Bibliothek

Notizen: Maximal oxygen uptake (Vo2max was evaluated after high-altitude training in rowers. Nine rowers trained in a camp at 1822 m for 3 weeks with no change in Vo2max or 6-min work capacity on a rowing ergometer at sea level. In contrast, 9 control rowers training at sea level increased Vo2max by 4 (0-8)% and work capacity by 3 (0-11)% (median and range). In rowers emphasizing endurance training during a summer of competitive rowing (n=9), Vo2max and work capacity increased by 6 (0-13)% and 3 (-1-6)%, respectively and no significant changes were noted in rowers performing interval training (n= 9). Exhaustive rowing on an ergometer was characterized by elevated plasma adrenaline, noradrenaline (n=13) and lactate (n=14) (to 19 (11-31), 74 (50-109) nmol l1 and 15 (11-22) mmol-I1, respectively). In heavyweight rowers (n=11), blood volume was 7.0 (5.9-8.3) litres, left ventricular wall thickness 13 (11-15) mm and end-diastolic diameter 57 (54-66) mm (n=11). This study demonstrated an elevated blood volume in rowers as well as myocardial hypertrophy and large internal heart diameters. In well-trained rowers, endurance training is superior to interval training for elevating Vo2max and work capacity, but high-altitude training does not contribute to increasing Vo2max or work capacity at sea level.

Notizen: Tubes composed of butyl rubber have been placed in a small English lake in an area where the water is 11-12 m deep. Each tube, when fully distended, contains over 18 000 m3 of water. The tubes are anchored to the shore and lake bottom. A boat can be rowed into them over a specially strengthened portion ofthe margin. The first was installed and its water isolated from that in the lake by the end of July 1970 and the second tube at the beginning of October 1970. The installation, maintenance, and performance of the tubes are described; as are suggested improvements. The temperature regime in the tubes closely follows that in the lake. If the chemical conditions are favourable, the seasonal cycle of Melosira in a tube is similar to that n i the lake. Contamination of the water in the tubes by that in the lake is slight and has a negligible effect on chemical conditions within them. Water can be lost from the tubes under certain conditions. The reverse does not happen. The phytoplankton communities in the tubes are similar in quality to those ofthe lake, even after 2-5 years of separation. The evidence suggests that the tubes are suitable for investigations on certain factors determining the abundance and seasonal cycles of algae in lakes and for other limnological studies.

Notizen: SUMMARY. 1. The factors influencing the seasonal and inter-annual variations in the numbers of Daphnia hyalina in Esthwaite Water between 1956 and 1972 are analysed. Esthwaite Water has always been eutrophic. but the phosphorus and nitrogen loadings to the lake increased significantly in the mid 1960s.2. Qualitatively, the phytoplankton and zooplankton populations in the lake changed relatively little during the period of study. Quantitatively, however, eutrophic species of algae became more abundant and the numbers of Eudiaptomus declined as the numbers of Daphnia increased.3. The seasonal dynamics of the Daphnia was governed partly by the seasonal temperature cycle, and partly by the periodicity of edible algae. The birth rate of the Daphnia was constrained by temperature from January to April and from October to December. At other times their rate of increase was governed by the relative abundance of edible and inedible algae.4. Edible and inedible species of algae tended 10 appear in a recurring annual sequence. Diatoms such as Asterionella were abundant in the spring, the early summer phytoplankton was dominated by edible flagellates, but inedible algae such as Aphanizomenon and Microcystis become dominant later in the year.5. Daphnia could only reproduce in late summer when there were periodic regrowths of edible algae. Such regrowths were most likely to occur when there had been some entrainment of deep nutrients by episodic wind mixing. Calm weather encouraged the growth of blue-green algae that effectively‘blocked’the development of the Daphnia for the remainder of the summer.6. The factors that controlled the seasonal dynamics of the Daphnia also influenced the average number recorded in a particular year. The average number of Daphnia increased in the early sixties when Cryptomonas was abundant and decreased in the late sixties when blooms of Aphanizomenon appeared in mid summer. Detailed analyses showed that a similar increase in the numbers of Aphanizometion had occurred in the late fifties. The critical factor throughout was the prolonged period of calm resulting in stable stratification.7. This ‘weather’ effect was highlighted by comparing de-trended timeseries of Daphnia and Aphanizometion numbers with a simple measure of thermocline stability. De-trending removed the superimposed effects of progressive enrichment and revealed a 10-year cycle of thermocline stability that matched the temperature cycle recently reported in Windermere, These cycles are related to the movement of weather systems in the Atlantic so could change if the pattern of atmospheric circulation is altered by global warming.8. The possible effects of climate change on Daphnia dynamics are discussed in relation to the findings in Esthwaite Water.

