Increase In Number Of Spikes Research Articles

Effects of continuous nitrogen application on seed yield, yield components and nitrogen-use efficiency of Leymus chinensis in two different saline-sodic soils of Northeast China

The effect of nitrogen (N) application on seed yields and yield components in Leymus chinensis (Trin.) Tzvel., a perennial rhizomatous grass, was measured in a field experiment with two saline-sodic soils at Da’an Sodic Land Experiment Station during 2010–11. Two grassland field sites were classified as moderately saline–sodic (MSSL) and severely saline–sodic (SSSL). Application rates of N at each site were 0, 30, 60, 90, 120, 150, 180 and 210 kg ha–1. Application of N significantly improved seed yield mainly through increased spike number (R2 = 0.96, P ≤ 0.001). Compared with nil N, seed yield increased 7.4–10.9 times with N application of 150 kg ha–1 at MSSL, and 5.3–7.5 times with N application of 120 kg ha–1 at SSSL. However, absolute increases at SSSL were relatively small. Some significant differences (P ≤ 0.01) in seed yield occurred between 2010 and 2011 with different N application rates in the same soil, and between MSSL and SSSL in the same year. Increasing N application rate significantly decreased N physiological efficiency (NPE) but increased N apparent-recovery fraction (NRF) and N partial-factor productivity (NPP) at both sites. Seed yield and NPP indicated that the optimal N application rates to increase yield were 150 kg ha–1 at MSSL and 120 kg ha–1 at SSSL. High soil pH was the major factor adversely impacting seed yield, and pH and soil salinity were major factors negative affecting NPE, NRF and NPP as well as decreasing the positive effect of N application. Nitrogen application is a practical and effective method to increase seed yield of L. chinensis in saline-sodic grasslands of Northeast China, particularly when soil pH and salinity are not limiting.

Trait Response and Change in Genetic Variation upon Selection for Spike Number in Salina Wildrye

Salina wildrye (Leymus salinus [M.E. Jones] Á. Löve) is a perennial cool-season grass that potentially could become an important restoration species in the Colorado Plateau. However, its seed production has never been commercially viable due to sparse heading. We compared a 4x ssp. salmonis population, Lakeside C3, to an 8x ssp. salinus population, 9043501, for seed production−related traits and measured the response of 9043501 to 2 cycles of selection for increased spike number over a 4-yr period at Millville, Utah. Seed yield of Lakeside and 9043501 was similar (P > 0.10) in 2013, but seed yield of 9043501 was 81% greater (P < 0.10) than Lakeside in 2014 and 191% greater (P < 0.01) in 2015. Lakeside spike number was 99% greater (P < 0.0001) than 9043501 in 2013, but they were similar (P > 0.10) in 2014 and 2015. Seeds per spike of 9043501 were 71% (P < 0.05), 80% (P < 0.05), and 209% (P < 0.01) greater than Lakeside in 2013, 2014, and 2015, respectively. Selection in 9043501 increased (P < 0.05) spike number by 4.3 spikes per plant (19.8%) per cycle of selection in the first seed-production yr (2013), but no change was seen in 2014 or 2015 (P > 0.10). Selection did not change (P > 0.10) seeds per spike or individual seed mass. Consequently, seed yield increased (P < 0.05) 0.32 g per plant per cycle (36.8%) in 2013, with no increase (P > 0.10) in 2014 or 2015. Dry matter per plant across the 4 yr increased (P < 0.01) 10.3 g per plant per cycle (9.3%), and canopy height increased (P < 0.01) 3.9 cm per cycle (6.6%) in 2013. AFLP DNA primers detected a 1.7% loss of genetic variation per cycle, presumably due to a combination of selection and genetic drift, but no plant traits were diminished as a result.

Light interception and radiation use efficiency response to tridimensional uniform sowing in winter wheat

