1,721,054 research outputs found
Inhibitory interneurons and their circuit motifs in the many layers of the barrel cortex
No full textRecent years have seen substantial progress in studying the structural and functional properties of GABAergic interneurons and their roles in the neuronal networks of barrel cortex. Although GABAergic interneurons represent only about 12% of the total number of neocortical neurons, they are extremely diverse with respect to their structural and functional properties. It has become clear that barrel cortex interneurons not only serve the maintenance of an appropriate excitation/inhibition balance but also are directly involved in sensory processing.In this review we present different interneuron types and their axonal projection pattern framework in the context of the laminar and columnar organization of the barrel cortex. The main focus is here on the most prominent interneuron types, i.e. basket cells, chandelier cells, Martinotti cells, bipolar/bitufted cells and neurogliaform cells, but interneurons with more unusual axonal domains will also be mentioned. We describe their developmental origin, their classification with respect to molecular, morphological and intrinsic membrane and synaptic properties. Most importantly, we will highlight the most prominent circuit motifs these interneurons are involved in and in which way they serve feed-forward inhibition, feedback inhibition and disinhibition. Finally, this will be put into context to their functional roles in sensory signal perception and processing in the whisker system and beyond
Synaptic structure, physiology and morphology of layer 4 excitatory neurons in rat barrel cortex
No full textPrecise processing of sensory signals is decisive for an adequate reaction to inputs from the environment. The barrel cortex is a very attractive model to study these processes because of its precise topographical relationship between the peripheral sensory receptor (the whisker on the snout) and the neocortical signal processing unit (the cortical column). Basic signal transformations were performed within such a cortical column. Hence, knowledge about the function and development of a single cortical column will help to better understand the processing of sensory signals in the whole barrel cortex. However, layer 4 (L4) of rodent barrel cortex is the main “input” layer of signals arriving from the sensory whiskers and thus the starting point of the cortical processing. Incoming signals are mainly processed by L4 spiny neurons. For the analysis of these L4 spiny neurons whole-cell recordings were performed. Action potentials elicited in the immature neurons were smaller and had longer durations than those in mature neurons. Moreover, the age-dependent decrease in input resistances, membrane time constants and the resting membrane potentials suggests that mature L4 spiny neurons have a reduced excitability compared to immature ones. During the recordings the neurons were filled with biocytin which allowed a clear identification of the patched neurons in the brain slices. Neurons were processed for electron microscopy and serial ultra-thin sections were cut to identify all input synapses on the L4 spiny neurons. Based on these sections three-dimensional volumetric reconstructions were performed. These 3D-models were used to investigate the structural parameters for the synaptic transmission, such as the distribution of the vesicles around the active zone. The number and distribution of synaptic vesicles near the active zone varied strongly indicating different maturational stages. However, on average only 5 synaptic vesicles were found within the releasable pool of the immature neurons. In addition, the number of vesicles in the intermediate pools and reserve pools was low. Accordingly, refilling of the releasable pool is probably slow in immature neurons. In summary, the small size of the vesicle pools suggests a fast run-down of these synapses and hence vesicle pool depletion which could cause synaptic depression. Thus, the organisation of the vesicles around the active zone assumes to be one reason why immature neuronal networks are not as reliable and effective than mature ones
Synaptic structure, physiology and morphology of layer 4 excitatory neurons in rat barrel cortex
