AD-AO84 823 CAMBRZIDG UNIV (ENGLAND) DEPT OF ZOOLOGY F/6 6/16CENTRAL NERVOUS IONIC HOMEOSTASIS (IONIC REGULATION BY THE INSE-ETCIU)MAR 80 J E TREHERNE DA-ERO-76G-OSO

NCLASSIFIED NL

i , uuum..huo :IIIIIIIINI

AD

CENtqRAL NERVOUS IONIC 1I1O EOSTrAIS "-

(Ionic Regulation by the Insect 1iood-lBrain Barrier).

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- 2 i.al Xechnical Aq

byIL

&Ekf aE/Treherne

United States Army % 1,C E

London England

GRA\NT NU _j- ERO-76--C-.s5a

University of Cambridge

Approved for Public Release; distribution unlimited

-J

80 5 2 7-161 i

EUtTY CLASSIFICATICONC 01- 'I ASC'?' au. rea) & 2REPORT DOCUMENTATION PAGE BFRED CINSTRUTINORM

1. REPORT NUMBER ?.GOVT ACCESSION NO. .4. f(ICILIT' CATALOG NUMBER

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ jw 1 k -4 3 F n a l T e c h n i c a l R e p o r t

4. TITLE (and Subtirle.) S. I YPL OF REPORT & PERIOD COVERED]

Ionic Regulation by the Insect Blood-BrainBarrier 6. PERFORMING ORG. REPORT NUMBER

7.- AUTHOR(..) S. CONTRACT OR GRANT NUMBER(s)

Dr. John E.'Trehierne DAER76-G-050 )J/

9. PERFO,0RMtINGfORGAN Z 10 t N tNE AND ADDRESS 10. PROGRAM EL-EMENT, PROJECT, TASKUnves t f tr deA AREA & WORK UNIT NUMBERSDepa.r-tmeat of Zoology, 6.11.02ADowning Street, Cambridge CB2 3E3 LT161102BH57-02

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USARSG(E) March 1980Box 65 13, NUMBER OF PAGES

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IS. SUPPLEI-JLNTARY NOTES

1T9. KEY WOjtu.s(CrIre on revcrue 8id ifnclsr n dniy by block ).mibr)

Neuronal environmentBlood brain interfaceGiant axonsNeurogl ia

1Ionic homeostasis20. BSTRACTr (Continue eu reverse oft~ It neceeaoz) and identify by block number)

This investigation has used invertebrate nervous systems to elucidatetwo basic aspects *of central nervous ionic homeostasis: neuronaladaptations to ionic and osmotic stress and ionic honmeostasis of thebrain microenvironment.

The research on the giant axons of polychaetes has established theimportant principle that some nerve cells can adapt to very large

DD FOB 1473 FIDITION OFI NOV 65IS OBSOLETE NLSSFE

SECURITY CLASSIFICATION OF THIS PAGE (When 1)ere Tiered)

- lit9'I{ AS FTI D)'rCLI ITY CL A'.%IWf- ATION -P: THIS , ! t.s l;:,rt'adJ

ti nuati on20. changes in the compositiol of thei r immediate fluid environment.

These adaptations involve structural uodiiication and chguWCs in thecellular mechanisms which mediate excitation and conduction.

The results of the investigation on the insect central nervous systemhas shed light on the piriability properties of the blood--braininterface, which shares some featurcs with the functional organizationof the mamalian central neirveus system. The physiologicalinformatinn obtained has enabled a physiological model to be erectedwhich ex)lains all of the available experimental inforinatioo andshould be susceptible to further experimental tests.

_N__rL ASSIFIIDSUCUMITY CL AS;I IC I ON O TillS PAG (7'tr I)nf,, I tor(cid)

SUMI\RY

This investiqation has used invertebrate ne(rvous svstems toelucidate two) basic aspects of central nervouc ionic homeostasis:neUronol adaptations to ionic; and osmotic stress and ionic homec-stasis of the brain microenvironment.

The research on the giant- axons of pclywhaetes has establishedthe important principle that somne nerve czlls can adapt to very largechanges in the composition of their immnediate fluid environment.These adaptations involve structural Modification- and changes in thecellular mechanisms which mediate excitat-ion and conduction.

The results of the investigation on the insect central nervoussyztem has shed ight on the pr'csiiyproperties of the blood-brain interface, which shares some features with the functionalorganiza-tion of the marrnalian central nvossystem-i. Thephioocainform-.tion obtained has enabledi a physiogical m-olel to be erectedwhich explains aill of the available exper4imental information and shouldbe susceptible to further experimental tests.

