Ventilation After Supplemental Oxygen Administration at High Altitude☆

OBJECTIVE

The present study assessed the effects of acute hyperoxia on resting-minute ventilation (VE) during altitude acclimatization to 4300 m.

METHODS

Resting-minute ventilation, end-tidal partial pressure carbon dioxide (PETCO2) and oxygen (P(ET)O2), and arterial oxygen saturation (SpO2) were measured during chronic poikilocapnic hypobaric hypoxia, supplemental oxygen breathing, and the subsequent return to hypobaric poikilocapnic hypoxia at altitude. Fifteen adult male lowlanders were studied at sea level and on the 3rd and 12th days at 4300 m. At sea level, subjects first breathed room air that was followed by 25-minute steady-state poikilocapnic hypoxia (FIO2 = 0.125). Ventilatory responses to acute poikilocapnic hypoxia (APH) were collected over the first 1-10 minutes, and responses to chronic poikilocapnic hypoxia (CPH) were collected over the last 3 minutes of the hypoxia exposure. At altitude, CPH was provided by ambient-air breathing (PIO2 = 86 mm Hg) that was interrupted by 10 minutes of oxygen breathing (FIO2 = 1.0, PIO2 = 460 mm Hg) and then a subsequent return to ambient air to measure APH ventilatory responses.

RESULTS

Between day 1 and day 12, during CPH, VE and SpO2 increased (P < .05) by 46% and 6%, respectively, whereas P(ET)CO2 decreased. On day 3 and day 12, breathing oxygen did not lower VE compared with CPH. However, the VE during APH immediately after oxygen breathing at high altitude was always greater (P < .05) than during CPH and did not change with duration of residence at altitude.

CONCLUSIONS

These results show that short-duration oxygen breathing increases the subsequent ventilatory response to poikilocapnic hypoxia in altitude-acclimatized lowlanders, resulting in a transient elevation of SpO2.

Whole-Farm Nitrogen Balance on Western Dairy Farms

Environmental legislation has made it necessary for livestock producers to be able to quantify and adjust the N balance on their farms. Whole-farm N balance and efficiencies were computed for 41 commercial dairies in Utah and Idaho using the University of Maryland Nutrient Balancer. The average N balance, or unaccounted for N, was 81 tonnes per year for the average herd size of 466 cows with 35.8% of the inputs accounted for in the outputs. The major inputs for farms that grew crops (n = 23, herd size = 284 total cows) were imported feed (57.4% of all inputs) and nitrogen fixation (30% of inputs). The major outputs were animal products (primarily milk and some meat, 80% of outputs). For farms that grew no crops (n = 18, herd size = 700 total cows), 98% of the inputs were from imported feed. Of the outputs, 57% of the N was in animal products and 42.9% in manure and compost. Whole-farm balance per product for those farms that grew crops was most affected by herd N utilization efficiency (kg feed N per kg product N), crop N utilization efficiency, and availability of manure N applied to crops, while manure N storage efficiency was of lesser importance. For farms that grew no crops, whole-farm N balance per product was most affected by herd N utilization efficiency and manure N storage efficiency. Maximizing conversion of feed N to product N was the best way to reduce whole-farm N balance.

The Association Between Milk Urea Nitrogen and DHI Production Variables in Western Commercial Dairy Herds

A retrospective observational study was conducted using data from Dairy Herd Improvement monthly tests to investigate the association between milk urea nitrogen (MUN) concentration and milk yield, milk protein, milk fat percentage, SCC, and parity for commercial Holstein and Jersey herds in Utah, Idaho, and Montana. Mean MUN for Holstein cows was 15.5 mg/ dl (5.5 mmol/L) MUN and 14.1 mg/dl (5.0 mmol/L) for Jersey cows. Mean MUN, categorized by 30-d increments of days in milk (DIM), paralleled changes in milk values and followed a curvilinear shape. For Holstein cows, concentrations of MUN were different among lactation groups 1, 2, and 3+ for the first 90 DIM for Holsteins. Overall, concentrations of MUN were lower during for the first 30 DIM compared with all other DIM categories for both Holstein and Jersey cows. Multivariate regression models of MUN by milk protein showed that as the milk protein percentage increased, MUN concentration decreased; however, models for Jersey cows showed that MUN did not decrease significantly until above 3.4% milk protein. Milk fat percentage also decreased as MUN increased, but by only 1 mg/dl MUN over the range of 2.2 to 5.8% milk fat. Somatic cell count showed a negative relationship with MUN. Holstein cows with milk protein percentage >3.2% had lower MUN compared with cows having milk protein <3.2% for milk yields from 27.3 to 54.5 kg/d and lower than cows having a milk protein <3.0% for milk yield of 54.5 to 63.6 kg/d. In Jersey cows, MUN concentrations were not different among milk protein percentage categorized by milk yield. This study found that MUN was inversely associated with milk protein percentage and paralleled change in milk yield over time.

