Visualization of the spread of electrical activity in rat hippocampal slices by voltage‐sensitive optical probes

114

Optical imaging, positron emission tomography, and functional magnetic resonance imaging (fMRI) all rely on vascular responses to image neuronal activity. Although these imaging techniques are used successfully for functional brain mapping, the detailed spatiotemporal dynamics of hemodynamic events in the various microvascular compartments have remained unknown. Here we used highresolution optical imaging in area 18 of anesthetized cats to selectively explore sensory-evoked cerebral blood-volume (CBV) changes in the various cortical microvascular compartments. To avoid the confounding effects of hematocrit and oximetry changes, we developed and used a new fluorescent blood plasma tracer and combined these measurements with optical imaging of intrinsic signals at a near-isosbestic wavelength for hemoglobin (565 nm). The vascular response began at the arteriolar level, rapidly spreading toward capillaries and venules. Larger veins lagged behind. Capillaries exhibited clear blood-volume changes. Arterioles and arteries had the largest response, whereas the venous response was smallest. Information about compartment-specific oxygen tension dynamics was obtained in imaging sessions using 605 nm illumination, a wavelength known to reflect primarily oximetric changes, thus being more directly related to electrical activity than CBV changes. Those images were radically different: the response began at the parenchyma level, followed only later by the other microvascular compartments. These results have implications for the modeling of fMRI responses (e.g., the balloon model). Furthermore, functional maps obtained by imaging the capillary CBV response were similar but not identical to those obtained using the early oximetric signal, suggesting the presence of different regulatory mechanisms underlying these two hemodynamic processes.

Section: Effects Of Light Scatteringmentioning

confidence: 59%

Compartment-Resolved Imaging of Activity-Dependent Dynamics of Cortical Blood Volume and Oximetry

Vanzetta¹,

Hildesheim²,

Grinvald³

2005

114

“…Both optical recording and patch-clamp experiments reveal a net inhibitory effect of serotonin 5-HT 3 receptor stimulation on evoked synaptic responses. Optical recording provides a faithf ul measure of the spatiotemporal properties of neuronal activity on a circuit level (Grinvald et al, 1982(Grinvald et al, , 1994Albowitz and Kuhnt, 1993;Sutor et al, 1994;Nelson and Katz, 1995;Jackson and Scharfman, 1996;Tanif uji et al, 1996). The depression of circuit activation revealed by optical recording peaked between P32-P35 and P40 -P45, which corresponds to the period of axonal cluster refinement and maturation of orientation tuning in the supragranular layers (Chapman and Stryker, 1993;Dalva and Katz, 1994;Nelson and Katz, 1995;Durack and Katz, 1996;Ruthazer and Stryker, 1996).…”

Section: Discussionmentioning

confidence: 99%

Modulation of Intrinsic Circuits by Serotonin 5-HT₃Receptors in Developing Ferret Visual Cortex

Roerig

Katz

1997

Serotonergic projections are widespread in the developing neocortex, but their functions are obscure. The effects of 5-HT 3 receptor agonists on cortical circuit response properties were studied in slices of ferret primary visual cortex using high-speed optical imaging of voltage-sensitive dye signals and whole-cell patch-clamp recording. Activation of the 5-HT 3 receptor decreased the amplitude and lateral extent of excitation throughout postnatal development. This effect peaks after eye opening, which indicates a function for serotonergic modulation of circuit responses during the period of refinement of cortical connections. Whole-cell patch-clamp recordings from single neurons revealed that synaptic responses evoked by white matter stimulation were reduced by 5-HT 3 receptor agonists, whereas the frequency of spontaneous GABAergic synaptic currents was enhanced dramatically. This indicates that the modulation of spontaneous synaptic activity by fast-acting serotonin receptors is reflected in an inhibition of the circuit response, in line with the notion of background synaptic activity altering the spatiotemporal integration properties of cortical cells by changing their membrane potential and their electrotonic structure. These mechanisms may regulate the response properties of intrinsic circuits in both the adult and developing neocortex.

“…Our data yielded an estimate of 0.2 m/s axonal conduction velocity. This was in the range of conduction velocities reported for the unmyelinated Schaffer collaterals (0.1-0.5 m/s) (Andersen et al, 1978;Grinvald et al, 1982;Soleng et al, 2003;Meeks et al, 2005).…”

Section: Signal Flow In a Cortical Columnmentioning

confidence: 99%

Efficient Recruitment of Layer 2/3 Interneurons by Layer 4 Input in Single Columns of Rat Somatosensory Cortex

Helmstaedter¹,

Staiger²,

Sakmann³

et al. 2008

108

109

Interneurons in layers 2/3 are excited by pyramidal cells within the same layer (Reyes et al., 1998; Gupta et al., 2000), but little is known about translaminar innervation of these interneurons by spiny neurons in the main cortical input layer 4 (L4). Here, we investigated (1) how efficiently L4 spiny neurons excite L2/3 interneurons via monosynaptic connections, (2) whether glutamate release from axon terminals of L4 spiny neurons depends on the identity of the postsynaptic interneuron, and (3) how L4-to-L2/3 interneuron connections compare with L4-to-L2/3 pyramidal neuron connections. We recorded from pairs of L4 spiny neurons and L2/3 interneurons in acute slices of rat barrel cortex of postnatal day 20 (P20) to P29 rats. The L4-to-L2/3 interneuron connections had an average unitary EPSP of 1.2 Ϯ 1.1 mV. We found an average of 2.3 Ϯ 0.8 contacts per connection, and the L4-to-L2/3 interneuron innervation domains were mostly column restricted. Unitary EPSP amplitudes and paired-pulse ratios in the L4-to-L2/3 interneuron connections depended on the "group" of the postsynaptic interneuron. Averaged over all L4-to-L2/3 interneuron connections, unitary EPSP amplitudes were 1.8-fold higher than in the translaminar L4-to-L2/3 pyramidal cell connections. Our results suggest that L4 spiny neurons may more efficiently recruit L2/3 interneurons than L2/3 pyramidal neurons, and that glutamate release from translaminar boutons of L4 spiny neuron axons is target cell specific.