Wednesday, August 29, 2012

Fixing a power hub for micromanipulators

   There was overnight leakage of the cooling water for the chilling stage under dissection microscope in one of our student's electrophysiology rig. The dripped water soaked the the entire power hub for micromanipulators under the anti-vibration table. It stopped working, of course. It is Siskiyou MC1000e. It would cost $$$ if you buy a new one.

   By checking around with an electrical tester, I found a disconnected path on the printed circuit board. I had to create a new path with a hook-up wire (red arrow).



















    There was another bad news. One of the pins in the male D-SUB connector was also broken. I don't know how it could happen but it was one of the critical one that feeds current to the manipulator. I created a fake pin from a piece of hook-up wire and attached into the connector. It worked well.

    Now the manipulator is moving fine.
    You know, I can be the author of "Zen and the art of electrophyiology rig maintenance" some day.



Tuesday, August 14, 2012

Organization of spinal circuitry for rodent locomotion


Neuronal activity in the isolated mouse spinal cord during spontaneous deletions in fictive locomotion: Insights into locomotor CPG organization

by Guisheng Zhong, Natalia A Shevtsova, Ilya A Rybak, Ronald M Harris-Warrick
Journal of Physiology (2012)

Deletions are spontaneous errors in the rhythmic locomotor pattern when a set of synergist motoneurons (for example, flexor motoneurons on one side) loses rhythmic firing or falls silent during a time period when they are normally active. 
In the non-resetting deletions, the phase of the rhythm after the deletion did not change. The resetting deletions show rhythm resetting which was recognized by a shift in the phase of the motor bursts after the deletion. This study follows Rybak-McCrea model of the locomotor CPG, which has two functional levels: a half-center rhythm-generator and pattern formation networks. 

Deletions occur simultaneously in motor activity across more than one spinal segment. Spontaneous non-resetting deletions on one side are independent of the other side. The CPG can be functional within an isolated hemisegment. The reduction in locomotor frequency after simulated hemisection results mainly from the elimination of excitatory input to the rhythm-generating ipsilateral RG-F population from the contralateral RG-E population. The resumption of activity an integer number of cyces later does not require input from other parts of the spinal cord. Each hemicord contains an independent rhythmogenic network that can function in the absence of the other hemicord, although the left and right networks are normally coupled via commissural interneurons.

Among V2a interneurons, there are deletion-sensitive types and insensitive type (type I and II V2a interneurons). Type I V2a does not respond to non-locomotory firing in iL2, whereas type II V2a does. Both neurons were depolarized by synaptic drive. The type I V2a interneurons are involved in rhythm generation and/or coordination between left and right networks via the CINs. In contrast, the type II V2a interneurons do not belong to rhythm generator networks, but can be components of the pattern gormation network and/or last-order interneurons that directly project to motoneurons. Commissural interneurons (CINs) send their axons to the opposite side of the cord and coordinate left-right alternation. CINs were not affected by motoneuronal deletion. There was asymmetry in deletion: During all of the flexor deletions, the ipsilateral extensor root showed sustained activity with no interruptions at the times of the missing flexor bursts. In contrast, during all extensor deletions, the ipsilateral flexor root continued unperturbed bursting.

Their computational model combines the Rybak-McCrea concept of the two-level locomotor CPG (Rybak et al., 2006a,b; McCrea and Rybak, 2007,2008) with the Duysens-Pearson concept of an asymmetric rhythm generator with a dominant flexor half-centre (Pearson and Duysens, 1976).

Saturday, August 11, 2012

3 talks in 2 weeks

   I did 3 different talks in 3 symposiums in 2 weeks.
   First two were in workshops in the Computational Neuroscience: "Dynamics of rhythm generation" and "Principles of motor pattern generation: experiments and modeling." Gennady and Andrey kindly invited me as a speake. The 3rd talk was a symposium talk in the 10th International Congress of Neuroethology.

   For "Dynamics of...," I talked about potential mechanism of termination of an episodic behavior. This was a difficult talk for me because I have not worked on this aspect of the CPG. Some of the data I presented were not my own; those were not conclusive results. Very hard to interpret. I did some additional experiments in last moments only for figures. I was very nervous, because I was not so confident of what I was going to talk. 

   In the second workshop I talked about swim CPGs of Melibe and Dendronotus.It was fun and I enjoyed it. Andrey always admires my work.

   For the Neuroethology symposium, I was very grateful that Dr. Ron Calabrese kindly invited me to give a talk in his symposium. This is such a great honor. I gave a talk in the same symposium with Dr. Eve Marder. She even used my own laser pointer!
   About 17 years ago, my friend took me to Univ of Maryland when I visited Washington DC. It was after visiting Birmingham, England to attend the International Congress of Comparative Biochemistry and Physiology. In those days I was reading papers written by Ron Calabrese and Eve Marder like textbooks. I admire them so much. And now, they have invited me to give a talk. So happy.
   I talked about individual variability in the effect of injury to the nervous system. Many people gave me good feedbacks. Some told me they got inspired by my story, which also made me very happy.