KEY W~ORDS

Neuronal environment -blood brain interface -giant axons -neuroglia

ionic hoymeostasis

Dustifi cion

TABLE OF CONTWrs

Page

I. INTRODUCTION

II. NEUtlONAL, ARA]:'TATIONS WO IONIC AMID OS.MOICSTRESS 1

(a) Experiments on Sabella giant axons 2

(b) Experiments on ercierella giant axons 4

III. IONIC HCaMDSTASIS OF THE BRAIN MICRO-ELVIRONIJINT IN INSE TS7

BIBLIOGRAPHY 12

T. INT'RODUCI' ION

The research carried out during the periWA of the grant was concernedwith an important and relatively unexplored aspect of neural function:central nervous ionic homc<stasis. This research has exploited somr, uniqueadvantages provided by some invertebrate animals by studying the physiologicaladaptations of nervous sTystems which are naturally exposed to very largefluctuations in blxl comx)sition, namely the giant axons of two estuarinepolychaetes (which are directly exposed to massive changes in the ionic andosMotic concentration of the exLra-axonal fluid) and the iervous connectivesof an insect species (in which ionic homeostasis is achieved by extremelyeffective regulation of the extracellular fluid environment of the nervecells).

The results of the investigations on the polychaete axons have shownthat nerve cells are not necessarily at the mercy of the composition of theirbody fluids and establish the important physiological principle that neuronesmay adapt relatively rapidly to massive changes in the osmotic and ioniccc.;Xsi tion of their immsediate fluid enviro.'nnt.

The results of the studies on the insect preparation have elucidatedand altcrn:-tive p-vysiclogical strategy to the preblc;r of body fluids offluctuating composition: the combination of an effective peripheral blood-brain barrier system and local glial-mediated regulation of the compositionof the brain microenviroment. This strategy is similar, in a nUnLber ofbasic features, to that of the manmalian central nervous system and, for thisreason, is a valuable model system for the quantitative studies of thephysiology of central nervous homeostasis. Such studies are of more thanfundamental physiological importance, for an understanding of the mode ofaction and the mechanisms of resistance to, insecticidal commounds requiresknYw;ledge of the permeability properties of the blood-brain interface and,also, of the associated underlying regulatory processes.

In this report account is given of the major findings and conclusionsof the research carried out during the tenure of the grant. First forthe studies of neuronal adaptability and then for the homeostatic mechanism'sin the regulation of the ionic composition of the brain microenvironment.

Nore d.tailed accounts of work can be found in the papers whichhave already been published. These are referred to in the text and arealso ited sepairately.

II. NEURONAL ADAPTATIONS TO IONIC AND OSMOCTIC STRESS

T\'o species of estuarine pol~haete worms were used for these studies,both were shc.n to be euryhaline osmoconformers. The nervous system ofSabe]la yy, nicillus was found to. experience changes in the osmotic concentrationof the blood, of between 543 and 1236 m-osmol, in response to changingexternal salinities (Carlson, Pichon & Treherne, 1978). More extreme fluctuationsoccur in the blood of the serpulid, Mercierella enigmatica, the range (between84 and 2304 m-rosmo.) being the most extreme known for any animal species(Skaer, 1974a; Benson & Treherne, 1978b).

2

a) Lxperiiments on Sabella qiant axons

The giant axonis of Sabelia can wi thstand abrupt hyposnotic dilution ofthle ibathing mledium f rom I4 CtoC- 520 ilYsm, ecuivalent to 50% dilution (Carlson,Pichon & Treherne, 1978). This is in marked contrast to the irreversibledam-,age i.ncuri-ed in the- spike generating mechanism of the stenohaline osme)-conformer-,. Furtherm, ::e, the axons of Sabella are unusual inl showing onlyrelatively slow electrica-l responses; to abrupt dilutions Of the surroan-lingfluids (Carlson et al., 19'/8). TLhus the overshoot of the intraceilularlyrecorded action po tntial declines slowl%,y anid with a rather comiplex timecourse in hyposimotic media, W-t the axons are conventionally dependent upx)nsodium and the spike is rapidly diinini.rheJ-* in low sod~ium conditions whenthe Osmotic concenltrat ionl is maintaine.:d with 'sucroso (Fig. 1) . This effcct,together with the,, slower rate of p-otassiLLm depolarization observed duringhyposmotic stress as compared with equivalent isos~xtic treatments, suggeststhat there is a reduced intracellular access to the axon surfaces when theosmotic concentration around the nerve is reduced. This could arise fromosmotically--inldUCd swelling of' the surrounding glial processes, and woculdprcsumcbly provider limite-Id £h;ort-terin, protc'ctinn frtz n the (vcs effr',cc 0 rftfluctuat-lons in blcx-Yi osimlr.ali ty.

