Characterization of the cholinergic system in macaque lateral intraparietal area: An investigation of neuromodulatory compartments in cortex

Abstract

Acetylcholine (ACh) is a ubiquitous and well-studied neurotransmitter, best characterized in the peripheral nervous system where it acts as the signaling molecule at the neuromuscular junction. Despite being among the first discovered and presently best studied neurotransmitters, ACh’s role in the central nervous system is less well understood, although it is believed to act as a neuromodulator in cortical circuits that support cognition. Specifically, ACh has been implicated in many cognitive processes including learning and memory consolidation, reward and addiction, and the sleep/wake cycle. More commonly, cholinergic modulation is associated with attention. In lateral intraparietal area LIP—an area believed to be involved in attentive processes—I characterized the anatomical cholinergic system in the macaque monkey. Specifically, I described ACh receptor expression and distribution across the cortical layers by cell type, I quantified expression and density of the cholinergic synthetic and break-down enzymes, and I provided measurements for the local cholinergic tone in an awake, behaving macaque. These data provide evidence for the existence of neuromodulatory compartments in primate cortex and further support the notion that anatomical characterization of neuromodulatory systems is necessary to infer mechanisms of function across cortex.