Visualization of nutrient translocation in ectomycorrhizal symbioses

Ectomycorrhizal (ECM) fungi receive photosynthetically fixed carbon from the host tree and, in return, supply nutrients such as phosphorus (P) and nitrogen (N) from the soil. An ECM symbiosis system in a two-dimensional, soil-free rhizobox was developed to visualize nutrient translocation during ECM symbioses using a digital, time-course autoradiographic technique with imaging plates. Several studies using 14C and 33P radioisotope tracing experiments are discussed to demonstrate the translocation of 33P-phosphoric acid and photosynthetically fixed carbon between fungi and host trees and between mycelia via mycelia anastomosis. Additionally, novel techniques that can visualize nutrient translocation during mycorrhizal symbioses are discussed.

Neurokinin-1 receptor antagonism in a rat model of subarachnoid hemorrhage: prevention of upregulation of contractile ETB and 5-HT1B receptors and cerebral blood flow reduction

Object Cerebral vasospasm following subarachnoid hemorrhage (SAH) leads to reduced cerebral blood flow (CBF) and to cerebral ischemia, in some cases even producing infarction and long-term disability. The goal of the present study was to investigate the hypothesis that inhibition of neurokinin-1 receptors (NK1Rs) by administration of L-822429 blunts the decrease in CBF as well as cerebrovascular receptor upregulation in an animal model of SAH. Methods Subarachnoid hemorrhage was induced in rats by injection of 250 μl of blood into the prechiasmatic cistern. The NK1R inhibitor L-822429 was injected intracisternally 30 minutes and 24 hours after the induction of SAH. Two days after SAH induction, the basilar arteries were harvested, and contractile responses to endothelin-1 (ET-1, an ETA- and ETB-receptor agonist) and 5-carboxamidotryptamine (a 5-hydroxytryptamine-1 [5-HT1]-receptor agonist) were investigated using sensitive myographs. To determine whether NK1R inhibition had an influence on local CBF after post-SAH, a quantitative autoradiographic technique was used. After SAH, the vascular receptor phenotype was changed in cerebral arteries through upregulation of contractile ETB and 5-HT1B receptors, while regional and total CBF were markedly reduced. Treatment with the selective NK1R inhibitor L-822429 prevented both the receptor upregulation and the reduction in regional and global CBF. Conclusions The data reveal the coregulation of vascular receptor changes and blood flow effects, and also show that interaction with a small-molecule NK1R antagonist is a promising area of focus for the development of specific treatments for SAH.

Group II Selective Metabotropic Glutamate Receptor Agonists and Local Cerebral Glucose use in the Rat

The novel mGluR agonist L Y354740 and a related analogue LY379268 are selective for mGluR2/3 receptors and are centrally active after systemic administration. In this study, rates of local cerebral glucose use were measured using the [14C]2-deoxyglucose autoradiographic technique to examine the functional consequences of their systemic administration in the conscious rat. Both LY354740 (0.3, 3.0, 30 mg/kg) and LY379268 (0.1, 1.0, 10 mg/kg) produced dose-dependent changes in glucose use. After LY354740 (3.0mg/kg), 4 of the 42 regions measured showed statistically significant changes from vehicle-treated controls: red nuclei (−16%), mammillary body (−25%), anterior thalamus (−29%), and the superficial layer of the superior colliculus (+50%). An additional 15 regions displayed significant reductions in function-related glucose use ( P < .05) in animals treated with L Y354740 (30 mg/kg). LY379268 (0.1, 1.0, 10 mg/kg) produced changes in glucose metabolism in 20% of the brain regions analyzed. Significant increases ( P < .05) in glucose use were evident in the following: the superficial layer of the superior colliculus (+81 %), locus coeruleus (+57%), genu of the corpus callosum (+31%), cochlear nucleus (+26%), inferior colliculus (+20%), and the molecular layer of the hippocampus (+14%). Three regions displayed significant decreases: mammillary body (−34%), anteroventral thalamic nucleus (−28%), and the lateral habenular nucleus (−24%). These results show the important functional involvement of the limbic system together with the participation of components of different sensory systems in response to the activation of mGluR2 and mGluR3 with LY354740 and LY379268.

