Relative Magnitude Of Response Research Articles

The induction of homo- vs. heterosynaptic LTD in area CA1 of hippocampal slices from adult rats

The induction of long-term depression (LTD) was investigated in area CAI of hippocampal slices from adult rats. To produce LTD, prolonged low-frequency stimulation (LFS, 900 stimuli at 1 Hz) was delivered to one of two independent Schaffer-collateral/commissural projections, while the second input served as a control to monitor heterosynaptic effects. The depression was calculated as percent decrease in the slope of the dendritic field EPSP relative to baseline values, and LTD was considered established if the response decrement was at least 15% in magnitude and stable for 30–60 min. By delivering LFS in conditions of different relative baseline response magnitudes, it was revealed that the intensity of afferent low-frequency activity has a significant impact on the induction frequency, magnitude and input-specificity of the depression: the rate of LTD occurrence and the effect of LFS on the absolute response decrement increased successively as the stimulation strength was raised, but the impact of LFS on the relative LTD magnitude decreased at higher stimulation intensities; the depression was specific to the stimulated input (homosynaptic LTD) when baseline responses were spike-free, but spread to the pathway which was silent during LFS (heterosynaptic LTD) in experiments conducted above spiking threshold. The results indicate that in the adult rat (i) the induction of input-specific LTD is dependent on the level of synaptic activation during LFS, and (ii) LTD can easily be obtained in strongly stimulated pathways but may be the result of a generalized decrease in the postsynaptic response.

Functional plasticity of regenerated and intact taste receptors in adult rats unmasked by dietary sodium restriction

Unilateral chorda tympani nerve sectioning was combined with institution of a sodium-restricted diet in adult rats to determine the role that environment has on the functional properties of regenerating taste receptor cells. Rats receiving chorda tympani sectioning but no dietary manipulation (cut controls) and rats receiving only the dietary manipulation (diet controls) had normal responses to a concentration series of NaCl, sodium acetate (NaAc), and NH4Cl. However, responses from the regenerated nerve in NaCl-restricted rats (40-120 d postsectioning) to NaCl and NaAc were reduced by as much as 30% compared to controls, indicating that regenerating taste receptors are influenced by environmental (dietary) factors. Responses to NH4Cl were normal; therefore, the effect appears specific to sodium salts. Surprisingly, in the same rats, NaCl responses from the contralateral, intact chorda tympani were up to 40% greater than controls. Thus, in the same rat, there was over a twofold difference in sodium responses between the right and left chorda tympani nerves. A study of the time course of the functional alterations in the intact nerve revealed that responses to NaCl were extremely low immediately following sectioning (about 20% of the normal response), and then increased monotonically during the following 50 d until relative response magnitudes became supersensitive. This function occurred even when the cut chorda tympani was prevented from reinnervating lingual epithelia, demonstrating that events related to regeneration do not play a role in the functional properties of the contralateral side of the tongue.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of peri-operative storage solution on the vascular reactivity of the human saphenous vein.

The performance of the saphenous vein as a bypass conduit in myocardial revascularisation may, in part, be determined by its vascular reactivity. The present study investigates whether the choice of peri-operative storage solution influences the response of this vessel to a range of vasoconstrictors and vasodilators. Saphenous vein ring segments (210) were obtained from 24 patients undergoing coronary artery bypass surgery, and following a 1 h incubation in either (1) heparinised blood, (2) heparinised saline, (3) 199-TC solution, (4) St. Thomas' cardioplegic solution or (5) plasma-lyte solution, rings of vein were set up as organ bath preparations. The relative magnitude of control constrictor response was: noradrenaline = 5-hydroxytryptamine > or = dopamine > histamine > acetylcholine. There was a significantly different (P < 0.05) enhanced response to noradrenaline and 5-hydroxytryptamine in segments stored in heparinised saline compared to 199-TC; similarly, dopamine and noradrenaline responses were significantly potentiated (P < 0.05) following storage in heparinised saline compared to cardioplegia. Storage in plasma-lyte enhanced the response significantly storage in heparinised saline compared to cardioplegia. Storage in plasma-lyte enhanced the response significantly (P < 0.05) to acetylcholine alone. None of the solutions had a significant effect on the potency (EC50) of the constrictors. Relaxations of pre-constricted segments were recorded to acetylcholine and sodium nitroprusside, but there was no difference in efficacy or potency in these responses following storage in the different solutions. This study demonstrates that the choice of peri-operative storage solution may influence the vascular reactivity of the human saphenous vein.

