Early Spike Research Articles

Functional mapping of the late stages of status epilepticus in the lithium-pilocarpine model in rat: a 14C-2-deoxyglucose study.

Pilocarpine administration to lithium chloride-pretreated rats results initially in discrete convulsive seizures, each behaviorally and electroencephalographically terminated, which then progress to convulsive activity with waxing-and-waning behavioral and electrographic severity; finally, a continuous convulsive state ensues, associated electrographically with continuous fast spiking. This stage does not last indefinitely but is followed by a dramatic electrographic change to periodic epileptiform discharges. The purpose of the present study was to determine with the 14C-2-deoxyglucose functional mapping technique what changes occur in the seizure anatomic substrate during and after this transition, in order to enable inferences about underlying mechanisms. Behavior associated with early and late continuous fast spiking consisted of head twitching; corresponding deoxyglucose autoradiographs displayed seizure-induced intense glucose utilization in most forebrain areas; extranigral brainstem was normal. At 2-3 h of status, fast spiking became interrupted by flat periods; periodic complexes soon dominated the electroencephalogram. Behaviorally, convulsive severity increased. Despite this dramatic electrographic evolution, little change in generalized forebrain metabolic hyperactivation occurred, except that the zona incerta/pretectal/superior colliculus complex displayed markedly increased activity. Deoxyglucose studies in late stages of periodic epileptiform discharges established a sequence of further changes. In late periodic discharges with clonic jerks, at 4 h after status entry, generalized forebrain hyperactivation still prevailed, but to a lesser degree than in early periodic discharges with clonic jerks. At a still later stage, late periodic discharges, subtle convulsive, autoradiographs revealed constriction of the seizure-activated anatomic substrate: hyperactivation was lost in most of neocortex and thalamus, and in caudal olfactory structures, cortical amygdala, and entorhinal areas, but retained in deep occipital cortex and many limbic areas. In the last stage, late periodic discharges, electrical, not associated with convulsive behavior, autoradiographs revealed residual activation in only Ammon's horn; in contrast, much of the forebrain displayed below-normal glucose utilization. These results demonstrate that in the later stages of status epilepticus, the transition from fast spiking to periodic complexes is not associated with a reduction in the seizure anatomic substrate. The electrographic entity of periodic epileptiform discharges is not anatomically or behaviorally homogeneous, but proceeds through successive stages characterized initially by a reduction of glucose utilization within generalized seizure-activated forebrain, then a contraction of the seizure anatomic substrate. Possible mechanisms underlying the transition to periodic complexes are discussed.

Krupin Disk Implantation for Complicated Glaucomas

The Krupin Eye Valve with Disk (Krupin disk) is a glaucoma shunt that incorporates a slit valve intended to minimize early postoperative hypotony. The medical records of all patients who have undergone Krupin disk implantation at the Doheny Eye Institute between July 1990 and December 1992 (25 eyes of 25 patients) were reviewed. Intraocular pressure (IOP) was reduced from a mean of 36.1 +/- 11.5 mmHg to 15.3 +/- 7.5 mmHg at follow-up intervals of 4 to 19 months (mean, 13.2 months). On the first postoperative day, IOPs ranged from 0 to 40 mmHg. In two eyes (8%), the IOP was less than 6 mmHg, and in five eyes (20%) the IOP was more than 21 mmHg. Serous choroidal effusion and/or choroidal hemorrhage occurred in seven patients (28%). Six- and 12-month life-table success rates (6 < or = IOP < or = 21 mmHg) were 84% and 66%, respectively. The Krupin disk lowers IOP in most patients; however, the presence of a slit valve does not eliminate either early postoperative hypotony with its attendant complications or early IOP spikes.