Improving radiation use efficiency (RUE) of the canopy is necessary to increase wheat (Triticum aestivum) production. Tridimensional uniform sowing (U) technology has previously been used to construct a uniformly distributed population structure that increases RUE. In this study, we used tridimensional uniform sowing to create a wheat canopy within which light was spread evenly to increase RUE. This study was done during 2014–2016 in the Shunyi District, Beijing, China. The soil type was sandy loam. Wheat was grown in two sowing patterns: (1) tridimensional uniform sowing (U); (2) conventional drilling (D). Four planting densities were used: 1.8, 2.7, 3.6, and 4.5 million plants ha−1. Several indices were measured to compare the wheat canopies: photosynthetic active radiation intercepted by the canopy (IPAR), leaf area index (LAI), leaf mass per unit area (LMA), canopy extinction coefficient (K), and RUE. In two sowing patterns, the K values decreased with increasing planting density, but the K values of U were lower than that of D. LMA and IPAR were higher for U than for D, whereas LAI was nearly the same for both sowing patterns. IPAR and LAI increased with increasing density under the same sowing pattern. However, the difference in IPAR and LAI between the 3.6 and 4.5 million plants ha−1 treatments was not significant for both sowing patterns. Therefore, LAI within the same planting density was not affected by sowing pattern. RUE was the largest for the U mode with a planting density of 3.6 million plants ha−1 treatment. For the D sowing pattern, the lowest planting density (1.8 million plants ha−1) resulted in the highest yield. Light radiation interception was minimal for the D mode with a planting density of 1.8 million plants ha−1 treatment, but the highest RUE and highest yield were observed under this condition. For the U sowing pattern, IPAR increased with increasing planting density, but yield and RUE were the highest with a planting density of 3.6 million plants ha−1. These results indicated that the optimal planting density for improving the canopy light environment differed between the sowing patterns. The effect of sowing pattern×planting density interaction on grain yield, yield components, RUE, IPAR, and LMA was significant (P<0.05). Correlation analysis indicated that there is a positive significant correlation between grain yield and RUE (r=0.880, P<0.01), LMA (r=0.613, P<0.05), and spike number (r=0.624, P<0.05). These results demonstrated that the tridimensional uniform sowing technique, particularly at a planting density of 3.6 million plants ha−1, can effectively increase light interception and utilization and unit leaf area. This leads to the production of more photosynthetic products that in turn lead to significantly increased spike number (P<0.05), kernel number, grain weight, and an overall increase in yield.

Effects of subsoil plastic film mulch on yield and water use of rainfed winter wheat

Water shortage is a limiting factor to crop production in North China. Mulching is a widely used approach to conserve soil water and improve crop yield. A 2-year field experiment was conducted at the Nanpi Eco-Agricultural Experimental Station of the Chinese Academy of Sciences in 2014–16, in which yields of winter wheat (Triticum aestivum L.) in a treatment with subsoil plastic film mulch were compared with non-mulch. The mulch treatment produced a 16.1% higher grain yield than the non-mulch treatment. The increase in grain yield was primarily due to a 10.1–10.9% increase in number of spikes per m2 and a 4.7–5.1% increase in number of grains per spike. Plants in the mulch treatment showed greater dry matter (DM) accumulation but similar harvest index. Yield improvement did not depend on increasing DM translocation, but was significantly related to DM accumulation at different growth stages. Increased DM accumulation before wintering, from jointing to heading and from anthesis to maturity, enhanced grain yield by promoting increased number of spikes and number of grains per spike. Soil evaporation was lower by 31.1% and transpiration increased by 28.0% in the mulch treatment, resulting in 8.9–9.4% higher water-use efficiency. Our results indicate that a subsoil plastic film mulch can effectively improve winter wheat yield and water-use efficiency under rain-fed conditions.

Compensation effect of winter wheat grain yield reduction under straw mulching in wide-precision planting in the North China Plain

Climate change and the growing demand for food security force growers to identify ways both to improve food production and to reduce agricultural carbon emissions. Although straw mulching is known to decrease CO2 emissions, winter wheat grain yield in the North China Plain was declined under straw mulching. In an effort to determine the most effective way to increase winter wheat yield under straw mulching, a field experiment was conducted using two planting patterns (wide-precision planting and conventional-cultivation planting) and two straw mulching rates (0 and 0.6 kg/m2). The results showed the wide-precision planting/non-mulching treatment significantly increased the leaf area index more than the other three treatments at the early growth stage. This treatment improved aboveground dry matter accumulation and was conducive to increased spike weight in the late growth stage. By contrast, straw mulching significantly reduced winter wheat grain yields by lowering both spike number and 1000-grain weight at the mature plant stage. In the wide-precision planting/mulching treatment, a significantly increased spike number compensated for grain yield losses. The results support the idea that wide-precision planting combined with straw mulching has the potential to decrease the winter wheat grain yield reduction previously observed with straw mulching in the North China Plain.