No full textPrecise processing of sensory signals is decisive for an adequate reaction to inputs from the environment. The barrel cortex is a very attractive model to study these processes because of its precise topographical relationship between the peripheral sensory receptor (the whisker on the snout) and the neocortical signal processing unit (the cortical column). Basic signal transformations were performed within such a cortical column. Hence, knowledge about the function and development of a single cortical column will help to better understand the processing of sensory signals in the whole barrel cortex. However, layer 4 (L4) of rodent barrel cortex is the main “input” layer of signals arriving from the sensory whiskers and thus the starting point of the cortical processing. Incoming signals are mainly processed by L4 spiny neurons. For the analysis of these L4 spiny neurons whole-cell recordings were performed. Action potentials elicited in the immature neurons were smaller and had longer durations than those in mature neurons. Moreover, the age-dependent decrease in input resistances, membrane time constants and the resting membrane potentials suggests that mature L4 spiny neurons have a reduced excitability compared to immature ones. During the recordings the neurons were filled with biocytin which allowed a clear identification of the patched neurons in the brain slices. Neurons were processed for electron microscopy and serial ultra-thin sections were cut to identify all input synapses on the L4 spiny neurons. Based on these sections three-dimensional volumetric reconstructions were performed. These 3D-models were used to investigate the structural parameters for the synaptic transmission, such as the distribution of the vesicles around the active zone. The number and distribution of synaptic vesicles near the active zone varied strongly indicating different maturational stages. However, on average only 5 synaptic vesicles were found within the releasable pool of the immature neurons. In addition, the number of vesicles in the intermediate pools and reserve pools was low. Accordingly, refilling of the releasable pool is probably slow in immature neurons. In summary, the small size of the vesicle pools suggests a fast run-down of these synapses and hence vesicle pool depletion which could cause synaptic depression. Thus, the organisation of the vesicles around the active zone assumes to be one reason why immature neuronal networks are not as reliable and effective than mature ones
Intra- and interlaminar excitatory synaptic connections of layer 4 spiny neurons and layer 6A pyramidal cells in rat barrel cortex
No full textIn the primary somatosensory (barrel) cortex of rodents, layer 4 (L4) and 6A are the main recipient layers of thalamocortical projections. In addition, a subset of L6A pyramidal neurons provide a direct corticothalamic feedback to the thalamus. Thus, neurons in layer 4 and 6A are an integral part of a thalamo-cortical-cortico-thalamic feedback circuit. To better understand the role of the intracortical unit in this circuit, we studied the anatomical and functional properties of excitatory synaptic connections from layer 4 to layer 6A in the rat barrel cortex by making dual whole-cell recordings with dye injection from L4 spiny neurons and L6A pyramidal cells in acute brain slices. Interlaminar monosynaptic L4-to-L6A excitatory connections (n = 17) were relatively rare. They were of low efficacy with an average excitatory postsynaptic potentials (EPSPs) of 0.32 ± 0.19 mV (n = 17) but of moderately high reliability with failure rate of 24.2 ± 17.7% (n = 16) and coefficient of variation (CV) of 0.56 ± 0.16 (n = 16). The EPSP amplitude was either depressing or weakly facilitating with paired-pulse ratio (PPR) of 0.45 - 1.38 (n = 17) at an interstimulus interval of 100 ms. Notably, we found a spatial separation of synaptic inputs on the dendritic domain of the postsynaptic L6A pyramidal cells depending on the presynaptic L4 neuron type: L4 spiny stellate neurons innervated predominantly the distal apical tuft dendrites of L6A pyramidal cells with synapse-to-soma distance of 591 ± 137 μm (n = 6) and elicited slow EPSPs (20-80% rise time = 6.7 ± 2.1 ms and latency = 3.8 ± 1.6 ms, n = 6) in L6A somata, while most of L4 star pyramidal neurons preferentially innervated the proximal basal and apical oblique dendrites with synapse-to-soma distance of 86 ± 54 µm (n = 7) and elicited fast EPSPs (20-80% rise time = 1.5 ± 0.9 ms and latency = 1.7 ± 0.2 ms, n = 7) in L6A somata with some star pyramids also forming synapses on the L6A apical tuft or oblique dendrites (synapse-to-soma distance = 524 ± 167 µm, n = 4) and eliciting relatively slow EPSPs (20-80% rise time = 5.4 ± 1.7 ms and latency = 3.7 ± 0.8 ms, n = 4). Other EPSP characteristics (i.e., amplitude, PPR, failure rate and CV) were not significantly different for the three types of L4-L6A connections. There was a tight correlation between the EPSP rise time, latency, and the synapse-to-soma distance. The synaptic location could not completely predicted solely on the basis of the axo-dendritic overlap suggesting that Peter’s rule of synaptic connectivity was not completely correct here. Using pharmacological treatment and neuronal modeling, we found that the occurrence of ‘slow’ and ‘fast’ EPSPs was not due to different receptor components in the postsynaptic densities but mainly due to the dendritic filtering effect during the EPSP propagation from synaptic location to soma. In addition, the cell-type specific selection of postsynaptic target region was a pre- but not postsynaptic phenomenon. As a comparison, we also performed some paired recordings in layer 4 and 6A and studied the characteristics of excitatory connections in layer 4 and 6A, respectively. For intralaminar monosynaptic L4-L4 and L6A-L6A excitatory connections, we found homogeneous dynamical properties of EPSPs, i.e., fast rise time (20-80% rise time = 1.59 ± 0.49 ms (n = 10) for L4-L4 and 1.39 ± 0.59 ms (n = 5) for L6A-L6A connections) and short latency (latency = 1.17 ± 0.41 ms (n = 10) for L4-L4 and 1.69 ± 0.65 ms (n = 5) for L6A-L6A connections), implying that, for both connections, synaptic inputs to postsynaptic neurons were electrotonically close to somata. The synaptic efficacy of L4-L4 connections were widely distributed from very weak connections (0.30 mV) to very strong ones (4.71 mV) with an average EPSP amplitude of 1.02 ± 1.33 mV (n = 10) compared with L6A-L6A connections that had a substantially lower average EPSP amplitude (0.58 ± 0.50 mV, n = 5), a relatively higher failure rate (17.5 ± 15.0%, n = 5) and a little higher CV (0.53 ± 0.23, n = 5)
Intralaminar and translaminar microcircuits involving excitatory and inhibitory neurons in layer 6B of the somatosensory rat barrel cortex. A morphological, physiological and immunofluorescence study
No full textIn this study the intralaminar and translaminar microcircuits involving excitatory and inhibitory neurons in layer 6B of the somatosensory rat barrel cortex were classified on their structure, function and on a possible FoxP2 expression to gain further information about layer 6B and which role it may play in cortical circuitry during the early postnatal, adolescent and adult brain. We found a distinct layer 6B (L6B) cell clustering and identified five major excitatory cell types. We further classified two pyramidal subtypes similar to corticocortical and corticothalamic L6A neurons. In addition, we compared the subplate (SP) morphology to those of layer 6B and identified the same five distinct cell types. We suggest that SP neurons may persist at least in part from the developing SP into adulthood and hypothesize that neocortical layer 6B consists of a mixture of newborn pyramidal and persistent non-pyramidal cells. Moreover, we analyzed the expression of the forkhead-box protein P2 (FoxP2) which is exclusively expressed in neocortical layer 6 neurons and found a ratio of 2:1 between FoxP2-positive and FoxP2-negative L6 cells. L6B pyramidal neurons were consistently found to be FoxP2-positive, while non-pyramidal excitatory projection neurons and interneurons in layer 6B were almost entirely FoxP2-negative. Additional neuromodulation studies revealed that each L6B cell type showed a dopamine-induced depolarization effect independently of its FoxP2 expression. Finally, we attempted to investigate the synaptic connectivity of L6B neurons. However, this subproject is at a very early stage and the connectivity rate is very low (~1.4%). Herein, we report about one monosynaptic L6B-to-L6B connection between two multipolar neurons showing short-term facilitation. Furthermore, we report about the putative innervation domain maps of excitatory L6B connections which might reveal a main innervation zone in cortical layers 6A and 6B of the cortical home and neighboring barrel columns. We can summarize that the SP as well as layer 6B comprise a comparable and distinct heterogeneous cell population in the early postnatal and adult somatosensory cortex. We suggest that layer 6B may partly constitute as a remnant of the SP. We further determined an isolated FoxP2 expression pattern for specific L6B cell types independently from a dopaminergic neuromodulation. Paired recording studies unveiling the L6B connectivity are yet preliminary and have to be expanded