Combined Cataract Extraction and Trabeculectomy: Phacoemulsification Compared With Extracapsular Technique

ABSTRACT Thirty-four eyes undergoing phacoemulsification and trabeculectomy (PHACO + TRAB) were followed prospectively for 1 year postoperatively. The results of surgery were compared with those, obtained retrospectively, of the previous 34 extracapsular cataract extractions with trabeculectomy (ECCE + TRAB) performed by the same surgical team. All eyes received posterior chamber intraocular lens implants. Preoperatively, the two groups did not differ significantly in terms of age, gender distribution, or degree and duration of glaucoma and cataract. Mean postoperative follow up for the ECCE + TRAB group was 13.6 months; for the PHACO + TRAB group, 12.6 months (P = .1). As compared with the ECCE + TRAB group, the PHACO + TRAB group had earlier visual rehabilitation, less postoperative astigmatism (P &lt; .001), and improved long-term intraocular pressure control (P = .04). Early postoperative pressure spikes occurred in 32% of the ECCE + TRAB eyes and in 23.5% of the PHACO + TRAB eyes (P = .2). Other postoperative complications occurred more commonly in the ECCE + TRAB group: hyphema (P &lt; .001), fibrinous iritis (P &lt; .01), choroidal detachment (P &lt; .05), and hypotony (P &lt; .05). Posterior capsular opacification was significantly more common in the ECCE + TRAB group (P &lt; .02). These major differences probably are attributable primarily to the small incision used in phacoemulsification, which is associated with sustained IOP control during the operation, a small stable wound with low postoperative astigmatism, and early stabilization of refraction.

A Convective Trigger for Supernova Explosions

The shock wave that stalls within ∼10 ms of its creation during the collapse and bounce of the core of a massive star leaves behind it unstable lepton and entropy profiles that can drive a violent Rayleigh-Taylor-like overturn. Coupling two-dimensional hydrodynamics with independent one-dimensional neutrino transport in 100 angular bins, we demonstrate the possible existence of a convective boost in the neutrino luminosities that can ignite a supernova explosion. While the shock-imposed negative entropy gradient drives the early convection, neutrino heat transfer can smooth it within 15 ms. However, the negative lepton gradient, generically created at shock break-out, is not smoothed and is reponsible for vigorous mantle overturn just interior to the early entropy spike

Control of resting bronchial hemodynamics in the awake dog.

In the resting awake dog a continuous-wave Doppler flow transducer on the right bronchoesophageal artery inscribes a sharp early systolic spike and low flow in late systole and throughout diastole, indicating a highly resistive bed. An analysis of autonomic factors using intravenous, cumulative, and randomly applied cholinoceptor, beta 1- and beta 2-adrenoceptor, and alpha 1- and alpha 2-adrenoceptor antagonists indicates that the low vascular conductance is due to cholinoceptor and alpha 1- and alpha 2-adrenoceptor effects in a ratio 3.6:1. No beta-adrenoceptor tone is present. Sighing behavior invokes a transient (< 2 s) fall in intrapleural pressure (and thus rise in bronchovascular transmural pressure) of 10-30 mmHg, which is followed by a two- to threefold increase over 30 s in bronchial flow and conductance, an effect simulated in 50% of dogs when bronchovascular transmural pressure is acutely raised and maintained over 40-60 s by inflating an intra-aortic balloon distal to the origin of the bronchial artery. Autonomic blockade has no effect on bronchovascular dilatation evoked either by sighing or by balloon inflation. It is concluded that, in the resting bronchial circulation, there exists strong cholinoceptor and alpha-adrenoceptor-based vasoconstrictor activity which can be overpowered by strong nonadrenergic noncholinergic local vasodilator reflexes evoked by sudden changes in intrathoracic transmural pressure possibly acting on stretch-sensitive sensory nerve endings containing substance P, calcitonin gene-related peptide, and neurokinins. The tonic vasoconstrictor but not the sigh-evoked vasodilator effects are sensitive to pentobarbital sodium anesthesia.

