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B W Ache

Publications and source records attributed to B W Ache.

50 records · Page 3Linked to original sources
PubMed1990

Nonselective cation channel activated by patch excision from lobster olfactory receptor neurons.

A nonselective cation channel activated by patch excision was characterized in inside-out patches from spiny lobster olfactory receptor neurons. The channel, which was permeable to Na+, K+ and Cs+, had a conductance of 320 pS and was weakly voltage dependent in the presence of micromolar divalent cations. Millimolar internal divalent cations caused a voltage- and concentration-dependent block of Na+ permeation. Analysis of the voltage dependence indicated that the proportion of the membrane's electric field sensed by Mg2+ was greater than 1, suggesting that the channel contains a multi-ion pore. Internal divalent cations also reduced the frequency of channel opening in a concentration-dependent, but not voltage-dependent, manner, indicating that different cation binding sites affect gating and conductance. While block of gating prevented determining if internal divalent cations permeate the channel, a channel highly permeable to external divalent cations was observed upon patch excision to the inside-out configuration. The monovalent and divalent cation conductances shared activation by patch excision, weak voltage dependence, and steady-state activity, suggesting that they are the same channel. These data extend our understanding of this type of channel by demonstrating permeation by monovalent cations, detailing Mg2+ block of Na+ permeation, and demonstrating the channel's presence in arthropods.

Animals↗
PubMed1989

Histamine directly gates a chloride channel in lobster olfactory receptor neurons.

Biogenic amines mediate many types of intercellular communication in multicellular organisms. Heretofore, little direct evidence has indicated that biogenic amines produce intracellular responses other than by triggering the enzymatic production of second messengers. Our electrophysiological studies of lobster olfactory receptor neurons now reveal that one biogenic amine, histamine, can directly gate an ion channel. The channel responds to histamine concentrations of 1 microM or more, is permeable primarily to Cl-, is more active at depolarized potentials, and has a conductance of 44 pS in the American lobster and 66 pS in the Caribbean spiny lobster. The expression of this ligand-gated channel in olfactory receptor neurons implies that these neurons are targets of a regulatory or feedback process.

Animals↗
PubMed1989

Ionic currents and ion channels of lobster olfactory receptor neurons.

The role of the soma of spiny lobster olfactory receptor cells in generating odor-evoked electrical signals was investigated by studying the ion channels and macroscopic currents of the soma. Four ionic currents; a tetrodotoxin-sensitive Na+ current, a Ca++ current, a Ca(++)-activated K+ current, and a delayed rectifier K+ current, were isolated by application of specific blocking agents. The Na+ and Ca++ currents began to activate at -40 to -30 mV, while the K+ currents began to activate at -30 to -20 mV. The size of the Na+ current was related to the presence of a remnant of a neurite, presumably an axon, and not to the size of the soma. No voltage-dependent inward currents were observed at potentials below those activating the Na+ current, suggesting that receptor potentials spread passively through the soma to generate action potentials in the axon of this cell. Steady-state inactivation of the Na+ current was half-maximal at -40 mV. Recovery from inactivation was a single exponential function that was half-maximal at 1.7 ms at room temperature. The K+ currents were much larger than the inward currents and probably underlie the outward rectification observed in this cell. The delayed rectifier K+ current was reduced by GTP-gamma-S and AIF-4, agents which activate GTP-binding proteins. The channels described were a 215-pS Ca(++)-activated K+ channel, a 9.7-pS delayed rectifier K+ channel, and a 35-pS voltage-independent Cl- channel. The Cl- channel provides a constant leak conductance that may be important in stabilizing the membrane potential of the cell.

Animals↗
PubMed1989

Whole cell recording from lobster olfactory receptor cells: responses to current and odor stimulation.