Integrated crop-N system management to establish high wheat yield population

It is essential to identify the main components that limit crop yield to achieve high crop yields. We collected data from 156 experimental field plots over six crop seasons to determine the degree to which wheat yield is limited by spike number and to further understand the effects of different sowing dates, seeding rates, and nitrogen (N) management on population development and yield. High yields in plots (>8.5tha−1) were attributable to increased spike numbers associated with elevated pre-winter stem numbers and higher percentage of productive stems. An early sowing date with a seeding rate of 350seedsm−2 significantly produced higher spike numbers than a late sowing date with a seeding rate of 540seedsm−2. High basal N fertilizer rate and dressing N at the regreening stage, typical of farmers’ N practices, markedly decreased productive stem percentage compared to an optimal basal N rate and N dressing at the stem-elongation stage. A dressing N rate of 120kgNha−1at stem-elongation stage increased spike number compared to applications of 0 or 60kgNha−1. Based on our results, we designed an integrated crop-N management (ICM-N) for generating high yields and high N use efficiency. The ICM-N strategy increased grain yield by 33% (p<0.05) while using a 27% lower N fertilizer rate led to an 87% increase in N use efficiency over three crop seasons compared to a standard farmers’ management strategy.

Analysis of Leaf Area Index Dynamic and Grain Yield Components of Intercropped Wheat and Maize under Straw Mulch Combined with Reduced Tillage in Arid Environments

&lt;p class="2"&gt;Knowledge on effect of yield formation under straw combined with plastic film mulch is important in highlighting the importance of cultivating high-efficient and high-yield crops in the arid environments. In this study, we developed a ‘double-mulching’ system, i.e., plastic film coupled with straw mulch, integrated together with intensified strip intercropping. We determined (i) the responses of leaf area index improvement to the integrated double mulching system, and (ii) Its effects on yield formation process and mechanism of intercropped wheat and maize under the integrated systems. Experiments were carried out in northwest China in 2009 to 2011. Results showed that wheat-maize strip intercropping in combination with plastic film and straw covering on the soil surface (i.e., NTS) increased maize yield by 27 to 42% compared to conventional monoculture maize, and increased wheat yield by 149 to 160% compared to conventional monoculture wheat. The crops on NTS had higher harvest index of maize, an increase of 8.2 to 21.6% than that of conventional monoculture maize. NTS system increased spike number (i.e., SN) by an average of 30.4%, increased kernel number per spike (i.e., KNS) by an average of 10.8%, and increased thousand-kernel weight (i.e., TKW) by an average of 7.0% of intercropped wheat in comparison with conventional monoculture wheat. Similarly, there was an average increase of 5.7% of SN, 23.8% of KNS, and 7.5% of TKW under intercropped maize in comparison with conventional monoculture maize. Moreover, the treatment on NTS had greater leaf area index (i.e., LAI) an average increase of 64.1% than that in conventional monoculture maize. Similarly, LAI had an average increase of 29.3% than conventional monoculture wheat. Path analysis exhibited that straw mulching combined with reduced tillage increased the grain yield of intercropped wheat by improving KNS, and increased the grain yield of intercropped maize by improving SN. We conclude that the intercropping system in combination with plastic film and straw mulching can be an effective system for boosting crop productivity via improving yield components and LAI under limited resources in arid enviroments.&lt;/p&gt;

Changes in intracellular potentials of snail neurons induced by β-phenylglutamic acid hydrochloride.

β-Phenylglutamic acid hydrochloride (RGPU-135, neuroglutamine, or glutarone) in concentrations of 1, 10, 100, and 1000 μM reversibly and dose-dependently modulated the intracellular action potentials in Plantorbarius corneus snail neurons and hyperpolarized the membrane by 9.1±2.5% with maximum shift of resting potential at 100μM. Hyperpolarization was accompanied by up-regulation of synaptic activity and changes in the pattern of impulse activity manifested by a decrease in the discharge rate, shortening of the interburst time, increase in the mean number of spikes in the bursts, and shortening of the interspike time within the bursts. Both hyperpolarization and impulse activity rearrangement persisted for 10-20 min after washing of RGPU-135.

Alterations in the Intrinsic Burst Activity of Purkinje Neurons in Offspring Maternally Exposed to the CB1 Cannabinoid Agonist WIN 55212-2

