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A simple staining method for visualizing unmyelinated axons in the rat olfactory bulb is described. A typical histological analysis of the glomerular layer showing the unmyelinated receptor axons in the olfactory bulb of the rat is presented.
(1) Regions which exert centrifugal influences on the olfactory bulb activity were studied by applying systematic stimulation to various areas of the ipsilateral telencephalon in the rabbit. By delivering electric stimuli to the anterior commissure (AC), the deep lying structures in the projection areas of the lateral olfactory tract (LOT) and the medial forebrain bundle situated between the lateral hypothalamic area and the lateral preoptic area, negative field potentials were evoked in the granule cell layer (GCL) of the bulb. (2) Intracellular recordings from the mitral cells and the GCL neurons in the olfactory bulb were performed in order to clarify the modes of the centrifugal influences on the olfactory bulb neurons. (3) EPSPs were recorded in the GCL neurons by stimulation of the deep-lying structure of the prepiriform cortex as well as by stimulation of the AC. The onset time and duration of the EPSPs corresponded well to those of the negative field potentials in the GCL. Thus, it was suggested that these negative potentials were caused by the EPSPs of the number of granule cells. (4) In almost all of the mitral cells, IPSPs were recorded by stimulation of the AC and the deep-lying structures of the LOT projection areas. The onsets of the IPSPs were found with delays of several milliseconds from those of the negative field potentials in the GCL. (5) It was postulated that the excitation of the centrifugal system mainly exerts a depressive influence on the activity of the mitral cell, and that the GCL neuron (presumably the granule cell) seems to be an inhibitory interneuron interpolated between the extrinsic fibers from the telencephalon and the mitral cell.
Chronic ethanol exposure, a key feature of alcohol use disorder (AUD), can affect the nervous system, but its molecular impact on the olfactory bulb remains unclear. In this study, an intermittent two-bottle voluntary drinking model was established in male mice, and transcriptome sequencing was performed on olfactory bulb tissues. DESeq2 analysis identified 188 differentially expressed genes, including 68 upregulated and 120 downregulated genes. Kyoto Encyclopedia of Genes and Genomes (KEGG) and Reactome pathway database (Reactome) analyses indicated that ethanol-responsive genes were predominantly enriched in receptor-mediated signaling pathways, particularly those linked to G protein-coupled receptor (GPCR) signaling. Protein-protein interaction analysis further identified eight core GPCR-related genes. Quantitative real-time PCR (qRT-PCR) validation revealed that Cxcl10, Grp, Pcp2, and Pdyn were markedly downregulated in the ethanol group. These results suggest that chronic ethanol exposure is associated with transcriptional alterations in the male mouse olfactory bulb and may selectively affect several GPCR-related signaling components. This study provides candidate molecular evidence for further investigation of ethanol-associated olfactory dysfunction.
Binding sites for the dipeptide L-carnosine (beta-alanyl-L-histidine) have been detected in membranes prepared from mouse olfactory bulbs. The binding of L-[3H]-carnosine was saturable, reversible and stereospecific and had a Kd of about 770 nM. The stereospecific binding of L-carnosine represented about 30% of the total binding at pH 6.8, and decreased markedly with increasing pH. Binding was stimulated by calcium, unaffected by zinc, magnesium or manganese and inhibited by sodium and potassium. Carnosine binding was sensitive to trypsin and phospholipases A and C, but not to neuraminidase. Nystatin and filipin, which interact with membrane lipids, also interferred with binding. Some peptide analogues of carnosine were potent inhibitors of binding, but a variety of drugs serving as potent inhibitors in other binding systems had no effect on carnosine binding. Carnosine binding to mouse olfactory bulb membranes was 15-fold higher than that seen in membranes prepared from cerebral hemispheres, 5-fold higher than that seen in membranes prepared from cerebral hemispheres, 5-fold higher than in cerebellum membranes and 3-fold higher than in membranes from spinal medulla and the olfactory tubercle-lateral olfactory tract area. Binding sites for 6 other radiolabeled receptor ligands were also detected in bulb membranes. Peripheral deafferentation of the olfactory bulbs by intranasal irrigation with ZnSO4 led to a loss greater than 90% of the L-[3H]carnosine binding in 4--5 days with much smaller losses in binding of the other 6 ligands over a 180-day observation period. This initial loss of carnosine binding after denervation was due to a loss of binding site stereo-specificity followed by a loss of binding sites. The characteristics of the carnosine binding site in olfactory bulb fulfil 6 of the 7 criteria considered relevant for a functional receptor.
