Cells In Rat Olfactory Bulb Research Articles

Odor modality is transmitted to cortical brain regions from the olfactory bulb.

Odor perception is the impetus for important animal behaviors with two predominate modes of processing: odors pass through the front of the nose (orthonasal) while inhaling and sniffing, or through the rear (retronasal) during exhalation and while eating. Despite the importance of olfaction for an animal's well-being and that ortho and retro naturally occur, it is unknown how the modality (ortho vs. retro) is even transmitted to cortical brain regions, which could significantly affect how odors are processed and perceived. Using multielectrode array recordings in tracheotomized anesthetized rats, which decouples ortho-retro modality from breathing, we show that mitral cells in rat olfactory bulb can reliably and directly transmit orthonasal versus retronasal modality with ethyl butyrate, a common food odor. Drug manipulations affecting synaptic inhibition via GABAA lead to worse decoding of ortho versus retro, independent of whether overall inhibition increases or decreases, suggesting that the olfactory bulb circuit may naturally favor encoding this important aspect of odors. Detailed data analysis paired with a firing rate model that captures population trends in spiking statistics shows how this circuit can encode odor modality. We have not only demonstrated that ortho/retro information is encoded to downstream brain regions but also used modeling to demonstrate a plausible mechanism for this encoding; due to synaptic adaptation, it is the slower time course of the retronasal stimulation that causes retronasal responses to be stronger and less sensitive to inhibitory drug manipulations than orthonasal responses.NEW & NOTEWORTHY Whether ortho (sniffing odors) versus retro (exhalation and eating) is encoded from the olfactory bulb to other brain areas is not completely known. Using multielectrode array recordings in anesthetized rats, we show that the olfactory bulb transmits this information downstream via spikes. Altering inhibition degrades ortho/retro information on average. We use theory and computation to explain our results, which should have implications on cortical processing considering that only food odors occur retronasally.

In vitro Maintenance of Olfactory Mucosa: with Enriched Olfactory Ensheathing Cells

Human Olfactory Mucosa (OM) regulates olfaction through axonal regeneration and myelination mediated by stem cells and Olfactory Ensheathing Cells (OECs) resident in the niche. Purified OECs/olfactory biopsies have been utilized for functional recovery in different Spinal Cord Injury (SCI) models. However, recent reports find this debatable where we propose primary culture of OM, basal cells of olfactory epithelium and olfactory ecto-mesenchymal stem cells. Our defined culture conditions improve the life span of OM with enrichment of OECs providing a strategy for employment for SCI/cochlear damage repair. Briefly, OM post-collection, was non-enzymatically sliced, cultured for 6 weeks and cells characterized morphologically, immuno-cytochemically and western blotting. By day 21, ~70% GFAP and p75NTR stained, spindle shaped astrocyte-like and flattened sheet-like OECs displayed axonal remyelination. By day 30, caspase 3, 8, 9 (gene-product and activity), phospho-p53 negative; GFAP and p75NTR positive dense, overlapping mass of cells was found. This was accompanied with degenerative changes by 6 weeks through GFAP staining. Conversely, trypsination on day 21 resulted in >95% OECs with flattened morphology, GFAP and p75NTR positivity. The human derived OECs were compared with the 2-day SD rat Olfactory Bulb Cells cultured for 2 weeks in F12 media (GFAP and p75NTR positive). Hence, cultured olfactory mucosa displaying axonal regeneration with OECs in culture provides a vehicle for SCI/cochlear damage repair studies.

The Role of Beta Receptors in Olfactory Induced Learning: Morphological Changes in the Mitral Cells of Rat Olfactory Bulb after Propranolol and Isoproterenol Treatment

Study ObjectivesThis study was designed to see the histological changes in the olfactory bulb after the administration of propranolol and isoproterenol.MethodsThirty Albino (Sprague‐Dawley) rats were divided into equal groups (n=10). Control group was treated with normal saline, experimental group I was treated with propranolol and experimental group II was treated with Isoproterenol. The morphology of the mitral cells was studied after staining with H & E and silver staining under microscope.ResultsThe histology of the olfactory bulb of the control group revealed the classic six laminae. Mitral cell layer consisted of a layer of cells, which were pyramidal in shape with prominent nucleoli.Differences in the morphological characteristics of mitral cells were observed in experimental groups. Experimental group I showed mitral cells had a vacuolar appearance; however, the nucleus was rounded in appearance with prominent nucleoli. Experimental group II showed that mitral cells present in the mitral cell layer had indistinct boundaries. Nucleus was less basophilic with prominent nucleoli.ConclusionWe conclude that by neuromodulating norepinephrine using propranolol and isoproterenol histological changes can be observed in the rat olfactory bulb especially in the morphology of the mitral cells.Research Support: Research was supported by University of Health Sciences, Lahore, Pakistan.