1. The basic electrical properties of olfactory (antennule) receptor cells were studied in an in situ preparation of the spiny lobster using whole cell patch-clamp recording. 2. The current-voltage relationship of the cells was linear for membrane potentials between -150 and -40 mV and rectified at more positive membrane potentials. The input resistance at rest averaged 508 M omega. The cells displayed two time constants, with mean values of 29.8 and 8.2 ms. 3. Depolarizing current steps elicited fast, overshooting action potentials at a mean threshold of -32 mV from an imposed resting membrane potential of -65 mV. The action potentials were tetrodotoxin (TTX) and tetraethylammonium (TEA) sensitive, suggesting they are typical sodium/potassium action potentials. 4. Odor stimulation evoked slow, dose-dependent, depolarizing receptor potentials up to 50 mV in amplitude. In approximately 30% of cells tested, these led to repetitive spiking when the cells were depolarized beyond -45 to -30 mV. The amplitude of the receptor potential was graded as a linear function of the logarithm of the odor concentration. 5. The amplitude of the receptor potential varied linearly with the membrane potential between -70 and -30 mV. Extrapolated reversal potentials appeared to be normally distributed around a mean value of -3.6 mV. 6. The results collectively indicate that lobster olfactory receptor cells have electrical properties similar to, but not necessarily identical with, those currently envisaged for olfactory receptor cells in other species.

Action Potentials↗
PubMed1989

Histamine-induced modulation of olfactory receptor neurones in two species of lobster, Panulirus argus and Homarus americanus.

In two species of lobster, application of the biogenic amine, histamine (HA), to the soma of olfactory receptor cells suppressed both spontaneous and odour-evoked activity, as shown by electrophysiological recording from single cells. The action of HA was graded, reversible, specific to HA, and had a threshold between 0.1 and 1 mumol l-1. HA increased the conductance of the membrane, primarily to chloride ions. The vertebrate HA receptor antagonist, cimetidine, and the nicotinic receptor antagonist, d-tubocurarine, but not other known vertebrate HA receptor antagonists, reversibly blocked the action of HA. These results suggest that a histaminergic mechanism modulates stimulus-response coupling in lobster olfactory receptor cells and potentially implicate a novel HA receptor, pharmacologically similar to the one recently described in the visual system of flies.

Action Potentials↗
PubMed1988

Morphology and physiological properties of interneurons in the olfactory midbrain of the crayfish.

1. Intracellular recording and staining was used to characterize neurons in the crayfish (Procambarus clarkii) brain that respond to chemical stimuli applied to the major olfactory organs, the antennules. 2. Two distinct morphological types of neurons that have major projections in the olfactory lobes (OLs) of the brain were characterized anatomically (Figs. 1, 2, 3; Table 2) and physiologically (Figs. 4, 5, 6; Table 3). 3. Different individual neurons of one type, with similar 'tree-like' projections in the OLs, have somata distributed in at least 5 different cell body clusters of the brain (Fig. 3) and link different subsets of neuropilar lobes through their distributed arbors (Fig. 1, Table 2). 4. Excitatory, inhibitory and mixed responses were recorded in different neurons when odorant mixtures or individual components of these mixtures were applied to the antennules. Response spectra to individual components were broad and overlapping, but not identical in the neurons tested (Fig. 4; Table 3). Mixture interactions appear to be additive in most of the neurons that we tested, but evidence was obtained for mixture suppression in several cases (Fig. 6). 5. Most of the neurons recorded in this study responded only to stimulation of the ipsilateral antennule (Fig. 5), although subthreshold activity to stimuli applied contralaterally was recorded in several neurons that were strongly excited by ipsilateral stimuli. 6. Chemoresponsive neurons without projections in OL's that have all of their branches confined to the brain, or that project an axon in the circumesophageal connective, are described (Fig. 7).

Action Potentials↗
PubMed1987

Purinergic modulation in the brain of the spiny lobster.

Earlier studies identified purinergic chemoreceptors in the olfactory organ of the spiny lobster, Panulirus argus. In this study, electrophysiological experiments demonstrate that purinergic substances can modulate both the spontaneous activity and the evoked responses of neurons within the brain of this animal. Perfusion of the brain with 100 microM adenosine 5'-monophosphate (AMP) modulated the spontaneous activity of 71% of the brain interneurons that were monitored. AMP also modulated the electrically or chemically evoked activity of 25% of the monitored interneurons. The effects were dose-dependent (down to 1 microM) and reversible. The modulatory effects of adenosine were similar to those of AMP, and were antagonized by the adenosine receptor antagonist 1,3-dipropyl-8-p-sulfophenylxanthine. The modulation by AMP or adenosine was depressive in most but not all neurons, as is the case with purinergic effects in the brain of vertebrates. We believe this is the first demonstration of modulatory effects of purinergic substances in the nervous system of any invertebrate.

