Anita A. Disney

Gain Modulation by Nicotine in Macaque V1

Acetylcholine is a ubiquitous cortical neuromodulator implicated in cognition. In order to understand the potential for acetylcholine to play a role in visual attention, we studied nicotinic acetylcholine receptor (nAChR) localization and function in area V1 of the macaque. We found nAChRs presynaptically at thalamic synapses onto excitatory, but not inhibitory, neurons in the primary thalamorecipient layer 4c. Furthermore, consistent with the release enhancement suggested by this localization, we discovered that nicotine increases responsiveness and lowers contrast threshold in layer 4c neurons. We also found that nAChRs are expressed by GABAergic interneurons in V1 but rarely by pyramidal neurons, and that nicotine suppresses visual responses outside layer 4c. All sensory systems incorporate gain control mechanisms, or processes which dynamically alter input/output relationships. We demonstrate that at the site of thalamic input to visual cortex, the effect of this nAChR-mediated gain is an enhancement of the detection of visual stimuli.

Muscarinic acetylcholine receptors in macaque V1 are most frequently expressed by parvalbumin-immunoreactive neurons

Acetylcholine (ACh) is believed to underlie mechanisms of arousal and attention in mammals. ACh also has a demonstrated functional effect in visual cortex that is both diverse and profound. We have reported previously that cholinergic modulation in V1 of the macaque monkey is strongly targeted toward GABAergic interneurons. Here we examine the localization of m1 and m2 muscarinic receptor subtypes across subpopulations of GABAergic interneurons—identified by their expression of the calcium‐binding proteins parvalbumin, calbindin, and calretinin—using dual‐immunofluorescence confocal microscopy in V1 of the macaque monkey. In doing so, we find that the vast majority (87%) of parvalbumin‐immunoreactive neurons express m1‐type muscarinic ACh receptors. m1 receptors are also expressed by 60% of calbindin‐immunoreactive neurons and 40% of calretinin‐immunoreactive neurons. m2 AChRs, on the other hand, are expressed by only 31% of parvalbumin neurons, 23% of calbindin neurons, and 25% of calretinin neurons. Parvalbumin‐immunoreactive cells comprise ≈75% of the inhibitory neuronal population in V1 and included in this large subpopulation are neurons known to veto and regulate the synchrony of principal cell spiking. Through the expression of m1 ACh receptors on nearly all of these PV cells, the cholinergic system avails itself of powerful control of information flow through and processing within the network of principal cells in the cortical circuit. J. Comp. Neurol. 507:1748–1762, 2008.

Differential expression of muscarinic acetylcholine receptors across excitatory and inhibitory cells in visual cortical areas V1 and V2 of the macaque monkey

Cholinergic neuromodulation, a candidate mechanism for aspects of attention, is complex and is not well understood. Because structure constrains function, quantitative anatomy is an invaluable tool for reducing such a challenging problem. Our goal was to determine the extent to which m1 and m2 muscarinic acetylcholine receptors (mAChRs) are expressed by inhibitory vs. excitatory neurons in the early visual cortex. To this end, V1 and V2 of macaque monkeys were immunofluorescently labelled for γ‐aminobutyric acid (GABA) and either m1 or m2 mAChRs. Among the GABA‐immunoreactive (ir) neurons, 61% in V1 and 63% in V2 were m1 AChR‐ir, whereas 28% in V1 and 43% in V2 were m2 AChR‐ir. In V1, both mAChRs were expressed by fewer than 10% of excitatory neurons. However, in V2, the population of mAChR‐ir excitatory neurons was at least double that observed in V1. We also examined m1 and m2 AChR immunoreactivity in layers 2 and 3 of area V1 under the electron microscope and found evidence that GABAergic neurons localize mAChRs to the soma, whereas glutamatergic neurons expressed mAChRs more strongly in dendrites. Axon and terminal labelling was generally weak. These data represent the first quantitative anatomical study of m1 and m2 AChR expression in the cortex of any species. In addition, the increased expression in excitatory neurons across the V1/V2 border may provide a neural basis for the observation that attentional effects gain strength up through the visual pathway from area V1 through V2 to V4 and beyond. J. Comp. Neurol. 499:49–63, 2006.

