A mixed diet of toxic plants enables increased feeding and anti-predator defense by an insect herbivore.

Some insect herbivores sequester plant secondary metabolites (PSMs) for their own defense, raising the interesting possibility that grazing herbivores are defended by combinations of PSMs from different plant species. In this study, we tested the hypothesis that the grazing caterpillar, Grammia incorrupta, deters the ant, Aphaenogaster cockerelli, by eating a mixture of plants containing iridoid glycosides (IGs) and those containing pyrrolizidine alkaloids (PAs), and that this deterrence is greater than that attained by eating either plant alone. This hypothesis was tested against the non-mutually exclusive hypothesis that mixing plants containing PAs with those containing IGs improves growth performance. Caterpillar survival and growth were measured on three experimental diets: a PA plant, an IG plant, and a mixture of the two. We measured the degree of deterrence associated with these, and an additional experimental diet devoid of PSMs at naturally occurring A. cockerelli nests. Caterpillars fed both plants gained more mass than those fed either plant alone, but took longer to develop. These differences were not caused by diet-based variation in growth efficiency, but by eating more food when offered the mixed-plant diet relative to single-plant diets. The mixed diet was shown to provide deterrence to ants, whereas caterpillars fed single-plant diets were not significantly more deterrent than caterpillars that had eaten the PSM-free diet. We hypothesize that enhanced defense results from increased food consumption in response to multiple plant species, perhaps leading to greater PSM sequestration. Through this mechanism, bottom-up and top-down effects may mutually reinforce the grazing dietary strategy.

Cyclic AMP-dependent protein kinases of Paramecium. I. Chromatographic and physical properties of the enzymes from cilia.

The cAMP-dependent protein kinases of the cilia of the protozoan Paramecium tetraurelia were resolved and characterized. Two cAMP-dependent activities were present in cilia; the two ciliary kinases resemble types I and II from vertebrate tissues. Part of the ciliary kinase activity (primarily type II) was released by freeze-thawing, but a significant amount remained particulate. Both kinases were found as aggregates of about 220 kDa and of about 70 kDa. A portion of the cAMP-binding activity in ciliary extracts separated from kinase activity, and eluted at 36 kDa during gel filtration. Photoaffinity labeling with 8-azido-cAMP identified cAMP-binding proteins of 45-52 kDa in type II kinase from cilia, and of 43-46 kDa in type I kinase. The type II kinase was apparently autophosphorylated, causing a decrease in mobility during sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Cyclic AMP-dependent protein kinases of Paramecium. II. Catalytic and regulatory properties of type II kinase from cilia.

The type II cAMP-dependent protein kinase (cAMP-PK-II) from cilia of Paramecium, purified free of type I cAMP-PK (cAMP-PK-I) and of cGMP-dependent protein kinase (cGMP-PK), phosphorylated several basic proteins and a heptapeptide containing serine (Kemptide). The enzyme was partially inhibited by the protein kinase inhibitor (Walsh inhibitor), but only at relatively high inhibitor concentrations. Half-maximal activation of cAMP-PK-II occurred at 15-25 nM cAMP. Several cAMP analogs were tested for ability to bind and activate the enzyme. 8-bromo-cGMP, a potent activator of Paramecium cGMP-PK, was a poor activator of Paramecium cAMP-PK-II. Activation of cAMP-PK-II was influenced by the phosphorylation assay buffer. Phosphate buffers provided increased activation by cAMP but decreased total activity relative to that measured in Mops-Tris buffer. The kinase was cAMP-independent when the pH of the assay buffer was high. Preincubation of cAMP-PK-II with histones also activated the enzyme in the absence of cAMP. The cAMP-PK-II bound cAMP with a Kd of 23 nM, and bound cAMP was released with a biphasic time course, suggesting two non-identical binding sites. The properties of the cAMP-PK of this ciliated protozoan appear to be closely similar to those of vertebrates.

