Showing papers by "McGill University published in 1978"

Patterns in Strategy Formation

Abstract: The literature on strategy formation is in large part theoretical but not empirical, and the usual definition of “strategy” encourages the notion that strategies, as we recognize them ex post facto, are deliberate plans conceived in advance of the making of specific decisions. By defining a strategy as “a pattern in a stream of decisions,” we are able to research strategy formation in a broad descriptive context. Specifically, we can study both strategies that were intended and those that were, realized.despite intentions. A research program suggested by this definition is outlined, and two of the completed studies are then reviewed---the strategies of Volkswagenwerk from 1934 to 1974 and of the United States government in Vietnam from 1950 to 1973. Some general conclusions suggested by these studies are then presented in terms of three central themes: that strategy formation can fruitfully be viewed as the interplay between a dynamic environment and bureaucratic momentum, with leadership mediating between the two forces; that strategy formation over time appears to follow some important patterns in organizations, notably life cycles and distinct change-continuity cycles within these; and that the study of the interplay between intended and realized strategies may lead us to the heart of this, complex organizational process.

The second image reversed: the international sources of domestic politics

Abstract: The international system is not only an expression of domestic structures, but a cause of them. Two schools of analysis exploring the impact of the international system upon domestic politics (regime types, institutions, coalitions, policies) may be distinguished: those which stress the international economy, and those which stress political-military rivalry, or war. Among the former are such arguments as: late industrialization (associated with Gershenkron); dependencia or core-periphery arguments (Wallerstein); liberal development model (much American writing in the 50s and 60s); transnational relation-modernization (Nye, Keohane, Morse); neo-mercantilists (Gilpin); state-centered Marxists (Schurmann). Arguments stressing the role of war include those which focus on the organizational requirements of providing security (Hintze, Anderson), the special nature of foreign relations (classical political theory), territorial compensation (diplomatic history), and strains of foreign involvement (analysis of revolutions). These arguments provide the basis for criticism of much of the literature which uses domestic structure as an explanation of foreign policy, in particular those which (such as the strong-state weak-state distinction) tend, by excessive focus on forms, to obscure the connection between structures and interests, and the role of politics. These arguments also permit criticism of the notion of a recent fundamental discontinuity in the nature of international relations.

Archetypes of Strategy Formulation

Abstract: There have been few attempts to understand the strategy making process by examining the organizational and environmental context in which it occurs Rather than adopting the stance of contingency theorists who focus mainly on bivariate relationships, we decided to look for simultaneous associations among a fairly large number of variables It was hoped that these variables would configure into models or archetypes which describe a series of different, though very frequently occurring modes or organizational failure and success The methodology used to isolate archetypes is explained Ten archetypes are described Successful archetypes are: the adaptive firm under moderate challenge, the adaptive firm in a very challenging environment, the dominant firm, the giant under fire, the entrepreneurial conglomerate, and the innovator Failure archetypes include: the impulsive firm, the stagnant bureaucracy, the headless giant, and the aftermath

The relations between structural changes in small airways and pulmonary-function tests.

Abstract: To examine the relation between small-airways abnormalities and specific lung functions, we performed pulmonary-function tests in 36 patients, of whom two were nonsmokers, one to three days before open-lung biopsy for localized pulmonary lesions. The primary lesion in the small airways was a progressive inflammatory reaction leading to fibrosis with connective-tissue deposition in the airway walls. Increase in disease in small airways correlated with deterioration in lung function. Lesions could be reliably detected (P<0.05) by tests for closing capacity, the volume at which air and helium flow were equal (a test of airway caliber and elastic recoil), and the slope of phase III of the single-breath washout curve (which tests evenness of ventilation). These tests showed abnormalities at a time when the pathologic changes were still potentially reversible and when other tests were not appreciably changed. (N Engl J Med 298:1277–1281, 1977)

Relationships between body size and some life history parameters.