Differential responses of IGF-I molecular complexes to military operational field training

Insulin-like growth factor (IGF) I and IGF binding proteins (IGFBPs) modulate metabolic activity and tissue repair and are influenced by nutritional status. IGF-I circulates in free, ternary [IGF-I + IGFBP-3 + acid labile subunit (ALS)], and binary (IGF-I + IGFBP) molecular complexes, and the relative proportions regulate IGF-I extravascular shifting and bioavailability. This study examined the hypothesis that sustained physical activity and sleep deprivation superimposed on a short-term energy deficit would alter the IGFBP concentrations and alter the proportions of IGF-I circulating in ternary vs. binary molecular complexes. Components of the IGF-I system (total and free IGF-I; IGFBP-1, -3, and ALS; nonternary IGF-I and IGFBP-3), biomarkers of metabolic and nutritional status (transferrin, ferritin, prealbumin, glucose, free fatty acids, glycerol, beta-hydroxybutyrate), and body composition were measured in 12 men (22 +/- 3 yr, 87 +/- 8 kg, 183 +/- 7 cm, 20 +/- 5% body fat) on days 1, 3, and 4 during a control and experimental (Exp) period. During Exp, subjects performed prolonged work (energy expenditure of approximately 4500 kcal/day) with caloric (1600 kcal/day) and sleep (6.2 h total) restriction. IGF-I and IGFBP-3 were measured by immunoassay before and after immunoaffinity depletion of ALS-based complexes (i.e., ternary complex removal). Exp produced losses in body mass (-3.0%), lowered total IGF-I (-24%), free IGF-I (-42%), IGFBP-3 (-6%), nonternary IGF-I (-27%), and IGFBP-3 (-16%), and increased IGFBP-1 (256%). No Exp effects were observed for ALS. No changes were observed in the proportion of IGF-I circulating in free ( approximately 1.2%), ternary ( approximately 87.4%), or nonternary ( approximately 11.4%) molecular complexes. During Exp, glucose concentrations were lower on day 3, but days 1 and 4 were statistically similar. In conclusion, during a short-term energy deficit in young, healthy men, 1). IGF-I system components differentially respond (both in direction and magnitude) to a given metabolic perturbation and 2). the relative proportion of IGF-I sequestered in ternary vs. nonternary molecular complexes appears to be well maintained.

Diet and physical performance

This paper provides a historical summary of military nutrition research into the role of diet for sustaining soldier physical performance. Studies of underfeeding document that physical performance is preserved during several days of underfeeding provided sufficient carbohydrate and minerals are consumed to minimize the diuresis associated with semi-starvation diets and serial intake of carbohydrate is available to support metabolism during prolonged work. The Military Recommended Dietary Allowances, AR 40-25, currently recommends that when restricted rations are required, that the ration contain at least 1,100-1,500 kcal, 50-70 g of protein, and a minimum of 100 g of carbohydrate on a daily basis. This low energy diet, however, is not recommended for subsistence for longer than 10 consecutive days. Dietary carbohydrate intakes of approximately 300-400 g will more closely match the quantity of carbohydrate oxidized to meet daily energy requirements during field operations. Research into the potential advantages of dietary supplements has generally not proved advantageous when compared to eating a well balanced diet. Future investigations of the role of diet for sustaining soldier health and performance should be directed toward a better understanding of the influence of energy intake and macro-nutrient composition for preserving lean body mass, reducing susceptibility to illness and injury and enhancing recovery during and after sustained operations.

