Efficient border biosecurity inspection leverages superspreading to reduce biological invasion risk

Biological invasions are a growing threat to biodiversity, food security, and economies. Rising pressure from increased global trade requires improving border inspection efficiency. Here, we depart from the conventional consignment-by-consignment approach advocated in current inspection standards. Instead, we suggest a broader perspective: evaluating border inspection regimes based on their ability to reduce propagule pressure across entire pathways. Additionally, we demonstrate that most biosecurity pathways exhibit superspreading behavior, that is, consignments from the same pathway have varying infestation rates and contain rare right-tail events (also called overdispersion). We show that greater overdispersion leads to more pronounced diminishing returns, with consequences on the optimal allocation of sampling effort. We leverage these two insights to develop a simple and efficient border inspection regime that can significantly reduce propagule pressure compared to current standards. Our analysis revealed that consignment size is a key driver of biosecurity risk and that sampling proportional to the square root of consignment size is near optimal. In testing, our framework reduced propagule pressure by 31 to 38% compared to current standards. We also identified opportunities to further improve inspection efficiency by considering additional pathway characteristics (i.e., overdispersion parameters, zero inflation, relative risk, sampling cost, detectability) and developed solutions for these more complex scenarios. We anticipate our result will mitigate biological invasion risk with significant implications for biodiversity conservation, food security, and economies worldwide.

Fuel reduction burning reduces wildfire severity during extreme fire events in south-eastern Australia

Extreme fire events have increased across south-eastern Australia owing to warmer and drier conditions driven by anthropogenic climate change. Fuel reduction burning is widely applied to reduce the occurrence and severity of wildfires; however, targeted assessment of the effectiveness of this practice is limited, especially under extreme climatic conditions. Our study utilises fire severity atlases for fuel reduction burns and wildfires to examine: (i) patterns in the extent of fuel treatment within planned burns (i.e., burn coverage) across different fire management zones, and; (ii) the effect of fuel reduction burning on the severity of wildfires under extreme climatic conditions. We assessed the effect of fuel reduction burning on wildfire severity across temporal and spatial scales (i.e., point and local landscape), while accounting for burn coverage and fire weather. Fuel reduction burn coverage was substantially lower (∼20-30%) than desired targets in fuel management zones focused on asset protection, but within the desired range in zones that focus on ecological objectives. At the point scale, wildfire severity was moderated in treated areas for at least 2-3 years after fuel treatment in shrubland and 3-5 years in forests, relative to areas that did not receive fuel reduction treatments (i.e., unburnt patches). Fuel availability strongly limited fire occurrence and severity within the first 18 months of fuel reduction burning, irrespective of fire weather. Fire weather was the dominant driver of high severity canopy defoliating fire by ∼3-5 years after fuel treatment. At the local landscape scale (i.e., 250 ha), the extent of high canopy scorch decreased marginally as the extent of recently (<5 years) treated fuels increased, though there was a high level of uncertainty around the effect of recent fuel treatment. Our findings demonstrate that during extreme fire events, very recent (i.e., <3 years) fuel reduction burning can aid wildfire suppression locally (i.e., near assets) but will have a highly variable effect on the extent and severity of wildfires at larger scales. The patchy coverage of fuel reduction burns in the wildland-urban interface indicates that considerable residual fuel hazard will often be present within the bounds of fuel reduction burns.

Long-term hydrological response emerges from forest self-thinning behaviour and tree sapwood allometry

Fires in forested catchments are of great concern to catchment managers due to their potential effect on water yield. Among other factors such as meteorological conditions and topography, dominant vegetation and its regeneration traits can play a key role in controlling the variability in the type and recovery-time of the hydrological response between forested catchments after stand-replacing fires. In temperate South-Eastern Australia, a long-term reduction in streamflow from catchments dominated by regenerating tall-wet Eucalyptus obligate seeder forests was observed, which has substantial implications for Melbourne's water supply. While the unusual hydrological response has been attributed to the higher water-use of the regrowth forests, the dominant underlying mechanism has not yet been identified. Here we show analytically and with a closed-form solution that this streamflow pattern can emerge from forest dynamics, namely the combination of growth and tree mortality as constrained by the self-thinning line (STL) and sapwood allometry of the dominant overstory tree species under non-limiting rainfall regimes. A sensitivity analysis shows that observed variations in the relative streamflow anomaly trend can be explained by parameters controlling: (i) the shape of the STL; (ii) regeneration success; (iii) radial tree growth rate; and (iv) fire severity. We conclude that the observed variation in long-term post-disturbance streamflow behaviour might have resulted from different trajectories of forest dynamics and suggest that to minimize uncertainty in future water-balance predictions, eco-hydrological models for even aged forests include a mechanistic representation of stand demography processes that are constrained by forest inventory data.