Abstract: Patterns in life history phenomena may be demonstrated by examining wide ranges of body weight. Positive relationships exist between adult body size and the clutch size of poikilotherms, litter weight, neonate weight life span, maturation time and, for homeotherms at least, brood or gestation time. The complex of these factors reduces r max in larger animals or, in more physiological terms, r max is set by individual growth rate. Comparison of neonatal production with ingestion and assimilation suggests that larger mammals put proportionately less effort into reproduction. Declining parental investment and longer development times would result if neonatal weight is scaled allometrically to adult weight and neonatal growth rate to neonatal weight. Body size relations represent general ecological theries and therefore hold considerable promise in the development of predictive ecology.

How adaptive behavior is produced: a perceptual-motivational alternative to response reinforcements

Abstract: The sway that the response-reinforcement framework (Spencer, Thorndike, Hull, Skinner) has held on the behavioral sciences for nearly a hundred years is finally ending. The strength of this framework lay in providing concepts and methods for studying the effects of hedonic (reinforcing) stimuli on the repetition of specified responses acquired in instrumental training situations of various kinds. Its weakness lay in the invalidity of its central assumptions, stimulus-response association and response-reinforcement, which could not deal with motor-equivalence and flexibility (or “intelligence”) in behavior. To the four decades of incisive criticism on particular theoretical and empirical grounds, a more comprehensive challenge to the response-reinforcement framework is now added by the newer ideas about the nature of cognitive, motivational, and response-production processes that have emerged from the work of ethologists, neuroscientists, and cognitive psychologists. An alternative framework, incorporating the newer ideas, is clearly needed.The particular framework proposed here is based on the ideas of perceptual learning of stimulus-stimulus correlations and of a motivational (rather than reinforcing) role of hedonic (incentive) stimuli. According to it, an act is produced when its act-assembly is activated by a pexgo (perceptual representation) of a certain eliciting stimulus complex (ES). When certain eliciting stimuli are correlated with incentive stimuli, they acquire motivational properties that serve to strengthen the pexgos generated by those eliciting stimuli and thereby increase the probability of activation of the corresponding act-assemblies. Motivation thus influences response production, not by directly instigating “existing” responses, but by modulating the strength of pexgos of eliciting stimuli for the succession of acts that comprise a response. Therefore, a response is always constructed afresh on the basis of current perceptions; not even a stable and stereotyped response occurs as a mere activation of a preformed motor program. The topography of any response that emerges is determined by the nature of the motivational state and the momentary spatiotemporal distribution of eliciting stimuli of changing motivational valence.By suggesting that the animal learns the overlapping and nested correlations between the stimulus events that commonly occur in a given situation, and by separating what is learned from the processes of response production, the proposed perceptual-motivational framework seems capable of dealing with the problems of motor equivalence and flexibility in adaptive behavior. Some implications of this approach for further behavioral and brain research on such problems as behavior modification, learning by observation of models, analysis of causality, and search for neural substrates of learning and response production, are outlined.

Clinical pharmacokinetics of theophylline.

