Water response of frog olfactory system is induced by a decrease in osmotic pressure

The frog olfactory response to deionized water (water response) was recorded from the olfactory bulb. The water response was suppressed by both electrolytes and non-electrolytes as a function of osmolarity, while the water response in taste cell was not suppressed by non-electrolytes. It was concluded that a decrease in osmotic pressure induced by application of deionized water is the origin of the water response in the frog olfactory system.     

Nucleus of the tractus solitarius projections to the olfactory tubercle: An HRP study

Labelled cells were found in the nucleus of the tractus solitarius (NTS) after horseradish peroxidase injections in the olfactory tubercle (OT) of the rat. These results suggest a direct pathway from the NTS to the OT. The importance of this pathway in a neural circuit related to autonomic functions is discussed.     

The lateral and medial compartments of the olfactory tubercle and their relation to olfactory-related input as determined by artificial neural network analysis

The current literature indicates that olfactory bulbar input projects throughout layer IA of the entire olfactory tubercle, with apparently more fibers in the lateral part than in the medial part of the tubercle. In addition, olfactory cortical association fibers project to layers IB, II, and III in all regions of the tubercle. This study exploited the phenomenon of transsynaptic transfer of WGA-HRP after injection into the olfactory bulb of rats to explore the degree of olfactory-related input to the tubercle. A computerized image analysis system was employed to quantify the amount of tracer transferred to layer II neurons of the tubercle. Qualitative analysis of the data indicates that the lateral tubercle consists of areas that receive little olfactory-related input. Nonparametric statistical tests and a novel application of artificial neural networks indicate regionally heterogeneous labeling across the tubercle and broad connections between homologous regions of the bulb and tubercle. These results have implications for understanding how olfactory sensory information is integrated into limbic-motor circuits by the olfactory tubercle.     

Baclofen inhibition of synaptic transmission in glomeruli of the olfactory bulb of the frog

The application of (+/-) baclofen (10(-5) M) to the frog olfactory bulb greatly reduced postsynaptic components of the orthodromic potential, but the antidromic potential was not affected. The effect was not antagonized by bicuculline (10(-4)-10(-3) M). The results suggest that bicuculline-insensitive GABAB-receptors are located on the primary olfactory afferents and may realize presynaptic inhibition in the olfactory bulb.     

Pharmacologic evidence for a tonic muscarinic inhibitory input to the Edinger-Westphal nucleus in the dog

The cholinergic characteristics of the parasympathetic preganglionic cell groups controlling pupillary diameter were investigated. Drugs dissolved in 0.5 μl 0.9% NaCl were microinjected into sites within or near the Edinger-Westphal nucleus (EW) that yielded pupilloconstriction to electrical stimulation in the decerebrate and awake dog. In the awake dog, carbachol (0.3 to 1.4 nmol), bethanechol (0.5 to 5 nmol), and physostigmine (7.5 and 15.4 nmol), but not nicotine (1.3 to 63 nmol), produced a dose-dependent mydriasis. This cholinergic-induced mydriasis was prevented by methylatropine nitrate (2.7 nmol in 1.0 μl) microinjected 30 min before the agonists. Equimolar doses (2.7 nmol) of- the nicotinic antagonists, mecamylamine and hexamethonium, did not block the carbachol-induced mydriasis. Microinjections of methylatropine, but not the nicotinic antagonists, produced miosis. A muscarinic-induced mydriasis appeared to be due to inhibition of the pupilloconstrictor neurons because (i) it occurred in the chronically sympathectomized and acutely decerebrated dog, and (ii) it did not correlate with sympathetic responses.     

