Histochemical localization of NADPH-diaphorase in the rat accessory olfactory bulb

The distribution of NADPH-diaphorase activity was examined inthe accessory olfactory bulb of the rat using a direct histochemicaltechnique. Labeled fibers and somata were found in all layersof the accessory olfactory bulb. The entire vomeronasal nerveand all vomeronasal glomeruli were strongly labeled, contraryto the main olfactory bulb, where only dorsomedial olfactoryglomeruli displayed NADPH-diaphorase activity. NADPH-diapborasepositive neurons were identified as periglomerular cells inthe glomerular layer and external plexiform layer, horizontalcells in the internal plexiform layer, and granule cells anddeep short-axon cells in the granule cell layer. The labeleddendrites of the granule cells formed a dense neuropile in thegranule cell layer, internal plexiform layer and external plexiformlayer. The staining pattern in the accessory olfactory bulbwas more complex than what has been previously reported, anddemonstrated both similarities and differences with the distributionof NADPH-diaphorase in the main olfactory bulb.     

Histochemical study on localization of adenosine triphosphatase and 5-nucleotidase in the olfactory bulb of the rat

Summary In the present paper, a histochemical study of the localization of adenosine triphosphatase and 5-nucleotidase in fixed frozen sections of rat olfactory bulb has been carried out by Wachstein and Meisel's method. The structures showing positive reaction are the neurons and blood vessels. The neurons show a wide range of variation of reaction in both intensity as well as distribution. The nucleolus shows an intense and variable reaction and the significance of these have been discussed. The reaction in the cytoplasm is diffuse when it is mild but tends to concentrate toward the cell wall as the intensity increases. It is suggested that the nucleolus may play an important role in the synthesis of the enzymes which can take part in providing the energy needed for the molecular transport concerned with the coduction of nerve impulses.     

Mitral cell differentiation and synaptogenesis of rat presumptive olfactory bulb in organ culture

Summary The ultrastructure of differentiating rat presumptive olfactory bulb in organ culture was investigated with particular reference to mitral cell differentiation and formation of synapses. The presumptive olfactory bulb and olfactory mucosa were dissected en bloc from rat embryos on the fifteenth day of gestation and cultured for 7 days, after which the expiants were examined by electron microscopy. The presumptive olfactory bulb had differentiated into a laminated structure with layers corresponding to the glomerular, external plexiform and mitral cell layers. Mitral-like cells were identified by their location and large cell size. Ultrastructural observations indicated that they were relatively well-differentiated. Their dendrites extended into the glomerular layer in which they were postsynaptic to incoming olfactory axons. The distal part of these dendrites frequently contained coated vesicles. Both asymmetrical and symmetrical synapses were found. The symmetrical synapses involved dendrodendritic contacts between periglomerular cells. Synapses in reciprocal arrangements were not observed in the organ cultures.     

The source of spontaneous activity in the main olfactory bulb of the rat

Introduction

In vivo, most neurons in the main olfactory bulb exhibit robust spontaneous activity. This paper tests the hypothesis that spontaneous activity in olfactory receptor neurons drives much of the spontaneous activity in mitral and tufted cells via excitatory synapses.

Methods

Single units were recorded in vivo from the main olfactory bulb of a rat before, during, and after application of lidocaine to the olfactory nerve. The effect of lidocaine on the conduction of action potentials from the olfactory epithelium to the olfactory bulb was assessed by electrically stimulating the olfactory nerve rostral to the application site and monitoring the field potential evoked in the bulb.

Results

Lidocaine caused a significant decrease in the amplitude of the olfactory nerve evoked field potential that was recorded in the olfactory bulb. By contrast, the lidocaine block did not significantly alter the spontaneous activity of single units in the bulb, nor did it alter the field potential evoked by electrical stimulation of the lateral olfactory tract. Lidocaine block also did not change the temporal patters of action potential or their synchronization with respiration.

Conclusions

Spontaneous activity in neurons of the main olfactory bulb is not driven mainly by activity in olfactory receptor neurons despite the extensive convergence onto mitral and tufted cells. These results suggest that spontaneous activity of mitral and tufted is either an inherent property of these cells or is driven by centrifugal inputs to the bulb.     

Myocardial fibrosis blunts nitric oxide synthase-related preload reserve in human dilated cardiomyopathy

It is clear that ischemia inhibits successful defibrillation by altering regional electro-physiology. However, the exact mechanisms are unclear. This study investigated whether regional gap junction inhibition increases biphasic shock defibrillation thresholds (DFT). Sixteen swine were instrumented with a mid-left anterior descending (LAD) perfusion catheter for regional infusion of 0.5 mM/h heptanol (n = 8) or saline (n = 8). DFT values and effective refractory periods (ERP) at five myocardial sites were determined. Regional conduction velocity (CV) was determined in an LAD drug-perfused and nondrug-perfused region in an additional seven swine. Regional heptanol infusion increased 50% DFT values by 33% (P = 0.01) and slowed CV by 42-59% (P < 0.01) but did not affect ERP. Regional heptanol also increased CV dispersion by approximately 270% (P < 0.05) but did not change ERP dispersion. Regional placebo did not alter any of these parameters. Furthermore, regional heptanol infusion induced spontaneous ventricular fibrillation in eight of eight animals. Increasing spatial conduction velocity dispersion by impairing regional gap junction conductance increased DFT values. Dispersion in conduction velocity slowing during regional ischemia may be an important determinant of defibrillation efficacy.     

