Comparison of the roles of neurohormones in the regulation of blood distribution from the hearts of American and Japanese lobsters

The decapod cardiovascular system consists of a single ventricle that pumps blood into seven arteries; previous work has shown that the outflow distribution patterns of intact animals are variable. In the present study, flow recordings were made from pairs of arteries in semi-isolated hearts whilst different cardioactive hormones were infused into the heart. Each hormone (5-hydroxytryptamine, octopamine, dopamine, proctolin and F1) changed the outflow pattern, heart rate and ventricular pressure in a unique way. The probable sites of hormone action are the cardioarterial valves located at the origin of each artery except one, the dorsal abdominal. Outflow from the dorsal abdominal is controlled downstream by valves located at the origin of the segmental lateral arteries. The responses to a particular hormone were sometimes different between the hearts of American and Japanese lobsters. Accepted: 11 May 1998     

Pharmacological dissection of a neural pattern generator

Summary Injection of picrotoxin solutions into the pericardium of lobsters,Homarus americanus, to produce final, estimated blood concentrations of between 8×10^–8M and 4.5×10^–6M led to disruption of the normal motor output to the scaphognathite. The phase separation of the starts of the bursts in the D1 and D2 muscles (Young, 1975) was reduced on the average by 49%; that of L1 and L2 muscles by 16%. The durations of the D1 and L1 bursts increased by 94% and 48% respectively. The phase separation between the starts of the levator and depressor portions of the cycle was not altered. Whilst rhythmic activity persisted ventilatory rates were depressed, and reversals and ventilatory pauses continued to occur. The rate of reversals and their pattern were not greatly altered. Inexplicably, tonic, synchronous spikes occurred in all four groups of muscles, levator and depressor, during periods of severe disruption. It was concluded that in spite of this, the observations supported the proposals of Young (1975) that (a) recruitment of the D2 and L2 bursts normally is delayed partly by inhibition from D1 and L1 units respectively, and (b) termination of D1 and L1 bursts results normally from inhibition due to activity in D2 and L2 units respectively. The findings also indicated that the synaptic mechanism determining timing within the depressor and levator sessions differs fundamentally from that operating between sessions. One mechanism may be based on picrotoxin-sensitive, and the other on picrotoxin-insensitive inhibition.Abbreviations GABA gamma-aminobutyric acid - SG scaphognathite     

Affinity Purification and Structural Features of the Yeast Vacuolar ATPase Vo Membrane Sector

The membrane sector (V_o) of the proton pumping vacuolar ATPase (V-ATPase, V₁V_o-ATPase) from Saccharomyces cerevisiae was purified to homogeneity, and its structure was characterized by EM of single molecules and two-dimensional crystals. Projection images of negatively stained V_o two-dimensional crystals showed a ring-like structure with a large asymmetric mass at the periphery of the ring. A cryo-EM reconstruction of V_o from single-particle images showed subunits a and d in close contact on the cytoplasmic side of the proton channel. A comparison of three-dimensional reconstructions of free V_o and V_o as part of holo V₁V_o revealed that the cytoplasmic N-terminal domain of subunit a (a_NT) must undergo a large conformational change upon enzyme disassembly or (re)assembly from V_o, V₁, and subunit C. Isothermal titration calorimetry using recombinant subunit d and a_NT revealed that the two proteins bind each other with a K_d of ∼5 μm. Treatment of the purified V_o sector with 1-palmitoyl-2-hydroxy-sn-glycero-3-[phospho-rac-(1-glycerol)] resulted in selective release of subunit d, allowing purification of a V_oΔd complex. Passive proton translocation assays revealed that both V_o and V_oΔd are impermeable to protons. We speculate that the structural change in subunit a upon release of V₁ from V_o during reversible enzyme dissociation plays a role in blocking passive proton translocation across free V_o and that the interaction between a_NT and d seen in free V_o functions to stabilize the V_o sector for efficient reassembly of V₁V_o.     

Laboratory test of suspended sediment effects on short‐term survival and swimming performance of juvenile Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus,Mitchill, 1815)

Tested was the hypothesis that juvenile Atlantic sturgeon (Acipenser oxyrinchus oxyrinchus) would exhibit no response in short‐term survival or swimming performance when exposed to varying concentrations of suspended sediment simulating dredge plumes in waterways where this species may be impacted by dredging operations. Sediment collected from Savannah Harbor, South Carolina, USA was used to simulate a worst‐case scenario. Juvenile sturgeon were contained for a 3‐day period in flow‐through aquaria, with limited opportunity for movement, in sediment of varying concentrations (100, 250 and 500 mg L^?1 total suspended solids [TSS]) mimicking prolonged exposure to suspended sediment plumes near an operating dredge. Of the 90 fish exposed, 86 (96%) survived the test. Of the four fish that died, one was exposed to 250 TSS and three to 500 TSS. Swimming performance results indicated that nearly all fish were positively rheotactic. Critical swim speeds (U_crits) were moderate, whether measured as absolute values (21–31 cm s^?1) or as relative values (1.4–2.1 body lengths s^?1), with no significant differences among treatments (F < 0.83, P ≥ 0.4874). Behavior was dominated by contact‐based locomotion and station‐holding. Absence of substantial or significant immediate effects on survival and swimming performance suggest that impacts of sediment plumes in nature, where fish have freedom of movement and the power to escape rapidly, are minimal.     

A proof of principle experiment for microbeam radiation therapy at the Munich compact light source

Microbeam radiation therapy (MRT), a preclinical form of spatially fractionated radiotherapy, uses an array of microbeams of hard synchrotron X-ray radiation. Recently, compact synchrotron X-ray sources got more attention as they provide essential prerequisites for the translation of MRT into clinics while overcoming the limited access to synchrotron facilities. At the Munich compact light source (MuCLS), one of these novel compact X-ray facilities, a proof of principle experiment was conducted applying MRT to a xenograft tumor mouse model. First, subcutaneous tumors derived from the established squamous carcinoma cell line FaDu were irradiated at a conventional X-ray tube using broadbeam geometry to determine a suitable dose range for the tumor growth delay. For irradiations at the MuCLS, FaDu tumors were irradiated with broadbeam and microbeam irradiation at integral doses of either 3 Gy or 5 Gy and tumor growth delay was measured. Microbeams had a width of 50 µm and a center-to-center distance of 350 µm with peak doses of either 21 Gy or 35 Gy. A dose rate of up to 5 Gy/min was delivered to the tumor. Both doses and modalities delayed the tumor growth compared to a sham-irradiated tumor. The irradiated area and microbeam pattern were verified by staining of the DNA double-strand break marker γH2AX. This study demonstrates for the first time that MRT can be successfully performed in vivo at compact inverse Compton sources.