Medullary neurons in the core white matter of the olfactory bulb: a new cell type

Abstract

The structure of a new cell type, termed the medullary neuron (MN) because of its intimate association with the rostral migratory stream (RMS) in the bulbar core, is described in the adult rat olfactory bulb. The MN is a triangular or polygonal interneuron whose soma lies between the cellular clusters of the RMS or, less frequently, among the neuron progenitors therein. MNs are easily distinguished from adjacent cells by their large size and differentiated structure. Two MN subtypes have been categorized by the Golgi technique: spiny pyramidal neurons and aspiny neurons. Both MN subtypes bear a large dendritic field impinged upon by axons in the core bulbar white matter. A set of collaterals from the adjacent axons appears to terminate on the MN dendrites. The MN axon passes in close apposition to adjacent neuron progenitors in the RMS. MNs are immunoreactive with antisera raised against gamma-aminobutyric acid and glutamate decarboxylase 65/67. Electron-microscopic observations confirm that MNs correspond to fully differentiated, mature neurons. MNs seem to be highly conserved among macrosmatic species as they occur in Nissl-stained brain sections from mouse, guinea pig, and hedgehog. Although the functional role of MNs remains to be determined, we suggest that MNs represent a cellular interface between endogenous olfactory activity and the differentiation of new neurons generated during adulthood.

Chandelier and Interfascicular Neurons in the Adult Mouse Piriform Cortex

“…In an attempt to improve the neuronal staining quality and completeness in the adult rodent brain, two different, straightforward, strategies were applied, namely longer incubation of the specimens with silver and larger number of assays (more than 250 brains). As it is clear from the present account and our previous studies (Larriva-Sahd et al, 2002; Larriva-Sahd, 2006, 2008; Paredes and Larriva-Sahd, 2010) the adoption of these strategies has enhanced our ability to disclose neuronal fine structure.…”

“…Characterization of additional cells in the basic circuitry of the PC represents a first, necessary step to elucidate the role of specific neuron phenotypes in the overall PC physiology. To accomplish this, the Golgi technique was utilized, as it has proven to be a reliable tool to fully visualize novel neurons and neuropil in the adult rodent forebrain (Larriva-Sahd et al, 2002; Larriva-Sahd, 2006, 2008; Paredes and Larriva-Sahd, 2010). Since molecular biological studies and genetically modified mice have become indispensable tools for most recent neuroscience research, the adult mouse was elected for the present study.…”

Clusters of secretagogin-expressing neurons in the aged human olfactory tract lack terminal differentiation

“…The continued identification of molecularly and morphologically diverse neuronal subtypes in the human olfactory circuitry, like in rodents (29), may be rewarding because it can uncover striking phylogenetic differences (30). Here, we show the existence of spatially segregated neurons expressing secretagogin, as well as a battery of markers nonconventional for differentiated neurons that had integrated into a synaptic circuitry.…”

Cytological organization of the alpha component of the anterior olfactory nucleus and olfactory limbus

“…An additional set of neurons, has been recently described in association with to the rostral migratory stream, the so-called “medullary neurons” (Paredes and Larriva-Sahd, 2010). …”

“…As part of a series of ongoing studies aimed at depicting the neuronal organization of the rodent rhinencephalon (Larriva-Sahd, 2008, 2010; Paredes and Larriva-Sahd, 2010), the present study was conducted to describe the cytological organization of the aAON and a complex region between the anterior aspect of the AOB and the caudal limit of the MOB. The study was primarily conducted in specimens from adult rats, although mouse and guinea—pig specimens from our collection were examined to define interspecies homology.…”