Norepinephrine and thyrotropin stimulation of [Ca++]i in PC C13 a rat thyroid epithelial cell line: Effect of transformation by E1A gene of adenovirus and polyomavirus middle-T antigen gene

The effect of thyrotropin and norepinephrine on cytosolic calcium levels were evaluated in normal (PC C13) and transformed (PC E1A, PC Py and PC E1APy) rat thyroid epithelial cell lines. A different pattern of response to both norepinephrine and thyrotropin was observed among the distinct cell lines. In PC C13 the cytosolic calcium rise induced by norepinephrine, characterized by an early transient spike followed by a second phase of sustained calcium levels, was greatly enhanced by thyrotropin. The effect of norepinephrine on calcium concentrations was less affected by thyrotropin in PC C13 transformed by the adenovirus E1A oncogene. Conversely, in Polyoma middle-T transformed PC C13 the increase in cytoplasmic calcium was still sensitive to thyrotropin. The most malignant PC E1APy were totally independent of thyrotropin.

Chronic/semichronic limbic epilepsy produced by microinjection of tetanus toxin in cat hippocampus.

We describe an animal preparation in which a semichronic or chronic limbic epileptiform syndrome can be produced reliably by unilateral microinjection of tetanus toxin in cat ventral hippocampus. Injections were given at 1-week intervals until abnormal EEG activity was observed. After two to five injections, the animals abruptly began to exhibit intermittent spikes and subclinical discharges that soon gave way to spontaneous and recurrent behavioral seizures which gradually increased in frequency, duration, and severity in the next 12-48 h. Anticonvulsant therapy (phenobarbital, PB) was required within the first 3 days of the syndrome, since life-threatening generalized tonic-clonic seizures (GTCS) and status epilepticus would develop if the animal were left untreated. If severe seizures were prevented by antiepileptic drugs (AEDs) there was complete remission of the syndrome and repeat injection was necessary to reinitiate seizures. Animals that experienced severe seizures or that were reinjected after remission developed a chronic seizure syndrome and could be maintained with AEDs for long times (greater than 1 year) without significant debilitation. Although early spikes and subclinical discharges were typically focal to ipsilateral limbic sites, initial seizures appeared explosively in the form of a high-amplitude, high-frequency discharge, which often had an apparently bilateral limbic onset. On the other hand, chronic seizures had much more gradual onset and spread, often consisting of periodic sharp waves or low-amplitude sinusoidal discharge that was more clearly focal to ipsilateral limbic sites. Throughout the syndrome, ictal behavioral manifestations were highly stereotyped and very comparable to those described by other investigators in studies of clinical and experimental limbic epilepsy. All animals exhibited signs of independent contralateral involvement during the syndrome, ranging from independent contralateral spikes to subclinical discharges with a clear contralateral onset. None of the animals exhibited structural lesions on histologic examination at the level of light microscopy.

The Protective Effect of Early Intraoperative Injection of Viscoelastic Material in Trabeculectomy

In a prospective study, we evaluated the effect of intracameral injection of sodium hyaluronate (HA) in trabeculectomy on short- and long-term results, including the effect on the corneal endothelium. Twenty-two patients were randomly assigned into two groups: group A, consisting of 11 patients, underwent standard trabeculectomy; in group B (11 patients), additionally, HA was injected into the anterior chamber immediately following paracentesis in an attempt to minimize shallowing of the chamber after the subsequent trabeculectomy. Both groups had comparable age distributions, preoperative intraocular pressures (IOPs), preoperative endothelial cell counts, postoperative IOPs after 3 months, and glaucoma medication indices. The reduction in the number of endothelial cells after 1 month was significantly greater in group A than in group B (16.1% vs 6.7%). Also, significantly more shallow anterior chambers occurred in group A (three eyes vs one eye). However, 1 day postoperatively, the average IOP was 16.4 mm Hg in group A, as compared with 25 mm Hg in group B. Thus, although HA, injected early in trabeculectomy, appeared to protect against corneal endothelial loss and flat anterior chamber, it also seemed to be associated with early IOP spikes.

