Effect of Lincocin Treatment on the Greening Process in Bean (Phaseolus vulgaris) Leaves

The effect of lincocin (a plastid protein synthesis inhibitor) treatment on the greening process of bean (Phaseolus vulgaris L.) leaves have been studied. In comparison with control leaves treated ones had a decreased rate of chloroplast development. They had a marked chlorophyll deficiency and a decreased chlorophyll a/b ratio. Some long and short wavelength forms of chlorophyll a were lacking as evidenced from the absorption spectra at 25°C and the fluorescence spectra at 77°K. The –¹⁴CO₂ fixation was inhibited by 80–90% in treated leaves. The fluorescence induced by the measuring light was greater in the treated leaves than in the control ones, and the kinetics of the decline of the relative fluorescence intensity were also different. Electron microscopic studies showed macrogranum-like structures and incomplete membrane vesicles in the treated plastids. After longer treatment a destruction of membranes was observed. The results indicate some structural and functional membrane deficiencies and instability of the membranes.     

Lecithotrophic development and metamorphosis in the Indo-West Pacific brittle star Ophiomastix venosa (Echinodermata: Ophiuroidea)

Summary

The larval development of the ophiocomid ophiuroid Ophiomastix venosais described using SEM. The gastrula transforms into a uniformly ciliated early larva which progressively changes into a lecithotrophic late premetamorphic larva with a continuous bilateral ciliated band. This stage is short-lived and equivalent to a highly reduced ophiopluteus. Comparisons between O. venosa and other ophiuroid species whose development has been investigated suggest that, whatever the developmental mode (lecithotrophic or planktotrophic), a pluteus stage always occurs in ophiuroids with planktonic development. Two metamorphic stages were identified, the late metamorphic larva differing from the early one by the closure of the larval mouth. The appearance of the permanent mouth marks the end of the metamorphosis. The postlarva still possesses remnants of larval features. The transformation of the reduced ophiopluteus into a barrel-shaped metamorphic larva with transverse ciliated bands, a vitellaria larva, is followed. The possible occurrence of a unique type of metamorphic larva in non-brooding ophiuroids is discussed. Verification of this, however, needs further SEM investigations on metamorphic larva from species having “regular” planktotrophic development.     

The cortico-thalamic theory for generalised spike-wave discharges

The origin of generalized absence epilepsy is still not known. In the last century, four theories have dominated the debate about the origin of the bilateral synchronous generalized spike-wave discharges associated with absence seizures: the "centrencephalic" theory [Penfield and Jasper], the "cortical" [Bancaud, Niedermeyer, Luders], the "cortico-reticular" theory [Gloor, Kostop[oulos, Avoli] and the "thalamic clock" theory [Buzsaki]. There is now some evidence that absence epilepsy, as studied in the WAG/Rij model, is a corticothalamic type of epilepsy. A new hypothesis is proposed which suggests that a cortical focus in the somatosensory cortex is driving the widespread corticothalamic networks during spontaneous absence seizures. This modern theory was given the name "hot spot' theory" [Meeren et al., 2002]. According to the present view three brain structures are critically involved and their integrity seems a minimal and sufficient condition for the occurrence of spike-wave discharges. Firstly, the reticular thalamic nucleus is involved and most likely its rostral pole. Secondly, the thalamocortical relay cells in the ventrobasal complex play a role and, thirdly and most importantly, the cerebral cortex with its epileptic zone. The zone in which the epileptic focus seems to be localised is located on the somato-sensory cortex, and more precisely in the area on which the peri-oral region including the upper lip, projects.     

Peptidergic mechanisms of hypothermia-induced seizures in rats during early ontogenesis

Arginine-vasopressin reduced the tonic-clonic seizures' latency as well as the duration of the seizures brain-stem generalisation on the 3rd and 5th postpartum days in rats. The reduced latency was also observed after the PACAP38 low doses administration, whereas higher doses diminished and then enhanced the threshold of generalised hyperthermia-induced seizures on the 3rd and 5th days and the 7th and 9th days, resp. The arginine-vasopressin-treated animals had a dramatically enhanced duration of the tonic-clonic seizures up to the epileptic status on the 9th postpartum day. The findings suggest the PACAP involvement in mechanisms of experimental febrile seizures through its effect upon arginine-vasopressin neurosecretion.     

