Expression of connexin 36 in second order neurons of the mouse olfactory bulb

LORENA RELA; CHARLES A. GREER

La Falda, Córdoba, Argentina

Taller; Taller de Neurociencias; 2007

Taller de Neurociencias

In the olfactory bulb (OB) synchronized activity among mitral cells (MCs) is believed to be partly mediated by electrical coupling via connexin 36 (Cx36) homotypic gap junctions. To better understand the possible role of Cx36 in the developing OB, we studied its spatio-temporal distribution using RT-PCR and immunohistochemistry in tissue slices of CD-1 mice at embryonic day 14 (E14), E17, postnatal day 0 (P0), P6 and adult (> P50). We analyzed the subcellular localization of Cx36 immunoreactivity (IR) in MCs using transgenic mice (YFP-G) expressing yellow fluorescent protein in a subpopulation of MCs and tufted cells (TCs). Cx36 was expressed at all ages tested, however, its spatial distribution changed with age. In adults, Cx36 IR was largely seen in puncta within the glomerular neuropil and perisomatic region of MCs, a pattern indistinguishable in the CD-1 and YFP mice. Within glomeruli, Cx36 IR colocalized with YFP positive dendritic branches of MCs/TCs. At E14 and E17, Cx36 IR was located in discrete areas which we tentatively identified as protoglomeruli. Perisomatic clusters were only found in the adult and not at E14 – P6. We suggest that coupling between MCs can arise early in apical arbors as the dendrites differentiate. Coupling via the somata seems to occur much later and may contribute to stabilization. Changes in distribution of Cx36 IR across ages may result from maturation of chemical neurotransmission, as seen in the hypothalamus. Cx36 knockout mice show normal MC structure, however, a role of coupling in MC maturation cannot be discarded, as other Cxs or compensatory mechanisms may be involved.