Bistable membrane potential of the ciliate Coleps hirtus. (65/2436)

In normal recording solution, the swimming pattern of the freshwater ciliate Coleps hirtus, belonging to the class Prostomatea, consists of alternating periods of nearly linear forward swimming and circular swimming within a small area. Current-clamp recordings were performed to elucidate the mechanism for this behaviour. No members of this class have previously been studied using electrophysiological techniques. The ciliates were maintained in culture and fed on the planctonic alga Rhodomonas minuta. The membrane potential showed spontaneous shifts between a more negative (deep) level of approximately -50 mV and a less negative (shallow) level of approximately -30 mV. The input resistance and capacitance at the more negative level were approximately 400 M capomega and 120 pF respectively. C. hirtus displayed a pronounced inward rectification, which was virtually insensitive to 1 mmol l(-1) Cs(+) and almost completely blocked by 1 mmol l(-1) Ba(2+). Depolarising current injections failed to evoke graded, regenerative Ca(2+) spikes. However, current-induced depolarisations from the more negative potential level (-50 mV) showed a pronounced shoulder during the repolarising phase. Increased current injections prolonged the shoulder, which occasionally stabilised at the shallow membrane potential (-30 mV). The membrane potential could be shifted to the deep level by brief hyperpolarising current injections. Similar biphasic membrane properties have not been reported previously in any ciliate. The bistability of the membrane potential was abolished in Ca(2+)-free solution containing Co(2+) or Mg(2+). In Ca(2+)-free solution containing 1 mmol l(-1) Ba(2+), brief depolarising current injections at the deep potential level evoked all-or-nothing action potentials with a prolonged plateau coinciding with the shallow potential. We conclude that the deep membrane potential in C. hirtus corresponds to the traditional resting potential, whereas the shallow level is a Ca(2+)-dependent plateau potential. In normal solution, the direction of the ciliary beat was backwards at the deep potential level and forwards at the shallow membrane potential, probably reflecting the two main phases of the swimming pattern.  (+info)

Effects of fin size on swimming performance, swimming behaviour and routine activity of zebrafish Danio rerio. (66/2436)

The zebrafish Danio rerio exhibits substantial morphological variability in the sizes and shapes of the body and the caudal fin. The present study describes swimming performance, swimming behaviour and routine locomotor activity patterns in three of the major morphotypes: wild-type, long-finned and no-tail. Wild-type and long-finned differ in total length (TL), fork length (FL), caudal fin length (CFL) and caudal fin height (CFH). No-tail has no caudal fin and is significantly smaller in standard length (SL) than the other types. Critical swimming speeds (U(crit)) were measured at 28 degrees C in a modified Brett-type water tunnel. U(crit) of wild-type fish was 56.0+/-4.8 cm s(-1) or 15.5 SL s(-)(1) (mean +/- s.d., N=21), significantly faster than the U(crit) of long-finned fish (43.7+/-6.8 cm s(-1) or 12.5 SL s(-1), N=17); both were significantly faster than the U(crit) of no-tail fish (19. 8+/-4.7 cm s(-1) or 6.9 SL s(-1), N=15). When forced to swim in the water tunnel, zebrafish tended to turn and swim downstream for short periods at slow water velocities. Turning frequencies (turns per minute, f(T)) at the slowest velocity (4 cm s(-1)) were 10. 1+/-6.5 min(-)(1) (N=63) and 8.6+/-4.7 min(-1) (N=51) for wild-type and long-finned, respectively, significantly different from that of the no-tail fish, 4.7+/-2.8 min(-1) (N=45). These frequencies decreased below 1 min(-1) at 56%, 64% and 61% of U(crit) in wild-type, long-finned and no-tail fish, respectively. Activity levels of wild-type fish were generally significantly higher than those of long-finned fish, and the levels of both were significantly higher than those of no-tail fish. The pattern of differences in relative activity levels between types was similar to that for U(crit). The results show that the wild-type fish, on a size-scaled basis, is one of the fastest-swimming fishes ever measured, reaching the maximum predicted theoretical sustained swimming speed. U(crit) of long-finned fish was 22% lower than that of wild-type fish, and U(crit) of no-tail fish was 65% lower. Similar differences were found in turning frequencies and routine activity level.  (+info)

Strain differences in the behavioral effects of antidepressant drugs in the rat forced swimming test. (67/2436)