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In spite o~f this short-term I imitation of access, the giant axons ofablanevcrtIheless develop a reversible conduct ion block after prolonqedc

expx.)ure to 60%? hy X)Siotir solutions (i.2A) . But the axons are able toadapt to this situation if the dilution is gradually impo-sed, and wi] 1l thencontinue to conduILct action potentiajls (Fig. 2B) .

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This hyposmotic adaptation in the giant axons involves an appreciablereduction in intracellular [otassiumn concentration, as revealed by a comparisonof the changes in resting potential with varying [K+] 0 before and afteradaptation (Treherrn & Pichon, 1978). This reduction is alproxinm-trlvproportionail to the rxotassium dilution in the extern :J me:diumi, so tI-het a60% reduction of [K(+]o) is associated with a 69% decline in [K+fl, from 4,,1 n'Mto 340 mrM. This effect ensures that there is no marked change in axonalresting potential, in contrast with the situation in a iiore extrem-,e conformerIFMercierella, in which intracellular potassium is not proportionately reducedand a marked hyperpolarization results.

The decline in intracellular potassium observed in Sabella axons duringprogressive dilution of the external medium does not appear to result from.axonal swellinj 'and cell dilution (Carlson et al., 1978). -The recorded declinein [K4f]i during adaptation must, therefore, result frcom a net loss of thismajor intracellular- cation f rom the axoplasm, an apparently cm~fon strategyused by cells to reuILcC the internal osmotic concentration during hyposmoticstress (cf. Hoffina-n, 1977).

The active membrane in axons from seawater-adapted Sabella is not completelyselective for sodium ions. This is shown by the signifi-cant departure in theslope of the line relating overshoot to internal sodium concentration from thle58 mW per decade change in [Na+J 0 predicted by the Nernst relation for an idealsodium electrode (Fig. 3). However, in hyposmotically adapted axons the sodlium

4

selectivity increases (Fig. 3), a factor which pxrtia]l]y comnjens.ates forthe reduction in sodium gra dient acroFss the axon mnrbranes as the externalfluids are diluted. The overshoot of the action potential is theebyincreas x in hy).-motically-acapt as comr~aured with seawater-adaptedaxons at equivalent external sodiumi concentrations (Treherne & Pichon, 1978).

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"he -s p7 " , _ .o. ,, .n o ,/C.IX.J.&T CgCnt O>'onIs ac thus adctiz (,

to rr rmit a maintranance ofi excitabiility uu,::er the rCe'i:nes of limiited os.r~ot-;cSte.- exp1x 1. J; c, by-i,' a -d lost os , ,xnfo)yme',. F.J rs tly, the :oions receiveshort-term protection by restriction oE the intercllular Cccess to theirsurfaces during abrupt hypj.-motic stress. Secondly, there is a substantialrcd iction in intracellular j]otassium, which is presumably accompanied by onequivalent loss of intracellular anions (cf. Gilles, 1979) , contributing tothe achievetm:,nt of osmotic cquilihrium with the hlcx:,d or bathing mediuM.Thirdly, the relative s~xlium perme-)hiity of the active membrane increasesduring hypisctic adaptation so as to pertiaily c pensate for the reductionin external soAi. urn concentrations.

b) ExFjriments on Mercin'J]a giant axons

Despite the very large fluctuations in osmotic and ionic concentrationof the blood experienced by this extreme osmoconformer the giant axons appearto be unprotected by a recognizab]e bar.rier system. The giant axons are over-laid only by narrow glial processes which provide an incomplete covering of

axOI11 I1 C (' ~;n~~idtc covering oc-curE; th~e inlteOrcelularab, t it! by jt'1)ctitfl A(X);1eX(5NC anld ionic laLknn ee a~r;

to t h' ,III ()IXI) ol4 1--kh -ea %- tcr cjdapted itictivichials (in norm-,l~~~u1 ~ i !11' LW dl l i I:.1~..nrti te and in those which are hIyrxxL;irti-

c Yl -1 et a . 19712; Ircherne, 1978)