Burst firing plays an important role in normal neuronal function and dysfunction. In Purkinje neurons, where the firing rate and discharge pattern encode the timing signals necessary for motor function, any alteration in firing properties, including burst activity, may affect the motor output. Therefore, we examined whether maternal exposure to the cannabinoid receptor agonist WIN 55212-2 (WIN) may affect the burst firing properties of cerebellar Purkinje cells in offspring. Whole-cell somatic patch-clamp recordings were made from cerebellar slices of adult male rats that were exposed to WIN prenatally. WIN exposure during pregnancy induced long-term alterations in the burst firing behavior of Purkinje neurons in rat offspring as evidenced by a significant increase in the mean number of spikes per burst (p<0.05) and the prolongation of burst firing activity (p<0.01). The postburst afterhyperpolarization potential (p<0.001), the mean intraburst interspike intervals (p<0.001) and the mean intraburst firing frequency (p<0.001) were also significantly increased in the WIN-treated group. Prenatal exposure to WIN enhanced the firing irregularity as reflected by a significant decrease in the coefficient of variation of the intraburst interspike interval (p<0.05). Furthermore, whole-cell voltage-clamp recordings revealed that prenatal WIN exposure significantly enhanced Ca(2+) channel current amplitude in offspring Purkinje neurons compared to control cells. Overall, the data presented here strongly suggest that maternal exposure to cannabinoids can induce long-term changes in complex spike burst activity, which in turn may lead to alterations in neuronal output.

Activation of κ opioid receptors increases intrinsic excitability of dentate gyrus granule cells

The dentate gyrus of the hippocampus is thought to control information flow into the rest of the hippocampus. Under pathological conditions, such as epilepsy, this protective feature is circumvented and uninhibited activity flows throughout the hippocampus. Many factors can modulate excitability of the dentate gyrus and ultimately, the hippocampus. It is therefore of critical importance to understand the mechanisms involved in regulating excitability in the dentate gyrus. Dynorphin, the endogenous ligand for the kappa (κ) opioid receptor (KOR), is thought to be involved in neuromodulation in the dentate gyrus. Both dynorphin and its receptor are widely expressed in the dentate gyrus and have been implicated in epilepsy and other complex behaviours such as stress-induced deficits in learning and stress-induced depression-like behaviours. Administration of KOR agonists can prevent both the behavioural and electroencephalographic measures of seizures in several different models of epilepsy. Antagonism of the KORs also prevents stress-induced behaviours. This evidence suggests the KORs as possible therapeutic targets for various pathological conditions. In addition, KOR agonists prevent the induction of LTP. Although there are several mechanisms through which dynorphin could mediate these effects, no studies to date investigated the effects of KOR activation on intrinsic membrane properties and cell excitability. We used whole-cell, patch-clamp recordings from acute mouse hippocampus slices to investigate the effect of KOR activation on dentate gyrus granule cell excitability. The agonist U69,593 (U6, 1 μM) resulted in a lower spike threshold, a decreased latency to first spike, an increased spike half-width, and an overall increase in spike number with current injections ranging from 15 to 45 pA. There was also a reduction in the interspike interval (ISI) both early and late in the spike train, with no change in membrane potential or input resistance. Preincubation of the slice with the selective KOR antagonist, nor-binalthorphimine (BNI, 1 μM) inhibited the effect of U6 on the latency to first spike and spike half-width suggesting that these effects are mediated through KORs. The inclusion of GDP-βS (1 mM) in the recording pipette prevented all of the U6 effects, suggesting that all effects are mediated via a G-protein-dependent mechanism. Inclusion of the A-type K+ current blocker, 4-aminopyridine (4-AP, 5 mM) in the pipette also antagonised the effects of U6. Kv4.2 is one of the channel α subunits thought to be responsible for carrying the A-type K+ current. Incubation of hippocampus slices with U6 resulted in a decrease in the Kv4.2 subunit protein at the cell surface. These results are consistent with an increase in cell excitability in response to KOR activation and may reflect new possibilities for additional opioid functions.

Effects of Application of Two Organomineral Fertilizers on Nutrient Leaching Losses and Wheat Crop

The topic of how to decrease environmentally adverse effects of agriculture without losing too much crop yield is an important issue. In this respect, nutrient leaching losses were studied from a soil (land fallowing is not practiced) treated with two types of organomineral fertilizers [organomineral fertilizer (OMF) and organic + inorganic fertilizer mixture (O+IF), respectively]. Inorganic N losses were greatest in the soil treated with the O+IF, followed by those treated with the OMF, the former of which resulted in more gradual losses than the latter. Losses of other elements supplied by the fertilizers, particularly P and K, were greatest for the O+IF, followed by OMF treatment. The high nutrient losses observed in the soil treated with the O+IF make it advisable to use an OMF in soils with an abundant water supply. The highest N/P ratios were produced by the OMF, which suggest a lower eutrophication risk in drainage waters from soils treated with this fertilizer. Wheat (Triticum aestivum L. cv. Cajeme) yield parameters obtained and the alveographic assays showed that the OMF has a great potential of being used, at least on the wheat variety tested and under the pedoclimatic conditions prevailing in the study area. In this respect, application of OMF gave a significant increase in grain gross protein content of 2.9%, an increase in number of grains per spike of 2.2%, a significant increase in number of spikes per square meter of 3.4%, an increase in 1000‐grain weight of 3.9%, and a significant yield increase of 2.5% with respect to the O+IF treatment.