Response of aldosterone and 18-hydroxycorticosterone to angiotensin II in normal subjects and patients with essential hypertension, Conn's syndrome, and nontumorous hyperaldosteronism.

Dose-response curves relating plasma angiotensin II (AII) concentration during AII infusion to blood pressure (BP), to plasma aldosterone, and to plasma 18-hydroxycorticosterone were compared in normal subjects and in patients with essential hypertension, Conn's syndrome, and nontumorous hyperaldosteronism. The BP response was steeper than normal in patients with Conn's syndrome and essential hypertension. Before infusion, mean plasma aldosterone concentration was approximately four-fold higher in Conn's syndrome than in the normal group, while that of 18-hydroxycorticosterone was ninefold higher. Neither increased significantly during AII infusion. In essential hypertension, both corticosteroids were within the normal range, but their responses to AII infusion were greater than normal. In the three subjects with non-tumorous hyperaldosteronism, plasma aldosterone and 18-hydroxycorticosterone concentrations were raised, and their responses to AII infusion resembled those found in essential hypertension and were different from those found in Conn's syndrome. This suggests that nontumorous hyperaldosteronism is not a variant of Conn's syndrome. In the response to AII and in other ways, it is indistinguishable from essential hypertension.

Why do mammalian mitochondria possess a mismatch repair activity?

All nucleated mammalian cells contain mitochondrial DNA, a small (approximately 15-17 kb) circular genome found in the matrix. This molecule is present in multiple copies, with numbers routinely exceeding 1000 per cell. Many pathogenic mutations of this genome have been reported, with the vast majority being highly recessive. A mismatch repair activity has been recently described in mitochondria that shows no strand bias for correcting point mutations. What could be the physiological function of such an activity? Mammalian mtDNA is remarkable in being a patchwork of many short repeat sequences. With reference to several recent publications, we hypothesise that the function of this activity is to preserve the mitochondrial genome by repairing short loop out sequences that would otherwise be lost as mitochondrial DNA polymerase gamma replicates the mitochondrial genome.

Stress reactivity of the brain noradrenergic system in three rat strains differing in their neuroendocrine and behavioral responses to stress: implications for susceptibility to stress-related neuropsychiatric disorders.

The brain noradrenergic system is activated by stress, modulating the activity of forebrain regions involved in behavioral and neuroendocrine responses to stress. In this study, we characterized brain noradrenergic reactivity to acute immobilization stress in three rat strains that differ in their neuroendocrine stress response: the inbred Lewis (Lew) and Wistar-Kyoto (WKY) rats, and outbred Sprague-Dawley (SD) rats. Noradrenergic reactivity was assessed by measuring tyrosine hydroxylase mRNA expression in locus coeruleus, and norepinephrine release in the lateral bed nucleus of the stria terminalis. Behavioral measures of arousal and acute stress responsivity included locomotion in a novel environment, fear-potentiated startle, and stress-induced reductions in social interaction and open-arm exploration on the elevated-plus maze. Neuroendocrine responses were assessed by plasma adrenocorticotropic hormone. Compared to SD, adrenocorticotropic hormone responses of Lew rats were blunted, whereas those of WKY were enhanced. The behavioral effects of stress were similar in Lew and SD rats, despite baseline differences. Lew had similar elevations of tyrosine hydroxylase mRNA, and initially greater norepinephrine release in the lateral bed nucleus of the stria terminalis during stress, although both noradrenergic responses returned toward baseline more rapidly than in SD rats. WKY rats showed depressed baseline startle and lower baseline exploratory and social behavior than SD. However, unlike the Lew or SD rats, WKY exhibited a lack both of fear potentiation of the startle response and of stress-induced reductions in exploratory and social behavior, indicating attenuated stress responsivity. Acute noradrenergic reactivity to stress, measured by either tyrosine hydroxylase mRNA levels or norepinephrine release, was also attenuated in WKY rats. Thus, reduced arousal and behavioral responsivity in WKY rats may be related to deficient brain noradrenergic reactivity. This deficit may alter their ability to cope with stress, resulting in the exaggerated neuroendocrine responses and increased susceptibility to stress-related pathology exhibited by this strain.

