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Emery, N. J. (2000). The eyes have it: the neuroethology, function and evolution of social gaze. Neurosci Biobehav Rev, 24(6), 581–604.
Abstract: Gaze is an important component of social interaction. The function, evolution and neurobiology of gaze processing are therefore of interest to a number of researchers. This review discusses the evolutionary role of social gaze in vertebrates (focusing on primates), and a hypothesis that this role has changed substantially for primates compared to other animals. This change may have been driven by morphological changes to the face and eyes of primates, limitations in the facial anatomy of other vertebrates, changes in the ecology of the environment in which primates live, and a necessity to communicate information about the environment, emotional and mental states. The eyes represent different levels of signal value depending on the status, disposition and emotional state of the sender and receiver of such signals. There are regions in the monkey and human brain which contain neurons that respond selectively to faces, bodies and eye gaze. The ability to follow another individual's gaze direction is affected in individuals with autism and other psychopathological disorders, and after particular localized brain lesions. The hypothesis that gaze following is “hard-wired” in the brain, and may be localized within a circuit linking the superior temporal sulcus, amygdala and orbitofrontal cortex is discussed.
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Buchner, H. H. F., Obermuller, S., & Scheidl, M. (2000). Body Centre of Mass Movement in the Sound Horse. The Veterinary Journal, 160(3), 225–234.
Abstract: The body centre of mass (BCM) is a key factor in the analysis of equine locomotion, as its position and movement determines the distribution and magnitude of loads on the limbs. In this study, the three-dimensional (3D) movement of the BCM in walking and trotting horses was assessed using a kinematic, segmental method. Thirty markers representing 20 body segments were recorded in 12 sound horses while standing, walking and trotting on a treadmill using a high-speed video system. Based on segmental inertial data, 3D positions of the segmental centres of mass as well as the total BCM were calculated. The position within the trunk during square standing and the movements of the BCM were determined for the three planes. The position of the BCM in the standing horse is presented relative to external reference points. At the trot, vertical displacement amplitude of the BCM amounted to 53 (6) mm as mean (sd), which was 27% smaller than external trunk movement. Medio-lateral displacement amplitude of the BCM was 19 (4) mm, 34% less than trunk amplitude. Sagittal forward-backward oscillations of the BCM independent from general forward movement were 13 (3) mm, being 24% less than trunk movements. At the walk, vertical, medio-lateral and sagittal BCM movements were smaller than trunk movements by 43, 65 and 65% respectively. The results show reduced and efficient BCM movements compared to the trunk and form a basis for the assessment of various clinical conditions such as lameness, the influence of a rider and various dressage performances.
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Pierce, M. M., & Nall, B. T. (2000). Coupled kinetic traps in cytochrome c folding: His-heme misligation and proline isomerization. J Mol Biol, 298(5), 955–969.
Abstract: The effect of His-heme misligation on folding has been investigated for a triple mutant of yeast iso-2 cytochrome c (N26H,H33N,H39K iso-2). The variant contains a single misligating His residue at position 26, a location at which His residues are found in several cytochrome c homologues, including horse, tuna, and yeast iso-1. The amplitude for fast phase folding exhibits a strong initial pH dependence. For GdnHCl unfolded protein at an initial pH<5, the observed refolding at final pH 6 is dominated by a fast phase (tau(2f)=20 ms, alpha(2f)=90 %) that represents folding in the absence of misligation. For unfolded protein at initial pH 6, folding at final pH 6 occurs in a fast phase of reduced amplitude (alpha(2f) approximately 20 %) but the same rate (tau(2f)=20 ms), and in two slower phases (tau(m)=6-8 seconds, alpha(m) approximately 45 %; and tau(1b)=16-20 seconds, alpha(1b) approximately 35 %). Double jump experiments show that the initial pH dependence of the folding amplitudes results from a slow pH-dependent equilibrium between fast and slow folding species present in the unfolded protein. The slow equilibrium arises from coupling of the His protonation equilibrium to His-heme misligation and proline isomerization. Specifically, Pro25 is predominantly in trans in the unligated low-pH unfolded protein, but is constrained in a non-native cis isomerization state by His26-heme misligation near neutral pH. Refolding from the misligated unfolded form proceeds slowly due to the large energetic barrier required for proline isomerization and displacement of the misligated His26-heme ligand.
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Hagen, S. J., & Eaton, W. A. (2000). Two-state expansion and collapse of a polypeptide. J Mol Biol, 301(4), 1019–1027.
