Spectral breadth and laminar distribution of thalamocortical inputs to A1.

Article date: 2016/12/20

PubMed ID: 1372236

Journal name: Journal of neurophysiology (ISSN: 1522-1598)

DOI: 10.1152/jn.00887.2015


The GABAergic agonist muscimol is used to inactivate brain regions in order to reveal afferent inputs in isolation. However, muscimol's use in primary auditory cortex (A1) has been questioned on the grounds that it may unintentionally suppress thalamocortical inputs. We tested whether muscimol can preferentially suppress cortical, but not thalamocortical, circuits in urethane-anesthetized mice. We recorded tone-evoked current source density profiles to determine frequency receptive fields (RFs) for three current sinks: the “layer 4” sink (fastest onset, middle-layer sink) and current sinks 100 μm above (“layer 2/3”) and 300 μm below (“layer 5/6”) the main input. We first determined effects of muscimol dose (0.01-1 mM) on the characteristic frequency (CF) tone-evoked layer 4 sink. An “ideal” dose (100 μM) had no effect on CF-evoked sink onset latency or initial response but reduced peak amplitude by >80%, implying inhibition of intracortical, but not thalamocortical, activity. We extended the analysis to current sinks in layers 2/3 and 5/6 and for all three sinks determined RF breadth (quarter-octave steps, 20 dB above CF threshold). Muscimol reduced RF breadth 42% in layer 2/3 (from 2.4 ± 0.14 to 1.4 ± 0.11 octaves), 14% in layer 4 (2.2 ± 0.12 to 1.9 ± 0.10 octaves), and not at all in layer 5/6 (1.8 ± 0.10 to 1.7 ± 0.12 octaves). The results provide an estimate of the laminar and spectral extent of thalamocortical projections and support the hypothesis that intracortical pathways contribute to spectral integration in A1.

Author List: Intskirveli Irakli, Joshi Anar, Vizcarra-Chacón Bianca Julieta, Metherate Raju

Publication Types: Journal Article; Research Support, N.I.H., Extramural

Article Date: 2016/02/17

Substances mentioned in the article: GABA-A Receptor Agonists; Muscimol;

Mesh terms: Action Potentials; Animals; Cerebral Cortex/cytology; GABA-A Receptor Agonists/pharmacology; Male; Mice; Muscimol/pharmacology; Neural Pathways/cytology; Neurons/drug effects; Thalamus/cytology;

Citations: - Synaptic strength between motoneurons and terminals of the dorsolateral funiculus is regulated by GABA receptors in the turtle spinal cord.

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