Altu 11! vaI o ct etd I on the extrumve flIuctuatioils in o~tic conce-,ntrationof th, bhxkxi t-,k Z'.y'elIiaons riRvrtheloss exhibit structural specializa-tiorrM which, 3A is ox~rd enaible dhemi to withstand an appreciable excessof IntuILI "Ir byb&~~Lcpressure re!-uitinq fromn osmotic imba-lance duringhvN .m~ i Thjese ore 11 dsvcre1h tructures, associ ated withthe >:n;cnoIewhich a;re conn cted- to a network of rieurofilament.s -withinth,- aixon. ihf, provision of regularly, clor;ely-syoced, supports for theaxoilal m'lr2eC pasto he a hi~jhi y effective way of limiting the tensionOil it by reducinq the rad ,-ius of curvature (--(kaer (A al. , 1 978a) . For examgple,a flotionV1 NC:2 of internal conccn-tration of 100j -InD: wil~l produce aninternal r~ieof 2.42 x 105 Pa (2.42 x 106 dyn cm)wti agataoof 15 iem rW Under these Cirurtane it can be calcula5ted tha anl increa-.se

huiircit1 t t xc.1e orthe unstretc!icd axon Lnd roujihl y ecquivae-.ent if the

Of~a~ (1sna IW boor

Theqi'~ ~ of W.irona! Ijze t. :.ccnycornStrategyOf ITCChicing t") c I reect ro] 'te concenrtra tes during hypas-!oticadapL, i ion. !-,%:Ith ' xn (i ir 1 973a) , but urlike thr, giant axonsof j2~e~ "Tfl : r & P ,1976) , ti-!e is rein-propartional retention ofboth !') ilt si i i-qp w 'r dilution)I Of the external IrediUM

~1oao &Trc1 Ile, 19-1'01,; Fooer e ') E r extle eduction of thecxtc-ina] io' ncota o: to 25' ill 0l.aa :dy zAn approximate halvingof [XJ j.) and [ )] i *.f ro:1 3 1) to !",- in' Fol furetcssium a-nd 87 to 44 -,,Ifor anium ionr

The nyon-i io'.ortianal retention of aspeo lrltirscium ionis is ofcritical imlxa Lance in th2 yx;oti ' it. u of thre 1M4rcierella gian-t axons.

iha L; correlA 'I ~i th the.( unui 31; eccIta1:n(3 M)

'Ic ~ i07 lieri ~11'oa13Orn a steecp yu j t!, I. :N rnr;t r.Iox!, which ro) c-Ites -th- o tnj)I. re ii 1.Otential to r ti o n rcontra;t ion (Carlson &

T . 1977;1 ruo 1,i*,,,-iu, 1 .~

[4jThe nct effe,-t of thte L,.nitivit I'' o th' rrstinq pot .nti al to changes in-KJ0 And 13nneJ o~ eotit fhIi! that ther- is a proportional

increaise in thr awr-ydicui ajn o xasu ions durinqi hypa-snmaticdjlition (Vnn&T hee,1976k ) . Tikz., ccounat for- the. appreciable hyp-er-TXolariza tion observ(-JdJu7 i o datzq o of 111f ;-rui erel i giant axons todil ution of' the, external Hiii-um (Fig4. 4).

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in [lNa+1 0 &nd, thus coTntI ii 'tes to t)e 1c. tc .v Of the 1tjrOf th"

actioai :xtcntial. Sec-Ja]y, 0 oiireec rc\';,tin-3 ikotnt i11 u C

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poitential during extreme dilution of the bathinAg 111icxium.

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(F~.6) 0(eimri 1'eh'i 0 1 978h) .Jt Tllil i0 1cd-L iof fl jpeiiv Loe ,p( cif£icY(.')p3IS(? to 0 rC(10u1, 0Xt-CiiIIl i0lniC CCnCCiflt] rcaon , I .or it: ccin's (in the--absunce ok tho eoliu-wdxiiTt reduLCtjOn inl [I J ~ uring i 0 umotic d'ili tion oftile bu-.thin me1dium (beLnroCn 1.'Drchcrne, 1 978,). 'The rcciuct iof in Wij is;al.i ci ll thle ofO~nZ (.ou)JWain and could, therefore, r esul t Itrum aninci:c.-Ise inl 110t sodium fflCJUY such) jas Cx~curs in the cjuid coant a>'rn insodium-deficient sa-line (11odg(kin & ~ye,1955) .h ei ( (uv. ffl uxfrom le cephjalo~xxJ gauint ax~on aup:ars not to be passively ir' cb I Jeo for it-was found to be ilihitC-d b)), dilUtQe dinitrj ,C 2±enl. it ugc; !7712jht th

increu-sedi sodli-mi efflux is acCCxp--1iced by all Outwalrd ;u 9ve'fmr t (A an intr-