Notizen: SUMMARY. The composition of bulk (wet and dry) precipitation in 1975 and 1976 was similar to that found 22 years previously. In 1975, mean values for nine precipitation samplers at one site (Wraymires) ranged from pH 4.3 to 4.5; similar values were obtained in 1976. Samplers covered with fine-mesh plastic gauze caught substantially more Ca2+ and K+ than open samplers, but pH and SO2-4+ NO3- concentrations were similar in open and covered samplers. In precipitation, c. 50% of H+ was balanced by NO3- and c. 50% by SOi; 80% of the SO2-4 was balanced by Ca2+ and Mg2+.Conccntrations of major cations (H+, Na+, K+,Ca2+, Mg2+) and anions (CI-, NO3- SO2-4 and alkalinity [Alk—largely HCO3-]) in upland water- bodies were similar to those found in precipitation, but pH levels were generally higher and above 6.0 m some tarns. At lower altitudes, on base-rich roeks and soils, Ca2+ and Alk become dominant. Results of a survey of lakes and tarns in 1974–78 are compared with a survey in 1953–56 and published data (chiefly for pH and Alk) for 1947–50, 1932 and 1928. Comparisons are also made with other measurements of Alk in three productive lakes (Blelham Tarn, Esthwaite Water and Windermere) for 1936–39 and 1945–80. Winter levels of NO3-N, PO4-P and Si are given for these lakes; although the first two have increased during the late 1960s and the 1970s there has been no significant change in the last. NO3- and probably some SO2-4. In productive lakes a substantial (c. 50%) rise in mean Alk occurred during the late 1960s and the 1970s, possibly related to increased winter levels of NO3-N and PO4-P derived from sewage and fertilizers. In this period the maximum pH levels reached in summer were notably high, sometimes exceeding pH 10. The rise in Alk, conductivity and pH of surface waters is influenced by climatic factors (a decade of drier years), sewage input and biological productivity within the lakes.Considerable seasonal fluctuations in the concentrations of major ions, a characteristic feature of surface waters in the English Lake District, are illustrated and some implications for cation-anion balance briefly discussed. Mid-winter concentrations are usually high forNa+, K+, Cl-. NO3-and low for Ca2+, Mg2+, Alk. SO2-4.Alkalinity. pH and conductivity of Lake District tarns and lakes show no signs of acidification during the period 1928–80. On the contrary, productive lakes have become more alkaline and some unproductive low-alkalinity (〈 100 μ-equiv. 1-1) lakes also show signs of alkalization, with increased mean concentrations of Na+. Ca2+ and Mg2+, balanced by Alk.

Notizen: SUMMARY. 1. The abundance and species composition of the phytoplankton of Grasmere were monitored over a 12-year period following the commissioning of a small sewage treatment works, upstream of the lake.2. Although Grasmere has been subject to increased phosphorus-loading and has quickly developed many features associated with eutrophication, the composition of its plankton has retained the characteristics of a mesotrophic, soft-water lake: a vernal diatom maximum, generally dominated by Asterionella, is followed by summer growths of nanoplanktonic species, of various colonial Chlorophyceae, before a substantial return to Asterionella-dominance in the autumn. In cooler summers there have been episodes of renewed diatom growth. followed by truncated recapitulations of the essential summer sequence. Anabaena solitaria was relatively common in drier summers when dissolved inorganic nitrogen fell to low concentrations, although many of the ‘larger’ algal species associated with stratified eutrophic lakes (Aphanizomenon, Microcystis, Ceratium spp.) have failed to become abundant in Grasmere.3. Mean biomass levels (as indicated by chlorophyll concentration) have increased in response to the enrichment, though they do not conform well with most chlorophyll/phosphorus regression-models.4. The key factor resisting a more complete transition to a typical eutrophic plankton appears to be the efficiency of episodic flushing of the lake during periods of high fluvial discharge sustained by heavy rainfall over the extensive, mountainous catchment. The probabilities that these limnological conditions might fail to deter the development of ‘nuisance’ blooms are briefly assessed.

