Prelude. Cycle 1. Introduction. Cycle 2. Structure defines function. Cycle 3. Diversity of cortical functions is provided by inhibition. Cycle 4. Windows on the brain. Cycle 5. A system of rhythms: from simple to complex dynamics. Cycle 6. Synchronization by oscillation. Cycle 7. The brain's default state: self-organized oscillations in rest and sleep. Cycle 8. Perturbation of the default patterns by experience. Cycle 9. The gamma buzz: gluing by oscillations in the waking brain. Cycle 10. Perceptions and actions are brain state-dependent. Cycle 11. Oscillations in the "other cortex:" navigation in real and memory space. Cycle 12. Coupling of systems by oscillations. Cycle 13. The tough problem. References.

Rhythms of the brain

A fluorometric method for determination of oxidized and reduced glutathione in tissues.

Solubilization of membranes by detergents

Four adenosine receptors have been cloned and characterized from several mammalian species. The receptors are named adenosine A(1), A(2A), A(2B), and A(3). The A(2A) and A(2B) receptors preferably interact with members of the G(s) family of G proteins and the A(1) and A(3) receptors with G(i/o) proteins. However, other G protein interactions have also been described. Adenosine is the preferred endogenous agonist at all these receptors, but inosine can also activate the A(3) receptor. The levels of adenosine seen under basal conditions are sufficient to cause some activation of all the receptors, at least where they are abundantly expressed. Adenosine levels during, e.g., ischemia can activate all receptors even when expressed in low abundance. Accordingly, experiments with receptor antagonists and mice with targeted disruption of adenosine A(1), A(2A), and A(3) expression reveal roles for these receptors under physiological and particularly pathophysiological conditions. There are pharmacological tools that can be used to classify A(1), A(2A), and A(3) receptors but few drugs that interact selectively with A(2B) receptors. Testable models of the interaction of these drugs with their receptors have been generated by site-directed mutagenesis and homology-based modelling. Both agonists and antagonists are being developed as potential drugs.

https://pharmrev.aspetjournals.org/content/pharmrev/53/4/527.full.pdf

International Union of Pharmacology. XXV. Nomenclature and Classification of Adenosine Receptors

Afhnity for Monovalent Cations. 597 Relationship of Enzyme System to ATP. 598 Isolation of Enzyme System from Other Cells with Active Transport of Na+ and K+ 602 Location of Enzyme System in the Cell. 604 Effect of Cardiac Glycosides. 605 Quantitative Relation between Effect of Na+ + K+ on Enzyme System and Active Transport in Intact Cell. 606 Nature of Enzyme System. 607 Relation of (Na + + K+)-Activated Enzyme System to Active Transport of Cations. 6 10 Conclusion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6’4

/pdf/enzymatic-basis-for-active-transport-of-na-and-k-across-cell-2agxcysijj.pdf

Enzymatic basis for active transport of na+ and k+ across cell membrane.

SINCE electrical stimulation was demonstrated to produce biochemical responses in mammalian brain slices in vitro, it has been postulated that applied pulses, in the first place, activated neurons in the tissue and this excitation in turn brought about the observed biochemical reaction (MCILWAIN, 1951 ; 1963). Although depolarization of tissue elements was observed to follow a train of pulses, there has been no direct evidence that mammalian brain slices in artificial media can respond to individual stimuli by changes in membrane potential. On the contrary no discernible potential could be recorded from the surface of slices of cerebral cortex in response to a single shock or to a burst of electrical pulses (HILLMAN, CAMPBELL and MCILWAIN, 1963). Response was also found lacking when electrical currents were passed intracellularly in the cells maintaining resting potentials in such slices (HILLMAN et ul., 1963). This has been attempted also with the double-barrelled electrodes of COOMSS, ECCLES and FATT (19557) but has not yet been successful (YAMAMOTO and MCILWAIN, unpublished). In the present experiments, instead of taking slices from the dorsal surface of the cerebrum samples obtained from the cortex of the piriform lobe, especially from the pre-piriform area, were used and were incubated in buffered, glucose-containing saline media. On the surface of the pre-piriform area, the lateral olfactory tract which originates in the olfactory bulb runs rostro-caudally, and sends a number of axon terminals extensively to the pyramidal cells in the pre-piriform area (CAJAL, 1955; VALWRDE, 1965). As a consequence of this powerful input from the lateral olfactory tract, it was expected that in this slice the cortical neurons could be more effectively activated and might exhibit some detectable electrical activities. In fact, it was found during the present experiments that in this slice post-synaptic potentials could indeed be produced by electrical stimulation of the lateral olfactory tract. In addition, data were obtained suggesting that the neurons in the tissue were able to generate spike potentials. The method of BOLLARD and MCILWAIN (1959) gave metabolic evidence also for spread of stimulation from the lateral olfactory tract to an appreciable proportion of tissue beyond the tract. M E T H O D S Preparation of the tissue. Guinea pigs were used. After stunning the animal by a blow on the back of the neck, the carotid arteries were cut and the skin covering the skull was removed. With scissors the occipital and frontal bones were prised away. The removal of the frontal bones was

Electrical activities in thin sections from the mammalian brain maintained in chemically-defined media in vitro.

