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PubMedDate not supplied

Hypothalmic influences on the electrical activity of the olfactory pathway.

By means of evoked potentials a direct efferent connection was found to run from the posterior hypothalmus and medial forebrain bundle to primary olfactory structures (olfactory bulb, olfactory tubercle and prepyriform cortex). The pathway from the hypothalmus to the olfactory bulb follows in the lateral olfactory tract at a conduction velocity 5-10 m/sec. The olfactory tubercle functions as a relay station for the efferent fibers from various sources, running to the olfactory bulb. In animals with electrodes chronically implanted in the olfactory structures, hypothalamic stimulation gives rise to a prolonged train of hypersynchronous bursts of activity (40-50 Hz), which resemble the arousal reaction. This response is modified by transecting the cervical sympathetic trunk. By pathways still to be defined, potentials are evoked in the olfactory bulb by stimulation of the cervical sympathetic trunk and the termination of these sympathetic fibers shows a common postsynaptic neuronal pool with axons of hyopothalmic origin. Epinephrine topically applied to the olfactory mucosa induced hypersynchronous activity in olfactory structures, quite similar to that consequent to hypothalmic stimulation. These results suggest a multichanneled hypothalmic modulation of olfactory input.

Animals↗
PubMed1986

Ultrastructural morphology of the olfactory pathway for cerebrospinal fluid drainage in the rabbit.

Previous physiological studies indicate that the olfactory region serves as a major pathway for cerebrospinal fluid (CSF) drainage into the lymphatic system. The present study was undertaken to determine the ultrastructural characteristics of this egress route. New Zealand White rabbits received a single bolus injection of the tracer ferritin (MW 400,000) into both lateral ventricles in such a manner as not to raise the intraventricular pressure above the normal level. The animals were sacrificed via intracardiac perfusion of fixative between less than 12 minutes and 4 hours following injection. The cribriform region was removed en bloc, decalcified, sectioned coronally, and prepared for light and electron microscopic examination. The arachnoid, dura, and periosteum surrounding the fila olfactoria passing through the cribriform plate merge together and form the perineurium, which consists of multiple layers of loosely overlapping cells with widely separated junctions and few vesicles. The perineurium surrounding the olfactory filaments at the superficial submucosal level is only one cell thick. The subarachnoid space freely communicates with the perineural space surrounding each filament. No morphological barrier between the perineural space and the loose submucosal connective tissue was identified. Whether or not the perineurium was multi- or single-layered, ferritin was noted in abundance between the loosely overlapping perineural cells and in the submucosal connective tissue. The distribution of ferritin at 12 minutes was similar to that at 4 hours; however, the quantity of ferritin was increased at 4 hours. These results indicate that no significant barrier to CSF drainage is present at the rabbit cribriform region and that CSF reaches the submucosal region rapidly via open pathways.

Animals↗
PubMed1986

Basal plasma corticosterone level after bilateral selective lesions of the olfactory pathways in the rat.

In comparison to control rats, basal plasma corticosterone level and lactacidemia significantly increased in rats submitted to a bilateral lesion of the lateral olfactory tract and/or the anterior branch of the anterior commissure. Only the lesion of the anterior branch of the anterior commissure induced hyperglycemia; that of the lateral olfactory tract exerted an opposite effect.

Adrenal Glands↗
PubMed2003

Inhaled iron, unlike manganese, is not transported to the rat brain via the olfactory pathway.

