Biomedical subjects

B W Ache

Publications and source records attributed to B W Ache.

At least 37 records · Page 2Linked to original sources

PubMed1995

Odor-induced currents in Xenopus olfactory receptor cells measured with perforated-patch recording.

1. Odor-evoked currents were recorded in Xenopus laevis olfactory receptor neurons (ORNs) by the use of conventional, as well as nystatin and gramicidin-perforated, whole cell recording. The odor-evoked current ran down quickly in conventional, but not in perforated, whole cell recording. All three types of recording gave similar values for the amplitude, latency, time-to-peak, recovery time, and reversal potential of the odor-evoked current. 2. A secondary Cl current comprised a significant part of the odor-evoked current (55-65%). ECl measured by gramicidin perforation, which does not alter [Cl-]i, was -2.3 +/- 5.0 (SE) mV, indicating that these neurons maintain a high [Cl-]i and that the secondary Cl current plays an excitatory role in olfactory transduction.

Animals↗

PubMed1994

Inositol 1,3,4,5-tetrakisphosphate-gated channels interact with inositol 1,4,5-trisphosphate-gated channels in olfactory receptor neurons.

Inositol 1,4,5-trisphosphate [InsP3(1,4,5)] is a major second messenger regulating Ca2+ signaling in excitable and nonexcitable cells. InsP3(1,4,5) is extensively metabolized through a network of phosphorylation and dephosphorylation steps to products with potential second messenger function. Inositol 1,3,4,5-tetrakisphosphate [InsP4(1,3,4,5)], the direct metabolite of InsP3(1,4,5), has also been associated with Ca2+ signaling, but whether InsP4(1,3,4,5) acts in combination with InsP3(1,4,5) or whether it regulates Ca2+ signaling directly and independently is unclear, particularly in neurons. We report that olfactory receptor neurons in the lobster (Panulirus argus) express an InsP4(1,3,4,5) receptor in the plasma membrane that is a functional channel. The channel differs in conductance, kinetics, and voltage sensitivity from two plasma membrane InsP3(1,4,5)-gated channels previously reported in these neurons. In close spatial proximity, the InsP4(1,3,4,5)-and InsP3(1,4,5)-gated channels interact reciprocally to alter the channels' open probabilities in what may be a novel mechanism for regulating Ca2+ entry in neurons.

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PubMed1994

FMRFamide-like immunoreactivity in presumptive chemosensory afferents of the spiny lobster, Panulirus argus.

Stainings with an antibody against the neuropeptide FMRFamide in the CNS of the spiny lobster revealed strong immunoreactivity in a special class of sensory afferents. These afferents are extremely thin and numerous and innervate all sensory neuropils except the optical and olfactory lobes. In the target neuropils the terminals of the afferents branch in parallel and form very densely labeled net-like structures. Due to their size, number and distribution we conclude that the immunoreactive afferents represent a specialized chemosensory system not related to food detection. We propose that a FMRFamide-related peptide present in the afferent terminals serves as sensory transmitter.

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PubMed1994

Cyclic nucleotide- and inositol phosphate-gated ion channels in lobster olfactory receptor neurons.

The idea of having two second messenger pathways in olfaction, one mediated by cAMP and the other by inositol 1,4,5-trisphosphate, is supported by evidence that both second messengers directly activate distinct ion channels in the outer dendrite of lobster olfactory receptor neurons. Evidence that both types of second messenger-gated channels can occur in the same patch of membrane suggests that channels of both types can be expressed in one neuron. Evidence of more than one type of inositol phosphate-gated channel in this highly specialized region of the neuron furthers the idea that the output of individual olfactory receptor cells is regulated through multiple effectors and allows that effector diversity may contribute to functional diversity among olfactory receptor cells.

Animals↗

PubMed1994

Towards a common strategy for transducing olfactory information.

Olfactory receptor cells in phylogenetically diverse animals are strikingly similar, notwithstanding species-specific differences in organizational details. As we learn more about how olfactory receptor cells function, we see the first evidence that phylogenetic similarity may extend to the functional level. Conservation of form and function in phylogenetically diverse animals would suggest the presence of a fundamental strategy for detecting and discriminating odors. Emerging data on how olfactory receptor cells transduce odor information offers some insight into what this still unresolved strategy may be.

Action Potentials↗

PubMed1994

Descending neurons with dopamine-like or with substance P/FMRFamide-like immunoreactivity target the somata of olfactory interneurons in the brain of the spiny lobster, Panulirus argus.