Abstract: Knowledge acquired of the kinetic disposition and effects of theophylline over the past 8 years has increased the clinical utility of the drug in the treatment of cardiorespiratory disorders. Although the anhydrous theophylline content varies greatly between products, there is similar excellent oral bioavailability. An average 96% (range 75 to 105%) of an uncoated theophylline tablet is absorbed, with peak concentrations occurring from 0.5 to 2.0h. Enteric coated and many sustained release preparations have poor bioavailability. Intravenous preparations of aminophylline contain from 75 to 85% theophylline by weight. Other routes of administration are not to be recommended. In plasma, some 53 to 65% of theophylline is reversibly bound to protein. Premature neonates and adults with hepatic cirrhosis have reduced binding. The apparent volume of distribution in the steady state averages 0.5L/kg body weight regardless of sex, age (1 to 87 years), history of cigarette smoking, asthma, or acute pulmonary oedema. Premature neonates and adults with acidaemia, hepatic cirrhosis or obesity tend to have larger volumes of distribution for theophylline. Theophylline is eliminated by biotransformation in the liver and urinary excretion of its metabolites. Approximately 7 to 13% is excreted unchanged in the urine by a first order process. One of the metabolites, 3-methylxanthine, which is pharmacologically active but less potent than theophylline, is eliminated by Michaelis-Menten kinetics. Removal of dietary methylxanthines can increase the rate of elimination of a single dose of theophylline. Dose dependent elimination kinetics has been suggested but not conclusively demonstrated. The plasma theophylline concentration time curve after intravenous administration fits a 2 compartment open kinetic model with a rapid a distribution phase completed within 30 to 45 minutes after an intravenous dose. The β elimination phase t½β) is quite variable and in healthy adults ranges from 3 to 13h. As the apparent volume of distribution is little altered under most conditions, variations in theophylline elimination half-life reflect alterations in plasma theophylline clearance. The predominant factors which alter theophylline clearance are age, body weight, diet, smoking habits, other drugs and cardiorespiratory or hepatic disease. The elimination of theophylline is markedly decreased in premature infants and increased in childhood. The rapid clearance in childhood decreases toward adult values in the late teens. Some authors believe old age per se decreases an individual’s capacity to eliminate theophylline. However, this may be a reflection of the inability of hepatic enzymes in the elderly to respond to factors in the diet or environment which usually stimulate theophylline clearance. The elimination half-life of theophylline is prolonged in obese subjects and maintenance doses must be calculated from ideal body weight. Theophylline clearance can be decreased by a high carbohydrate-low protein diet, as well as the ingestion of other methylxanthines such as caffeine. In contrast, a low carbohydrate-high protein diet, especially charcoal broiled meat, may enhance theophylline clearance. Theophylline clearance is markedly increased by tobacco or marihuana smoke. The rate of recovery from the stimulated state on cessation of smoking is unknown. Although there is some evidence that phenobarbitone treatment can slightly induce the hepatic metabolism of theophylline in vitro, the evidence in man for such an effect is inconclusive. The macrolide antibiotics, troleandomycin and erythromycin, are potent inhibitors of theophylline elimination. There is no evidence that uncomplicated asthma or chronic bronchitis alters theophylline clearance but, as chronic obstructive lung disease ensues with complications such as pneumonia or cor pulmonale, theophylline clearance can be markedly impaired. The elimination of theophylline is also reduced by congestive heart failure or acute pulmonary oedema. The mechanism responsible for reduced theophylline clearance in patients with cardiorespiratory disease is unclear. Reduced hepatocellular function is apparently responsible for the most marked decrease in theophylline clearance in patients with hepatic cirrhosis. It is not clear if one or several biochemical tests of liver function will allow prediction of the degree of impairment of theophylline elimination in individual patients. Reduced theophylline clearance has been observed in febrile children with acute viral exanthems. The bronchodilator effect of theophylline is related to plasma theophylline concentrations in the post-distribution period, indicating that the site of its bronchodilator activity is outside of the central kinetic compartment. Continuous improvement in forced expiratory volumes can be observed over the plasma theophylline concentration range of 5 to 20mg/L. These concentrations can reduce the frequency of asthmatic attacks, abolish exercise induced bronchospasm and increase the ventilatory response to hypoxaemia. Plasma theophylline concentrations of 5 to 20mg/L can produce concentration related increases in forearm blood flow and reductions in cerebral blood flow. The mechanism responsible for the reduction in cerebral blood flow is not clear. Peripheral venous distensibility is maximally increased at 10mg/L. Cardiac output and heart rate are variably increased. Although myocardial oxygen consumption increases, there appears to be a greater increase in oxygen delivery by increased coronary blood flow, suggesting a direct reduction of coronary vascular resistance. Pulmonary vascular resistance is reduced with increased ventilation/perfusion abnormalities. Arterial oxygen tension may decrease in asthmatic patients even though airway obstruction is relieved. Serious adverse effects are rare at plasma theophylline concentrations below 20mg/L. The most frequent adverse effects involve the gastrointestinal system (anorexia, nausea, vomiting, abdominal discomfort) and the nervous system (headache, nervousness, anxiety), which usually occur with concentrations over 15mg/L. Between 20 and 40mg/L, sinus tachycardia and atrial or ventricular arrhythmias occur with increasing frequency. Above 40mg/L, focal or generalised seizures, or cardiorespiratory arrest can occur. For rapid attainment of therapeutic plasma theophylline concentrations, a loading dose of aminophylline 5.6mg/kg can be given over 20 minutes via a peripheral vein. Although this dose is relatively safe and almost universally applicable, caution must be exercised if the patient has received theophylline in the previous 12 to 24 hour period. Maintenance doses of theophylline for intravenous or oral use should be calculated based on ideal body weight and modified for the presence of factors which alter theophylline clearance. Dose guidelines are approximations only and the wide variability in theophylline clearance between individuals and with disease makes their indiscriminant application hazardous. It is rational to begin with smaller than recommended doses and increase at intervals as tolerated until the recommended amounts are administered. In adult patients, one may limit theophylline doses to 16mg/kg daily unless a plasma theophylline concentration is obtained as a guide for further adjustment. With the proper resources, interpretive skills, and timing of plasma samples, theophylline concentrations can give the clinician sufficient information to prescribe ideal theophylline doses for an individual patient, provided the clinician searches for and recognises factors which alter theophylline clearance in that patient.

