title: Muscarinic acetylcholine receptors are expressed by most parvalbumin-immunoreactive neurons in area MT of the macaque.
abstract: BACKGROUND
  In the mammalian neocortex, cells that express parvalbumin (PV neurons) comprise a dominant class of inhibitory neuron that substantially overlaps with the fast/narrow-spiking physiological phenotype. Attention has pronounced effects on narrow-spiking neurons in the extrastriate cortex of macaques, and more consistently so than on their broad-spiking neighbors. Cortical neuromodulation by acetylcholine (ACh) is a candidate mechanism for aspects of attention and in the primary visual cortex (V1) of the macaque, receptors for ACh (AChRs) are strongly expressed by inhibitory neurons. In particular, most PV neurons in macaque V1 express m1 muscarinic AChRs and exogenously applied ACh can cause the release of γ-aminobutyric acid. In contrast, few PV neurons in rat V1 express m1 AChRs. While this could be a species difference, it has also been argued that macaque V1 is anatomically unique when compared with other cortical areas in macaques.
  
  
  OBJECTIVE
  The aim of this study was to better understand the extent to which V1 offers a suitable model circuit for cholinergic anatomy in the macaque occipital lobe, and to explore cholinergic modulation as a biological basis for the changes in circuit behavior seen with attention.
  
  
  METHODS
  We compared expression of m1 AChRs by PV neurons between area V1 and the middle temporal visual area (MT) in macaque monkeys using dual-immunofluorescence confocal microscopy.
  
  
  CONCLUSIONS
  We find that, as in V1, most PV neurons in MT express m1 AChRs but, unlike in V1, it appears that so do most excitatory neurons. This provides support for V1 as a model of cholinergic modulation of inhibition in macaque visual cortex, but not of cholinergic modulation of visual cortical circuits in general. We also propose that ACh acting via m1 AChRs is a candidate underlying mechanism for the strong effects of attention on narrow-spiking neurons observed in behaving animals.
authors.affiliation: Systems Neurobiology Laboratories, The Salk Institute for Biological Studies La Jolla, California.
authors.forename: Anita A
authors.initials: AA
authors.lastname: Disney
authors.affiliation: Systems Neurobiology Laboratories, The Salk Institute for Biological Studies La Jolla, California.
authors.forename: Hussein A
authors.initials: HA
authors.lastname: Alasady
authors.affiliation: Systems Neurobiology Laboratories, The Salk Institute for Biological Studies La Jolla, California.
authors.forename: John H
authors.initials: JH
authors.lastname: Reynolds
mesh_terms: D000818:Animals; D008253:Macaca mulatta; D008254:Macaca nemestrina; D008297:Male; D009474:Neurons / Q000378:metabolism*; D010320:Parvalbumins / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism*; D013702:Temporal Lobe / Q000378:metabolism*; D014793:Visual Cortex / Q000378:metabolism*
chemical_list: D010320:Parvalbumins; D011976:Receptors, Muscarinic
keywords: Anatomy; calcium-binding proteins; immunofluorescence; neuromodulation; parvalbumin; quantitative; visual cortex