bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multiple receptors mediate the modulatory effects of serotonergic neurons in a small neural network
Authors: Zhang Bing , Harris-Warrick Ronald M. 
Published: April 2021

ABSTRACT
The gastropyloric receptor (GPR) cells are a set of cholinergic/serotonergic mechanosensory neurons that modulate the activity of neural networks in the crab stomatogastric ganglion (STG). Stimulation of these cells evokes a variety of slow modulatory responses in different STG neurons that are mimicked by exogenously applied serotonin (5-HT); these responses include tonic inhibition, tonic excitation and induction of rhythmic bursting. We used pharmacological agonists and antagonists to show that these three classes of modulatory response in the STG neurons are mediated by distinct 5-HT receptor subtypes. GPR stimulation or application of 5-HT or 2-me-5HT (a vertebrate 5-HT3 agonist) inhibited the pyloric constrictor (PY) neurons; these actions were selectively antagonized by gramine. GPR stimulation or application of 5-HT induced rhythmic bursting in the electrically coupled anterior burster (AB) and pyloric dilator (PD) neurons; these effects were antagonized by the 5-HT1c/2 antagonist cinanserin and by atropine at concentrations that do not block muscarinic cholinergic receptors in the crab STG. The 5-HT agonists 5-CT (5-HT1 ) and α-me-5HT (5-HT2 ) also induced AB/PD bursting, which was blocked by cinanserin, but not by atropine. GPR stimulation or application of 5-HT and 5-CT evoked tonic excitation of the lateral pyloric (LP) neuron. These effects were blocked by cinanserin. Several other 5-HT agonists and nearly all the vertebrate 5-HT antagonists we tested had little or no effect on the crab pyloric 5-HT receptors. These results provide further evidence that the modulatory sensory GPR neuron uses serotonin to evoke multiple modulatory responses via multiple 5-HT receptors. However, the 5-HT receptors in the crab STG neurons are not pharmacologically similar to vertebrate 5-HT receptors.
A Microcalorimetric Study of Turtle Cortical Slices: Insights Into Brain Metabolic Depression
Authors: Doll Christopher J. , Hochachka Peter W. , Hand Steven C. 
Published: April 2021

ABSTRACT
In previous papers, we have examined turtle cortical neurons in vitro for mechanisms of anoxic metabolic depression (‘channel arrest’ and changes in electrical parameters). Negative results prompted the current study with the aim of examining more closely the energy profile and metabolism of turtle cortical slices. Calorimetry is used to measure heat dissipation during normoxia and nitrogen perfusion (120 min) and the results are converted into an ATP utilization rate. These indicate that the control rate of ATP utilization (1.72 μmol ATP g−1 min−1) agrees closely with in vivo whole-brain metabolic measurements. Both nitrogen perfusion and pharmacologically induced anoxic (cyanide+N2) groups depressed heat dissipation considerably compared with the control value (nitrogen 37%; pharmacological anoxia 49%). The resulting ATP utilization estimates indicate metabolic depressions of 30% (nitrogen) and 42% (pharmacological anoxia). The slice preparation did not exhibit a change in any measured adenylate parameter for up to 120 min of anoxia or pharmacological anoxia. Significant changes did occur in [ADP], ATP/ADP ratio and energy charge after 240 min of exposure to anoxic conditions. These results support the idea that the turtle cortical slice preparation has a profound resistance to anoxia, with both nitrogen perfusion and pharmacological anoxia causing a rapid decline in heat dissipation and metabolism.
Cardiovascular Responses to Scyliorhinin I and II in the Rainbow Trout, Oncorhynchus Mykiss, in Vivo and In Vitro
Authors: Kågström Jens , Axelsson Michael , Holmgren Susanne 
Published: April 2021

