Synaptic junctions between sympathetic axon terminals and pinealocytes in the monkey Macaca fascicularis

Area of Science:

• Neuroscience
• Cell Biology
• Histology

Background:

• The pineal gland's innervation is crucial for regulating circadian rhythms and hormone production.
• Understanding the precise neural pathways and synaptic connections within the pineal gland is essential.

Purpose of the Study:

• To investigate the distribution and ultrastructure of axon terminals in the monkey pineal gland.
• To determine the impact of superior cervical ganglionectomy on these axon terminals and their synaptic connections.
• To elucidate the neural control of pinealocytes and intrapineal ganglion cells.

Main Methods:

• Electron microscopy was used to examine the pineal gland of normal and post-ganglionectomy monkeys.
• Morphological changes in axon terminals and synaptic structures were analyzed.
• Time points included 5, 7, and 30 days after surgery.

Main Results:

• Numerous sympathetic axon terminals with small vesicles were found in normal monkeys.
• Bilateral superior cervical ganglionectomy induced degenerative changes in these terminals, including glycogen accumulation and vesicle displacement.
• Degenerating terminals formed synaptic contacts with pinealocytes, showing postsynaptic membrane thickening.
• In long-term survivors, remaining terminals primarily contacted intrapineal ganglion cells, with some presynaptic input to pinealocytes.

Conclusions:

• Sympathetic postganglionic neurons from the superior cervical ganglia directly innervate pinealocytes via synaptic contacts.
• Intrapineal ganglion cells receive input from the central nervous system.
• Some central nervous system fibers may also directly synapse with pinealocytes.