Assessing the quality of offshore Binomial sampling biosecurity inspections using onshore inspections

Introduction of pests and diseases through trade is one of the main socio-ecological challenges worldwide. Although Binomial sampling inspection at the border can reduce pest entry risk, it is common for consignments to fail inspection, wasting resources for both exporter and importer. Outsourcing the inspection to the exporting country could reduce the cost of inspection for both parties. However, there is then a need to assess the quality of the offshore inspection. In this paper, we develop an inverse method combining past inspection data on the pathway, an onshore inspection sample, and the Beta-Binomial model to infer the sample size of the offshore inspection. We illustrate the method on two case studies: the importation of live plants through germplasm into Australia and the importation of pelleted seeds in New Zealand. In these case studies, we found that detecting four to five infested units in a single onshore inspection was typically sufficient to significantly doubt the presence of a compliant offshore inspection. We also ran a simulation experiment to quantify the statistical power to reject or accept the presence of compliant offshore inspection in practice: In highly infested pathways, we could detect the absence of offshore inspections after inspecting five consignments onshore. Less infested pathways required inspecting 20 to 60 consignments onshore. Our study demonstrates that Binomial sampling onshore can be used to assess the quality of offshore inspections.

The effect of species, size, and fire intensity on tree mortality within a catastrophic bushfire complex

Infrequent, high-intensity disturbances can have profound impacts on forested landscapes, changing forest structure and altering relative species abundance. However, due to their rarity and the logistical challenges of directly observing such extreme events, both the spatial variability of disturbance intensity and the species-specific responses to this variability are poorly understood. We used observed patterns of mortality across a fire severity gradient following the 2009 Black Saturday fires in southeastern Australia to simultaneously estimate (1) species- and size-specific susceptibility to fire-induced mortality and (2) fire intensity. We found broad variation in patterns of fire susceptibility among the 10 tree species (five eucalypts and five non-eucalypts) sufficiently abundant for analysis. Among the eucalypts, Eucalyptus obliqua was the most resistant to fire-induced mortality, with trees of ~25 cm DBH having a 50% probability of surviving even the most intense fires. In contrast, E. regnans had 100% mortality across all size classes when subjected to high-intensity fire. Basal resprouting occurred in six of the study species and, when accounted for, fundamentally changed the mortality profile of these species, highlighting the importance of resprouting as an adaptation to fire in these landscapes. In particular, the two iconic cool temperate rainforest species (Nothofagus cunninghami and Atherosperma moschatum) were strong resprouters (~45% of individuals were able to resprout after being top-killed by fire). We also found evidence for compositional shifts in regeneration above threshold values of fire intensity in cool temperate rainforest and mixed forest sites, both of which have important conservation values within these landscapes. The observed patterns of species- and size-specific susceptibility to fire-induced mortality may be used to anticipate changes in forest structure and composition in the future. In addition, they may also help guide forest management strategies that reduce the length of time individual trees are exposed to potentially lethal fires, thereby increasing the resilience of these forests to future fires.

