Dopamine gates action potential backpropagation in midbrain dopaminergic neurons

Dopamine is released from both axonal and somatodendritic sites of midbrain dopaminergic neurons in an action potential-dependent manner. In contrast to the majority of central neurons, the axon of dopaminergic neurons typically originates from a dendritic site, suggesting a specialized computational function. Here, we examine the initiation and spread of action potentials in dopaminergic neurons of the substantia nigra pars reticulata and reveal that the displacement of the axon to a dendritic site allows highly compartmentalized electrical signaling. In response to a train of synaptic input, action potentials initiated at axon-bearing dendritic sites formed a variable trigger for invasion to the soma and contralateral dendritic tree, with action potentials often confined to the axon-bearing dendrite. The application of dopamine increased this form of electrical compartmentalization, an effect mediated by a tonic membrane potential hyperpolarization leading to an increased availability of a class of voltage-dependent potassium channel. These data suggest that the release of dopamine from axonal and somatodendritic sites are dissociable, and that dopamine levels within the midbrain are dynamically controlled by the somatodendritic spread of action potentials

Offline orbitofrontal cortex reactivation depends on recency of place-reward changes and coheres with hippocampal replay

The orbitofrontal cortex, one of the key neocortical areas in valuation and emotion, is critical for cognitive flexibility but its role in the consolidation of recently acquired information remains unclear. Here, we demonstrate orbitofrontal offline replay in the context of a place-reward association task on a maze with varying goal locations. When switches in place-reward coupling were applied, replay was enhanced relative to sessions with stable contingencies. Moreover, replay strength was positively correlated with the subsequent overnight change in behavioral performance. Interrogating relationships between orbitofrontal and hippocampal activity, we found that orbitofrontal and hippocampal replay could occur independently but became coordinated during a type of cortical state with strong spiking activity. These findings reveal a structured form of offline orbitofrontal ensemble activity that is correlated with cognitive flexibility required to adapt to changing task contingencies, and becomes associated with hippocampal replay only during a specific state of high cortical excitability

Functional diversity of supragranular GABAergic neurons in the barrel cortex

Although the neocortex forms a distributed system comprised of several functional areas, its vertical columnar organization is largely conserved across areas and species, suggesting the existence of a canonical neocortical microcircuit. In order to elucidate the principles governing the organization of such a cortical diagram, a detailed understanding of the dynamics binding different types of cortical neurons into a coherent algorithm is essential. Within this complex circuitry, GABAergic interneurons, while forming approximately only 15-20% of all cortical neurons, appear critical in maintaining a dynamic balance between excitation and inhibition. Despite their importance, cortical GABAergic neurons have not been extensively studied in vivo and their precise role in shaping the local microcircuit sensory response still remains to be determined. Their paucity, combined with their molecular, anatomical and physiological diversity, has made it difficult to even establish a consensual nomenclature.However, recent technological advances in microscopy and mouse genetics have fostered a renewed interest in neocortical interneurons by putting them within visible reach of experimenters. The anatomically well-defined whisker-to-barrel pathway of the rodent is particularly amenable to studies attempting to link cortical circuit dynamics to behavior. To each whisker corresponds a discrete cortical unit equivalent to a single column, specialized in the encoding and processing of the sensory information it receives. In this review, we will focus on the functional role that each subtype of supragranular GABAergic neuron embedded within such a single neocortical unit may play in shaping the dynamics of the local circuit during somatosensory integration

Data from: Membrane potential dynamics of spontaneous and visually evoked gamma activity in V1 of awake mice

Cortical gamma activity (30–80 Hz) is believed to play important functions in neural computation and arises from the interplay of parvalbumin-expressing interneurons (PV) and pyramidal cells (PYRs). However, the subthreshold dynamics underlying its emergence in the cortex of awake animals remain unclear. Here, we characterized the intracellular dynamics of PVs and PYRs during spontaneous and visually evoked gamma activity in layers 2/3 of V1 of awake mice using targeted patch-clamp recordings and synchronous local field potentials (LFPs). Strong gamma activity patterned in short bouts (one to three cycles), occurred when PVs and PYRs were depolarizing and entrained their membrane potential dynamics regardless of the presence of visual stimulation. PV firing phase locked unconditionally to gamma activity. However, PYRs only phase locked to visually evoked gamma bouts. Taken together, our results indicate that gamma activity corresponds to short pulses of correlated background synaptic activity synchronizing the output of cortical neurons depending on external sensory drive

