A multichannel event timer for real-time laboratory computer systems.

Tomato plants (Lycopersicon esculentum) accumulate proteinase inhibitor 2 (pin2) mRNA in response to insect attack, crushing and flaming in leaves distant from those treated. Most earlier work suggests that the systemic wound signals are chemical; here we try to determine whether electrical or physical (hydraulic) signals can also evoke pin expression. We used a mild flame to evoke a systemic hydraulic signal and its local electrical aftermath, the variation potential (VP), and we used an electric stimulus to evoke a systemic electrical signal, the action potential (AP). We determined the kinetic parameters of both the VP and AP. Flame-wounded plants essentially always exhibited major electrical responses throughout the plant and a several-fold increase in pin2 mRNA within 1 h. Electrically stimulated plants that generated and transmitted a signal (AP) into the analyzed leaf exhibited similarly large, rapid increases in pin2 mRNA levels. Plants which generated no signal, or signals of just a few microvolts, had unchanged levels of pin2 mRNA. Since the AP and VP both arrived in the receiving leaf before accumulation of pin2 mRNA began, we conclude that, in addition to the previously shown chemical signals, both hydraulically induced VPs and electrically induced APs are capable of evoking pin2 gene expression.

Action Potentials↗

PubMed1996

Influence of dendritic structure on firing pattern in model neocortical neurons.

Neocortical neurons display a wide range of dendritic morphologies, ranging from compact arborizations to highly elaborate branching patterns. In vitro electrical recordings from these neurons have revealed a correspondingly diverse range of intrinsic firing patterns, including non-adapting, adapting and bursting types. This heterogeneity of electrical responsivity has generally been attributed to variability in the types and densities of ionic channels. We show here, using compartmental models of reconstructed cortical neurons, that an entire spectrum of firing patterns can be reproduced in a set of neurons that share a common distribution of ion channels and differ only in their dendritic geometry. The essential behaviour of the model depends on partial electrical coupling of fast active conductances localized to the soma and axon and slow active currents located throughout the dendrites, and can be reproduced in a two-compartment model. The results suggest a causal relationship for the observed correlations between dendritic structure and firing properties and emphasize the importance of active dendritic conductances in neuronal function.

Action Potentials↗

PubMed1996

Synaptic strengthening through activation of Ca2+-permeable AMPA receptors.

Postsynaptic Ca2+ elevation during synaptic transmission is an important trigger for short- and long-term changes in synaptic strength in the vertebrate central nervous system. The AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionate) receptors, a subfamily of glutamate receptors, mediate much of the excitatory synaptic transmission in the brain and spinal cord. It has been shown that a subtype of the AMPA receptor is Ca2+-permeable and is present in the subpopulations of neurons. When synaptically localized, these receptors should mediate postsynaptic Ca2+ influx, providing a trigger for changes in synaptic strength. Here we show that Ca2+-permeable AMPA receptors are synaptically localized on a subpopulation of dorsal horn neurons, and that they provide a synaptically gated route of Ca2+ entry, and that activation of these receptors strengthens synaptic transmission mediated by AMPA receptors. This pathway for postsynaptic Ca2+ influx may provide a new form of activity-dependent modulation of synaptic strength.

Action Potentials↗