Amygdalospinal projections in the macaque monkey

Area of Science:

• Neuroscience
• Primate Anatomy

Background:

• The central nucleus of the amygdala plays a role in processing various stimuli.
• Neural pathways connecting the spinal cord to higher brain centers are crucial for sensory integration.

Purpose of the Study:

• To investigate the neural connections between the cervical spinal cord and the central nucleus of the amygdala in macaque monkeys.
• To determine if retrograde neuronal tracing could identify amygdala neurons projecting from the cervical cord.

Main Methods:

• Horseradish peroxidase (HPP) enzyme injections into the cervical spinal cord (upper and middle segments) of macaque monkeys.
• Retrograde neuronal labeling to identify neurons with axonal projections to the injection site.
• Microscopic examination of brain tissue to locate labeled neurons in the amygdala.

Main Results:

• Retrograde labeling of neurons was observed in the caudal part of the central nucleus of the amygdala.
• Labeled neurons were consistently found ipsilateral to the side of the spinal cord injection.
• The number of labeled neurons was small but present across all 7 monkeys studied (3 Japanese, 3 crab-eating, 1 rhesus).

Conclusions:

• A direct neural pathway exists from the upper and middle cervical spinal cord to the central nucleus of the amygdala in macaque monkeys.
• This pathway involves neurons located in the caudal portion of the central amygdala nucleus.
• The findings contribute to understanding the neuroanatomical substrates of sensory processing and integration involving the spinal cord and amygdala.