Iron and manganese share structural, biochemical, and physiological similarities. The objective of this study was to determine whether iron, like manganese, is transported to the rat brain via the olfactory tract following inhalation exposure. Eight-week-old male CD rats were exposed to approximately 0.31 mg Fe per m(3) (mass median aerodynamic diameter = 2.99 microm; geometric standard deviation = 1.15) via inhalation for a target duration of 90 min. Following exposure, rats were euthanized immediately (0) or at 1, 2, 4, 8, or 21 days postexposure. In addition to nasal and regional brain tissues, blood, and viscera were also collected. 59Fe concentrations were determined by gamma spectrometry. Further, heads were collected and frozen, and autoradiograms were prepared to visualize the location of 59Fe from the nose to the brain. Finally, olfactory mucosa samples collected at 0, 2, 4, and 21 days postexposure were further analyzed using high-performance liquid chromatography (HPLC) plus gamma spectroscopy to determine the association between 59Fe and transferrin. Data obtained from gamma spectrometry revealed that most of the iron remained in the nasal regions of the olfactory system and that less than 4% of iron deposited on the olfactory mucosa was observed in the olfactory bulb. Autoradiograms confirmed the data obtained from gamma spectrometry. 59Fe activity was absent in the olfactory regions of the brain even 4 days postexposure. Further, HPLC-gamma spectroscopy analyses indicated that 59Fe in the olfactory mucosa was coeluted with transferrin. Hence iron, unlike manganese, is not readily transported to the brain via the olfactory tract.

Administration, Inhalation↗
PubMed1982

Vomeronasal and olfactory pathways to the amygdala controlling male hamster sexual behavior: autoradiographic and behavioral analyses.

Previous studies suggest that the rostral corticomedial amygdala (CMA), particularly the medial nucleus, is an important site where vomeronasal and olfactory stimuli critical to male hamster copulatory behavior are processed. To test the possibility that mating deficits seen after lesions of the rostrally-placed medial nucleus may be due to the interruption of chemosensory afferents to more caudal areas, we injected tritiated amino acids into the accessory and main olfactory bulbs of male hamsters in which we had first produced bilateral electrolytic lesions or sham lesions in either the rostral CMA or basolateral amygdala, and then observed mating behavior. Autoradiographic analysis of "vomeronasal' projections from the accessory olfactory bulb and "olfactory' projections from the main bulb, revealed that rostral CMA lesions which damaged the medial nucleus and extended to the ventral surface of the brain (ventral lesions) interrupted vomeronasal input to the more caudally-placed posteromedial cortical nucleus, but spared olfactory inputs to adjacent caudal areas of the amygdala and piriform lobe. In contrast, lesions which damaged a major portion of the medial nucleus but left its ventral surface intact (dorsal lesions) spared both vomeronasal and olfactory inputs to more caudal areas. Animals with both dorsal and ventral lesions failed to mate postoperatively, whereas animals bearing sham lesions of basolateral amygdaloid lesions, which, like dorsal lesions, spared caudally-directed chemosensory afferents, continued to mate normally. We conclude that mating deficits seen after rostral CMA lesions are due primarily to destruction of the medial nucleus.

Amygdala↗
PubMed1983

A non-thalamic olfactory pathway to the orbital gyrus in the cat.

Extracellular unit responses were recorded from the cortical layer of the orbital gyrus following stimulation of the piriform cortex fronting on that gyrus. The responses were obtained only from the dorsal bank of the rhinal sulcus. The responses were presynaptic axon and postsynaptic soma spikes with latencies of about 4 and 4.8 msec, respectively. When the dorsal bank of the rhinal sulcus was stimulated, antidromic responses with a latency of about 4.4 msec were recorded from the superficial and deep soma layers of the piriform cortex. Following injections of horseradish peroxidase into the dorsal bank of the rhinal sulcus, labeled cells were found in the piriform cortex, the lateral, basolateral and central amygdaloid nuclei, and the prelimbic area. These results indicate that the piriform cortex projects directly to part of the orbital gyrus by way of association fiber pathways.

Animals↗
PubMed2003

Active dendritic properties constrain input-output relationships in neurons of the central olfactory pathway in the crayfish forebrain.

