Using a confocal laser scanning microscope (CLSM) and an electron microscope, we investigated the organization of the main olfactory bulb (MOB) of tenrecs, which were previously included into insectivores but now considered to be in a new order "Afrosoricida" in the superclade 'Afrotheria'. We confirmed that the overall structural organization of the tenrec MOB was similar to that of rodents: (1) the compartmental organization of glomeruli and two types of periglomerular cells we proposed as the common organizational principles were present; (2) there were characteristic dendrodendritic and axo-dendritic synapses in the glomerulus and external plexiform layer (EPL) and gap junctions in glomeruli; and (3) no nidi, particular synaptic regions reported only in laboratory musk shrew and mole MOBs, were encountered. However, instead of nidi, we often observed a few tangled olfactory nerves (ONs) with large irregular boutons in the glomerular-external plexiform layer border zone, with which dendrites of various displaced periglomerular cells were usually found to be intermingled. Electron microscopic (EM) examinations confirmed characteristic large mossy terminal-like ON terminals making asymmetrical synapses to presumed mitral/tufted cell and displaced periglomerular cell dendrites. In addition, gap junctions were also encountered between dendritic processes in these tiny particular regions, further showing their resemblance to glomeruli.
"We employed eight (3 females and 5 males) Madagascan lesser tenrecs (Echinops telfairi) raised in a breeding colony in Munich , weighing 66–153 g (110.5 g mean weight). The animals were deeply anesthetized (tribromoethanol, 1 ml/100 g body weight, ip.) and perfused as previously described . We obtained 50 µm thick sagittal and coronal sections of the olfactory bulbs with a freezing microtome. "
[Show abstract][Hide abstract] ABSTRACT: The vomeronasal system (VNS) mediates pheromonal communication in mammals. From the vomeronasal organ, two populations of sensory neurons, expressing either Galphai2 or Galphao proteins, send projections that end in glomeruli distributed either at the rostral or caudal half of the accessory olfactory bulb (AOB), respectively. Neurons at the AOB contact glomeruli of a single subpopulation. The dichotomic segregation of AOB glomeruli has been described in opossums, rodents and rabbits, while Primates and Laurasiatheres present the Galphai2-pathway only, or none at all (such as apes, some bats and aquatic species). We studied the AOB of the Madagascan lesser tenrec Echinops telfairi (Afrotheria: Afrosoricida) and found that Galphai2 and Galphao proteins are expressed in rostral and caudal glomeruli, respectively. However, the segregation of vomeronasal glomeruli at the AOB is not exclusive, as both pathways contained some glomeruli transposed into the adjoining subdomain. Moreover, some glomeruli seem to contain intermingled afferences from both pathways. Both the transposition and heterogeneity of vomeronasal afferences are features, to our knowledge, never reported before. The organization of AOB glomeruli suggests that synaptic integration might occur at the glomerular layer. Whether intrinsic AOB neurons may make synaptic contact with axon terminals of both subpopulations is an interesting possibility that would expand our understanding about the integration of vomeronasal pathways.
PLoS ONE 11/2009; 4(11):e8005. DOI:10.1371/journal.pone.0008005 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We analyzed the cellular composition of the juxtaglomerular region in the main olfactory bulb of C57B/6J strain mice, focusing on 1) the compartmental organization of the glomerulus and the presence of type 1 and 2 periglomerular cells, 2) the colocalization relationships among the 4 major chemically identified groups of periglomerular cells, glutamic acid decarboxylase (GAD)/gamma-aminobutyric acid (GABA), tyrosine hydroxylase, calretinin and calbindin D28k positive periglomerular cells, and 3) the chemical properties of the nitric oxide synthase (NOS)-positive juxtaglomerular cells. We confirmed the compartmental organization of the glomerulus and the presence of both type 1 and 2 periglomerular cells in the mice. Similar to rat periglomerular cells, the tyrosine hydroxylase-positive cells were type 1 and GAD/GABA-positive. On the other hand, both the calbindin D28k-positive and calretinin-positive cells were type 2 periglomerular cells, but in contrast to those in rats, which are GAD/GABA-negative, all of the calbindin D28k-positive periglomerular cells and 65% of the calretinin-positive periglomerular cells were GAD/GABA-positive. The GAD/GABA-positive cells thus included both type 1 and type 2 periglomerular cells. Juxtaglomerular NOS-positive cells have been proposed as a subgroup of type 1 periglomerular cells that are separate from the calretinin-positive and calbindin D28k-positive cells in rats. However, in the mice, about 70% of the NOS-positive cells were calretinin-positive, and 50% of the calretinin-positive cells were NOS-positive. We herein reveal the significant species differences in the chemical properties of periglomerular cells and suggest that the cellular organization of the mouse main olfactory bulb cannot be extrapolated from that of rats.
Brain Research 10/2007; 1167(1):42-55. DOI:10.1016/j.brainres.2007.04.087 · 2.84 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Temporally correlated spike discharges are proposed to be important for the coding of olfactory stimuli. In the olfactory bulb, correlated spiking is known in two classes of output neurons, the mitral cells and external tufted cells. We studied a third major class of bulb output neurons, the middle tufted cells, analyzing their bursting and spike timing correlations, and their relation to mitral cells. Using patch-clamp and fluorescent tracing, we recorded spontaneous spiking from tufted-tufted or mitral-tufted cell pairs with visualized dendritic projections in mouse olfactory bulb slices. We found peaks in spike cross-correlograms indicating correlated activity on both fast (peak width 1-50 ms) and slow (peak width>50 ms) time scales, only in pairs with convergent glomerular projections. Coupling appeared tighter in tufted-tufted pairs, which showed correlated firing patterns and smaller mean width and lag of narrow peaks. Some narrow peaks resolved into 2-3 sub-peaks (width 1-12 ms), indicating multiple modes of fast correlation. Slow correlations were related to bursting activity, while fast correlations were independent of slow correlations, occurring in both bursting and non-bursting cells. The AMPA receptor antagonist NBQX (20 microM) failed to abolish broad or narrow peaks in either tufted-tufted or mitral-tufted pairs, and changes of peak height and width in NBQX were not significantly different from spontaneous drift. Thus, AMPA-receptors are not required for fast and slow spike correlations. Electrical coupling was observed in all convergent tufted-tufted and mitral-tufted pairs tested, suggesting a potential role for gap junctions in concerted firing. Glomerulus-specific correlation of spiking offers a useful mechanism for binding the output signals of diverse neurons processing and transmitting different sensory information encoded by common olfactory receptors.
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