Two sets of descending neurons primarily target the somata of neurons in the olfactory deutocerebrum of the spiny lobster, Panulirus argus. Hundreds to thousands of dopamine-like immunoreactive fibers originate in the lateral protocerebrum and terminate among the clustered somata of the olfactory deutocerebrum projection neurons (lateral soma cluster) and those of the olfactory deutocerebrum local interneurons (medial soma cluster). A pair of giant neurons with substance P- and FMRFamide-like immunoreactivity from the median protocerebrum terminate primarily in the lateral soma cluster, but also branch in the core of the olfactory lobe itself. Neurons of both types terminate in numerous bouton-like swellings. The terminals in the lateral cluster at least contain numerous, large, dense-core and small, clear vesicles. The terminals contact the somata and the primary neurites through both traditional chemical synapses and large zones of direct membrane appositions. In most instances, a vesicle-containing profile forms a triadic arrangement with a neurite and a soma the latter being frequently connected via large gap-junction-like structures. Rosette-like arrangements formed by a vesicle-containing profile surrounded by up to eight neurites are also common. Dissociated lateral cluster somata support both fast inward and sustained outward voltage-activated currents. Substance P, but not dopamine or FMRFamide-related peptides, alters the fast inward current. The somata of the olfactory projection neurons, and possibly those of the olfactory local interneurons, appear to serve an integrative, and not merely a supportive role in these invertebrate central neurons.

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PubMed1994

Odor-evoked inhibition in primary olfactory receptor neurons.

Odors can inhibit as well as excite lobster olfactory receptor cells. Inhibitory components of an odor mixture act within the normal, first 500 ms odor sampling interval of the animal to reduce the peak magnitude and increase the latency of the net excitatory receptor potential in a concentration-dependent manner. The intracellular effects are reflected in the propagated output of the cell. The results argue that inhibitory odor input is functional in olfaction by potentially serving to increase the diversity of the neuronal patterns that are thought to be the basis of odor discrimination.

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PubMed1994

Single odors differentially stimulate dual second messenger pathways in lobster olfactory receptor cells.

Quench-flow measurements are used to determine the subsecond kinetics of odor-induced changes in second messenger concentrations in lobster olfactory receptor neurons. Individual odors transiently and differentially increase the production of both adenosine cAMP and inositol 1,4,5-trisphosphate (IP3) within 50 msec of odor stimulation. The ability of two different odors to stimulate cAMP and IP3 correlates with the odors' ability to excite and inhibit receptor cells physiologically. These results strengthen the proposition, heretofore based largely on evidence from cultured cells, that dual second messenger pathways mediate excitatory and inhibitory input to lobster olfactory receptor cells.

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PubMed1993

Antennular projections to the midbrain of the spiny lobster. III. Central arborizations of motoneurons.

The central organization of antennular motoneurons in the brain of the spiny lobster, Panulirus argus, was analyzed by combining biocytin backfills with serial reconstructions of the antennular nerves and the brain. Eighty-nine to 99 antennular motoneurons occur in each hemibrain. The somata of the motoneurons are distributed in a consistent pattern in two complex soma clusters, the ventral paired mediolateral cluster of the deutocerebrum and the dorsal unpaired median cluster of the tritocerebrum. The motoneurons arborize ipsilaterally in the lateral and median antennular neuropils and the tegumentary neuropil. The backfills indicate a minimum of five morphological types of motoneurons with different arborization patterns. The innervation pattern of the motoneurons, together with previously reported innervation patterns of antennular sensory afferents, suggest that the lateral antennular neuropil is a lower motor center driving local antennular reflexes in response to chemical and mechanical stimulation of the antennule, whereas the median antennular neuropil is a lower motor center for equilibrium responses.

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PubMed1993

Signal transmission in lobster olfactory receptor cells: functional significance of electrotonic structure analysed by a compartmental model.

The electrotonic structure of lobster olfactory receptor cells was evaluated using general purpose simulation software in a compartmental model derived from electron-microscopic reconstruction. The model with non-uniform membrane resistance (Rm) was used to (i) simulate current spread and (ii) determine if the electronic structure of the cell improves signal recognition in the soma. The odor-evoked conductance change in dendrites was calculated according to the Michaelis-Menten equation with the assumption that the outer dendritic segments function as independent stimulus detectors. The inflection point of the concentration-response function measured in the soma was shifted to lower concentrations relative to that measured in the ciliary (outer dendritic) arbor. The shift, which was greater for inputs with lower efficacy (represented in the model by smaller Hill coefficients) and for the dynamic phase of the response than for the steady-state phase, effectively increased the selectivity of the somatic response. Randomized input distributed uniformly to progressively more restricted areas of the ciliary arbor showed that stimulation of larger areas (presumably the entire ciliary arbor) decreased the statistical variability of the somatic response.

Animals↗

PubMed1993

Odor sensitivity of cultured lobster olfactory receptor neurons is not dependent on process formation.

