Testing quantum dynamics in genetic information processing

Does quantum dynamics play a role in DNA replication? What type of tests would reveal that? Some statistical checks that distinguish classical and quantum dynamics in DNA replication are proposed.     

Circadian pacemaker neurons transmit and modulate visual information to control a rapid behavioral response

Circadian pacemaker neurons contain a molecular clock that oscillates with a period of approximately 24 hr, controlling circadian rhythms of behavior. Pacemaker neurons respond to visual system inputs for clock resetting, but, unlike other neurons, have not been reported to transmit rapid signals to their targets. Here we show that pacemaker neurons are required to mediate a rapid behavior. The Drosophila larval visual system, Bolwig's organ (BO), projects to larval pacemaker neurons to entrain their clock. BO also mediates larval photophobic behavior. We found that ablation or electrical silencing of larval pacemaker neurons abolished light avoidance. Thus, circadian pacemaker neurons receive input from BO not only to reset the clock but also to transmit rapid photophobic signals. Furthermore, as clock gene mutations also affect photophobicity, the pacemaker neurons modulate the sensitivity of larvae to light, generating a circadian rhythm in visual sensitivity.     

A modified radial isochron clock with slow and fast dynamics as a model of pacemaker neurons

A simple mathematical model of living pacemaker neurons is proposed. The model has a unit circle limit cycle and radial isochrons, and the state point moves slowly in one region and fast in the remaining region; regions can correspond to the subthreshold activity and to the action potentials of pacemaker neurons, respectively. The global bifurcation structure when driven by periodic pulse trains was investigated using one-dimensional maps (PTC), two-dimensional bifurcation diagrams, and skeletons involving stimulus period and intensity. The existence of both the slow and the fast dynamics has a critical influence on the global bifurcation structure of the oscillator when stimulated periodically.Supported by Trent H. Wells Jr. Inc.     

Circadian pacemaker neurons: membranes and molecules

1. A circadian pacemaker is located in the eyes of a variety of marine gastropods, including Aplysia and Bulla. It produces a circadian rhythm in the frequency of spontaneously occurring optic nerve (ON) compound action potentials (CAPs). The circadian pacemaker in Bulla includes a population of 100 retinal pacemaker neurons, that produce the rhythmic CAP output. Intracellular recording from the Bulla pacemaker neurons has yielded new insight into their time-keeping ability. 2. Intracellular injection of Lucifer yellow dye into a single pacemaker neuron results in the spread of dye to several neurons. This dye coupling is presumably mediated by the gap junctions among neurons that are responsible for the synchronous firing of the population of pacemaker neurons and the generation of ON CAPs. 3. The circadian pacemaker in each eye interacts with the paired pacemaker in the contralateral eye. The interaction results in the coordinating firing of CAPs from each eye and in the coordinated phasing of the circadian rhythms of CAP activity generated in each eye. This interaction occurs by reciprocal excitatory chemical synapses. These synaptic receptors occur in the ON as well as in the retinal neuropil and CAP synchrony occurs in the ON as well as in the basal retina. 4. Pacemaker neurons are depolarized by 5-HT and membrane permeable cAMP analogues. The membrane resistance increases during the depolarization suggesting a background potassium current is decreased. 5. The tetrapeptide FMRF-HN2 hyperpolarizes the pacemaker neurons. It reverses the effect of 5-HT and cAMP, suggesting 5-HT and FMRF-NH2 may be acting on the same membrane channel, the S channel.(ABSTRACT TRUNCATED AT 250 WORDS)     

Multiplicity of pacemaker zones in Helix pomatia neurons

Intracellular microelectrode recordings from neurons ofHelix pomatia revealed several local zones of action potential generation both on the soma and on some of the branches of the neurons. Under certain conditions the activity of individual loci of the neuron membrane was synchronized to produce a normal action potential. It is suggested that the somatic membrane of neurons is heterogeneous in structure and consists of separate loci of an electrically excitable membrane, incorporating active and latent pacemaker zones. Neurons ofH. pomatia are characterized by two types of action potential with different triggering mechanisms: one (synaptic) type is generated under the influence of the EPSP, the other (pacemaker) arises through activation of endogenous factors for the neuron (pacemaker potentials). The interaction between synaptic and pacemaker potentials during integrative activity of the neuron is discussed.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 5, No. 1, pp. 88–94, January–February, 1973.     

Adaptability and the integration of computer-based information processing into the dynamics of organizations

The structure of a system influences its adaptability. An important result of adaptability theory is that subsystem independence increases adaptability [Conrad, M., 1983. Adaptability. Plenum Press, New York]. Adaptability is essential in systems that face an uncertain environment such as biological systems and organizations. Modern organizations are the product of human design. And so it is their structure and the effect that it has on their adaptability. In this paper we explore the potential effects of computer-based information processing on the adaptability of organizations. The integration of computer-based processes into the dynamics of the functions they support and the effect it has on subsystem independence are especially relevant to our analysis.     