Estimating Consignment-Level Infestation Rates from the Proportion of Consignment that Failed Border Inspection: Possibilities and Limitations in the Presence of Overdispersed Data

Introduction of pests and diseases through trade is one of the main socioecological challenges worldwide. Targeted sampling at border security can efficiently provide information about biosecurity threats and also reduce pest entry risk. Prioritizing sampling effort requires knowing which pathways are most infested. However, border security inspection data are often right-censored, as inspection agencies often only report that a consignment has failed inspection (i.e., there was at least one unit infested), not how many infested units were found. A method has been proposed to estimate the mean infestation rate of a pathway from such right-censored data (Chen et al.). Using simulations and case study data from imported germplasm consignments inspected at the border, we show that the proposed method results in negatively biased estimates of the pathway infestation rate when the inspection data exhibit overdispersion (i.e., varying infestation rates among different consignments of the same pathway). The case study data also show that overdispersion is prevalent in real data sets. We demonstrate that the method proposed by Chen et al. recovers the median infestation rate of the pathway, rather than its mean. Therefore, it underpredicts the infestation rate when the data are overdispersed (in right-skewed distributions, the mean is above the median). To allow better monitoring and optimizing sampling effort at the border, we recommend that border protection agencies report all the data (the number of infested units found together with the sample size of the inspection) instead of only that the consignment failed inspection.

Lignite effects on NH3, N2O, CO2 and CH4 emissions during composting of manure

Production of compost from cattle manure results in ammonia (NH₃) and greenhouse gas emissions, causing the loss of valuable nitrogen (N) and having negative environmental impacts. Lignite addition to cattle pens has been reported to reduce NH₃ emissions from manure by approximately 60%. However, the effect of lignite additions during the manure composting process, in terms of gaseous emissions of NH₃, nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) is not clear. This composting study was conducted at a commercial cattle feedlot in Victoria, Australia. Prior to cattle entering the feedlot, we applied 4.5 kg m^-2 of dry lignite to a treatment pen, and no lignite to a control pen. After 90 days of occupancy, the cattle were removed and the accumulated manure from each pen was used to form two separate compost windrows (control and treatment). During composting we collected manure samples regularly and quantified gaseous emissions of NH₃, N₂O, CO₂, and CH₄ from both windrows with an inverse-dispersion technique using open-path Fourier transform infrared spectroscopy (OP-FTIR). Over the 87-day measurement period, the cumulative gas fluxes of NH₃, N₂O, CO₂, and CH₄ were 3.4 (± 0.6, standard error), 0.4 (± 0.1), 932 (± 99), and 1.2 (± 0.3) g kg^-1 (initial dry matter (DM)), respectively for the lignite amended windrow, and 7.2 (± 1.3), 0.1 (± 0.03), 579 (± 50) and -0.5 (± 0.1) g kg^-1 DM, respectively for the non-lignite windrow. The addition of lignite reduced NH₃ emissions by 54% during composting, but increased total greenhouse gas (GHG) emissions by 2.6 times. Total N losses as NH₃-N and N₂O-N were approximately 11 and 25% of initial N for the lignite and non-lignite windrows, respectively. The effectiveness of retaining N was obvious in the first three weeks after windrow formation. A cost-benefit analysis indicated that the benefit of lignite addition to cattle pens by reduced NH₃ emission could justify the trade-off of increased GHG emissions.

Stand density, tree social status and water stress influence allocation in height and diameter growth of Quercus petraea (Liebl.)

Even-aged forest stands are competitive communities where competition for light gives advantages to tall individuals, thereby inducing a race for height. These same individuals must however balance this competitive advantage with height-related mechanical and hydraulic risks. These phenomena may induce variations in height-diameter growth relationships, with primary dependences on stand density and tree social status as proxies for competition pressure and access to light, and on availability of local environmental resources, including water. We aimed to investigate the effects of stand density, tree social status and water stress on the individual height-circumference growth allocation (Δh-Δc), in even-aged stands of Quercus petraea Liebl. (sessile oak). Within-stand Δc was used as surrogate for tree social status. We used an original long-term experimental plot network, set up in the species production area in France, and designed to explore stand dynamics on a maximum density gradient. Growth allocation was modelled statistically by relating the shape of the Δh-Δc relationship to stand density, stand age and water deficit. The shape of the Δh-Δc relationship shifted from linear with a moderate slope in open-grown stands to concave saturating with an initial steep slope in closed stands. Maximum height growth was found to follow a typical mono-modal response to stand age. In open-grown stands, increasing summer soil water deficit was found to decrease height growth relative to radial growth, suggesting hydraulic constraints on height growth. A similar pattern was found in closed stands, the magnitude of the effect however lowering from suppressed to dominant trees. We highlight the high phenotypic plasticity of growth in sessile oak trees that further adapt their allocation scheme to their environment. Stand density and tree social status were major drivers of growth allocation variations, while water stress had a detrimental effect on height in the Δh-Δc allocation.