Cultured lobster olfactory receptor neurons (ORNs) were surveyed for their odor sensitivity with whole-cell, voltage-clamp recording. The nature of the adequate stimuli, the degree of tuning (response spectra) of the cells, the threshold of sensitivity and the dual polarity of the odor-evoked currents are consistent with chemosensitivity in the cultured ORNs being olfactory. The ability of odors to evoke currents in cultured ORNs that lack processes suggests that lobster ORNs can be induced in vitro to insert all the elements of the transduction cascade in the soma, including those that might normally be confined to processes. This should greatly facilitate analysis of olfactory transduction in these cells.

Action Potentials↗

PubMed1992

Physiological and pharmacological evidence for histamine as a neurotransmitter in the olfactory CNS of the spiny lobster.

Perfusing histamine (HA, 0.1 microM-1 mM) into the brain of the spiny lobster reversibly altered the spontaneous activity in 24 (86%) of 28 morphologically unidentified, odor-responsive interneurons. The effects of HA were dose-dependent and could be selectively and reversibly antagonized by cimetidine, a vertebrate H2 antagonist, suggesting that the action of HA in the central nervous system (CNS) was mediated by a receptor pharmacologically similar to an HA receptor expressed by lobster olfactory receptor cells. Perfusing HA into the brain also reversibly altered the spontaneous and/or odor-evoked activity of 6 (67%) of 9 morphologically identified, odor responsive interneurons that arborized in the olfactory lobe (OL). These results extend previous evidence from our lab that the OL contains HA-immunoreactive interneurons and that OL tissue can synthesize HA from its precursor and further implicate HA as a putative neurotransmitter in the olfactory CNS of the spiny lobster.

Action Potentials↗

PubMed1992

Antennular projections to the midbrain of the spiny lobster. I. Sensory innervation of the lateral and medial antennular neuropils.

The organization of sensory afferents in the antennular nerve (AN) of the spiny lobster and the central arborization of the afferents in the lateral and medial antennular neuropils (LAN, MAN) were analyzed by backfilling the AN with biocytin. The MAN receives primarily thick afferents (diameter greater than or equal to 10 microns) with a consistent pattern of arborization from the medial of the three major divisions of the AN. The LAN, in contrast, receives many thin to medium-sized afferents (diameter less than or equal to 0.3-5 microns), in addition some with diameters greater than or equal to 5 microns, from the lateral and dorsal divisions of the AN. In contrast to the consistent pattern of arborization in the MAN, afferents projecting to the LAN arborize in widely different patterns. Serially arranged, orthogonal side branches that are suggestive of topographical representation of the serially arranged sensilla on the antennule contribute to the stratification of the LAN. Together with existing electrophysiological data, these morphological findings are consistent with the idea that the MAN receives primarily mechanosensory (largely statocyst) input, as previously thought, but that the LAN receives chemosensory as well as mechanosensory input. The chemosensory input to the LAN would represent a novel pathway for processing chemosensory input from the antennule.

Afferent Pathways↗

PubMed1992

Antennular projections to the midbrain of the spiny lobster. II. Sensory innervation of the olfactory lobe.

The projection pattern of antennular sensory afferents in the olfactory lobe (OL) of the spiny lobster, Panulirus argus, was examined by backfilling axons in the antennular nerve (AN) with biocytin. Thin, presumptive olfactory afferents from the lateral division of the AN form a tract in the brain that diverges into a dense plexus that completely envelops the glomerular cortex of the OL. Most of the thin (diameter less than or equal to 0.3-1 microns) afferents project to single glomeruli. About 10% of the thin afferents, however, branch in the plexus and project to multiple glomeruli. A smaller number of medium-sized to thick (diameter 2-10 microns), presumably mechanosensory, afferents also innervate the OL and co-project to multiple glomeruli with the thin afferents. Afferents arborize profusely within the columnar glomeruli into very fine processes that penetrate to the base of the columns, but selectively terminate in either the cap/subcap region or in the innermost part of the base of the columns, often with conspicuous terminal boutons, forming two distinct regions of presumptive synaptic output. These results suggest that 1) The majority of the OL innervation is provided by olfactory sensilla (aesthetascs), but that other types of sensilla provide additional, likely mechanosensory, input to the OL. 2) The projection of olfactory afferents is not strictly uniglomerular. 3) The columnar organization of crustacean olfactory glomeruli is functionally significant and may provide an evolutionary correlate of the recently proposed subdivision of the vertebrate olfactory bulb into "functional columns."

Animals↗

PubMed1992

Plasma membrane inositol 1,4,5-trisphosphate-activated channels mediate signal transduction in lobster olfactory receptor neurons.