Notizen: Neurons of the dorsal nucleus reticularis pontis caudalis (nPontc) fire rhythmically during fictive mastication, while neurons of the ventral half tend to fire tonically (Westberg et al., 2001). This paper describes the changes in the pattern of rhythmical mastication elicited by stimulation of the sensorimotor cortex during inhibition or excitation of neurons in this nucleus and adjacent parts of nucleus reticularis gigantocellularis (Rgc) in the anaesthetized rabbit. Masticatory movements and electromyographic (EMG) activity of the masseter and digastric muscles produced by cortical stimulation were recorded before, during and after injections of a local anaesthetic (lidocaine) or excitatory amino acid N-methyl-d-aspartate (NMDA) into nPontc and Rgc through a microsyringe with attached microelectrode to record neuronal activity. Lidocaine inhibited local neurons and modified the motor program, and the effects varied with the site of injection. Most injections into the ventral half of nPontc increased cycle duration, digastric burst duration and burst area. The action of lidocaine in dorsal nPontc was more variable, although burst duration and area were often decreased. The effects on the muscle activity were always bilateral. Lidocaine block of the rostromedial part of Rgc had no effect on movements or on EMGs. Injections of NMDA excited local neurons and when injected into ventral nPontc, it completely blocked mastication. Dorsal injections either had no effect or increased cycle frequency, while decreasing burst duration and area. No increases in EMG burst duration or area were observed with NMDA. Our findings suggest that neurons of ventral nPontc tonically inhibit other parts of the central pattern generator during mastication, while dorsal neurons have mixed effects. We incorporated these findings into a new model of the masticatory central pattern generator.

Notizen: In this study, we describe functional characteristics of neurons forming networks generating oral ingestive motor behaviours. Neurons in medial reticular nuclei on the right side of the brainstem between the trigeminal and hypoglossal motor nuclei were recorded in anaesthetized and paralysed rabbits during two types of masticatory-like motor patterns induced by electrical stimulation of the left (contralateral) or right (ipsilateral) cortical masticatory areas. Sixty-seven neurons in nucleus reticularis pontis caudalis (nPontc), nucleus reticularis parvocellularis (nParv), and nucleus reticularis gigantocellularis (Rgc) were studied. These were classified as phasic or tonic depending on their firing pattern during the fictive jaw movement cycle. Phasic neurons located in the dorsal part of nPontc were active during the jaw opening phase, whilst those in dorsal nParv tended to fire during the closing phase. In most neurons, burst duration and firing frequency changed between the two motor patterns, but there was little change in phase of firing. Tonic units were mainly recorded in the ventral half of nPontc, and at the junction between Rgc and caudal nParv. Cortical inputs with short latency from the contralateral masticatory area were more frequent in phasic (82%) than tonic (44%) neurons, whilst inputs from the ipsilateral cortex were equal in the two subgroups (57% and 56%). Phasic neurons had significantly shorter mean contralateral than ipsilateral cortical latencies, whilst there was no difference among tonic neurons. Intra- and perioral primary afferent inputs activated both types of neurons at oligo-synaptic latencies. Our results show that subpopulations of neurons in medial reticular nuclei extending from the caudal part of the trigeminal motor nucleus to the rostral third of the hypoglossal motor nucleus are active during the fictive masticatory motor behaviour. Unlike masticatory neurons in the lateral tegmentum, the medial subpopulations are spatially organized according to discharge pattern.

Notizen: The trigeminal principal sensory nucleus (NVsnpr) contains both trigemino-thalamic neurons and interneurons projecting to the reticular formation and brainstem motor nuclei. Here we describe the inputs and patterns of firing of NVsnpr neurons during fictive mastication in anaesthetized and paralysed rabbits to determine the role that NVsnpr may play in patterning mastication. Of the 272 neurons recorded in NVsnpr, 107 changed their firing patterns during repetitive stimulation of the left or right sensorimotor cortex to induce fictive mastication. Thirty increased their firing tonically. Seventy-seven became rhythmically active, but only 31 fired in phase with mastication. The others discharged in bursts at more than twice the frequency of trigeminal motoneurons. Most rhythmic masticatory neurons were concentrated in the dorsal part, and those which fired during the jaw closing phase of the cycle were confined to the anterior pole of the nucleus. Most of these cells had inputs from muscle spindle afferents, whereas most of those firing during jaw opening had inputs from periodontal receptors. Non-masticatory rhythmical neurons had receptive fields on the lips and face. The majority of rhythmical masticatory units were modulated during fictive mastication evoked by both the left and right cortices and only four changed their phase of firing when switching from one cortex to the other. When coupled with the finding that NVsnpr neurons exhibit spontaneous bursting in vitro[Sandler et al. (1998) Neuroscience, 83, 891], the results described here suggest that neurons of dorsal NVsnpr may form the core of the central pattern generator for mastication.