A genetic approach to visualization of multisynaptic neural pathways using plant lectin transgene.
The wiring patterns among various types of neurons via specific synaptic connections are the basis of functional logic employed by the brain for information processing. This study introduces a powerful method of analyzing the neuronal connectivity patterns by delivering a tracer selectively to specific types of neurons while simultaneously transsynaptically labeling their target neurons. We developed a novel genetic approach introducing cDNA for a plant lectin, wheat germ agglutinin (WGA), as a transgene under the control of specific promoter elements. Using this method, we demonstrate three examples of visualization of specific transsynaptic neural pathways: the mouse cerebellar efferent pathways, the mouse olfactory pathways, and the Drosophila visual pathways. This strategy should greatly facilitate studies on the anatomical and functional organization of the developing and mature nervous system. (+info)
Sodefrin: a novel sex pheromone in a newt.
The abdominal gland in the male red-bellied newt, Cynops pyrrhogaster, is the source of a female-attracting pheromone. An attempt was made to isolate and characterize the female-attracting pheromone in the abdominal glands of male newts. The active substance, named sodefrin (from the Japanese 'sodefuri' which means 'soliciting') has been isolated and shown to be a novel decapeptide with the sequence, Ser-Ile-Pro-Ser-Lys-Asp-Ala-Leu-Leu-Lys. Its minimum effective concentration in water is 0.1-1.0 pmol 1-1. Synthetic sodefrin shows a female-attracting activity similar to that of the native peptide, and acts through the olfactory organ of female newts. Electrophysiological studies reveal that sodefrin evokes a marked electroolfactogram response in the vomeronasal epithelium in sexually mature females and in ovariectomized females treated with prolactin and oestrogen. The pheromonal activity of sodefrin appears to be species-specific since it does not attract females of a congeneric species, the sword-tailed newt C. ensicauda. However, C. ensicauda has a variant of sodefrin differing from that in C. pyrrhogaster by substitutions of Leu for Pro at position 3 and Gln for Leu at position 8. The C. ensicauda variant sodefrin does not attract C. pyrrhogaster females. Genes encoding the sodefrin precursor protein have been cloned in both C. pyrrhogaster and C. ensicauda. Immunostaining of the abdominal gland using the antiserum against sodefrin shows that sodefrin occurs in the epithelial cells, predominantly within the secretory granules. Sodefrin content, detected by immunoassay, in C. pyrrhogaster males decreases after castration and hypophysectomy and increases markedly in the castrated and hypophysectomized newts after treatment with androgen and prolactin. This combination of hormones also enhances sodefrin mRNA content in the abdominal gland as assessed by northern blot analysis using sodefrin cDNA. (+info)
A novel family of divergent seven-transmembrane proteins: candidate odorant receptors in Drosophila.
Although insects have proven to be valuable models for exploring the function, organization, and development of the olfactory system, the receptor molecules that bind odors have not been identified in any insect. We have developed a novel search algorithm, used it to search the Drosophila genomic sequence database, and identified a large multigene family encoding seven transmembrane domain proteins that are expressed in olfactory organs. We show that expression is restricted to subsets of olfactory receptor neurons (ORNs) for a number of these genes. Different members of the family initiate expression at different times during antennal development. Some of the genes are not expressed in a mutant of the Acj6 POU-domain transcription factor, a mutant in which a subset of ORNs show abnormal odorant specificities. (+info)
The odor specificities of a subset of olfactory receptor neurons are governed by Acj6, a POU-domain transcription factor.
Little is known about how the odor specificities of olfactory neurons are generated, a process essential to olfactory coding. We have found that neuronal identity relies on the abnormal chemosensory jump 6 (acj6) gene, originally identified by a defect in olfactory behavior. Physiological analysis of individual olfactory neurons shows that in acj6 mutants, a subset of neurons acquires a different odorant response profile. Certain other neurons do not respond to any tested odors in acj6. Molecular analysis of acj6 shows that it encodes a POU-domain transcription factor expressed in olfactory neurons. Our data suggest that the odor response spectrum of an olfactory neuron, and perhaps the choice of receptor genes, is determined through a process requiring the action of Acj6. (+info)
Crossmodal associative memory representations in rodent orbitofrontal cortex.
Firing patterns of neurons in the orbitofrontal cortex (OF) were analyzed in rats trained to perform a task that encouraged incidental associations between distinct odors and the places where their occurrence was detected. Many of the neurons fired differentially when the animals were at a particular location or sampled particular odors. Furthermore, a substantial fraction of the cells exhibited odor-specific firing patterns prior to odor presentation, when the animal arrived at a location associated with that odor. These findings suggest that neurons in the OF encode cross-modal associations between odors and locations within long-term memory. (+info)
Blind smell: brain activation induced by an undetected air-borne chemical.