ABSTRACT
Changes in cardiac output, heart rate, dorsal aortic blood pressure and coeliac artery blood flow were measured in unrestrained rainbow trout, Oncorhynchus mykiss, following injections of the elasmobranch tachykinins scyliorhinin I and II. The resistance in the coeliac vascular bed and the total systemic vasculature were calculated from blood pressure and flow. In addition, isolated tails were perfused to investigate the effect of the peptides on the somatic vasculature. Scyliorhinin I (SCY I) produced a biphasic change in the coeliac vascular resistance: an initial decrease was followed by an increase. The decrease in coeliac vascular resistance was accompanied by a decrease in the total systemic vascular resistance, leading to an increased cardiac output. The ensuing increase in coeliac vascular resistance caused a slight increase in blood pressure. In the perfused tail, SCY I produced a marked increase in the somatic vascular resistance. Scyliorhinin II (SCY II) decreased the systemic vascular resistance, causing an increase in cardiac output. SCY II also caused a late increase in the coeliac vascular resistance, which led to hypertension and bradycardia. In vitro, SCY II produced a biphasic response in which an initial decrease in the somatic resistance was followed by a larger increase. The results demonstrate that exogenous SCY I and II are vasoactive peptides that act by different mechanisms in the rainbow trout cardiovascular system. Their actions also differ from the actions of substance P previously observed in the cod, Gadus morhua, and possibly involve a neural reflex.
Variations in Force–Time Histories of cat Gastrocnemius, Soleus and Plantaris Muscles for Consecutive Walking Steps
Authors: Herzog W. , Zatsiorsky V. , Prilutsky B. I. , Leonard T. R. 
Published: April 2021

ABSTRACT
Force-sharing among muscles during locomotion has been studied experimentally using ‘representative’ or ‘average’ step cycles. Mathematical approaches aimed at predicting individual muscle forces during locomotion are based on the assumption that force-sharing among muscles occurs in a consistent and unique way. In this study, we quantify normal variations in muscular force–time histories for step cycles executed at a given nominal speed, so that we can appreciate what it means to analyze ‘representative’ or ‘average’ step cycles and can evaluate whether these normal variations in muscular force–time histories are random or may be associated with variations in the kinematics of consecutive step cycles. Forces in gastrocnemius, soleus and plantaris muscles were measured for step cycles performed at a constant nominal speed in freely moving cats. Gastrocnemius forces were always larger than peak plantaris or soleus forces. Also, peak gastrocnemius forces typically occurred first after paw contact, followed by peak soleus and then peak plantaris forces. Furthermore, it was found that variations in muscular force–time histories were substantial and were systematically related to step-cycle durations. The results of this study suggest that findings based on ‘representative’ or ‘average’ step cycles for a given nominal speed of locomotion should be viewed cautiously and that variations in force-sharing among muscles are systematically related to variations in locomotor kinematics.
Ammonia Excretion in Freshwater Rainbow Trout (Oncorhynchus Mykiss) and the Importance of Gill Boundary Layer Acidification: Lack of Evidence for Na+/NH4+ Exchange
Authors: Wilson Rod W. , Wright Pam M. , Munger Steve , Wood Chris M. 
Published: April 2021

ABSTRACT
Net ammonia fluxes (JAmm) were measured in adult freshwater rainbow trout in vivo under a variety of conditions designed to inhibit unidirectional sodium uptake (; low external [NaCl], 10−4 mol l−1 amiloride), alter transbranchial and NH4+ gradients [24 h continuous (NH4)2SO4 infusion, or exposure to 1 mmol l−1 external total ammonia at pH 8] and prevent gill boundary layer acidification (5 mmol l−1 Hepes buffer). Inhibition of with amiloride or low external [NaCl] under normal conditions reduced JAmm by about 20%, but did not prevent the net excretion of ammonia during exposure to high concentrations of external ammonia. Increasing the buffer capacity of the ventilatory water with Hepes buffer (pH 8) reduced JAmm by 36% and abolished the effect of amiloride on ammonia excretion.
No evidence could be found to support a directly coupled apical Na+/NH4+ exchange. We suggest that any dependence of ammonia excretion on sodium uptake is caused by alteration of transbranchial gradients within the gill microenvironment secondary to changes in net H+ excretion. Under normal conditions (pH 8, low external ammonia) gill boundary layer acidification facilitates over one-third of the total ammonia excretion. During exposure to high concentrations of external ammonia in poorly buffered water, estimates of transbranchial gradients from measurements of bulk water pH and total ammonia concentration (TAmm) may be grossly in error because of boundary layer acidification. Prevention of boundary layer acidification with Hepes buffer during exposure to high cocncentrations of external ammonia revealed that the local transbranchial gradient at the gill may in fact be positive (blood to water), negating the need for an active NH4+ transport mechanism. In freshwater trout, NH3 diffusion may account for all ammonia excretion under all experimental conditions used in the present study.
Morphological Changes and Functional Recovery Following Axotomy of a Serotonergic Cerebrobuccal Neurone in the Land Snail Achatina Fulica
Authors: Chiasson Bernard J. , Baker Michael W. , Croll Roger P. 
Published: April 2021

