Abstract
IntroductionRelease of the neuromodulator acetylcholine into cortical circuits supports cognition, although its precise role and mechanisms of action are not well understood. Little is known about functional differences in cholinergic modulatory effects across cortical model systems, but anatomical evidence suggests that such differences likely exist because, for example, the expression of cholinergic receptors differs profoundly both within and between species.MethodsIn the primary visual cortex (V1) of macaque monkeys, cholinergic receptors are strongly expressed by inhibitory interneurons. Using dual‐immunofluorescence confocal microscopy, we examine m1 muscarinic acetylcholine receptor expression by two subclasses of inhibitory interneurons—identified by their expression of the calcium‐binding proteins calbindin and calretinin—in the middle temporal extrastriate area (MT) of the macaque.Results and ConclusionsWe find that the majority of calbindin‐immunoreactive neurons (55%) and only few calretinin‐immunoreactive neurons (10%) express the m1 acetylcholine receptor. These results differ from the pattern observed in V1 of the same species, lending further support to the notion that cholinergic modulation in the cortex is tuned such that different cortical compartments will respond to acetylcholine release in different ways.
Highlights
Acetylcholine (ACh) is a neuromodulator that contributes to the dynamic specification of cortical state (Jasper and Tessier, 1971; Metherate et al, 1992; Everitt and Robbins, 1997; Duque et al, 2000; Hasselmo and McGaughy, 2004; Steriade, 2004; Sarter et al, 2005; Herrero et al, 2008; Mena‐Segovia et al, 2008)
ACh is delivered to cortex by neurons whose cell bodies lie in the basal forebrain, and cholinergic signaling occurs partly through volume transmission (Umbriaco et al, 1994; Mrzljak et al, 1995), a signaling mode in which molecules are released from varicosities that are not apposed to a specialized receptive surface
We quantified dual immunofluorescence to determine the extent to which the m1 ACh receptor (m1AChR) is expressed by putatively inhibitory interneurons that are immunoreactive for either CB or CR in area middle temporal extrastriate area (MT) of the macaque monkey
Summary
Acetylcholine (ACh) is a neuromodulator that contributes to the dynamic specification of cortical state (Jasper and Tessier, 1971; Metherate et al, 1992; Everitt and Robbins, 1997; Duque et al, 2000; Hasselmo and McGaughy, 2004; Steriade, 2004; Sarter et al, 2005; Herrero et al, 2008; Mena‐Segovia et al, 2008). ACh is delivered to cortex by neurons whose cell bodies lie in the basal forebrain, and cholinergic signaling occurs partly through volume transmission (Umbriaco et al, 1994; Mrzljak et al, 1995), a signaling mode in which molecules are released from varicosities that are not apposed to a specialized receptive surface (i.e. that do not make a synapse). Under these conditions, molecules diffuse some distance through the bioRxiv preprint extracellular space, eventually reaching receptors to which they can bind (Fuxe and Agnati, 1991). Variations in the local anatomical features of cortical circuits can enhance this capacity for local control of neuromodulation
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