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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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Synaptic connection between L4 interneurons and spiny neurons. (A) Presynaptic AP (blue) in a L4 BIn (cluster 3 neuron) and 10 consecutive IPSPs (red) in a L4 spiny neuron recorded at a membrane potential of −55 mV. Note the amplitude fluctuation between individual IPSPs. (B) Distribution of the coefficient of IPSP variation for BIn–L4 spiny neuron connections. (C) Relationship between unitary IPSP amplitudes and CVs displaying a high reliability (low variation) even for small IPSP amplitudes (n = 13). The 2 dashed lines represent the predictions of simple binomial release statistics for the CV as a function of the IPSP amplitude assuming 4 synaptic contacts (close to the number of putative synaptic contacts identified for this connection) and low qS = 0.14 mV (left) and high qS = 0.6 mV (right), respectively. (D) Latency distribution for this synaptic connection; the average latency was 0.55 ± 0.12 ms. (E1) Paired pulse behavior at BIn–L4 spiny neuron connection. Five APs (blue) elicited in a BIn and individual IPSPs (light red) evoked in the L4 spiny neuron together with the corresponding average IPSP (red) are shown. (E2) Paired pulse depression for 5 consecutive IPSPs elicited by APs at either 100 ms (10 Hz) or 25 ms (40 Hz) intervals. At both frequencies, a marked depression can be observed. The depression at 25-ms intervals between APs is markedly stronger.
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BHT263F4: Synaptic connection between L4 interneurons and spiny neurons. (A) Presynaptic AP (blue) in a L4 BIn (cluster 3 neuron) and 10 consecutive IPSPs (red) in a L4 spiny neuron recorded at a membrane potential of −55 mV. Note the amplitude fluctuation between individual IPSPs. (B) Distribution of the coefficient of IPSP variation for BIn–L4 spiny neuron connections. (C) Relationship between unitary IPSP amplitudes and CVs displaying a high reliability (low variation) even for small IPSP amplitudes (n = 13). The 2 dashed lines represent the predictions of simple binomial release statistics for the CV as a function of the IPSP amplitude assuming 4 synaptic contacts (close to the number of putative synaptic contacts identified for this connection) and low qS = 0.14 mV (left) and high qS = 0.6 mV (right), respectively. (D) Latency distribution for this synaptic connection; the average latency was 0.55 ± 0.12 ms. (E1) Paired pulse behavior at BIn–L4 spiny neuron connection. Five APs (blue) elicited in a BIn and individual IPSPs (light red) evoked in the L4 spiny neuron together with the corresponding average IPSP (red) are shown. (E2) Paired pulse depression for 5 consecutive IPSPs elicited by APs at either 100 ms (10 Hz) or 25 ms (40 Hz) intervals. At both frequencies, a marked depression can be observed. The depression at 25-ms intervals between APs is markedly stronger.

Mentions: The resting membrane potential of the postsynaptic L4 spiny neurons (−70 ± 8.2 mV) was close to the GABAergic IPSP reversal potential (which was calculated to be −84 ± 4.5 mV using the IV curve). Thus, the driving force for the current passing through GABAA receptors at resting potential is small; postsynaptic neurons were therefore held at a membrane potential of −55 mV to better resolve the inhibitory response (Fig. 4A). The mean unitary IPSP amplitude at BIn-L4 spiny neuron connections was 0.93 ± 0.81 mV (n = 27) under this condition; at resting potential, this amounts to a unitary IPSP amplitude of only 0.45 mV.Figure 4.


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)

Synaptic connection between L4 interneurons and spiny neurons. (A) Presynaptic AP (blue) in a L4 BIn (cluster 3 neuron) and 10 consecutive IPSPs (red) in a L4 spiny neuron recorded at a membrane potential of −55 mV. Note the amplitude fluctuation between individual IPSPs. (B) Distribution of the coefficient of IPSP variation for BIn–L4 spiny neuron connections. (C) Relationship between unitary IPSP amplitudes and CVs displaying a high reliability (low variation) even for small IPSP amplitudes (n = 13). The 2 dashed lines represent the predictions of simple binomial release statistics for the CV as a function of the IPSP amplitude assuming 4 synaptic contacts (close to the number of putative synaptic contacts identified for this connection) and low qS = 0.14 mV (left) and high qS = 0.6 mV (right), respectively. (D) Latency distribution for this synaptic connection; the average latency was 0.55 ± 0.12 ms. (E1) Paired pulse behavior at BIn–L4 spiny neuron connection. Five APs (blue) elicited in a BIn and individual IPSPs (light red) evoked in the L4 spiny neuron together with the corresponding average IPSP (red) are shown. (E2) Paired pulse depression for 5 consecutive IPSPs elicited by APs at either 100 ms (10 Hz) or 25 ms (40 Hz) intervals. At both frequencies, a marked depression can be observed. The depression at 25-ms intervals between APs is markedly stronger.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4318534&req=5

BHT263F4: Synaptic connection between L4 interneurons and spiny neurons. (A) Presynaptic AP (blue) in a L4 BIn (cluster 3 neuron) and 10 consecutive IPSPs (red) in a L4 spiny neuron recorded at a membrane potential of −55 mV. Note the amplitude fluctuation between individual IPSPs. (B) Distribution of the coefficient of IPSP variation for BIn–L4 spiny neuron connections. (C) Relationship between unitary IPSP amplitudes and CVs displaying a high reliability (low variation) even for small IPSP amplitudes (n = 13). The 2 dashed lines represent the predictions of simple binomial release statistics for the CV as a function of the IPSP amplitude assuming 4 synaptic contacts (close to the number of putative synaptic contacts identified for this connection) and low qS = 0.14 mV (left) and high qS = 0.6 mV (right), respectively. (D) Latency distribution for this synaptic connection; the average latency was 0.55 ± 0.12 ms. (E1) Paired pulse behavior at BIn–L4 spiny neuron connection. Five APs (blue) elicited in a BIn and individual IPSPs (light red) evoked in the L4 spiny neuron together with the corresponding average IPSP (red) are shown. (E2) Paired pulse depression for 5 consecutive IPSPs elicited by APs at either 100 ms (10 Hz) or 25 ms (40 Hz) intervals. At both frequencies, a marked depression can be observed. The depression at 25-ms intervals between APs is markedly stronger.
Mentions: The resting membrane potential of the postsynaptic L4 spiny neurons (−70 ± 8.2 mV) was close to the GABAergic IPSP reversal potential (which was calculated to be −84 ± 4.5 mV using the IV curve). Thus, the driving force for the current passing through GABAA receptors at resting potential is small; postsynaptic neurons were therefore held at a membrane potential of −55 mV to better resolve the inhibitory response (Fig. 4A). The mean unitary IPSP amplitude at BIn-L4 spiny neuron connections was 0.93 ± 0.81 mV (n = 27) under this condition; at resting potential, this amounts to a unitary IPSP amplitude of only 0.45 mV.Figure 4.

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