Action Potentials↗
PubMed1987

Chemoreceptors of crustaceans: similarities to receptors for neuroactive substances in internal tissues.

A description is given of crustacean chemosensory systems and the neurophysiological procedures used to study them. Their response properties and tuning characteristics are discussed. A review is then provided of specific crustacean chemoreceptors that are stimulated selectively by either purine nucleotides, taurine, glutamate, or glycine, all of which have neuroactive properties in internal tissues. Two distinctly different types of purinergic chemoreceptors occur on the antennules of the spiny lobster. P1-like chemoreceptors have a potency sequence of AMP greater than ADP greater than ATP greater than adenosine and show a strict structural requirement for the ribose phosphate moiety. P2-like chemoreceptors have a potency sequence of ATP greater than ADP greater than AMP or adenosine and show a broad sensitivity to nucleotide triphosphates with modifications in both the purine and ribose phosphate moieties. Sensilla containing the dendrites of chemosensory neurons also possess an ectonucleotidase(s) that inactivates excitatory nucleotides to yield adenosine which is subsequently internalized by a sensillar uptake system. Narrowly tuned taurinergic chemoreceptors are present on both the antennules and legs of lobsters. Although taurine itself is the most effective stimulant, the taurine analogs hypotaurine and beta-alanine are also very excitatory. Structure-activity studies indicate these chemoreceptors have marked similarities to taurine-sensitive systems in internal tissues of vertebrates. By contrast, comparative studies of glutamatergic chemoreceptors on the legs of lobsters indicate response spectra different from those of the glutamate receptors in lobster neuromuscular junctions and the three classes of excitatory amino acid receptors identified internally in vertebrates. Crustacean chemoreceptors for glycine, ecdysteroids, and pyridine are also described. The hypothesis that receptors for internal neuroactive agents may have originally evolved as external chemoreceptors of primitive aquatic organisms is discussed.

Animals↗
PubMed1985

Voltage- and current-clamp recordings of the receptor potential in olfactory receptor cells in situ.

Intracellular recordings obtained using the whole cell configuration of the patch recording technique show that isolated somas of olfactory receptor cells are electrogenic, producing fast overshooting action potentials when depolarized. In situ, these cells produce graded receptor potentials and action potentials when stimulated chemically. The receptor potential can be voltage clamped for analysis of the ionic basis of sensory transduction in olfaction.

Animals↗
PubMed1985

Amino acid suppression of taurine-sensitive chemosensory neurons.

Single unit recordings from chemoreceptors on the antennule of the spiny lobster revealed a population of taurine-sensitive cells whose response is suppressed when taurine is presented in mixture with certain amino acids. A synthetic mixture of 21 amino acids plus betaine, which mimics the composition of a natural food stimulus (crab muscle tissue) and itself contains taurine, totally and reversibly blocked the taurine response of this group of receptor cells. An analysis of the contribution to this suppression by the six major components (based on concentration) in the mixture revealed partial or complete inhibitory activity by five of the compounds. In a sample group of the inhibited cells, mean percent suppression of the taurine response was 99% for glycine and L-arginine, 98% for L-glutamine, 60% for L-alanine and 43% for L-proline. Both glycine and alanine in binary mixture with taurine caused a right-shift in the concentration-response function for taurine, suggesting a competitive mechanism of suppression. pA2 values determined from these data yielded 4.17 for glycine and 3.55 for alanine. These results suggest that the processing of chemical information in quality and/or intensity coding of natural stimulus mixtures can be tempered by interactions of the components at the receptor-cell level, and possibly at the receptor-sites themselves.

Amino Acids↗
PubMed1984

Processing of olfactory information at three neuronal levels in the spiny lobster.

