0088 Gravity Dreams Following a Virtual Reality Flight Simulation

Introduction

Flying is a prevalent but infrequent experience in dreams. Despite a broad interest in such unique dream experiences, there is still no experimental procedure for reliably inducing them. Our study aimed 1) to induce flying dreams in the laboratory using virtual reality (VR), 2) to examine phenomenological correlates of flying dreams, such as lucidity and emotions and 3) to investigate the dynamics of dreamed gravity imagery in relation to participant state and trait factors.

Methods

A total of 137 healthy participants (24.01±4.03 y.o.; 85 F; 52 M) took part in a custom-built immersive VR task in which they learn how to ‘fly’ as precisely and quickly as possible, engaging vestibular, motor and visuo-spatial systems. Dreams were collected a) from home dream journals for 5 days before and 10 days after the laboratory VR task and b) after a 90-min morning nap in laboratory. Dream reports were scored by 2 independent judges for flying and other gravity-related imagery. Linear mixed models statistics were used to compare dreams from this cohort with a separate control cohort (N=52) that followed a similar protocol in the same lab but did not undertake a virtual flying task.

Results

The VR task successfully increased the likelihood of experiencing flying in dreams from both the laboratory nap (7.1%) and the following night (10.6%) compared to baseline (1.3%) and the control cohort on those days (Lab: 2.4%; following night: 0%). In contrast, the occurrence of other gravity imagery showed no differences. Flying dreams were altered qualitatively, exhibiting higher levels of lucid-control and emotional intensity after VR exposure. Moreover, various factors such as sex, prior dream experiences and sensory immersion in VR differentially modulated flying dream induction.

Conclusion

Our findings provide both quantitative and qualitative insights into flying dreams that may facilitate understanding of these typical dream experiences and future developments in dream flight-induction technologies.

Support

Natural Sciences and Engineering Research Council of Canada

Effects of divalent cations on the E-4031-sensitive repolarization current, I(Kr), in rabbit ventricular myocytes

The effects of divalent cations on the E-4031-sensitive repolarization current (I(Kr)) were studied in single ventricular myocytes isolated from rabbit hearts. One group of divalent cations (Cd2+, Ni2+, Co2+, and Mn2+) produced a rightward shift of the I(Kr) activation curve along the voltage axis, increased the maximum I(Kr) amplitude (i.e., relieved the apparent inward rectification of the channel), and accelerated I(Kr) tail current kinetics. Another group (Ca2+, Mg2+ and Sr2+) had relatively little effect on I(Kr). The only divalent cation that blocked I(Kr) was Zn2+ (0.1-1 mM). Under steady-state conditions, Ba2+ caused a substantial block of I(K1) as previously reported. However, block by Ba2+ was time dependent, which precluded a study of Ba2+ effects on I(Kr). We conclude that the various effects of the divalent cations can be attributed to interactions with distinct sites associated with the rectification and/or inactivation mechanism of the channel.

A quantitative description of the E-4031-sensitive repolarization current in rabbit ventricular myocytes

We have measured the E-4031-sensitive repolarization current (IKr) in single ventricular myocytes isolated from rabbit hearts. The primary goal of this analysis was a description of the IKr kinetic and ion transfer properties. Surprisingly, the maximum time constant of this component was 0.8 s at 33-34 degrees C, which is significantly greater than the value of 0.18 s previously reported under similar conditions in the original measurements of IKr from guinea pig ventricular myocytes. The primary, novel feature of our analysis concerns the relationship of the bell-shaped curve that describes the voltage dependence of the kinetics and the sigmoidal curve that describes the activation of IKr. The midpoint of the latter occurred at approximately +10 mV on the voltage axis, as compared to -30 mV for the point on the voltage axis at which the maximum time constant occurred. Moreover, the voltage dependence of the kinetics was much broader than the steepness of the activation curve would predict. Taken together, these results comprise a gating current paradox that is not resolved by the incorporation of a fast inactivated state in the analysis. The fully activated current-voltage relation for IKr exhibited strong inward-going rectification, so much so that the current was essentially nil at +30 mV, even though the channel opens rapidly in this voltage range. This result is consistent with the lack of effect of E-4031 on the early part of the plateau phase of the action potential. Surprisingly, the reversal potential Of /Kr was ~15 mV positive to the potassium ion equilibrium potential,which indicates that this channel carries inward current during the latter part of the repolarization phase of the action potential.

Primary structure of bovine cathepsin S. Comparison to cathepsins L, H, B and papain

The primary structure of bovine cathepsin S was determined by combining results of protein and peptide sequencing with the sequence deduced from nucleic acid sequencing. Using polymerase chain reaction (PCR) technology, cDNA clones commencing at amino acid 22 of the mature enzyme and continuing through the 3' untranslated region of bovine cathepsin S mRNA were isolated and sequenced. The open reading frame in these overlapping clones correctly predicts the determined amino acid sequence of 13 tryptic peptides derived from purified bovine spleen cathepsin S. The deduced amino acid sequence shows that mature bovine cathepsin S consists of 217 amino acids corresponding to a molecular weight of 23.7 kDa. Cathepsin S belongs to the papain superfamily of lysosomal cysteine proteinases and shares 41% identity with papain. Amino acid sequence identities of bovine cathepsin S to human cathepsins L, H, and B are 56%, 47% and 31% respectively.

