Aplysia brasiliana

Charuni, a grad student in our lab, is now studying the swimming behavior of a sea hare, Aplysia brasiliana. Compared to other sea slugs, this one looks very intelligent. Especially when they are swimming. Peeping over the water, flipping over, making quick turns... They are not sluggish at all. Their playful behaviors make me even think like these creatures are almost as intelligent as dolphins.

The Dendronotus and Melibe paper in Current Biology

My latest paper appeared in Current Biology!

Different Roles for Homologous Interneurons in Species Exhibiting Similar Rhythmic Behaviors

This paper describes the differences in synaptic properties and organization of the swim CPGs in closely-related nudibranch species, Melibe leonina and Dendronotus iris. These animals show very similar swimming behaviors with left-right body flexions. However, their CPGs have quite different network organization; they have different synaptic connectivity and responded differently when perturbed by current injections. Thus, similarity in species-typical behavior is not necessarily predictive of common neural mechanisms.



We also discuss about how species-specific behaviors have developed through the animal evolution. We showed that, even though closely-related animals with similar neuronal architectures exhibit similar behaviors, some degree of divergence can be found in the underlying neural circuitry. A pair of homologous neurons in one species have regulatory role to modify the motor rhythm, whereas in the other species they are part of the CPG and reinforce the rhythm regularity. We don't know what is the functional significance; maybe such difference will be hidden until some time when it becomes more critical in the face of some environmental perturbations.

Plateau potentials in sacrocaudal motoneurons of chronic spinal rats, recorded in vitro

David J. Bennet, Yunru Li, and Merek Siu
J. Neurophysiol. 86, 2001

Jerky limb movements often develop after spinal cord injury. This general spasticity syndrome is caused at least in part by enhanced plateau potentials in the MNs. Depolarization in MN triggers the plateau potential and causes its sustained firing, which lead to exaggerated muscle contraction. This paper describes the basic properties of this plateau potential and the sustained firing in MNs after spinal cord transection. The recurrent GABAergic and Glycinergic inhibitions may play a role in suppressing this enhanced plateau potential. This will be studied in following paper.

A new pump from Pentair Aquatics

A few weeks ago on Saturday I installed a new pump in one of our animal tanks. It is Quiet One Aquarium Pump 3000 - 780 gph from Pentair Aquatics. It can directly connect to Lifegard Module Filter System. But I didn't do that. I didn't want to do the plumbing job for all the circuitry of the PVC pipes under the tank on weekend. I just used plastic tubes to put it in.



Little Giant pumps were originally installed when Paul purchased them in 1997. Since then we had been using them with no specific reason despite their frequent failures. I like this new one better. It's real quiet. It is waterproof. And it's cheap (~$60)! Little Giant pumps usually cost more than $200. I will switch from Little Giant to Quiet One for all tanks.

Dendronotus swim movie

OK, this is another nudibranch, Dendronotus iris.



Just like Melibe, it swims by lateral body flexions.

Swimming Melibe leonina

Melibe leonina swimming in a glass tank.



Shooting a movie is tough!
To make this, I spent 2 days in the tank room and 2 nights on computer.

次世代エネルギーはどんなものか

　いま話題の原子力発電も，火力発電も，水力発電も，風力発電も，地熱発電も，波力発電も，磁石とコイルからなるモーターを回転させることによっておこる　『電磁誘導』　によって電気をつくり出しているという点では同じである
　唯一の例外は太陽電池だろう
　太陽電池は，光がモノに当たったときに放出される光電子を集めて，それを電流にしている
　いずれの方法も，エネルギー変換の効率は，すこぶる悪い

　これら人間の手によるエネルギー変換と比べたとき，それらをはるか凌ぐ高効率のエネルギー変換が生物の細胞内で起こっている
　植物の葉緑体では　『光合成』　によって太陽光を炭水化物の化学エネルギーに変換しているし，一方，ミトコンドリアでは　『呼吸』　によって有機物に蓄えられた化学エネルギーを，より利用しやすいリン酸化合物の化学エネルギーへと変換している
　また，呼吸も，光合成も，膜のプロトン濃度勾配という電気エネルギーによって仲介されているという点で似ている
　呼吸でつくり出された化学エネルギーは，細胞内外のタンパク質の形を変化させ，最終的には筋の収縮や細胞膜の電気現象をひき起こす

　次世代のエネルギーの開発というのは，新しいエネルギー源を見つけるというより，むしろ我々が入手できるエネルギーをいかに効率よく電気エネルギーに置換するかという点に絞られるんじゃないだろうか
　おそらくそれは従来の磁石とコイルを使ったものではなく，むしろ上記の光合成や呼吸にみられるような生体内のエネルギー変換機構を巧みに利用するか，あるいはそれと似たものを人為的に作りだすことによってもたらされるんじゃないかと思うがどうだろう