The organization of centrifugal projections from the anterior olfactory nucleus, ventral hippocampal rudiment, and piriform cortex to the main olfactory bulb in the hamster: An autoradiographic study

Rodents can localize odor sources by comparing odor inputs to the right and left nostrils. However, the neuronal circuits underlying such odor localization are not known. We recorded neurons in the anterior olfactory nucleus (AON) while administering odors to the ipsilateral or contralateral (ipsi-or contra-) nostril. Neurons in the AON pars externa (AONpE) showed respiration phase-locked excitatory spike responses to ipsinostril-only stimulation with a category of odorants, and inhibitory responses to contranostril-only stimulation with the same odorants. Simultaneous odor stimulation of the ipsi-and contranostrils elicited significantly smaller responses than ipsinostril-only stimulation, indicating that AONpE neurons subtract the contranostril odor inputs from ipsinostril odor inputs. An ipsilateral odor source induced larger responses than a centrally located source, whereas an odor source at the contralateral position elicited inhibitory responses. These results indicate that individual AONpE neurons can distinguish the right or left position of an odor source by referencing signals from the two nostrils.olfactory cortex | binasal inputs | odor localization

Section: Discussionmentioning

confidence: 99%

Neurons in the anterior olfactory nucleus pars externa detect right or left localization of odor sources

Kikuta

Sato

Kashiwadani

et al. 2010

“…The apical dendrite can be divided into an unbranched segment emerging from the soma followed by a branched segment (distal domain). The basal dendrite (basal domain) and unbranched apical dendrite receive axo-dendritic glutamatergic input from axon collaterals of the OB's projection neurons and from the olfactory cortices (3)(4)(5)(6). The distal domain of the apical dendrite has bidirectional dendrodendritic synapses present in spines where input and output synapses are colocalized and functionally coupled.…”

mentioning

confidence: 99%

Sequential development of synapses in dendritic domains during adult neurogenesis

Kelsch

Lin²,

Lois³

2008

126

178

During the process of integration into brain circuits, new neurons develop both input and output synapses with their appropriate targets. The vast majority of neurons in the mammalian brain are generated before birth and integrate into immature circuits while these are being assembled. In contrast, adult-generated neurons face an additional challenge as they integrate into a mature, fully functional circuit. Here, we examined how synapses of a single neuronal type, the granule cell in the olfactory bulb, develop during their integration into the immature circuit of the newborn and the fully mature circuit of the adult rat. We used a genetic method to label pre and postsynaptic sites in granule neurons and observed a stereotypical development of synapses in specific dendritic domains. In adult-generated neurons, synapses appeared sequentially in different dendritic domains with glutamatergic input synapses that developed first at the proximal dendritic domain, followed several days later by the development of inputoutput synapses in the distal domain and additional input synapses in the basal domain. In contrast, for neurons generated in neonatal animals, input and input-output synapses appeared simultaneously in the proximal and distal domains, respectively, followed by the later appearance of input synapses to the basal domain. The sequential formation of synapses in adult-born neurons, with input synapses appearing before output synapses, may represent a cellular mechanism to minimize the disruption caused by the integration of new neurons into a mature circuit in the adult brain.bulb ͉ dendrite I ntegration of new neurons continues throughout life in the adult mammalian olfactory bulb (OB) (1, 2). During the process of integration into brain circuits, new neurons develop both input and output synapses with their appropriate targets. Whereas the majority of neurons in the olfactory bulb integrate into an immature circuit while it is being assembled, neurons generated in adulthood face an additional challenge as they integrate into a mature, fully functional circuit. In particular, the formation of synapses by a new neuron in a functioning circuit may interfere with circuit operation and, thus, it could result in maladaptive behaviors. Additionally, it is still not known whether new neurons integrating into the neonatal and adult olfactory system have the same or different functions in the circuit and, therefore, adult-and neonatal-generated neurons could employ different modes of integration. To compare how new neurons are added to neonatal and adult circuits, we examined the pattern of synapse development of a single neuronal type, the granule cell (GC) in the olfactory bulb, during its integration into the immature circuit of the newborn and the mature circuit of the adult rat.The majority of neurons added to the OB of adult rats are GC neurons. GCs are axonless inhibitory interneurons that have both a basal dendrite and an apical dendrite (Fig. 1A). The apical dendrite can be divided into an unbranched segm...

“…As a result, relatively little is known about the role of local inhibitory interneurons in generating and maintaining network oscillations, although pioneering studies proposed dendrodendritic inhibition as a key element for inducing fast rhythms (15)(16)(17). This assumption is also supported by the fact that interneurons constitute the main target of excitatory centrifugal fibers (18,19) known to control oscillatory activities in the OB circuitry (5).…”

mentioning

confidence: 99%

GABAergic inhibition at dendrodendritic synapses tunes γ oscillations in the olfactory bulb

Lagier

Panzanelli²,

Russo³

et al. 2007

116

In the olfactory bulb (OB), odorants induce oscillations in the ␥ range (20 -80 Hz) that play an important role in the processing of sensory information. Synaptic transmission between dendrites is a major contributor to this processing. Glutamate released from mitral cell dendrites excites the dendrites of granule cells, which in turn mediate GABAergic inhibition back onto mitral cells. Although this reciprocal synapse is thought to be a key element supporting oscillatory activity, the mechanisms by which dendrodendritic inhibition induces and maintains ␥ oscillations remain unknown. Here, we assessed the role of the dendrodendritic inhibition, using mice lacking the GABA A receptor ␣1-subunit, which is specifically expressed in mitral cells but not in granule cells. The spontaneous inhibitory postsynaptic current frequency in these mutants was low and was consistent with the reduction of GABA A receptor clusters detected by immunohistochemistry. The remaining GABA A receptors in mitral cells contained the ␣3-subunit and supported slower decaying currents of unchanged amplitude. Overall, inhibitory-mediated interactions between mitral cells were smaller and slower in mutant than in WT mice, although the strength of sensory afferent inputs remained unchanged. Consequently, both experimental and theoretical approaches revealed slower ␥ oscillations in the OB network of mutant mice. We conclude, therefore, that fast oscillations in the OB circuit are strongly constrained by the precise location, subunit composition and kinetics of GABA A receptors expressed in mitral cells.␣1 knockout ͉ GABAA receptor ͉ olfaction ͉ reciprocal synapses I n the olfactory bulb (OB), ␥ frequency (20-80 Hz) oscillations of local field potentials (LFP) reflect synchronized spike discharges of principal neurons (i.e., mitral/tufted cells), and may be part of the encoding of sensory information (reviewed in refs. 1 and 2). In line with this assumption, the strength of ␥ oscillations correlates with both discrimination abilities (3) and learning capacities (4, 5) in rodents.In vivo experimental approaches revealed that ␥ oscillations are intrinsic to the OB circuitry (5-7) and are even preserved in slice preparations (8, 9), which suggests that intrinsic properties of the OB connectivity are sufficient to give rise to large-scale synchronization. Analysis of the mechanisms involved has focused almost exclusively on the excitatory principal neurons (i.e., mitral cells) and included intrinsic subthreshold oscillations (10, 11) or mutual excitation through electrical coupling and glutamate spillover between mitral cells sharing the same glomerulus (12-14). As a result, relatively little is known about the role of local inhibitory interneurons in generating and maintaining network oscillations, although pioneering studies proposed dendrodendritic inhibition as a key element for inducing fast rhythms (15)(16)(17). This assumption is also supported by the fact that interneurons constitute the main target of excitatory centrifugal fibers (18,19) k...