Richter, D. & Dawson, R. M. C. (1948). Amer. J. Phy8iol. 154, 73. Rosenberg, A. J., Buchel, L., Etling, N. & Levy, J. (1950). C.R. Acad. Sci., Pari8, 230, 480. Schmidt, C. F., Kety, S. S. & Pennes, H. H. (1945). Amer. J. Phy8iol. 143, 33. Schueler, F. W. & Gross, E. G. (1950). J. Pharmacol. 98,28. Stone, W. E. (1938). Biochem. J. 32, 1908. Swank, R. L. & Watson, C. W. (1949). J. Neurophy8iol. 12, 137. Warburg, 0. (1910). Hoppe-Seyl. Z. 68, 305. Webb, J. L. & Elliott, K. A. C. (1951). J. Pharmacol. 103, 24. Westfall, B. A. (1949). J. Pharmacol. 96, 193. Westfall, B. A. (1951). Amer. J. Phy8iol. 66, 219. Wikler, A. (1950). Pharmacol. Rev. 2, 435. Wilkins, D. S., Featherstone, R. M., Schwidde, J. T. & Brotman, M. (1950). J. Pharmacol. 98, 36. Zorn, C. M., Muntwyler, E. & Barlow, 0. W. (1939). J. Pharmacol. 66, 326.

/pdf/techniques-in-tissue-metabolism-1-a-mechanical-chopper-3x3im64qjc.pdf

Techniques in tissue metabolism. 1. A mechanical chopper

Adenine nucleotides of guinea-pig neocortical tissues were labelled by incubation with [(14)C]adenine and excess of adenine was then removed by superfusion with precursor-free medium. Adenine derivatives released from the tissue during continued superfusion, including a period of electrical stimulation of the tissue, were collected by adsorption and examined after elution and concentration. The stimulation greatly increased the (14)C output, and material collected during and just after stimulation had a u.v. spectrum which indicated adenosine to be a major component. The additional presence of inosine and hypoxanthine was shown by chromatography and adenosine was identified also by using adenosine deaminase. Total adenine derivatives released from the tissue during a 10min period of stimulation were obtained as hypoxanthine, after deamination and hydrolysis of adenosine and inosine, and amounted to 159nmol/g of tissue. This corresponded to the release of approx. 7pmol/g of tissue per applied stimulus. The hypoxanthine sample derived from superfusate hypoxanthine, inosine and adenosine was of similar specific radioactivity to the sample of inosine separated chromatographically, and each was of higher specific radioactivity than the adenine nucleotides obtained by cold-acid extraction of the tissue.

Adenine derivatives as neurohumoral agents in the brain. The quantities liberated on excitation of superfused cerebral tissues.

1. Uptake of [ 14 C]adenine and [ 14 C]adenosine from surrounding fluids to guinea-pig cerebral tissues was measured during incubation in vitro . Output of 14 C-labelled compounds from the loaded tissues to superfusion fluids occurred on continued incubation, at about 0.2% of the tissue9s content/min, and this rate was increased about fourfold by electrical excitation of the tissue. 2. The compounds released from the tissue to superfusion fluids included adenine, adenosine, inosine and hypoxanthine with small amounts of nucleotides. Output of all these compounds, except adenine, increased on excitation. Media depleted of oxygen or glucose also increased the output of 14 C-labelled derivatives from [ 14 C]adenine-loaded tissues, and this augmented output was further increased by electrical stimulation. 3. [ 14 C]Adenosine was found as the main product from [ 14 C]ATP when this was added at low concentrations to fluids superfusing cerebral tissue. Metabolic and neurohumoural explanations of the liberation and action of adenosine derivatives in the tissue are discussed.

/pdf/metabolism-of-14c-adenine-and-derivatives-by-cerebral-i12eaxlsgl.pdf

Metabolism of [14C]adenine and derivatives by cerebral tissues, superfused and electrically stimulated

(1) Synaptosomal fractions from guinea pig neocortical dispersions prepared in sucrose solutions were deposited from saline media as ‘beds’ on nylon bolting cloth. When incubated with 0.5–10 μm-[14C]adenine or adenosine in glucose bicarbonate salines, uptake of 14C from adenosine proceeded at about four times the rate of uptake of [14C]adenine. This contrasted with the relative uptake of the two compounds to neocortical tissue slices or to beds made from mitochondrial fractions, where uptake was similar with the two precursors. Uptake of both precursors to synaptosome beds was much greater than uptake of inosine.



(2) Synaptosome beds, [14C]adenosine-loaded, contained 88 per cent of the 14C as 5′-adenine nucleotides, the remainder being present as cyclic AMP, inosine, hypoxanthine and adenosine. When superfused, the 14C output consisted mainly of adenosine, inosine and hypoxanthine, with some 7 per cent of 5′-nucleotides and 4 per cent of cyclic AMP.



(3) Electrical pulses and the addition of 50 mm-KCl each increased the efflux of 14C from superfused [14C]adenosine-loaded beds. The superfusates issuing after excitation contained the same 14C-labelled compounds as issued before, with a small increase in the proportional yield of adenosine. The additional output of 14C following electrical pulses was diminished by about 50 per cent by 0.5 μm-tetrodotoxin while that following KCl was not affected; it was however prevented when the superfusing fluids were free of Ca2+.

Henry McIlwain

Papers

Electrical activities in thin sections from the mammalian brain maintained in chemically-defined media in vitro.

Techniques in tissue metabolism. 1. A mechanical chopper

Adenine derivatives as neurohumoral agents in the brain. The quantities liberated on excitation of superfused cerebral tissues.

Metabolism of [14C]adenine and derivatives by cerebral tissues, superfused and electrically stimulated

Uptake and release of [14c]adenine derivatives at beds of mammalian cortical synaptosomes in a superfusion system