ABSTRACT
We have examined an identified serotonergic neurone in Achatina fulica and described the normal morphological and physiological characteristics of this cell. Injury-induced changes in this neurone following in vivo recovery are described and compared with in vitro gastropod models of regeneration. Nickel–lysine and biocytin dye-fills of the metacerebral giant (MCG) neurone, together with serotonin-like immunoreactivity, revealed an extensive innervation of the ipsilateral buccal ganglion, much greater than that previously reported. Labelled MCG fibres were seen to ramify throughout the ganglion, providing extensive neuropilar innervation. Serotonin-immunoreactive fibres were seen not only within the neuropile but also within the cell body layer of the buccal ganglia, surrounding many of the cell bodies with varicose fibres. Dye-fills also revealed a minor contralateral buccal innervation not previously described. This view of a predominantly ipsilateral innervation of the buccal ganglia by the MCG was supported by electrophysiological measurements. The ipsilateral buccal follower cell B1 displayed an increase in depolarization in response to repeated trains of action potentials to the MCG, whereas the contralateral B1 showed only a weak depolarization in response to the identical stimuli.
Following a crush to the cerebral–buccal connective (CBC), the MCG rapidly regenerated its injured projections, displaying both morphological and physiological recovery within 5–10 days. The original, severed fibres of the MCG were, however, replaced by a multitude of smaller neurites, which persisted for up to 3 months (the longest recovery period examined). Despite this morphological difference between normal and regenerated fibres, the MCG re-established functionally equivalent connections upon B1. In contrast with previous in vitro studies using gastropods, serotonin-like immunoreactivity revealed that severed distal fibres from the MCG rapidly degenerated (2–6 days), resulting in a transient unilateral depletion of serotonin in the buccal ganglia. We suggest that this loss of serotonin in the lesioned ganglion may play a functional role in regeneration, as has been suggested in vitro.
Structural Basis for Wavelength Discrimination in the Banked Retina of the Firefly Squid Watasenia Scintillans
Authors: Michinomae Masanao , Masuda Hiroko , Seidou Masatsugu , Kito Yuji 
Published: April 2021

ABSTRACT
There is a greatly thickened region of retina in the ventral part of the eye of the firefly squid Watasenia scintillans, with an outer segment (OS) layer around 600 μm thick. The distal two-thirds of this OS layer is yellow and contains a visual pigment, based on 4-hydroxyretinal (A4), with an absorbance maximum at 470nm. The proximal third is pink and contains a visual pigment, based on dehydroretinal (A2), with an absorbance maximum at 500nm. Light and electron microscopic investigations demonstrate the presence of four types of photoreceptor cell. In the pink layer, three of the four types (α, β and γ) produce no microvilli and are columnar in structure. These cells form square microvillous rhabdoms only in the distal yellow layer. The fourth cell type (δ) produces microvilli in the pink layer only. These observations led us to propose that the A2-based visual pigment is contained in the pink-layer cells and that the A4-based visual pigment is contained in the three types of yellow-layer cells. The absorbance of fresh retina was determined by microspectrophotometry. The yellow OS layer, with an absorbance of 0.7 per 100 μm thickness at 470nm, is expected to act as a short-wavelength cut-off filter to the underlying pink OS cells, shifting their photosensitivity peak by an estimated 50nm to 550nm. Possible wavelength discrimination by this squid is discussed.
Activity of Giant Interneurones and Other Wind-Sensitive Elements of the Terminal Ganglion in the Walking Cricket
Authors: Kohstall-Schnell Dorothea , Gras Heribert 
Published: April 2021

ABSTRACT
Using intracellular recording techniques in stationary walking crickets (Gryllus bimaculatus), we have investigated the relationship between locomotion and the activity of interneurones ascending from the terminal ganglion. Nine different types of giant interneurones (GI) were characterized during walking and standing. One third of them reduced their activity, while the others enhanced their spike rate, during walking. These physiological properties were strictly correlated with morphological characteristics such as axon position in the longitudinal tracts of the terminal ganglion. In general, ventral GIs reduced and dorsal GIs increased their spike frequency during walking. In some of them, there was a weak but significant correlation between the spike rate and translational speed, but no correlation with rotational speed.
In all GIs except 10-3a, the changes in activity occurred at the start of walking. In GI 10-3a, an increase in membrane potential and spike rate was observed before the start of locomotion. Therefore, an intrinsic mechanism within the central nervous system operating on GI 10-3a is suggested.
Additionally, the activities of filiform hair receptors and of previously undescribed small ascending interneurones (SAI) have been studied during walking. About 80% of the receptors slightly increased their spike rate during walking, while one SAI became more active during walking and another one was hardly affected.
The physiological properties of ascending interneurones are discussed with respect to their modulation and particular function during walking.
Efficiency of Fast- and Slow-Twitch Muscles of the Mouse Performing Cyclic Contractions
Authors: Barclay C. J. 
Published: April 2021

