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The purpose of this study was to assess the utility of intercostal muscle pacing by spinal cord stimulation (SCS) to provide artificial ventilation in ventilator-dependent quadriplegic patients. Five ventilator-dependent quadriplegics with phrenic nerve injury (and therefore not candidates for phrenic nerve pacing) were studied. During an initial surgical procedure, a quadripolar epidural disc electrode was positioned on the ventral portion of the upper thoracic spinal cord via a hemilaminectomy and subsequently connected to a radio-frequency receiver implanted subcutaneously over the anterior rib cage. In four of the five patients, initial SCS stimulation resulted in inspired volumes between 150 and 240 ml. Stimulation resulted in no effect in one patient, due to probable cystic degeneration of the thoracic spinal cord. Reconditioning of the intercostal muscles caused substantial increases in inspired volume in three of four patients of 670 to 850 ml. In one patient, reconditioning resulted in a much smaller increase (to 470 ml). The maximum duration that ventilation could be sustained by low-frequency (13 Hz) intercostal pacing ranged between 20 min and 2 3/4 h. Our findings indicate that intercostal pacing via SCS does not result in sufficient inspired volume production to support ventilation for prolonged periods. However, this modality may be a useful adjunct to enhance tidal volume in patients with suboptimal inspired volume by phrenic nerve pacing.

Pinealocytes of rhesus monkeys that had been ovariectomized and given intramuscular injections of 250 micrograms estradiol-benzoate for 3 consecutive days tended to have more synaptic ribbons (SR) and exhibited a significantly greater size of ribbon fields (RF) compared to untreated animals. These data are consistent with hypotheses that pinealocyte function in primates is altered by hormonal imbalances and that the SR participates in this response. RF were positioned in various parts of the cytoplasm and along the plasma membrane. Participation of SR in direct cell-to-cell contacts was suggested by the formation of densities along the plasma membrane. It is postulated that large RF serve as storage organelles and that the formation of RF results from division of pre-existing SR in each field. Reconstructions made from serial thin sections revealed that profiles of RF comprised separate SR that were not folded and sectioned along various planes.