Social status regulates growth rate: Consequences for life-history strategies

The life-history strategies of organisms are sculpted over evolutionary time by the relative prospects of present and future reproductive success. As a consequence, animals of many species show flexible behavioral responses to environmental and social change. Here we show that disruption of the habitat of a colony of African cichlid fish, Haplochromis burtoni (Günther) caused males to switch social status more frequently than animals kept in a stable environment. H. burtoni males can be either reproductively active, guarding a territory, or reproductively inactive (nonterritorial). Although on average 25–50% of the males are territorial in both the stable and unstable environments, during the 20-week study, nearly two-thirds of the animals became territorial for at least 1 week. Moreover, many fish changed social status several times. Surprisingly, the induced changes in social status caused changes in somatic growth. Nonterritorial males and animals ascending in social rank showed an increased growth rate whereas territorial males and animals descending in social rank slowed their growth rate or even shrank. Similar behavioral and physiological changes are caused by social change in animals kept in stable environmental conditions, although at a lower rate. This suggests that differential growth, in interaction with environmental conditions, is a central mechanism underlying the changes in social status. Such reversible phenotypic plasticity in a crucial life-history trait may have evolved to enable animals to shift resources from reproduction to growth or vice versa, depending on present and future reproductive prospects.

Heterogeneity of Mitochondrial Protein Biogenesis during Primary Leaf Development in Barley1

The natural developmental gradient of light-grown primary leaves of barley (Hordeum vulgare L.) was used to analyze the biogenesis of mitochondrial proteins in relation to the age and physiological changes within the leaf. The data indicate that the protein composition of mitochondria changes markedly during leaf development. Three distinct patterns of protein development were noted: group A proteins, consisting of the E1 β-subunit of the pyruvate dehydrogenase complex, ORF156, ORF577, alternative oxidase, RPS12, cytochrome oxidase subunits II and III, malic enzyme, and the α- and β-subunits of F1-ATPase; group B proteins, consisting of the E1 α-subunit of the pyruvate dehydrogenase complex, isocitrate dehydrogenase, HSP70A, cpn60C, and cpn60B; and group C proteins, consisting of the four subunits of the glycine decarboxylase complex (P, H, T, and L proteins), fumarase, and formate dehydrogenase. All of the proteins increased in concentration from the basal meristem to the end of the elongation zone (20.0 mm from the leaf base), whereupon group A proteins decreased, group B proteins increased to a maximum at 50 mm from the leaf base, and group C proteins increased to a maximum at the leaf tip. This study provides evidence of a marked heterogeneity of mitochondrial protein composition, reflecting a changing function as leaf cells develop photosynthetic and photorespiratory capacity.

Rapid Up-Regulation of HKT1, a High-Affinity Potassium Transporter Gene, in Roots of Barley and Wheat following Withdrawal of Potassium1

High-affinity K+ uptake in plant roots is rapidly up-regulated when K+ is withheld and down-regulated when K+ is resupplied. These processes make important contributions to plant K+ homeostasis. A cDNA coding for a high-affinity K+ transporter, HKT1, was earlier cloned from wheat (Triticum aestivum L.) roots and functionally characterized. We demonstrate here that in both barley (Hordeum vulgare L.) and wheat roots, a rapid and large up-regulation of HKT1 mRNA levels resulted when K+ was withdrawn from growth media. This effect was specific for K+; withholding N caused a modest reduction of HKT1 mRNA levels. Up-regulation of HKT1 transcript levels in barley roots occurred within 4 h of removing K+, which corresponds to the documented increase of high-affinity K+ uptake in roots following removal of K+. Increased expression of HKT1 mRNA was evident before a decline in total root K+ concentration could be detected. Resupply of 1 mm K+ was sufficient to strongly reduce HKT1 transcript levels. In wheat root cortical cells, both membrane depolarizations in response to 100 μm K+, Cs+, and Rb+, and high-affinity K+ uptake were enhanced by K+ deprivation. Thus, in both plant systems the observed physiological changes associated with manipulating external K+ supply were correlated with levels of HKT1 mRNA expression. Implications of these findings for K+ sensing and regulation of the HKT1 mRNA levels in plant roots are discussed.