ABSTRACT
The mechanical efficiency of mouse fast- and slow-twitch muscle was determined during contractions involving sinusoidal length changes. Measurements were made of muscle length, force production and initial heat output from bundles of muscle fibres in vitro at 31°C. Power output was calculated as the product of the net work output per sinusoidal length cycle and the cycle frequency. The initial mechanical efficiency was defined as power output/(rate of initial heat production + power output). Both power output and rate of initial heat production were averaged over a full cycle of length change. The amplitude of length changes was ±5% of muscle length. Stimulus phase and duration were adjusted to maximise net work output at each cycle frequency used. The maximum initial mechanical efficiency of slow-twitch soleus muscle was 0.52±0.01 (mean ±1 S.E.M. N=4) and occurred at a cycle frequency of 3 Hz. Efficiency was not significantly different from this at cycle frequencies of 1.5–4 Hz, but was significantly lower at cycle frequencies of 0.5 and 1 Hz. The maximum efficiency of fast-twitch extensor digitorum longus muscle was 0.34±0.03 (N=4) and was relatively constant (0.32–0.34) over a broad range of frequencies (4–12 Hz). A comparison of these results with those from previous studies of the mechanical efficiency of mammalian muscles indicates that efficiency depends markedly on contraction protocol.
Acid–Base Regulation, Branchial Transfers and Renal Output in a Marine Teleost Fish (The Long-Horned Sculpin Myoxocephalus Octodecimspinosus) During Exposure to low Salinities
Authors: Claiborne James B. , Walton Julie S. , Compton-McCullough Dana 
Published: April 2021

ABSTRACT
A number of studies have implied a linkage between acid–base and ion exchanges in both freshwater and seawater fish, although little is known about the branchial and renal acid–base transfers involved as the animals move between different salinities. To investigate the role of these transfers in a marine teleost fish as it is exposed to a dilute environment, we measured plasma acid–base values and net movements from fish to water of NH4+, HCO3− and H+ in long-horned sculpin (Myoxocephalus octodecimspinosus) placed in 100%, 20%, 8% or 4% sea water for 24–48h. Renal excretion of H+ was also monitored in fish exposed to 4% sea water. Sculpin proved to be somewhat euryhaline for they were able to maintain plasma ion and acid–base transfers in hypo-osmotic (20%) sea water, but could not tolerate greater dilutions for more than several days. Plasma pH and carbon dioxide concentration increased in the 20% and 8% dilution groups, with nearly doubling (control, 4.56mmol l−1; 8% group, 8.56mmol l−1) as a result of a combined increase in the partial pressure of plasma CO2 and [HCO3−]. During a 44–46h exposure, HCO3− transfers increased progressively in the most dilute water, with animals in the 8% and 4% groups exhibiting a net H+ loss that was smaller than that of seawater fish (control, 5.1mmolkg−1; 8%, 0.9mmolkg−1; 4%, -2.9mmolkg−1). Animals exposed to 4% sea water for 24h and then returned to normal sea water had a variable plasma pH, an elevated and a net efflux of H+ that effectively stopped (control, 0.10mmolkg−1 h−1; 4%, 0.02mmolkg−1 h−1; seawater recovery, 0.20mmolkg−1 h−1) during the low-salinity period. Renal acid excretion remained relatively constant throughout the experiment but only made up a significant portion (approximately 40%) of the total acid transfers during the 4% dilution period (control rate approximately 3 µmolkg−1 h−1: 3% of branchial rate).
We postulate that the increase in plasma during exposure to low salinity may be due to mobilization of base from the intracellular bone compartment. The decrease in external salinity could induce base loss by alteration of gill ion exchanges (Na+/H+, Cl−/HCO3−) and/or changes in branchial HCO3− permeability. For the first time, we have shown that the effects of a dilute environment on acid–base transfers may be an important limitation to the survival of a euryhaline species in brackish or fresh water.
Unique Permeability Barrier of the Apical Surface of Parietal and Chief Cells in Isolated Perfused Gastric Glands
Authors: Boron Walter F. , Waisbren Steven J. , Modlin Irvin M. , Geibel John P. 
Published: April 2021

