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J Comp Neurol. 2016 Feb 1;524(2):408-28. doi: 10.1002/cne.23874. Epub 2015 Aug 20.

Cryptic laminar and columnar organization in the dorsolateral pallium of a weakly electric fish.

Author information

1
Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada.
2
Departamento de Biofísica, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil.
3
Center for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada.

Abstract

In the weakly electric gymnotiform fish, Apteronotus leptorhynchus, the dorsolateral pallium (DL) receives diencephalic inputs representing electrosensory input utilized for communication and navigation. Cell counts reveal that, similar to thalamocortical projections, many more cells are present in DL than in the diencephalic nucleus that provides it with sensory input. DL is implicated in learning and memory and considered homologous to medial and/or dorsal pallium. The gymnotiform DL has an apparently simple architecture with a random distribution of simple multipolar neurons. We used multiple neurotracer injections in order to study the microcircuitry of DL. Surprisingly, we demonstrated that the intrinsic connectivity of DL is highly organized. It consists of orthogonal laminar and vertical excitatory synaptic connections. The laminar synaptic connections are symmetric sparse, random, and drop off exponentially with distance; they parcellate DL into narrow (60 μm) overlapping cryptic layers. At distances greater than 100 μm, the laminar connections generate a strongly connected directed graph architecture within DL. The vertical connectivity suggests that DL is also organized into cryptic columns; these connections are highly asymmetric, with superficial DL cells preferentially projecting towards deeper cells. Our experimental analyses suggest that the overlapping cryptic columns have a width of 100 μm, in agreement with the minimal distance for strong connectivity. The architecture of DL and the expansive representation of its input, taken together with the strong expression of N-methyl-D-aspartate (NMDA) receptors by its cells, are consistent with theoretical ideas concerning the cortical computations of pattern separation and memory storage via bump attractors.

KEYWORDS:

RRID: SciRes_000114; RRID: SciRes_000137; RRID: nif-0000-00314; RRID: nlx_153890; RRID: rid_000085; attractor network; columnar organization; pallial homologies; random graph; recurrent synapses; telencephalon; weakly electric fish

PMID:
26234725
DOI:
10.1002/cne.23874
[Indexed for MEDLINE]
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