Orthogonal micro-organization of orientation and spatial frequency in primate primary visual cortex

Orientation and spatial frequency tuning are highly salient properties of neurons in primary visual cortex (V1). The combined organization of these particular tuning properties in the cortical space will strongly shape the V1 population response to different visual inputs, yet it is poorly understood. In this study, we used two-photon imaging in macaque monkey V1 to demonstrate the three-dimensional cell-by-cell layout of both spatial frequency and orientation tuning. We first found that spatial frequency tuning was organized into highly structured maps that remained consistent across the depth of layer II/III, similarly to orientation tuning. Next, we found that orientation and spatial frequency maps were intimately related at the fine spatial scale observed with two-photon imaging. Not only did the map gradients tend notably toward orthogonality, but they also co-varied negatively from cell to cell at the spatial scale of cortical columns.

Quantitative analysis of neurons with Kv3 potassium channel subunits, Kv3.1b and Kv3.2, in macaque primary visual cortex

Voltage‐gated potassium channels that are composed of Kv3 subunits exhibit distinct electrophysiological properties: activation at more depolarized potentials than other voltage‐gated K+ channels and fast kinetics. These channels have been shown to contribute to the high‐frequency firing of fast‐spiking (FS) GABAergic interneurons in the rat and mouse brain. In the rodent neocortex there are distinct patterns of expression for the Kv3.1b and Kv3.2 channel subunits and of coexpression of these subunits with neurochemical markers, such as the calcium‐binding proteins parvalbumin (PV) and calbindin D‐28K (CB). The distribution of Kv3 channels and interrelationship with calcium‐binding protein expression has not been investigated in primate cortex. We used immunoperoxidase and immunofluorescent labeling and stereological counting techniques to characterize the laminar and cell‐type distributions of Kv3‐immunoreactive (ir) neurons in macaque V1. We found that across the cortical layers ≈25% of both Kv3.1b‐ and Kv3.2‐ir neurons are non‐GABAergic. In contrast, all Kv3‐ir neurons in rodent cortex are GABAergic (Chow et al. [ 1999 ] J Neurosci. 19:9332–9345). The putatively excitatory Kv3‐ir neurons were mostly located in layers 2, 3, and 4b. Further, the proportion of Kv3‐ir neurons that express PV or CB also differs between macaque V1 and rodent cortex. These data indicate that, within the population of cortical neurons, a broader population of neurons, encompassing cells of a wider range of morphological classes may be capable of sustaining high‐frequency firing in macaque V1. J. Comp. Neurol. 516:291–311, 2009.

Expression of m1‐type muscarinic acetylcholine receptors by parvalbumin‐immunoreactive neurons in the primary visual cortex: A comparative study of rat, guinea pig, ferret, macaque, and human

Cholinergic neuromodulation is a candidate mechanism for aspects of arousal and attention in mammals. We have reported previously that cholinergic modulation in the primary visual cortex (V1) of the macaque monkey is strongly targeted toward GABAergic interneurons, and in particular that the vast majority of parvalbumin‐immunoreactive (PV) neurons in macaque V1 express the m1‐type (pirenzepine‐sensitive, Gq‐coupled) muscarinic ACh receptor (m1AChR). In contrast, previous physiological data indicates that PV neurons in rats rarely express pirenzepine‐sensitive muscarinic AChRs. To examine further this apparent species difference in the cholinergic effectors for the primary visual cortex, we have conducted a comparative study of the expression of m1AChRs by PV neurons in V1 of rats, guinea pigs, ferrets, macaques, and humans. We visualize PV‐ and mAChR‐immunoreactive somata by dual‐immunofluorescence confocal microscopy and find that the species differences are profound; the vast majority (>75%) of PV‐ir neurons in macaques, humans, and guinea pigs express m1AChRs. In contrast, in rats only ∼25% of the PV population is immunoreactive for m1AChRs. Our data reveal that while they do so much less frequently than in primates, PV neurons in rats do express Gq‐coupled muscarinic AChRs, which appear to have gone undetected in the previous in vitro studies. Data such as these are critical in determining the species that represent adequate models for the capacity of the cholinergic system to modulate inhibition in the primate cortex. J. Comp. Neurol. 522:986–1003, 2014.

