Antal M, Acuna-Goycolea C, Pressler RT, Blitz DM, Regehr WG. Cholinergic activation of M2 receptors leads to context-dependent modulation of feedforward inhibition in the visual thalamus.
PLoS Biol 2010;
8:e1000348. [PMID:
20386723 PMCID:
PMC2850378 DOI:
10.1371/journal.pbio.1000348]
[Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2010] [Accepted: 02/22/2010] [Indexed: 11/18/2022] Open
Abstract
The temporal dynamics of inhibition within a neural network is a crucial determinant of information processing. Here, the authors describe in the visual thalamus how neuromodulation governs the magnitude and time course of inhibition in an input-dependent way.
In many brain regions, inhibition is mediated by numerous classes of specialized interneurons, but within the rodent dorsal lateral geniculate nucleus (dLGN), a single class of interneuron is present. dLGN interneurons inhibit thalamocortical (TC) neurons and regulate the activity of TC neurons evoked by retinal ganglion cells (RGCs), thereby controlling the visually evoked signals reaching the cortex. It is not known whether neuromodulation can regulate interneuron firing mode and the resulting inhibition. Here, we examine this in brain slices. We find that cholinergic modulation regulates the output mode of these interneurons and controls the resulting inhibition in a manner that is dependent on the level of afferent activity. When few RGCs are activated, acetylcholine suppresses synaptically evoked interneuron spiking, and strongly reduces disynaptic inhibition. In contrast, when many RGCs are coincidently activated, single stimuli promote the generation of a calcium spike, and stimulation with a brief train evokes prolonged plateau potentials lasting for many seconds that in turn lead to sustained inhibition. These findings indicate that cholinergic modulation regulates feedforward inhibition in a context-dependent manner.
Within the visual thalamus, a single type of inhibitory interneuron regulates activity evoked by retinal ganglion cells and controls the visual signals that reach the cortex. Here, we find that neuromodulation, of the sort thought to occur when an animal is attending to a task, regulates the firing mode of these interneurons and controls the resulting inhibition in an input-dependent manner. When few ganglion cells are activated, neuromodulation greatly decreases the number of spikes in interneurons, and as a result, strongly reduces the inhibition of relay neurons. This favors the lossless transmission of weak visual signals to the cortex by virtually eliminating inhibition within the thalamus. In contrast, when many ganglion cells are activated, the same neuromodulator leads to strong and prolonged inhibition. This is accomplished by promoting the generation of calcium spikes and prolonged depolarizations in interneurons. In this way, a modulator can regulate the flow of visual information in a context-dependent manner.
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