Inositol 1,4,5-trisphosphate (IP3) selectively evokes an inward (excitatory) current in cultured lobster olfactory receptor neurons (ORNs) and directly activates two types of channels in cell-free patches of plasma membrane from the ORNs. The IP3-activated channels have kinetic properties of odor-activated channels in the ORNs and pharmacological properties of intracellular IP3-activated channels in other systems. An antibody directed against an intracellular, cerebellar IP3 receptor recognizes a protein with a molecular weight similar to the mammalian receptor in the ORNs. The antibody selectively increases odor-evoked inward currents and IP3-activated unitary currents in the ORNs. The data provide further evidence for IP3 as an olfactory second messenger and implicate at least one and possibly two novel plasma membrane IP3 receptors in olfactory transduction.

Animals↗

PubMed1992

Cyclic nucleotides mediate an odor-evoked potassium conductance in lobster olfactory receptor cells.

Odors activate at least two distinct transduction pathways in lobster olfactory receptor cells that, respectively, excite and inhibit the cell. Data presented suggest that odors selectively activate the inhibitory conductance through the second messenger cAMP. Not all cells support both odor-evoked excitatory and inhibitory conductances; in the current investigation, about 50% of the cells tested were inhibited by odors. In the majority of cells that, as a group, support an inhibitory response to odor stimulation, activation of adenylate cyclase with forskolin or inhibition of phosphodiesterase activity with 3-isobutyl-1-methylxanthine (IBMX) elicits an outward current with a time course similar to that of odor-evoked outward currents. The membrane-permeant cyclic nucleotide analogs 8-Br-cAMP and 8-Br-cGMP have a similar effect. Forskolin and IBMX enhance the magnitude of odor-evoked outward currents when the drug and the odor are copresented to the cell. In contrast, these same drugs have little or no effect on cells that, as a group, fail to support an inhibitory response to odor stimulation. This study provides the first direct evidence implicating cAMP in olfactory transduction in an invertebrate and contrasts with similar studies in vertebrates that have implicated cAMP as a second messenger mediating excitation.

1-Methyl-3-isobutylxanthine↗

PubMed1991

Inhibition of lobster olfactory receptor cells by an odor-activated potassium conductance.

1. Whole cell current-clamp recordings show that odors not only depolarize but may also hyperpolarize lobster olfactory receptor cells. Odor-evoked hyperpolarizations occurred in 36% of 178 receptor cells examined. Cell-attached recordings of action potentials followed by current-clamp recordings in the same cell indicate that depolarizing and hyperpolarizing responses were associated with increases (excitation) and decreases (inhibition) in action potential frequency, respectively. Since odorants that hyperpolarized one receptor cell depolarized other cells and since individual cells may be both excited and inhibited, the inhibitory and excitatory nature of the response must be conferred by the odorant-receptor and transduction processes expressed by the receptor cell. 2. The input resistance dropped from 1.73 G omega at rest to 1.45 G omega during odor-evoked hyperpolarization, and the membrane time constant correspondingly decreased from 114 to 61 ms. The increased conductance persisted throughout the stimulation period (5 s). 3. Shifting the K+ reversal to a more negative potential by lowering the [K+]o from 14 to 2.8 mM increased the magnitude of hyperpolarization. The hyperpolarization could be reversibly blocked by dendritic treatment with 5-10 mM 4-aminopyridine (4-AP) or 10 mM cesium ion, but not by 10 mM tetraethylammonium (TEA). 4. Substituting 80% of the [Cl-]o with NO3- increased the amplitude of the hyperpolarization. Based on a calculated equilibrium potential of -32 mV for chloride, an increase in chloride conductance in a low [Cl-]o environment should have decreased the magnitude of the response. Presumably the change in [Cl-]o acts through the dendritic steady-state chloride conductance to shift the membrane potential further from the reversal potential for K+.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Aminopyridine↗

PubMed1990

Immunohistochemical and biochemical evidence for the putative inhibitory neurotransmitters histamine and GABA in lobster olfactory lobes.

As an initial effort to investigate possible inhibitory interactions in the olfactory system of the spiny lobster, studies were conducted to identify and localize the putative inhibitory neurotransmitters histamine and GABA in the olfactory lobe. Biochemical studies demonstrated that olfactory lobe tissue was capable of synthesizing histamine from radioactive histidine and GABA from glutamic acid. Immunohistochemistry was used to localize histamine and GABA in brain sections, by using either avidin-biotin conjugated peroxidase or fluorescein conjugated secondary antibody. Specific histamine-like and GABA-like immunoreactivity was found in soma clusters of olfactory interneurons, adjacent to the olfactory lobe. Small, putative glial cells displaying intense histamine-like immunoreactivity were found interspersed among the glomeruli of the lobe. The accessory lobe exhibited moderate immunostaining for both histamine and GABA. Positive immunostaining for histamine and GABA was also found in the olfactory lobes, with a predominance of staining in the outer caps of the glomeruli, which are thought to be the regions where the primary afferent terminals contact the processes of second-order olfactory neurons. These findings collectively implicate inhibition at the first synaptic level of the olfactory pathway in the spiny lobster.

Animals↗