Character of hearwaters adjustment to base level drop, investigated by digital modeling

Using a computer model written for dynamic river profile modeling (Snow and Slingerland, 1987), long-term profile adjustments to constant-rate base level lowering/tectonic block uplift have been simulated with varied conditions of outflow discharge (10 and 100 m 3/s), sediment diameter (0.1, 0.4 and 2.0 mm) and sediment load (concentrations of 1200 and 400 ppm by weight). Tweleve sets of initially graded profile data cover all possible combinations of the variables. Each modeled stream has been subjected to each of three base level drop rates (0.1, 1.0 and 10.0 mm/yr), for 10,000 years of model time. Modeled histories of headwaters erosional response differ in two ways. The first is length of lag time of response, characterized by a period of quiescence in erosion at the headwaters prior to the channel steepening sufficiently for erosion to commence at this upstream point. Variations in discharge and sediment concentration affect the lag time of response in all cases. The second variable aspect of response is the relative magnitude of eventual headwaters erosion. The main control is the drop rate; a high drop rate yields a low relative magnitude whereas a low drop rate yields a high relative magnitude of response. The rate of base level drop also controls to what degree the other controlling variables of discharge, sediment concentration, and sediment diameter affect the eventual magnitude of headwaters erosion. Rates of trunk stream and headwaters erosion indicate that 21 out of 36 of the modeled stream systems attain a condition approximating parallel profile erosion after 10,000 years. Some examples, notably those with low power to erode and high imposed drop rates, exhibit headwaters erosion rates that continue to be well below rates of base level lowering, creating profile steepening with no apparent time limit.

Responses of olfactory receptor cells of spiny lobsters to binary mixtures. II. Pattern mixture interactions

1. The effect of mixture interactions in individual olfactory receptor cells of the spiny lobster on neural coding of odorant quality of binary mixtures and their components is examined in this paper. Extracellular responses of 98 olfactory receptor cells in the antennules of spiny lobsters to seven compounds [adenosine-5'-monophosphate (AMP), betaine (Bet), L-cysteine (Cys), L-glutamate (Glu), ammonium chloride (NH4), DL-succinate (Suc), taurine (Tau)] and their binary mixtures were recorded, and mixture interactions in individual olfactory receptor cells were identified. 2. Coding of odorant quality was evaluated by examining across neuron patterns (ANPs)--the relative response magnitudes across neuronal populations. ANPs are a feature of the neuronal population response and are a possible concentration-independent code of odorant quality in this system, as indicated by previous studies and present results. 3. For most binary mixtures the diversity of types and degrees of mixture interactions across the individual cells of a population of cells resulted in ANPs for each mixture to be different from the ANPs for the components of the mixture and different from the ANP predicted for the mixture from the responses to the components (Figs. 2-10). These effects are called pattern mixture interactions (PMIs). PMIs occurred for most binary mixtures, even those that did not produce statistically significant intensity mixture interactions (IMIs) for this same population of cells. 4. The results suggest that PMIs can influence coding of stimulus quality, in some cases by causing an improvement of the contrast between the quality of mixtures and some of their components.

Delineation of a resistive drainage channel by EM conductivity survey

EM conductivity surveys have been carried out over an air-filled drainage conduit, near Alcala de Henares, Spain. The surveys failed to detect a measurable response from the gallery, but successfully delineated a desaturated drainage channel above the conduit. Target diagnosis was assisted by theoretical one-dimensional modelling, which showed that relative response magnitudes can provide a limited basis for source discrimination. The results confirm that conductive features are more likely to be detected than resistive voids. More versatile 2D modelling schemes are required, however, to provide greater interpretative insight and to exploit the full potential of the EM31 34 systems.

