Modelling the exchange and transformation of matter and energy in ecosystems requires the development of hierarchical structured models of the considered ecosystem compartments. In this context, a model describing the coupled CO2 and H2O gas exchange of a winter wheat canopy was developed and calibrated. The formidation of the model was related to the problems of linking processes at different systém levels. For model calibration, ecophysiological gas exchange characteristics and micro-meteorological data were obtained on both leaf and canopy levels and completed by results of structural and Chemical plant analysis. The gas exchange was measured by a computer-controlled multi-channel systém. On the basis of this data pool, the canopy gas fluxes were calculated by the model as the integrál of the corresponding local fluxes over the area elements of the canopy. The model describes correctly physiological interactions and gas exchange characteristics at both the leaf and canopy levels.
GABA exhibits depolarizing action in the immature neurons due to high intracellular activity of chloride ions. It is maintained by cation-chloride cotransporter NKCC1 which is present in immature brain. Bumetanide is a specific inhibitor of this cotransporter. We studied possible anticonvulsant activity of bumetanide in pentyl enetetrazol-induced seizures in three age groups of rat pups (7, 12, and 18 days old). Pretreatment with bumetanide (0.2-1 mg/kg i.p.) resulted in dose-dependent decrease of incidence of the tonic phase of generalized tonic-clonic seizures in 12-day-old rats only. No effect was observed in younger and older animals. Higher dose of bumetanide (2.5 mg/kg) did not affect tonic convulsions but, on the contrary, decreased latencies of generalized seizures in 12-day-old animals. Lack of marked anticonvulsant effect is probably due to relative maturity of neurons in the brainstem where the generator of generalized seizures is localized. Age- and dose-specific suppression of the tonic phase needs further analysis. and Obsahuje seznam literatury
The effects of phenytoin on threshold intensities of stimulation were studied in cortical epileptic afterdischarges (ADs) in 12-day-old and adult rats with implanted electrodes. Stimulation of the sensorimotor cortical area induced movements directly related to the stimulation as well as EEG afterdischarges (ADs) of the spike-and-wave type and of the limbic type. Rat pups exhibited lower thresholds for stimulation-bound movements and spike-and- wave ADs than adult animals. On the contrary, the limbic type of ADs was elicited with lower current intensity in adult than in immature rats. Phenytoin increased the threshold for stimulation-related movements only in adult rats, whereas threshold intensities for spike-and-wave ADs were increased and thresholds for limbic type of ADs remained uninfluenced in both age groups. The age-dependent effect on stimulation-related movements might be due to a maturation of connectivity in the motor system or to developmental changes in the voltage-gated sodium channels as the main target of phenytoin action.
Metabotropic glutamate receptors (mGluRs) represent a potential therapeutic target. Possible anticonvulsant action of AMN 082, an agonist of mGluR7 subtype, was studied in immature rats using pentylenetetrazol (PTZ)-induced seizures as a model. Five age groups of rats (7-, 12-, 18-, 25-day-old and adult animals) were pretreated with AMN 082 in doses of 0.5, 1, 2, and 5 mg/kg i.p. and 30 min later PTZ was administered (100 mg/kg s.c.). Controls received saline instead of the agonist. AMN 082 did not exhibit clear anticonvulsant action with the exception of suppression of the tonic phase of generalized tonic-clonic seizures (GTCS) in 12-day-old rats. Shorter latencies of GTCS after AMN 082 pretreatment indicate a proconvulsant action. Involuntary movements (mostly tremor) appeared after AMN 082 before PTZ administration, therefore we performed another experimental series with AMN 082 only (1, 2, 5, and 10 mg/kg i.p.). During 60-min observation period tremor appeared in all age groups; sensitivity to this action decreased with age from the 2 mg/kg dose in 7- and 12-day-old rats to the 10 mg/kg dose in adult rats. Mixed anti- and proconvulsant actions of AMN 082 together with unwanted motor effects makes clinical use of this drug highly improbable., Pavel Mareš., and Obsahuje bibliografii a bibliografické odkazy
