IA in Kenyon cells of the mushroom body of honeybees resembles shaker currents: kinetics, modulation by K+, and simulation.
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Cultured Kenyon cells from the mushroom body of the honeybee, Apis mellifera, show a voltage-gated, fast transient K+ current that is sensitive to 4-aminopyridine, an A current. The kinetic properties of this A current and its modulation by extracellular K+ ions were investigated in vitro with the whole cell patch-clamp technique. The A current was isolated from other voltage-gated currents either pharmacologically or with suitable voltage-clamp protocols. Hodgkin- and Huxley-style mathematical equations were used for the description of this current and for the simulation of action potentials in a Kenyon cell model. Activation and inactivation of the A current are fast and voltage dependent with time constants of 0.4 +/- 0.1 ms (means +/- SE) at +45 mV and 3.0 +/- 1.6 ms at +45 mV, respectively. The pronounced voltage dependence of the inactivation kinetics indicates that at least a part of this current of the honeybee Kenyon cells is a shaker-like current. Deactivation and recovery from inactivation also show voltage dependency. The time constant of deactivation has a value of 0.4 +/- 0.1 ms at -75 mV. Recovery from inactivation needs a double-exponential function to be fitted adequately; the resulting time constants are 18 +/- 3.1 ms for the fast and 745 +/- 107 ms for the slow process at -75 mV. Half-maximal activation of the A current occurs at -0.7 +/- 2.9 mV, and half-maximal inactivation occurs at -54.7 +/- 2.4 mV. An increase in the extracellular K+ concentration increases the conductance and accelerates the recovery from inactivation of the A current, affecting the slow but not the fast time constant. With respect to these modulations the current under investigation resembles some of the shaker-like currents. The data of the A current were incorporated into a reduced computational model of the voltage-gated currents of Kenyon cells. In addition, the model contained a delayed rectifier K+ current, a Na+ current, and a leakage current. The model is able to generate an action potential on current injection. The model predicts that the A current causes repolarization of the action potential but not a delay in the initiation of the action potential. It further predicts that the activation of the delayed rectifier K+ current is too slow to contribute markedly to repolarization during a single action potential. Because of its fast activation, the A current reduces the amplitude of the net depolarizing current and thus reduces the peak amplitude and the duration of the action potential. (+info)
Interactions between the foot and bud patterning systems in Hydra vulgaris.
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In the freshwater coelenterate, hydra, asexual reproduction via budding occurs at the base of the gastric region about two-thirds of the distance from the head to the foot. Developmental gradients of head and foot activation and inhibition originating from these organizing centers have long been assumed to control budding in hydra. Much has been learned over the years about these developmental gradients and axial pattern formation, and in particular, the inhibitory influence of the head on budding is well documented. However, understanding of the role of the foot and potential interactions between the foot, bud, and head patterning systems is lacking. The purpose of this study was to investigate the role of the foot in the initiation of new axis formation during budding by manipulating the foot and monitoring effects on the onset of first bud evagination and the time necessary to reach the 50% budding point. Several experimental situations were examined: the lower peduncle and foot (PF) were injured or removed, a second PF was laterally grafted onto animals either basally (below the budding zone) or apically (above the budding zone), or both the head and PF were removed simultaneously. When the PF was injured or removed, the onset of first bud evagination was delayed and/or the time until the 50% budding point was reached was longer. The effects were more pronounced when the manipulation was performed closer to the anticipated onset of budding. When PF tissue was doubled, precocious bud evagination was induced, regardless of graft location. Removal of the PF at the same time as decapitation reduced the inductive effect of decapitation on bud evagination. These results are discussed in light of potential signals from the foot or interactions between the foot and head patterning systems that might influence bud axis initiation. (+info)
Olfactory adaptation depends on the Trp Ca2+ channel in Drosophila.
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Olfactory adaptation is shown to occur in Drosophila, at both behavioral and physiological levels. In a behavioral paradigm, the extent of adaptation is shown to depend on the dose and duration of the adapting stimulus. Half-maximal adaptation occurred after 15 sec of exposure to an odor, and recovery occurred with a half-time of 1. 5 min, under a set of test conditions. Cross-adaptation was observed among all odor combinations tested, although to a lesser extent than when the same odor was used as both the adapting and the test stimulus. Mutants of the transient receptor potential (Trp) Ca2+ channel were normal in olfactory response, but defective in olfactory adaptation, when measured either behaviorally or in tests of antennal physiology. These results indicate that olfactory response and adaptation can be distinguished. Trp expression was detected in the developing antenna but, surprisingly, not in the mature antenna. These results, together with temperature-shift analysis of a temperature-sensitive trp mutant, provide evidence of a role of Trp in olfactory system development. (+info)
A lobster phospholipase C-beta that associates with G-proteins in response to odorants.
