Neuroanatomical Substrates of Circuit-Specific Cholinergic Modulation across the Primate Anterior Cingulate Cortex

Area of Science:

• Neuroscience
• Neuroanatomy
• Receptor Pharmacology

Background:

• Acetylcholine is a key neuromodulator in the limbic system, regulating arousal and emotions.
• The anterior cingulate cortex (ACC) and amygdala (AMY) are crucial limbic structures involved in emotional regulation.
• Cholinergic modulation of ACC microcircuits and their amygdala outputs is vital for cognitive-emotional integration.

Purpose of the Study:

• To investigate the distribution of muscarinic acetylcholine receptors (m1 and m2) on neurons within distinct ACC areas.
• To identify the localization of these receptors on excitatory, inhibitory, and amygdala-targeting projection neurons.
• To elucidate the structural basis of cholinergic modulation in ACC microcircuits and their amygdala outputs.

Main Methods:

• Utilized immunohistochemistry to detect m1 and m2 receptor expression.
• Employed neural tracers injected into the basolateral amygdala to identify projection neurons.
• Examined receptor distribution across different cell types and laminar layers in ACC areas of adult rhesus monkeys.

Main Results:

• Laminar densities of m1 and m2 expressing neurons varied by ACC area and cell type.
• The ventral subgenual ACC (A25) showed higher m2 localization on inhibitory terminals.
• Ventral ACC exhibited greater m1 and m2 expression on amygdala-targeting pyramidal neurons.

Conclusions:

• Findings suggest robust cholinergic disinhibition and potentiation of amygdala outputs from the ventral ACC.
• These patterns may link ventral ACC hyperexcitability in depression to cholinergic mechanisms.
• Reveals the anatomical substrate for diverse cholinergic modulation of ACC microcircuits and amygdala outputs in affective disorders.