MODIFICATION OF RECEPTIVE-FIELDS OF POSTERIOMEDIAL BARREL SUBFIELD NEOCORTICAL SINGLE UNITS BY KNOWN CONCENTRATIONS OF IONTOPHORESED NORADRENALINE IN THE RAT

Using quantitative electromechanical stimulation of vibrissae poststimulus time histograms were used to map the receptive fields of single units from laminae II/III (12 units), IV (24 units) and V (12 units) of the posteriomedial barrel subfield in urethane anaesthetized rats prior to, and during the iontophoresis of known concentrations of Noradrenaline. All units had multivibrissae receptive fields prior to noradrenaline iontophoresis with laminae II/III units having the smallest size of center and surround receptive field and laminae V the largest. Lamina IV showed the strongest center receptive field response probability magnitude (spikes/stimulus) and the shortest modal latency of evoked responses. Noradrenaline iontophoresis diminished the size of surround receptive fields in each lamina and additionally decreased the size of center receptive fields in laminae IV and V. In Lamina IV, in contrast to laminae II/III and V, response probability magnitude from center receptive field vibrissae was not significantly depressed whilst modal latency of the evoked response was significantly reduced.