Pregnenolone binding sites in the rat olfactory bulb

High concentrations of pregnenolone and its sulfate have been found in several areas of rat and human brain and seem to be controlled by local mechanisms. In the present experiments we have demonstrated pregnenolone binding sites in the cytosolic fraction of the rat olfactory bulb. The pregnenolone binding component showed a Kd = 2.34 +/- 0.66 x 10(-7) M and Nmax = 7.25 +/- 1.20 pmol/mg protein. Pregnenolone, pregnenolone sulfate and 17OH-pregnenolone competed equally for the binding sites while other steroids were less competitive. Protease and trypsin inhibited binding by 48 and 60% respectively. Sucrose density gradient analysis showed a minor peak at 4.6 s and a major one at 3.6 s. After gel filtration chromatography the pregnenolone binding component appeared as 2 peaks corresponding to molecular weights of approximately 150 and 220 kDa. Heating at 60 degrees C increased binding by 150%. These results indicate that the olfactory bulb pregnenolone binding component is complex in nature. Rat plasma also bound pregnenolone. Plasma binding sites could be partially differentiated from those in the olfactory bulb on the basis of susceptibility to lipoprotein lipase, effect of heating and mobility during polyacrylamide gel electrophoresis.     

一氧化氮与嗅觉识别记忆

在解剖及功能完全不同的两套嗅觉系统中 ,一氧化氮 (NO)对嗅觉识别记忆的作用可能有所不同 :在犁鼻系统介导的信息素的识别记忆形成中 ,NO不起直接和关键的作用。由NO诱导的非交配雌鼠对雄鼠信息素的特异性记忆是通过调制神经递质尤其是去甲肾上腺素来实现的 ;在主要嗅觉系统介导的气味识别记忆中 ,NO可能是通过NO cGMP途径对记忆的形成起直接的作用。在嗅觉记忆的获得与巩固中 ,NO也可能参与调制催产素与加压素的释放     

gamma-Aminobutyric acid activity in the olfactory bulb of the rat during the sexual cycle and response to olfactory stimuli.

Glutamic acid decarboxylase activity in the main and accessory olfactory bulbs throughout the sexual cycle of the rat was studied. The effect of male pheromonal secretion on enzyme activity during proestrus and estrus day was also tested. The enzyme activity showed circadian rhythm during the estrous cycle. This rhythm was disrupted during diestrus-2 afternoon in the main bulb and came back during proestrus afternoon. A different pattern of enzyme activity was present in the accessory bulb, since the circadian rhythm was altered during proestrus morning, returning during estrus afternoon. Male odor exposition did not change enzyme profile activity during proestrus day and during estrus morning in the main bulb. In contrast, in the accessory bulb the olfactory stimuli induced opposite changes to that found in rats from the vivarium during proestrus. Comparison of enzyme activity in olfactory stimuli-deprived rats with that of pheromone-stimulated rats during proestrus showed that male odor exposure specifically affects accessory bulb enzyme activity. It is concluded that the changes of the olfactory bulb GABAergic system during proestrus and estrus day, or that evoked by odor stimuli, demonstrate the discriminative response of this system between the accessory olfactory bulb and the main olfactory bulb.     

Proteome profile of the mature rat olfactory bulb

Olfactory bulbs (OBs) are one of the few brain areas, which show active neurogenesis and neuronal migration processes in adult rats. We constructed a proteome map of the 21 days old rat OBs and identified total 196 proteins, out of which 76 proteins were not reported earlier from rat brain. This includes 24 neuronal activity‐specific proteins present at high levels, 7 of which are reported for the first time from OBs.     

Unilateral naris occlusion and the rat accessory olfactory bulb

Blocking airflow through half of the nasal cavity during early life results in a 25% reduction in the size of the ipsilateral main olfactory bulb. The present study indicates that the size of the accessory bulb is relatively unaffected by the procedure.      

Histochemical and immunohistochemical localization of neuronal nitric oxide synthase in the olfactory epithelium of the axolotl, Ambystoma mexicanum.