Whole-farm phosphorus balance on western dairy farms

Environmental concerns have focused attention on animal agriculture and its contribution to P accumulation in soils and runoff to surface waters. Monitoring P inputs and outputs on farms is a means of calculating the potential P build-up in farm soils. The objective of this study was to determine whole-farm P balance and the relative importance of the farm components (herd, manure storage, cropping systems) that contribute to it in dairies of the western United States. Whole-farm balances were computed for 41 commercial dairies in Utah and Idaho using the Maryland Nutrient Balancer. The average whole-farm P balance in the study was 6.6 tonne/yr with an average herd size of 466 cows. Imported feed made up 85.4% of the total P inputs and exported animal products (milk and meat), and manure and compost made up 53.1 and 45.9%, respectively, of the total P outputs. Farms were divided into those that grew crops and those that did not. Whole-farm balance (kg of P balance per animal) for farms that grew crops had more unaccounted for P (difference between P inputs and output) than farms that grew no crops. They also had more imported fertilizer and less imported feed and exported manure and compost. Multiple regression analysis of the relative effects of herd management, manure storage, and cropping system on whole-farm balance per product found that herd P utilization efficiency was the most important factor in determining whole-farm P balance on farms where crops were grown. Crop uptake of available P was the only other subsystem important for these farms. Increased conversion of feed P to P in product is an important way to decrease whole-farm P balance.

Radioimmunoassay of prolactin for the meerkat (Suricata suricatta), a cooperatively breeding carnivore

We report the development and validation of a highly specific heterologous radioimmunoassay (RIA) to measure meerkat prolactin (PRL) by using rabbit antiserum to human prolactin and canine [125I]iodo-PRL. Dilutions of meerkat pituitary standard and plasma gave parallel inhibition curves in the assay. Gel filtration of meerkat pituitary extracts and canine [125I]iodo-PRL run separately on a Sephadex G-100 generated identical peaks of activity, and Western blot analysis of meerkat pituitary extract with the human prolactin antiserum used in the RIA gave a molecular weight similar to canine prolactin (21kDa). We carried out a biological validation of the prolactin assay by administering three different doses each of sulpiride and cabergoline to adult male meerkats. Increasing doses of sulpiride and cabergoline caused substantial increases and decreases, respectively, in the plasma prolactin of the study animals as expected. Activation of the stress response in meerkats by capture and ketamine hydrochloride anesthesia caused short-term but significant increases in prolactin levels in individuals bled repeatedly. The RIA developed and described here was able to determine plasma concentrations of prolactin in all animals sampled. We conclude, however, that it will be important in all future studies to confine blood sampling times to 4-7 min after capture/administration of anesthesia to avoid the confounding effects of the stress response on prolactin levels.

Measurement of insulin-like growth factor-I during military operational stress via a filter paper blood spot assay

Insulin-like growth factor-I (IGF-I) is sensitive to nutritional stress and is reduced in soldiers during stressful field training. Methods have recently been developed to measure IGF-I from filter paper blood spots. Filter paper has advantages over traditional blood sampling in that neither blood separation equipment nor refrigeration is necessary after sample collection. This study determined whether filter paper blood spots collected in a field environment could measure IGF-I and subsequent changes during military operational stress. Thirty-four Marines participating in an 8-day military field exercise characterized by near-continuous physical work (total daily energy expenditure 17-25 MJ/day) and underfeeding (dietary intake 7.0 MJ/day) had blood samples taken on day 0, day 4, and day 8. IGF-I was measured by filter paper blood spot assays from fingertip blood samples and by conventional methods using serum. Correlation and measurement agreement were assessed. Blood spot (Day 0 152 +/- 6 ng mL(-1) > Day 4 111 +/- 6 ng mL(-1) > Day 8 74 +/- 4 ng mL(-1)) and serum IGF-I (Day 0 412 +/- 10 ng mL(-1) > Day 4 258 +/- 14 ng mL(-1) > Day 8 203 +/- 13 ng mL(-1)) concentrations declined (p < 0.05) progressively over the 8-day exercise. Overall, the two methods significantly (p < 0.05) correlated (r = 0.92); however, the blood spot values were on average 61% lower than serum, but could be used to predict serum values ( +/- 10%). IGF-I is a biomarker of metabolic status. The filter paper blood spot method for IGF-I detected reductions accompanying nutritional stress and may be of potential value for characterizing the IGF-I response when conventional blood sampling methods are not feasible.

Spatial variation of plasma flow in the oxazolone-stimulated microcirculation

INTRODUCTION

In cutaneous lymphocytic inflammation, enhanced regional blood flow is suggested by persistent erythema and warmth. Direct assessment of the microcirculation, however, has been limited by tissue edema and skin thickness.