The distribution of [3H]gamma-aminobutyric acid (GABA) labeled elements in rat olfactory bulb was studied by light and electron microscopic autoradiography. [3H]GABA was strongly taken up into glial cells and pericytes in all layers of the bulb. The neuronal uptake of [3H]GABA was mainly seen in certain types of nerve terminals. About one-third of the granule dendritic terminals, some nerve endings of short axon cells, and certain nerve endings of extrabulbar origin showed a strong labeling. Labeling was seen in a small population of the periglomerular, short axon and granule cell bodies. Most cell bodies of these 3 types as well as the mitral cells did not, however, accumulate any appreciable amo9nt of [3H]GABA. The labeling pattern seen after injection of [3H]glycine and [3H]leucine was clearly different from the pattern seen after [3H]GABA injection. The labeling was more uniformly distributed over the components of the neuropil with a considerably higher activity over certain cell somata such as the mitral cells. The present results demonstrate that neuronal uptake and accumulation of [3H]GABA occur into populations of olfactory bulb cells and processes, which from neurophysiological and/or immunohistochemical studies are supposed to use GABA as a neurotransmitter.
The impulse activity of anterior portions of the fish olfactory bulb depends on coming of signals from the receptors as shown by the fact that action of novokain on the receptors entirely suppressed the activity. A direct application of CoCl2 solution (1--1.5 mM) had no effect on either spontaneous or evoked by adequate stimulation impulse activity in these areas which indicates its presynaptic, i.e. the receptor nature. The surface structures of the bulb anterior portions did not respond to electric stimulation of the olfactory tract while the electric stimulation of these structures evoked a response in the olfactory nerve which corresponds to the conclusion of the receptor nature of the impulse activity in fibers on the surface of the bulb anterior portions.
The role of the pineal gland, olfactory bulbs and photoperiod in the regulation of the two daily surges of plasma prolactin in the pseudopregnant rat has been investigated. Pinealectomy had no effect on the surges of prolactin in pseudopregnant rats maintained on either a long (14 h light : 10 h darkness; 14L : 10D) or a short (2L : 22D) photoperiod, but olfactory bulbectomy decreased the nocturnal surge in animals maintained on 14L : 10D. This effect of bulbectomy was eliminated if the rats maintained on 14L : 10D were also pinealectomized. After cervical stimulation, bulbectomized rats maintained on a 2L : 22D photoperiod had nocturnal-type prolactin surges similar to those of intact rats maintained on the same photoperiod. These results indicate that the pineal gland andlength of photoperiod are not involved in the regulation of the surges of plasma prolactin in pseudopregnant rats but that the olfactory bulbs may enhance the nocturnal surge.
1. A method for delivering odour pulses of controlled onset, steady plateau and abrupt termination, has been developed and applied to a single unit study of mitral cell responses in the olfactory bulb of the salamander. The pulses have been monitored during the experiments near the site of stimulation on the olfactory mucosa.2. Responses have been categorized as excitatory or suppressive based on the initial response to the odour pulse.3. Initially excitatory responses had sustained discharges near threshold. With increasing concentration, the discharge changed to a brief burst followed by suppression. The briefest latency of a unit response was 120 msec, using stimulation of medium concentration, after the start of the pulse; the majority of units appeared to be excited within 200-300 msec. Ramp stimuli gave increasing periods of excitation as the rise time of the odour front became less abrupt.4. Initially suppressive responses showed suppression at all levels of concentration. The majority of units appeared to have an onset of suppression about 300-400 msec after the start of the pulse.5. These basic responses, involving suppression or excitatory-suppressive sequences, can be correlated with some basic properties of the synaptic circuits in the olfactory bulb. The time courses of the initial responses appear to be within the time periods of the inhalation cycle of the salamander, and therefore may reflect mechanisms of processing of natural olfactory stimuli.
