An Electron-Microscopic Study of the Termination of the Afferent Fibres to the Olfactory Bulb from the Cerebral Hemisphere

1970 ◽  
Vol 7 (1) ◽  
pp. 157-187
Author(s):  
J. L. PRICE ◽  
T. P. S. POWELL
Keyword(s):  
Olfactory Bulb ◽  
Cerebral Hemisphere ◽  
Granule Cells ◽  
Anterior Commissure ◽  
Plexiform Layer ◽  
Granule Cell Layer ◽  
Electron Microscopic ◽  
Anterior Olfactory Nucleus ◽  
Axon Terminals ◽  
Axon Collaterals

An experimental investigation has been made of the site and mode of termination of the 3 groups of afferent fibres to the olfactory bulb which come from more caudal parts of the cerebral hemisphere. Lesions have been placed in the relevant parts of the brain of the rat and the resulting degeneration of axon terminals in the olfactory bulb studied with the electron microscope. All 3 groups of these extrinsic afferent fibres end in asymmetrical synapses upon the granule cells, and they have a differential termination upon its various processes. The possibility that these fibres also end upon other cells in the bulb (particularly the short-axon and periglomerular cells) cannot be excluded. The centrifugal fibres end upon gemmules in the deep half of the external plexiform layer only; no degenerating terminals were found in relation to the glomeruli although degenerating centrifugal axons are present here. The fibres of the anterior commissure terminate upon spines and varicosities of the deep dendrites and upon somatic spines of the granule cells. After lesions of the anterior olfactory nucleus, degenerating terminals were found in the ipsilateral olfactory bulb, which could not be ascribed to the centrifugal fibres or to the fibres of the anterior commissure, as they ended upon the spines of peripheral processes in the granule cell layer, and upon gemmules in the superficial as well as in the deep half of the external plexiform layer. It is proposed that these terminals are those of the axon collaterals from the ipsilateral anterior olfactory nucleus. The axons which form symmetrical synapses, and many which form asymmetrical synapses, do not degenerate even after a lesion immediately behind the olfactory bulb, and are therefore intrinsic to the bulb. It is suggested that the axons which are associated with symmetrical synapses are those of the short-axon cells, and the asymmetrical synapses are formed by the axon collaterals of the mitral and tufted cells.

The Morphology of the Granule Cells of the Olfactory Bulb

1970 ◽  
Vol 7 (1) ◽  
pp. 91-123 ◽  
Author(s):  
J. L PRICE ◽  
T. P. S POWELL
Keyword(s):  
Electron Microscope ◽  
Olfactory Bulb ◽  
Cell Body ◽  
Granule Cells ◽  
Plexiform Layer ◽  
Golgi Method ◽  
Granule Cell Layer ◽  
Electron Microscopic ◽  
Microscopic Features ◽  
Large Spine

The granule cells of the olfactory bulb of the rat have been studied in material prepared by the Golgi-Kopsch method for examination with the light microscope, and in material examined with the electron microscope. With the Golgi method, the granule cells are found to have no process which can be identified as a typical axon, but from the superficial aspect of the somata stout peripheral processes arise and pass into the overlying external plexiform layer, while from the opposite side of the cell body several thinner deep dendntes extend towards the deeper parts of the bulb. Both types of processes, as well as the perikarya, have numerous spine-like appendages. On the distal portions of the peripheral processes in the external plexiform layer the appendages are much larger than on the deeper parts of the cell. The deep dendrites have localized swellings along their length which give them a varicose appearance, appendages often arise from these varicosities. The electron-microscopic features of the granule cells correspond well with the appearance of these cells in material impregnated with the Golgi method. The cell somata are small, with very little cytoplasm, and have a relatively large nucleus. The peripheral processes can be identified passing superficially from the perikarya of the granule cells; at their junction with the cell body their appearance is typically dendritic; all the cytoplasmic organelles found in the cytoplasm extend into these processes and none of the features of the initial segments of axons are found. In the external plexiform layer large spine-like appendages, which have been termed ‘gemmules’, arise from the distal portions of the peripheral processes, and participate in reciprocal synapses with the dendrites of mitral and tufted cells. The deep dendrites are much finer than the peripheral processes, and the varicosities which are seen in Golgi material may also be found with the electron microscope. Spines are found on all parts of the granule cells in the granule cell layer, including the peripheral processes, the perikarya and the deep dendrites. In addition to a spine apparatus, these spines commonly have numerous inclusions, including mitochondria, ribosomes, and vesicles which are the same size and shape as the synaptic vesicles present in the gemmules; no synapses oriented away from the spines have ever been found.