Odor quality coding was analyzed at three neuronal levels, receptor cells and two levels of chemosensory interneurons, in the olfactory system of the spiny lobster Panulirus argus . Responses to three of the most stimulatory compounds for this animal - taurine, glutamate and betaine - were recorded at each level in order to compare basic neuronal response properties, single cell and population response spectra, and across-neuron patterns. Mean response specificity increased for cells at each successive neuronal level. The increase in breadth of tuning between receptor cells and low-order interneurons was paralleled by an increase in interstimulus across-neuron correlations. However, in high-order interneurons, there was a relative decline in across-neuron correlations, indicating that the more broadly-tuned high-order interneurons are better able to discriminate between any two compounds than are the more narrowly-tuned low-order interneurons. Although stimulus quality appears to be coded by interneurons as an across-fiber pattern, the fact that some low-order and high-order interneurons retained the narrow specificity of receptor cells suggests that labeled lines may have an important function in coding throughout the olfactory pathway of the spiny lobster.

Animals↗
PubMed1984

Quality coding of a complex odorant in an invertebrate.

Mechanisms whereby the olfactory system of the spiny lobster codes food odors were quantitatively analyzed. A 23-component chemical mixture, with a composition based on a tissue extract from a known food of lobsters, and 8 of the mixture's components were used to describe responses of single cells at two neural levels: a) olfactory receptor cells and b) low-order interneurons projecting from the main olfactory center of the brain. Cluster analysis identified six classes of narrowly tuned receptor cells. Interneurons, on the other hand, were significantly more broadly tuned than receptor cells and could not be grouped into a small number of discrete, highly correlated cell types. Nonetheless, some chemosensory interneurons (unimodal interneurons) had specificities as narrow as receptor cells. Across-neuron correlations between stimuli showed that the increase in neuronal breadth of responsiveness from the level of receptors to the level of interneurons was paralleled by an increase in similarity in across-neuron patterns and, therefore, a decline in ability to discriminate between any two compounds. Across-neuron correlations between concentrations of a given compound showed that stimulus quality had a much stronger effect on across-neuron patterns than did stimulus quantity and, hence, stimulus qualities could be distinguished in spite of concurrent changes in stimulus quantity. Coding of odor quality could be accomplished at the receptor level by a labeled-lines code. At the interneuronal level, odor quality appears to be coded by across-fiber patterns. However, the finding that unimodal interneurons were as narrowly tuned as receptor cells indicates that specific channels for some food-odor components (e.g., taurine and glycine) are conserved even at higher neuronal levels. These narrow-spectrum interneurons may have a special function in quality coding either by dominating the interneuronal across-fiber pattern for that stimulus or by being processed independently of the broad-spectrum interneurons and thereby transferring information about certain components by way of specific channels to even higher neuronal levels.

Animals↗
PubMedDate not supplied

GABA-mediated inhibition of primary olfactory receptor neurons.

Applying GABA (1 microM-1 mM) to the soma of cultured lobster olfactory receptor neurons evokes an inward current (V(m) = -60 mV) accompanied by an increase in membrane conductance, with a half-effect of 487 microM GABA. The current-voltage relationship of this current is linear between -100 and 100 mV and reverses polarity at the equilibrium potential for Cl(-). The current is blocked by picrotoxin and bicuculline methiodide, and is evoked by trans-aminocrotonic acid, isoguvacine, muscimol, imidazole-4-acetic acid, and 3-amino-1-propanesulfonic acid, but not by the GABA(C)-receptor agonist cis-4-aminocrotonic acid and the GABA(B)-receptor agonist 3-aminopropylphosphonic. Applying GABA to the soma of the cells in situ reversibly suppresses the spontaneous discharge and substantially decreases the odor-evoked discharge. The effects of GABA on the cell soma in situ are antagonized by both picrotoxin and bicuculline methiodide. Taken together with evidence that GABA directly activates a chloride channel in outside-out patches excised from the soma of these neurons, we conclude that lobster olfactory receptor neurons express an ionotropic GABA receptor that can potentially regulate the output of these cells.

Animals↗