GABA-B receptor agonist SKF97541 exhibits age-dependent anticonvulsant and proconvulsant actions in developing rats. It suppressed tonic phase of generalized seizures induced by pentetrazol in 7-, 12- and 18-day-old rats and increased their latency in 7- and 12-day-old animals. Other results in 18-day-old animals are not so clear. SKF 97541 blocked the appearance of minimal clonic seizures, but tended to decrease latencies of both types of seizures. In addition, it significantly decreases latency of generalized seizures in adult rats. The mixed effects of SKF97541 are in agreement with those of baclofen but there are substantial differences between the actions of these two agonists in individual age groups., P. Mareš., and Obsahuje bibliografii a bibliografické odkazy
Action potentials (APs) and the force of isometric contractions of the right ventricular papillary muscles were measured in adult and newborn guinea-pigs. The measurements were carried out in the steady state with the rate of stimulation of 0.1, 1, and 2 Hz, and further some measurements were done in which Sr2+ was substituted for Ca2- The duration of APs of the newborn animals without pharmacological treatment was significantly shorter in comparison with that of the adults at all the used stimulation frequencies. An analogous sensitivity was found in the contractile force to increased stimulation frequency and when the steady state stimulation was discontinued by the insertion of interpolated extrasystoles in papillary muscles of adult or newborn animals. The biphasic contractions of papillary muscles were evoked in both groups of animals by the incomplete substitution of Sr2+ by Ca2+ in the presence of isoprenaline. The early component of the biphasic contractions had a faster course as compared to the late component and disappeared in the presence of caffeine in both groups of animals. Our results suggest that the heart cells of newborn guinea-pigs probably possess the sarcoplasmic reticulum (SR), whose function does not differ in quality from that of the adult guinea-pigs. The postnatal prolongation of APs is therefore not probably the result of postnatal development changes of the functions of SR, but could be related to changes in the relations between the surface and volume of the heart cell during its growth.
Sexual differences in the total content of ribosomal RNA, established by cytophotometric measurements in neurones from selected brain regions, were studied in rats of the Wistar strain. In females of reproductive age, cyclic changes of RNA were synchronized with their oestrous cycle, the values being higher in the oestrous phase than in dioestrus. These changes were observed in pyramidal cells of the hippocampus and of the frontal cortex, in cells of anterior thalamus, of ventromedial and lateral hypothalamus and of tuberculi olfactorii. However, cycling cells were not disclosed in septum and thalamus posterior. A dependence upon the actual level of ovarial hormones was found in ventromedial hypothalamic cells only. In general, the RNA values in males of the same age corresponded to values of dioestrous females. The differences between newborn and 7-day-old pups were not marked enough and did not allow to define the critical period responsible for initiation of this sexual difference. In senescent rats, this difference persisted. During the stable phase of long-lasting dioestrus, the total RNA content in cells of the frontal cortex, hippocampus and hypothalamus was higher in females than in males of the same age which may suggest a faster reduction of this substance in aged males. The prolonged influence of oestrogens in the oestrous phase of the climacteric period (preceding the permanent dioestrus) decreased the RNA values in hippocampal and hypothalamic neurones even below the level established during the permanent dioestrus (and thus reached male values). On the contrary, in frontal cortical neurones, the female values remained higher in the permanent dioestrus as well as during long-lasting oestrus. A discussion concerns the possible participation of genetic determination and of the actual state of ovarial hormones in the manifestation of sexual differences in brain cells of the rat.