Some pharmacological properties of piperazine.

1. The action of piperazine on mammalian smooth, cardiac and skeletal muscles has been studied.2. Piperazine increased tone and produced a dose dependent contraction of isolated smooth muscle, which was antagonized by atropine.3. With cardiac muscle, piperazine depressed both the rate and force of contraction and was antagonized by atropine. At higher concentrations, a non-specific depression of cardiac muscle was found. The intravenous injection of piperazine produced a transient decrease in both heart rate and blood pressure and this was followed by an increase.4. In about half of the mammalian skeletal muscle preparations, piperazine potentiated the twitch of the muscle evoked by electrical stimulation.5. On the frog neuromuscular preparation, piperazine produced potentiation of the twitch but this was followed first by blockade of the effects of nerve stimulation and then by depression of the effects of direct muscle stimulation.

Estimation of aldosterone, 11-deoxycorticosterone, 18-hydroxy-11-deoxy-corticosterone, corticosterone, cortisol and 11-deoxycortisol in human plasma by gas-liquid chromatography with electron capture detection.

A method for determining the plasma concentrations of six major corticosteroids, aldosterone, 18-hydroxy-11-deoxycorticosterone (18-OH-DOC), corticosterone, deoxycorticosterone (DOC), cortisol and 11-deoxycortisol using gas-liquid chromatography with electron capture detection is described. Esterification of suitable derivatives of these compounds with heptafluorobutyric anhydride (HFB) allowed detection of quantitities of steroid, ranging from 0-3 pg for androstenetrione HFB (from cortisol) to 2-3 pg for corticosterone HFB. No detectable reagent blank was obtained for any compound when water was used instead of plasma and this was also the case when plasma from an adrenalectomized subject was analysed, with the exception of 18-OH-DOC where a reproducible but negligibly small blank occurred. Coefficients of variation for replicate determinations ranged from 8% for corticosterone to 17% for aldosterone. Concentrations in a series of normal human plasma samples were as follows: aldosterone, 4-0- 18-0 ng/100 ml; 18-OH-DOC, 20-16- ng/ml; corticosterone, 0-08 - 0.-80 mug/100 ml; DOC, 2-8 - 16-0 ng/100 ml; cortisol, 2-5 - 10-0 mug/100 ml; and 11-deoxycortisol, 40-0 - 400-0 ng/100 ml. When seven normal subjects were treated with dexamethasone concentrations of DOC, cortisol and 11-deoxycortisol fell to below the limit of the normal range, those of 18-OH-DOC and corticosterone were at the lower end of the normal range while the concentration of aldosterone was not significantly affected.

The influence of acid mists on growth, dry matter partitioning, nutrient concentrations and mycorrhizal fruiting bodies in red spruce seedlings.

Two-year-old spruce (Picea rubens Sarg.) seedlings were exposed to acid mists containing equimolar ammonium sulphate and nitric acid giving treatments of pH 2.5, 3.0 and 5.0. Acid mist treatments were applied twice weekly from late July until early October, 1987, when the plants were harvested. There were no significant differences in biomass accumulation or in height growth between treatments, but marked differences in root morphology were found. Significantly larger amounts of coarse roots were produced in the pH 5.0 acid mist treatment and plants in the pH 3.0 treatment produced significantly greater amounts of fine roots. Plants receiving acid mists of pH 3.0 or less had a greater frequency of fine root branches along their coarse roots. Production of mycorrhizal fruiting bodies of Thelephora terrestris Ehrenb.: Fr. was significantly greater (P < 0.001) at pH 5.0 than in the other treatments. Plants in the pH 2.5 and 3.0 treatments contained larger concentrations of N, 1.54 and 1.12% and S, 0.52 and 0.28% respectively, than those receiving acid mist at pH 5.0, i.e. 1.00 and 0.21% respectively. However, the between treatment differences of tissue nutrient concentrations were small relative to the differences in inputs between treatments. Foliar S exceeded concentrations recommended for nursery stock by 50 and 150% at pH 3.0 and 2.5 respectively.