Translational potential of olfactory mucosa for the study of neuropsychiatric illness

The olfactory mucosa (OM) is a unique source of regenerative neural tissue that is readily obtainable from living human subjects and thus affords opportunities for the study of psychiatric illnesses. OM tissues can be used, either as ex vivo OM tissue or in vitro OM-derived neural cells, to explore parameters that have been difficult to assess in the brain of living individuals with psychiatric illness. As OM tissues are distinct from brain tissues, an understanding of the neurobiology of the OM is needed to relate findings in these tissues to those of the brain as well as to design and interpret ex vivo or in vitro OM studies. To that end, we discuss the molecular, cellular and functional characteristics of cell types within the olfactory mucosa, describe the organization of the OM and highlight its role in the olfactory neurocircuitry. In addition, we discuss various approaches to in vitro culture of OM-derived cells and their characterization, focusing on the extent to which they reflect the in vivo neurobiology of the OM. Finally, we review studies of ex vivo OM tissues and in vitro OM-derived cells from individuals with psychiatric, neurodegenerative and neurodevelopmental disorders. In particular, we discuss the concordance of this work with postmortem brain studies and highlight possible future approaches, which may offer distinct strengths in comparison to in vitro paradigms based on genomic reprogramming.     

Disynaptic olfactory input to the hippocampus mediated by stellate cells in the entorhinal cortex

Electrophysiological and anatomical studies indicate functional relationships between the olfactory bulb and the hippocampus, mediated by the lateral olfactory tract and perforant path. Fibres from the lateral olfactory bulb terminate in the molecular layer of the lateral entorhinal cortex, which contains stellate and pyramidal cells that project to the hippocampus. Therefore this study was performed to analyze whether a trineuronal, disynaptic chain connects the olfactory bulb and the hippocampus. In adult rats, Fast Blue was unilaterally injected into the septal hippocampus to label cells of origin of the entorhinohippocampal pathway. Lesions of the ipsilateral olfactory bulb induced anterograde terminal degeneration in the entorhinal cortex of the same animals. Fast Blue labelled, and thus hippocampally projecting entorhinal neurones in fixed vibratome slices of the operated brains were injected with Lucifer Yellow. Most of these neurones were stellate layer II and pyramidal layer III cells; in addition there were some sparsely spinous multipolar cells in layers II and III and sparsely spinous horizontal cells at the layer I/II border. Injected cells were photoconverted and processed for electron microscopy. Olfactory bulb lesions resulted in electron-dense degeneration of abundant terminal boutons in the outer zone of entorhinal layer I. The relative frequency of degenerating boutons decreased towards deeper zones of the layer. In the outer zone, degenerated terminals predominantly contacted dendritic spines. These contacts could be seen on injected stellate cells but not on pyramidal cells. This study shows that the area dentata of the rat is reached by disynaptic afferent input from the olfactory bulb and thus is likely to process olfactory information. Oligosynaptic pathways might provide the hippocampus also with visual and auditory inputs; such fast transmitted polysensory information could be essential for the proposed participation of the hippocampus in attention-related mechanisms.     

Organization of projections from olfactory epithelium to olfactory bulb in the frog, Rana pipiens

One hypothesis for the coding of olfactory quality is that regions of the olfactory epithelium are differentially sensitive to particular odor qualities and that this regional sensitivity is conveyed to the olfactory bulb in a topographic manner by the olfactory nerve. A corollary to this hypothesis is that there is a sufficiently orderly connection between the epithelium and the olfactory bulb to convey this topographical coding. Thus we examined topography in the projection from epithelium to bulb in the frog, which has been the subject of numerous electrophysiological studies but has not yet been examined using modern neuroanatomical techniques. The tracer WGA-HRP was applied to the ventral or to the dorsal olfactory epithelium, or both. Anterograde transport of label to the olfactory bulb was seen after as few as 2 days; label was still present in the bulb as long as 21 days postinjection. In cases where WGA-HRP was applied to the entire epithelium, there was dense anterograde labelling of the ipsilateral olfactory bulb. In addition, a small medial portion of the contralateral bulb was labelled. Injections limited to either the ventral or dorsal epithelium produced patterns of anterograde labelling in the glomerular layer of the olfactory bulb, which varied with the size and location of the injection. With very large injections in either the dorsal or ventral epithelium, label appeared to be evenly distributed in the glomerular layer. With smaller injections in the ventral epithelium, there was heavier labelling in the lateral than in the medial portions of the glomerular layer, although light labelling was found in all regions of the glomerular layer. In contrast, injection sites restricted to the dorsal epithelium produced more anterograde labelling in the medial than lateral portions of the glomerular layer. These patterns extended throughout the dorsal-ventral extent of the bulb. Within the limits of the anterograde tracing technique used, we were unable to detect any systematic relationship between the pattern of labelling in the glomerular layer and the medial-lateral or rostral-caudal location of the injection site in either the ventral or dorsal epithelium. We conclude that in the frog, as in other amphibia, there is only a limited degree of topographic order between the epithelium and the olfactory bulb.     