A Drosophila seminal fluid protein, Acp26Aa, stimulates egg laying in females for 1 day after mating.

Mating triggers behavioral and physiological changes in the Drosophila melanogaster female, including an elevation of egg laying. Seminal fluid molecules from the male accessory gland are responsible for initial behavioral changes, but persistence of these changes requires stored sperm. Using genetic analysis, we have identified a seminal fluid protein that is responsible for an initial elevation of egg laying. This molecule, Acp26Aa, has structural features of a prohormone and contains a region with amino acid similarity to the egg-laying hormone of Aplysia. Acp26Aa is transferred to the female during mating, where it undergoes processing. Here we report the generation and analysis of mutants, including a null, in Acp26Aa. Females mated to male flies that lack Acp26Aa lay fewer eggs than do mates of normal males. This effect is apparent only on the first day after mating. The null mutation has no other detectable physiological or behavioral effects on the male or the mated female.

Early physiological abnormalities after simian immunodeficiency virus infection

Central nervous system (CNS) damage and dysfunction are devastating consequences of HIV infection. Although the CNS is one of the initial targets for HIV infection, little is known about early viral-induced abnormalities that can affect CNS function. Here we report the detection of early physiological abnormalities in simian immunodeficiency virus-infected monkeys. The acute infection caused a disruption of the circadian rhythm manifested by rises in body temperature, observed in all five individuals between 1 and 2 weeks postinoculation (p.i.), accompanied by a reduction in daily motor activity to 50% of control levels. Animals remained hyperthermic at 1 and 2 months p.i. and returned to preinoculation temperatures at 3 months after viral inoculation. Although motor activity recovered to baseline values at 1 month p.i., activity levels then decreased to approximately 50% of preinoculation values over the next 2 months. Analysis of sensory-evoked responses 1 month p.i. revealed distinct infection-induced changes in auditory-evoked potential peak latencies that persisted at 3 months after viral inoculation. These early physiological abnormalities may precede the development of observable cognitive or motor deficiencies and can provide an assay to evaluate agents to prevent or alleviate neuronal dysfunction.

Signal changes in the spinal cord of the rat after injection of formalin into the hindpaw: Characterization using functional magnetic resonance imaging

Changes in metabolism and local circulation occur in the spinal cord during peripheral noxious stimulation. Evidence is presented that this stimulation also causes signal intensity alterations in functional magnetic resonance images of the spinal cord during formalin-induced pain. These results indicate the potential of functional magnetic resonance imaging in assessing noninvasively the extent and intensity of spinal cord excitation in this well characterized pain model. Therefore, the aim of this study was to establish functional magnetic resonance imaging as a noninvasive method to characterize temporal changes in the spinal cord after a single injection of 50 μl of formalin subcutaneously into the hindpaw of the anesthetized rat. This challenge produced a biphasic licking activity in the freely moving conscious animal. Images of the spinal cord were acquired within 2 min, enabling monitoring of the site and the temporal evolution of the signal changes during the development of formalin-induced hyperalgesia without the need of any surgical procedure. The time course of changes in the spinal cord functional image in the isoflurane-anesthetized animal was similar to that obtained from behavioral experiments. Also, comparable physiological data, control experiments, and the inhibition of a response through application of the local anesthetic agent lidocaine indicate that the signal changes observed after formalin injection were specifically related to excitability changes in the relevant segments of the lumbar spinal cord. This approach could be useful to characterize different models of pain and hyperalgesia and, more importantly, to evaluate effects of analgesic drugs.