Oxidative stress precedes circulatory failure induced by 35-GHz microwave heating.

Sustained whole-body exposure of anesthetized rats to 35-GHz radio frequency radiation produces localized hyperthermia and hypotension, leading to circulatory failure and death. The physiological mechanism underlying the induction of circulatory failure by 35-GHz microwave (MW) heating is currently unknown. We hypothesized that oxidative stress may play a role in the pathophysiology of MW-induced circulatory failure and examined this question by probing organs for 3-nitrotyrosine (3-NT), a marker of oxidative stress. Animals exposed to low durations of MW that increased colonic temperature but were insufficient to produce hypotension showed a 5- to 12-fold increase in 3-NT accumulation in lung, liver, and plasma proteins relative to the levels observed in control rats that were not exposed to MW. 3-NT accumulation in rats exposed to MW of sufficient duration to induce circulatory shock returned to low, baseline levels. Leukocytes obtained from peripheral blood showed significant accumulation of 3-NT only at exposure levels associated with circulatory shock. 3-NT was also found in the villus tips and vasculature of intestine and within the distal tubule of the kidney but not in the irradiated skin of rats with MW-induced circulatory failure. The relationship between accumulation in liver, lung, and plasma proteins and exposure duration suggests either that nitro adducts are formed in the first 20 min of exposure and are then cleared or that synthesis of nitro adducts decreases after the first 20 min of exposure. Taken together, these findings suggest that oxidative stress occurs in many organs during MW heating. Because nitration occurs after microwave exposures that are not associated with circulatory collapse, systemic oxidative stress, as evidenced by tissue accumulation of 3-NT, is not correlated with circulatory failure in this model of shock.

Exercise in the heat is limited by a critical internal temperature.

We examined whether fatigue during exertional heat stress occurred at a critical internal temperature independent of the initial temperature at the start of exercise. Microwaves (2.1 GHz; 100 mW/cm(2)) were used to rapidly (3-8 min) heat rats before treadmill exercise to exhaustion. In a repeated-measures design, food-restricted male Sprague-Dawley rats (n = 11) were preheated to three levels (low, medium, and high). In addition, two sham exposures, Sham 1 and Sham 2, were administered at the beginning and end of the study, respectively. At the initiation of exercise, hypothalamic (T(hyp)) and rectal (T(rec)) temperatures ranged from 39.0 degrees C to 42.8 degrees C (T(hyp)) and 42.1 degrees C (T(rec)). The treadmill speed was 17 m/min (8 degrees grade), and the ambient temperature during exercise was 35 degrees C. Each treatment was separated by 3 wk. Run time to exhaustion was significantly reduced after preheating. There was a significant negative correlation between run time and initial T(hyp) and T(rec) (r = 0.73 and 0.74, respectively). The temperatures at exhaustion were not significantly different across treatments, with a range of 41.9-42.2 degrees C (T(hyp)) and 42.2-42.5 degrees C (T(rec)). There were no significant differences in run time in the sham runs administered at the start and end of the investigation. No rats died as a result of exposure to any of the treatments, and body weight the day after each treatment was unaffected. These results support the concept that a critical temperature exists that limits exercise in the heat.

HSP70 expression in the CNS in response to exercise and heat stress in rats.