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I II. IONIC 0.1IE§''sI OF rilj-l' BRPAIN T.lC ~l~~:m N iNSECJ'd

The research carried out cduying thce tenure of this grant hx3 enabled anoflK~ to be devised AWch accounts for the available information ob)tained

usinq. cl cr ysioLogical, ill tras tructur-a 1, radio4 sotopic all- fl1amephotonietric techniques.

K~ IN)

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clring to the rro~d (FPig 7) intcrcell-ularz dififuSion hrtvcQi th- 1b)l&oo

that 'uravezisoe h-Supc.fic.-1 la, r of rrri:d c~'la th- ernur(Lanec, 19742) .Tis r'en for 1.r n ')'i.Iie h-at altered cu irn J icln

(Trehere E-t 1 1970; P chon F, Trh CAn, 1970; Pichn .0I Ac on & Tri,-A iioe1971) .The rl:-triti~on is suage --'ted to result frc on the titjunctions, "ALthe. inner l ( '"- n t r lal cc "arnd 1 Ji.,&P:y'mr Loa limitl t

Ofl I- ;-l n th, cl~efts 7T-*

un;7cjrabTe r' L'-7 1-" C1 t -e1 1 ra (i

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prnc-LIatiOrl Of t-hr (! it' al nekw o2Ii a and)etac i unlU3f ine t ipploo , I iyh-reI17O" F'm V10, Ifilu ~oAuli t rcfi 0 ;. Our Oh)scIrV t 1l -os hcl;that.l ch tt;it pl iunc'c ]11i ~0 ~I .1,)I. tothcmeasured att dc 'i'per ]-(-vc,]1 in the C! N;) -it dej it Ji!t of' onl y 5 1vlicj_;Ii t! Ineural larella, The u ii cial li alt ioj ()," thep iini-nud

extranouron,-il poLclnt a I; pr ovides citIPt1ttL videltic fr lnterce-1 11 tIll-restriction of inw~ird (,: alo'flr1 i n te- wi tr alelIte such is~jInn )rpxor~ltrec inl the o eljliefrVK in PigI. 7.

9

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The pxerineurial neuroglia and the underlying glial cells are reprc-.ented,.-in the model, as confluent compa,,)'rtments which allows intra-cellular r~e'~aof sodium ions, and: other sma1 -water-soluble ions, to occur vija theo cPpjunctions that link adjacent pcorineurial and gli-al uembranes (Lane, Skaer &

Sas,1977; Lane & Swalez, 1978).

According to the model the sodxium content of the perineurial cells -willbe largely determined by the uptake of sodium from the bloo d and it,-extrus;ion into thoe xtrew-e1 1ular fluid a;nd the blond- by the Na/K pun.mps.In the abs ence of external scxdium ions there will be a net out-ward mo~vewlr-sntOf OD-' cat ion cwiosthe cuJterprncl2l 'elreyI1Ketdzthe Na/Nl pulips. Because of the pastulcitod likae ith. the unJerlyinq CLIlathe charnges in intracellular sodiuml concentration) inl the perincourial-nytoplasrnM will be accompa.:-nied- by ecp-ivakont change iti h dexrgielcerits.

The above iwdel also accounts For the inability of external- lithiumlions to gain accces's to the a-zon surLucr-s (Schoflield & Treherne, 1978) , deupjitea suhb-tantial accuIMulatLion of this catiion within the central nervous ti!,sues,2(13vnnett, JBuchln '& Trchorn, 19'75) . Tlhn inabil it y of lithium to restore 'Lheaction potentials in) sodium--depleted connecctives implies that this catior;(which can sub-'stitute for Sodiulm in mi itaining the inward current of theaxonal action potential) must be excluded from the extracellular fluid and,consequently, contained in the glial cytLoplasm. This is accounted for inl tilemodel by the presence of Na/K pumps on the glial membranes for it is kiiiownr thatlinked sodiumr pumps, in frog muscle (Keynos & Swan, 1959) and crab neuronecs(Baker, 1965), will not accept lithiuim ions. The retention of lithium ionswithin the central nervous tissues, after prolonged washing in normal salinle(Benner(,tt et al1., 1975) is expl~ained by the outwa)rdly-dirocted linked sodiiumi pompson the outer peorineurial membranes which, similarly, are presumed not to accep~tlithium ions.

