High-density lipoprotein remodeling affects the osmotic properties of plasma in goldfish under critical salinity.

To investigate the stress response and physiological adaptations of goldfish (Carassius auratus) to critical salinity (CS) waters, we analyzed high-density lipoprotein (HDL) stoichiometry, stress markers (cortisol, glucose), and plasma osmotic properties (Na+ , osmolality, water content) using ichthyology, biochemistry, and proteomics approaches. After 21 days of exposure to CS, plasma concentrations of cortisol, glucose, and Na+ increased, indicating stress. Total plasma osmolality (Osmtotal ) and osmolality generated by inorganic (Osminorg ) and organic osmolytes (Osmorg ) also increased, the latter by ~2%. We associated the increase of Osmorg with (1) increased metabolite concentration (glucose), (2) dissociation of HDL particles resulting in increased HDL number per unit plasma volume (~1.5-2-fold) and (3) increased HDL osmotic activity. HDL remodeling may be the reason for the redistribution of bound and free water in plasma, which may contribute to water retention in plasma and, at the same time, to hemodynamic disturbances under CS conditions. The study's findings suggest that HDL remodeling is an important mechanism for maintaining osmotic homeostasis in fish, which is consistent with current capillary exchange models in vertebrates.

Does serotonin-modulating anticonsolidation protein (SMAP) influence the choice of turning direction in carps, Cyprinus carpio, in a T-maze?

Serotonin-modulating anticonsolidation protein (SMAP) can impair the formation of memory traces in mammals and fish. We have studied the influence of SMAP on behavioral lateralization of juvenile carps Cyprinus carpio in a T-maze without food reinforcement in three experimental groups (n = 8 each): (1) negative control (intact animals); (2) experimental group (fish injected ICV with SMAP; 2 µl, 1.2 mg ml(-1)) and (3) active control group (fish injected ICV with inactivated SMAP). The behavioral lateralization of carps was observed on the 1st, 2nd, 3rd and 6th days after the injections. In each observation session, a fish was placed five times in a start chamber of the T-maze. The direction of the turn upon leaving the start chamber, as well as the latency from the opening of start chamber flap to the fish's turn was registered. The number of right turns (of all five turns observed during the session) was a criterion of lateralization. It was found that carps have no inherent preference for turning left or right. The SMAP injection did not influence the choice of turning direction, but increases latency values insignificantly. The results are important for the correct interpretation and clarification of data reporting the role of SMAP in training and formation of spatial memory of fish in a maze.

[Effect of serotonin-modulated anticonsolidation protein on formation of long-term memory in carps Cyprinus carpio in the model of active avoidance learning].

Effect of serotonin-modulated anticonsolidation protein (SMAP) that has property of disturbing formation of memory trace in mammals and of learning and memory in teleost fish was studied in the model of active avoidance learning. The experiment was performed in three stages: (1) fry of carps Cyprinus carpio L. was injected intracerebrovenricularly with the SMAP protein at a dose of 0.3 µg/g; control individuals were administered with equal amount of the buffered saline for poikilothermic animals; (2) 24 h after the injection, fish were learnt during 8 sèances for 2 days the conditioned reflex of active avoidance; (3) 48 h after the learning the testing of the skill was performed. The administration of the protein was shown to lead to disturbance of reproduction of the skill in the fish: the latent time of the skill reproduction in experimental individuals exceeded that in control fish more than two times, while the number of individuals succeeding the task in the experimental group was non-significantly lower than in the control group. However, unlike mammals, injection of the SMAP protein in this model produced no effect on the process of learning in carps. Thus, there was first demonstrated the inhibiting effect of the SMAP protein whose concentration correlated positively with the content of the neurotransmitter serotonin in brain on consolidation of memory traces in teleost fish.

The long-term effect of serotonin on the thermoregulatory behavior in juvenile cyprinidae (Cyprinus carpio and Carassius auratus).

The effect of serotonin after intracerebroventricular (ICV) injections in dosage of 0.3 and 0.15 µg/g of the body weight on the thermoregulatory behavior in juvenile carp Cyprinus carpio L. and goldfish Carassius auratus (L.) has been studied in two experiments of 10- to 11-day duration. It has been found that ICV injection of serotonin in dosage of 0.3 µg/g caused the initial decrease in preferred temperatures (PT) (2-3 days) followed by their further increase (4-8 days after the administration) in carp. ICV injection of serotonin in dosage of 0.15 µg/g caused more durable initial decrease in PT (2-8 days) followed by the increase of once (9-11 days of observation) in goldfish. The values of the ultimate preferred temperature in fish of the experimental group exceeded that in control specimens by 4.1 °C at the first experiment and by 3.1 °C in the second experiment. The data for the first time demonstrated long-term effect of a single ICV injection of serotonin on the thermoregulatory behavior in two closely related species of teleosts.

[Effect of food deprivation on quantitative and time characteristics of feeding of goldfish Carassius auratus in norm and under action of adrenaline].

There was studied effect of intraperitoneally administered adrenaline (0.14 mg/kg) on volume and time characteristics of feeding (duration of single, grouped, and total nutrition) of goldfish Carassius auratus (L.) previously maintained on normal and restricted (for 10 and 15 days) diet. The fish on restricted diet demonstrated the biphasic alimentary response to the adrenaline administration, similar with that in the normally fed fish: a decrease of volume, duration of the grouped and total feeding at the first phase of action of hormone and an increase--at the second phase; however, the value of the response at the first phase of the hormone action was lower, whereas at the second phase--higher than in the fish obtaining a sufficient amount of food prior to the experiment. Duration of the single feeding rose in fish of all groups including the control one, the maximum increase being observed in the goldfish submitted to food deprivation. The glycogen content in hepatopancreas of the normally fed goldfish exceeded by the end of the experiment 4.5-6 times that in the food-deprived ones. The obtained results confirm suggestion that a decrease of the level of reserve substances in the body leads to a decrease of the fish receptivity to the stress hormone--adrenaline and, hence, to a change of the value of its effects on the food-searching goldfish activity, with preservation of dynamics of the parameters.

The effect of epinephrine on feeding and motion patterns in goldfish Carassius auratus (L.).

The effect of intraperitoneal injections of epinephrine (0.14 and 0.70 mg/kg) on some characteristics of feeding activity (ration and total time of feeding) as well as on motion patterns (time of swimming in group and separately) in juvenile goldfish has been investigated. Two-phase (short-term decrease in the first phase, increase in the second one) feeding response under both doses of epinephrine has been revealed. More pronounced effect of epinephrine at the dose of 0.14 mg/kg on the ration and time of feeding (comparing to the dose of 0.70 mg/kg and Ringer injection) was observed in the second phase. Furthermore, significant decrease of time of "separated" swimming in the first phase under both doses of the hormone is revealed. The hyperglycemic response induced by the injections of epinephrine, with synchronous reduction of the concentration of glycogen in hepatopancreas allows to suggest that glycogen-phosphorylase activating mechanism was underlying the "first-phase" change of feeding reactions of goldfish.