Wistar-Kyoto (WKY) rats provide a model of stress-induced depressive behavior, because they show enhanced vulnerability to the effects of stressors. The present study examined differences in the behavioral response to different types of antidepressant drugs between WKY and Sprague-Dawley (SD) rats in the forced swimming test (FST). WKY rats displayed significantly greater immobility than SD rats during their exposure to the FST. The noradrenergic antidepressant, desipramine, produced a dose-dependent reduction of immobility and increase of climbing behavior in the SD rats. In WKY rats, desipramine reduced immobility at a lower dose and produced increases of both swimming and climbing behavior. The serotonergic compounds, fluoxetine and 8-OH-DPAT, produced dose-dependent reductions of immobility and increases of swimming behavior in the FST in SD rats, but the response to the serotonergic drugs were blunted in WKY rats. These results indicate that genetic or constitutive differences may determine the distinct behavioral profiles for antidepressant compounds with selective pharmacological effects in different rat strains, and these effects may be related to genetic heterogeneity of antidepressant responses in depressed patients.  (+info)

Effects of swimming training on three superoxide dismutase isoenzymes in mouse tissues. (68/2436)

The purpose of the present study was to investigate the effects of swimming training on the changes in three superoxide dismutase (SOD) isoenzymes in mice. The trained mice underwent a 6-wk swimming program (1 h/day, 5 days/wk) in water at 35-36 degrees C. Immunoreactive extracellular SOD (EC-SOD), copper- and zinc-containing SOD (CuZn-SOD), and manganese-containing SOD (Mn-SOD) contents and their mRNA abundance were determined in serum, heart, lung, liver, kidney, and gastrocnemius muscle. EC-SOD content in liver and kidney was significantly increased with training. After training, CuZn-SOD content rose significantly only in kidney but decreased significantly in heart, lung, and liver. Mn-SOD content showed a significant increase in lung, kidney, and skeletal muscle but a significant decrease in liver. In most tissues, however, the changes in SOD isoenzyme contents were not concomitant with those in their mRNA levels. The results obtained thus suggest that, except for kidney, the responses in mouse tissues of three SOD isoenzymes (protein levels and mRNA abundance) to swimming training are different and that kidney may be one of the most sensitive organs to adapt to oxidative stress during physical training, although the mechanism remains vague.  (+info)

Paradoxical actions of the serotonin precursor 5-hydroxytryptophan on the activity of identified serotonergic neurons in a simple motor circuit. (69/2436)

Neurotransmitter synthesis is regulated by a variety of factors, yet the effect of altering transmitter content on the operation of neuronal circuits has been relatively unexplored. We used electrophysiological, electrochemical, and immunohistochemical techniques to investigate the effects of augmenting the serotonin (5-HT) content of identified serotonergic neurons embedded in a simple motor circuit. The dorsal swim interneurons (DSIs) are serotonergic neurons intrinsic to the central pattern generator (CPG) for swimming in the mollusc Tritonia diomedea. As expected, treatment with the serotonin precursor 5-hydroxytryptophan (5-HTP) increased the intensity of serotonin immunolabeling and enhanced the potency of synaptic and modulatory actions elicited by the DSIs. It also greatly enhanced the ability of the DSIs to evoke rhythmic CPG activity. After 5-HTP treatment, microvoltammetric measurements indicated an increase in a putative 5-HT electrochemical signal during swim CPG activation. Paradoxically, the spiking activity of the serotonergic neurons decreased to a single burst at the onset of the rhythmic motor program, whereas the overall duration of the episode remained about the same. 5-HTP treatment gradually reduced the rhythmicity of the CPG output. Thus, more serotonin did not result in a more robust swim motor program, suggesting that serotonin synthesis must be kept within certain limits for the circuit to function correctly and indicating that altering neurotransmitter synthesis can have serious consequences for the output of neural networks.  (+info)

Enhancement of swimming endurance in mice by highly branched cyclic dextrin. (70/2436)

