Thursday, October 15, 2009

The recovery paper



My latest paper will appear in the Journal of Neuroscience.
October 21, 2009 | Volume 29 | Number 42 |

They will introduce my paper in "This Week in The Journal"
Development/Plasticity/Repair
- "Nerve Transection Induces Circuit Reorganization in Tritonia"

The article title is:
"Functional Recovery after Lesion of a Central Pattern Generator"
by Akira Sakurai and Paul S. Katz

In this paper, we found that severing a set of connections between some CPG neurons impaired motor pattern production but that the system spontaneously recovered over the course of a few hours to a day. Furthermore, we observed corresponding changes in synaptic strength that can account for the functional recovery.

Wednesday, October 14, 2009

Neuromodulation of motor systems




Among many reviews about CPG funciton, I like this one by Ole Kiehn and Paul S. Katz.
The introduction starts with a brief talk about dancing.

"...by changing cellular and synaptic properties, neuromodulators choreograph circuits from an ensemble of interacting neurons capable f dancing with a variety of partners."

2. The elements of neuromodulation in motor systems: alterations of cellular and synaptic properties
The CPGs - Localized neuronal networks in the central nervous system control the timing of the coordinated muscle activities, capable of producing rhythmic movement even when isolated from the sensory input (Delcomyn 1980).

The CPG function depends on synaptic interconnections and intrinsic membrane properties.
Neuromodulation changes both of them.

1) Rewiring circuits
We may often think of the nervous system as a hard-wired device whose connectivity is changed only during the developental period or as a result of learning.
NO, the strength of connections between neurons is not fixed, but can vary continusously under moment-to-moment neuromodulatory control.
The wiring diagram for a circuit is merely an outline of potential connections and does not uniquely determine the flow of information at all times.
- Modulation of chemical transmission
The effect of neuromodulation can be a functional disconnection of cells or a strengthening of the communication between cells.
Thus, the wiring diagram of synaptic connections is strongly dependent upon which neuromodulator is present.
In vertebrate locomotion, 5-HT and noradrenaline modulate glycinergic synapses to increase circuit flexibility.
- Modulation of electrical coupling

2) Changing neuronal personalities

- Modulation of resting conductances can determine neuronal participation in a network

- Modulation of conductances involved in phase transisions

- Modulation of conductances that determine spike rate

- Modulation of conductances underlying neuronal bistability

- Modulation of conductances underlying conditional bursting


3) Changes in cellular and synaptic properties produce secondary effects

The differential actions of neuromodulators on neurons in motor circuits underlie some forms of behavioral plasticity such as motor pattern selection.


3. Choreographing motor patterns: the effects of neuromodulators on the output of motor circuits

Neuromodulatory substances can initiate motor patterns by endowing neurons with the properties that are needed to form a functional CPG circuit.
Neuromodulatory sunstances can alter (or reorganize) motor patterns by changing those properties.

1) Neuromodulators can activate motor patterns
As a rule, the initiation of rhythmic movements requires non-rhythmic input from a source external to the CPG network itself.
-fast synaptic input (tadpole escape)
-neuromodulatory input (Tritonia swim, cats, rats, rabbits)

2) Neuromodulators can alter ongoing motor activity
- changing the speed/frequency
- muscle force
- phase relationship

3) Neuromodulators can reconfigure networks
-stomatogastric system
- At the moment, little is known about these types of network reorganizations in CPGs other than those in the stomatogastric system. Reconfiguration in the larger neuronal networks that control thythmic activity in vertebrates is difficult to evaluate because the CPG networks are poorly difined and it is impossible to be sure that one has recorded from all possible members of a functional circuit.

4) Neuromodulation can alter the ability of a CPG to drive its follower motor neurons

4. INtegrating neuromodulation into neuronal circuits

1) Properties of neuromodulatory neurons

2) Sources of neuromodulation
- Extrinsic vs Intrinsic

3) Convergence of modulation

5. Long-term alteration of motor patterns
Fast proprioceptive adjustment mechanisms are plastic and that they can adjust to long-term changes in the sensory signaling.

- in spinalized cats where locomotion on a treadmill is evoked by L-DOPA injection, cutting the lateral-gastrocnemius-soleus nerve results in long-term up-regulation of the load-compensating effects from group I afferents in the synergistic medial-gastrocnemius nerve, allowing the cat to slowly recover its normal stepping behavior (Whelan and Pearson 1997).

Neuromodulatory inputs may play a role in promoting long-term plasticity of CPG circuits. In spinalized cats, daily intraperitoneal or intrathecal injections of the alpha-2 adrenergic receptor agonist, clonidine, enhanced the recovery of locomotion when combined with training on a treadmill (Chau et al., 1998).

Friday, October 9, 2009

Melibe leonina



I am working on Melibe brain now. It is so small.

There are two small ganglia on Pleural-Pleural connective nerve. What they do?
A copepod is sitting on the brain in the dish. I think it came out from the stomach, but it is still alive. It is so pity that I have to kill it to protect my prep.

I saw a pair of green tube that seem to go to the dorsal gill from the stomach.
Is it also solar-powered?

Thursday, October 8, 2009

Long-Term Modifications in Motor Cortical Dynamics Induced by Intensive Practice

Bjørg E. Kilavik, Sébastien Roux, Adrián Ponce-Alvarez, Joachim Confais, Sonja Grün, and Alexa Riehle

The timing of the task is represented in the temporal structure of significant spike synchronization at the population level. By practice, the temporal structure of synchrony was shaped. Synchrony became stronger and more localized in time during late experimental sessions, in parallel with a behavioral improvement, whereas the firing rate in the same neurons mainly decreased.




The brain processes in parallel sensory, temporal, and contextual information, which has to be combined appropriately to organize a movement.

It is widely accepted that sensorimotor funcitons are based on activity modulations in neuronal networks distributed over various brain structures. (Wise, 1984; Tanji and Kurata 1989; Riehle, 2005).
The timing of modulation of synchrony and firing rate at the population level in motor cortex suggests that synchrony may be preferentially involved in early preparatory and cognitive processes, whereas rate modulation may rather control movement initiation and execution (Riehle et al., 2000; Grammont and Riehle, 2003).