Beta-adrenergic modulation of insulin binding in skeletal muscle

Both a high physiological concentration (13.1 nM) of epinephrine (E) and acute exercise (AEx) have previously been shown to increase 125I-insulin binding in skeletal muscle. To investigate the site and mechanism of the effect of epinephrine on binding and the possible link between epinephrine- and AEx-enhanced insulin binding, we measured insulin binding in three different preparations: 1) crude membranes derived from whole soleus muscle incubated in vitro with 13.1 nM E, 2) crude membranes with E present in the binding assay, and 3) purified plasma membranes with E present. Epinephrine enhanced binding in all three preparations by 169, 144, and 164%, respectively, at low concentrations of insulin but had little effect at high concentrations. Epinephrine, therefore appears to have its effect at the plasma membrane. Propranolol (10 microM), a beta-adrenergic antagonist, blocked E-enhanced insulin binding and when added to crude membranes made from soleus and extensor digitorum longus muscle of AEx rats reversed the increase in binding seen with exercise. This indicates that E-enhanced insulin binding is mediated by beta-adrenergic receptors and that AEx enhances insulin binding via beta-adrenergic receptors. Sodium orthovanadate (3 mM), a phosphotyrosyl-protein phosphatase inhibitor, also inhibited the increase in insulin binding due to E, implying that E may increase insulin binding by activating a phosphotyrosyl-protein phosphatase which decreases the phosphorylation of a plasma membrane protein, presumably the insulin receptor.

Quantitative autoradiographic evidence for insulin receptors in the choroid plexus of the rat brain

Techniques of in vitro receptor autoradiography were used to visualize binding of 125I-insulin on slices of frozen rat brain. Slide-mounted sections of frozen rat brain were incubated in 0.05 nM porcine 125I-monoiodoinsulin, alone or mixed with 1 microM unlabeled porcine insulin, ribonuclease, or glucagon, for 2 h at 22 degrees C. The labeled brain slices were apposed to LKB Ultrofilm to generate autoradiograms. The method permitted equal access of labeled insulin to both sides of the blood-brain barrier and localization of insulin binding sites in small anatomic regions. Quantitative estimates of specific iodoinsulin binding were made by computer digital image densitometry of the autoradiographic film images. High concentrations of specific binding sites for iodoinsulin were present in the choroid plexus of the lateral (26.9 +/- 2.0 X 10(-3) fmol/mm2), fourth (18.3 +/- 3.0 X 10(-3) fmol/mm2), and third (13.2 +/- 1.5 X 10(-3) fmol/mm2) ventricles (insulin binding is expressed per unit area of autoradiographic image). Binding to the third ventricular choroid plexus was similar to the concentrations observed for liver slices and the external plexiform layer of the olfactory bulb. Specific binding of iodoinsulin in the cingulate cortex and other surrounding regions was less than in choroid plexus. Ribonuclease or glucagon had no measurable effect on binding when mixed with labeled insulin. The results support the hypothesis that the choroid plexus has a high density of receptors for insulin, and suggests that the choroid plexus may be a target of CSF insulin action and/or a site of insulin transport into the CSF.

Acute exercise, epinephrine, and diabetes enhance insulin binding to skeletal muscle

We measured insulin binding to crude membranes from rat skeletal muscle, with binding expressed relative to the sarcolemmal marker, cholesterol ester (CE). The amount of CE in the sarcolemma remained constant after streptozotocin-induced diabetes and acute exercise (swam for 90 min). Soleus (predominantly slow-twitch fibers) had higher insulin binding capacity than extensor digitorum longus (predominantly fast twitch). Both diabetes and acute exercise enhanced insulin binding. The shape of the enhanced insulin binding curve differed, however, between diabetes and acute exercise. Diabetes elicited a uniform increase in binding across the insulin concentrations measured (0.04-166 nM); acute exercise elicited the largest increase at the lower concentrations, suggesting different mechanisms cause the enhanced binding. Addition of 13.1 nM epinephrine to the perfusate in a rat hindlimb preparation increased insulin binding in a pattern similar to acute exercise. In contrast, muscular contraction stimulated by the sciatic nerve (1 Hz) or reduction of perfusate insulin from 100 to 40 pM, two additional correlates of acute exercise, had no effect. The increased insulin binding after acute exercise, therefore, appears to be mediated through elevated levels of catecholamines and not upregulation of the insulin receptor.

Brain and liver insulin binding is decreased in Zucker rats carrying the 'fa' gene

Insulin binding was measured in membrane particles prepared from the liver and several brain regions of 4-month-old female Zucker fa/fa (obese), Fa/fa (heterozygous), and Fa/Fa (lean) rats. High affinity insulin binding was decreased in the olfactory bulb of fatty (0.23 pmol bound/mg protein) and heterozygous (0.16 pmol/mg) rats compared with that in the lean controls (0.64 pmol/mg). Total binding was not changed in the cerebral cortex or hypothalamus. High affinity insulin binding was also decreased in the liver of both fatty (0.44 +/- 0.22 pmol/mg; P less than 0.01) and heterozygous (0.75 +/- 0.35 pmol/mg) animals compared with that in the lean rats (2.10 +/- 1.55 pmol/mg). This decreased binding is probably not due to down-regulation of receptors in the heterozygous rats, as they do not exhibit the hyperinsulinemia observed in the fatty rats. Rather, our findings suggest that there is a gene-related alteration in insulin binding in the Zucker rat, as low binding was observed in rats carrying either one (Fa/fa) or two (fa/fa) doses of the gene. We postulate that this central defect in insulin binding may contribute to inadequate perception of a central insulin feedback signal and to the hyperphagia observed in the obese rats.