Effect of smoking on caffeine clearance

Abstract: The elimination of caffeine from saliva was compared in groups of healthy smokers (n = 13) and nonsmokers (n = 13). Mean caffeine t1/2 in smokers (3.5 hr) was shorter than that in the nonsmokers (6.0 hr). The body clearance of caffeine in the smokers (155 +/- 16 ml . kg-1 . hr-1) was greater than that in the nonsmokers (94 +/- 18 ml . kg-1 . hr-1) (p less than 0.05). No significant difference was noted in the apparent volume of distribution in smokers (720 +/- 67 ml . kg-1) and nonsmokers (610 +/- 80 ml . kg-1). These differences probably reflect the induction of hepatic aryl hydrocarbon hydroxylase (AHH) activity in smokers. The increased clearance of caffeine by smokers may contribute to the higher consumption of coffee reported to occur in this group.

Differences in secretion of the proteinase cathepsin B at the edges of human breast carcinomas and fibroadenomas

Abstract: IN 1925 Fischer1 observed that pieces of explanted chicken tumours, unlike normal tissue, caused the lysis of plasma clots. Since then, there have been several investigations into the secretion of degradative enzymes by tumours. An increased extracellular activity of enzymes capable of the destruction of extracellular substances has long been an attractive concept for facilitating the infiltration of normal tissue by tumour cells2–9. Proteinases are natural candidates for study, as extracellular macromolecules and cell surfaces are rich in proteins and glycoproteins. We report here our study of possible differences in the secretion of the lysosomal proteinases, cathepsin D and cathepsin B, from explants of human tumours, both malignant (breast carcinomas) and non-malignant (breast fibroadenomas) and from normal breast tissue, as previously suggested3. Cathepsin B secretion was significantly higher for malignant than non-malignant tissue (fibroadenomas and normal breast tissue). Such a difference in the secretion and extracellular activity of this enzyme might help to explain further the ability of malignant tumours to infiltrate and metastasise.

Auditory streaming and the building of timbre.

Abstract: In a natural environment, the auditory system must analyse an incoming wave train to determine two things: (a) which series of frequency components arose over time from the same source and should be integrated into a sequential stream, and (b) which set of simultaneous components arose from one source and should be fused into a timbre structure. A set of experiments was performed in which subject judged the stream organization and the timbre of a repeating cycle formed by a pair of more or less synchronous pure tones, B and C, and a preceding pure tone, A, whose frequency was varied in its proximity to that of the upper tone of the BC pair. These experiments demonstrated that fusion and sequential organization of streams are carried out using two sorts of information which compete to determine the best perceptual description of the input. Proximal frequencies between sequential components promotes a sequential organization and the simultaneity of onset of frequency components promotes perceptual fusion.

