Computational properties of use of biological organisms or to the construction of computers can emerge as collective properties of systems having a large number of simple equivalent components (or neurons). The physical meaning of content-addressable memory is described by an appropriate phase space flow of the state of a system. A model of such a system is given, based on aspects of neurobiology but readily adapted to integrated circuits. The collective properties of this model produce a content-addressable memory which correctly yields an entire memory from any subpart of sufficient size. The algorithm for the time evolution of the state of the system is based on asynchronous parallel processing. Additional emergent collective properties include some capacity for generalization, familiarity recognition, categorization, error correction, and time sequence retention. The collective properties are only weakly sensitive to details of the modeling or the failure of individual devices.

https://www.pnas.org/content/pnas/79/8/2554.full.pdf

Neural networks and physical systems with emergent collective computational abilities

Computational properties of use to biological organisms or to the construction of computers can emerge as collective properties of systems having a large number of simple equivalent components (or neurons). The physical meaning of content-addressable memory is described by an appropriate phase space flow of the state of a system. A model of such a system is given, based on aspects of neurobiology but readily adapted to integrated circuits. The collective properties of this model produce a content-addressable memory which correctly yields an entire memory from any subpart of sufficient size. The algorithm for the time evolution of the state of the system is based on asynchronous parallel processing. Additional emergent collective properties include some capacity for generalization, familiarity recognition, categorization, error correction, and time sequence retention. The collective properties are only weakly sensitive to details of the modeling or the failure of individual devices.

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The Na+/Ca2+ exchanger, an ion transport protein, is expressed in the plasma membrane (PM) of virtually all animal cells. It extrudes Ca2+ in parallel with the PM ATP-driven Ca2+ pump. As a reversible transporter, it also mediates Ca2+ entry in parallel with various ion channels. The energy for net Ca2+ transport by the Na+/Ca2+ exchanger and its direction depend on the Na+, Ca2+, and K+ gradients across the PM, the membrane potential, and the transport stoichiometry. In most cells, three Na+ are exchanged for one Ca2+. In vertebrate photoreceptors, some neurons, and certain other cells, K+ is transported in the same direction as Ca2+, with a coupling ratio of four Na+ to one Ca2+ plus one K+. The exchanger kinetics are affected by nontransported Ca2+, Na+, protons, ATP, and diverse other modulators. Five genes that code for the exchangers have been identified in mammals: three in the Na+/Ca2+ exchanger family (NCX1, NCX2, and NCX3) and two in the Na+/Ca2+ plus K+ family (NCKX1 and NCKX2). Genes homologous to NCX1 have been identified in frog, squid, lobster, and Drosophila. In mammals, alternatively spliced variants of NCX1 have been identified; dominant expression of these variants is cell type specific, which suggests that the variations are involved in targeting and/or functional differences. In cardiac myocytes, and probably other cell types, the exchanger serves a housekeeping role by maintaining a low intracellular Ca2+ concentration; its possible role in cardiac excitation-contraction coupling is controversial. Cellular increases in Na+ concentration lead to increases in Ca2+ concentration mediated by the Na+/Ca2+ exchanger; this is important in the therapeutic action of cardiotonic steroids like digitalis. Similarly, alterations of Na+ and Ca2+ apparently modulate basolateral K+ conductance in some epithelia, signaling in some special sense organs (e.g., photoreceptors and olfactory receptors) and Ca2+-dependent secretion in neurons and in many secretory cells. The juxtaposition of PM and sarco(endo)plasmic reticulum membranes may permit the PM Na+/Ca2+ exchanger to regulate sarco(endo)plasmic reticulum Ca2+ stores and influence cellular Ca2+ signaling.

https://www.physiology.org/doi/pdf/10.1152/physrev.1999.79.3.763

Sodium/Calcium Exchange: Its Physiological Implications

Platelets are anucleate cells that are crucial mediators of haemostasis. Most immunologists probably don't think about platelets every day, and may even consider these cells to be 'nuisances' in certain in vitro studies. However, it is becoming increasingly clear that platelets have inflammatory functions and can influence both innate and adaptive immune responses. Here, we discuss the mechanisms by which platelets contribute to immunity: these small cells are more immunologically savvy than we once thought.

Platelets and the immune continuum

Fueled by innovation in the computer vision and artificial intelligence communities, recent developments in computational neuroscience have used goal-driven hierarchical convolutional neural networks (HCNNs) to make strides in modeling neural single-unit and population responses in higher visual cortical areas. In this Perspective, we review the recent progress in a broader modeling context and describe some of the key technical innovations that have supported it. We then outline how the goal-driven HCNN approach can be used to delve even more deeply into understanding the development and organization of sensory cortical processing.