Abstract: The initial phase of folding for many proteins is presumed to be the collapse of the polypeptide chain from expanded to compact, but still denatured, conformations. Theory and simulations suggest that this collapse may be a two-state transition, characterized by barrier-crossing kinetics, while the collapse of homopolymers is continuous and multi-phasic. We have used a laser temperature-jump with fluorescence spectroscopy to measure the complete time-course of the collapse of denatured cytochrome c with nanosecond time resolution. We find the process to be exponential in time and thermally activated, with an apparent activation energy approximately 9 k(B)T (after correction for solvent viscosity). These results indicate that polypeptide collapse is kinetically a two-state transition. Because of the observed free energy barrier, the time scale of polypeptide collapse is dramatically slower than is predicted by Langevin models for homopolymer collapse.
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Abbruzzetti, S., Crema, E., Masino, L., Vecli, A., Viappiani, C., Small, J. R., et al. (2000). Fast events in protein folding: structural volume changes accompanying the early events in the N-->I transition of apomyoglobin induced by ultrafast pH jump. Biophys J, 78(1), 405–415.
Abstract: Ultrafast, laser-induced pH jump with time-resolved photoacoustic detection has been used to investigate the early protonation steps leading to the formation of the compact acid intermediate (I) of apomyoglobin (ApoMb). When ApoMb is in its native state (N) at pH 7.0, rapid acidification induced by a laser pulse leads to two parallel protonation processes. One reaction can be attributed to the binding of protons to the imidazole rings of His24 and His119. Reaction with imidazole leads to an unusually large contraction of -82 +/- 3 ml/mol, an enthalpy change of 8 +/- 1 kcal/mol, and an apparent bimolecular rate constant of (0.77 +/- 0.03) x 10(10) M(-1) s(-1). Our experiments evidence a rate-limiting step for this process at high ApoMb concentrations, characterized by a value of (0. 60 +/- 0.07) x 10(6) s(-1). The second protonation reaction at pH 7. 0 can be attributed to neutralization of carboxylate groups and is accompanied by an apparent expansion of 3.4 +/- 0.2 ml/mol, occurring with an apparent bimolecular rate constant of (1.25 +/- 0.02) x 10(11) M(-1) s(-1), and a reaction enthalpy of about 2 kcal/mol. The activation energy for the processes associated with the protonation of His24 and His119 is 16.2 +/- 0.9 kcal/mol, whereas that for the neutralization of carboxylates is 9.2 +/- 0.9 kcal/mol. At pH 4.5 ApoMb is in a partially unfolded state (I) and rapid acidification experiments evidence only the process assigned to carboxylate protonation. The unusually large contraction and the high energetic barrier observed at pH 7.0 for the protonation of the His residues suggests that the formation of the compact acid intermediate involves a rate-limiting step after protonation.
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Marc, M., Parvizi, N., Ellendorff, F., Kallweit, E., & Elsaesser, F. (2000). Plasma cortisol and ACTH concentrations in the warmblood horse in response to a standardized treadmill exercise test as physiological markers for evaluation of training status. J. Anim Sci., 78(7), 1936–1946.
Abstract: Reliable physiological markers for performance evaluation in sport horses are missing. To determine the diagnostic value of plasma ACTH and cortisol measurements in the warmblood horse, 10 initially 3-yr-old geldings of the Hannovarian breed were either exposed to a training schedule or served as controls. During experimental Phase 1, horses were group-housed, and half of the horses were trained for 20 wk on a high-speed treadmill. During Phase 2, groups were switched and one group was trained for 10 wk as during Phase 1, whereas the control group was confined to boxes. During Phase 3 horses were initially schooled for riding. Thereafter, all horses were regularly schooled for dressage and jumping, and half of the horses received an additional endurance training for 24 wk. During all phases horses were exposed at regular intervals to various standardized treadmill exercise tests. During and after the tests frequent blood samples were taken from an indwelling jugular catheter for determination of ACTH and cortisol. Treadmill exercise increased both hormones. Maximum ACTH concentrations were recorded at the end of exercise, and maximum cortisol levels were recorded 20 to 30 min later. Except for one test there were no differences in ACTH levels between trained horses and controls. There was no significant effect of training on the cortisol response (net increase) to treadmill exercise in any of the tests during Phase 1. During Phase 2 higher cortisol responses were recorded in controls than in trained horses (P < .05) after 10 wk of training (controls confined to boxes). During Phase 3 plasma cortisol responses were also higher in controls than in trained horses (P < .05 after 6, 18, and 24, P < or = .07 after 12 wk of training) when the inclination of the treadmill was 5%, but not at 3%. There was no overlap in net cortisol responses at 30 min between trained and untrained horses. An ACTH application after 24 wk of training resulted in higher cortisol responses in controls than in trained horses (P < or = .05), without any overlap between the groups at 30 min after ACTH. Plasma cortisol responses to either treadmill exercise or ACTH injection may be a reliable physiological marker for performance evaluation. Prerequisites are sufficient differences in training status and sufficient intensity of exercise test conditions.
