Our objectives are to determine in rodents, (a) the levels at which sensory afferents to heart and lungs enter the spinal cord and (b) the termination of cardiothoracic afferent fibers in spinal gray matter. Such information is required to understand neurostimulation and to progress development of rodent experimental models.
Under general anaesthesia and mechanical ventilation, 50 young Wistar rats were subjected to thoracotomy such that a neuroanatomical retrograde tracer (horseradish peroxidase or Fast Blue) could be injected with precision into either the pericardium, left atrium, root of the left lung, or the left lung parenchyma.After appropriate survival times animals were sacrificed and perfused with the adequate fixatives. Spinal ganglia and segments were identified, and those between C4 and Th12 were removed individually and cryoprotected. Segments were sectioned at 50μm and studied under the microscope to create a “map” of the column and the distribution of tracer deposit within it.
Segments C8 through T4 contained retrogradely labeled dorsal root neurons projecting to the heart, while C8-T6 were labeled after depositing tracer in the lung.Central branches of dorsal root ganglion cells entered laminae I and II.
Information from the heart is collected in the four upper segments of the thoracic cord, but some information from the lungs also arrives in these segments. Neurostimulation of spinal segments C8-T4 will block afferents entering laminae I and II, including pain afferents from the heart. The blocking of pain afferents from the heart may explain the clinical improvement observed in angina patients under neurostimulation.
The description of the anatomical basis of cardiothoracic neurostimulation provides a long-awaited scientific explanation of clinical findings. The experimental model developed and described here provides a way to further investigate cardiac neurostimulation.
Anselmo De La Fuente, None.