Community attributes along a perturbation gradient in a shortgrass steppe

Abstract. We constructed a perturbation (response) gradient that encompassed several types of disturbances (causes) affecting shortgrass steppe communities, and that was confounded by time scales of initiation and duration. The objectives were to (1) examine the type of disturbance and the relative magnitude of response in relation to the history of the shortgrass steppe, and (2) determine which attributes of the plant communities displayed relationships across the perturbation gradient, rather than across traditional successional ‐ time gradients.Comparisons of disturbance types indicated that long‐term heavy grazing by cattle resulted in plant communities which differ less from communities resulting from other disturbances than did long‐term ungrazed sites. The removal of grazers from this system promoted attributes of earlier serai stages. Water addition, below‐ground grazing by white grubs, and water‐plus‐nitrogen enrichment had distinct and large impacts on community composition. Nitrogen enrichment resulted in additions but not losses of species. The shortgrass steppe has a high degree of adaptation to both short‐term drought and aboveground grazing. Belowground grazing and semi‐aridity may be considered antagonistic pressures on the community.Community attributes that displayed a relationship with increasing level of perturbation were decreasing dominance and increasing diversity, and fluctuation in species composition during short‐term wet/dry cycles. The level of perturbation was related to negative impacts on the two primary species and a corresponding increase of other warm‐season species, but was not related to densities of any other species, life‐form, or functional group.

Corticotropin-releasing hormone increases tonic but not sensory-evoked activity of noradrenergic locus coeruleus neurons in unanesthetized rats

These studies were designed to further test the hypothesis that corticotropin-releasing hormone (CRH) is released from axons innervating the noradrenergic neurons of the locus coeruleus (LC) and serves to activate these neurons during stress responses. Specifically, the effects of exogenous CRH on the electrophysiological activity of LC neurons in unanesthetized rats were characterized. Intracerebroventricular (I.C.V.) injection of CRH (0.3-3.0 micrograms) caused a dose-dependent increase in LC spontaneous discharge rates that became statistically significant 6-9 min after injection and was still evident 30-40 min later. A 1.0 and 3.0 micrograms amount of CRH caused peak increases of 86 +/- 32% and 184 +/- 29% (SEM), respectively. In contrast, neither the lowest dose of CRH (0.3 microgram) nor a high dose of Ala 14CRH (3.0 micrograms), an inactive analog of CRH, altered LC spontaneous activity. The effects of CRH administration on sensory-evoked activity of LC neurons were also determined. As previously reported (Foote et al., 1980; Aston-Jones and Bloom, 1981b), the repeated presentation of auditory tone stimuli resulted in a brief enhancement of LC discharge, which was usually followed by a period of relatively decreased activity. Administration of 1.0 or 3.0 micrograms CRH enhanced basal discharge during sensory testing, but discharge rates during the excitatory component of the sensory response were not altered. Quantitative analyses revealed that these doses of CRH produced a statistically significant decrease in the ratio of sensory-evoked to basal discharge rates. Additional analyses of the temporal distribution of discharge activity for individual recording sites during sensory testing demonstrated that 1.0 and 3.0 micrograms CRH altered relative response magnitudes to a statistically significant extent in 7 of 10 and 5 of 7 cases, respectively, while 0.3 microgram CRH and 3.0 micrograms Ala 14CRH were without effect. The present results are consistent with previous studies of CRH effects on LC activity in anesthetized rats (Valentino et al., 1983; Valentino and Foote, 1987). However, in unanesthetized animals, CRH is more potent in increasing tonic activity and does not decrease the absolute magnitude of sensory-evoked activity. The present results support the hypothesis that CRH released from fibers innervating the LC may affect the tonic activity of these cells and the relationship between tonic discharge and phasic, sensory-evoked activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Central and baroreflex control of sympathetic nerve activity to the heart and kidney in a daily life of the cat.

We measured simultaneously and continuously the sympathetic nerve activity to the heart (CSNA) and kidney (RNA) together with heart rate (HR) and arterial blood pressure (AP) in conscious cats. The time course and magnitude of their responses to behavioral stimuli and norepinephrine iv administration were analyzed quantitatively. The increases in CSNA and RNA occurred almost simultaneously with the onset of standing, walking or eating behavior. The abrupt increases in CSNA and RNA were not preceded by a decrease in AP so it was unlikely to have been a reflex initiated by baroceptors. Rather, the increases in CSNA and RNA were followed by increases in HR and AP. The lag time ranged from 2 to 10 sec. Relative response magnitude of CSNA differed significantly from that of RNA. Thus, when AP increased spontaneously by behavioral stimuli, there was always preceding nonuniform increases in CSNA and RNA. On the other hand, when AP was elevated by norepinephrine iv administration, CSNA and RNA were inhibited proportionally to a rise in AP due to baroreflexes. At rest, the baroreflex effect on CSNA was greater than that on RNA. Cardiac-related discharges of CSNA and RNA, which were induced reflexly by baroceptor input, occurred dominantly at rest. However, with excitement or at the onset of body movements, they were diminished significantly. Our results suggested that AP adjustment associated with various behavior was made directly by a nonuniform central activation of the sympathetic nerve activity to the heart and blood vessels and partly by a central modulation of the baroceptor input.