Parasol cells are multimodal sensory interneurons of the hemi-ellipsoid body in the decapod forebrain. In reptant crustaceans, the hemi-ellipsoid body resides in the base of the eyecup, as an appendage to the terminal medulla. Parasol cells exhibit periodic depolarizations at a frequency of 0.5-1.0 Hz. I have investigated the role of these periodic depolarizations and their superimposed impulse bursts in affecting the input/output properties of these neurons. Parasol cells receive input from photic, olfactory, and mechanosensory pathways. Strong stimulation over any one of these pathways can lead to the generation of one or more impulse bursts in a subset of parasol cells, timed to occur at the peak of successive periodic depolarizations. A role for the periodic depolarizations in the function of the parasol cells has yet to be established. I suggest the possibility that they may act as a nonlinear amplifier that boosts spatially-summated excitatory synaptic potentials from strong or appropriate stimuli above threshold for burst generation. Another possibility includes modification of voltage-sensitive ion channels in the dendritic membrane, permitting a more effective spread of excitatory synaptic currents to impulse or burst initiating zones. Impulse bursts may be a highly effective mode of output for these neurons, especially so as they occur synchronously in a subset of cells in response to strong sensory input. Furthermore, backfiring of bursts into the dendritic tree has a brief (2-3 second) but effective suppressive action upon weak sensory input, which can thereby be masked by stronger, burst-generating input. This masking phenomenon is seen in other arthropod sensory interneurons, where its physiological basis appears to be a transient accumulation of intracellular Ca(++) ions that open calcium-sensitive potassium channels.

Animals↗
PubMed1994

Vomeronasal organ-mediated induction of fos in the central accessory olfactory pathways in repetitively mated female rats.

Removal of the VNO significantly reduced the enhancement of lordosis and the induction of fos immunoreactivity in luteinizing hormone-releasing hormone (LHRH) neurons in ovariectomized estrogen-primed rats. There was a significant positive correlation between the two variables. In the accessory olfactory bulb (AOB) of the repetitively mated rats, the number of fos-positive cells in the granule (G) cell layer was significantly lower in the VNO-removed rats, whereas that in the mitral (M) cell layer was not significantly different between VNO-removed and VNO-sham females. The G/M ratio (calculated by dividing the mean number of fos-positive cells in the G cell layer by that in the M cell layer), taken as an estimate of the output of the AOB, was relatively larger in the VN-sham as compared with the VNO-removed rats. There were significant positive correlations between G/M ratio and the increase in LQ and between the G/M ratio and the percentage of fos-positive LHRH cells. The positive correlation between the number of fos-positive cells in the posterodorsal medial amygdala (PDMA) and the increase in LQ and that between the number of fos-positive cells in the PDMA and the percentage of fos-positive LHRH cells were significant, supporting the role of the medial nucleus of amygdala in lordosis. However, the correlation between G/M ratio and the number of fos-positive cells in the PDMA was not significant, indicating that fos immunoreactivity in the PDMA is not directly related to that in the AOB.(ABSTRACT TRUNCATED AT 250 WORDS)

Amygdala↗
PubMed2004

Influence of season and environment on adult neurogenesis in the central olfactory pathway of the shore crab, Carcinus maenas.

In most vertebrates hitherto examined including humans, certain brain areas retain the capacity to build new neurons during adult life. In some arthropods, above all in crustaceans, continuous genesis of brain neurons has also been shown, namely for soma clusters of the olfactory brain. Several factors as, e.g., sensory input, living conditions, or stress, are known to influence the rate of cell proliferation, survival, and cell differentiation. The present study was undertaken to test whether seasonal changes and/or captivity would influence the proliferation of cells in the lateral cluster (LC) of the olfactory lobe (OL) and in the cluster of the hemiellipsoid body (HB) of the eyestalk of shore crabs. During a period of more than a year, 5-bromo-deoxyuridine (BrdU) injections were administered to freshly caught animals and to animals kept for 12 weeks after capture under artificial conditions. Counts of BrdU-labeled cells showed that animal size, seasonal changes as well as captivity had an influence on the number of proliferating cells. Further, in the lateral soma cluster and the soma cluster of the hemiellipsoid body, cell proliferation is most likely regulated independently. While the lateral soma cluster showed two peaks of cell proliferation (spring and late summer), the soma cluster of the hemiellipsoid body had only one peak in early summer. Furthermore, proliferation decreased with size and hence age of the animal only in the lateral soma cluster but not in the soma cluster of the hemiellipsoid body. Although captivity reduced the number of newborn cells in general, cell proliferation remained synchronous with the seasons of the year, indicating that an endogenous circannual rhythm regulates neurogenesis.

