Stereological Estimate of the Total Number of Neurons in Spinal Segment D9 of the Red-Eared Turtle

Walløe, Solveig; Nissen, Ulla Vig; Berg, Rune W.; Hounsgaard, Jørn; Pakkenberg, Bente

doi:10.1523/jneurosci.3938-10.2011

Cited by 26 publications

(18 citation statements)

References 54 publications

(58 reference statements)

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“…This inherent network sparseness could also explain the large number of interneurons, which is eightfold more numerous than MNs. 54 Such a new perspective on the purpose of inhibition in spinal networks remains to be substantiated in future experiments. The population of neurons investigated in the current study was classified according to their electrical activity, which is agnostic towards their genetic identity.…”

Section: Discussionmentioning

confidence: 99%

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Decoupling of timescales reveals sparse convergent CPG network in the adult spinal cord

Radosevic

Willumsen

Petersen

et al. 2018

Preprint

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During the generation of rhythmic movements, most spinal neurons receive an oscillatory synaptic drive. The neuronal architecture underlying this drive is unknown, and the corresponding network size and sparseness have not yet been addressed. If the input originates from a small central pattern generator (CPG) with dense divergent connectivity, it will induce correlated input to all receiving neurons, while sparse convergent wiring will induce a weak correlation, if any. Here, we use pairwise recordings of spinal neurons to measure synaptic correlations and thus infer the wiring architecture qualitatively. A strong correlation on a slow timescale implies functional relatedness and a common source, which will also cause correlation on fast timescale due to shared synaptic connections. However, we consistently find marginal coupling between slow and fast correlations regardless of neuronal identity. This suggests either sparse convergent connectivity or a CPG network with recurrent inhibition that actively decorrelates common input.Movement is an essential part of our daily lives, and disorders of the motor system, such as spasticity, amyotrophic lateral sclerosis, and spinal cord injury are particularly debilitating for individuals. Simple rhythmic movements, such as walking and breathing, have constituted models for fundamental aspects of the motor system. In spite of extensive investigations, 1, 2, 3, 4, 5, 6 the connectivity of the network responsible for generating the motor activity remains unknown. A circuit component, known as a central pattern generator (CPG), is believed to transmit command signals to motoneurons and local premotor interneurons. 7,8,9,10 Although the size of the respiratory motor network, i.e. the preBötzinger complex, 1, 11 is well-known, the size and wiring of other CPG networks are not well understood. A feedforward organization is often proposed between groups of neurons or modules, which exhibit alternating rhythmic bursting 12 (Fig. 1a). Common drive modules are thought to be small, e.g., the preBötzinger complex has only 600 neurons, 1 which provides rhythmic drive for the rest of the network. The projection is also believed to diverge onto a much larger population of receiving neurons. 13,14,15 Thus, the receiving neurons would share the same connections via a dense divergent connectivity ( Fig. 1b). Since the transmission is communicated by action potentials, which are precise in time, a dense connectivity will manifest as a strong temporal correlation between synaptic potentials in the receiving neurons, and this correlation can be verified experimentally through pairwise recordings. If the drive network is not a small but rather a large population, however, the receiver neurons are likely to collect sparse convergent input without correlation (Fig. 1c). Hence, the assessment of correlation CPG connectivity from decoupled timescales Extensor network Flexor network extensor Common drive Common drive flexor IN IN MN MN MN e x o r e x te ns or knee MN Dense Common drive Sparse c b ...

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Section: Discussionmentioning

confidence: 99%

“…These are lumbar segments in the turtle corresponding to L2-L5 in mammals. 54 In addition, an intracellular sharp electrodes was inserted from the ventral side and ipsilaterally to the probe in D10. Spike sorting was performed in open source software (Klustakwik-suite: SpikeDetekt, KlustaKwik v.3.0 and KlustaViewa 63 ).…”

Section: Local Connectivitymentioning

confidence: 99%

Decoupling of timescales reveals sparse convergent CPG network in the adult spinal cord

Radosevic

Willumsen

Petersen

et al. 2018

Preprint

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“…In our experiments we sampled from neurons, which were likely to be primarily interneurons since they are more numerous than motoneurons. The fraction of motoneurons to interneurons is 1:8 (Walloe et al, 2011), but we were also likely to sample motorneurons, since they have large somata. To explore this further, we investigated the population activity and its relation to cellular identity by taking advantage of their spatial segregation in the dorsoventral axis (Arber, 2012; Jessell, 2000).…”

Section: Discussionmentioning

confidence: 99%

Lognormal firing rate distribution reveals prominent fluctuation–driven regime in spinal motor networks

Petersen

Berg

2016

eLife

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When spinal circuits generate rhythmic movements it is important that the neuronal activity remains within stable bounds to avoid saturation and to preserve responsiveness. Here, we simultaneously record from hundreds of neurons in lumbar spinal circuits of turtles and establish the neuronal fraction that operates within either a ‘mean-driven’ or a ‘fluctuation–driven’ regime. Fluctuation-driven neurons have a ‘supralinear’ input-output curve, which enhances sensitivity, whereas the mean-driven regime reduces sensitivity. We find a rich diversity of firing rates across the neuronal population as reflected in a lognormal distribution and demonstrate that half of the neurons spend at least 50 0pt3.5pt% of the time in the ‘fluctuation–driven’ regime regardless of behavior. Because of the disparity in input–output properties for these two regimes, this fraction may reflect a fine trade–off between stability and sensitivity in order to maintain flexibility across behaviors.DOI: http://dx.doi.org/10.7554/eLife.18805.001

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“…Quantification of total cell numbers, densities and projections in tissue while preserving spatial information has been a challenge in stereology, since it relies on interpretation of 2D sections of tissues and statistical sampling methods from several histological tissue sections (Gundersen and Jensen, 1987;Walloe et al, 2011). Applying stereological methods to cleared tissues eliminates the need for labour-intensive sectioning.…”

Section: Stereologymentioning

confidence: 99%

Advances and perspectives in tissue clearing using CLARITY

Jensen

Berg

2017

Preprint

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CLARITY is a tissue clearing method, which enables immunostaining and imaging of large volumes for 3D-reconstruction. The method was initially time-consuming, expensive and relied on electrophoresis to remove lipids to make the tissue transparent. Since then several improvements and simplifications have emerged, such as passive clearing (PACT) and methods to improve tissue staining. Here, we review advances and compare current applications with the aim of highlighting needed improvements as well as aiding selection of the specific protocol for use in future investigations.

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Stereological Estimate of the Total Number of Neurons in Spinal Segment D9 of the Red-Eared Turtle

Cited by 26 publications

References 54 publications

Decoupling of timescales reveals sparse convergent CPG network in the adult spinal cord

Decoupling of timescales reveals sparse convergent CPG network in the adult spinal cord

Lognormal firing rate distribution reveals prominent fluctuation–driven regime in spinal motor networks

Advances and perspectives in tissue clearing using CLARITY

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