In the orbitofrontal olfactory area (LPOF) which was delineated in a previous paper, the capacity for odor discrimination was studied and compared with that in the anterior pyriform cortex (AP), the medial portion of the amygdala (MA), and the olfactory bulb (OB). Unanesthetized monkeys were used and eight odors were applied. 1. In the OB, 12.5% of the cells responded to only one odor, and the cells which responded to five odors were most numerous (25%). The total of the cells which responded to two, three, and four odors was 52%, which was less than the total of the cells responding to three, four, and five odors (67.5%). A small number oc cells responded to all eight odors (2.5%). The responses were classified as an increase (+type), a decrease (-type), or no change (no-type) in the rate of spike discharge. 2. In the AP and MA, no difference in the response patterns was found. The cells which responded to only one odor were 12.3% of the total, and the cells which responded to three different kinds of odors were most numerous (34.3%). The total of the cells responding to two, three, and four odors was 80%, much more than that in the OB. In addition, no cell responded to all eight odors. Concerning the response types, an increase followed by a decrease, or vice versa, in the rate of spike discharges (mixed-type) was observed which did not appear in the OB. Thus, an advance was found in the processing of olfactory information when compared with the OB. 3. A most striking finding in the LPOF was that 50% of the cells responded to only one odor. The cells which responded to two, three, and four odors decreased in this order, and no cell responded to more than five odors. These cells never responded to light or sound. 4. Using three very similar odors and five very different odors, it was apparent that the ability to discriminate odors of the same category is far more advanced in the LPOF than in the lower olfactory areas; and, in contrast, the lower olfactory areas also play a significant role in the discrimination of odors which belong to different categories. 5. It was concluded that the capacity for odor discrimination definitely improves along the olfactory nervous system from the lower to the higher areas. It is highly probable that a fine and sepcific discrimination of odors is performed in the LPOF.
Responses of 75 single units in the goldfish olfactory bulb were analyzed in detail for their relationship to the time-course of the change in odor concentration during each odor stimulus. Odor stimuli were controlled for rise time, duration, and peak concentration by an apparatus developed for the purpose. This apparatus enabled aqueous odor stimuli to be interposed into a constant water stream without changes in flow rate. The time-course of the concentration change within the olfactory sac was inferred from conductivity measurements at the incurrent and excurrent nostrils. Temporal patterns of firing rate elicited by stimuli with relatively slow rising and falling phases could be quite complex combinations of excitation and suppression. Different temporal patterns were produced by different substances at a single concentration in most units. Statistical measures of the temporal pattern of response for a small number of cells at a given concentration were more characteristic of the stimulus substance than any of three measures of magnitude of response. The temporal patterns change when the peak concentration, duration, and rise time of the stimuli are varied. The nature of these changes suggests that the different patterns are due primarily to the combined influence of two factors: (a) a stimulus whose concentration varies over time and (b) a relationship between concentration and impulse frequency which varies from unit to unit. Some units produce patterns suggestive of influence by neural events of long time constant. The importance of temporal patterns in odor quality and odor intensity coding is discussed.
The giant cells in the olfactory bulb of labyrinth fish, most likely belonging to the nervus terminalis, show ultrastructural features of active synthesis of secretory material. Dense core vesicles (70--100 nm in diameter), found in the perikaryon as well as in the axon, are the possible storage sites of the secretory substance. Its chemical nature is unknown. In some of these vesicles acid phosphatase is demonstrable. Large membrane-bound bodies (up to 2000 nm in diameter), either containing an electron dense matrix or debris of cytoplasmic organelles, are also acid phosphatase-positive, suggesting their lysosomal nature. Some other ultrastructural characteristics of these cells are also described.
The spatial pattern of EEG activity at the surface of the olfactory bulb tends to be invariant with respect to input and to change to a new pattern whenever an animal is trained to expect or search for a particular odor. It is postulated here that the spatial EEG pattern is dependent on a neural template for that odor that is formed during training. This hypothesis is expressed in the form of a model consisting of an array of interconnected elements (1 X 10 or 6 X 6). Each element represents 2 excitatory and 2 inhibitory subsets of neurons with 3 types of internal feedback: negative, mutually excitatory, and mutually inhibitory. The elements are interconnected only by mutual excitation and mutual inhibition. Each neural subset is represented by a nonlinear differential equation; the connections are represented by modifiable coupling coefficients. With appropriate values of the time, coupling, and gain coefficients, and with input that is modelled on olfactory input, the set of 40 or 144 equations gives output that simulates the time and space patterns of the EEG. In the naive state the coefficients are uniform. A template is formed by giving input to selected elements, cross-correlating the outputs, and weighting the mutually excitatory coupling coefficient between each pair of elements by the corresponding correlation coefficient. When a template has been formed, input to nontemplate elements is treated as noise. Optionally a matched filter is made to simulate habituation by reducing the synaptic gain coefficients of those excitatory subsets that receive the noise. The model is tested by giving input to nontemplate elements and to none, part or all of the template elements. There are two outputs of the model. One is the spatial pattern Vj of the root mean square (rms) amplitudes of the individual outputs v(j, t) of the elements. The other output is the rms amplitude Erms of the ensemble average E(t) over v(j, t). The results show that Vj depends on the template and is relatively insensitive to input, whether or not input is given to template elements. However, Erms increases in proportion to the number of "hits" on the template. If the number of elements receiving noise does not exceed the number of elements in a template, or if the noise is matched with a habituation filter, then Erms rises above the noise level for a "hit" on any one or more template elements irrespective of location or combination. Vj conforms to the performance of the surface EEG. Erms is not yet accessible to physiological measurement.