The circadian system controls the timing of behavioral and physiological functions in most organisms studied. The review addresses the question of when and how the molecular clockwork underlying circadian oscillations within the central circadian clock in the suprachiasmatic nuclei of the hypothalamus (SCN) and the peripheral circadian clocks develops during ontogenesis. The current model of the molecular clockwork is summarized. The central SCN clock is viewed as a complex structure composed of a web of mutually synchronized individual oscillators. The importance of development of both the intracellular molecular clockwork as well as intercellular coupling for development of the formal properties of the circadian SCN clock is also highlighted. Recently, data has accumulated to demonstrate that synchronized molecular oscillations in the central and peripheral clocks develop gradually during ontogenesis and development extends into postnatal period. Synchronized molecular oscillations develop earlier in the SCN than in the peripheral clocks. A hypothesis is suggested that the immature clocks might be first driven by external entraining cues, and therefore, serve as “slave” oscillators. During ontogenesis, the clocks may gradually develop a complete set of molecular interlocked oscillations, i.e., the molecular clockwork, and become self-sustained clocks., A. Sumová, Z. Bendová, M. Sládek, R. El-Hennamy, K. Matějů, L. Polidarová, S. Sosniyenko, H. Illnerová., and Obsahuje bibliografii a bibliografické odkazy
Lithium-pilocarpine status epilepticus (SE) resulted in delayed changes of single cortical in terhemisperic (transcallosal) responses in immature rats. Low-frequency stimulation inducing depression and/or potentiation was studied to analyze possible dynamic changes in cortical responses. Status was elicited in 12-day-old (SE12) or 25-day-old (SE25) rats. Control siblings received saline instead of pilocarpine. Interhemispheric responses were elicited by stimulation of the sensorimotor region of the cerebral cortex 3, 6, 9, 13, or 26 days after status. A series of 5 biphasic pulses with intensity equal to twofold threshold were used for stimulation. The interval between pulses was 100, 125, 160, 200 or 300 ms, eight responses were always averaged. Peak amplitude of the first positive, first negative and second positive waves was measured and responses to the second, third, fourth and fifth pulse were compared with the first one. Animals after status epilepticus as well as lithium-paraldehyde controls exhibit a frequency depression at nearly all the intervals studied. An outlined increase of responses in SE rats in comparison with the controls three days after SE stayed just below the level of statistical significance. In addition, animals in the SE12 group exhibited potentiation of responses at this interval after SE. With longer intervals after SE, the relation between SE and control animals changed twice resulting in a tendency to lower amplitude of responses in SE than in control rats 26 days after SE. Rats in the SE25 group exhibited higher responses than controls 13 days after status, but this difference was not present at the longest interval after SE. Low-frequency stimulation did not reveal increased cortical excitability as a long-lasting consequence of status epilepticus induced in immature rats. In addition, the outlined differences between SE and control rats changed with the time after SE., G. Tsenov, P. Mareš., and Obsahuje bibliografii a bibliografické odkazy
We present a developmental study focusing on the development of coloration patterns in a subgroup of Neotropical cichlids, the subfamily Cichlasomatinae. Based on the presented coloration ontogenetic series of 40 species we show that developmental information is a necessary prerequisite for any serious attempts in understanding adult coloration patterns. The center of our contribution is a detailed description of coloration ontogenies in a selected sample of cichlids and their discussion in a much wider taxonomical sampling. The pigmentation pattern ontogeny is specifically used to determine developmental homology of individual vertical bars. Early ontogeny is documented from the onset of the free-swimming period, which is also used as a point of reference for possible heterochronic shifts as presented here. A single universal process is responsible for the transformation of longitudinal melanophore migration lines into vertical bars, which form the dominant elements of adult coloration of most cichlids. Adult vertical bars vary interspecificaly in their numbers, whereas their ontogenetic precursors are stable in number across all surveyed species. The diversity of adult barring patterns is produced by differential fusions of a conserved number of developing bars, from which the different taxon specific numbers of adult bars develop. The possibility of determining individual homology of cichlid vertical bars is a prerequisite for the use of coloration pattern characters in cichlid phylogenetic studies. Several ontogenetic characters are formulated as synapomorphic at various systematic levels.