Agonist-induced frequency modulation of Ca2+ oscillations in salt gland secretory cells

Oscillations in intracellular calcium concentration ([Ca2+]i) induced by the acetylcholine analogue carbachol (CCh) were characterized by microspectrofluorimetry of fura-2 in single secretory cells from the avian salt gland. The frequency of oscillations increased in graded fashion with [CCh] between 25 nM (2.7 +/- 0.6 min-1) and 250 nM (11.8 +/- 1.4 min-1), whereas the amplitude of the spikes was independent of [CCh]. An interperiod return to prestimulatory [Ca2+]i was generally seen only at very low (25 nM) CCh. Between 50 and 250 nM CCh, oscillations were associated with sustained elevated [Ca2+]i levels. The amplitude of the oscillatory spikes was found not to exceed that of initial spikes arising from prestimulatory [Ca2+]i, despite the dose-dependent [effective concentration at 50% (EC50) = 200 nM CCh] sustained rise in [Ca2+]i. At 1 microM CCh, oscillations gave way to a maximal sustained increase in [Ca2+]i. Reduction of [Ca2+]o to 1.5 microM during an oscillatory train or blockage of Ca2+ influx with Ni+ resulted in a reduction in sustained Ca2+i levels and in frequency, but not amplitude, of oscillations. A relationship between the sustained partial rise in [Ca2+]i derived from Ca2+ influx and the oscillatory frequency at a given [CCh] was further indicated by the lower frequency (P less than 0.01) of the early spikes in a train when interspike [Ca2+]i initially returned to near-basal levels. In some cells, oscillations were slow enough (less than 2 min-1) to resolve an interperiod of elevated baseline [Ca2+]i, showing that the latter can occur independent of the repetitive Ca2+ spikes. (ABSTRACT TRUNCATED AT 250 WORDS)

Caffeine inhibits inositol-trisphosphate-induced membrane potential oscillations inXenopusoocytes

Immature Xenopus oocytes injected with inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) give a complex electrophysiological response comprising an a early depolarizing spike followed by a burst of oscillations. These two components have been interpreted on the basis of an interaction between two internal calcium stores: an Ins(1,4,5) P3-sensitive pool responsible for the early spike which then primes an Ins(1,4,5) P3-insensitive pool to begin to oscillate through a process of calcium-induced calcium release (Berridge, M. J., J. Physiol., Lond. 403, 589-599 (1988)). The role of the latter was investigated in Xenopus oocytes by using the drug caffeine which can trigger calcium-induced calcium release in muscle cells. Caffeine had no effect on the early Ins(1,4,5)P3-induced spike but it suppressed the subsequent oscillations. The spontaneous oscillations observed in some oocytes were also abolished by caffeine. Oscillation amplitude and duration was slightly reduced following incubation of oocytes with adenosine or isobutylmethylxanthine. Because these two agents gave large membrane hyperpolarizations indicative of an increase in cyclic AMP, it can be concluded that this second messenger is not responsible for the inhibitory action of caffeine. The ability of caffeine to abolish oscillations while not affecting the early Ins(1,4,5) P3 response is discussed with regard to the two-pool model for generating calcium oscillations.

Variable paths to seed production within the Kangaroo Valley cultivar of Lolium perenne