A Theory of Stock Price Responses to Alternative Corporate Cash Disbursement Methods: Stock Repurchases and Dividends

ABSTRACTThis paper develops a model in which managers can signal their firms' true values by using either a dividend or a stock repurchase or both. The authors explain a number of stylized facts about these cash‐disbursement mechanisms, particularly those concerning the relative magnitudes of stock price responses to dividends and repurchases. Most importantly, they explain why a stock repurchase elicits a significantly higher price response, on average, than a dividend announcement.

Classification of primate spinothalamic and somatosensory thalamic neurons based on cluster analysis.

Data analyzed in this study were derived from the responses of 128 spinothalamic tract (STT) cells and 110 thalamic neurons recorded in 75 anesthetized monkeys. A k-means cluster analysis, a nonhierarchical clustering technique, was performed using the relative magnitudes of responses to a graded series of innocuous and noxious mechanical stimuli applied to the receptive field. For comparison, a parallel analysis was performed based on definitions of low-threshold (LT), wide dynamic range (WDR), and high-threshold (HT) cells used by our laboratory. For 128 STT cells, a classification scheme with three clusters was found statistically to be the best. This yielded groups of 22, 57, and 49 cells in clusters 1, 2, and 3, respectively. Cluster 1 cells were activated best by low-intensity mechanical stimuli, whereas cluster 3 cells were activated primarily by nociceptive stimuli. Cluster 2 cells had intermediate characteristics. When the classification scheme based on the cluster analysis was compared with the classification of the same neurons as LT, WDR, and HT cells, cluster 1 cells were divided into LT and WDR cells, whereas cluster 2 and 3 cells included WDR and HT cells. For 110 thalamic neurons, a classification scheme with five clusters was found statistically to be the best. Clusters 1-5 contained 25, 34, 17, 10, and 24 cells, respectively. Response characteristics of cells in each group indicated a gradual change in sensitivity to higher intensities of peripheral input from cluster 1 to 5. When this classification scheme was compared with the classification scheme previously used by our laboratory, cluster 1 cells belonged to the LT group, clusters 2 and 3 split into LT and WDR cells, and clusters 4 and 5 included WDR and HT cells. It is concluded that a classification scheme based on a cluster analysis of the responses of neurons to standardized stimuli may provide an objective and functionally meaningful way to categorize somatosensory neurons.

Neuronal responses to borders with and without luminance gradients in cat visual cortex and dorsal lateral geniculate nucleus.

We investigated responses of neurones in cortical areas 17 and 18 and in the dorsal lateral geniculate nucleus (dLGN) of the cat to a phase shift in a moving line pattern forming a border without a luminance gradient ("subjective contour"). In both areas 17 and 18, S cells and B cells respond only slightly or not at all along the phase shift while C cells respond strongly. The response of C cells is strongest for line patterns with medium line separation and decreases with smaller and larger separation. In the dLGN the relative magnitude of neuronal responses along a phase shift is similar to that of C cells. However, C cells respond uniformly along the entire phase shift, whereas geniculate cells merely respond to individual line ends along the phase shift. In addition we compared responses along a phase shift and those to a luminance gradient formed by a dotted line whose dots were separated by the same distance as the line ends along the phase shift. S cells and B cells respond preferentially to dotted lines whereas C cells and geniculate cells respond equally well along both phase shifts and dotted lines. Possible explanations for these results in terms of receptive field structure and differences in inhibitory input to the cells are discussed. Differential neurone responses may account for the perceptual distinctness of the contours with and without luminance gradients.

IgE responses in human filariasis. III. Specificities of IgE and IgG antibodies compared by immunoblot analysis.

