Defensive functions provoke similar psychophysiological reactions in reaching and comfort spaces.

The space around the body crucially serves a variety of functions, first and foremost, preserving one's own safety and avoiding injury. Recent research has shown that emotional information, in particular threatening facial expressions, affects the regulation of peripersonal-reaching space (PPS, for action with objects) and interpersonal-comfort space (IPS, for social interaction). Here we explored if emotional facial expressions may similarly or differently affect both spaces in terms of psychophysiological reactions (cardiac inter-beat intervals: IBIs, i.e. inverse of heart rate; Skin Conductance Response amplitude: SCR amplitude) and spatial distance. Through Immersive Virtual Reality technology, participants determined reaching-distance (PPS) and comfort-distance (IPS) from virtual confederates exhibiting happy/angry/neutral facial expressions while being approached by them. During these interactions, spatial distance and psychophysiological reactions were recorded. Results revealed that when interacting with angry virtual confederates the distance increased similarly in both comfort-social and reaching-action spaces. Moreover, interacting with virtual confederates exhibiting angry rather than happy or neutral expressions provoked similar psychophysiological activations (SCR amplitude, IBIs) in both spaces. Regression analyses showed that psychophysiological activations, particularly SCR amplitude in response to virtual confederates approaching with angry expressions, were able to predict the increase of PPS and IPS. These findings suggest that self-protection functions could be the expression of a common defensive mechanism shared by social and action spaces.

The experience of virtual reality: are individual differences in mental imagery associated with sense of presence?

The concept of "presence" describes the quality of subjective experience in immersive virtual reality (IVR). Presence refers to a specific state of consciousness: we behave and feel as if we actually were in the virtual world even though we know there is nothing there. In their handbook of Virtual Reality, Burdea and Coiffet (Virtual reality technology, Wiley, New York, 2003) suggested that the experience of presence in IVR would emerge from the combination of three Is: Immersion or capacity to isolate from the external world, Interaction or capacity to naturally exploring the virtual environment, and Imagination or individual aptitudes with mental imagery. So far, several studies have investigated the technological and psychological factors affecting the degree of immersion and interaction. However, no study has explored the relationship between perceived presence and mental imagery. Here we aim at filling this gap through a correlational study comparing self-reports about sense of presence and mental imagery abilities. After experiencing two IVR scenarios (an art gallery and a living room), 142 male and female users were administered with questionnaires assessing the degree of presence (Igroup Presence Questionnaire), the degree of vividness (Vividness of Visual Imagery Questionnaire) and control (Test of Visual Imagery Control) of subjective mental images. Results showed a clear positive correlation between presence and vividness: the higher the vividness of mental images the stronger the reported sense of presence felt in IVR scenarios. Instead, the capacity to control mental imagery showed a weaker association with presence. We may conclude that individual differences in the degree of perceived presence and mental imagery ability are associated.

Phosphorylation of the insulin receptor by a casein kinase I-like enzyme.

A serine protein kinase that phosphorylates the beta-subunit of the insulin receptor has been partially purified 5,000-fold from HeLa cell membranes. The enzyme has been purified by ion-exchange and hydroxylapatite chromatography and sucrose gradient centrifugation; it has an apparent molecular weight of 36,000-43,000 daltons. It exhibits the following properties: (a) it catalyzes the phosphorylation of the autophosphorylated insulin receptor more efficiently than the nonautophosphorylated insulin receptor, (b) it decreases insulin receptor phosphorylation of tubulin but has no effect on insulin receptor phosphorylation of microtubule-associated proteins or reduced and carboxyamidomethylated lysozyme. The enzyme also phosphorylates casein and ribosomal protein S6 and shares many properties with casein kinase I: (a) similar molecular weight, (b) utilization of ATP but not GTP as phosphoryl donor, and (c) sensitivity to inhibition by heparin. Based on several criteria the receptor serine kinase is neither protein kinase C nor the cAMP-dependent protein kinase.

Opposing effects of calcium entry and phorbol esters on fusion of chick muscle cells.