EEG and behavioural evidence suggests that air-borne chemicals can affect the nervous system without being consciously detected. EEG and behaviour, however, do not specify which brain structures are involved in chemical sensing that occurs below a threshold of conscious detection. Here we used functional MRI to localize brain activation induced by high and low concentrations of the air-borne compound oestra-1,3,5(10),16-tetraen-3yl acetate. Following presentations of both concentrations, eight of eight subjects reported verbally that they could not detect any odour (P = 0.004). Forced choice detection performed during the presentations revealed above-chance detection of the high concentration, but no better than chance detection of the low concentration compound. Both concentrations induced significant brain activation, primarily in the anterior medial thalamus and inferior frontal gyrus. Activation in the inferior frontal gyrus during the high concentration condition was significantly greater in the right than in the left hemisphere (P = 0.03). A trend towards greater thalamic activation was observed for the high concentration than the low concentration compound (P = 0.08). These findings localize human brain activation that was induced by an undetectable air-borne chemical (the low concentration compound). (+info)
Adenovirus-mediated expression of an olfactory cyclic nucleotide-gated channel regulates the endogenous Ca2+-inhibitable adenylyl cyclase in C6-2B glioma cells.
Previous studies have established that Ca2+-sensitive adenylyl cyclases, whether endogenously or heterologously expressed, are preferentially regulated by capacitative Ca2+ entry, compared with other means of elevating cytosolic Ca2+ (Chiono, M., Mahey, R., Tate, G., and Cooper, D. M. F. (1995) J. Biol. Chem. 270, 1149-1155; Fagan, K. A., Mahey, R., and Cooper, D. M. F. (1996) J. Biol. Chem. 271, 12438-12444; Fagan, K. A., Mons, N., and Cooper, D. M. F. (1998) J. Biol. Chem. 273, 9297-9305). These findings led to the suggestion that adenylyl cyclases and capacitative Ca2+ entry channels were localized in the same functional domain of the plasma membrane. In the present study, we have asked whether a heterologously expressed Ca2+-permeable channel could regulate the Ca2+-inhibitable adenylyl cyclase of C6-2B glioma cells. The cDNA coding for the rat olfactory cyclic nucleotide-gated channel was inserted into an adenovirus construct to achieve high levels of expression. Electrophysiological measurements confirmed the preservation of the properties of the expressed olfactory channel. Stimulation of the channel with cGMP analogs yielded a robust elevation in cytosolic Ca2+, which was associated with an inhibition of cAMP accumulation, comparable with that elicited by capacitative Ca2+ entry. These findings not only extend the means whereby Ca2+-sensitive adenylyl cyclases may be regulated, they also suggest that in tissues where they co-exist, cyclic nucleotide-gated channels and Ca2+-sensitive adenylyl cyclases may reciprocally modulate each other's activity. (+info)
From embryo to adult: persistent neurogenesis and apoptotic cell death shape the lobster deutocerebrum.
Neuronal plasticity and synaptic remodeling play important roles during the development of the invertebrate nervous system. In addition, structural neuroplasticity as a result of long-term environmental changes, behavioral modifications, age, and experience have been demonstrated in the brains of sexually mature insects. In adult vertebrates, persistent neurogenesis is found in the granule cell layer of the mammalian hippocampus and the subventricular zone, as well as in the telencephalon of songbirds, indicating that persistent neurogenesis, which is presumably related to plasticity and learning, may be an integral part of the normal biology of the mature brain. In decapod crustaceans, persistent neurogenesis among olfactory projection neurons is a common principle that shapes the adult brain, indicating a remarkable degree of life-long structural plasticity. The present study closes a gap in our knowledge of this phenomenon by describing the continuous cell proliferation and gradual displacement of proliferation domains in the central olfactory pathway of the American lobster Homarus americanus from early embryonic through larval and juvenile stages into adult life. Neurogenesis in the deutocerebrum was examined by the in vivo incorporation of bromodeoxyuridine, and development and structural maturation of the deutocerebral neuropils were studied using immunohistochemistry against Drosophila synapsin. The role of apoptotic cell death in shaping the developing deutocerebrum was studied using the terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling method, combined with immunolabeling using an antiphospho histone H3 mitosis marker. Our results indicate that, in juvenile and adult lobsters, birth and death of olfactory interneurons occur in parallel, suggesting a turnover of these cells. When the persistent neurogenesis and concurrent death of interneurons in the central olfactory pathway of the crustacean brain are taken into account with the life-long turnover of olfactory receptor cells in crustacean antennules, a new, highly dynamic picture of olfaction in crustaceans emerges. (+info)