マウス視床におけるbarreloid （バレロイド）の形成とそのニューロピルの発達

POSTNATAL DEVELOPMENT OF BARRELOID NEUROPILS IN THE VENTROBASAL COMPLEX OF MOUSE THALAMUS:A HISTOCHEMICAL STUDY FOR CYTOCHROME OXIDASE

　抄録　マウス視床腹側基底核の背側亜核（VBm）におけるバレロイドの組織構成と，出生日から21日までの生後発達について，チトクローム酸化酵素法を基に調べた。一側の視床VBmにみられる一群のバレロイドは，対側における顔面洞毛の配置とよく対応した構成を示す。バレロイドの区画区分は，生後3日にみえはじめ，6日までに編成されるのに対し，バレロイドのニューロピル内にみられた特異なシナプス糸球体は，生後13日に成熟型の形態をとるようになる。すなわち，視床のレベルでは，構築区画としてのバレロイドの枠組が先にでき，遅れて，ニューロピル内の組織分化が充実すると考えられる。

Postnatal development of barreloid neuropils was studied in the ventrobasal complex of mouse thalamus. A single barreloid neuropil which topo-graphically represented a corresponding facial vibrissa on the contralateral side was demonst-rated as a solid reaction mass with the method for cytochrome oxidase. This architectural unit was callled a vibrissa compartment.

On postnatal Day 0, the nuclear area of the ventrobasal complex showed higher activity for the enzyme than in regions around, but no bar-reloids were seen. Barreloid neuropils became detectable on postnatal Day 3 in the dorsomedial subnucleus of the ventrobasal complex and the septal delimitation of barreloids was established on postnatal Day 6. The arrangement of bar-reloids showed a distinct orderliness similar to that of facial vibrissae on a horizontal section.

Barreloid neuropils contained synaptic glomeruli ensheathed with glial processes, in which dendritic processes and their excrescences of nerve cells received large terminal knobs in well-organized manner. On postnatal Day 10, immature glomeru-lar forms were found in barreloid neuropils. The synaptic glomerulus of mature type, however, was not formed till postnatal Day 13.

The number of synaptic junctions was examined in barreloid neuropils from postnatal Day 3 to 21. The result that the growth rate of synaptic junc-tions was the highest in a short period from post-natal Day 10 to 13 suggested rapid maturation of barreloid neuropils in this period.

On postnatal Day 21, several types of synapticcontacts became remarkable in matured glomeruli. One of them, a filamentous type with association of clear synaptic vesicles at presynaptic sites was indicated. And non-synaptic junctional complex accompaning tubular structures beneath dense materials at dendritic sites was remarked between terminal knobs and dendritic processes.

From results the following conclusions are re-marked that at the level of mouse thalamus, septal delimitation of vibrissa compartments ap-peared on postnatal Day 3 and was established until postnatal Day 6. On the other hand, barreloid neuropils containing glomerular synaptic complexes became a maturing state on postnatal Day 13, that is, about one week later after architectural compartmentalization.