Components of seed yield were measured in an erect, early-flowering biotype and a prostrate, late-flowering biotype of Lolium perenne cv. Kangaroo Valley at temperatures from 15/10 to 24/19�C (12/12 h day/night). We aimed to determine if each biotype had distinctive components of seed yield, and if these varied according to temperature. The two biotypes had distinctive paths to seed yield. Seed yield per plant in an erect biotype depended more on seed weight per spike and less on spike number than in a prostrate biotype. The distinctive paths to seed yield, and relative stability in paths across temperatures, indicated that it was possible to select genotypes from within the Kangaroo Valley cultivar which had particular correlations among components of yield. Floral development was accelerated, but seed yield per plant and most of its components were reduced, at high temperature; only the mean daily rate of dry weight accumulation by individual seeds was the same at all temperatures. At any temperature, seed weight per spike declined almost linearly with lateness of spike emergence within a plant: spikes which emerged within 21 days of the earliest spike contributed 80% of the seed yield per plant. We conclude that biotypes can be selected within the Kangaroo Valley cultivar to have distinctive components of seed yield and, based on the two biotypes we studied, commercial seed production should be based at a location having relatively low temperatures.

The role of transcranial Doppler in confirming brain death

We performed transcranial Doppler (TCD) examinations on 54 comatose patients over a 1-year period. Of 49 patients with technically adequate TCD examinations, 23 met criteria for determination of brain death by clinical and EEG criteria (21) or clinical criteria alone (2; EEG not performed). A TCD waveform abnormality, consisting of absent or reversed diastolic flow, or small early systolic spikes, in at least 2 intracranial arteries, occurred in 21 brain-dead patients, but in none of the other patients in coma. With appropriate guidelines for performance and interpretation, TCD could be incorporated into institutional protocols as a rapid and convenient alternative to EEG for confirmation of brain death.

Sodium- and Calcium-Dependent Mechanisms in the Action Potential of the Secretory Epithelium of a Clam Mantle

ABSTRACT The secretory epithelium of the mantle of the clam Anomalocardia brasiliana is excitable. The ionic dependence of its action potentials was investigated. Two distinct phases could be recognized by their ionic dependences. The early spike phase, that appeared in all action potentials, was dependent on the Na+ concentration of the solution in the interstitial space and was insensitive to tetrodotoxin (TTX) at concentrations as high as 36μmoll−1. It was inhibited by local anesthetics, and its repolarization was inhibited by veratrine. The data show this electrogenesis is caused by TTX-insensitive sodium channels located at the basolateral membrane of this epithelium. Cardiac-like action potentials were recorded in several specimens: the rapid Na+-dependent spike was followed by a slower repolarization phase that formed a plateau and increased the action potential duration. The plateau amplitude was markedly increased when the external Ca2+ concentration was increased to 60 mmol I−1 and it was inhibited by the addition of inorganic calcium channel blockers such as Mn2+ and Cd2+. These observations suggest that inward Ca2+ currents cause the sustained depolarization during the plateau.

Pathophysiology of the spinal cord studied in vitro

We describe the use of isolated hemisected mouse spinal cords for pathophysiological investigations and analyze the responses evoked and recorded with suction electrodes in spinal roots. Dorsal root (DR) recordings from preparations in control solution show a directly evoked fiber volley (FV); an early postsynaptic spike generated by neurons in spinal gray matter and picked up by volume conduction (DRR1); and a ‘slow’ dorsal root potential (DRP). The ‘conventional’ dorsal root reflex (here termed DRR2) was absent or very small in control medium but became very prominent in elevated bath [Ca 2+]. DRP and DRR2 but not DRR1 are depressed by GABA A antagonists. Recordings from VR contain the electrotonically conducted VR epsp and superimposed monosynaptic reflex discharge (VRR1). Rarely in control medium but regularly in elevated bath [Ca 2+] a GABA-dependent late reflex (VRR2) appears (see also Duchen, 1986). The effects of varying bath concentrations of K +, Ca 2+ and Mg 2+ on evoked responses are briefly summarized. Irregularly timed spontaneous discharges appear in DR and VR recordings when [Ca 2+] is elevated above 1.8 or 2.4 mM, and when [Mg 2+] is lowered to 0.4 mM. In hypoxic solution synaptically transmitted responses fail in 10 to 20 min, but persist longer when [Ca 2+] is elevated. Unexpectedly, spreading depression (SD)-like responses were recorded in some preparations during hypoxia. Following hypoxia, after synaptically transmitted responses recovered, spontaneous activity developed in DR and VR recordings.

