Adrenergic innervation of the calvarium of the neonatal rat. Its relationship to the sagittal suture and developing parietal bones.

The presence and distribution of adrenergic nerves in the developing calvarium of the newborn rat documented by means of the formaldehyde-induced fluorescence technique in rats aged 2 or 7 days. Nerve fibres exhibiting catecholamine-specific fluorescence were seen within the developing calvarium of all animals. In coronal sections, these fibres could be seen in the developing bone, especially in the lamina interna, while in sagittal sections, they were seen to traverse the tissue to reach the central of the diploë. These fibres originate from a denser plexus within the dura mater. Especially in the younger age group, the fluorescent fibres often exhibited an immature appearance, being coarse and devoid of varicosities. In the older animals the fibres were often varicose. The sutural tissue proper was always found to be devoid of adrenergic innervation. The possible origin and functional significance of the adrenergic innervation in the developing bone in relation to skull growth and sutural closure are discussed.