Herbivory of an invasive slug in a model grassland community can be affected by earthworms and mycorrhizal fungi

Invasion of non-native species is among the top threats for the biodiversity and functioning of native and agricultural ecosystems worldwide. We investigated whether the herbivory of the slug Arion vulgaris (formerly Arion lusitanicus; Gastropoda), that is listed among the 100 worst alien species in Europe, is affected by soil organisms commonly present in terrestrial ecosystems (i.e. earthworms-Annelida: Lumbricidae and arbuscular mycorrhizal fungi-AMF, Glomerales). We hypothesized that slug herbivory would be affected by soil organisms via altered plant nutrient availability and plant quality. In a greenhouse experiment, we created a simple plant community consisting of a grass, a forb, and a legume species and inoculated these systems with either two earthworm species and/or four AMF taxa. Slugs were introduced after plants were established. Earthworms significantly reduced total slug herbivory in AMF-inoculated plant communities (P = 0.013). Across plant species, earthworms increased leaf total N and secondary metabolites, AMF decreased leaf thickness. Mycorrhizae induced a shift in slug feeding preference from non-legumes to legumes; the grass was generally avoided by slugs. AMF effects on legume herbivory can partly be explained by the AMF-induced increase in total N and decrease in C/N ratio; earthworm effects are less clear as no worm-induced alterations of legume plant chemistry were observed. The presence of earthworms increased average AMF colonization of plant roots by 140 % (P < 0.001). Total shoot mass was significantly increased by AMF (P < 0.001). These data suggest that the feeding behavior of this invasive slug is altered by a belowground control of plant chemical quality and community structure.

New method of cardiac output measurement using ultrasound velocity dilution in rats

The aim of this study was to validate a new technique for the measurement of cardiac output (CO) based on ultrasound and dilution (COUD) in anesthetized rats. A transit time ultrasound (TTU) probe was placed around the rat carotid artery, and ultrasound velocity dilution curves were generated on intravenous injections of saline. CO by COUD were calculated from the dilution curves for normal and portal hypertensive rats in which CO was known to be increased. COUD was compared with the radiolabeled microsphere method and with direct aortic TTU flowmetry for baseline CO and drug-induced CO variations. CO in direct aortic TTU flowmetry was the ascending aorta blood flow measured directly by TTU probe (normal use of TTU flowmetry). The reproducibility of COUD within the same animal was also determined under baseline conditions. COUD detected the known CO increase in portal hypertensive rats compared with normal rats. CO values by COUD were correlated with those provided by microsphere technique or direct aortic TTU flowmetry (adjusted r = 0.76, P < 10(-4) and r = 0.79, P < 0.05, respectively). Baseline CO values and terlipressin-induced CO variations were detected by COUD and the other techniques. Intra- and interobserver agreements for COUD were excellent (intraclass r = 0.99 and 0.98, respectively). COUD was reproducible at least 10 times in 20 min. COUD is an accurate and reproducible method providing low-cost, repetitive CO measurements without open-chest surgery. It can be used in rats as an alternative to the microsphere method and to direct aortic flowmetry.

Splenorenal shunt blood flow by transit-time ultrasound as an index of collateral circulation in portal hypertensive rats

The aim of this study was to develop a technique that could serve as an index of portosystemic shunt (PSS) blood flow in portal hypertensive rats whose main shunt is the splenorenal shunt (SRS). The main hemodynamic measurements performed were: SRS blood flow by the transit-time ultrasound (TTU) method, percentage of PSS, and regional blood flows by the microsphere method. We determined the accuracy and reproducibility of SRS blood flow measurements under baseline and pharmacological (octreotide) conditions. SRS blood flow was compared with other hemodynamic characteristics. Two models of portal hypertension were used: secondary biliary and dimethylnitrosamine cirrhosis. The SRS blood flow was correlated with mesenteric (r = .76; P < .001) and splenic (r = .67; P < .01) PSS percentages. The intra- and interobserver agreements for SRS blood flow were excellent: ric = .99 and ric = .98, respectively. SRS blood flow was six times higher in portal hypertensive rats (0.6 +/- 0.7 mL . min-1 . 100 g-1) than in sham rats (0.1 +/- 0.1 mL . min-1 . 100 g-1 [P < .01]). Octreotide significantly decreased SRS blood flow but not mesenteric or splenic PSS percentages. SRS is the main PSS in rats. The measurement of SRS blood flow by TTU is accurate and reproducible. This method can be used to identify new mechanisms in hemodynamic studies that differ from those identified by the measurement of the percentage of PSS by the microsphere method, especially in pharmacological studies.