Odor Discrimination by Mitral Cells in Rat Olfactory Bulb Using Microwire Array Recording

Odor Discrimination by Mitral Cells in Rat Olfactory Bulb Using Microwire Array Recording

Calcium permeable AMPA receptors and autoreceptors in external tufted cells of rat olfactory bulb

Glomeruli are functional units of the olfactory bulb responsible for early processing of odor information encoded by single olfactory receptor genes. Glomerular neural circuitry includes numerous external tufted (ET) cells whose rhythmic burst firing may mediate synchronization of bulbar activity with the inhalation cycle. Bursting is entrained by glutamatergic input from olfactory nerve terminals, so specific properties of ionotropic glutamate receptors on ET cells are likely to be important determinants of olfactory processing. Particularly intriguing is recent evidence that AMPA receptors of juxta-glomerular neurons may permeate calcium. This could provide a novel pathway for regulating ET cell signaling. We tested the hypothesis that ET cells express functional calcium-permeable AMPA receptors. In rat olfactory bulb slices, excitatory postsynaptic currents (EPSCs) in ET cells were evoked by olfactory nerve shock, and by uncaging glutamate. We found attenuation of AMPA/kainate EPSCs by 1-naphthyl acetyl-spermine (NAS), an open-channel blocker specific for calcium permeable AMPA receptors. Cyclothiazide strongly potentiated EPSCs, indicating a major contribution from AMPA receptors. The current–voltage (I–V) relation of uncaging EPSCs showed weak inward rectification which was lost after >∼10 min of whole-cell dialysis, and was absent in NAS. In kainate-stimulated slices, Co 2+ ions permeated cells of the glomerular layer. Large AMPA EPSCs were accompanied by fluorescence signals in fluo-4 loaded cells, suggesting calcium permeation. Depolarizing pulses evoked slow tail currents with pharmacology consistent with involvement of calcium permeable AMPA autoreceptors. Tail currents were abolished by Cd 2+ and (±)-4-(4-aminophenyl)-2,3-dioxo-6-nitro-1,2,3,4-tetrahydrobenzo[f]quinoxaline-7-sulfonamide (NBQX), and were sensitive to NAS block. Glutamate autoreceptors were confirmed by uncaging intracellular calcium to evoke a large inward current. Our results provide evidence that calcium permeable AMPA receptors reside on ET cells, and are divided into at least two functionally distinct pools: postsynaptic receptors at olfactory nerve synaptic terminals, and autoreceptors sensitive to glutamate released from dendrodendritic synapses.

Hyperpolarisation-activated current in glomerular cells of the rat olfactory bulb

Whole-cell patch-clamp recordings were carried out in visually identified periglomerular and external tufted cells of rat olfactory bulb. Most of the neurones showed a slowly developing hyperpolarisation-activated current with a threshold generally positive to resting potential and with a strongly voltage-dependent activation time constant. The current, identified as Ih, was sodium- and potassium-sensitive, suppressed by external caesium, and insensitive to barium. Under current-clamp conditions, perfusion with caesium induced a 10 mV hyperpolarisation and a marked reduction of the rate of low-frequency oscillations induced experimentally. It is concluded that most of the cells in the rat glomerular layer present a distinct h-current, which is tonically active at rest and which may contribute to the oscillatory behaviour of the bulbar network.

Odor-Induced, Activity-Dependent Transneuronal Gene InductionIn Vitro: Mediation by NMDA Receptors

Expression of tyrosine hydroxylase (TH) by juxtaglomerular (JG) neurons of the olfactory bulb (OB) requires innervation of the bulb by olfactory receptor neurons (ORNs). ORN lesion selectively downregulates TH in JG neurons. In reversible odor deprivation, TH expression is downregulated as the naris is closed and then upregulated upon naris reopening. The mechanism or mechanisms regulating this dependence are unknown. TH expression could be regulated by trophic factor release and/or synaptic activity from ORN terminals. We investigated TH expression in cocultures of dissociated postnatal rat OB cells and embryonic olfactory neuroepithelium (OE) slice explants. TH-positive neurons in control dissociated OB cell cultures alone comprise only a small fraction of the total population of cells present in the culture. However, when OE slice explants are cocultured with dispersed OB cells, there is a mean 2.4-fold increase in the number of TH-positive neurons. ORNs in vivo use glutamate as a neurotransmitter. Broad spectrum excitatory amino acid antagonists (kyurenic acid) or selective antagonists of the NMDA receptor (APV) both prevent induction of TH expression in OE-OB cocultures. Furthermore, pulse application of NMDA stimulates TH expression in OB neurons in the absence of OE. In vitro, OB TH neurons express NMDA receptors, suggesting that NMDA stimulation is acting directly on TH neurons. Exposure of OE explants to natural odorants results in upregulation of TH, presumably through increased ORN activity, which could be blocked by APV. These findings indicate that odorant-stimulated glutamate release by ORN terminals regulates TH expression via NMDA receptors on JG dopaminergic neurons.