IgE and IgG immune responses were qualitatively characterized in three well-defined groups of patients with different clinical manifestations of lymphatic filariasis caused by infection with Wuchereria bancrofti; viz. tropical pulmonary eosinophilia (TPE), chronic lymphatic obstruction with elephantiasis (CP), and asymptomatic microfilaremia (MF). A complex filarial antigen preparation extracted from adult filarial parasites was separated on SDS-polyacrylamide gels, and was electrophoretically transferred to nitrocellulose paper before being incubated with individual sera and being probed with radiolabeled anti-IgE or protein A. Three clinical groups of patients showed distinct patterns of antigen recognition by both IgE and IgG antibodies, with TPE patients showing the most diverse patterns and microfilaremic individuals the most restricted responses for both antibody isotypes. "Dual recognition" of antigens by IgE and IgG antibodies seemed to be the rule rather than the exception for each individual's immune response to the parasite antigens, but the relative magnitudes of IgG and IgE responses differed among the three groups. The ratio of IgG to IgE antibody was generally greater in patients with MF and CP than in those with TPE. These findings of the comparative specificities and relative abundance of IgE and IgG antibodies in infected patients may have fundamental importance in explaining the clinical expression (especially allergic reactivity) and disease pathogenesis of human filarial infections.

Mode of high temperature injury to wheat during grain development

High temperature stress adversely affects wheat growth in many important production regions, but the mode of injury is unclear. Wheat (Triticum aestivum L. cv. Newton) was grown under controlled conditions to determine the relative magnitude and sequences of responses of source and sink processes to high temperature stress during grain development. Regimes of 25°C day/15°C night, 30°C day/20°C night, and 35°C day/25°C night from 5 days after anthesis to maturity differentially affected source and sink processes. High temperatures accelerated the normal decline in viable leaf blade area and photosynthetic activities per unit leaf area. Electron transport, as measured by Hill reaction activity, declined earlier and faster than other photosynthetic processes at the optimum temperature of 25/15 °C and at elevated temperatures. Changes in RUBP carboxylase activities were similar in direction but smaller in magnitude than changes in photosynthesic rate. Increased protease activity during senscence was markedly accentuated by high temperature stress. Specific protease activity increased 4‐fold at 25/15 °C and 28‐fold at 35/25 °C from 0 to 21 days after initiation of temperature treatments. Grain‐filling rate decreased from the lowest to the highest temperature, but the change was smaller than the decrease in grain‐filling duration at the same temperatures. We concluded that a major effect of high temperature is acceleration of senescence, including cessation of vegetative and reproductive growth, deterioration of photosynthetic activities, and degradation of proteinaceous constituents.

Directional sensitivity of auditory neurons in the superior colliculus of the bat (Myotis lucifugus)

The directional sensitivity of auditory neurons in the deep layers of the superior colliculus was examined in unanesthetized bats stimulated in the free field with frequency‐modulated (FM) sounds (100 to 40 kHz) mimicking their natural orientation sounds. The minimum threshold of a unit was first measured when the sound was presented directly in front of the animal. Sounds 10, 30, and 50 dB above threshold were then delivered at every 10° azimuth from a hoop‐mounted speaker that rotated along the horizontal plane from 80° ipsilateral to 80° contralateral. Many units exhibited spatial selectivity to a sound source that was restricted between 10° ipsilateral to 20° contralateral and had an intensity 10 dB above threshold. Sound of higher intensity was effective throughout the contralateral side in driving these neurons, although the relative response magnitude differed at the individual angles. Mapping experiments did not reveal any systematic representation of best azimuth in this midbrain structure. Nevertheless, faint echoes returning from a target along a line near the bat's flight path provide directional cues necessary for accurate target localization. [Work supported by NIH.]

Application of Genotype‐Environment Interaction Analysis to Niche Quantification

Current methods of calculating niche breadth are often inadequate for plant study. Classical analysis techniques of genotype—environment interaction are offered as a better method of quantifying the niches of organisms, particularly plants. The analysis which is widely used in the fields of genetics and crop and stock breeding can be used to examine ecological relationships between genotypes in a population, populations of a species, or species within a community. The analysis gives measures of the relative niche breadth (equability) and magnitude of response between organims being compared. All that is required for input into the analysis is the performance of each organism (entity) in a number of environments (states). Quantification of the environment is not necessary and different resource gradients can be lumped together in a single analysis. A step—by—step description of the analysis is given. The techniques are demonstrated with two examples, one using a hypothetical data set and the other employing data from the classic experiments of Clausen, Keck, and Hiesey on Potentialla glandulosa. This analysis has advantages over classical niche metrics in that the magnitude or level of response of organisms is measured as well as the breadth of response.