Measurement of collateral circulation blood flow in anesthetized portal hypertensive rats

AIMS

The aim of this study was to develop a technique to measure collateral blood flow in portal hypertensive rats.

METHODS

Morphological techniques included inspection, casts and angiographies of portosystemic shunts. The main hemodynamic measurements were splenorenal shunt blood flow (transit time ultrasound method), percentage of portosystemic shunts and regional blood flows (microsphere method). In study 1, a model of esophageal varices was developed by ligating the splenorenal shunt. In study 2, morphological studies of the splenorenal shunt were performed in rats with portal vein ligation. In study 3, the relationship between splenorenal shunt blood flow with percentage of portosystemic shunts was evaluated in dimethylnitrosamine cirrhosis. In study 4, secondary biliary, CCl4 and dimethylnitrosamine cirrhosis were compared. In study 5, rats with portal vein ligation received acute administration of octreotide. In study 6, rats with dimethylnitrosamine cirrhosis received acute administration of vapreotide.

RESULTS

Blood flow of para-esophageal varices could not be measured. SRS blood flow was correlated with the mesenteric percentage of portosystemic shunts (r = 0.74, P < 0.05), splenic percentage of portosystemic shunts (r = 0.54, P < 0.05) and estimated portosystemic blood flow (r = 0.91, P < 0.01). Splenorenal shunt blood flow was 6 to 12 times higher in portal hypertensive rats, e.g., in portal vein ligated rats: 2.8 +/- 2.7 vs 0.3 +/- 0.1 mL.min-1 in sham rats (P < 0.01), and was similar in the different cirrhosis models but was higher in portal vein ligated rats than in cirrhotic rats (1.2 +/- 0.7 vs 0.6 +/- 0.6 mL.min-1.100 g-1, P = 0.05). Octreotide significantly decreased splenorenal shunt blood flow: -23 +/- 20% (P < 0.01) vs -6 +/- 8% (not significant) in placebo rats. The variation of splenorenal shunt blood flow after vapreotide was significant but not that of the splenic percentage of portosystemic shunts compared to placebo.

CONCLUSIONS

The splenorenal shunt is the main portosystemic shunt in rats. The measurement of splenorenal shunt blood flow is easy, accurate and reproducible and should replace the traditional measurement of the percentage of portosystemic shunts in pharmacological studies.

Hemodynamic effects of terlipressin and octreotide administration alone or in combination in portal hypertensive rats

BACKGROUND/AIMS

The action sites and kinetic effects of octreotide and terlipressin may be different. Therefore, we studied the hemodynamic effects of acute administration of these drugs alone or in combination in rats with portal hypertension due to portal vein ligation.

METHODS

In a first study performed in anesthetized rats, hemodynamics were measured before and after drug administration (placebo, octreotide: 8 microg x kg(-1) x h(-1) for 30 min, terlipressin: 50 microg/kg bolus, terlipressin + octreotide at the same doses). The second study, performed in conscious rats, included the same groups and drug doses; hemodynamics were measured every 10 min for 1 h. The third study tested the effect of preinfusion of octreotide on responsiveness to terlipressin.

RESULTS

Terlipressin produced more marked systemic effects than octreotide by decreasing heart rate and cardiac output and increasing mean arterial pressure. Terlipressin produced a greater decrease in portal pressure than octreotide: placebo: -3+/-5%, terlipressin: -42+/-8%, octreotide: -16+/-10%, combination: -44+/-8% (conscious rats at 20 min, p<10(-4)). The decrease in portal pressure was immediate and lasted at least 60 min with both drugs. Octreotide significantly decreased spleno-renal shunt blood flow (% variation): placebo: -6+/-8, terlipressin: -15.5+/-20, octreotide: -22.5+/-20, combination: -27+/-10 (p<10(-2)). Octreotide preinfusion significantly increased the responsiveness of arterial pressure and heart rate to terlipressin.