The Mitral and Short Axon Cells of the Olfactory Bulb

1970 ◽  
Vol 7 (3) ◽  
pp. 631-651
Author(s):  
J. L. PRICE ◽  
T. P. S. POWELL
Keyword(s):  
Electron Microscope ◽  
Olfactory Bulb ◽  
Granule Cells ◽  
Primary Dendrite ◽  
Plexiform Layer ◽  
Mitral Cell ◽  
Granule Cell Layer ◽  
Mitral Cells ◽  
Axon Initial Segments ◽  
Large Neurons

A description is given of the mitral and short axon cells of the olfactory bulb of the rat from Golgi material examined with the light microscope and from material examined with the electron microscope. The mitral cells are large neurons with primary and secondary dendrites which both extend into the overlying external plexiform layer, although only the primary dendrite enters the glomerular formations. No predominant antero-posterior orientation of the secondary dendrites has been found. Within the glomeruli the mitral cell dendrites are in synaptic contact with the olfactory nerves and also with the periglomerular cells, but elsewhere the only synapses on the mitral cells are the ‘reciprocal synapses’ with the granule cells. Synaptic-type vesicles are found in all parts of the mitral cells, including the axon initial segments; they appear to be especially concentrated in the distal portions of the dendrites. Several types of short axon cells have been found in the granule cell layer in Golgi-impregnated material. Their cell bodies can also be distinguished with the electron microscope, and from previous work it is probable that the axons of at least some of these cells form flattened-vesicle symmetrical synapses upon the granule cells.

scholarly journals Short-Term Plasticity in Cortical GABAergic Synapses on Olfactory Bulb Granule Cells Is Modulated by Endocannabinoids

2021 ◽  
Vol 15 ◽  
Author(s):  
Fu-Wen Zhou ◽  
Adam C. Puche
Keyword(s):  
Olfactory Bulb ◽  
Sensory Processing ◽  
Granule Cell ◽  
Granule Cells ◽  
Cb1 Receptor ◽  
Granule Cell Layer ◽  
Short Term ◽  
Frequency Dependent ◽  
Short Term Plasticity ◽  
Cortical Feedback

Olfactory bulb and higher processing areas are synaptically interconnected, providing rapid regulation of olfactory bulb circuit dynamics and sensory processing. Short-term plasticity changes at any of these synapses could modulate sensory processing and potentially short-term sensory memory. A key olfactory bulb circuit for mediating cortical feedback modulation is granule cells, which are targeted by multiple cortical regions including both glutamatergic excitatory inputs and GABAergic inhibitory inputs. There is robust endocannabinoid modulation of excitatory inputs to granule cells and here we explored whether there was also endocannabinoid modulation of the inhibitory cortical inputs to granule cells. We expressed light-gated cation channel channelrhodopsin-2 (ChR2) in GABAergic neurons in the horizontal limb of the diagonal band of Broca (HDB) and their projections to granule cells in olfactory bulb. Selective optical activation of ChR2 positive axons/terminals generated strong, frequency-dependent short-term depression of GABAA-mediated-IPSC in granule cells. As cannabinoid type 1 (CB1) receptor is heavily expressed in olfactory bulb granule cell layer (GCL) and there is endogenous endocannabinoid release in GCL, we investigated whether activation of CB1 receptor modulated the HDB IPSC and short-term depression at the HDB→granule cell synapse. Activation of the CB1 receptor by the exogenous agonist Win 55,212-2 significantly decreased the peak amplitude of individual IPSC and decreased short-term depression, while blockade of the CB1 receptor by AM 251 slightly increased individual IPSCs and increased short-term depression. Thus, we conclude that there is tonic endocannabinoid activation of the GABAergic projections of the HDB to granule cells, similar to the modulation observed with glutamatergic projections to granule cells. Modulation of inhibitory synaptic currents and frequency-dependent short-term depression could regulate the precise balance of cortical feedback excitation and inhibition of granule cells leading to changes in granule cell mediated inhibition of olfactory bulb output to higher processing areas.