The rat olfactory bulb was studied with the Falck-Hillarp formaldehyde fluorescence technique, including recent modifications, autoradiography and electron microscopic cytochemistry (permanganate fixation). Some periglomerular cells and few superficial tufted cells take up and accumulate catecholamines and precursors. They probably represent dopamine cells. In the glomeruli, probable 5-hydroxy-tryptamine nerve terminals could be identified. In the granular and external plexiform layers, noradrenaline axon terminals were present. At the ultrastructural level, monoamine boutons were in synaptic contact with dendritic spines of granule cells and in the glomeruli, probable 5-hydroxytryptamine boutons formed synapses with periglomerular cell dendrites. Therefore, monoamine afferents to the bulb may exert their influence via interneurons.
The authors report a very rare case of ruptured intracranial aneurysm at the olfactory bulb. The aneurysm was located at the tip of an abnormal loop of the proximal anterior cerebral artery and was buried in the olfactory sulcus. Preoperative examination revealed hyposmia.
Responses of 50 olfactory bulb neurons of the bullfrog to odorous solutions of ethyl n-butyrate were composed mainly of facilitation, inhibition and no response, whereas those of the same neurons to water were mainly of facilitation and delayed facilitation. The responses to water tended to continue longer than those to the odorous solutions.
Bipolar EEG records of olfactory activity of Caiman sclerops were computer analyzed and the derived power spectral density functions (PSD) were statistically compared by the method of Bendat and Piersol (1971) and Fails and Verlander (1977). These recordings included surface and underwater episodes. The Caiman olfactory EEG may legitimately be divided into four types of activity: a spindle form of high amplitude and long duration (1-3 sec), a spindle of lower amplitude, short duration (less than 1 sec) and significantly lower power generation irregular surface background activity, and an irregular underwater activity. PSD analysis showed a great deal of moment-to-moment variability in both quantity of power generated and the frequency regions containing significant power generation during surface background activity. A statistical comparison of surface background and underwater background activity also showed significant differences.
Application of [3H]proline to the vomeronasal organ (VNO) in mice results in the transport of labelled material along the vomeronasal axons to their terminals in the glomerular layer of the accessory olfactory bulb (AOB). In addition labelled material leaves the vomeronasal nerve terminals and is found over the external plexiform layer (EPL), where a previous electron microscopic autoradiographic study showed that it is preferentially accumulated in mitral cells. Grain densities over the glomerular layer and the EPL were counted in light micrographs. After subtracting background, the overall density of grains in the EPL is about 10% of that over the glomerular layer at 6 h after administration of [3H]proline to the VNO (5 mice). In a further 7 mice, puromycin (or saline) was applied directly to the AOB at hourly intervals during the 6 h after [3H]proline administration. Under these circumstances the labelling in the EPL is only 2--4% of that in the glomerular layer (9% for the 2 saline controls). These observations are evidence that a major part of the transsynaptic transfer mechanism is dependent on protein synthesis, and also favour the view that free amino acids are an important component of the material transferred.
The spatial patterns of activity elicited in the rat olfactory bulb under different odor conditions have been analysed using the 2-deoxyglucose (2DG) technique. Rats were injected with 14C-2DG, exposed to controlled environments of amyl acetate, camphor, cage air, dimethyl disulfide, and pure air and autoradiographs prepared by the method of Sokoloff. Amyl acetate was associated with regions of glomerular layer densities in the anterolateral and mid- to posteromedial parts of the bulbar circumference, as previously reported. The extents of the densities increased with increasing concentration. Camphor odor was associated with regions of increased density in the anterodorsal and mid- to posteromedial parts of the bulb. Exposure to cage air produced scattered densities in the posteromedial and posterolateral bulb. Exposure to dimethyl disulfide gave variable results. Pure air was associated with a minimal number of small dense foci. The results with amyl acetate, camphor and cage air suggest that patterns for different odors are distinguishably different but overlapping. The regions of activity are greatest in extent and density with the highest odor concentrations. These define the regions within which more restricted and isolated foci appear at lower concentrations. The results thus provide evidence for the specific role of spatial factors in the neural processing of odor quality and odor concentration.