CONCLUSIONS

Terlipressin decreases portal pressure significantly more than octreotide, while only octreotide significantly decreases collateral blood flow. Simultaneous administration of these drugs does not have significant additive effects but has complementary effects. The preadministration of octreotide alters systemic response to terlipressin.

Effects of antidotes to cocaine on the deregulation of the baroreflex by the alkaloid

Cocaine exerts in the rat an inhibitory effect on the baroreflex induced by bilateral clamping of the carotid arteries. The present series of experiments were designed to test the effectiveness of cocaine antidotes on this deregulation of the baroreflex. Sprague-Dawley rats were fitted under pentobarbital anesthesia with a catheter in the caudal artery, and their carotid arteries were exposed. The pressure signal from the caudal artery was treated on line by a microcomputer for continuous display of blood pressure and heart rate measurements. The animals were administered intraperitoneally either 50 mg cocaine or an equal volume of saline. Five minutes later, they were administered either saline or proven antidotes to cocaine (diltiazem, nicardipine, enzyme converting inhibitor [ECI], enalaprilat associated with diazepam). After 2 min, stimulation of the baroreceptor was performed by bilateral clamping of the two carotids for a period of 2 min. The measures of the maximal variation in systolic pressure before and after clamping indicated a significant difference between saline and cocaine treated animals (P < 0.05), with the former displaying a much greater increment in blood pressure after clamping. The cocaine-treated animals, administered diltiazem, nicardipine, and ECI associated with diazepam, presented after clamping of the carotid arteries a normal baroreflex with increments in blood pressure not significantly different from those occurring in the animals receiving saline, but significantly different from those administered cocaine only (P < 0.05). Baroreflex deregulation by cocaine may also be restored by an angiotensin II receptor antagonist. The possible role of this peptide in mediating in part baroreflex activity is discussed.

Inhibition by cocaine of the baroreflex in the rat

Sprague-Dawley rats were fitted under pentobarbital anesthesia with a catheter in the caudal artery and their carotid arteries were exposed. The pressure signal from the caudal artery was treated on line by a microcomputer for continuous display of blood pressure and heart rate measurements. The animals were administered intraperitoneally either 50 mg/kg of cocaine or an equal volume of saline. Five minutes later, stimulation of the baroreflex was performed by bilateral clamping of the two carotids for a period of 2 min. The same maneuver was repeated at 12, 24, and 31 min. Analysis of variance for repeated measures indicated that before carotid artery clamping, there was no significant difference between blood pressure measurements of the saline- and cocaine-treated groups. A two-factor analysis of variance of the repeated measures of the maximal variation in systolic pressure after each clamping showed a significant difference between control and cocaine-administered groups (P < 0.001), with the former displaying a much greater increment in blood pressure after carotid clamping. Cocaine exerts an inhibitory effect on the baroreflex that may be mediated through the increased angiotension II caused by the alkaloid.

[Potentiation of the acute toxic effects of cocaine by ethyl alcohol]

Ethyl alcohol increases significantly the lethality of cocaine intoxication in the rat. This lethality is not modified by nicardipine or flunarizine, antidotes to cocaine, and might be due to the formation of a newly identified active metabolite cocaethylene. In addition alcohol like cocaine inhibits the baro receptor reflex.