Animals↗
PubMed1996

[Magnetic resonance imaging of the olfactory pathways in Kallmann de Morsier syndrome].

INTRODUCTION: Kallmann syndrome is a disease clinically characterized by the association of hypogonadotrophic hypogonadism and anosmia or hyposmia. Most cases have been recorded among men. It is a genetic disorder with a specific gene location on the X chromosome. The cells that normally express luteinizing hormone-releasing hormone or LHRH fail to migrate the olfactory placode to the forebrain. The lateral projections of the olfactory placode also fail to induce development of the olfactory bulbs and tracts. MATERIAL AND METHODS: The aim of this study was to compare the MRI appearance of the olfactory sulci, the olfactory bulbs and frontal lobe between groups. The first reference group was composed of 20 subjects and the second group of 18 patients suffering from Kallmann syndrome. For all studies we used a 1.5 T magnet system (Signa GE). We performed two sagittal and coronal T1-weighted sequences in spin echo (TR = 600 ms, TE = 12 ms) with interleaved 3 mm slices and a 14 cm field of view. RESULTS: In the first group, the two olfactory bulbs were always seen on coronal slices just behind the crista galli measuring 2 to 3.2 mm transversally. On sagittal slices, in 60% of the cases two bulbs were seen (3 mm laterally of the pituitary stalk) and in the other 40% only one bulb was seen. The length of the bulb has been measured between 6 and 11 mm. We noticed a plat frontal lobe in 85% of the cases. In the second group the olfactory bulbs were never visible among the 18 patients suffering from Kallmann syndrome. The hypoplasic sulci were hardly visible and their size was less or equal to 1 cm and the frontal lobe was triangular in 80% of the cases. One patient had hypoplasia of corpus callosum. CONCLUSION: MRI is helpful tool to demonstrate abnormalities of the olfactory system which are always present among patients suffering from Kallmann syndrome. MRI can also show, at the same time, a possible associated brain abnormality.

Adult↗
PubMed1998

p59fyn and pp60c-src modulate axonal guidance in the developing mouse olfactory pathway.

The Src-family tyrosine kinases p59fyn and pp60c-src are localized on axons of the mouse olfactory nerve during the initial stages of axonal growth, but their functional roles remain to be defined. To study the role of these kinases, we analyzed the trajectory of the olfactory nerve in E11.5 homozygous null mutant mice lacking single src or fyn gens and double mutants lacking both genes. Primary olfactory axons of single and double mutants exited the olfactory epithelium and projected toward the telencephalon, but displayed differences in fasciculation. The fyn-minus olfactory nerve had significantly more fascicles than than src-minus nerve. Most strikingly, the primary olfactory nerve of src/fyn double mutants showed the greatest degree of defasciculation. These defects, identified by NCAM labeling, were not due to apparent changes in the size of the olfactory epithelium. With the exception of the src-minus mice, which had fever fascicles than the wild type, no obvious differences were observed in coalescence of vomeronasal axons from mutant mice. The mesenchyme of the double and single mutants exhibited only subtle changes in laminin and fibronectin staining, indicating that the adhesive environment of the mesenchyme may contribute in part to defects in fasciculation. The results suggest that signaling pathways mediated by p59fyn and pp60c-src contribute to the appropriate fasciculation of axons in the nascent olfactory system, and comprise partially compensatory mechanisms for axonal adhesion and guidance.

Animals↗