The aim of this study was to describe the anatomic distribution of neuronal nitric oxide synthase immunoreactivity (nNOS-IR) and nicotinamide-adenine dinucleotide phosphate-diaphorase (NADPH-d) staining in the olfactory epithelium of the axolotl, juvenile, and neotenic adult, Ambystoma mexicanum. Nitric oxide (NO, nitrogen monoxide) is a widespread molecule that has been identified both as a neuromodulator and as an intracellular messenger. In the olfactory system, NO has been proposed to play a role in olfactory transduction. Nitric oxide synthase (NOS) can be detected by histochemical (NADPH-d) and immunohistochemical techniques. NADPH-d staining has been described in olfactory receptor neurons (ORN) of several species; however, nNOS-IR has not always been found at ORN. Present results show intense NADPH-d staining and nNOS-IR in the dendrites and cell bodies of ORN in both the nasal cavity and the vomeronasal organ of axolotls. Unilateral olfactory axotomy was conducted to confirm that labels were at ORN. Two weeks after this procedure an important decrease in NADPH-d staining and nNOS-IR was observed. The remaining labels were mostly in basal cells. By 5 weeks postaxotomy both labels were almost totally absent. Thus, both NADPH-d staining and nNOS-IR were mainly localized in ORN. NADPH-d staining and nNOS-IR were also found in nerve fibers surrounding arterioles, as well as in secretory and duct cells of the Bowman's glands. This last anatomical localization suggests that in the A. mexicanum NO might be involved in functions other than only olfactory transduction, such as regulation of local blood flow, glandular secretion, and ORN development.     

High-resolution analysis of the spatio-temporal activity patterns in rat olfactory bulb evoked by enantiomer odors

Understanding how mammals process olfactory stimuli has motivated the development of tools and techniques which permit the simultaneous study of finely structured spatial and temporal patterns of neural activity. A technique is described that uses an array of 32 penetrating microelectrodes implanted bilaterally into the dorsal aspect of rat olfactory bulb to investigate the responses of mitral and tufted neurons to stimulation with simple enantiomer odor pairs at a number of concentrations. It is shown that stable, simultaneous recordings from up to 49 single- and multi-units can be performed for periods of up to 14 h. We show that such odors evoke unique spatial and fast-temporal activity patterns which may subserve odor discrimination. This technique is extensible to other systems neuroscience investigations of olfactory sensory processing.     

Functional activity of the rat olfactory bulb related to different durations of odor exposure

We have studied the effects of different odor exposure durationson the functional activity of the rat olfactory bulb by usingthe 2-deoxyglucose (2-DG) method. This technique brings outodor-specific patterns of labeling in the glomerular layer ofthe bulb. In a first set of experiments, rats designated ascontrols were submitted to two stimulation conditions with cyclohexanonefor 40 min following 2-DG injection: group C-5—alternatestimulation (5 min odor–5 mm pure air); group C-20—continuousstimulation (20 mm odor-20 min pure air). In a second set ofexperiments, rats designated as ‘adapted’ were exposedfor 3 h to cyclohexanone before the 2-DG injection; then, threeconditions of stimulation were tested with the same odor duringthe post-injection period; group Adap-5—alternate stimulation;group Adap-20—continuous stimulation; group Adap-0—stimulationwith pure air only. In the two control groups, the total numbersof labeled glomerular foci were similar; however, group C-20showed a significant increase in the number of ‘heavily’labeled foci. This result suggests that under conditions of20 min continuous odor exposure, receptor cells do not adaptrapidly and totally. Results from the adapted groups showedthat only the group Adap-20 presented significant changes infunctional bulbar activity. An important decrease in the totalnumber of labeled glomerular foci and an absence of ‘heavily’labeled foci were noted in all rats of this group; their patternsof 2-DG uptake were greatly reduced in both complexity and contrast.These results highlight the importance of olfactory receptoradaptation under conditions of long-duration odor exposure.Fast recovery of receptor sensitivity when the stimulation isinterrupted is also suggested.     

Generation of spike activity by dendrites of secondary neurons of the rat olfactory bulb

Experiments on secondary neurons of the rat olfactory bulb showed the existence of a third region of action potential generation. It evidently consists of dendrites. This is shown by the distance from the soma of the point where action potentials arise initially and by the recording of spontaneous action potentials of comparatively low amplitude, not spreading into the axon. Action potentials are generated by apical dendrites and also, perhaps, by basal dendrites. Besides partial action potentials with stable amplitude, partial action potentials with, for practical purposes, a stepwise changing amplitude also were recorded. It is suggested that the amplitude of the partial action potentials is modified by IPSPs in the spike-generating zones.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 282–290, May–June, 1976.     

Calbindin D-28k-positive neurons in the rat olfactory bulb

Summary We have studied the distribution of calbindin D-28k immunoreactivity in the rat olfactory bulb using specific monoclonal antibodies and the avidin-biotin-immunoperoxidase method. The largest number of positive neurons was located in the periglomerular layer. These neurons were identified as periglomerular cells; they have been described also by other authors as calbindin-positive elements. Close to these neurons, a second population of nerve cells was identified as superficial shortaxon neurons. The remaining layers showed a smaller number of stained elements. Other labeled neurons were located along the external border of the external plexiform layer; the scarce neurons marking its internal border were identified as van Gehuchten cells. No immunoreactive structures were found in the mitral cell layer, although we observed another population of immunostained short-axon cells at its internal border. Some reactive structures, identified by us as horizontal and vertical cells of Cajal, were located in the boundary zone between the internal plexiform layer and the granule layer. In the white matter, we found a neuronal type characterized by its large size and oriented arborization of varicose dendrites.