We have previously documented the regional distribution of 70-kDa heat shock protein (HSP70) in brains of rats made hyperthermic by brief exposure to high-powered microwaves (HPM; 2.06 GHz). We now compare HSP70 expression induced by HPM exposure to that induced by exertional and/or environmental heat stress. Rats were chronically implanted with a temperature probe guide in the hypothalamic region of the brain (Tbr). After recovery, the following treatment groups were examined: HPM; sham exposed; treadmill exercise at room temperature (24 degreesC; Ex-1); treadmill exercise in a warm environment (34 degreesC; Ex-2); and sedentary groups (Sed-1 and Sed-2), in which ambient temperature was adjusted so that the Tbr mimicked the Tbr in the corresponding exercise groups. Significant HSP70 expression occurred only in the hyperthermic (Ex-2, Sed-2, and HPM) groups. The pattern of HSP70 expression was similar among Ex-2 and Sed-2 rats but differed from that in HPM rats. We conclude that 1) the pattern of HSP70 expression differs between HPM and nonmicrowave heating, and 2) exercise alone was not sufficient to induce central HSP70 expression.

Short- and long-term summation characteristics of electrical self-stimulation reward.

Using a Y-maze preference test paradigm, we examined the characteristics of the neural networks that integrate trains of rewarding stimulation pulses. Rats compared the rewarding effectiveness of various durations of a test reinforcement to those of 3 durations of a standard reinforcement. By changing the duration of the standard reinforcement while keeping the pulse frequency constant, we varied the stimulation magnitude to which the test reinforcement was being compared. This enabled us to examine the relationships between stimulation parameters both within a constant stimulation magnitude and across different stimulation magnitudes. The data were inconsistent with a simple integrating system with a single decay time constant such as is usually assumed. They can most parsimoniously be accounted for by two systems having quite widely differing time constants. The time constant of the first integrator is ca. 450 ms, whereas that of a second integrator is ca. 6.5 s.

Establishing orally self-administered cocaine as a reinforcer in rats using home-cage pre-exposure.

1. Rats were force-exposed to a cocaine + saccharin solution in their home cage water bottles for five days. They were then given 5 h home-cage access to both cocaine and cocaine-free solutions for 40 days. 2. The subjects consumed large doses of the cocaine solution despite the ad libitum availability of water. 3. The animals were then trained on a task consisting of operant bar pressing rewarded on an intermittent schedule with a liquid cocaine reinforcer. 4. All subjects performed the operant task and consumed doses of cocaine solution which are preferred over water in other paradigms. 5. Levels of responding were significantly reduced in three of four subjects when vehicle was substituted for liquid cocaine as the reward. 6. This demonstrates that orally self-administered cocaine can be used as a reinforcer in rats.

Regional distribution of Hsp70 in the CNS of young and old food-restricted rats following hyperthermia.

We examined the effect of aging on the capacity of the brain to produce heat shock protein (Hsp70) in response to heat stress, using high-powered microwaves (HPM, 2.06 GHz, 2.2 W/cm(2)) to induce hyperthermia for periods so brief that thermoregulatory factors were functionally eliminated as confounding variables. Unanesthetized young (6 months) and old (25 months) male, food-restricted Sprague-Dawley rats were exposed to HPM to induce a mean peak tympanic temperature (T(ty)) of 42.2 degrees C within 30 s. T(ty) returned to <40.0 degrees C within 6 min post-exposure in both age groups. Rats were euthanized 6 or 24 h later for immunohistochemical determination of Hsp70 accumulation in 10 brain regions. HPM exposure induced significant increases in 7 of the 10 regions. There were no significant differences observed in the pattern or density of Hsp70 accumulation between the young and old rats at 6 h post-HPM exposure, with the exception of the medial vestibular nucleus, which demonstrated significantly greater Hsp70 accumulation in the old rats. There were significant differences between the age groups at 24 h post-exposure, however, there was no general pattern; i.e., depending on the brain region, aged rats displayed significantly greater, lesser, or similar increases in Hsp70 expression compared with young. Taken together, these results demonstrate that the brain of aged, food-restricted rats does not display a loss of capacity to accumulate Hsp70 in response to heat stress.

Ascorbic acid concentration in the lateral hypothalamus is related to plasma osmolality.

