Neonatal CX26 removal impairs neocortical development and leads to elevated anxiety

Abstract

Electrical coupling between excitatory neurons in the neocortex is developmentally regulated. It is initially prominent but eliminated at later developmental stages when chemical synapses emerge. However, it remains largely unclear whether early electrical coupling networks broadly contribute to neocortical circuit formation and animal behavior. Here, we report that neonatal electrical coupling between neocortical excitatory neurons is critical for proper neuronal development, synapse formation, and animal behavior. Conditional deletion of Connexin 26 (CX26) in the superficial layer excitatory neurons of the mouse neocortex around birth significantly reduces spontaneous firing activity and the frequency and size of spontaneous network oscillations at postnatal day 5-6. Moreover, CX26-conditional knockout (CX26-cKO) neurons tend to have simpler dendritic trees and lower spine density compared with wild-type neurons. Importantly, early, but not late, postnatal deletion of CX26, decreases the frequency of miniature excitatory postsynaptic currents (mEPSCs) in both young and adult mice, whereas miniature inhibitory postsynaptic currents (mIPSCs) were unaffected. Furthermore, CX26-cKO mice exhibit increased anxiety-related behavior. These results suggest that electrical coupling between excitatory neurons at early postnatal stages is a critical step for neocortical development and function.CX26 | development | anxiety | neocortex D uring neocortical development, gap junction-mediated electrical coupling plays a critical role in various developmental processes, including neuronal migration (1, 2), synaptogenesis (3), and synchronous firing (4, 5). It is generally believed that gap junction-mediated communication between excitatory neurons during development is required for the formation of chemical synapses (6). For example, we previously showed that sister excitatory neurons in the neocortex are initially electrically coupled, and blockade of this electrotonic communication impairs the subsequent formation of specific chemical synapses between them in ontogenetic neuronal clones (7), as well as the functional similarity (8). Whereas these studies have provided crucial insights into the role of gap junctions in the precise microcircuit assembly of excitatory neurons and functional organization of the neocortex, whether electrical coupling-mediated networks contribute to the overall development of the neocortex and animal behavior remains largely unknown.Electrical coupling networks among excitatory neurons in the neocortex are developmentally regulated. Electrical couplings are the morphological correlates of dye coupling and low resistance intercellular pathways (9). Functional electrical coupling between excitatory neurons has been abundantly observed at late embryonic and early postnatal stages (10, 11). As electrical synapses approach the time point of their elimination, chemical connections between excitatory neurons begin to emerge, illustrating a sequential developmental time course for the two types of connect...

Gap Junction Dependent Cell Communication Is Modulated During Transdifferentiation of Mesenchymal Stem/Stromal Cells Towards Neuron-Like Cells

“…Cx43, Cx40 and Cx45 play the major role in the gap junction coupling capabilities of MSCs ( Bodi et al, 2004 ; Valiunas et al, 2004 ). We expected that the differentiation of MSCs into neuron-like cells would down-regulate mesenchymal connexins like Cx43, Cx40 and Cx37 while up-regulating neuronal connexins like Cx26, Cx45 and especially Cx36 ( Rozental et al, 2000 ; Söhl et al, 2005 ; Eugenin et al, 2012 ; Su et al, 2017 ). Our analysis of connexin expression in the transdifferentiated neuron-like cells showed a significant down-regulation of the mesenchymal connexins Cx43, Cx40 and Cx37 and an upregulation of Cx26, thereby confirming our expectations.…”

“…MSCs are extensively gap junction-coupled and mainly express Cx43, as well as Cx40 and Cx45 ( Dorshkind et al, 1993 ; Bodi et al, 2004 ; Valiunas et al, 2004 ). Neurons are also coupled by gap junctions ( Lo Turco and Kriegstein, 1991 ; Bittman et al, 1997 ) which are mainly composed of the connexins Cx26, Cx30.2, Cx45 and particularly Cx36 ( Leung et al, 2002 ; Kreuzberg et al, 2008 ; Eugenin et al, 2012 ; Su et al, 2017 ). Amongst these, Cx36 is the most prominent neuronal connexin in adult electrical synapses and plays important roles in the developing brain ( Belluardo et al, 2000 ; Condorelli et al, 2000 ).…”

Spikelets in pyramidal neurons: generating mechanisms, distinguishing properties, and functional implications

“…Vertebrate gap junction channels are composed of proteins called connexins. In neurons, connexin 36 is the predominant gap-junctional protein (Connors and Long, 2004), although other connexins are present as well: for example, Cx45 was found in retinal neurons (Li et al, 2008), and Cx26 occurs in neonatal excitatory cells of the neocortex (Su et al, 2017).…”

Could electrical coupling contribute to the formation of cell assemblies?

“…Yu et al (2012) reported that sister pyramidal neurons are most likely to be coupled during development and that such coupling in turn regulates specific local chemical synaptic excitatory circuits, which may also occur in a similar sequence during the development of other brain and spinal cord regions. Su et al (2017) found that Cx26 occurs in superficial layers of the cortex and is important for the development not only of synaptic connections but also of dendrites and for the ability of the more mature cortex to produce network oscillations. However, immunofluorescence labeling of Cx26 is not detectable in mature cortex, and its expression in adult brain appears to be restricted to a minor subpopulation of astrocytes (Nagy et al, 2001(Nagy et al, , 2011.…”