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A barrel-related interneuron in layer 4 of rat somatosensory cortex with a high intrabarrel connectivity.

Koelbl C, Helmstaedter M, Lübke J, Feldmeyer D - Cereb. Cortex (2013)

Bottom Line: Three distinct clusters of FS L4 interneurons were identified based on their axonal morphology relative to the barrel column suggesting that these neurons do not constitute a homogeneous interneuron population.We found on average 3.7 ± 1.3 putative inhibitory synaptic contacts that were not restricted to perisomatic areas.In conclusion, we characterized a novel type of barrel cortex interneuron in the major thalamo-recipient layer 4 forming dense synaptic networks with L4 spiny neurons.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Physiology, Max Planck Institute of Medical Research, Jahnstr. 20, D-69120 Heidelberg, Germany Current address: Section of Cardiovascular Medicine, Boston University Medical Center, 88 East Newton Street, Boston, MA 02118, USA.

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Connectivity between cell pairs of L4 interneurons and excitatory L4 spiny neurons. (A) Connectivity ratio for L4 FS interneuron–L4 spiny neuron pairs; inhibitory connectivity was found to be 67% (29 of 43 postsynaptic spiny neurons tested). Traces show average IPSPs (red, upper row) and EPSPs (blue, lower row) of unidirectional inhibitory connections (left) and reciprocal connections (right), respectively, between L4 BIns and spiny neurons (BIn, blue; SN, red). (B) AP-to-PSP latencies for reciprocal BIn–SN pairs in layer 4. The latency for the excitatory postsynaptic response was significantly longer than the inhibitory response (1.09 ± 0.31 vs. 0.55 ± 0.11 ms, P < 0.001).
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BHT263F5: Connectivity between cell pairs of L4 interneurons and excitatory L4 spiny neurons. (A) Connectivity ratio for L4 FS interneuron–L4 spiny neuron pairs; inhibitory connectivity was found to be 67% (29 of 43 postsynaptic spiny neurons tested). Traces show average IPSPs (red, upper row) and EPSPs (blue, lower row) of unidirectional inhibitory connections (left) and reciprocal connections (right), respectively, between L4 BIns and spiny neurons (BIn, blue; SN, red). (B) AP-to-PSP latencies for reciprocal BIn–SN pairs in layer 4. The latency for the excitatory postsynaptic response was significantly longer than the inhibitory response (1.09 ± 0.31 vs. 0.55 ± 0.11 ms, P < 0.001).

Mentions: The assessment of the connection probability has certain experimental constraints, the most important factors being the position of the neurons within the slice as well as the slice-cutting angle. In our experiments, between 1 and 3 excitatory neurons had to be patched to find a inhibitory synaptic connection between a L4 interneuron and a L4 spiny neuron. We found a total of 29 L4 interneurons (data pooled together from all 3 morphological clusters) that were synaptically connected to a L4 spiny neuron in the same barrel (Figs 4 and 5). The calculated connectivity for the inhibitory connection of those 29 pairs was 67% (i.e., a total of 43 spiny neurons were patched to find 29 connections). All pairs with an established inhibitory connection were tested for a reciprocal excitatory contact. Out of the 29 cell pairs 20 were reciprocally connected, which translates into a excitatory connectivity ratio of 69% at L4-spiny neuron–L4 interneuron synapses. For BIn–L4 spiny neuron connections, in particular, we determined a connectivity ratio of 63% (n = 15 cell pairs); the reciprocal connection ratio was 67% (n = 10). Notably, in contrast to many excitatory neurons, these high connectivity ratios were independent of the distance between the somata of the pre- and postsynaptic neurons. This is likely to be due to the high density of both the L4 FS interneuron and the L4 spiny neuron axon within a cortical barrel. Somatic distances between pre- and postsynaptic neurons in a barrel were high with an average of 109 ± 39 µm (n = 19). Specifically for BIn–spiny neuron pairs, the average soma distance was 120 ± 43 µm (n = 11). As for unidirectional inhibitory connections, the likelihood of a reciprocal excitatory connection was independent of the distances between pre- and postsynaptic soma.Figure 5.


