Calretinin-positive L5a pyramidal neurons in the development of the paralemniscal pathway in the barrel cortex

Abstract

BackgroundThe rodent barrel cortex has been established as an ideal model for studying the development and plasticity of a neuronal circuit. The barrel cortex consists of barrel and septa columns, which receive various input signals through distinct pathways. The lemniscal pathway transmits whisker-specific signals to homologous barrel columns, and the paralemniscal pathway transmits multi-whisker signals to both barrel and septa columns. The integration of information from both lemniscal and paralemniscal pathways in the barrel cortex is critical for precise object recognition. As the main target of the posterior medial nucleus (POm) in the paralemniscal pathway, layer 5a (L5a) pyramidal neurons are involved in both barrel and septa circuits and are considered an important site of information integration. However, information on L5a neurons is very limited. This study aims to explore the cellular features of L5a neurons and to provide a morphological basis for studying their roles in the development of the paralemniscal pathway and in information integration.Results1. We found that the calcium-binding protein calretinin (CR) is dynamically expressed in L5a excitatory pyramidal neurons of the barrel cortex, and L5a neurons form a unique serrated pattern similar to the distributions of their presynaptic POm axon terminals.2. Infraorbital nerve transection disrupts this unique alignment, indicating that it is input dependent.3. The formation of the L5a neuronal alignment develops synchronously with barrels, which suggests that the lemniscal and paralemniscal pathways may interact with each other to regulate pattern formation and refinement in the barrel cortex.4. CR is specifically expressed in the paralemniscal pathway, and CR deletion disrupts the unique L5a neuronal pattern, which indicates that CR may be required for the development of the paralemniscal pathway.ConclusionsOur results demonstrate that L5a neurons form a unique, input-dependent serrated alignment during the development of cortical barrels and that CR may play an important role in the development of the paralemniscal pathway. Our data provide a morphological basis for studying the role of L5a pyramidal neurons in information integration within the lemniscal and paralemniscal pathways.

Adult axolotls can regenerate original neuronal diversity in response to brain injury

“…Finally, Rorb labels locally connected excitatory interneurons of layer IV ( Jabaudon et al, 2012 ). Among Gad2 + cortical GABAergic interneurons, Sst and Calb2 mark specific subtypes ( Bartolini et al, 2013 ), although Calb2 has been shown to also be transiently expressed in pyramidal neurons residing in layer Va ( Liu et al, 2014 ).…”

Foxg1 Regulates the Postnatal Development of Cortical Interneurons

“…Since CR is expressed in several types of neurons, including cortical interneuron subtypes and pyramidal excitatory neurons in layer Vb (Liu et al 2014), we examined the ectopic CRpositive cells by double immunostaining for anti-CR and CTIP2, a specific marker for deeper layer excitatory neurons (Chen et al 2008). As shown in Figure 3A,B, none of the CR-positive cells co-expressed CTIP2, suggesting that the ectopic CRpositive cells were not excitatory neurons.…”

Loss of Calretinin in L5a Impairs the Formation of the Barrel Cortex Leading to Abnormal Behaviors

“…Previously, we showed that CR is dynamically expressed in L5a pyramidal neurons in the developing barrel cortex and displays a unique predominantly serrated pattern that mirrors the presynaptic projection pattern of the posterior medial nucleus (Pom) to L5a [10,30]. In this study, by analyzing Cr KO mice, we found that loss of Cr results in a reduced complexity of L5a pyramidal neuron dendrites, which leads to abnormal formation of the barrel wall and subsequently impairs the barrel and septa microcircuits.…”