Mathias Dewald

Low-Dimensional Dynamics in Sensory Biology 2: Facial Cold Receptors of the Rat

We report the results of a search for evidence of unstable periodic orbits in the sensory afferents of the facial cold receptors of the rat. Cold receptors are unique in that they exhibit a diversity of action potential firing patterns as well as pronounced transients in firing rate following rapid temperature changes. These characteristics are the result of an internal oscillator operating at the level of the membrane potential. If such oscillators have three or more degree of freedom, and at least one of which also exhibits a nonlinearity, they are potentially capable of complex activity. By detecting the existence of unstable periodic orbits, we demonstrate low-dimensional dynamical behavior whose characteristics depend on the temperature range, impulse pattern, and temperature transients.

Stimulus sensitivity and neuromodulatory properties of noisy intrinsic neuronal oscillators

Intrinsic subthreshold oscillations in the membrane potential are a common property of many neurons in the peripheral and central nervous system. When such oscillations are combined with noise, interesting signal encoding and neuromodulatory properties are obtained which allow, for example, sensitivity adjustment or differential encoding of stimuli. Here we demonstrate that a noisy Hodgkin/Huxley-model for subthreshold oscillations, when tuned to maximum sensitivity, can be significantly modulated by even minor physiological changes in the oscillation parameters amplitude or frequency. Given the ubiquity of subthreshold oscillating neurons, it can be assumed that these findings reflect principle encoding properties which are relevant for an understanding of sensitivity and neuromodulation in peripheral and central neurons.

Stochastic encoding in sensory neurons: impulse patterns of mammalian cold receptors

Abstract Intrinsic oscillations at the level of the membrane potential are a widespread feature of nerve cells. Several evidences exist that, in particular, sensory neurons combine their oscillatory membrane potentials with intrinsic, membrane and/or synaptic noise to obtain sensitive encoding properties. An interesting example are mammalian cold receptors where stimulus transduction results from modulation of intrinsic receptor oscillations with essential contribution of noise thereby generating a rich spectrum of impulse patterns. To further explore the dynamics of these receptors we here investigate an HH-type model for oscillations and spike initiation in cold receptors. By use of a biophysically plausible temperature scaling and with addition of noise, the model successfully mimicks the principle temperature-dependence of stationary impulse patterns of real cold receptors. Our results suggest that interactions between stochastic and deterministic dynamics are of functional importance for the encoding charcteristics of cold receptors.

Finding unstable periodic orbits in electroreceptors, cold receptors and hypothalamic neurons☆

Abstract Recently, searches for low-dimensional dynamical activity in various biological preparations have become fashionable. In particular, demonstrations of the existence of unstable periodic orbits (UPOs) and bifurcations between unstable and stable states are of interest. Here, we report the detection of UPOs in three diverse preparations: electroreceptor, cold receptor and hypothalamic neurons. Inherent, noise mediated oscillators are common to these temperature sensitive neurons, and the UPOs arise in them in the absence of external periodic stimulation. The external temperature is the bifurcation parameter. Behaviors in response to temperature transients are also shown.

The neuromodulatory properties of “noisy neuronal oscillators”

Many neurons, in various areas of the nervous system, exhibit spontaneous and intrinsic oscillations of their membrane potential or can develop oscillations on depolarization. Here we consider so-called subthreshold oscillations which operate close to the threshold of spike-generation. To analyze the principle neuromodulatory properties of such neuronal mechanisms we developed a computer model consisting of only a mnimal set of ironic conductances but which nevertheless attains subthreshold membrane potential oscillations of variable frequency and amplitude. With the addition of stochastic components, the oscillations generate typical impulse patterns which originate from a mixture of spike-triggering and subthreshold oscillations. The spiking probability thereby depends on the oscillation and noise parameters. According to the experimental data, the model can be tuned from complete silence to tonic firing with maximum sensitivity between these two extremes. Range and steepness of the activity and sensiti...

Phasic bursting activity of paraventricular neurons is modulated by temperature and angiotensin II

Abstract 1. Impulse activity of phasically firing (bursting) paraventricular neurons, which are assumed to be of the vasopressinergic type, have been extracellularly recorded in brain slices of the rat. 2. Analysis of burst patterns during temperature changes, angiotensin II application and combined application of both stimuli demonstrated that certain burst parameters are effected much stronger than the mean firing rate and also for a longer period of time. 3. The most sensitive parameter was the intraburst frequency which is considered to be the most effective parameter for increased vasopressin release. 4. These data indicate that there are functionally relevant changes in the impulse patterns which are not necessarily manifested in the mean firing rate.

Computational properties of a neuronal model for noisy subthreshold oscillations

Intrinsic subthreshold oscillations are a rather common feature of a variety of neurons in the peripheral and central nervous system. Examples reach from neurons in the amygdala, entorhinal and frontal cortex to sensory receptors such as mammalian cold receptors or multimodal ampullary sensory receptors of teleosts1–6. The phenomenon is characterized by oscillatory changes in the membrane potential which are below or close to the spike threshold. In this situation, naturally occuring stochastic influences due to membrane or synaptic noise seem to be an essential component for signal encoding. The reason is, that now the noise actually determines whether a spike is triggered during an oscillation cycle or not. Typical mixed patterns result consisting of spike-triggering and subthreshold oscillations (figure 1, see also ref. 3).