Auditory Streaming Is Cumulative

Abstract: The auditory system appears to begin listening to an input with a basis toward hearing the input as a single stream, but it gradually accumulates evidence over a period of seconds which may lead to the input's being split into substreams. Several seconds of silence or of unpatterned noise slowly remove the bias of the mechanism in favor of these streams. The effects were demonstrated in experiments in which young adult listeners sped up sequences of tones until they split. The sequences varied in the number of tones packaged between recurrent "separators" (periods of silence or of white noise) and in the lengths of these separators.

Control of breathing in patients with chronic obstructive lung disease.

Abstract: Summary 1. Using the mouth occlusion pressure tech­ nique, we have studied the control of breathing in seven hypercapnic and eight non-hypercapnic patients with chronic obstructive lung disease. 2. When breathing room air, pulmonary ven­ tilation, mean inspiratory flow and P0.i (mouth occlusion pressure developed 0-1 s after the onset of occluded inspiration at functional residual capacity) were not significantly different between the two groups of patients. Tidal volume, however, was significantly lower in the hypercapnic than in the non-hypercapnic patients, as a result of a significantly lower duration of inspiration. 3. The lower tidal volume in the hypercapnic patients leads to decreased alveolar ventilation, and appears to be the main cause of retention of carbon dioxide.

Radioautographic investigation of gliogenesis in the corpus callosum of young rats. II. Origin of microglial cells.

Abstract: Microglial cells are absent from the corpus callosum of newborn rats. In the hope of finding out when and how microglial cells appear with age, 3H-thymidine was given intraperitoneally as single or three shortly spaced injections to 5-day-old rats weighing about 15 g; and these animals were sacrificed at various time intervals from 2 hours to 35 days later. Pieces of corpus callosum were taken near the superior lateral angle of the lateral ventricles; and semithin sections were radioautographed and stained with toluidine blue. The corpus callosum of 5-day-old rats is composed of loosely arranged unmyelinated fibers and scattered cells. Among these cells, microglia are rare; there are a few astrocytes, many immature glial cells, rare pericytes, and 6-7% of phagocytic “ameboid cells” consisting of a few monocytes and many macrophages. In the animals sacrificed two hours after 3H-thymidine administration, label is present only in immature cells and “ameboid cells.” As time elapses and the fibers of corpus callosum become myelinated, oligodendrocytes and, later, microglial cells appear. At the age of 12 days, microglial cells are present in substantial number; and by 19 days, the number doubles to reach a plateau. Many of the new microglial cells are labeled, e.g., 78.1% in 12-day-old animals (7 days after 3H-thymidine administration). The labeled microglial cells must have come from the transformation of cells that acquired label early, that is, from the immature cells or the “ameboid cells.” The height of the peaks of labeling – 59.8% at nine days for immature cells and 77.8% at 12 days for “ameboid cells” – points to the latter as precursors of the highly labeled microglial cells. Furthermore, the “ameboid cells” disappear as microglial cells appear and there are transitional elements between these two cell types. Cell counts suggest that about a third of the “ameboid cells” transform into microglial cells, while the others degenerate and die. Thus, the microglial cells which appear in the corpus callosum during the first three weeks of life result from transformation of the “ameboid cells” – a group of macrophages showing various stages of transition from monocytes. As for the occasional microglial cell appearing after the third week or in the adult, they presumably come directly from monocytes. In either case, monocytes would be the intial precursors.

Neuroleptic-Induced Supersensitivity Psychosis

Abstract: drops from neurologic disease, pilocarpine, a parasympathomimetic agent, is safe and reliable. It causes ·constriction of the iris sphincter unless atropine or an·other postsynaptic blocker, such as tropicamide, the substance involved in this case, has been used. Physostigmine salicylate (Antilirium) was not used, · but it is effective in treating anticholinergic intoxica.' tion when administered intramuscularly (l mg repeated in 15-20 minutes if necessary). In Ms. A's case, the anticholinergic effects of chlorpromazine, amitriptyline, scopolamine (Sominex) (0), and tropicamide were probably additive. Although her disorientation cleared rapidly, Ms. A maintained that her hallucinations persisted during her 2-week hospitalization. However, it is difficult to know : whether this was actually the case. Given the previous diagnosis of Munch~lUsen syndrome and her unusual willingness to assume the psychiatric patient role as well as the medical-surgical patient role, it is not unlikely that she was attempting to prolong her hospitalization.