Microvascular effects of cocaine; interaction with nitrendipine and enalaprilat

Cocaine abuse can cause cardiovascular damage leading to hypertension, myocardial ischaemia and infarction. This might be partly due to the effects of cocaine on the microcirculation about which little is known, although its effects on the macrovessels are well documented. Accordingly, we used in vivo videomicroscopy to study the vasoconstrictive effect of cocaine on arterioles of different diameter. They were classified into three orders (A2, A3, A4) according to their position in the microvascular network and their diameter. Since calcium antagonists have been reported to exert a protective effect against the cardiovascular disorders induced by cocaine, we tested the hypothesis that this protective action occurs in the microcirculation. We found that intra-arterial administration of the calcium antagonist Nitrendipine greatly inhibited the vasoconstriction induced by cocaine in all three arteriole orders. The degree of inhibition ranged from 44 to 56%. Combined administration of benzodiazepine and an angiotensin converting enzyme inhibitor has also been reported to protect rats against cocaine-induced hypertension and to increase survival rates after a toxic dose of cocaine. Since the mechanisms of this protection are not yet clear, we also studied the effect of the angiotensin converting enzyme inhibitor Enalaprilat on cocaine-induced vasoconstriction. Intra-arterial administration of Enalaprilat inhibited this vasoconstriction slightly but significantly in arteriole orders 2 and 3 by 27 and 24% respectively, but not in order 4. We concluded that Nitrendipine is a powerful inhibitor of cocaine-induced vasoconstriction in the microcirculation. The small but significant inhibition found with Enalaprilat for the larger arterioles suggests that the local angiotensin II level may affect the response to cocaine. However, since the Enalaprilat-induced inhibition was very limited, we conclude that mechanisms other than those occurring in the peripheral microcirculation account for the protection afforded by Enalaprilat against the harmful effects of cocaine.

Antidotes to lethal cocaine toxicity in the rat

Cocaine, like catecholamines or angiotensin II, may induce lethal cardiac or cerebral damage. Restrained rats were fitted with a caudal arterial catheter for on-line cardiovascular monitoring and antidote administration. They were given 60 mg/kg of cocaine i.p., a dose which produces behavioral and cardiovascular effects, convulsions and death in an average time of 10 min. Selected antidotes were administered 5 min after the lethal dose of cocaine. Incidence of lethality was not changed by propranolol, prazosin, labetalol, diazepam or enalaprilat, a converting enzyme inhibitor. Animals treated with any one of the following agents, alpha- or beta-blockers, diazepam or competitive inhibitors of angiotensin II [Sar-1-ile-8] and [Sar-1-thr-8] angiotensin II, presented myocardial infarction. All animals treated with calcium channel antagonists or enalaprilat, whether they survived or not, did not present myocardial infarction. Treatment with nitrendipine, flunarizine or diltiazem, resulted in survival of the animals with no observable aftereffects. Similar results were observed when enalaprilat was administered, with diazepam as an antidote, to a lethal dose of cocaine. Antagonists to the sympatho-adrenal system and to the renin angiotensin system appear to be effective antidotes to cocaine toxicity in the present experimental model.

Interactions of nimodipine and cocaine on endogenous catecholamines in the squirrel monkey

The effects of nimodipine on the cocaine-induced alterations in blood pressure, heart rate, and plasma catecholamines were studied in the squirrel monkey. Cocaine in intravenously administered doses of 0.5, 1, and 2 mg/kg produced significant increases in blood pressure and significant decreases in heart rate. These cardiovascular changes were associated with transient episodes of arrhythmias and with significant increases in plasma concentrations of dopamine, epinephrine, and norepinephrine. Nimodipine, 1 micrograms/kg/min for 5 min administered intravenously 5 min after cocaine, corrects the cardiovascular and plasma catecholamine concentration changes induced by this alkaloid. The same dose of nimodipine administered 5 min before cocaine prevents elevations of blood pressure. Plasma catecholamine increments are also prevented except for the highest dose of cocaine. Cardiovascular changes induced by cocaine administration in the squirrel monkey are temporally associated with significant increments in plasma catecholamines. Administration of nimodipine prevents or minimizes these endocrine and physiologic changes.

[Cocaine and disturbances of adrenergic neurotransmission]

Cocaine releases peripheral and central stores of catecholamines and their plasma concentration increases in very significantly under the influence of the drug. One also observes a vaso-constriction of cerebral and coronary arteries. Decreases in blood flow through those vessels have been observed in cocaine addicts examined with the magnetic resonance and positron emission tomography techniques. Some of these changes may still be present 15 days after withdrawal. The authors suggest an hypothesis to account for the general mode of action of cocaine. The synaptic increase in catechol produced by this drug is calcium dependent and would induce an "up regulation" of receptor proteins of calcium channels with increased calcium intracellular fluxes. There would be an increase in catecholamine neuronal turnover and synthesis not a depletion. Conversely the adrenergic post-synaptic receptors would undergo a "down regulation". Such impairment of adrenergic neurotransmission is associated with an increase in Angiotensin II release and a decreased GABA activity. Sensory stimuli resulting from this impairment induce a dominant memory associated with drug seeking and consuming behavior.