In VitroGeneration of Adult Rat Olfactory Sensory Neurons and Regulation of Maturation by Coculture with CNS Tissues

Olfactory sensory neurons (OSNs) are continually generated throughout life. Although previous studies have examined neurogenesis in olfactory cell cultures derived from embryonic or newborn rodents, we demonstrate neurogenesis in cell cultures derived from adult rat tissues. Dissociated cells taken from adult rat nasal mucosal tissues (ANM cells) were plated onto a feeder layer of newborn rat cortical glia (astrocytes) in serum-free conditions. Immature OSNs (stained for neuron-specific tubulin, NST) increased in number between 1 and 5 d in vitro (DIV) and in mass thereafter. Mature OSN (stained for olfactory marker protein, OMP) numbers decreased between 1 and 5 DIV, then increased over 5 DIV values by 12 and 15 DIV. Pulse labeling with [3H]thymidine confirmed in vitro neurogenesis. To determine whether the target cells for OSNs, olfactory bulb (OB) neurons, provide trophic support, dissociated newborn rat OB cells were cocultured with ANM cells on glia. This resulted in greater numbers of OMP-positive (OMP+) neurons after 9 DIV than ANM-alone cultures. This neurotrophic effect was not OB specific. Addition of newborn rat cerebellar and embryonic rat ventral mesencephalic cells to ANM cells also increased OMP+ neurons, whereas addition of newborn rat cortical cells or controls (purified glia or fibroblasts) did not. Changes in numbers of dopaminergic neurons (stained for tyrosine hydroxylase), present in OB and VM cultures, did not correlate with OMP+ neuronal increases. Thus, cultures of adult rat OSNs demonstrate neurogenesis, and trophic/maturation support is variably provided by CNS neurons (and not glia).

Sodium current in periglomerular cells of rat olfactory bulb in vitro.

The capacity of periglomerular cells (PGc) to give fast, Na-dependent action potentials is a crucial and debated issue for the comprehension of how sensory information is processed in the olfactory bulb (OB). Using patchclamp whole cell recording in thin slices of rat OB (P8-P20) we showed that fast sodium conductance is present in all the PGc studied, that this current is sufficiently large to generate action potentials and that action potentials can be evoked in these cells by direct stimulation of the olfactory nerve. A comprehensive kinetic characterization of INa is also presented.

Transient expression of neurotensin mRNA in the mitral cells of rat olfactory bulb during development

The transient expression of neurotensin mRNA in the mitral cells of the rat olfactory bulb was demonstrated during the perinatal period using non-radioactive in situ hybridization in which an alkaline phosphatase labelled oligodeoxynucleotide probe was used. The relative cellular content of neurotensin mRNA signal was measured by use of a microdensitometer. Neurotensin mRNA positive cells were observed in the primordium of mitral cells on embryonic day 14 and their mRNA content increased gradually up to the day of birth. During the first postnatal week, the strength of their neurotensin mRNA signal decreased dramatically, and continued to decrease until in the adult olfactory bulb neurotensin mRNA was no longer detectable. This decrease of the neurotensin mRNA content coincided with a parallel decrease of neurotensin immunoreactivity observed in the lateral olfactory tract.

Selective immunocytochemical staining of mitral cells in rat olfactory bulb with affinity purified antibodies against N-acetyl-aspartyl-glutamate

Polyclonal antibodies were raised in rabbits against N-acetyl-aspartyl-glutamate (NAAG) coupled to bovine serum albumin (BSA) with carbodiimide and were purified by affinity chromatography sequentially over BSA-agarose and NAAG-agarose resins. Solid-phase RIA revealed a distinct pattern of specificity of the antibodies for N-acetylated acidic peptides, with highest signal obtained for NAAG, and essentially no immunoreactivity demonstrable for aspartate or glutamate. Coronal sections through carbodiimide-fixed rat olfactory bulb were incubated with the purified antiserum and antigen localization visualized by the avidin-biotin peroxidase techniques. Immunoreactivity was restricted to the mitral cells, the major excitatory projection neurons of the lateral olfactory tract, a putative glutamatergic pathway. Immunoreactivity was selectively blocked by preincubation of the antibody with 1 μg/ml of NAAG-BSA. These results demonstrate a specific neuronal localization of NAAG-like immunoreactivity and support the candidacy of NAAG as a neurotransmitter of the lateral olfactory tract.

Aspartate-like immunoreactivity in mitral cells of rat olfactory bulb

Antisera against aspartate (Asp) were prepared by immunizing rabbits with Asp conjugated to bovine serum albumin by glutaraldehyde, after which the antisera were purified using an Asp-immobilized epoxy-activated affinity column. The purified Asp antiserum showed no cross-reactivity, except for a 3% cross-reactivity against d-Asp. Asp-like immunoreactivity in mitral cells of the rat olfactory bulb was demonstrated, using this purified Asp antiserum.