Work Satisfaction and Age: Some Evidence for the ‘Job Change’ Hypothesis

Abstract: Previous research on work satisfaction has consistently shown that older people are more satisfied with their jobs than younger people. The present paper addresses three possible explanations for this tendency: (1) the "1now generation" of workers subscribes to a set of post-material values that contradict the demands of the industrial system and cause greater work discontent; (2) the standards of the old are systematically eroded by their years in the system, such that they learn to be satisfied with less; and (3) older workers simply have better jobs. A decisive choice among these hypotheses cannot be made without longitudinal data; nonetheless, the bulk of the evidence presented here (for economically active, salaried white males, drawn from the University of Michigan's 1972-73 Quality of Employment survey) clearly favors the last hypothesis. The academic literature on job satisfaction encompasses something in excess of 3000 independent studies (Campbell et al.; Kahn). Much of the existing research has focused on one of three basic topics: the sheer amount of satisfaction; the relationship between satisfaction and productivity; and the relationship between satisfaction and status, occupation, or social class. Concerning the first, the near-unanimous finding is that there is relatively little outright discontent; most people say they are "pretty satisfied" with their work (Kahn, 169).1 There is much less consensus on the second. Kahn's review, for example, concludes that "satisfaction is related to productivity in some circumstances and not in others, and that these circumstances have yet to be defined" (193). As for the link to social class, Jencks and associates have argued that the correlations between work satisfaction and various measures of social status "are surprisingly weak" (247). Prior studies, they suggest, simply "stress the importance of small differences between occupations." In contrast to the voluminous literature on work satisfaction and SES, there has not been much analysis of the relation between satisfaction

Decisions about identity and orientation of rotated letters and digits.

Abstract: In three experiments, human observers made timed decisions about alphanumeric characters, displayed singly in different orientations and versions (normal vs. backward). Latency to identify the characters was longer for backward than for normal versions, regardless of angular orientation and even under conditions in which latency was independent of angular orientation. Subjects also took longer to respond to a target orientation (whatever the character) than to respond to a target character (whatever the orientation). The results suggest that the observer first induces a description of a character that is largely independent of orientation but not of version, although the representation of version is too weak at this stage to permit an overt decision about it. Next, the angular orientation of the character is determined. Finally, the observer might “mentally rotate” the representation to the standard upright, for matching against an internally generated template.

The principal components of mixed measurement level multivariate data: An alternating least squares method with optimal scaling features

Abstract: A method is discussed which extends principal components analysis to the situation where the variables may be measured at a variety of scale levels (nominal, ordinal or interval), and where they may be either continuous or discrete. There are no restrictions on the mix of measurement characteristics and there may be any pattern of missing observations. The method scales the observations on each variable within the restrictions imposed by the variable's measurement characteristics, so that the deviation from the principal components model for a specified number of components is minimized in the least squares sense. An alternating least squares algorithm is discussed. An illustrative example is given.

Catecholamines and self-stimulation: Reward and performance effects dissociated

Abstract: Drug-induced changes in the specifically rewarding effect of brain stimulation can be shown by shifts in the location of the sharp rise in the function (reward summation function, RSF) which relates running speed in an alley to the number of pulses received as a reward. This method was used to characterize the depressions of self-stimulation induced by the dopamine antagonist pimozide (0.2–0.9 mg/kg) and clonidine, a drug which acts on presynaptic α-adrenoceptors to inhibit noradrenaline release. Pimozide shifted RSFs in the direction indicating a reduced rewarding effect of brain stimulation but did not proportionately depress the maximum running speed. The larger doses of pimozide led to extinction of alley running. Clonidine (0.03 and 0.15 mg/kg) similarly reduced the rewarding potency of brain stimulation but also depressed running speed. Piperoxane antagonized clonidine's effect on the RSF location but added to the depression of running speed, thus confirming that drug effects on reward are dissociable from performance effects with the RSF method. In the light of these and other recent findings it is suggested that dopaminergic mechanisms are directly involved in the putative reward system and noradrenaline may be indirectly involved in self-stimulation via an effect on cerebral metabolism.