Optogenetic manipulation of neural circuits in awake marmosets.

Optogenetics has revolutionized the study of functional neuronal circuitry (Boyden ES, Zhang F, Bamberg E, Nagel G, Deisseroth K. Nat Neurosci 8: 1263-1268, 2005; Deisseroth K. Nat Methods 8: 26-29, 2011). Although these techniques have been most successfully implemented in rodent models, they have the potential to be similarly impactful in studies of nonhuman primate brains. Common marmosets (Callithrix jacchus) have recently emerged as a candidate primate model for gene editing, providing a potentially powerful model for studies of neural circuitry and disease in primates. The application of viral transduction methods in marmosets for identifying and manipulating neuronal circuitry is a crucial step in developing this species for neuroscience research. In the present study we developed a novel, chronic method to successfully induce rapid photostimulation in individual cortical neurons transduced by adeno-associated virus to express channelrhodopsin (ChR2) in awake marmosets. We found that large proportions of neurons could be effectively photoactivated following viral transduction and that this procedure could be repeated for several months. These data suggest that techniques for viral transduction and optical manipulation of neuronal populations are suitable for marmosets and can be combined with existing behavioral preparations in the species to elucidate the functional neural circuitry underlying perceptual and cognitive processes.

Muscarinic acetylcholine receptors are expressed by most parvalbumin-immunoreactive neurons in area MT of the macaque

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.

A multi-site array for combined local electrochemistry and electrophysiology in the non-human primate brain.

BACKGROUND Currently, the primary technique employed in circuit-level study of the brain is electrophysiology, recording local field or action potentials (LFPs or APs). However most communication between neurons is chemical and the relationship between electrical activity within neurons and chemical signaling between them is not well understood in vivo, particularly for molecules that signal at least in part by non-synaptic transmission. NEW METHOD We describe a multi-contact array and accompanying head stage circuit that together enable concurrent electrophysiological and electrochemical recording. The array is small (<200 μm) and can be assembled into a device of arbitrary length. It is therefore well-suited for use in all major in vivo model systems in neuroscience, including non-human primates where the large brain and need for daily insertion and removal of recording devices places particularly strict demands on design. RESULTS We present a protocol for array fabrication. We then show that a device built in the manner described can record LFPs and perform enzyme-based amperometric detection of choline in the awake macaque monkey. Comparison with existing methods Existing methods allow single mode (electrophysiology or electrochemistry) recording. This system is designed for concurrent, dual-mode recording. It is also the only system designed explicitly to meet the challenges of recording in non-human primates. CONCLUSIONS Our system offers the possibility for conducting in vivo studies in a range of species that examine the relationship between the electrical activity of neurons and their chemical environment, with exquisite spatial and temporal precision.

Modulatory compartments in cortex and local regulation of cholinergic tone.

Neuromodulatory signaling is generally considered broad in its impact across cortex. However, variations in the characteristics of cortical circuits may introduce regionally-specific responses to diffuse modulatory signals. Features such as patterns of axonal innervation, tissue tortuosity and molecular diffusion, effectiveness of degradation pathways, subcellular receptor localization, and patterns of receptor expression can lead to local modification of modulatory inputs. We propose that modulatory compartments exist in cortex and can be defined by variation in structural features of local circuits. Further, we argue that these compartments are responsible for local regulation of neuromodulatory tone. For the cholinergic system, these modulatory compartments are regions of cortical tissue within which signaling conditions for acetylcholine are relatively uniform, but between which signaling can vary profoundly. In the visual system, evidence for the existence of compartments indicates that cholinergic modulation likely differs across the visual pathway. We argue that the existence of these compartments calls for thinking about cholinergic modulation in terms of finer-grained control of local cortical circuits than is implied by the traditional view of this system as a diffuse modulator. Further, an understanding of modulatory compartments provides an opportunity to better understand and perhaps correct signal modifications that lead to pathological states.