from both regions to the EC revealed an even higher incidence of asymmetric synapses onto GABA+ dendrites (35 and 32{\%}, respectively) than what was observed in the neocortical projection to areas 36 and 35. Furthermore, some of the neocortical and perirhinal terminals containing PHAL and GABA immunolabeling formed symmetric synapses onto GABA-negative dendrites in their projection sites (neocortex to area 35, 16{\%}; area 36 to 35, 7{\%}; areas 36-35 to EC, 12{\%}). Taken together, these findings suggest that impulse transmission through the rhinal circuit is subjected to strong inhibitory influences, reconciling anatomical and physiological data about this network.",
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Feedforward inhibition regulates perirhinal transmission of neocortical inputs to the entorhinal cortex : Ultrastructural study in guinea pigs. / Pinto, Aline; Fuentes, Cesar; Paré, Denis.

In: Journal of Comparative Neurology, Vol. 495, No. 6, 10.04.2006, p. 722-734.

Research output: Contribution to journalArticle

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