Stable oscillations in mathematical models of biological control systems

Abstract: Oscillations in a class of piecewise linear (PL) equations which have been proposed to model biological control systems are considered. The flows in phase space determined by the PL equations can be classified by a directed graph, called a state transition diagram, on anN-cube. Each vertex of theN-cube corresponds to an orthant in phase space and each edge corresponds to an open boundary between neighboring orthants. If the state transition diagram contains a certain configuration called a cyclic attractor, then we prove that for the associated PL equation, all trajectories in the regions of phase space corresponding to the cyclic attractor either (i) approach a unique stable limit cycle attractor, or (ii) approach the origin, in the limitt→∞. An algebraic criterion is given to distinguish the two cases. Equations which can be used to model feedback inhibition are introduced to illustrate the techniques.

Ectopic generation of impulses and cross-talk in spinal nerve roots of “dystrophic” mice

Abstract: In "dystrophic" mice, many spinal root axons are bare and closely apposed to one another in midroot. The direction of nerve impulse traffic in lubosacral spinal nerve roots was determined by biphasic recording of spontaneous activity. In normal mice, impulse traffic in dorsal and ventral roots is directed toward and away from the spinal cord, respectively. However, in spinal root fibers of dystrophic mice, impulses also originate in midroot and are propagated toward both the spinal cord and the periphery. Impulses originate in midroot as single isolated events, in bursts at frequencies of up to 100 Hz, or as continuous activity persisting for several minutes in single fibers. Ectopically arising activity in some single fibers is consistently associated with transmission of an impulse in another fiber past the site of origin of the ectopically arising impulse. Thus impulses arise in the spinal root axons of dystrophic mice both spontaneously and as a result of cross-talk between single fibers.

Heritability of external morphology in Darwin's finches

Abstract: ECOLOGISTS use measurements of avian morphological characters to test and modify evolutionary theories. But virtually nothing is known about the inheritance of such characters, although the theories are usually based on genetic models. As a result, either implicitly or explicitly, avian ecologists have used the terms phenotype and genotype almost interchangeably1. At the same time, theoreticians have assumed in their calculations that heritabilities are equal to one2. This problem is particularly acute when intraspecific variation itself is the focus of attention, as it is in studies of the niche-variation hypothesis1. We show here that several ecologically significant characters have high heritabilities in Darwin's medium ground finch (Geospiza fortis).

Antiserum to somatostatin reverses starvation-induced inhibition of growth hormone but not insulin secretion.

Abstract: The role of SRIF in starvation-induced inhibition of GH and insulin secretion was assessed by passive immunization with anti-SRIF serum. Six-hour secretory profiles obtained from chronically cannulated male rats deprived of food for 72 h showed marked suppression of GH secretory bursts and significant depression of plasma insulin levels. Administration of 1 ml SRIF antiserum (SRIF AS) iv to starved rats resulted in rapid (within 15 min) restoration of high amplitude GH pulses (600–800 ng/ml) and significant elevation of GH trough values. The mean 6-h GH level of starved SRIF, AS-treated rats (189.2 ± 23.9 ng/ml) was significantly higher than that of starved, normal sheep serumtreated control animals (62.8 ± 5.8 ng/ml) (P < 0.005). In contrast to the effects on GH, plasma insulin levels in starved rats administered SRIF AS remained low. No significant difference was observed in the mean 6-h plasma insulin level of starved-SRIF, AS-treated rats when compared to starved, normal sheep serum-treated controls. ...