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A cDNA clone encoding a protein of 1116 amino acids with significant homology to beta-isoforms of phospholipase C was isolated from lobster olfactory organ cDNA libraries and named lobPLCbeta. This cDNA hybridized predominantly to a 9 kb transcript in RNA from olfactory organ, pereiopod, brain, and eye-eyestalk and to several smaller minor transcripts only in eye-eyestalk. An antiserum raised to the C terminus of lobPLCbeta detected immunoreactivity in a single 130 kDa band in olfactory aesthetasc hairs, olfactory organ, pereiopod, dactyl, and brain. In eye-eyestalk this 130 kDa band was abundant, and minor bands of 100, 79, and 57 kDa also were detected. In cross sections of the aesthetasc hairs, immunoreactivity was detected in the outer dendritic segments of the olfactory receptor neurons, the site of olfactory transduction. A complex odorant caused lobPLCbeta immunoreactivity to increase in membrane fractions and decrease in soluble fractions of homogenates of aesthetasc hairs. The odorant also increased the amount of lobPLCbeta in immunoprecipitates of Galphaq and Gbeta from homogenates of aesthetasc hairs. These results support the conclusion that lobPLCbeta mediates olfactory transduction. (+info)
Differential expression of Tbx4 and Tbx5 in Zebrafish fin buds.
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In here we report the identification of two new members of the T-box gene family, zf-tbx5 and zf-tbx4, from the Zebrafish, Danio rerio. The amino acid sequences within the T-box domain share high homology with the mouse, chick, and newt orthologs. Whole mount in situ hybridization revealed specific expression of these genes in the eye and Fin buds. zf-tbx5 expression is restricted to the pectoral Fin bud, whilst zf-tbx4 transcripts are confined in the pelvic Fin bud. These results reveal the conserved expression pattern of Tbx5 and Tbx4 during appendage development in all animal species studied to date. (+info)
Response characteristics of an identified, sexually dimorphic olfactory glomerulus.
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Partitioning of synaptic neuropil into glomeruli is a common feature of primary olfactory centers in most animal species. The functional significance of glomeruli, however, is not yet well understood. The present study is part of our effort to test the hypothesis that each glomerulus is a functional unit dedicated to processing information about a particular odorant or attribute of odor molecules and that the glomerular array constitutes a map of "odor space." We investigated the physiological and morphological features of uniglomerular projection neurons (PNs) associated with an identified glomerulus in each antennal lobe of the female sphinx moth, Manduca sexta. This "lateral large female glomerulus" (latLFG) is sexually dimorphic and therefore may play a female-specific role, such as processing of information about one or more odorants important for orientation of a female to host plants for oviposition. Together with the medial LFG (medLFG), the latLFG resides outside the array of spheroidal ordinary glomeruli, near the entrance of the antennal (olfactory) nerve. Each LFG is innervated by four to five PNs. Using intracellular recording and staining, we examined the responses of latLFG-PNs to odorants that represent major classes of volatiles released by host plants of M. sexta. All latLFG-PNs were excited when the ipsilateral antenna was stimulated with low concentrations of the monoterpenoid linalool. Dose-response analysis showed that neither other monoterpenoids nor representatives of other classes of host plant volatiles were similarly stimulatory to latLFG-PNs. These findings are consistent with the idea that each glomerulus has a characteristic, limited molecular receptive range. (+info)
amos, a proneural gene for Drosophila olfactory sense organs that is regulated by lozenge.
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In a variety of organisms, early neurogenesis requires the function of basic-helix-loop-helix (bHLH) transcription factors. For the Drosophila PNS, such transcription factors are encoded by the proneural genes (atonal and the achaete-scute complex, AS-C). We have identified a proneural gene, amos, that has strong similarity with atonal in its bHLH domain. We present evidence that amos is required for olfactory sensilla and is regulated by the prepattern gene lozenge. Between them, amos, atonal, and the AS-C can potentially account for the origin of the entire PNS. (+info)
Essential roles of Drosophila RhoA in the regulation of neuroblast proliferation and dendritic but not axonal morphogenesis.
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The pleiotropic functions of small GTPase Rho present a challenge to its genetic analysis in multicellular organisms. We report here the use of the MARCM (mosaic analysis with a repressible cell marker) system to analyze the function of RhoA in the developing Drosophila brain. Clones of cells homozygous for null RhoA mutations were specifically labeled in the mushroom body (MB) neurons of mosaic brains. We found that RhoA is required for neuroblast (Nb) proliferation but not for neuronal survival. Surprisingly, RhoA is not required for MB neurons to establish normal axon projections. However, neurons lacking RhoA overextend their dendrites, and expression of activated RhoA causes a reduction of dendritic complexity. Thus, RhoA is an important regulator of dendritic morphogenesis, while distinct mechanisms are used for axonal morphogenesis. (+info)