Osmotically Induced Cell Volume Changes Alter Anterograde and Retrograde Transport, Golgi Structure, and COPI Dissociation

Physiological conditions that impinge on constitutive traffic and affect organelle structure are not known. We report that osmotically induced cell volume changes, which are known to occur under a variety of conditions, rapidly inhibited endoplasmic reticulum (ER)-to-Golgi transport in mammalian cells. Both ER export and ER Golgi intermediate compartment (ERGIC)-to-Golgi trafficking steps were blocked, but retrograde transport was active, and it mediated ERGIC and Golgi collapse into the ER. Extensive tubulation and relatively rapid Golgi resident redistribution were observed under hypo-osmotic conditions, whereas a slower redistribution of the same markers, without apparent tubulation, was observed under hyperosmotic conditions. The osmotic stress response correlated with the perturbation of COPI function, because both hypo- and hyperosmotic conditions slowed brefeldin A-induced dissociation of βCOP from Golgi membranes. Remarkably, Golgi residents reemerged after several hours of sustained incubation in hypotonic or hypertonic medium. Reemergence was independent of new protein synthesis but required PKC, an activity known to mediate cell volume recovery. Taken together these results indicate the existence of a coupling between cell volume and constitutive traffic that impacts organelle structure through independent effects on anterograde and retrograde flow and that involves, in part, modulation of COPI function.

Physiological astrocytic calcium levels stimulate glutamate release to modulate adjacent neurons

Astrocytes can release glutamate in a calcium-dependent manner and consequently signal to adjacent neurons. Whether this glutamate release pathway is used during physiological signaling or is recruited only under pathophysiological conditions is not well defined. One reason for this lack of understanding is the limited knowledge about the levels of calcium necessary to stimulate glutamate release from astrocytes and about how they compare with the range of physiological calcium levels in these cells. We used flash photolysis to raise internal calcium in astrocytes, while monitoring astrocytic calcium levels and glutamate, which evoked slow inward currents that were recorded electrophysiologically from single neurons grown on microislands of astrocytes. With this approach, we demonstrate that modest changes of astrocytic calcium, from 84 to 140 nM, evoke substantial glutamatergic currents in neighboring neurons (−391 pA), with a Hill coefficient of 2.1 to 2.7. Because the agonists glutamate, norepinephrine, and dopamine all raise calcium in astrocytes to levels exceeding 1.8 μM, these quantitative studies demonstrate that the astrocytic glutamate release pathway is engaged at physiological levels of internal calcium. Consequently, the calcium-dependent release of glutamate from astrocytes functions within an appropriate range of astrocytic calcium levels to be used as a signaling pathway within the functional nervous system.

Inositol hexakisphosphate is a physiological signal regulating the K+-inward rectifying conductance in guard cells

(RS)-2-cis, 4-trans-abscisic acid (ABA), a naturally occurring plant stress hormone, elicited rapid agonist-specific changes in myo-inositol hexakisphosphate (InsP6) measured in intact guard cells of Solanum tuberosum (n = 5); these changes were not reproduced by (RS)-2-trans, 4-trans-abscisic acid, an inactive stereoisomer of ABA (n = 4). The electrophysiological effects of InsP6 were assessed on both S. tuberosum (n = 14) and Vicia faba (n = 6) guard cell protoplasts. In both species, submicromolar concentrations of InsP6, delivered through the patch electrode, mimicked the inhibitory effects of ABA and internal calcium (Cai2+) on the inward rectifying K+ current, IK,in, in a dose-dependent manner. Steady state block of IK,in by InsP6 was reached much more quickly in Vicia (3 min at ≈1 μM) than Solanum (20–30 min). The effects of InsP6 on IK,in were specific to the myo-inositol isomer and were not elicited by other conformers of InsP6 (e.g., scyllo- or neo-). Chelation of Ca2+ by inclusion of 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid or EGTA in the patch pipette together with InsP6 prevented the inhibition of IK,in, suggesting that the effect is Ca2+ dependent. InsP6 was ≈100-fold more potent than Ins(1,4,5)P3 in modulating IK,in. Thus ABA increases InsP6 in guard cells, and InsP6 is a potent Ca2+-dependent inhibitor of IK,in. Taken together, these results suggest that InsP6 may play a major role in the physiological response of guard cells to ABA.

