title: Functional and laminar dissociations between muscarinic and nicotinic cholinergic neuromodulation in the tree shrew primary visual cortex.
abstract: Acetylcholine is an important neuromodulator involved in cognitive function. The impact of cholinergic neuromodulation on computations within the cortical microcircuit is not well understood. Here we investigate the effects of layer-specific cholinergic drug application in the tree shrew primary visual cortex during visual stimulation with drifting grating stimuli of varying contrast and orientation. We describe differences between muscarinic and nicotinic cholinergic effects in terms of both the layer of cortex and the attribute of visual representation. Nicotinic receptor activation enhanced the contrast response in the granular input layer of the cortex, while tending to reduce neural selectivity for orientation across all cortical layers. Muscarinic activation modestly enhanced the contrast response across cortical layers, and tended to improve orientation tuning. This resulted in highest orientation selectivity in the supra- and infragranular layers, where orientation selectivity was already greatest in the absence of pharmacological stimulation. Our results indicate that laminar position plays a crucial part in functional consequences of cholinergic stimulation, consistent with the differential distribution of cholinergic receptors. Nicotinic receptors function to enhance sensory representations arriving in the cortex, whereas muscarinic receptors act to boost the cortical computation of orientation tuning. Our findings suggest close homology between cholinergic mechanisms in tree shrew and primate visual cortices.
authors.affiliation: Visual Cognition Laboratory, Department of Medicine, University of Fribourg, Chemin du Musée 5, CH-1700 Fribourg, Switzerland.
authors.forename: Anwesha
authors.initials: A
authors.lastname: Bhattacharyya
authors.forename: Felix
authors.initials: F
authors.lastname: Bießmann
authors.forename: Julia
authors.initials: J
authors.lastname: Veit
authors.forename: Robert
authors.initials: R
authors.lastname: Kretz
authors.forename: Gregor
authors.initials: G
authors.lastname: Rainer
mesh_terms: D000818:Animals; D018678:Cholinergic Agents / Q000494:pharmacology; D015350:Contrast Sensitivity / Q000187:drug effects / Q000502:physiology*; D008564:Membrane Potentials / Q000187:drug effects; D009415:Nerve Net / Q000187:drug effects / Q000502:physiology; D018377:Neurotransmitter Agents / Q000494:pharmacology; D009949:Orientation / Q000187:drug effects / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011976:Receptors, Muscarinic / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000378:metabolism*; D014418:Tupaiidae / Q000033:anatomy & histology; D014793:Visual Cortex / Q000033:anatomy & histology / Q000187:drug effects / Q000502:physiology*
chemical_list: D018678:Cholinergic Agents; D018377:Neurotransmitter Agents; D011976:Receptors, Muscarinic; D011978:Receptors, Nicotinic