Most calbindin-immunoreactive neurons, but few calretinin-immunoreactive neurons, express the m1 acetylcholine receptor in the middle temporal visual area of the macaque monkey

Release 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. In the primary visual cortex (V1) of macaque monkeys, cholinergic receptors are strongly expressed by inhibitory interneurons. Here, 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. Using dual-immunofluorescence confocal microscopy, we find that the majority of calbindin-immunoreative neurons (55%) and only few calretinin-immunoreactive neurons (10%) express the m1 acetylcholine receptor. This differs from the pattern observed in V1 of the same species, lending further support to the notion that cholinergic modulation in cortex is tuned such that different cortical compartments will respond to acetylcholine release in different ways.