Systemic hypoxia changes the organ-specific distribution of vascular endothelial growth factor and its receptors

Vascular endothelial growth factor (VEGF) plays a key role in physiological blood vessel formation and pathological angiogenesis such as tumor growth and ischemic diseases. Hypoxia is a potent inducer of VEGF in vitro. Here we demonstrate that VEGF is induced in vivo by exposing mice to systemic hypoxia. VEGF induction was highest in brain, but also occurred in kidney, testis, lung, heart, and liver. In situ hybridization analysis revealed that a distinct subset of cells within a given organ, such as glial cells and neurons in brain, tubular cells in kidney, and Sertoli cells in testis, responded to the hypoxic stimulus with an increase in VEGF expression. Surprisingly, however, other cells at sites of constitutive VEGF expression in normal adult tissues, such as epithelial cells in the choroid plexus and kidney glomeruli, decreased VEGF expression in response to the hypoxic stimulus. Furthermore, in addition to VEGF itself, expression of VEGF receptor-1 (VEGFR-1), but not VEGFR-2, was induced by hypoxia in endothelial cells of lung, heart, brain, kidney, and liver. VEGF itself was never found to be up-regulated in endothelial cells under hypoxic conditions, consistent with its paracrine action during normoxia. Our results show that the response to hypoxia in vivo is differentially regulated at the level of specific cell types or layers in certain organs. In these tissues, up- or down-regulation of VEGF and VEGFR-1 during hypoxia may influence their oxygenation after angiogenesis or modulate vascular permeability.

Multifaceted Physiological Response Allows Yeast to Adapt to the Loss of the Signal Recognition Particle-dependent Protein-targeting PathwayD⃞

Translational control has recently been recognized as an important facet of adaptive responses to various stress conditions. We describe the adaptation response of the yeast Saccharomyces cerevisiae to the loss of one of two mechanisms to target proteins to the secretory pathway. Using inducible mutants that block the signal recognition particle (SRP) pathway, we find that cells demonstrate a physiological response to the loss of the SRP pathway that includes specific changes in global gene expression. Upon inducing the loss of the SRP pathway, SRP-dependent protein translocation is initially blocked, and cell growth is considerably slowed. Concomitantly, gene expression changes include the induction of heat shock genes and the repression of protein synthesis genes. Remarkably, within hours, the efficiency of protein sorting improves while cell growth remains slow in agreement with the persistent repression of protein synthesis genes. Our results suggest that heat shock gene induction serves to protect cells from mislocalized precursor proteins in the cytosol, whereas reduced protein synthesis helps to regain efficiency in protein sorting by reducing the load on the protein translocation apparatus. Thus, we suggest that cells trade speed in cell growth for fidelity in protein sorting to adjust to life without SRP.

Behind the scenes of functional brain imaging: A historical and physiological perspective

At the forefront of cognitive neuroscience research in normal humans are the new techniques of functional brain imaging: positron emission tomography and magnetic resonance imaging. The signal used by positron emission tomography is based on the fact that changes in the cellular activity of the brain of normal, awake humans and laboratory animals are accompanied almost invariably by changes in local blood flow. This robust, empirical relationship has fascinated scientists for well over a hundred years. Because the changes in blood flow are accompanied by lesser changes in oxygen consumption, local changes in brain oxygen content occur at the sites of activation and provide the basis for the signal used by magnetic resonance imaging. The biological basis for these signals is now an area of intense research stimulated by the interest in these tools for cognitive neuroscience research.

Kinetic coupling between electron and proton transfer in cytochrome c oxidase: simultaneous measurements of conductance and absorbance changes.