Pregnancy in WAG/Rij rats--changes in the levels of progesterone,estradiol and generalized absence epilepsy

Progesterone and oestradiol serum level was investigated in WAG/Rij rats with genetically determined absences. Blood samples were drawn before and after the pregnancy following the parturition. The serum concentration of progesterone increased after the 3rd day of pregnancy. There is no increasing of oestradiol during pregnancy as large as this. The progesterone is kept high to the 18th day of pregnancy and drastically decreased before the parturition. Common duration of absences--spontaneous spikewave discharges (SWD), frequency and the duration of every SWD decreased from 3rd to 19th days of pregnancy before the parturition. On the basis of these data and modern investigations, regulation of GABAA receptor expression during pregnancy by progesterone (Brusaartd A. B. et al., 1999) it can be assumed that the changes in the parameters of SWD are possibly correlated with the progesterone changes in serum during pregnancy in WAG/Rij rats.     

The piriform cortex and the cortical nucleus of the amygdala in epileptogenesis--the role of the rostrocaudal gradient

The seizure susceptibility of amygdaloid complex in rat was investigated. In piriform cortex and cortical nucleus of amygdaloid complex the structural and electrophysiological rostro-caudal differences were found (using relative spectral densities EEG, seizure thresholds, electrical kindling rate). The fundamental dependence of severity of motor seizures from structural (nuclear or cortical) organization of stimulating area was shown. There were more of limbic stages while stimulating anterior and posterior cortical nuclei, and there were more generalized stages while stimulating piriform and periamygdaloid cortex. Using the model of electrical kindling anticonvulsant effects of Sacricin were demonstrated. Sacricin is one of the compounds of polycarbonic acid. Sacricin has fully coped the process of secondary generalization of epileptic seizures.     

Status epilepticus--the new mechanisms and lines of inhibition (the lithium-pilocarpine model)

This review focuses on the modeling of status epilepticus in animal brain and modern data on the mechanisms of epileptical seizures initiation using the pilocarpine binding with the muscarinic cholinoreceptors (litium pilocarpine model). The character of epileptics seizures in developing brain and adult brain of rats were investigated. The lines of modulation and inhibition epileptics statues by sacricine and intranasal application of neuropeptide thyroliberin in ultra-low doses are demonstrated. The role of the short-term changes (signal regulated kinase signaling cascade, Kv 4.2 potassium channels, hippocampal and cortical spike-wave discharges) and the long-term changes (loss of selective type of interneurons, excitatory circuits by mossy fiber sprouting) that promotion the epileptic state and recurrent seizures in limbic structure are discussed.     

RELATIONSHIPS BETWEEN GROWTH RATE,CELL SIZE,AND INDUCTION OF SPERMATOGENESIS IN THE CENTRIC DIATOM THALASSIOSIRA WEISSFLOGII (BACILLARIOPHYTA)1

Patterns of changes in cell size, growth rate, and the inducibility of spermatogenesis were followed in eight sub‐clones of two isolates of the centric diatom Thalassiosira weissflogii (Grunow) Fryxell & Hasle grown at saturating light. One isolate originated from Long Island Sound, New York, USA and the other originated from Jakarta Harbor, Indonesia. As expected from previous studies, oscillations between intervals of cell size reduction and cell size enlargement were observed for each sub‐clone. For both isolates, sperm were easily detected, but cells resembling eggs and auxospores were rarely observed and fertilization was not confirmed, suggesting that the observed cell size increases may have resulted from a combination of asexual cell enlargement and rare auxosporulation. The two isolates differed in their minimum and maximum sizes, and the threshold size for the induction of sperm formation. However, the two sets of isolated sub‐clones displayed comparable relationships between growth rate, sperm inducibility, and cell size relative to the minimum, maximum, and threshold sizes. Growth rate increased as cell size decreased during vegetative divisions until the threshold for sperm inducibility was crossed. Below the size threshold for sperm inducibility, growth rate declined as cell size continued to decrease. Smaller cells were susceptible to failure of normal cytokinesis and valve deposition, resulting in the formation of abnormally long and often multinucleate cells. Culture conditions may select against restoration of cell size via auxosporulation due to the relationship between growth rate and cell size.