The Synaptology of the Granule Cells of the Olfactory Bulb

1970 ◽  
Vol 7 (1) ◽  
pp. 125-155
Author(s):  
J. L. PRICE ◽  
T. P. S POWELL
Keyword(s):  
Olfactory Bulb ◽  
Synaptic Vesicles ◽  
Granule Cells ◽  
Mitral Cell ◽  
Synaptic Membrane ◽  
Quantitative Evidence ◽  
Axon Terminals ◽  
Quantitative Measurements ◽  
Asymmetrical Synapse ◽  
Cell Somata

The synapses related to the granule cells of the olfactory bulb of rat brain have been studied in aldehyde-fixed material. The synapses can be divided into three classes: (1) those which have asymmetrical synaptic membrane thickenings and spheroidal synaptic vesicles; (2) those with symmetrical synaptic thickenings and flattened vesicles; and (3) the reciprocal synapses, one half of which (from mitral to granule cell) has an asymmetrical synaptic thickening associated with spheroidal vesicles, while the other half (from granule to mitral cell) has a symmetrical synaptic thickening and flattened vesicles. Qualitative observations, supported by preliminary quantitative measurements, suggest that it may be possible to divide both the spheroidal and flattened-vesicle types into two further varieties, on the basis of size, The smaller variety of spheroidal vesicles is found in most axon terminals, while the larger spheroidal vesicles are present in mitral cell dendrites and in some of the axon terminals. The flattened vesicles associated with symmetrical synapses which are oriented on to the granule cells are smaller than the spheroidal vesicles, but the flattened vesicles in the spines and gemmules of the granule cells are the same size or larger than the spheroidal vesicles. The division of flattened vesicles into two sizes is supported by statistical analysis of measurements of these vesicles, but because of difficulty in identifying the axon terminals with asymmetrical synapses there is no quantitative evidence for such a division of spheroidal vesicles. The asymmetrical synapses are found predominantly on spines, gemmules, and dendritic varicosities, although they are occasionally present on shafts of dendrites and on the cell somata. The symmetrical synapses are almost completely restricted to the shafts of the peripheral processes and the deep dendrites, and to the cell somata; only very rarely are synapses of this type found on spines, and then always in conjunction with an asymmetrical synapse.

The Termination of Centrifugal Fibres in the Glomerular Layer of the Olfactory Bulb

1972 ◽  
Vol 10 (3) ◽  
pp. 621-635
Author(s):  
A. J. PINCHING ◽  
T. P. S. POWELL
Keyword(s):  
Electron Microscope ◽  
Olfactory Bulb ◽  
Mitral Cell ◽  
Lateral Olfactory Tract ◽  
Anterior Olfactory Nucleus ◽  
Axon Terminals ◽  
Glomerular Layer ◽  
Olfactory Tract ◽  
Functional Implications