Background sodium current stabilizes bursting in respiratory pacemaker neurons

Endogenous pacemaker properties have been proposed to generate rhythmic activity underlying many behaviors including respiration. For pacemakers to generate regenerative bursting, background currents maintain their membrane potential (Vm) within a range where bi-stable properties are expressed, thereby stabilizing rhythmogenesis. We previously found that the baseline Vm of respiratory pacemakers is stabilized against hyperpolarizing shifts in their Vm. In response to prolonged hyperpolarizing current injection synaptically isolated respiratory pacemakers steadily depolarize and resume bursting, suggesting a stabilizing background current is involved. What is the ionic basis of this background current in respiratory pacemakers? Here we demonstrate that in low-[Na(+)](o) ACSF, synaptically isolated respiratory pacemakers hyperpolarized and remained outside the bursting window, but could burst upon depolarizing current injection. These data suggest that pacemakers possess a background sodium current that is necessary to bring their Vm into a bursting range. Low-[Na(+)](o) ACSF also abolished the depolarizing shift evoked during prolonged hyperpolarizing current injection, and bursting did not resume. This depolarizing shift persisted in the presence of I(h)-current blockers, but was abolished in tetrodotoxin. Although, under control conditions, the Vm of synaptically isolated respiratory pacemaker neurons was not significantly affected when [K(+)](o) was changed from 3 to 8 mM, the Vm is altered when [K(+)](o) was raised in low-[Na(+)](o) ACSF. Thus, current-clamp studies suggest that respiratory pacemaker neurons possess a background sodium current that maintains their membrane potential within a range where they express bursting, thereby stabilizing rhythmogenesis.     

From population dynamics to ecoinformatics: Ecosystems as multilevel information processing systems

In classical ecological theory the concept population plays a central role. Most models are formulated in terms of changes in the number/biomass/fraction of interacting populations. In the passed 30 years slowly alternative viewpoints have been developed. In this paper we trace some of these alternative developments which lead to viewing ecosystems in terms of local multilevel information processing and evolution. We will sketch the methodological developments, indicate some fundamental insight gained through the methodological innovations and focus our discussion on the central problem of the development and maintenance of diversity in ecosystems. We will explore the circumstances in which individual based diversity (plasticity, regulatory adaptation, intelligence) or population based diversity (speciation) develops.     

Peculiarities of orthodromic inhibition in pacemaker neurons in Helix pomatia

We used the intracellular recording method to study the effect of a group of nerves in the visceral complex on the activity of a pacemaking giantneuron located in the peripheral part of the visceral ganglion in a mollusk. Single excitations of the left and right pallial, the intestinal, and the anal nerves with electrical stimuli evoked similar responses, consisting of phases of rapid depolarization (duration 100 msec, amplitude 3–5 mV) and slower hyperpolarization (duration 400 msec, amplitude 5–8 mV). The excitation also had an aftereffect, which was expressed in inhibition of the background activity of the pacemaker for several seconds. The most interesting of the functional characteristics of that response was the effects of summation. With rhythmic excitation by stimuli of low frequency (0.5–1 c/sec) the result of summation was general hyperpolarization of the neuron and the appearance of giant inhibitory postsynaptic potentials (IPSP's) with an amplitude of 12–16 mV. With higher frequency of excitation (2–3 c/sec and upward) we observed depolarization replacing the hyperpolarization of the neuron, but IPSP's of large amplitude were absent. At the end of rhythmic excitation prolonged inhibition of the pacemaker's activity, lasting some minutes, occurred in all cases. This article discusses the possible mechanisms of that type of prolonged inhibition of the pacemaker's activity, the origin of the phases in biphasic responses, and the reasons for differences in the course of summation of biphasic postsynaptic potentials.M. V. Lomonosov Moscow State University. Translated from Neirofiziologiya, Vol. 3, No. 4, pp. 426–433, July–August, 1971.     

A stochastic model and a functional central limit theorem for information processing in large systems of neurons

The paper deals with information transmission in large systems of neurons. We model the membrane potential in a single neuron belonging to a cell tissue by a non time-homogeneous Cox-Ingersoll-Ross type diffusion; in terms of its time-varying expectation, this stochastic process can convey deterministic signals. We model the spike train emitted by this neuron as a Poisson point process compensated by the occupation time of the membrane potential process beyond the excitation threshold. In a large system of neurons 1≤i≤N processing independently the same deterministic signal, we prove a functional central limit theorem for the pooled spike train collected from the N neurons. This pooled spike train allows to recover the deterministic signal, up to some shape transformation which is explicit.     

Pigment-dispersing hormone-immunoreactive neurons in the cockroach Leucophaea maderae share properties with circadian pacemaker neurons

Neurons immunoreactive with antisera against the crustacean peptide -pigment dispersing hormone fullfill several anatomical criteria proposed for circadian pacemakers in the brain of the cockroach Leucophaea maderae. These include position of somata, projections to the lamina and midbrain and possible coupling pathways between the two pacemakers through commissural fibers. In behavioral experiments combined with lesion studies and immunocytochemical investigations we examined whether the presence of pigment-dispersing hormone-immunoreactive arborizations in the midbrain of the cockroach correlates with the presence of circadian locomotor activity. No rhythm was detected after severing both optic stalks in any animal for at least 12 days. Within the same time pigment-dispersing hormone-immunoreactive fibers in the midbrain disappeared. Two to seven weeks after the operation some of the cockroaches regained circadian locomotor activity, while others remained arrhythmic. In all cockroaches which regained rhythmic behavior pigment-dispersing hormone-immunoreactive fibers had regenerated and had largely found their original targets within the brain. In all arrhythmic cockroaches either none or very little regeneration had occurred. The period of the regained circadian activity inversely correlated with the number of regenerated immunoreactive commissural fibers. These data provide further evidence for the involvement of pigment-dispersing hormone-immunoreactive neurons in circadian clocks of orthopteroid insects.Abbreviations DD constant darkness - PDH pigment-dispersing hormone - PDHLI pigmentdispersing hormone-like immunoreactivity - PDFL a pigment-dispersing factor containing cells in the lamina - PDFMe pigment-dispersing factor containing cells in the medulla - QV quantification value