Using goal-driven deep learning models to understand sensory cortex

Comprehensive Insect Physiology, Biochemistry and Pharmacology

1. The ionic composition of the blood of insects, unlike that of vertebrates and most other invertebrates, shows a wide range of values, especially in regard to the physiologically important ions of sodium and potassium. 2. Preparations are described in which the effect of potassium on the active nerve and muscle properties of Locusta migratoria have been investigated. 3. The nerve axons are depolarized by high concentrations of potassium ions in the same way as vertebrate and crustacean axons. 4. The whole nervous system is surrounded by a sheath which is an effective barrier to the diffusion of potassium ions. 5. The muscle-fibre membrane is also depolarized by high concentrations of potassium ions in a similar way to muscle-fibre membranes of other animals which have been previously investigated. 6. The tracheolated membranes surrounding the muscles, and the close arrangement of the constituent fibres, delay the passage of potassium ions through the muscles. 7. It is predicted that the mechanical properties of the muscles of a herbivorous insect will be found to be subject to fairly marked changes if the blood potassium rises or falls to an appreciable extent.

Potassium Ions and Insect Nerve Muscle

A preparation of the desert locust, Schistocera gregaria, has been developed, in which it was possible to work with identified neurons while still allowing some behavior. A total of 26 motorneurons to the hind leg were studied singly, and in various pairs, both by direct stimulation, and by recording during spontaneous activity and various reflex actions. Motorneurons were identified by passing current into their somata and correlating the evoked somata spikes with extracellularly or intracellularly recorded events in the muscles. Tension of the muscle was also recorded and motor axons were stimulated to evoke antidromic spikes in the somata. Both epsp's and ipsp's can be seen clearly in recordings from the somata; spikes appear as electrotonically conducted remnants only. Somata exhibited little or no electrogenesis. It is inferred that impulses are initiated in a zone tentatively identified with the region of emergence of the motor axon from the neuropil. Integration occurs in the neuropilar segment, with the soma serving as a parallel RC element. Data was obtained on the central mechanisms of coordination of synergistic and antagonistic motorneurons and on the modes of excitation of slow and fast neurons to the same muscles.

Neural mechanisms underlying behavior in the locust Schistocerca gregaria I. Physiology of identified motorneurons in the metathoracic ganglion

The natural insect neuromodulator octopamine (OCT) was released iontophoretically into regions of neuropil in locust metathoracic ganglia. A narrowly-defined site was found on one side of the ganglion at which release caused a prolonged bout of repetitive flex-extend-flex movements of the tibia on the injected side, at a frequency of from 2-3.5 Hz. When a bout had terminated, repetition of the OCT release caused an extremely similar bout to occur, and again with further treatments, indefinitely. OCT iontophoresis at the equivalent site on the contralateral side caused the contralateral flexor to make stepping movements. Two sites were found, in each half of the ganglion, at which similar OCT release evoked a bout of flight motor activity at 10 Hz. The flight bout involved both sides synchronously and nearly equally, except for a slightly greater motor output on the injected side. Evoked bouts lasted from 20 sec to 25 min depending on the preparation and amount of OCT released. At a site in the 6th abdominal ganglion of mature female locusts OCT release suppressed ongoing rhythmic oviposition digging evoked by severing the ventral nerve cord. A number of previously undescribed DUM neurons was encountered and their dendritic patterns, which are distinctive, determined following dye injection. A hypothesis, termed the Orchestration Hypothesis is presented, which considers how modulator neurons such as locust octopaminergic neurons, might be involved in the generation of specific behaviors.

Generation of specific behaviors in a locust by local release into neuropil of the natural neuromodulator octopamine

The dorsal unpaired median neuron innervating the extensor tibiae (DUMETi) of locusts and grasshoppers, as well as some other DUM neurons, cause long-term inhibition of the slow intrinsic rhythm of contraction of the muscle by releasing a neurohumoral agent. Large, (600 - 1900 A), dense-core vesicles are present in the nerve terminals. The inhibitory action is mimicked by infusioninto the leg of a minute (0.01 ml.) drop of locust saline containing a very low concentration (10(-6)M) of dopamine or noradrenaline, or an extraordinarily low concentration of octopamine (2.5 x 10(-9) M). The amplitude and frequency of the contractions slowly return to normal. Neither the cell body nor the neuron fluoresces with the Falck-Hillarp treatment, even after a period of ligature has caused an accumulation of vesicles. Octopamine does not fluoresce with this treatment. Accordingly, it is suggested that this neuron, and the other efferent DUM neurons, are octopaminergic.?23Author

Graham Hoyle

Papers

Comprehensive Insect Physiology, Biochemistry and Pharmacology

Potassium Ions and Insect Nerve Muscle

Neural mechanisms underlying behavior in the locust Schistocerca gregaria I. Physiology of identified motorneurons in the metathoracic ganglion

Generation of specific behaviors in a locust by local release into neuropil of the natural neuromodulator octopamine

Evidence that insect dorsal unpaired medican (DUM) neurons are octopaminergic.