[Calcium channel modulators as antidotes in fatal imipramine poisoning]

Calcium entry modulators were tested as antidotes to imipramine lethal toxicity. 42 rats were administered intraperitoneally 85 mg/kg of imipramine. In 6 control rats, hypotension and bradycardia were observed. Survival time was 15' +/- 5'. Survival time of rats treated with intraarterial nitrendipine was 21' +/- 11'. Survival time of 5 out of 6 rats treated by intraarterial verapamil or diltiazem was respectively 19'00" +/- 14'30" and 40'30" +/- 32'00". 5 out of 6 rats treated by intraarterial nimodipine, as well as all of the rats treated by flunarizine or nicardipine survived and were alive and active 48 hours later. Intoxication with imipramine may induce life threatening complications for which there are no specific medication. Nicardipine might be considered in the treatment of acute poisoning by imipramine and related tricyclic compounds.

[Analgesic effect of tiapride in healthy volunteers]

Twenty male volunteers, average age 23, were studied in the fasting state at a week interval in the morning between nine and ten a.m. A brachial blood pressure cuff was inflated to a pressure of 250 mmHg and the subject squeezed a hand dynamometer to half of maximum strength for two ten seconds periods. The subject then started to report his sensory experience every ten seconds for 15 minutes by pointing at a scale consisting of six categories from "nothing" to "extremely painful". The first trial was performed on all unmedicated subjects, the non dominating arm was used. The second trial was performed on the opposite arm, 45 minutes after oral double-blind randomized administration of a capsule containing either 1 g aspirin or 300 mg tiapride. The answers of the subjects were statistically analysed using paired comparisons tests. Results indicate that tiapride exerts a significant antalgic effect from the 6th minute to the end of the experiment when compared to the control (p less than 0.05 to p less than 0.01). Aspirin produces a similar antalgic effect which occurs earlier, after 4 minutes. The mechanism of the antalgic effect of tiapride has been attributed to the release of beta-endorphine produced by benzamide which is associated with a decrease in plasma dopamine and a parallel increase in prolactine.

Developmental changes in the pattern of amino acid transport at the blood-brain barrier in rats

Oldendorf's method has been widely used to estimate and characterize the transport of amino acids across the blood-brain barrier in rats. However, it cannot be used with very young animals. A modification of this method (retrograde injection into the right brachial artery, instead of orthograde injection into the common carotid artery) allowed the estimation of the brain uptake index of some amino acids in 5-, 12- and 19-day-old rats, as well as the study of self- and cross-inhibition and of sodium dependency. The results obtained showed that the pattern of transport of amino acids was different in 5-day-old and in 19-day-old rats. In young rats, besides the presence of the L-system, which transported large neutral amino acids as in adult rats, the presence of another system of transport for neutral amino acids was strongly suggested. The activity of this system which transported alanine, serine, cysteine and threonine, decreased during development and it had many of the characteristics of the ASC system described by Christensen. In addition, the presence of a system of transport for beta-amino acids at the blood-brain barrier is suggested.

[Comparison of blood-brain barrier of various amino acids in 5, 12 and 21 day old rats]

The bolus injection technique described by Oldendorf has been modified in order to study the blood brain transport of amino acids in immature Rats. The brain uptake indices (BUI) of lysine, leucine, alanine, proline, glucose and glutamic acid have been compared at tracer dose and at 10 mM concentration in 5, 12 and 21 day-old Rats. At every time-period, the BUIs of proline, glycine and glutamic acid were not decreased by the 10 mM concentration and were similar to that of sucrose. Between day 5 to 21, the saturable fraction of the BUI of lysine decreased by 50% that of leucine increased by about 50% and that of alanine which represented only a small fraction of the total uptake decreased with time; the unsaturable fraction of the BUIs of these 3 amino acids was higher than the BUI of sucrose and declined progressively.