Studies utilizing cultured muscle cells have shown that myoblast fusion requires extracellular Ca2+ and involves transient coordinated changes in cell membrane topography and cytoskeletal organization. However, neither the mechanisms by which Ca2+ influences these changes nor its cellular sites of action are known. We have investigated the effects of Ca2+ channel modulators and phorbol esters on fusion of embryonic chick myoblasts in culture. Myoblast fusion was inhibited by the Ca2+ channel blockers D600 and nitrendipine and stimulated by the Ca2+ channel activator Bay K 8644. We have obtained evidence that the tumor promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) inhibits fusion through activation of protein kinase C. Myoblasts prevented from fusing by Ca2+ channel blockers or TPA display a distinctive elongated morphology that is characteristic of cells prevented from fusion by Ca2+ deprivation. The inhibition of fusion by D600 and TPA is significantly diminished in the presence of the Ca2+ ionophore A23187. TPA arrest of myoblast fusion was found to be accompanied by an increase in phosphorylation of the 20-kDa light chain of cytoplasmic myosin in a dose- and time-dependent manner. The effects of TPA on myoblast fusion and phosphorylation of myosin light chain were mimicked by the cell permeant diacylglycerol sn-1,2-dioctanoylglycerol, a potent activator of protein kinase C. The present results suggest that activators of protein kinase C block fusion by interfering with a Ca2+ signal transduction pathway and that this interference may be associated with a protein kinase C catalyzed inhibitory phosphorylation of myosin light chain.

Induction of phosphorylation and cell surface redistribution of acetylcholine receptors by phorbol ester and carbamylcholine in cultured chick muscle cells.

We have investigated the mechanisms regulating the clustering of nicotinic acetylcholine receptor (AChR) on the surface of cultured embryonic chick muscle cells. Treatment of these cells with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), a potent activator of protein kinase C, was found to cause a rapid dispersal of AChR clusters, as monitored by fluorescence microscopy of cells labeled with tetramethylrhodamine-conjugated alpha-bungarotoxin. The loss of AChR clusters was not accompanied by an appreciable change in the amount of AChR on the surface of these cells, as measured by the specific binding of [125I]Bgt. Analysis of the phosphorylation pattern of immunoprecipitable AChR subunits showed that the gamma- and delta-subunits are phosphorylated by endogenous protein kinase activity in the intact muscle cells, and that the delta-subunit displays increased phosphorylation in response to TPA. Structural analogues of TPA which do not stimulate protein kinase C have no effect on AChR surface topography or phosphorylation. Exposure of chick myotubes to the cholinergic agonist carbamylcholine was found to cause a dispersal of AChR clusters with a time course similar to that of TPA. Like TPA, carbamylcholine enhances the phosphorylation of the delta-subunit of AChR. The carbamylcholine-induced redistribution and phosphorylation of AChR is blocked by the nicotinic AChR antagonist d-tubocurarine. TPA and carbamylcholine have no effect on cell morphology during the time-course of these experiments. These findings indicate that cell surface topography of AChR may be regulated by phosphorylation of its subunits and suggest a mechanism for dispersal of AChR clusters by agonist activation.

Phosphorylation and assembly of nicotinic acetylcholine receptor subunits in cultured chick muscle cells.

The assembly of the nicotinic acetylcholine receptor (AChR), an oligomeric cell surface protein, was studied in cultured muscle cells. To measure this process, the incorporation of metabolically labeled alpha-subunit into oligomeric AChR was monitored in pulse-chase experiments, either by the shift of this subunit from the unassembled (5 S) to the assembled (9 S) position in sucrose density gradients, or by its coprecipitation with antisera specific for the delta-subunit. We have found that AChR assembly is initiated 15-30 min after subunit biosynthesis and is completed within the next 60 min. The alpha-subunit is not overproduced, as all detectable pulse-labeled alpha-subunit can be chased into the oligomeric complex, suggesting that AChR assembly in this system is an efficient process. The rate of AChR assembly is decreased by metabolic inhibitors and by monensin, an ionophore that impairs the Golgi apparatus. We have observed that the gamma- and delta-subunits of AChR are phosphorylated in vivo. The delta-subunit is more highly phosphorylated in the unassembled than in the assembled state, indicating that its phosphorylation precedes assembly and that its dephosphorylation is concomitant with AChR assembly. These findings suggest that subunit assembly occurs in the Golgi apparatus and that phosphorylation/dephosphorylation mechanisms play a role in the control of AChR subunit assembly.