ABSTRACT
Although many factors can influence intracellular pH (pHi), some of the most important are those that involve the movement of acids and bases across the cell membrane. We will discuss recent results concerning barriers to the movement of H+, NH3 and CO2 across the apical cell membranes of gastric gland cells. Cell membranes are generally highly permeable to small, lipophilic molecules such as NH3 and CO2. In fact, only two examples are known of membranes relatively impermeable to NH3 and none of membranes permeable to CO2. We recently developed a technique for perfusing the lumen of a single hand-dissected gastric gland on the stage of a microscope, while monitoring pHi with a fluorescent dye. We observed the expected pHi changes when we exposed the basolateral (i.e. blood-side) membrane to a pH 6.4 solution (a large, rapid pHi decrease), to a pH 7.4 solution containing approximately 0.3 mmol l−1 NH3 (a large and rapid pHi increase) or to a pH 7.4 solution equilibrated with 1% CO2 (a rapid pHi decrease of -0.08). However, pHi was not significantly affected by perfusing the lumen with a pH 1.4 solution, with a pH 7.4 solution containing as much as 2.7 mmol l−1 NH3 or with a pH 6.1 solution equilibrated with 100% CO2. These data indicate that a barrier at or near the apical membrane has a uniquely low permeability to H+, NH3 and CO2.
Na+/H+ Antiport: Modulation by Atp and Role in Cell Volume Regulation
Authors: Demaurex Nicolas , Grinstein Sergio 
Published: April 2021

ABSTRACT
Na+/H+ antiport is a major determinant of intracellular pH (pHi) and also plays an important role in the maintenance of cellular volume. Na+/H+ exchange through NHE-1, the ubiquitous isoform of the antiporter, is accelerated by cytosolic acidification and also by osmotically induced cell shrinking, thereby promoting recovery of the physiological pHi and volume, respectively. Although hydrolysis of ATP is not required for transport of ions through the antiporter, metabolic depletion exerts a marked inhibitory effect. Depletion of ATP also prevents osmotic activation and volume regulation. Contrary to earlier suggestions, however, changes in the phosphorylation state of the antiporter itself are not involved in the effects of either metabolic depletion or osmotic stimulation. Nevertheless, the cytosolic carboxy-terminal segment of the antiporter, which contains the major phosphorylation sites, is essential for the ATP dependence as well as for osmotic activation. It is conceivable that this domain interacts with ancillary phosphorylated or nucleotide-binding proteins, with the cytoskeleton and/or with specific phospholipids, which modulate the rate of transport.
Nucleotide dependence and osmotic sensitivity have been compared in three different isoforms of the antiporter, heterologously expressed in fibroblastic cells. Like NHE-1, NHE-2 and NHE-3 were severely inhibited by depletion of ATP. In contrast, whereas NHE-2 was stimulated by osmotic shrinkage, NHE-3 was inhibited. The possible physiological significance of the ATP-dependence and osmotic responsiveness of the antiporter isoforms is discussed.
Bacterial and Plant Antiporters
Authors: Maloney Peter C. 
Published: April 2021

ABSTRACT
Articles in this chapter emphasize the phenomenon of ion exchange across biomembranes. This topic has been of interest at least since 1947, when Hans Ussing articulated his model of ‘exchange diffusion’ to account for an unexpected elevation in the rate of 22Na+ efflux from skeletal muscle (Ussing, 1947). Ussing had tried to measure net Na+ movement by following tracer flux, but found that this approach greatly overestimated the true value. To explain this overestimate, Ussing postulated that isotopic flux reflected only isotopic exchange rather than net movement of mass, and he proposed the following model. Perhaps a negatively charged carboxyl group on some membrane element accepts the positively charged 22Na+ so that the neutral complex can move through the membrane (mechanism unspecified) without interference from the electric field? If so, at the opposite surface, tracer could be discharged, replaced by (non-radioactive) 23Na+, and the neutral complex would return to the original membrane surface, and at that point 23Na+ would be released to let the cycle begin again. Clearly, by following the movement of 22Na+, one might considerably overestimate the true net movement of Na+ itself.