The termination of the centrifugal fibres running in the lateral olfactory tract to the glomerular layer of the rat olfactory bulb has been determined with the electron microscope; this has been done with material perfused at various times after section of the lateral olfactory tract, as well as after a combination of this lesion with the long-term degeneration of olfactory nerves. The axon terminals are sparse at the glomerular level, but undergo typical degenerative changes; they are distributed solely in the periglomerular region and intermediate zone. The most common post-synaptic profiles are the processes of periglomerular cells, but a few centrifugal fibres terminate on short-axon, tufted and mitral cell dendrites. Evidence is produced to suggest that the anterior olfactory nucleus does not project as far as the glomerular layer. The findings are discussed in relation to previous studies with normal material and silver degeneration methods on similar experimental material; the functional implications of the centrifugal pathways in the bulb are briefly discussed.

scholarly journals Postnatal Developmental Expression of Calbindin, Calretinin and Parvalbumin in Mouse Main Olfactory Bulb

2005 ◽  
Vol 37 (4) ◽  
pp. 276-282 ◽  
Author(s):  
Zhao-Ping Qin ◽  
Shu-Ming Ye ◽  
Ji-Zeng Du ◽  
Gong-Yu Shen
Keyword(s):  
Olfactory Bulb ◽  
Cell Layer ◽  
Plexiform Layer ◽  
Olfactory Nerve ◽  
Mitral Cell ◽  
Granule Cell Layer ◽  
Developmental Expression ◽  
Main Olfactory Bulb ◽  
Glomerular Layer ◽  
Layer 4

Abstract The distribution of calbindin, calretinin and parvalbumin during the development of the mouse main olfactory bulb (MOB) was studied using immunohistochemistry techniques. The results are as follows: (1) calbindin-immunoreactive profiles were mainly located in the glomerular layer, and few large calbindin-immunoreactive cells were found in the subependymal layer of postnatal day 10 (P1 0) to postnatal day 40 (P40) mice; (2) no calbindin was detected in the mitral cell layer at any stage; (3) calretinin-immunoreactive profiles were present in all layers of the main olfactory bulb at all stages, especially in the olfactory nerve layer, glomerular layer and granule cell layer; (4) parvalbumin-immunoreactive profiles were mainly located in the external plexiform layer (except for P10 mice); (5) weakly stained parvalbumin-immunoreactive profiles were present in the glomerular layer at all stages; and (6) no parvalbumin was detected in the mitral cell layer at any stage.

scholarly journals Effect of intervening lesions on amino acid distributions in rat olfactory cortex and olfactory bulb.

1980 ◽  
Vol 28 (11) ◽  
pp. 1157-1169 ◽  
Author(s):  
D A Godfrey ◽  
C D Ross ◽  
J A Carter ◽  
O H Lowry ◽  
F M Matschinsky
Keyword(s):  
Amino Acids ◽  
Olfactory Bulb ◽  
Granule Cells ◽  
Anterior Commissure ◽  
Piriform Cortex ◽  
Mitral Cell ◽  
Olfactory Cortex ◽  
Gamma Aminobutyric Acid ◽  
Lateral Olfactory Tract ◽  
Mapping Procedure

Levels of the proposed neurotransmitter amino acids glutamate, aspartate, gamma-aminobutyric acid (GABA), and glycine were measured within the layered structures of the olfactory bulb and olfactory cortex following unilateral transections of the lateral olfactory tract or of virtually all fiber tracts of the olfactory peduncle. Distributions of the amino acids on both lesion and control sides were examined and compared by means of a mapping procedure. The results suggest: 1) Glutamate and aspartate are specifically associated with mitral (and presumably also tufted) cell axons and terminals in the piriform cortex. The distribution of aspartate in the olfactory bulb is further suggestive of a specific association of aspartate with mitral cell dendrites and somata. 2) Glutamate might be specifically associated with some centrifugal fibers traveling to the olfactory bulb in or near the anterior commissure. 3) GABA might be specifically related to some certrifugal fibers to the olfactory bulb in addition to its prominent association with granule cells of the bulb. 4) Glycine is unlikely to play a prominent neurotransmitter role in either the olfactory bulb or olfactory cortex.

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