Synaptic background noise controls the input/output characteristics of single cells in an in vitro model of in vivo activity
Section snippets
In vivo experiments
The methods used in the in vivo preparations are similar to those described elsewhere (Henze et al., 2000). Three Sprague–Dawley rats (300–500 g) were anesthetized with urethane (1.65 g/kg; Sigma) and placed in a stereotaxic apparatus (Kopf, Tujunga, CA, USA). The body temperature of the rat was monitored and kept around 35 °C. A small portion of the skull was drilled (about 1 mm×1 mm) above the pre-limbic/infra-limbic areas of the prefrontal cortex (2.0 mm anterior from Bregma, 1.0 mm lateral,
Recreation of in vivo-like activity
Intracellularly recorded (n=5) layer 5 pyramidal cells of rat prefrontal cortex in vivo under urethane anesthesia exhibit large fluctuations in their membrane potentials, accompanied by occasional spontaneous discharges (Fig. 1A). These membrane fluctuations had a S.D. of about 4 mV (3.9±0.5 mV; n=4), the average membrane potential was around −65 mV (−65±2.6 mV; n=4), and the spontaneous discharge rate was highly irregular with a CV around 1 (0.94±0.17; n=4) and an average firing rate of about
Discussion
Although the properties of neurons recorded in vitro are quite different from those recorded in vivo, they were much more similar when neurons in vitro were stimulated with two stochastic processes simulating excitatory and inhibitory conductances. We used the dynamic clamp technique to inject these conductances in layer 5 pyramidal cells of the rat prefrontal cortex. As a consequence, cells were depolarized by about 15 mV, their input resistances were decreased four-five-fold, and their
Acknowledgements
We thank Darrel Henze and G. Buzsaki (Rutgers University) for their invaluable help with the in vivo experiments. Research was supported by the Howard Hughes Medical Institute, the National Institutes of Health (NIH) and the Centre National pour la Recherche Scientifique (CNRS).
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