Influence of hypoxia on endothelin-1 binding sites in neonatal porcine pulmonary vasculature

Exposure to chronic hypobaric hypoxia in the newborn piglet causes pulmonary hypertension and structural abnormalities in the intrapulmonary arteries that resemble those seen in babies with pulmonary hypertension of the newborn. To investigate whether the density and subtype of endothelin (ET) receptors in intrapulmonary arteries were altered by exposure to chronic hypobaric hypoxia (50.8 kPa) and changed on recovery, (125)I-labeled ET-1 binding was studied using an in vitro autoradiographic technique on 67 piglets. Plasma ET was measured in 116 control, hypoxic, and recovery animals. In piglets exposed to hypoxia from birth, plasma ET was greater than normal for age (P < 0.05), and the binding density of ET-1 was increased in elastic arteries, muscular arteries, and veins due to an increase in the density of ET(A) binding (P < 0.05 for all vessel types). On recovery, plasma ET level became normal after 6 days. After 1 day of recovery, the binding density of ET-1 and ET(A) was normal in elastic arteries but was greater than normal in muscular arteries even after 6 days (P < 0.05). Exposure to hypoxia from 3 to 6 or from 14 to 17 days did not alter the plasma ET or the binding density in muscular arteries, but the density of binding of ET-1, ET(A), and ET(B) in elastic pulmonary arteries decreased (P < 0.05). On recovery, it returned to normal by 6 days. In summary, the increases in plasma ET and ET-1 and ET(A) binding density suggest a role for ET in the pathogenesis of hypoxic pulmonary hypertension in the newborn period. An initial normal period of adaptation is protective.

Calcium Movements in Traumatic Brain Injury: The Role of Glutamate Receptor-Operated Ion Channels

Ion-selective microelectrodes were used to study acute effects of N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazole (AMPA) receptor blockade on posttraumatic calcium disturbances. An autoradiographic technique with 45Ca2+ was used to study calcium disturbances at 8, 24, and 72 h. Compression contusion trauma of the cerebral cortex was produced by a 21-g weight dropped from a height of 35 cm onto a piston that compressed the brain 2 mm. Pre- and posttrauma interstitial [Ca2+] ([Ca2+]e) concentrations were measured in the perimeter, i.e., the shear stress zone (SSZ) and in the central region (CR) of the trauma site. For the [Ca2+]e studies the animals were divided into controls and groups pretreated with dizocilipine maleate (MK-801) or with 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo[F]quinoxaline (NBQX). In all groups, [Ca2+]e decreased from pretrauma-values of approximately 1 m M to posttraumatic values of 0.1 m M in both the CR and the SSZ. This was followed by a slow restitution toward pretraumatic levels during the 2-h observation period. There was no significant difference in recovery pattern between controls and pretreated animals. Accumulation of 45Ca2+ and serum proteins was seen in the entire SSZ, while neuronal necrosis was confined to a narrow band within the SSZ. The CR was unaffected apart from occasional eosinophilic neurons and showed no accumulation of 45Ca2+. Posttraumatic treatment with MK-801 or NBQX had no obvious effect on neuronal injury in the SSZ. We conclude that (a) acute [Ca2+]e disturbances in compression contusion brain trauma are not affected by blockade of NMDA or AMPA receptors, (b) 45Ca2+ accumulation in the SSZ reflects mainly protein accumulation due to blood–brain barrier breakdown rather than cell death, and (c) acute cellular Ca2+ overload per se does not seem to be a major determinant of cell death after cerebral trauma in our model.

Increased Blood–Brain Permeability with Hyperosmolar Mannitol Increases Cerebral O2 Consumption and O2 Supply/Consumption Heterogeneity

This study was performed to evaluate whether increasing the permeability of the blood–brain barrier by unilateral intracarotid injection of hyperosmolar mannitol would alter O2 consumption and the O2 supply/consumption balance in the ipsilateral cortex. Rats were anesthetized with 1.4% isoflurane using mechanical ventilation. Retrograde catheterization of a unilateral external carotid artery was performed to administer 25% mannitol at a rate of 0.25 ml/kg/s for 30 s. The blood–brain barrier transfer coefficient ( K of 14C-α aminoisobutyric acid was measured in one group (N = 7) after administering mannitol. Regional cerebral blood flow (rCBF), regional arterial and venous O2 saturation and O2 consumption were measured in another group using a 14C-iodoantipyrine autoradiographic technique and micro-spectrophotometry (N = 7). Vital signs were similar before and after administering mannitol. K i was significantly higher in the ipsilateral cortex (IC) (22.3 ± 8.4 μl/g/min) than in the contralateral cortex (CC) (4.4 ± 1.1). rCBF was similar between the IC (105 ± 21 ml/g/min) and the CC (93 ± 20). Venous O2 saturation was lower in the IC (43 ± 7%) than in the CC (55 ± 4%). The coefficient of variation (100 × SD/mean) of venous O2 saturation was significantly elevated in the IC (32.3) compared with the CC (18.2), indicating increased heterogeneity of O2 supply/consumption balance. O2 consumption was higher in the IC (9.6 ± 3.0 ml O2/100 g/min) than in the CC (6.7 ± 1.5). Our data suggested that increasing permeability of the blood–brain barrier increased cerebral O2 consumption and the heterogeneity of local O2 supply/consumption balance.