Effects of dopamine and norepinephrine on neuronal activity of the olfactory tubercle

The effects of iontophoretic administration of norepinephrine (NE) and dopamine (DA) on olfactory tubercle (OT) neurons that respond to lateral hypothalamus (LH) or locus coeruleus (LC) electrical stimulation were studied. NE and DA decreased the frequency of OT neurons which were increased or decreased by the LH stimulation. An increased firing of OT neurons following NE or DA administration was less frequently observed. NE administration decreased the firing of OT neurons that responded to LC stimulation. These results suggest that the LC fibers which reach the OT use NE as a neurotransmitter. DA administration also suppressed the unitary discharge of OT neurons responding to LC stimulation. The increase in frequency of OT neurons observed following LH stimulation cannot be attributed to DA. The possibility that other suspected neural transmitters are involved in this effect is discussed.     

A horseradish peroxidase study of the olfactory system of the frog, Rana esculenta

The olfactory system of the frog Rana esculenta was studied by using horseradish peroxidase (HRP) tracing of axonal pathways. Injections of HRP were made in the main olfactory bulb (MOB), accessory olfactory bulb (AOB), anterior olfactory nucleus (AON), the amygdala (AMY), and in a zone of the leteral wall of the telencephalic hemisphere immediately posterior to the AOB. Projections from these sites are described and are generally similar to those obtained by degeneration methods. However, HRP reveals more extensive olfactory connections than previously reported. Ipsilateral, contralateral, and bilateral projections are described. The MOB, AOB, and AON have ipsilateral connections to each other. The MOB and AOB have very different projections. The MOB and AON project via the habenular commissure (HC) to the contralateral medial wall of the telencephalon. Ipsilateral MOB fibers also terminate in this cell-free zone where the medial forebrain bundle (MFB) originates. The AOB projects to the lateral cortex of the contralateral telencephalic hemisphere via the HC and also to the ipsilateral AMY and lateral forebrain bundle (LFB) from where some fibers project contralaterally. HRP injections in the AMY retrogradely fill cells in the ipsilateral AOB, two nuclei of the ipsilateral hypothalamus and a nucleus of cells caudal to the ipsilateral nucleus isthmi. Fibers are also labeled that project to the contralateral AMY. Few fibers were observed to decussate in the interpeduncular nucleus or optic chiasma. No olfactory fibers were found to project to the habenular nuclei, and no labeled neurons were found to project to the olfactory bulbs. No morphological asymmetry was observed qualitatively in the distribution of olfactory fibers in the two halves of the brain.     

Monoclonal antibody to carnosine synthetase identifies a subpopulation of frog olfactory receptor neurons

A monoclonal antibody directed against the synthetic enzyme for the dipeptide carnosine was used on cryostat sections of olfactory epithelium from the grass frog Rana pipiens. A subpopulation of what morphologically resembled olfactory receptor neurons were immunolabelled by this antibody. Labelled cells were completely stained, including the cell body, axonal and dendritic processes, dendritic knobs and cilia-like projections from the knobs.     