METHODS

To assess the microcirculatory adaptations to the epicutaneous antigen oxazolone, we studied the first pass kinetics and microvascular topography of the inflammatory skin microcirculation using a specially adapted epi-illumination intravital microscopy system. The fluorescence intravital videomicroscopy and streaming image acquisition of fluorescein-labeled dextran (approximately 500,000 MW) injections were used to assess changes in plasma flow.

RESULTS

Direct plasma tracer injections of both the oxazolone-stimulated and control microcirculation demonstrated comparable transit times (leading edge and intensity-weighted peak times) from the carotid artery to the superficial vascular plexus (p > 0.05). In contrast to transit times, continuous infusion of the plasma tracer demonstrated a significant increase in the delivery of the fluorescein-labeled dextran to the oxazolone-stimulated microcirculation. Quantitative morphometry of intravital microscopic images demonstrated a 2.2-fold increase in the mean diameter of vessels in the superficial vascular plexus (p < 0.01). Further, fluorescence intensity mapping indicated that the increase was associated with increased perfusion of focal regions of the superficial vascular plexus (p < 0.001).

CONCLUSIONS

These results indicate that the oxazolone-stimulated adaptations of the inflammatory microcirculation include both microvascular dilatation and the redistribution of plasma flow.

Relationship between DHI production values and Myers-Briggs type indicator as a measure of management ability

Associations between owners' Myers-Briggs Type Indicator (MBTI) preferences (E = extraversion vs. I = introversion; S = sensing vs. N = intuition; T = thinking vs F = feeling; J = judging vs. P = perceiving) and 21 Dairy Herd Improvement (DHI) production variables were determined on 60 farms. Of 60 dairy farmers participating, 51 were from Holstein farms (85%) and nine from farms with other breeds, primarily Jersey. Cows were milked either twice (n = 44 herds, 73%) or three times (n = 16) per day. Farmers were evenly split between the "E" and "I" dimension, whereas 93% of the farmers were "S," 75% "T," and 62% "J.". Individuals with a preference for the "I" dimension were associated with higher peak and mature equivalent milk yield than those individuals with a preference for the "E" dimension. The "T" and "J" dimensions had a significantly higher percentage of the herd with records usable by USDA and a lower percentage of animals pregnant by the goal set by the dairy producer than the "F" and "P" dimensions. Herds managed by individuals with a combination preference of "E" and "P" produced 7 to 10 kg of 3.5% FCM/cow per day less or 1,820 to 2,752 kg/ cow RHA ECM less than other combinations of the "E-I" and "J-P" dimensions. Those herds also had longer days dry and a lower percentage of records usable by USDA, suggesting that the "E-P" preference is less favorably associated to those measures of herd performance. The MBTI had limited association with many DHI production variables, but relationships to measures of labor and business management should be examined.

The binding of Xanthophylls to the bulk light-harvesting complex of photosystem II of higher plants. A specific requirement for carotenoids with a 3-hydroxy-beta-end group

The pigment composition of the light-harvesting complexes (LHCs) of higher plants is highly conserved. The bulk complex (LHCIIb) binds three xanthophyll molecules in combination with chlorophyll (Chl) a and b. The structural requirements for binding xanthophylls to LHCIIb have been examined using an in vitro reconstitution procedure. Reassembly of the monomeric recombinant LHCIIb was performed using a wide range of native and nonnative xanthophylls, and a specific requirement for the presence of a hydroxy group at C-3 on a single beta-end group was identified. The presence of additional substituents (e.g. at C-4) did not interfere with xanthophyll binding, but they could not, on their own, support reassembly. cis isomers of zeaxanthin, violaxanthin, and lutein were not bound, whereas all-trans-neoxanthin and different chiral forms of lutein and zeaxanthin were incorporated into the complex. The C-3 and C-3' diols lactucaxanthin (a carotenoid native to many plant LHCs) and eschscholtzxanthin (a retro-carotenoid) both behaved very differently from lutein and zeaxanthin in that they would not support complex reassembly when used alone. Lactucaxanthin could, however, be bound when lutein was also present, and it showed a high affinity for xanthophyll binding site N1. In the presence of lutein, lactucaxanthin was readily bound to at least one lutein-binding site, suggesting that the ability to bind to the complex and initiate protein folding may be dependent on different structural features of the carotenoid molecule. The importance of carotenoid end group structure and ring-to-chain conformation around the C-6-C-7 torsion angle of the carotenoid molecule in binding and complex reassembly is discussed.