Early and late components in cat renshaw cell responses to random stimulation of motor axons: Their differential sensitivity to preceding activation

Lumbosacral Renshaw cells were activated by random stimulation of motor axons in muscle nerves or ventral roots. The stimulus patterns had mean rates of 9.5–13 or 20–23 pulses per second. The Renshaw cell responses were evaluated by two kinds of peristimulus-time histograms. “Conventional” peristimulus-time histograms were calculated by averaging the cell discharge with respect to all the stimuli in a train. “Conditional” peristimulus-time histograms were determined by averaging the cell discharge with respect to the second (“test”) stimulus in pairs of stimuli which were separated by varied intervals. The effects of the conditioning stimuli were evaluated after correcting for the effect of linear superposition of the conditioning and test stimuli. The conventional peristimulus-time histograms showed an excitatory response which often consisted of two distinct components: a narrow and high “early” peak and a broad and low “late” elevation of firing probability. The early and late excitatory components were conditioned in different ways. Whereas the late component was virtually always depressed, the early component showed three patterns: (1) uniform depression; (2) uniform facilitation; (3) a mixture of depression and facilitation. Frequency responses (coherence and gain estimates) were also calculated separately for the cell discharges underlying either the early or the late components. The estimates for the “late spikes” showed a stronger decline with increasing frequency than those for the “early spikes”. The origin of the different conditioning effects probably lies in a combination of pre and postsynaptic factors. They may play a role in tremor mechanisms.

Sea level changes, carbonate dissolution and history of the Benguela Current in the Oligocene-Miocene off Southwest Africa (DSDP Site 362, Leg 40)

A coarse fraction analysis has been performed on sediments from DSDP Site 362 (Leg 40), in a water depth of 1325 m at the Eastern Walvis Ridge. The influence of carbonate dissolution has been revealed by benthos/plankton foraminifera ratio variations and by fragmentation of planktonic foraminifera. Carbonate dissolution shows strong variations: An Early Oligocene preservation spike, followed by a Middle Oligocene dissolution pulse, an Early Miocene preservation maximum, a dissolution increase in the Middle Miocene (14–15 m.y. ago) and a strong increase in dissolution at 10 m.y. ago, with several small-scale cyclic changes, with a maximum in dissolution between 10 and 9.5 m.y. ago and between 6 and 5.2 m.y. ago. These dissolution variations can be related to sea level fluctuations and ice extent in Antarctica. The history of the Benguela Current can be recreated by means of the opal content of the sediments. The W-turning Benguela Current transports opal from the near-coastal upwelling area to the continental slope. The Benguela Current first reached the Walvis Ridge 10 m.y. ago. During glacial periods in the interval 6–10 m.y. ago, the Benguela Current turned to the west over the Walvis Ridge and produced high opal contents. During interglacial periods in the interval 6–10 m.y. ago, the Benguela Current turned to the west within the Cape Basin. Opal contents in interglacial sequences of Site 362 in the interval 6–10 m.y. ago are lower than the glacial opal contents. Beginning at 5.2 m.y. ago, the reverse relationship has been found: The highest opal contents occur in interglacial sediments, and the smallest contents occur in glacial sequences. This observation reflects the northward shift of the Benguela Current.

Ocular bioavailability of pilocarpic acid mono- and diester prodrugs as assessed by miotic activity in the rabbit