Agronomic evaluation of a tiller inhibition gene (tin) in wheat. I. Effect on yield, yield components, and grain protein

Reduced tillering cereals have been proposed as being advantageous under terminal drought conditions through their reported reduction in non-productive tiller number and reduced soil water use prior to anthesis. This study was conducted to determine whether wheat (Triticum aestivum L.) lines containing the tiller inhibition (tin) gene have a yield penalty over their commercial near-isogenic counterparts. A terminal drought was experienced in all experiments. The effects of the tin gene were investigated in 4 different near-isogenic pairs of lines grown at 2 sowing densities at 4 locations in the eastern Australian wheatbelt over a 3-year period. Averaged over all experiments and lines, grain yield was unaffected by the presence of the tin gene. However, the highest yielding line contained the tin gene and its yield was 5% higher than all other lines. Averaged across the different genetic backgrounds, the tin gene decreased fertile spike number by 11%, increased the number of kernels/spike by 9%, and there was a 2% increase in kernel weight. The tin gene increased the harvest index by an average of 0.02, whereas above-ground biomass was reduced by 7%. Increasing sowing density from 50 to 100 kg/ha had little influence on yield or yield-related characteristics in both the restricted tillering and freely tillering lines. There was an interaction between sowing rate and the presence of the tin gene on yield, with tin lines yielding 0.2 t/ha more than the freely tillering lines at the higher sowing rate, whereas there was no effect at the lower sowing rate. The response of several lines containing the tin gene to nitrogen fertiliser was also investigated at 2 sites. Nitrogen increased spike number in all lines but the number remained around 20% less than in the freely tillering cultivars. The yield of wheat lines containing the tin gene was 6% greater than their near-isogenic pairs where nitrogen status was high in the presence of terminal drought. Grain protein concentration was unaffected by the presence of the tin gene at high grain protein sites, whereas at lower grain protein sites it had a positive effect.

Yield response of wheat and barley to inoculation of plant growth promoting rhizobacteria at various levels of nitrogen fertilization

AbstractThe yield response of a wheat (Kirik) and a barley (Tokak 157/37) cultivar to inoculation with Azospirillum brasilense Sp246 and Bacillus sp. OSU‐142 was studied in relation to three levels of N fertilization (0, 40, and 80 kg ha–1) under field conditions in Erzurum, Turkey, in 1999 and 2000. Seed inoculation with A. brasilense Sp246 significantly affected yield and yield components, both in wheat and barley. On average of years and N doses, inoculation with A. brasilense Sp246 increased spike number per m2, grain number per spike, grain yield, and crude protein content by 7.2, 5.9, 14.7, and 4.1 % in wheat and by 6.6, 8.1, 17.5, and 5.1 % in barley, respectively, as compared to control. Inoculation with Bacillus sp. OSU‐142 significantly increased kernel number per spike in wheat, but no significant effect was determined in the other characteristics. Grain yields and yield components were also higher at all levels of nitrogen fertilizer in the inoculated plots as compared to the control. However, these increases diminished at high fertilizer levels. These results suggest that application of the growth promoting bacteria A. brasilense Sp246 may have the potential to be used as a biofertilizer for spring wheat and barley cultivation in organic and low‐N input agriculture.

Response characteristics of ventral posteromedial thalamic nociceptive neurons in the anesthetized rat

Extracellular single unit recordings were made from the ventral posteromedial thalamic (VPM) nociceptive neurons to determine mechanoreceptive field (RF) and response properties. A total of 44 VPM thalamic nociceptive neurons were isolated from rats anesthetized with urethane-chloralose. Based on responses to various mechanical stimuli including touch, pressure and pinch applied to the RF, 32 of 44 neurons were classified as nociceptive specific (NS) neuron. The other 12 neurons, classified as wide dynamic range (WDR), showed a graded response to increasingly intense stimuli, with a maximum discharge to noxious pinch. The VPM nociceptive neurons showed various spontaneous activity ranged from 0-6 Hz. They were located throughout the VPM, and had an contralateral RF including mainly intraoral (and perioral) regions. The RF size was relatively small, and very few neurons had a receptive field involving 3 trigeminal divisions. The NS neurons activated only by pressure and pinch stimuli had high mechanical thresholds compared to WDR neurons activated also by touch stimuli. The VPM nociceptive neurons were tested with suprathershold graded mechanical stimuli. Most of 21 NS and 8 WDR neurons showed a progressive increase in number of spikes as mechanical stimulus intensity was increased. In some neurons, the responses reached a peak before the highest intensity was given. Application of 5 mM solution to the trigeminal subnucleus caudalis did not produce any significant changes in the spontaneous activity, RF size, mechanical threshold, and response to suprathreshold mechanical stimuli of 9 VPM nociceptive neurons tested. 17 of 33 VPM nociceptive neurons responded to noxious heat as well as noxious mechanical stimuli applied to their RF. Application of the mustard oil, a small-fiber excitant and inflammatory irritant, to the right maxillary first molar tooth pulp induced an immediate but short-lasting neuronal discharges upto approximately 4 min in 16 of 42 VPM nociceptive neurons. These results suggest that VPM thalamic nucleus may contribute to the sensory discriminative aspect of orofacial nociception.