A barrel-related interneuron in layer 4 of rat somatosensory cortex with a high intrabarrel connectivity.

Koelbl C, Helmstaedter M, Lübke J, Feldmeyer D - Cereb. Cortex (2013)

Connectivity between cell pairs of L4 interneurons and excitatory L4 spiny neurons. (A) Connectivity ratio for L4 FS interneuron–L4 spiny neuron pairs; inhibitory connectivity was found to be 67% (29 of 43 postsynaptic spiny neurons tested). Traces show average IPSPs (red, upper row) and EPSPs (blue, lower row) of unidirectional inhibitory connections (left) and reciprocal connections (right), respectively, between L4 BIns and spiny neurons (BIn, blue; SN, red). (B) AP-to-PSP latencies for reciprocal BIn–SN pairs in layer 4. The latency for the excitatory postsynaptic response was significantly longer than the inhibitory response (1.09 ± 0.31 vs. 0.55 ± 0.11 ms, P < 0.001).
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4318534&req=5

BHT263F5: Connectivity between cell pairs of L4 interneurons and excitatory L4 spiny neurons. (A) Connectivity ratio for L4 FS interneuron–L4 spiny neuron pairs; inhibitory connectivity was found to be 67% (29 of 43 postsynaptic spiny neurons tested). Traces show average IPSPs (red, upper row) and EPSPs (blue, lower row) of unidirectional inhibitory connections (left) and reciprocal connections (right), respectively, between L4 BIns and spiny neurons (BIn, blue; SN, red). (B) AP-to-PSP latencies for reciprocal BIn–SN pairs in layer 4. The latency for the excitatory postsynaptic response was significantly longer than the inhibitory response (1.09 ± 0.31 vs. 0.55 ± 0.11 ms, P < 0.001).
Mentions: The assessment of the connection probability has certain experimental constraints, the most important factors being the position of the neurons within the slice as well as the slice-cutting angle. In our experiments, between 1 and 3 excitatory neurons had to be patched to find a inhibitory synaptic connection between a L4 interneuron and a L4 spiny neuron. We found a total of 29 L4 interneurons (data pooled together from all 3 morphological clusters) that were synaptically connected to a L4 spiny neuron in the same barrel (Figs 4 and 5). The calculated connectivity for the inhibitory connection of those 29 pairs was 67% (i.e., a total of 43 spiny neurons were patched to find 29 connections). All pairs with an established inhibitory connection were tested for a reciprocal excitatory contact. Out of the 29 cell pairs 20 were reciprocally connected, which translates into a excitatory connectivity ratio of 69% at L4-spiny neuron–L4 interneuron synapses. For BIn–L4 spiny neuron connections, in particular, we determined a connectivity ratio of 63% (n = 15 cell pairs); the reciprocal connection ratio was 67% (n = 10). Notably, in contrast to many excitatory neurons, these high connectivity ratios were independent of the distance between the somata of the pre- and postsynaptic neurons. This is likely to be due to the high density of both the L4 FS interneuron and the L4 spiny neuron axon within a cortical barrel. Somatic distances between pre- and postsynaptic neurons in a barrel were high with an average of 109 ± 39 µm (n = 19). Specifically for BIn–spiny neuron pairs, the average soma distance was 120 ± 43 µm (n = 11). As for unidirectional inhibitory connections, the likelihood of a reciprocal excitatory connection was independent of the distances between pre- and postsynaptic soma.Figure 5.

Bottom Line: Three distinct clusters of FS L4 interneurons were identified based on their axonal morphology relative to the barrel column suggesting that these neurons do not constitute a homogeneous interneuron population.We found on average 3.7 ± 1.3 putative inhibitory synaptic contacts that were not restricted to perisomatic areas.In conclusion, we characterized a novel type of barrel cortex interneuron in the major thalamo-recipient layer 4 forming dense synaptic networks with L4 spiny neurons.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Physiology, Max Planck Institute of Medical Research, Jahnstr. 20, D-69120 Heidelberg, Germany Current address: Section of Cardiovascular Medicine, Boston University Medical Center, 88 East Newton Street, Boston, MA 02118, USA.

Show MeSH
Related in: MedlinePlus