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Devienne, M. F., & Guezennec, C. Y. (2000). Energy expenditure of horse riding. Eur J Appl Physiol, 82(5-6), 499–503.
Abstract: Oxygen consumption (VO2), ventilation (VE) and heart rate (HR) were studied in five recreational riders with a portable oxygen analyser (K2 Cosmed, Rome) telemetric system, during two different experimental riding sessions. The first one was a dressage session in which the rider successively rode four different horses at a walk, trot and canter. The second one was a jumping training session. Each rider rode two horses, one known and one unknown. The physiological parameters were measured during warm up at a canter in suspension and when jumping an isolated obstacle at a trot and canter. This session was concluded by a jumping course with 12 obstacles. The data show a progressive increase in VO2 during the dressage session from a mean value of 0.70 (0.18) l x min(-1) [mean (SD)] at a walk, to 1.47 (0.28) l x min(-1) at a trot, and 1.9 (0.3) l x min(-1) at a canter. During the jumping session, rider VO2 was 2 (0.33) l x min(-1) with a mean HR of 155 beats x min(-1) during canter in suspension, obstacle trot and obstacle canter. The jumping course significantly enhanced VO2 and HR up to mean values of 2.40 (0.35) l x min(-1) and 176 beats x min(-1), respectively. The comparison among horses and riders during the dressage session shows differences in energy expenditure according to the horse for the same rider and between riders. During the jumping session, there was no statistical difference between riders riding known and unknown horses. In conclusion these data confirm that riding induces a significant increase in energy expenditure. During jumping, a mean value of 75% VO2max was reached. Therefore, a good aerobic capacity seems to be a factor determining riding performance in competitions. Regular riding practice and additional physical training are recommended to enhance the physical fitness of competitive riders.
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Miyashita, Y., Nakajima, S., & Imada, H. (2000). Differential outcome effect in the horse. J Exp Anal Behav, 74(2), 245–253.
Abstract: hree horses were trained with a discrimination task in which the color (blue or yellow) of a center panel signaled the correct (left or right) response (lever press). Reinforcing outcomes for the two correct color-position combinations (blue-left and yellow-right) were varied across phases. Discrimination performance was better when the combinations were differentially reinforced by two types of food (chopped carrot pieces and a solid food pellet) than when the combinations were randomly reinforced by these outcomes or when there was a common reinforcer for each of the correct combinations. However, the discrimination performance established by the differential outcome procedure was still 80% to 90% correct, and an analysis of two-trial sequences revealed that the stimulus color of the preceding trial interfered with discrimination performance on a given trial. Our demonstration of the differential outcome effect in the horse and its further analysis might contribute to more efficient control of equine behavior in the laboratory as well as in horse sports.
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McKinley, J., & Sambrook, T. D. (2000). Use of human-given cues by domestic dogs (Canis familiaris) and horses (Equus caballus). Anim. Cogn., 3(1), 13–22.
Abstract: Sixteen domestic dogs (Canis familiaris) and four horses (Equus caballus) were tested for their ability to use human-given manual and facial cues in an object-choice task. Two of the four horses used touch as a cue and one horse successfully used pointing. The performance of the dogs was considerably better, with 12 subjects able to use pointing as a cue, 4 able to use head orientation and 2 able to use eye gaze alone. Group analysis showed that the dogs performed significantly better in all experimental conditions than during control trials. Dogs were able to use pointing cues even when the cuer's body was closer to the incorrect object. Working gundogs with specialised training used pointing more successfully than pet dogs and gundog breeds performed better than non-gundog breeds. The results of this experiment suggest that animals' use of human given communicative signals depends on cognitive ability, the evolutionary consequences of domestication and enculturation by humans within the individual's lifetime.
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Mercado E., Killebrew D.A., Pack A.A., Macha I.V.B., & Herman L.M. (2000). Generalization of 'same-different' classification abilities in bottlenosed dolphins. Behav. Process., 50, 79–94.
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