Ultrastructural changes in the sinuatrial and atrioventricular nodes of the heart of the monkey (Macaca fascicularis) after bilateral vagotomy.

This study describes the ultrastructural changes in the sinu-atrial (SA) and atrio-ventricular (AV) nodes of the monkey (Macaca fascicularis) after bilateral mid-cervical vagotomy at 1, 3, 5, 7 and 14 days post-operations. The changes were similar in both types of nodal cells. The most obvious feature of the degenerating nodal cells was the swollen mitochondria with disrupted cristae. Other changes include increased granular sarcoplasmic reticulum, increased glycogen particles, vacuolation of mitochondria and increased lysosomal activity. Axonal profiles in the vicinity of the nodal cells showed swelling and vacuolation. Cardiac neurons also showed some changes such as distended granular endoplasmic reticulum, increased accumulation of glycogen particles and increased lipofuscin granules. Macrophages and Schwann cells were the main scavengers in removing the degenerated nodal cells and axonal profiles. In the case of affected cardiac neurons, satellite cells seemed to act as main scavenger cells. It is postulated that the nodal cells are dependent on the incoming fibres of the vagus nerve for their survival. By an understanding of the ultrastructural changes in the nodal cells after bilateral vagotomy, it may help in developing new strategies to explore in depth of the conducting system of the heart.