Bovine heart cytochrome c oxidase is an electron-current driven proton pump. To investigate the mechanism by which this pump operates it is important to study individual electron- and proton-transfer reactions in the enzyme, and key reactions in which they are kinetically and thermodynamically coupled. In this work, we have simultaneously measured absorbance changes associated with electron-transfer reactions and conductance changes associated with protonation reactions following pulsed illumination of the photolabile complex of partly reduced bovine cytochrome c oxidase and carbon monoxide. Following CO dissociation, several kinetic phases in the absorbance changes were observed with time constants ranging from approximately 3 microseconds to several milliseconds, reflecting internal electron-transfer reactions within the enzyme. The data show that the rate of one of these electron-transfer reactions, from cytochrome a3 to a on a millisecond time scale, is controlled by a proton-transfer reaction. These results are discussed in terms of a model in which cytochrome a3 interacts electrostatically with a protonatable group, L, in the vicinity of the binuclear center, in equilibrium with the bulk through a proton-conducting pathway, which determines the rate of proton transfer (and indirectly also of electron transfer). The interaction energy of cytochrome a3 with L was determined independently from the pH dependence of the extent of the millisecond-electron transfer and the number of protons released, as determined from the conductance measurements. The magnitude of the interaction energy, 70 meV (1 eV = 1.602 x 10(-19) J), is consistent with a distance of 5-10 A between cytochrome a3 and L. Based on the recently determined high-resolution x-ray structures of bovine and a bacterial cytochrome c oxidase, possible candidates for L and a physiological role for L are discussed.

Olfactory marker protein (OMP) gene deletion causes altered physiological activity of olfactory sensory neurons.

Olfactory marker protein (OMP) is an abundant, phylogentically conserved, cytoplasmic protein of unknown function expressed almost exclusively in mature olfactory sensory neurons. To address its function, we generated OMP-deficient mice by gene targeting in embryonic stem cells. We report that these OMP-null mice are compromised in their ability to respond to odor stimull, providing insight to OMP function. The maximal electroolfactogram response of the olfactory neuroepithelium to several odorants was 20-40% smaller in the mutants compared with controls. In addition, the onset and recovery kinetics following isoamyl acetate stimulation are prolonged in the null mice. Furthermore, the ability of the mutants to respond to the second odor pulse of a pair is impaired, over a range of concentrations, compared with controls. These results imply that neural activity directed toward the olfactory bulb is also reduced. The bulbar phenotype observed in the OMP-null mouse is consistent with this hypothesis. Bulbar activity of tyrosine hydroxylase, the rate limiting enzyme of catecholamine biosynthesis, and content of the neuropeptide cholecystokinin are reduced by 65% and 50%, respectively. This similarity to postsynaptic changes in gene expression induced by peripheral olfactory deafferentation or naris blockade confirms that functional neural activity is reduced in both the olfactory neuroepithelium and the olfactory nerve projection to the bulb in the OMP-null mouse. These observations provide strong support for the conclusion that OMP is a novel modulatory component of the odor detection/signal transduction cascade.

Operant conditioning of H-reflex changes synaptic terminals on primate motoneurons.

Operant conditioning of the primate triceps surae H-reflex, the electrical analog of the spinal stretch reflex, creates a memory trace that includes changes in the spinal cord. To define the morphological correlates of this plasticity, we analyzed the synaptic terminal coverage of triceps surae motoneurons from animals in which the triceps surae H-reflex in one leg had been increased (HRup mode) or decreased (HRdown mode) by conditioning and compared them to each other and to motoneurons from unconditioned animals. Motoneurons were labeled by intramuscular injection of cholera toxin-horseradish peroxidase. A total of 5055 terminals on the cell bodies and proximal dendrites of 114 motoneurons from 14 animals were studied by electron microscopy. Significant differences were found between HRup and HRdown animals and between HRup and naive (i.e., unconditioned) animals. F terminals (i.e., putative inhibitory terminals) were smaller and their active zone coverage on the cell body was lower on motoneurons from the conditioned side of HRup animals than on motoneurons from the conditioned side of HRdown animals. C terminals (i.e., terminals associated with postsynaptic cisterns and rough endoplasmic reticulum) were smaller and the number of C terminals in each C complex (i.e., a group of contiguous C terminals) was larger on motoneurons from the conditioned side of HRup animals than on motoneurons either from the conditioned side of HRdown animals or from naive animals. Because the treatment of HRup and HRdown animals differed only in the reward contingency, the results imply that the two contingencies had different effects on motoneuron synaptic terminals. In combination with other recent data, they show that H-reflex conditioning produces a complex pattern of spinal cord plasticity that includes changes in motoneuron physiological properties as well as in synaptic terminals. Further delineation of this pattern should reveal the contribution of the structural changes described here to the learned change in behavior.