We investigated the ergogenic effect in mice of administering highly branched cyclic dextrin (HBCD), a new type of glucose polymer, on the swimming endurance in an adjustable-current swimming pool. Male Std ddY mice were administered a HBCD, a glucose solution or water via a stomach sonde 10 min before, 10 min after or 30 min after beginning swimming exercise, and were then obliged to swim in the pool. The total swimming period until exhaustion, an index of the swimming endurance, was measured. An ergogenic effect of HBCD was observed at a dose of 500 mg/kg of body weight, whereas it had no effect at a dose of 166 mg/kg of body wt (p < 0.05). The mice administered with the HBCD solution 10 min after starting the exercise were able to swim significantly longer (p < 0.05) than the mice who had ingested water or the glucose solution. The rise in mean blood glucose level in the mice administered with HBCD, which was measured 20 min after starting swimming, was significantly lower (p < 0.05) than that in the mice administered with glucose, although it was significantly higher (p < 0.05) than that in the mice administered with water. The mean blood insulin rise in the mice given HBCD was significantly lower (p < 0.05) than that in the mice given glucose. The mice administered with HBCD 30 min after starting the exercise swam significantly longer (p < 0.05) than the mice who had ingested water, although the enhancement of swimming time was similar to that of the glucose-ingesting mice. The gastric emptying rate of the HBCD solution was significantly faster (p < 0.05) than that of the glucose solution. However, this glucose polymer must have spent more time being absorbed because it has to be hydrolyzed before absorption, reflecting a lower and possibly longer-lasting blood glucose level. We conclude that the prolongation of swimming endurance in mice administered with HBCD depended on its rapid and longer-lasting ability for supplying glucose with a lower postprandial blood insulin response, leading to a delayed onset of fatigue.  (+info)

Sustained swimming at low velocity following a bout of exhaustive exercise enhances metabolic recovery in rainbow trout. (71/2436)

Sustained swimming at 0.9 BL s(-)(1), where BL is fork body length, following a bout of exhaustive exercise enhanced recovery of metabolite and acid-base status in rainbow trout compared with fish held in still water. The most striking effect of an active recovery was a total absence of the elevation cortisol concentration typically associated with exhaustive exercise. In fish swimming at 0. 9 BL s(-)(1), plasma cortisol levels averaged 20-25 ng ml(-)(1) throughout the 6 h recovery period. In contrast, plasma cortisol increased to a peak level of 128.4+/-11.2 ng ml(-)(1) (mean +/- s.e. m., N=6) in fish recovering in still water. Muscle glycogen was completely resynthesized and lactate cleared within 2 h of exercise in swimming fish compared with more than 6 h required in the fish held in still water. Similarly, blood lactate level and acid-base status were restored more quickly in the swimming fish. These observations suggest that the prolonged recovery usually associated with exhaustive exercise in rainbow trout is due to elevations in plasma cortisol concentration and that the stimulus for cortisol release is not exercise per se, but rather post-exercise inactivity.  (+info)

Activity of reticulospinal neurons during locomotion in the freely behaving lamprey. (72/2436)

The reticulospinal (RS) system is the main descending system transmitting commands from the brain to the spinal cord in the lamprey. It is responsible for initiation of locomotion, steering, and equilibrium control. In the present study, we characterize the commands that are sent by the brain to the spinal cord in intact animals via the reticulospinal pathways during locomotion. We have developed a method for recording the activity of larger RS axons in the spinal cord in freely behaving lampreys by means of chronically implanted macroelectrodes. In this paper, the mass activity in the right and left RS pathways is described and the correlations of this activity with different aspects of locomotion are discussed. In quiescent animals, the RS neurons had a low level of activity. A mild activation of RS neurons occurred in response to different sensory stimuli. Unilateral eye illumination evoked activation of the ipsilateral RS neurons. Unilateral illumination of the tail dermal photoreceptors evoked bilateral activation of RS neurons. Water vibration also evoked bilateral activation of RS neurons. Roll tilt evoked activation of the contralateral RS neurons. With longer or more intense sensory stimulation of any modality and laterality, a sharp, massive bilateral activation of the RS system occurred, and the animal started to swim. This high activity of RS neurons and swimming could last for many seconds after termination of the stimulus. There was a positive correlation between the level of activity of RS system and the intensity of locomotion. An asymmetry in the mass activity on the left and right sides occurred during lateral turns with a 30% prevalence (on average) for the ipsilateral side. Rhythmic modulation of the activity in RS pathways, related to the locomotor cycle, often was observed, with its peak coinciding with the electromyographic (EMG) burst in the ipsilateral rostral myotomes. The pattern of vestibular response of RS neurons observed in the quiescent state, that is, activation with contralateral roll tilt, was preserved during locomotion. In addition, an inhibition of their activity with ipsilateral tilt was clearly seen. In the cases when the activity of individual neurons could be traced during swimming, it was found that rhythmic modulation of their firing rate was superimposed on their tonic firing or on their vestibular responses. In conclusion, different aspects of locomotor activity-initiation and termination, vigor of locomotion, steering and equilibrium control-are well reflected in the mass activity of the larger RS neurons.  (+info)