Selective depression of nociceptive responses of dorsal horn neurones by SNC 80 in a perfused hindquarter preparation of adult mouse

Detailed electrophysiological characterisation of spinal opioid receptors in the mouse has been limited due to various technical difficulties. In this study, extracellular single unit recordings were made from dorsal horn neurones in a perfused spinal cord with attached trunk-hindquarter to investigate the role of δ-opioid receptor in mediating nociceptive and non-nociceptive transmission in mouse. Noxious electrical shock, pinch and heat stimuli evoked a mean response of 20.8±2.5 ( n=10, P<0.005), 30.1±5.4 ( n=58, P<0.005) and 40.9±6.3 ( n=29, P<0.005) spikes per stimulus respectively. In 5 of 22 cells, repetitive noxious electrical stimuli applied to the hindpaw for 20 s produced a progressive increase in spike number, the phenomenon known as ‘wind-up’ and/or hyperactivity. When the selective δ-opioid receptor agonist (+)-4-[(α R)-α-((2 S,5 R)-4-allyl-2,5-dimethyl-1-piperazinyl)-3-methoxybenzyl]- N, N-diethylbenzamide (SNC 80) was perfused for 8–10 min, these evoked nociceptive responses were reversibly depressed. SNC 80 (2 μM) depressed the nociceptive responses evoked by electrical shock, pinch and heat by 74.0±13.7% ( n=8, P<0.01), 66.5±16.6% ( n=10, P<0.01) and 74.1±17.0% ( n=10, P<0.01) respectively. The maximum depression by 5 μM SNC 80 was 92.6±6.8% ( n=3). SNC 80 at 5 μM also completely abolished the wind-up and/or hypersensitivity ( n=5). The depressant effects of SNC 80 on the nociceptive responses were completely blocked by 10 μM naloxone ( n=5) and 3 μM 17-(cyclopropylmethyl)-6,7-dehydro-4,5α-epoxy-14β-ethoxy-5β-methylindolo [2′,3′:6′,7′] morphinan-3-ol hydrochloride (HS 378, n=8), a novel highly selective δ-opioid receptor antagonist. Interestingly, HS 378 (3 μM) itself potentiated the background activity and evoked responses to pinch and heat by 151.8±38.4% ( P<0.05, n=8), 34.2±6.1% ( P<0.01, n=7) and 45.5±11.8% ( P<0.05, n=5) respectively. In contrast, the responses of non-nociceptive dorsal horn neurones were not inhibited by SNC 80 at a dose of up to 10 μM ( n=5). These data demonstrate that δ-opioid receptor modulate nociceptive, but not non-nociceptive, transmission in spinal dorsal horn neurones of the adult mouse. The potentiation of neuronal activity by HS 378 may reflect an autoregulatory role of the endogenous δ-opioid in nociceptive transmission in mouse.

Winter Wheat Cultivar Performance as Affected by Production Systems in Croatia

The use of intensive production systems (IPS) may substantially increase winter wheat (Triticum aestivum L.) grain yields in Croatia because the national average yield of 4.14 t ha−1 is low compared with the yield potential of currently grown cultivars. Field experiments were conducted during 1996 through 1998 to evaluate the agronomic responses of 15 modern cultivars grown at two seeding rates (440 and 770 seeds m−2) in both an IPS and an extensive production system (EPS). The IPS consisted of plowing at 30 to 32 cm; fertilization at 194, 130, and 130 kg ha−1 N, P, and K; and high input of crop protection chemicals. The EPS involved plowing at 20 to 22 cm; fertilization at 59, 104, and 104 kg ha−1 N, P, and K; and less effective herbicide application. Grain yields significantly increased in the IPS and averaged 7840 kg ha−1 compared with 5910 kg ha−1 for the EPS. This difference was due to a 16.8 and 19.6% increase in spike number and kernel number per spike, respectively, while 1000‐kernel weight for the IPS decreased by 6.0% compared with the EPS. Higher seeding rate maximized grain yields in both production systems except for one growing season in the IPS, primarily due to improved spike number. Cultivars responded similarly to seeding rates regardless of the production system. A significant interaction between cultivars and the two production systems was found because some cultivars were highly responsive to the IPS while others were not. Thus, cultivar selection is an important consideration for Croatian farmers when they decide to adopt the IPS.

