The underestimated role of a somatosensory neural network on thyroid gland morphology: an experimental subarachnoid hemorrhage model study

Abstract

Objectives: Innervation of the thyroid gland has been attributed to the autonomic nervous system. Although peripheral sympathetic and parasympathetic innervations of the thyroid gland are well known, little is known about the somatosensory innervation of the thyroid gland. In this study, alterations on the somatosensory neural network of the thyroid gland following an experimental subarachnoid hemorrhage were investigated in rabbits. Methods: Experiments were conducted on 23 rabbits under no medical intervention. Five rabbits were used as control group. Five rabbits were used as the sham group and serum physiologic (SF) was injected into their cisterna magna. The remaining 13 animals were used as the subarachnoid hemorrhage (SAH) group; their own blood (1 ml) was re-injected into the cisterna magna. Thyroid hormone levels of animals were measured at the end of one month. Then, histological sections of the middle parts of the thyroid glands were stained with haematoxylin-eosin (H&E) for investigation of SAH-related damage. The total follicle volume (TFV) per cubic millimeter of the thyroid gland was estimated by stereological methods. Comparison of degenerated neuronal density (DND) in the C4 dorsal root ganglia (DRG) was examined bilaterally using H&E and TUNEL stainings. Results: Following SAH, neuronal degeneration in the cervical DRG caused somatic innervation deficiency, follicular atrophy and thyroid hormone depletion in the thyroid gland. T3 and T4 hormone levels of the SAH group (T3: 61±8 μg/dl; T4: 1.01±0.12 μg/dl) were significantly (p<0.005) lower than those of control (T3; 103±6 μg/dl, T4: 1.37±0.36 μg/dl) and sham (T3; 94±10 μg/dl; T4: 1.24±0.87 μg/dl) groups. In control groups, mean TFV was 41% / mm3 and DND of C4 DRG was 6±2 / mm3. These values were significantly lower than those in sham (TFV: 35%/mm3 and DND: 22±7/mm3) and experimental SAH (TFV: 23%/mm3 and DND: 253±49/mm3) groups (p<0.0005 and p<0.0001, respectively). Conclusion: Thyroid follicle growth and its secretory activity are under the control of a quite complex, multi-originated, yet incompletely understood innervation pattern. We propose the presence of an underestimated role of a somatosensory neural network - an interganglionary link between the superior cervical, thyroid, laryngeal, nodose, trigeminal and dorsal root ganglia - on thyroid gland morphology.

Keywords

• cisterna magna,dorsal root ganglion,rabbit,subarachnoid hemorrhage,thyroid gland

References

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