Responses to somatosensory input by afferent and efferent neurons in the vestibular nerve of the frog

In the frog, we have recorded the activity of efferent and afferent fibers in the nerve of the horizontal semicircular canal in response to somatosensory stimulation. Recordings were made extracellularly by means of glass micropipettes filled with 2 M NaCl, and somatosensory stimulation was produced either by electrical stimulation of the sciatic nerve (ipsi- or contralateral to the recording side) or by vibratory stimulation of the gastrocnemius. The discharge frequency of 43% of the efferent fibers recorded was significantly increased by such stimulation, while the activity of the others was unaffected. The discharge rate of the afferent fibers was either significantly increased (in about 11% of the cases when the results were pooled together) or significantly decreased (in about 22% of the cases) by stimulation of the somatosensory system. The latencies of the responses ranged from 5 to 50 ms. These results show that: somatosensory input can influence the activity of the vestibular apparatus at the most peripheral level; modulation of the afferent discharge is mediated by the efferent vestibular system (EVS); the influence of the EVS on the vestibular afferent activity is both inhibitory and facilitatory, and the responses to somatosensory stimulation are mediated by both long-latency polysynaptic and short-latency oligosynaptic pathways. The functional significance of these two pathways is discussed.     

On the presence of a peculiar alpha rhythm in the olfactory tubercle of waking armadillos

A very regular 8-12 rhythm was found in the olfactory tubercle of the armadillo Chaetophractus villosus. The rhythm was observed during wakefulness. Considerable sinusoidal activity was also observed not only during wakefulness, but during synchronized (slow) and desynchronized (paradoxical) sleep. The significance of this novel rhythm is discussed together with considerations that establish an important difference between it and the other 'alpha rhythms' known.     

An olfactory input to the hippocampus of the cat: Field potential analysis

Hippocampal responses to electrical stimulation of the prepyriform cortex in the cat were studied both in acute experiments under halothane anesthesia and in awake cats with chronically indwelling electrodes. Analysis of field potentials and unit activity indicated the extent to which different hippocampal subareas were activated, the laminar level at which the synaptic action took place and the dynamics of the evoked responses. It was found that: (1) the main generator of evoked responses in the hippocampus upon prepyriform cortex stimulation is localized in the fascia dentata and CA3 (CA1 pyramidal cells, and probably also subiculum cells, are activated but in a lesser degree); (2) the initial synaptic activity takes place at the most distal part of the dendrites of fascia dentata granule cells and CA3 pyramidal cells; and (3) this synaptic activity corresponds to an EPSP that leads to a transient increase in the firing rate of the hippocampal units, which is often followed by a long-lasting decrease in firing rate.We conclude that the pathway from the prepyriform cortex via lateral entorhinal cortex to hippocampal neurons may enable olfactory inputs to effectively excite hippocampal neurons.     

Spatial dimension in olfactory coding: a representation of the 2-deoxyglucose patterns of glomerular labeling in the olfactory bulb

A method has been developed for visualizing the patterns of uptake of radioactive 2-deoxyglucose (2-DG) induced in the glomerular layer of rat olfactory bulbs by various olfactory stimuli. Some characteristics of these patterns such as shape, contrast, symmetry, specificity and variability, are discussed. This method is thought to be useful for understanding olfactory coding at the glomerular level.     

An experimental study of the ventral striatum of the golden hamster. II. Neuronal connections of the olfactory tubercle