Dendritic mechanisms of phase precession in hippocampal CA1 pyramidal neurons.

Dual whole-cell patch clamp recordings from the soma and dendrites of CA1 pyramidal neurons located in hippocampal slices of adult rats were used to examine the potential mechanisms of phase precession. To mimic phasic synaptic input, 5-Hz sine wave current injections were simultaneously delivered both to the soma and apical dendrites (dendritic current was 180 degrees out-of-phase with soma). Increasing the amplitude of the dendritic current injection caused somatic action potential initiation to advance in time (move forward up to 180 degrees). The exact pattern of phase advancement is dependent on the dendritic location of input, with more distal input causing a more gradual temporal shift in spike initiation and a smaller increase in spike number. Patterned stimulation of Schaffer collateral/perforant path synaptic input can produce phase precession that is very similar to that observed with sine wave current injections. Finally, the exact amount of synaptic input required to produce phase advancement was found to be regulated by dendritic voltage-gated ion channels. Together, these data demonstrate that the summation of primarily proximal inhibition with an increasing amount of out-of-phase, primarily distal excitation can result in a form of phase advancement similar to that seen during theta activity in the intact hippocampus.

Epinephrine Produces a β-Adrenergic Receptor-Mediated Mechanical Hyperalgesia and In Vitro Sensitization of Rat Nociceptors

Hyperalgesic and nociceptor sensitizing effects mediated by the beta-adrenergic receptor were evaluated in the rat. Intradermal injection of epinephrine, the major endogenous ligand for the beta-adrenergic receptor, into the dorsum of the hindpaw of the rat produced a dose-dependent mechanical hyperalgesia, quantified by the Randall-Selitto paw-withdrawal test. Epinephrine-induced hyperalgesia was attenuated significantly by intradermal pretreatment with propranolol, a beta-adrenergic receptor antagonist, but not by phentolamine, an alpha-adrenergic receptor antagonist. Epinephrine-induced hyperalgesia developed rapidly; it was statistically significant by 2 min after injection, reached a maximum effect within 5 min, and lasted 2 h. Injection of a more beta-adrenergic receptor-selective agonist, isoproterenol, also produced dose-dependent hyperalgesia, which was attenuated by propranolol but not phentolamine. Epinephrine-induced hyperalgesia was not affected by indomethacin, an inhibitor of cyclo-oxygenase, or by surgical sympathectomy. It was attenuated significantly by inhibitors of the adenosine 3',5'-cyclic monophosphate signaling pathway (the adenylyl cyclase inhibitor, SQ 22536, and the protein kinase A inhibitors, Rp-adenosine 3',5'-cyclic monophosphate and WIPTIDE), inhibitors of the protein kinase C signaling pathway (chelerythrine and bisindolylmaleimide) and a mu-opioid receptor agonist DAMGO ([D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin). Consistent with the hypothesis that epinephrine produces hyperalgesia by a direct action on primary afferent nociceptors, it was found to sensitize small-diameter dorsal root ganglion neurons in culture, i. e., to produce an increase in number of spikes and a decrease in latency to firing during a ramped depolarizing stimulus. These effects were blocked by propranolol. Furthermore epinephrine, like several other direct-acting hyperalgesic agents, caused a potentiation of tetrodotoxin-resistant sodium current, an effect that was abolished by Rp-adenosine 3',5'-cyclic monophosphate and significantly attenuated by bisindolylmaleimide. Isoproterenol also potentiated tetrodotoxin-resistant sodium current. In conclusion, epinephrine produces cutaneous mechanical hyperalgesia and sensitizes cultured dorsal root ganglion neurons in the absence of nerve injury via an action at a beta-adrenergic receptor. These effects of epinephrine are mediated by both the protein kinase A and protein kinase C second-messenger pathways.

