Abstract
The striatum is predominantly composed of medium spiny projection neurons, with the remaining neurons consisting of several types of interneurons. Among the interneurons are a group of cells that express tyrosine hydroxylase (TH). Although the intrinsic electrical properties of these TH-expressing interneurons have been characterized, there is no agreement on the number of TH-expressing cell types and their electrical properties. Here, we have used transgenic mice in which YFP-tagged channelrhodopsin-2 (ChR2) was expressed in potential TH-expressing cells in a Cre-dependent manner. We found that the YFP+ neurons in the striatum were heterogeneous in their intrinsic electrical properties; unbiased clustering indicated that there are three main neuronal subtypes. One population of neurons had aspiny dendrites with high-frequency action potential (AP) firing and plateau potentials, resembling the TH interneurons (THIN) described previously. A second, very small population of labeled neurons resembled medium-sized spiny neurons (MSN). The third population of neurons had dendrites with an intermediate density of spines, showed substantial AP adaptation and generated prolonged spikes. This type of striatal neuron has not been previously identified in the adult mouse and we have named it the Frequency-Adapting Neuron with Spines (FANS). Because of their distinctive properties, FANS may play a unique role in striatal information processing.
Highlights
The striatum is a major component of the basal ganglia circuit and is involved in a number of functions such as motor planning, motivation and reward perception
Positive striatal cells could be identified, in live brain slices prepared from these mice, by the fluorescence of YFP fused to the ChR2
Due to the possibility of ectopic expression of ChR2-YFP in neurons that do not express tyrosine hydroxylase (TH) in adulthood (Lammel et al, 2015; Stuber et al, 2015), we do not assume that neurons expressing ChR2-YFP express TH and instead will conservatively refer to these cells as YFP+ neurons
Summary
The striatum is a major component of the basal ganglia circuit and is involved in a number of functions such as motor planning, motivation and reward perception. MSN are GABAergic and are the only known projection neurons of the striatum. Novel Striatum Neuron Type calretinin-expressing GABAergic interneurons have been observed in immunohistochemical studies but their electrophysiological properties are unknown (Rymar et al, 2004; Tepper et al, 2010). The use of transgenic mice expressing neuron-specific markers has revealed still other types of striatal interneurons. These include a NPY-expressing interneuron that differs from the NPY-LTS cell (Ibáñez-Sandoval et al, 2011; Assous et al, 2017), as well as a heterogeneous population of interneurons that express 5HT3a receptors (Faust et al, 2015, 2016; Muñoz-Manchado et al, 2016)
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