Intra- and interlaminar excitatory synaptic connections of layer 4 spiny neurons and layer 6A pyramidal cells in rat barrel cortex
No full textIn the primary somatosensory (barrel) cortex of rodents, layer 4 (L4) and 6A are the main recipient layers of thalamocortical projections. In addition, a subset of L6A pyramidal neurons provide a direct corticothalamic feedback to the thalamus. Thus, neurons in layer 4 and 6A are an integral part of a thalamo-cortical-cortico-thalamic feedback circuit. To better understand the role of the intracortical unit in this circuit, we studied the anatomical and functional properties of excitatory synaptic connections from layer 4 to layer 6A in the rat barrel cortex by making dual whole-cell recordings with dye injection from L4 spiny neurons and L6A pyramidal cells in acute brain slices. Interlaminar monosynaptic L4-to-L6A excitatory connections (n = 17) were relatively rare. They were of low efficacy with an average excitatory postsynaptic potentials (EPSPs) of 0.32 ± 0.19 mV (n = 17) but of moderately high reliability with failure rate of 24.2 ± 17.7% (n = 16) and coefficient of variation (CV) of 0.56 ± 0.16 (n = 16). The EPSP amplitude was either depressing or weakly facilitating with paired-pulse ratio (PPR) of 0.45 - 1.38 (n = 17) at an interstimulus interval of 100 ms. Notably, we found a spatial separation of synaptic inputs on the dendritic domain of the postsynaptic L6A pyramidal cells depending on the presynaptic L4 neuron type: L4 spiny stellate neurons innervated predominantly the distal apical tuft dendrites of L6A pyramidal cells with synapse-to-soma distance of 591 ± 137 μm (n = 6) and elicited slow EPSPs (20-80% rise time = 6.7 ± 2.1 ms and latency = 3.8 ± 1.6 ms, n = 6) in L6A somata, while most of L4 star pyramidal neurons preferentially innervated the proximal basal and apical oblique dendrites with synapse-to-soma distance of 86 ± 54 µm (n = 7) and elicited fast EPSPs (20-80% rise time = 1.5 ± 0.9 ms and latency = 1.7 ± 0.2 ms, n = 7) in L6A somata with some star pyramids also forming synapses on the L6A apical tuft or oblique dendrites (synapse-to-soma distance = 524 ± 167 µm, n = 4) and eliciting relatively slow EPSPs (20-80% rise time = 5.4 ± 1.7 ms and latency = 3.7 ± 0.8 ms, n = 4). Other EPSP characteristics (i.e., amplitude, PPR, failure rate and CV) were not significantly different for the three types of L4-L6A connections. There was a tight correlation between the EPSP rise time, latency, and the synapse-to-soma distance. The synaptic location could not completely predicted solely on the basis of the axo-dendritic overlap suggesting that Peter’s rule of synaptic connectivity was not completely correct here. Using pharmacological treatment and neuronal modeling, we found that the occurrence of ‘slow’ and ‘fast’ EPSPs was not due to different receptor components in the postsynaptic densities but mainly due to the dendritic filtering effect during the EPSP propagation from synaptic location to soma. In addition, the cell-type specific selection of postsynaptic target region was a pre- but not postsynaptic phenomenon. As a comparison, we also performed some paired recordings in layer 4 and 6A and studied the characteristics of excitatory connections in layer 4 and 6A, respectively. For intralaminar monosynaptic L4-L4 and L6A-L6A excitatory connections, we found homogeneous dynamical properties of EPSPs, i.e., fast rise time (20-80% rise time = 1.59 ± 0.49 ms (n = 10) for L4-L4 and 1.39 ± 0.59 ms (n = 5) for L6A-L6A connections) and short latency (latency = 1.17 ± 0.41 ms (n = 10) for L4-L4 and 1.69 ± 0.65 ms (n = 5) for L6A-L6A connections), implying that, for both connections, synaptic inputs to postsynaptic neurons were electrotonically close to somata. The synaptic efficacy of L4-L4 connections were widely distributed from very weak connections (0.30 mV) to very strong ones (4.71 mV) with an average EPSP amplitude of 1.02 ± 1.33 mV (n = 10) compared with L6A-L6A connections that had a substantially lower average EPSP amplitude (0.58 ± 0.50 mV, n = 5), a relatively higher failure rate (17.5 ± 15.0%, n = 5) and a little higher CV (0.53 ± 0.23, n = 5)
Methods for Synaptic Interrogation
No full textThis eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contac
Effects of noradrenaline on neuronal networks in rat neocortex : an in vitro patch-clamp study
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Morphologische und elektrophysiologische Charakterisierung von Lamina 6a Neuronen des medialen präfrontalen Kortex der Ratte
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