Evolution and development of sex differences in cooperative behavior in meerkats

In cooperatively breeding birds, where helpers of both sexes assist with the provisioning and upbringing of offspring who are not their own, males tend to contribute more than females to rearing young. This sex difference has been attributed to paternity uncertainty, but could also occur because males contribute more where they are likely to remain and breed in their group of origin. In contrast to most birds, female meerkats (Suricata suricatta) are more likely to breed in their natal group than males. We show that female meerkat helpers contribute more to rearing young than males and that female helpers feed female pups more frequently than males. Our results suggest that sex differences in cooperative behavior are generated by sex differences in philopatry and occur because females derive greater direct benefits than males from raising recruits to their natal group. These findings support the view that direct, mutualistic benefits are important in the evolution of specialized cooperative behavior.

Bioelectrical impedance to estimate changes in hydration status

Bioelectrical impedance analysis (BIA) has been suggested as a simple, rapid method to assess changes in hydration status. BIA measures the electrical impedance to a low amperage current that is affected by both water and electrolyte content of the body. While BIA can reliably estimate total body water and body density in euhydrated individuals under standardized clinical conditions, changes in fluid and electrolyte content can independently alter bioimpedance measurements. Because hydration changes typically involve concomitant changes in fluid and electrolyte content, the interpretation of a change in bioimpedance will often be confounded. This paper examines the assumptions underlying estimations of total body water from BIA and addresses the factors known to influence bioimpedance independently from actual change in total body water. The results indicate that current BIA methodology may not provide valid estimates of total body water when hydration state is altered.

Amnesia during cold water immersion: a case report

This report describes a case of amnesia during a cold-water experiment. The volunteer was exposed three times in 1 day (120 min duration each time) to 20 degrees C water. During the third immersion, from min 95 to min 115, the subject experienced transient global amnesia for 20 min. The rectal temperature during this time was 35.6 degrees C. This single case demonstrates that memory loss in a young individual apparently can occur after cold-water exposure and at core temperatures above 35 degrees C.

Pituitary-adrenal and pituitary-thyroid hormone responses during exercise-cold exposure after 7 days of exhaustive exercise

BACKGROUND

After several days of exhaustive exercise in mild-warm environments, cutaneous vasoconstrictor responses to cold exposure are less effective in conserving body heat than in the rested condition. Hypothalamic-pituitary-adrenal and hypothalamic-pituitary-thyroid axes hormones could mediate this response since they may affect vasoconstriction. The effects of exertional fatigue on pituitary-adrenal hormones and thyroid hormone responses to exercise-cold stress are unknown.

HYPOTHESIS

We hypothesized that 7 consecutive days of exercise would decrease adrenocorticotropin (ACTH) and cortisol, while elevating thyroid stimulating hormone (TSH), triiodothyronine (T3), and thyroxine (T4) and that these hormones would be related to a blunted vasoconstrictor response to cold.

METHODS

Nine male volunteers walked, completely wetted, for up to 6 h in 5 degrees C air, when rested (day 0, control) and after 7 consecutive days (day 7) of exhaustive exercise (4 h each day of mixed aerobic and anaerobic activities in thermoneutral conditions). Blood was sampled on day 0 and day 7 at baseline (0700 hours), and before and immediately after cold exposure.

RESULTS

At 0700 hours, ACTH and cortisol were elevated (p < 0.05) after 7 d of exercise, compared with control conditions. Following exercise-cold exposure, cortisol, T3, and T4 increased (p < 0.05) similarly on both day 0 and day 7. ACTH and TSH did not increase as a result of exercise-cold exposure on either day.

CONCLUSIONS

These data indicate that 7 d of exercise elevates basal (0700 hours) pituitary-adrenal stress hormones (ACTH, cortisol). However, 7 d of exercise did not modify adrenal or thyroid hormone responses, relative to the day 0 cold exposure, suggesting that they are not responsible for the blunted vasoconstriction during exercise-cold exposure following 7 consecutive days of exercise.

A study of the effect of a single neurotoxic dose of 3,4-methylenedioxymethamphetamine (MDMA; "ecstasy") on the subsequent long-term behaviour of rats in the plus maze and open field

RATIONALE

Decreased 5-HT function has been shown to induce behaviour consistent with an "anxiolytic" effect. Administration of a single dose of 3,4-methylenedioxymethamphetamine (MDMA; "ecstasy" 12.5 mg/kg IP) to rats results in prolonged damage to central serotonergic nerve terminals. Thus we wished to assess whether an MDMA-induced lesion may have longer-term behavioural consequences.

