Ionic composition of the rectal contents and excreta of the reduviid bug Triatoma infestans.

We have investigated the chemical composition of the rectal contents, faeces and urine of the blood-sucking bug Triatoma infestans. This is the environment in which the important disease-causing organism, Trypanosoma cruzi, lives. Directly after feeding of Triatoma infestans, the pH of the excreta switched from an acidic to an alkaline pH and, 1 day later, back to a slightly acidic pH. The osmolality varied in the initial excreta and in the rectal contents on the day following the meal between 300 and 460 mosmol/kg H(2)O, but after an additional day it increased to 350-970 mosmol/kg H(2)O. Determinations by ion capillary electrophoresis showed that sulphate and phosphate dominated the rectal contents in unfed bugs. After feeding, the first four drops of fluid excreta were mainly a sodium chloride solution (>150 mM for each). One to 10 days after feeding strong individual variations in the concentrations of individual ions were evident, especially for potassium and sodium. Mean concentrations of chloride remained at about 70 mM; sulphate and phosphate showed an increase within the first 1 or 2 days and then reached a level of about 160 and 210 mM, respectively. The rectal contents of long-term starved bugs contained high concentrations of phosphate and potassium; sulphate and sodium were slightly lower.

Gene expression of receptors and enzymes involved in GABAergic and glutamatergic neurotransmission in the CNS of rats behaviourally dependent on ethanol.

The steady state levels of the messenger RNA (mRNA) of eight GABA(A) receptor subunits, five glutamate receptor subunits and seven enzymes involved in the synthesis of glutamate and GABA were measured in eight regions of rat brain in a recently developed animal model of 'behavioural dependence' on ethanol. 'Behavioural dependence' including loss of control was induced by offering the rats the choice between ethanol and water over a 9-month period (Group A). This group was compared with a group given the choice between ethanol and water for only 2 months (not yet 'behaviourally dependent', Group B), a group forced to consume ethanol as sole fluid over a 9-month period (also not 'behaviourally dependent', Group C) and ethanol-naive control rats (Group D). All groups were sacrificed 1 month after the ethanol was withdrawn. The mRNA concentrations of all eight GABA receptor subunits, four out of the five subunits of different glutamate receptors and those of seven enzymes involved in GABA and glutamate production were reduced almost exclusively in the parieto-occipital cortex in Groups A and B, but not Group C. These data suggest that the synthesis of glutamate and GABA and the activities of their respective neurons are selectively impaired in the parieto-occipital cortex in the groups having consumed ethanol in a free-choice design, in which its rewarding properties can better take effect than after forced administration. As the parieto-occipital cortex is believed to contain emotional memory structures, it may be hypothesized that the glutamatergic and GABAergic neuronal systems in this area are involved in the development of memory for reward from ethanol. However, they are not specifically associated with 'behavioural dependence'.

Hemolymph ion composition and volume changes in the supralittoral isopod Ligia pallasii Brandt, during molt.

We analyzed ion composition and volume of the hemolymph of Ligia pallasii in four different stages of the molt cycle using capillary electrophoresis and 3H-inulin. The main ions in the hemolymph were Na+, K+, Mg2+ , Ca2+, and Cl-. The Ca2+ concentration increased significantly during the molt by 47% from intermolt to intramolt and by 37% from intermolt to postmolt, probably due to resorption of Ca2+ from the cuticle and sternal CaCO3 deposits. The K+ concentration increased significantly by 20% during molt. The hemolymph volume normalized to the dry mass of the animals decreased by 36% from intermolt to late premolt. This was due to a reduction in the hemolymph volume and to an increase in dry mass of the animals during premolt. A sudden increase in the hemolymph volume occurring between late premolt and intramolt served to expand the cuticle. Since the Na+, K+, Mg2+, and Cl- concentrations did not change significantly from late premolt to intramolt, the increase in hemolymph volume suggests an uptake of seawater rather than freshwater.

Comparison of calcium storage between a Baikalian gastropod and holarctic relatives.

In Lake Baikal, extremely thin shells are reported as a typical feature of endemic gastropods. This statement derived only from observations; no experimental data were available up to now. Therefore, we quantitatively investigated the calcium distribution in the endemic prosobranch gastropod Benedictia baicalensis and compared the results with those of Lithoglyphus naticoides, a near relative, non-endemic, palaearctic species. The shell of the endemic mollusc B. baicalensis consists of 94.9+/-26.0 microg Ca(2+)/microl animal volume (n=43), and in L. naticoides 865.0+/-271.5 microg Ca(2+)/microl (n=10). Calcium contents in the tissue of B. baicalensis vary between different sampling stations and different sampling dates (from 9.4+/-5.1 (n=33) to 20.5+/-8.4 microg Ca(2+)/mg dry weight DW (n=16)) and are only 1/5-1/10 compared to L. naticoides (88.5+/-39.1 microg Ca(2+)/mg DW (n=9)). But the values for hemolymph calcium concentration and osmolality in both species are identical (B. baicalensis: osmolality: 84.4+/-5.3 mosm/kg (n=40); hemolymph calcium concentration: 4.6+/-1.7 mmol/l (n=40). L. naticoides: osmolality: 85.0+/-2.0 mosm/kg (n=8); hemolymph calcium concentration: 5.2+/-5.0 mmol/l (n=40).). This is the first experimental study demonstrating, that - besides a similar hemolymph ionic composition - the Baikalian species is characterized by significantly lower calcium storage in shell and tissue than the nearly related non-endemic species.

Osmotic and ionic hemolymph concentrations of bathyal and abyssal amphipods of Lake Baikal (Siberia) in relation to water depth.

We studied the adaptive variations of the hemolymph concentrations in relation to water depth and pressure using deep-dwelling amphipods from Lake Baikal. Hemolymph osmolality was determined in six bathyal and abyssal species immediately after capture when values come closest to the habitat concentrations. In three species, hemolymph osmolalities correlated positively with depth of capture. Prevalent ions in the hemolymph are sodium and chloride. Lactate, our indicator for capture stress, was highest after trawling (2-6 mM) and lowest after retrieval from cages (0-0.6 mM). Acclimation to different pressure was studied by exposing the specimens to different water depths over several days. Hemolymph concentrations did not change after acclimation to surface pressure in the sublittoral Acanthogammarus albus, a native also to shallow water, but decreased by 30-80 mosmol/kg H2O in the bathyal and abyssal species Acanthogammarus grewingki, Acanthogammarus reicherti, and Parapallasea lagowskii. Similarly, hemolymph osmolality decreased in A. reicherti and P. lagowskii originating from deep water, when acclimated to reduced water depth, and, in A. reicherti hemolymph osmolality reached its original high value when returned to the depth of capture. Higher hemolymph osmolalities and NaCl concentrations, demonstrated here for the first time, may provide selective advantages to abyssal species.