RESPIRATION-RELATED FEATURES OF SYMPATHETIC DISCHARGES IN THE DEVELOPING KITTEN

The objectives of the present study were to identify sympathetic disch arge features, either spontaneous or evoked, which exhibited maturatio nal changes. The spontaneous sympathetic nerve discharge of all kitten s was comprised of tonic activity as well as phasic inspiratory activi ty; the latter occurred synchronously with the C5 phrenic discharge. S ympathetic activity during inspiration was depressed (inhibited or dis facilitated) by vagal afferent inputs as was indicated by the marked i ncreases of amplitude following vagotomy. Hypoxia (10% O2) elicited ch anges in the amplitude of the sympathetic inspiration-related discharg e which were identical to those of the phrenic; discharge amplitudes w ere either increased, or decreased, or increased and then decreased (i .e. biphasic response). Regardless of the change in sympathetic inspir ation-related activity during hypoxia, the amplitude of tonic activity during expiration was often increased. Such changes in the discharge characteristics of the cervical sympathetic nerve in response to vagot omy or hypoxia were not dependent upon maturational processes as they were similar to those of adult cats. However, an age-dependent phenome non was revealed by autopower spectral analyses which showed that the phrenic and sympathetic nerve activities in animals greater-than-or-eq ual-to 45 day old were modulated by inputs from a common source becaus e their coherence spectra exhibited correlated periodicities in the 7- 10 Hz range.