Juxtaglomerular neurons

Ma J, Lowe G. 2005. Dendrites of juxtaglomerular neurons in rat olfactory bulb express Ca -permeable AMPA receptors. AChemS Abstr 86. 

The majority of the juxtaglomerular neurons can be classified as one of three types ... 

Fig. 5. Basic circuitry of the main olfactory bulb. Axons of ORNs form the olfactory nerve (ON). These axons terminate in the glomeruli onto mitral (M) and tufted cells (external tufted cell, ET middle tufted cell, MT) and onto juxtaglomerular neurons including periglomerular cells (PG), ET cells and short axon cells (SA). There are one way and reciprocal synapses between the apical dendritic branches of mitral and tufted cells and the dendrites of juxtaglomerular neurons (upper inset - glomerular synapses). The lateral dendrites of mitral and tufted cells form one way and reciprocal synapses with the apical dendrites of granule cells (lower inset - dendrodendritic synapses).

While deafferentation does not influence the expression of GABA in periglomerular neurons, other transmitters are influenced by the olfactory nerve. In the hamster, many juxtaglomerular neurons express substance P and this peptide is downregulated following deafferentation (Kream et al. 1984). In addition, new results indicate that the influence of the olfactory nerve also extends to the expression of CCK in tufted cells and to CRF in mitral cells (Shipley et al. unpublished observations). 

Fig. 6. Dopamine neurons in the MOB. Bright (A) and darkfield (B) photomierographs of juxtaglomerular cells expressing the immunoreactivity to an TOH antibody. In B, there is a marked decrease in cellular expression of the dopamine phenotype due to lesion of the olfactory nerve input to the bulb using ZnS04. Bar in A, 100 pm.

Terminals of the olfactory nerve synapse both with the apical dendrites of mitral and tufted cells and with juxtaglomerular (JG) cells. JG cells, which send processes primarily into a single glomerulus, form reciprocal synapses with the apical dendrites of mitral and tufted cells many of these are symmetrical and, therefore, are considered inhibitory. There is thus a feedforward pathway for inhibition of mitral/tufted cells olfactory nerve terminals excite JG cells which, in turn inhibit mitral/tufted cells. The mitral/tufted side of the reciprocal synapses are asymmetrical and are, therefore, considered excitatory. Thus there is also a pathway for feedback inhibition from mitral and tufted cells back to JG cells. Some JG neurons send axons to neighboring glomeruli but it is not known if these local projections are excitatory or inhibitory (Schneider and Macrides,... 

There is no known extrinsic DA innervation of the olfactory bulb. As noted above, however, the MOB contains several hundred thousand intrinsic juxtaglomerular DA neurons... 

---