OBJECTIVE

The study was designed to examine the behaviour of MDMA-pretreated and control animals in the elevated plus-maze and open field at a number of time-points, up to 80 days, after the administration of a single neurotoxic dose of MDMA (12.5 mg/kg IP).

RESULTS

MDMA-pretreated Dark Agouti rats demonstrated a statistically significant reduction in anxiety-related behaviour, compared to saline-pretreated control rats, in both the elevated plus-maze and open field when the rats were tested on day 73 (open field) and day 80 (plus maze) after MDMA administration.

CONCLUSIONS

The behavioural consequences of a single neurotoxic dose of MDMA can be demonstrated over 2 months after administration of the compound, thereby indicating that long-term adaptive changes occur within the brain following the neurodegeneration of 5-HT neurones produced by this recreationally used drug.

Physiological responses to cold exposure in men: a disabled submarine study

A disabled submarine (DISSUB) lacking power and/or environmental control will become cold, and the ambient air may become hypercapnic and hypoxic. This study examined if the combination of hypoxia, hypercapnia, and cold exposure would adversely affect thermoregulatory responses to acute cold exposure in survivors awaiting rescue. Seven male submariners (33 +/- 6 yrs) completed a series of cold-air tests (CAT) that consisted of 20-min at T(air) = 22 degrees C, followed by a linear decline (1 degrees C x min(-1)) in T(air) to 12 degrees C, which was then held constant for an additional 150-min. CAT were performed under normoxic, normocapnic conditions (D0), acute hypoxia (D1, 16.75% O2), after 4 days of chronic hypoxia, hypercapnia and cold (D5, 16.75% O2, 2.5% CO2, 4 degrees C), and hypoxia-only again (D8, 16.75% O2). The deltaTsk during CAT was larger (P < 0.05) on D0 (-5.2 degrees C), vs. D1 (-4.8 degrees C), D5 (-4.5 degrees C), and D8 (-4.4 degrees C). The change (relative to 0-min) in metabolic heat production (deltaM) at 20-min of CAT was lower (P < 0.05) on D1, D5, and D8, vs. D0, with no differences between D1, D5 and D8. DeltaM was not different among trials at any time point after 20-min. The mean body temperature threshold for the onset of shivering was lower on D1 (35.08 degrees C), D5 (34.85 degrees C), and D8 (34.69 degrees C), compared to D0 (36.01 degrees C). Changes in heat storage did not differ among trials and rectal temperature was not different in D0 vs. D1, D5, and D8. Thus, mild hypoxia (16.75% F1O2) impairs vasoconstrictor and initial shivering responses, but the addition of elevated F1CO2 and cold had no further effect. These thermoregulatory effector changes do not increase the risk for hypothermia in DISSUB survivors who are adequately clothed.

A comparison between Dark Agouti and Sprague-Dawley rats in their behaviour on the elevated plus-maze, open-field apparatus and activity meters, and their response to diazepam

RATIONALE

Preliminary unpublished studies in our laboratory suggested that the behaviour of Sprague-Dawley (SD) and Dark Agouti (DA) rats was markedly different on both the elevated plus maze and in the open-field apparatus. We wished to confirm and extend this initial finding.

OBJECTIVE

The study was designed to examine the behaviour of SD and DA rats in the elevated plus maze, open-field apparatus and automated activity meters. The response of both strains on the elevated plus maze following diazepam (1 mg/kg and 1.5 mg/kg) administration was subsequently investigated.

RESULTS

DA rats showed markedly greater anxiety-like behaviour than SD rats in both the plus maze and open field, with fewer percentage open/total arm entries and percentage time spent on open/total arms in the plus maze and fewer crossings in the open field. Acute handling plus administration of vehicle abolished this difference in anxiety levels, with DA rats showing similar open-arm behaviour to that of SD rats. Both strains demonstrated a clear anxiolytic response to diazepam (1 mg/kg) in terms of percentage time spent on the open arms, but only SD rats had a statistically significant increase in percentage open-arm entries compared with vehicle-injected control animals.

CONCLUSIONS

While the high level of anxiety-like behaviour of DA rats versus SD rats could prove useful in future ethological studies on anxiety, the fact that acute handling decreased the anxiety-like behaviour on the elevated plus maze may limit the value of this strain for the study of putative anxiolytic drugs.