22 research outputs found
A Corticothalamic Switch: Controlling the Thalamus with Dynamic Synapses
SummaryCorticothalamic neurons provide massive input to the thalamus. This top-down projection may allow the cortex to regulate sensory processing by modulating the excitability of thalamic cells. Layer 6 corticothalamic neurons monosynaptically excite thalamocortical cells, but also indirectly inhibit them by driving inhibitory cells of the thalamic reticular nucleus. Whether corticothalamic activity generally suppresses or excites the thalamus remains unclear. Here we show that the corticothalamic influence is dynamic, with the excitatory-inhibitory balance shifting in an activity-dependent fashion. During low-frequency activity, corticothalamic effects are mainly suppressive, whereas higher-frequency activity (even a short bout of gamma frequency oscillations) converts the corticothalamic influence to enhancement. The mechanism of this switching depends on distinct forms of short-term synaptic plasticity across multiple corticothalamic circuit components. Our results reveal an activity-dependent mechanism by which corticothalamic neurons can bidirectionally switch the excitability and sensory throughput of the thalamus, possibly to meet changing behavioral demands
Thalamic microcircuits: presynaptic dendrites form two feedforward inhibitory pathways in thalamus
Infrabarrels Are Layer 6 Circuit Modules in the Barrel Cortex that Link Long-Range Inputs and Outputs
The rodent somatosensory cortex includes well-defined examples of cortical columns—the barrel columns—that extend throughout the cortical depth and are defined by discrete clusters of neurons in layer 4 (L4) called barrels. Using the cell-type-specific Ntsr1-Cre mouse line, we found that L6 contains infrabarrels, readily identifiable units that align with the L4 barrels. Corticothalamic (CT) neurons and their local axons cluster within the infrabarrels, whereas corticocortical (CC) neurons are densest between infrabarrels. Optogenetic experiments showed that CC cells received robust input from somatosensory thalamic nuclei, whereas CT cells received much weaker thalamic inputs. We also found that CT neurons are intrinsically less excitable, revealing that both synaptic and intrinsic mechanisms contribute to the low firing rates of CT neurons often reported in vivo. In summary, infrabarrels are discrete cortical circuit modules containing two partially separated excitatory networks that link long-distance thalamic inputs with specific outputs
HVC Neural Sleep Activity Increases With Development and Parallels Nightly Changes in Song Behavior
Patch Clamp Electrophysiology and Capillary Electrophoresis–Mass Spectrometry Metabolomics for Single Cell Characterization
The visual selection of specific
cells within an <i>ex vivo</i> brain slice, combined with
whole-cell patch clamp recording and
capillary electrophoresis (CE)–mass spectrometry (MS)-based
metabolomics, yields high chemical information on the selected cells.
By providing access to a cell’s intracellular environment,
the whole-cell patch clamp technique allows one to record the cell’s
physiological activity. A patch clamp pipet is used to withdraw ∼3
pL of cytoplasm for metabolomic analysis using CE–MS. Sampling
the cytoplasm, rather than an intact isolated neuron, ensures that
the sample arises from the cell of interest and that structures such
as presynaptic terminals from surrounding, nontargeted neurons are
not sampled. We sampled the rat thalamus, a well-defined system containing
gamma-aminobutyric acid (GABA)-ergic and glutamatergic neurons. The
approach was validated by recording and sampling from glutamatergic
thalamocortical neurons, which receive major synaptic input from GABAergic
thalamic reticular nucleus neurons, as well as neurons and astrocytes
from the ventral basal nucleus and the dorsal lateral geniculate nucleus.
From the analysis of the cytoplasm of glutamatergic cells, approximately
60 metabolites were detected, none of which corresponded to the compound
GABA. However, GABA was successfully detected when sampling the cytoplasm
of GABAergic neurons, demonstrating the exclusive nature of our cytoplasmic
sampling approach. The combination of whole-cell patch clamp with
single cell cytoplasm metabolomics provides the ability to link the
physiological activity of neurons and astrocytes with their neurochemical
state. The observed differences in the metabolome of these neurons
underscore the striking cell to cell heterogeneity in the brain