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1,2 1,2 1 1,3
4 - 1 1,5 1
1 1,6 1
1
2
3
JST, CREST 4 5
6 MRC
Corticothalamic projection neurons (CTNs) in the cerebral cortex
constitute an important component of the thalamocortical reciprocal
circuit, an essential input/output organization for cortical information
processing. However, the spatial organization of local excitatory
connections to CTNs is only partially understood. Here, applying a
newly developed adenoviral vector, we retrogradely visualized almost
all layer (L) 6 CTNs from their cell bodies to fine dendritic spines in
the rat barrel cortex. In cortical slices containing visualized L6 CTNs,
we intracellularly stained single L2/3, L4, L5, and L6 pyramidal/
spiny neurons and morphologically examined their local connections
to CTNs. The CTNs received strong and focused connections from
the L4 neurons just above them, and the most numerous nearby and
distant sources of local excitatory connections to CTNs were CTNs
themselves and L6 putative corticocortical neurons, respectively. The
present results suggest that, through CTNs, L4 neurons together with
L6 neurons may serve to modulate thalamic activity.
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Recurrent connection selectivity of layer V pyramidal
cells in frontal cortex
1,2 1,2
1
2
Pyramidal cells in the neocortex are differentiated into several
subgroups based on their extracortical projection targets. However,
little is known regarding the relative intracortical connectivity
of pyramidal cells specialized for their targets. We used paired
recordings and quantitative morphological analysis to reveal
distinct synaptic transmission properties, connection patterns, and
morphological differentiation of rat frontal cortex. Retrograde
tracers were used to label two projection subtypes in L5: crossedcorticostriatal
(CCS) cells projecting to both sides of the striatum,
and corticopontine (CPn) cells projecting to the ipsilateral pons.
Although CPn/CPn and CCS/CCS pairs had similar connection
probabilities, CPn/CPn pairs exhibited greater reciprocal connectivity,
stronger unitary synaptic transmission, and more facilitation of
paired-pulse responses. These synaptic characteristics were strongly
correlated to the projection subtypes. CPn and CCS cells were further
differentiated in their dendritic/ axonal arborization. Together, our
data demonstrate that the pyramidal projection system is segregated
according to subcortical target.
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A Hz Oscillation Synchronizes Prefrontal, VTA, and
Hippocampal Activities during Working memory
Gyorgy Buzsaki
Rutgers University
Network oscillations support transient communication across brain
structures. We show here, in rats, that task-related neuronal activity
in the medial prefrontal cortex (PFC), hippocampus and ventral
tegmental area (VTA), regions critical for working memory, is
coordinated by a 4-Hz oscillation. A prominent increase of power
and coherence of the 4-Hz oscillation in the PFC and VTA and its
phase-modulation of gamma power in both structures was present
during working memory. Subsets of both the PFC and hippocampal
neurons predicted the turn choices of the rat. The goal-predicting
PFC pyramidal neurons were more strongly phase-locked to both
4-Hz and hippocampal theta oscillations than non-predicting cells.
The 4-Hz and theta oscillations were phase-coupled and jointly
modulated both gamma waves and neuronal spikes in the PFC, VTA
and hippocampus. Thus, multiplexed timing mechanisms in the PFC-
VTA-hippocampus axis may support processing of information,
including working memory.
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Development of orientation and direction selectivity
in the mouse visual cortex
1,2 Nathalie Rochefort 2 Christine Grienberger 2
Nima Marandi 2 Daniel Hill 2 Arthur Konnerth 2
1
2 Inst. Neuroscience, Technical
Univ. Munich
Functional features of the cortical neurons such as direction
selectivity (DS) in the visual cortex are established during
development. Previous studies of the ferret visual cortex implied
that experience-dependent plasticity of local circuits in the cortex
contributed to the development of DS. In spite of their usefulness, it
has been less understood that how the rodent visual system develops.
Here we used two-photon Ca 2+ imaging to study the development of
DS in layer 2/3 neurons of the mouse visual cortex in vivo. At eyeopening,
nearly all orientation-selective neurons were also directionselective.
DS developed normally in dark-reared mice, indicating that
the early development of DS is independent of vision. Furthermore,
remarkable functional similarities existed between the development
of DS in cortical neurons and the previously reported development
of DS in the mouse retina. Together, these findings suggest a new
experience-independent circuit mechanism for the development of DS
in the mammalian brain. Since rodents lack columnar organization
in the visual cortex, difference in the local connectivity may explain
different developmental profile between species.