Olfactory nerve layer

Experimentally, the macrocyclic trichothecenes satra-toxin G, isosatratoxin F, and roridin A have been shown to cause nasal and pulmonary toxicity when administered intranasally or intratracheally to mice. Intranasal exposure of satratoxin G and roridin A induced apoptosis of olfactory sensory neurons resulting in atrophy of the olfactory epithelium and olfactory nerve layer of the olfactory bulb in the frontal brain (Islam et al, 2006, 2007). Alveolar-type II cells and alveolar macrophages were injured following intratracheal instillation of isosatratoxin F or Stachybotrys spores with marked changes in surfactant synthesis and secretion (Rand et al, 2002). 

OBI outer blade of the dentate gyrus 36-37 oc olivocerebellar tract 70-74,90-94 ocb olivocochlear bundle 58-61, 83, 85,92, 96 ON olfactory nerve layer 1-3... 

The outer and most superficial MOB layer, the olfactory nerve layer (ONL), consists of ON axons and glial... 

MeAa medial nucleus of the amygdala, anterior part MeApd medial nucleus of the amygdala, posterodorsal part MeApv medial nucleus of the amygdala, posteroventral part NLOT nucleus of the lateral olfactory tract ONL olfactory nerve layer... 

TiOz particles were taken up by the olfactory bulb via the primary olfactory neurons and accumulated in the olfactory nerve layer (ON), olfactory ventricle... 

The glomerular layer of the olfactory bulb contains a substantial population of dopaminergic neurons. Dopamine acting at D2-like heteroreceptors inhibits glutamate release from terminals of the olfactory sensory neurons and hence may modulate the olfactory nerve synapse (Table 1). 

In the olfactory bulb, D2 receptor immunoreactivity was detected in the glomerular and external plexiform layers the olfactory nerve also exhibited immunopositivity (Levey et ah, 1993). 

Kosaka K, Toida K, Margolis FL, Kosaka T. 1997. Chemically defined neuron groups and their subpopulations in the glomerular layer of the rat main olfactory bulb-II. Prominent differences in the intraglomerular dendritic arborization and their relationship to olfactory nerve terminals. Neuroscience 76 775-786. 

In addition to summation of inputs from olfactory nerve terminals, a second function of the circuitry of the glomerular layer is regulation of transmission from the olfactory nerve to mitral and tufted cells. The anatomy of the glomerular layer, reviewed above, provides a basis for such regulation (Fig. 5). 

Fig. 13. Basic olfactory network. Schematic of the networks linking the olfactory bulb and primary olfactory cortex. Olfactory nerve axons (ON) terminate in the glomeruli (glom) onto mitral (m) and tufted (t) cells which project via the lateral olfactory tract (LOT) to layer la of primary olfactory cortex to terminate on the dendrites of layer Il-III pyramidal (p) cells. Layer 11-111 pyramidal cells in rostral olfactory cortex project to layer Ib in caudal olfactory cortex and vice versa. Olfactory cortical pyramidal cells also send reciprocal projections back to the olfactory bulb. Thus olfactory bulb output is continuously modified by feedback from areas it targets. Inhibitory interneurons in olfactory bulb and olfactory cortex (shown in gray) modulate network function. Neurons in the ipsilateral (AONi) and contralateral anterior olfactory nuclei (AON) link olfactory networks in the two hemispheres via the anterior commissure.

Nickell, W.T., Norman, A.B., Wyatt, L.M. and Shipley, M.T. (1990) Localization of dopamine receptor subtypes in the olfactory bulb [ HJspirerone (D2) binding in the glomerular and nerve layers. Soc. Neurosci. Abslr, 16, 101. 

Figure 2. Sagittal section through the accessory olfactory bulb of an opossum stained with antibody to Goa. AOB=accessory olfactory bulb, AGL-anterior glomerular layer, PGL=posterior glomerular layer, Nl nerve layer, M/T=mitral/tufted cell layer, FCx=frontal cortex.

EP = exposed group (n = 3). OB = olfactory bulb OP = olfactory peduncle ON = olfactory nerve G1 = glomerular layer Epl = external plexi-form layer. Mi = mitral cell layer Ipl = internal plexiform layer GrO = granule cell layer of olfactory bulb Md = medullary layer GrA = granule cell layer of accessory olfactory bulb AOB = accessory olfactory bulb AOE = anterior olfactory nucleus external part AOL = anterior olfactory nucleus, lateral part lo = lateral tract. (Reprinted from Wang et alP 2007 Humana Press Inc.)... 

Although pheromones can be considered as a special form of odorants (scents), their actions, effects and functions have similarities to those of hormones. They bind to a specific receptor which then activates an effector system, which initiates an action potential. They bind to specific sensory cells, the neurones, in the olfactory epithelium, which is located on the roof of the nasal cavities. The epithelium consists of three types of cells, basal, supporting and sensory cells (neurones). The neurones are bipolar, that is they possess a single dendrite, which extends from the cell body to the surface of the olfactory epithelium, and an axon that forms a synapse with a nerve that transfers information to the olfactory centre in the brain. The epithelium is covered with a thick layer of mucus, in which the pheromones dissolve. The mucus contains proteins that bind the pheromone(s) for delivery to the olfactory receptors and then to remove them once they have been detected. 

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