Schistosoma mansoni: Splenic lymphocyte responses of mice after initial exposure to highly irradiated cercariae

Inbred C57 B1 6 and CBA mice were immunized with 60Co-irradiated (50 kR) Schistosoma mansoni cercariae. Based on the percentage reduction from controls in the numbers of adult parasites developing from a challenge cercarial exposure, the level of protection among immunized C57 B1 6 mice ranged from 56 to 74%, and among immunized CBA mice from 10 to 27%. In a longitudinal study, parallel in vitro comparisons of mitogen- and antigen-stimulated lymphocyte proliferative responses were performed with spleen cells from immunized and control mice of both strains. In contrast to decreased mitogen reactivity during a chronic, patent infection, immunization with irradiated cercariae resulted in no alteration in PHA and LPS responses in the reactivity of either strain. A vigorous antigen-specific reactivity was noted in the responses of immunized CBA mice. Additionally, a biphasic pattern of responsiveness characterized the CBA responses to antigens of cercarial, adult worm, or schistosomal egg origin. In comparison, there was a greatly diminished reactivity in immunized C57 B1 6 mice to the same antigens. Therefore, no obvious correlation existed in this model between the relative magnitude of antigen-specific responses between the two strains and the level of anti-schistosome immunity induced.

Olfactory receptor cell responses of dog and box turtle to aliphatic n-acetates and aliphatic n-fatty acids

Electrophysiological studies of groups of olfactory receptor cells in the dog and the box turtle have shown that an olfactory nerve twig response is generated when odorous air (aliphatic n-acetates C2-C9 and aliphatic n-fatty acids C3-C10) is applied to the mucosa. The dog's response to n-pentyl acetate is vigorous, like that of other air-breathing animals. It is concluded from this study that the sensitivity of olfactory receptor cells is similar in the dog and the box turtle. The behavioral discrepancy of olfactory sensitivity among many animals may be accounted for by the larger population of olfactory receptors. The relative response magnitudes plotted against the carbon chain length of aliphatic n-acetates show similar curves for the dog and the box turtle, although the relative response magnitudes plotted against the carbon chain length of aliphatic n-fatty acids show slightly different curves.

Follicle stimulating hormone, luteinizing hormone and estradiol-17 beta response in GnRH treated prepuberal Holstein heifers.

The effect of i.v. injection of 200 µg gonadotropin releasing hormone (GnRH) on plasma LH, FSH and estradiol-17β(E2-17β) was investigated in 18 prepuberal Holstein heifers at either 3,6 or 9 months of age. GnRH caused increased levels of both LH and FSH within 20 min postinjection. Both LH and FSH plasma concentrations reached peak values by 20 min following treatment in 3- and 9-month-old heifers, but in 6-month-old animals neither hormone reached maximum concentration until 2 h postinjection. Levels of both gonadotropins were not different with age. The profiles of both gonadotropins were similar following GnRH treatment (r = 0.86), but the relative magnitude of LH response (30-fold) was greater than FSH response (8-fold). FSH response was less variable in 9-month-old heifers than in younger animals. Concentration of plasma E2-17β was not altered by GnRH treatment by 6 h postinjection. It appears that the prepuberal heifer is capable of releasing large quantities of both LH and FSH and that this response is not different at 3, 6 or 9 months of age. However, it does not appear that the GnRH-induced rise in plasma gonadotropins is sufficient stimulus to promote increased E2-17β production within 6 h after CnRH administration in the prepuberal heifer.

Cardiac and ventilatory responses ofCrangon crangon to cadmium, copper and zinc

The acute (30 min) responses of heart and scaphognathite activities ofCrangon crangon on exposure to concentrations of 1–20 mg Cd, Cu or Zn 1−1 are increased beat frequencies. The relative magnitude of response(Δ f) is linearly related to immediate pretreatment frequency(f) and standardised responses(Δ fs) are given forf values of 70 and 100 beats min−1 for hearts and scaphognathites, respectively.Δ fs values for each organ are also linearly related to test concentration for each metal. Qualitative changes to organ activities described include an increased incidence of scaphognathite reversals in concentrations of 5.0 mg Cu 1−1 and in 20.0 mg Zn 1−1. Chronic (13 days) exposure to incipient lethal levels of the test metals produced increases in scaphognathite rates of the Cd-treated animals and in heart and scaphognathite rates of the coppertreated animals. The general applicability of these methods to studies of pollution stress in decapods is discussed.