Following topical ophthalmic dosing of rabbits with pilocarpic acid diester and monoester prodrug solutions, significant biological activity was observed. The response, measured as pupillary diameter, vs time profiles, showed a slightly longer time requirement for attainment of maximal activity, a plateauing region of sustained response, and a longer duration of action as compared to pilocarpine. Several monoesters were capable of maintaining durations of action 1.5 times that of pilocarpine while the diesters were active for up to 2.25 times as long, and from half the dosing concentration. The profile shapes eliminate the early spiking response seen with higher doses of pilocarpine. The bioavailability, as assessed by response, of the prodrugs relative to pilocarpine is a balance between 3 factors: prodrug lipophilicity, the kinetics of conversion from diester to monoester to pilocarpine, and ocular clearance or elimination rates. The increased bioavailability (response vs time) of the diesters is primarily a result of their lipophilicity, with an optimum being seen. For the monoesters, the increase is dependent on the rate of the monoester to pilocarpine conversion. A linear correlation has been established between the monoester structures and the activities observed following their dosing, through the use of the Taft σ ∗ values for the alcohol alkyl moieties. For the diesters, an inverted V-shaped correlation exists between the partition coefficients of the prodrugs and their relative bioavailabilities, as calculated from response data. In both cases, considerable predictability of response from prodrug structure should be possible.

Effect of Sodium Chloride and Nitrate on Dry Matter Production and Micronutrient Content of Wheat Plant

A sand culture experiment was conducted using four wheat varieties viz. Sakha 8 (V1), Sonalika (V2), Sakha 3 (V3) and Soltane (V4). Plants were irrigated with nutrient solutions containing three levels of salinity viz. 0 (S1), 44 (S2), and 88 (S2) meq NaCl/liter, and three levels of nitrate viz. 3 (N1, 6 (N2), and 9 (N3) meq NO3 1/liter. Plants were sampled at early spike emergence for measurement of dry matter and contents of Fe, Mn, and Zn. The results are summarized as follows. 1) The efficiency of spike dry matter production percent was promoted by increasing salinity, though, the opposite was observed for the dry matter yield of shoots and spikes. 2) The higher the nitrate level the higher was the dry matter yield per plant and the efficiency of spike dry matter yield production percent as well. 3) Tolerance of the tested wheat varieties to sodium chloride followed the order; V1 < V2 < V3 < V4 and the critical osmotic pressures of sodium chloride, for 50% reduction in dry matter yield, could be predi...

An Application of the Maas‐Hoffman Salinity Response Model for Boron Toxicity

AbstractThe Maas‐Hoffman model for salinity tolerance was tested for boron toxicity (reduction in yields only) using wheat (Triticum aestivum L., var. Inia 66R), barley (Hordeum vulgare L., var. Briggs), and sorghum (Sorghum bicolor L., var. Dekalb C42A) as test crops. These crops were grown to maturity in sand cultures containing low to excessive concentrations of boron. The leaf immediately below the Y‐leaf was collected at the early spike emergence stage and analyzed for boron. At harvest, the individual grain heads were collected, dried and weighed. Relative grain and shoot yields (Y, %) were related to the boron concentration of the nutrient solution (X, mg B L−1) using the following equation Y = 100 − m(X − A), where m is the decrease in yield per unit increase in soluble boron above the threshold concentration, and A, the maximum concentration not restricting yield (the threshold). The SALT computer program (van Genuchten, 1983) was used to derive the slope and threshold parameters. The respective threshold concentrations for the grain yields of wheat, barley, and sorghum were found to be 0.3, 3.4, and 7.4 mg B L−1, respectively, which categorized these crops as being sensitive, moderately tolerant, and very tolerant to boron. The relationship between relative yield and leaf boron was linear for wheat whereas barley and sorghum followed the Maas‐Hoffman model. The threshold leaf B values with reference to grain yield were found to be 55, 768, 171 mg B kg−1, respectively, for wheat, barley, and sorghum. The study indicates that yield under the influence of soluble boron may be fitted to the Maas‐Hoffman model for salt tolerance.

Overview of instabilities in laser systems

This paper contains a brief overview of the main types of instability in laser systems. The topics being discussed include the early spiking in solid-state lasers, single-mode lasers with homogeneous and inhomogeneous broadening, the effect of noise and modulation, multimode operation, and a brief survey of nonlinear dynamics.