PYR_IC

Current-Clamp Data for PYR cell

Membrane Potential Dynamics of Spontaneous and Visually Evoked Gamma Activity in V1 of Awake Mice

International audienceCortical gamma activity (30-80 Hz) is believed to play important functions in neural computation and arises from the interplay of parvalbumin-expressing interneurons (PV) and pyramidal cells (PYRs). However, the subthreshold dynamics underlying its emergence in the cortex of awake animals remain unclear. Here, we characterized the intracellular dynamics of PVs and PYRs during spontaneous and visually evoked gamma activity in layers 2/3 of V1 of awake mice using targeted patch-clamp recordings and synchronous local field potentials (LFPs). Strong gamma activity patterned in short bouts (one to three cycles), occurred when PVs and PYRs were depolarizing and entrained their membrane potential dynamics regardless of the presence of visual stimulation. PV firing phase locked unconditionally to gamma activity. However, PYRs only phase locked to visually evoked gamma bouts. Taken together, our results indicate that gamma activity corresponds to short pulses of correlated background synaptic activity synchronizing the output of cortical neurons depending on external sensory drive

Direct Measurement of Specific Membrane Capacitance in Neurons

The specific membrane capacitance (C(m)) of a neuron influences synaptic efficacy and determines the speed with which electrical signals propagate along dendrites and unmyelinated axons. The value of this important parameter remains controversial. In this study, C(m) was estimated for the somatic membrane of cortical pyramidal neurons, spinal cord neurons, and hippocampal neurons. A nucleated patch was pulled and a voltage-clamp step was applied. The exponential decay of the capacitative charging current was analyzed to give the total membrane capacitance, which was then divided by the observed surface area of the patch. C(m) was 0.9 μF/cm2 for each class of neuron. To test the possibility that membrane proteins may alter C(m), embryonic kidney cells (HEK-293) were studied before and after transfection with a plasmid coding for glycine receptor/channels. The value of C(m) was indistinguishable in untransfected cells and in transfected cells expressing a high level of glycine channels, indicating that differences in transmembrane protein content do not significantly affect C(m). Thus, to a first approximation, C(m) may be treated as a 'Biological constant' across many classes of neuron

Cell-type and state-dependent synchronization among rodent areas S1BF, V1, perirhinal cortex and hippocampus CA1

Beta and gamma rhythms have been hypothesized to be involved in global and local coordination of neuronal activity, respectively. Here, we investigated how cells in rodent area S1BF are entrained by rhythmic fluctuations at various frequencies within the local area and in connected areas, and how this depends on behavioral state and cell type. We performed simultaneous extracellular field and unit recordings in four connected areas of the freely moving rat (S1BF, V1M, perirhinal cortex, CA1). S1BF spiking activity was strongly entrained by both beta and gamma S1BF oscillations, which were associated with deactivations and activations, respectively. We identified multiple classes of fast spiking and excitatory cells in S1BF, which showed prominent differences in rhythmic entrainment and in the extent to which phase locking was modulated by behavioral state. Using an additional dataset acquired by whole-cell recordings in head-fixed mice, these cell classes could be compared with identified phenotypes showing gamma rhythmicity in their membrane potential. We next examined how S1BF cells were entrained by rhythmic fluctuations in connected brain areas. Gamma-synchronization was detected in all four areas, however we did not detect significant gamma coherence among these areas. Instead, we only found long-range coherence in the theta-beta range among these areas. In contrast to local S1BF synchronization, we found long-range S1BF-spike to CA1-LFP synchronization to be homogeneous across inhibitory and excitatory cell types. These findings suggest distinct, cell-type contributions of low and high-frequency synchronization to intra- and inter-areal neuronal interactions

PV_VC+10Data

Voltage-Clamp Data at +10mV for PV cell