As part of an experimental study of the ventral striatum, the horseradish peroxidase (HRP) method was used to examine the afferent and efferent neuronal connections of the olfactory tubercle. Following iontophoretic applications or hydraulic injections of HRP in the tubercle, neurons labeled by retrograde transport of HRP were observed ipsilaterally in the telencephalon in the main olfactory bulb, the medial, lateral, ventral, and posterior divisions of the anterior olfactory nucleus, and in the orbital, ventral, and posterior agranular insular, primary olfactory, perirhinal, and entorhinal cortices. Labeled cells were also present in the basolateral, basomedial, anterior cortical, and posterolateral cortical amygdaloid nuclei, and bilaterally in the nucleus of the lateral olfactory tract. In the diencephalon, ipsilateral HRP-containing neurons were observed in the midline nuclei paraventricularis, parataenialis, and reuniens, and in the parafascicular intralaminar nucleus. Retrograde labeling was present in the ipsilateral brainstem in cells of the ventral tegmental area, substantia nigra, and dorsal raphe. Many of the above projections to the tubercle were found to be topographically organized. Anterograde axonal transport of HRP from the olfactory tubercle labeled terminal fields ipsilaterally in all parts of the anterior olfactory nucleus, in the ventral pallidum, and in the substantia nigra, pars reticulata. Contralaterally, terminal fields were present in the dorsal and lateral divisions of the anterior olfactory nucleus. The projections to the tubercle from the orbital, ventral, and posterior agranular insular, and perirhinal neocortices, intralaminar thalamus, and dopamine-containing areas of the ventral mesencephalon are analogous to the connections of the caudatoputamen, as are the efferents from the tubercle to the ventral globus pallidus and substantia nigra. These connections substantiate the recent suggestion that the olfactory tubercle is a striatal structure, and provide support for the ventral striatal concept. In the present study of the olfactory tubercle, and in the first study in this series on the nucleus accumbens, the ventral striatum was found to receive projections from a number of limbic system structures, including the main olfactory bulb, anterior olfactory nucleus, amygdala, hippocampus, and subiculum, and the entorhinal and primary olfactory cortices. These findings suggest that the ventral striatum is concerned with integrating limbic information into the striatal system.     

In vitro study of the inhibition of coagulation induced by different radiocontrast molecules

The anticoagulant activity of seven intravascular radiocontrast molecules (RCM) was evaluated in different in vitro systems using citrated human plasma. Each RCM was tested in a concentration range of 5 to 50 mM. The thrombin time and the reptilase time showed a dose-dependent lengthening of fibrinoformation, the recording of fibrinoformation exhibited a significant delay of fibrin monomer generation and polymerization although the amplitude of the fibrino-formation was not decreased. The interfering effect with fibrin clot formation impairs also global coagulation tests and monospecific coagulation tests using fibrinoformation as the final step of the assay, but a possible interaction between RCM and some specific coagulation factors cannot be excluded. RCM potentiated the anti-thrombin action of heparin but the inhibition or delay of fibrino-formation is not related to an antithrombinic effect of contrast media. The thrombin amidolytic activity is not modified by RCM but the generation of FpA is delayed and decreased. The ultrastructure of the fibrin clot is not altered at the end of the polymerization.     

Changes in Fos-like immunoreactivity evoked by maturation of the sneeze reflex triggered by nasal air puff stimulation in kittens

The sneeze reflex is a valuable tool for exploring the maturation of the respiratory control in the newborn as it alters both inspiratory and expiratory activities. Air puff stimulation of the superior nasal meatus innervated by ethmoidal afferents consistently evokes sneeze in adult cats. Such stimulation evokes only a reinforcement of expiratory activities in newborn kittens. This study demonstrates that the pattern of Fos-like immunoreactivity evoked by nasal stimulation changes during functional maturation of sneeze. Nasal stimulation evoked immunoreactivity (i) in the trigeminal sensory complex, at the levels where nasal afferents project, (ii) in the reticular formation, (iii) in the solitary complex and (iv) in the parabrachial area of mature kittens. The evoked immunoreactivity was the same in newborn kittens as in mature kittens in the projection areas of the nasal primary afferents. Fos response was less than half that in mature kittens in the reticular formation and absent in the solitary complex or the parabrachial area. Sneeze can be elicited from the time when evoked immunoreactivity in the solitary complex and the parabrachial area is above control levels. These data provide evidence that the maturation of sneeze is dependent on the development of central relays allowing peripheral inputs to be integrated by neurons engaged in respiratory control.