Microdialysis was used to measure extracellular ascorbic and uric acid concentrations in the lateral hypothalamus of water-restricted rats as they drank distilled water or 1.5% NaCl. Other water-restricted rats, not implanted with microdialysis probes, were decapitated 2 h after beginning to drink these fluids. Rats were inverted and their blood was collected for measurements of plasma osmolality and percent hematocrit. Results showed that drinking distilled water produced a significant increase in the ascorbic acid concentration but not in the uric acid concentration. Drinking 1.5% NaCl produced a significant decrease in the uric acid concentration but not in the ascorbic acid concentration. Drinking distilled water decreased mean osmolality from 306.0 to 291.5 mOsm/kg, whereas drinking 1.5% NaCl maintained mean osmolality at water-restricted levels. These results indicate that the extracellular fluid concentration of ascorbic acid in the lateral hypothalamus rises in response to a fall in plasma osmolality.

Severe hypertension with absent secondary sex characteristics due to partial deficiency of steroid 17 alpha-hydroxylase activity.

A genotypically female patient with 17 alpha-hydroxylase deficiency, and typical symptoms of hypertension, hypokalaemia and lack of secondary sex characteristics, is described. Plasma 17 alpha-hydroxycorticosteroid levels (cortisol, 11-deoxycortisol) and oestradiol were low. Those of 11-deoxycorticosterone, corticosterone, their 18-hydroxy- derivatives, ACTH and gonadotrophins were high and, with the exception of the gonadotrophins, suppressed to normal with dexamethasone which also corrected blood pressure (BP) and electrolyte abnormalities. Plasma aldosterone levels, initially suppressed, increased during treatment but, at 3 months, showed some signs of subnormal responsiveness. Possible reasons for this are discussed. The patient remains well after 9 years on dexamethasone and oestrogen therapy.

Fuzzy-control of a hand orthosis for restoring tip pinch, lateral pinch, and cylindrical prehensions to patients with elbow flexion intact.

This study examines, through simulation, the use of fuzzy logic as a feasible control scheme for a hand orthosis that can restore fingertip pinch, lateral pinch, and cylindrical grasps to individuals suffering from C5-C7 spinal cord injuries. A simplified hand orthosis model, consisting of four fingers and a thumb, was derived for the purpose of planning appropriate grasp trajectories and for validating the fuzzy logic control architecture. For comparison a proportional-plus-integral-plus-derivative (PID) controller was also designed. Fuzzy logic is advantageous for this system since it eliminates solving coupled nonlinear equations of motion. For the various grips, the fuzzy controller produced better performance than the PID controller.

Temporal characteristics of electrical self-stimulation reward: fatigue rather than adaptation.

Using a Y-maze preference test paradigm, we examined the temporal characteristics of the neural network subserving self-stimulation reward. Rats were given a choice between two pulse trains of stimulation, which varied in duration and pulse frequency. The results showed that increasing the pulse frequency decreases the duration at which the rewarding effectiveness of brain stimulation reaches an asymptote. The data also indicated that when prolonged stimulation is delivered at a high pulse frequency, the initial pulses contribute the most to the rewarding effect. Later pulses are affected by the reduced ability of the neurons or synapses to transmit signals along the neural network due to fatigue. The data are explained in terms of an improved model of summation involving more than one integrator and fatigue.

Further evidence against adaptation of prolonged electrical self-stimulation reward.

Using a Y-maze preference test paradigm, we examined the temporal characteristics of the neural network subserving self-stimulation reward. The first part of the experiment demonstrated that when prolonged electrical brain stimulation is initially delivered with a low pulse frequency (100 Hz), rats prefer an increase over either a decrease or no change in the pulse frequency of subsequent stimulation. However, the second part showed that when prolonged brain stimulation is initially delivered with a high pulse frequency (250 Hz), an increase is not preferred. The data are inconsistent with an adaptation model of summation. These results are explained in terms of an improved model of summation involving two integrators and fatigue.