On the organization of astrocytic gap junctions in rat brain as suggested by LM and EM immunohistochemistry of connexin43 expression

Abstract

Gap junctions and the intercellular communication syncytium they form between glial cells are thought to play a critical role in glial maintenance of appropriate metabolic environments in neural tissues. We have previously suggested (Yamamoto et al., Brain Res. 508:313-319, '90) that the vast majority of astrocytes in rat brain express connexin43, one of several recently identified gap junction proteins. Here, we confirm ultrastructurally that astrocytes in a number of brain regions of rat are immunolabelled with an antibody against connexin43 and that neurons and oligodendrocytes are devoid of labelling. The distribution of connexin43 immunoreactivity throughout the brain is presented at the light microscope (LM) level. By LM, immunoreactive structures consisted primarily of round or elongated puncta ranging from 0.3 microns to 4 microns in length and of annular profiles ranging from 1 to 10 microns in diameter. Immunolabelled fibrous processes were only occasionally seen and no labelling was observed in astrocytic cell bodies. Long, linear arrays of puncta were rare in gray matter but were common in white matter where they were arranged parallel to myelinated fibers. Puncta organized in a honeycomb pattern were seen near the cerebral cortical surface and frequently around blood vessels. Regional immunoreaction density, which was a reflection of either the concentration or staining intensity of immunoreactive elements, was remarkably heterogeneous; dramatic differences in labelling intensity frequently delineated anatomical boundaries between adjacent nuclei. Abrupt as well as graded fluctuations of immunoreaction intensity were also observed within nuclear structures. By electron microscopy (EM), gap junctions of fibrous and protoplasmic astrocytes were intensely stained and labelled organelles were often observed intracellularly in areas near gap junctions. These junctions and the spread of immunoreaction product to perijunctional organelles in their vicinity were considered to correspond to puncta seen by LM. Labelling within astrocytic cell bodies was seen in only a few instances. In some brain areas, astrocytic processes commonly gave rise to immunoreactive lamellae that partially ensheathed neuronal cell bodies, axon terminals, dendrites, and synaptic glomeruli. Such lamellae were considered to correspond to immunoreactive annular profiles seen by LM. Perivascular endfoot processes of astrocytes displayed intense staining of their gap junctions and portions of their apposing membranes.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of connexin36 in gap junctions between neurons in rodent locus coeruleus

“…Neuronal somata in the adult LC are ensheathed by one or more thin glial processes (Shimizu and Imamoto, 1970;Groves and Wilson, 1980), just as in other brain regions, where thin-section immunoEM revealed labeling for Cx43 on gap junctions between astrocyte processes but not between astrocytes and neurons (Yamamoto, et al, 1990a(Yamamoto, et al, ,1990b(Yamamoto, et al, ,1992Nagy et al, 2004). By immunofluorescence, these Cx43-positive puncta often surround neurons, giving the appearance of Cx43 puncta on neuronal somata, as observed in the present study.…”

“…Early on, it was proposed that neurons share gap junctions only with neurons, and that glia share intercellular gap junctions only with glia (Brightman and Reese, 1969;Mugnaini, 1986). This "restricted coupling partner" hypothesis gained support based on TEM and FRIL immunocytochemical data showing that neuronal, astrocytic and oligodendrocytic gap junctions each express different complements of connexins Nagy and Dermietzel, 2000;Rash et al, 2000Rash et al, , 2001bKamasawa et al, 2005;Fukuda et al, 2006), with Cx43, Cx30 and (in limited areas) Cx26 in astrocytes and leptomeninges (Li et al, 1997;Nagy et al, 1999Nagy et al, ,2001Rash et al, 2001b); Cx29, Cx32 and Cx47 in oligodendrocytes (Rash et al, 2001a(Rash et al, ,2001bNagy et al, 2004;Kamasawa et al, 2005); and Cx36 exclusively in neurons (Rash et al, 2001b;Fukuda et al, 2006), extending data from immunofluorescence analysis and thin-section immunocytochemistry (Yamamoto et al, 1990a(Yamamoto et al, ,1990bScherer et al, 1995;Mercier and Hatton, 2001;Altevogt et al, 2002;Kleopas et al, 2004;Rash et al, 2005).…”

Differential Expression of Connexins during Neocortical Development and Neuronal Circuit Formation

“…The presence of Cx 43 in radial glial fibers during the period of neuronal migration suggests that neurons establish contact and communication with the scaffolding they use as they migrate to the cortical plate. As neuronal migration tapers off, radial glial cells are transformed into fibrillary and protoplasmic astrocytes (Choi and Lapham, 1978;Schmechel and Rakic, 1979) and are added to the existing population of astrocytes known to form networks connected by gap junctions in the cortex (Bennett and Goodenough, 1978;Massa and Mugnaini, 1982;Yamamoto et al, 1990). The localization of Cx 43 in radial glia indicates that these cells possess the necessary Cxs to form gap junctions.…”

Loss-of-function GJA12/Connexin47 mutations cause Pelizaeus–Merzbacher-like disease

“…Anatomical and functional studies of the rodent CNS have demonstrated that astrocytes and oligodendrocytes are coupled by gap junctions (Massa and Mugnaini 1982;Ransom and Kettenmann 1990;Robinson et al 1993;Rash et al 1997), and that each cell type expresses different connexins (Dermietzel et al 1989;Yamamoto et al 1990;Scherer et al 1995;Dermietzel et al 1997;Ochalski et al 1997;Nagy et al 1999;Altevogt et al 2002;Menichella et al 2003;Odermatt et al 2003;Kleopa et al 2004). Astrocyte/astrocyte (A/ A) coupling is likely mediated by Cx43/Cx43 and Cx30/Cx30 homotypic channels, and astrocyte/oligodendrocyte (A/O) coupling is most likely mediated by Cx43/Cx47 and Cx30/ Cx32 heterotypic channels, with an uncertain contribution of Cx26/Cx32 channels (Rash et al 2001;Nagy et al 2003;Altevogt and Paul 2004;Li et al 2004).…”