Journal Article

Long-range inhibitory intersection of a retrosplenial thalamocortical circuit by apical tuft-targeting CA1 neurons

Shepherd, Gordon M, Yamawaki Naoki, Lambot Laurie, Li, Xiaojian, Radulovic Jelena, Ren, Lynn Y

2019

Overview

Hippocampus, granular retrosplenial cortex (RSCg), and anterior thalamic nuclei (ATN) interact to mediate diverse cognitive functions. To identify cellular mechanisms underlying hippocampo–thalamo–retrosplenial interactions, we investigated the potential circuit suggested by projections to RSCg layer 1 (L1) from GABAergic CA1 neurons and ATN. We find that CA1→RSCg projections stem from GABAergic neurons with a distinct morphology, electrophysiology, and molecular profile. Their long-range axons inhibit L5 pyramidal neurons in RSCg via potent synapses onto apical tuft dendrites in L1. These inhibitory inputs intercept L1-targeting thalamocortical excitatory inputs from ATN to coregulate RSCg activity. Subicular axons, in contrast, excite proximal dendrites in deeper layers. Short-term plasticity differs at each connection. Chemogenetically abrogating CA1→RSCg or ATN→RSCg connections oppositely affects the encoding of contextual fear memory. Our findings establish retrosplenial-projecting CA1 neurons as a distinct class of long-range dendrite-targeting GABAergic neuron and delineate an unusual cortical circuit specialized for integrating long-range inhibition and thalamocortical excitation.Apical tuft dendrites of pyramidal neurons in retrosplenial cortex receive inhibition from a class of CA1 GABAergic neurons with long-range layer 1-targeting axons; this inhibition opposes matrix-type thalamocortical excitation from anterior thalamus.

• Publisher: Nature Publishing Group
• Subject: Axons / Cerebral cortex / Circuits / Cognitive ability / Dendrites / Electrophysiology / Memory / Morphology / Neurons / Nuclei (cytology) / Pyramidal cells / Synapses / Thalamic nuclei / Thalamus / γ-Aminobutyric acid