Ultrastructure of capillaries in mouse periodontium.

Considering the cellular density of periodontium, its vascularity is al)nlidant (PROVENZA ET AL, Oral Sutrg 13: 157-164, 1974) ivliicli ieflects the piecsonice of twvo periplei-allv locatedl celluilar laxers of honle des elopment and cemenital clepositioti, piocesses wshich N hen active hav Ihigh metabolic iequiiemetits. I'le mictocii-culatorv bed of the periolonititim serses funlctionally for the exchanige of gases and(I ntiitricnts at the cellulat level (MAJNO, Handbook of Ph7ysiological CiZrc7latiotn, \ol 3, 1965). The puirpose of this in estigation is to describe the distribution anld uiltrasti uLctuire of teo-minial s essels iin the pet iodonitiuim of motise mo lais. Mandibular first molairs vsith pel-ioslontiuim and1 sunrioundinig alveolar bone were temosed in block sections fi-om 25to 50s-la -old Sisiss-Webster mice undicler soditm aniytal. Blocks wsere trimmed, fixes! in one-half st-etegth Karnovskv fixatise, postfixedl in osmic acid, dehydiasec, emb)eddledl inl opoxi xiesin ," sectioned, dloublestainie(d isith utraniyl acetate atnd lead citrate, and exaluiated wvitl an electron micioscope. Thick sectionIs (I miciometer) were stainesl situb methvlene blue andCt viciessd vith a light microscope to (leteiminie ot iciutationi of the tissue anrd locatioln of the section. Observations fiom 25or 50-day-old mice slid niot xsarv significant Iv. Capillaries showved fin-gerlike piojectioins that piotruldesl iltO toie Ilumen. Tele citoplasm of the endothelial cells contained nutmetouis microsesicles, scatteted tibosomes, and small ox al mitochodli iala. Occasion-ial tiglht junctioIis appeaicld betiseen endIothielial cells lined completeli bh a clistitict basement laminia but inicompleteiv encirclcd hi pericites. Although ceniti-al capillat-ies in thie pet-iodonitiuim appeared devoid of fenestiationis, fenestrate(d capillat-ies appeared periphet-ally andcl close to the osteoblastic laxer. Pot-es appeated alonig flattenecl aieas of the capillary stall as 300 to 500 A openings bridged bvi thiln membrancs con-itinullouls wvith eithet side of tl-i enlothielial cell. Small pei-ipheral ai-terioles appeared near alveolat bone oiiear cemenituim anisI displayed an inicomplete muiscuilait coatinig. Myoendothelial junction's (RtHODIN, J Ulti-asth-uct Res 18: 181-223, 1967) wsere occasionalli obsersed betwsecn the endothelial cells antd investing smootlh muLscle. These fenestrations mav tepresent tapi(l path-