title: Cardiovascular and electrophysiological responses to sympathetic pathway stimulation.
abstract: Anesthetized, vagotomized, and paralyzed cats were used to study the relationship between changes in blood pressure and T2 preganglionic nerve activity elicited by stimulation of descending spinal sympathoexcitatory pathways. While low-frequency stimulation (1-10 Hz) resulted in a depressor response, an attenuation of sympathetic nerve evoked discharges was noted after the second pulse of twin-pulse stimulations with 1,000- to 100-ms intervals between stimuli (corresponding to 1-10 Hz). High-frequency stimulation (greater than 10 Hz) resulted in a pressor response, while preganglionic nerve-evoked discharges were enhanced during twin-pulse stimulations with intervals between stimuli less than 50 ms (corresponding to greater than 20 Hz). These data suggest that the depressor response during low-frequency stimulation may be explained by impulses occurring during the silent period of the previous response. During this time the preganglionic neuron is inexcitable and spontaneous activity is abolished; therefore, the blood pressure falls. High-frequency stimulation may result in a pressor response by increasing the number of preganglionic neurons that are activated. This may be due to a process of temporal summation, with initial stimuli bringing cells closer to their threshold for firing and additional stimuli close in time causing these neurons to discharge.
mesh_terms: D000818:Animals; D001794:Blood Pressure; D002415:Cats; D003714:Denervation; D004558:Electric Stimulation; D004594:Electrophysiology; D005071:Evoked Potentials; D005725:Ganglia, Autonomic / Q000502:physiology*; D006339:Heart Rate; D013116:Spinal Cord / Q000502:physiology*; D013564:Sympathetic Nervous System / Q000502:physiology*; D013997:Time Factors; D014628:Vagotomy; D014630:Vagus Nerve / Q000502:physiology