Stimulation-induced responses of the trigeminal caudal neurons in the brainstem preparation isolated from newborn rats

The brainstem preparation with the trigeminal mandibular nerve attached was isolated from rats postnatal day 0–6 (P0–P6) to test if the potentiation could be induced in neonatal neurons in the trigeminal subnucleus caudalis by stimulation of the primary afferents. The stimulation-induced potentials in 92 neurons recorded extracellularly, and the synaptic potentials in 16 neurons recorded by the whole-cell patch clamp technique were examined. The extracellularly recorded neurons responded to stimulation (0.5 Hz) with either an increase, a decrease, or little change in spike numbers, and were classified as Type 1, Type 2, and Type 3, respectively. Type 1 neurons at P4 and older responded in a low Mg 2+ solution with a progressive increase in spike number lasting for several minutes after the cessation of stimulation, i.e., short-term potentiation, STP. This potentiation was antagonized by 20 μM of (+)-MK-801 hydrogen maleate (MK-801) or 25 μM of 2-amino-5-phosphonovaleric acid. In contrast, Type 1 at P3 and younger did not exhibit STP. The age-related distinct response properties were observed between Type 1 neurons at P4–P6 and at P0–P3. The percentage of Type 1 in studied neurons increased from 24% at P0–P3 to 53% at P4–P6. In the intracellular experiment, the mean latency of excitatory postsynaptic potential (EPSP) of recorded neurons indicated that the conduction velocity of the convergent afferents was 0.37 m/s, in the range of C-fiber. Neurons were classified as Type E and Type I. Type E responded with EPSP only, or with both EPSP and inhibitory postsynaptic potentials (IPSP), while Type I responded with IPSP only. In Type E at P4 and older, a single stimulation produced a burst of spike discharges that lasted for several seconds. Stimulation at a hyperpolarized membrane potential showed that aggregated slow EPSPs lay under a burst of spike discharges, and that slow EPSPs, but not a short-latency EPSP, were completely blocked by MK-801. In contrast, Type E at P3 and younger did not evoke a burst of spikes. Morphological examination of recorded neurons showed that the formation of networks was sparse at P1 and rapidly developed up to P4. The results suggest that: (1) short-term potentiation is induced with the development of synaptic network formation in the caudal nucleus at P4 and older; (2) the summation of N-methyl- d-aspartate (NMDA)-mediated slow EPSPs build up a prolonged depolarization; and (3) the brainstem preparation is applicable for neurophysiological studies on the trigeminal pain system.

Metabotropic glutamate receptors are involved in long-term potentiation in isolated slices of rat medial frontal cortex.

The prelimbic region of medial frontal cortex in the rat receives a direct input from the hippocampus and this functional connection is essential for aspects of spatial memory. Activity-dependent changes in the effectiveness of synaptic transmission in the medial frontal cortex, namely long-term potentiation (LTP) and long-term depression (LTD) can persist for tens of minutes or hours and may be the basis of learning and memory storage. Glutamatergic activation of ionotropic receptors is required to induce both LTP and LTD. We now present evidence of the involvement of metabotropic glutamate receptors in LTP in isolated slices of frontal cortex. Repetitive bursts of stimulation at theta frequencies (TBS) were applied to layer II, and monosynaptic EPSPs were monitored in layer V neurons of the prelimbic area. TBS was found to be more effective at inducing LTP than tetanic stimulation at 100 Hz and produced LTP that lasted >30 min in 8 out of 14 neurons. Tetanic stimulation at 100 Hz in the presence of the N-methyl--aspartate (NMDA)-antagonist 2-amino-5-phosphonopentanoate (AP5) was reported to be a reliable method of inducing LTD in prelimbic cortex (). However we found that this protocol did not facilitate the induction of LTD. The role of metabotropic glutamate receptors (mGluR) in LTP was assessed by using the selective, broad-spectrum antagonist (R, S)-alpha-methyl-4- carboxyphenylglycine (MCPG). This drug significantly reduced the incidence of LTP after TBS to only 1 of 14 neurons (P < 0.02, chi2 test). The pooled responses to TBS in MCPG showed significantly reduced potentiation [(P < 0.02, analysis of variance (ANOVA)]. The broad-spectrum mGluR agonist (1S, 3R)-1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) and the selective group I agonist S-3 hydroxyphenylglycine(S-3HPG) both produced membrane depolarization, an increase in number of spikes evoked by depolarizing current pulses, and a reduction in the afterhyperpolarization. Similar effects were produced by these agonists even when synaptic transmission was blocked by use of the gamma-aminobutyric acid-B (GABAB) receptor agonist, 200 microM baclofen, which suggests that group I mGluRs are present on layer V neurons. We conclude that mGluRs participate in the production of LTP in prelimbic cortex, and that this excitatory effect could be mediated by the postsynaptic group I mGluRs.