100

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( ' % i l xpo ull () l I);iIli \ '1 ii' .'U C ( bil) a d () si ai

frnom :I sxwtkioc-gap revori g : lep tion of N.a exprescd ai ( -vs Inca C y) ; rcove ry expimwasdISI -- C' ' vIki iS (a~) to a 111 p1 if f V m Comparison \Nith dep~Ict ion. I hlf-: iic foi decl ine (b), 98 s;

(c), z1 i a . Ilaif-tittics for rccocety : (a), oS s; (h), ign s ; (r), t i I . 1I res fit'd by linear regivsloitont rcct iguar eo-utditvs except for thll brokun lit illi (a) ss hid. a fitted by eye.

We have shown that initial exposure of connectives to sodium-defiCienitSalin.e roesults in an extremely slow decline in ampl itude of the axonalaction potentials, (Schofie~ld & Treherne, 1978). Felatively rapid recoveryof the action potentials occur on return to normal, high-sodium, saline(Fig. 9a). Subsequent exposure to sodiuM11-dficient and normal salineIx-coiles rapid and syiytetricai (Fig. 9b) . These observations cannot beaccounted for by increased1 interce]llular leakage of todium ions for, asmentioned above, the action potentials in sodium-depleted preparationscannot be restored by prolonged exposure to lithium ions (a cation which cansubtitute for Poditim in carrying the inward current of the action potential).

The r5t SJ. shown iii Yig. 9 can be expliiio ie ccordinq to. our vrAiei by a 7postuL attod intra-cellulai S.odium ror;er vot r which fuc.j!i;to m-Jint.:iin

iO(:VLdtC' UXt raCc] uT Q: scxiufi concentrition:, dur ing rohsc' ixxi toExx~iiwit-dc'L uient: sal inc. 'his reser-,Ivoir can b rcchaucird Only re]'aot- ively,:lowly aind, thus, when uncha:rgecd IlvellienUs of soch urn ions botw, -en tie,externnj micd jum and the aIxon SurfaQces; aire re ' utivcly raipid, ?ml s-.y'm',itr ical,but are novertheiless sloaed by a meax iicInhilAtor , I)NP, ;Ind a sod itiltrarislxrt inhibitor, ethacrynic acid.

The po)stulated intracollular sodlium reviris, according to themodel, localized in the linked pxrnuilgiicytoplm, althoug;h it isposs ible to erect al.ternat ive local izati on, for examplea, in the axop acmitself. FExperime ,nts are currently in prcjross to identify~ th propos-edintracellula .r sod1ium- reservoir. Thes eoc i'at will involvce the, use Ofradi os~od jurn local izat ion in dtre-ratdpreparations, in n~-lcrly~soIlution, and also, the use of so0diumi-selective microelectrodes.

We are currently using radiosodium to study the exchanges of thiscation across- thre bloo-brain int :rface (JJT,.. Trehornc' & P.1 . SV(:ar rcst21Lct CanI iri;, (2 riiCr ()1~ i n ci.''rhre 19,hi

1972) thait rapid radiosodiumi fluxo,- oc'cur bevencck~roach ccnti - n'rvaoust isrsues ani the 1-ba thino me-dium . '.-Na efflux2 IcuS aat'-t: C'

with half-timeLls oL ':-) and 100 soc respcactively. ExtrLa-ax,,aal scx~j i,regulation is, therefore, a dynaic proc-ess wAich involvos raid konftis

acosthe blo-banintorfzce. 'I Inee I Ie do) not c~pcrto I~ ' Iavsignifiicant SclXiUM-Fsodiun exchanc7e as is r;,'nin saire c-pthel~ l tr - --,oi ts y -tecasi ,. mectabolic and sodium-transport inibtrshve little- c t11 tjrrapidly-exchanging coxmponent but slow., the sl~~vecag~ge~.x'tofradiosO jUJin efflux-. Further experiments will beL directed tnwaird2 1~ ,' tif -Cation of the rapidly-mcchanging sodlium fraction.

Reen~t research has indicated an involvement of the arincrgic sy:-,tclmin ion'ic homC_,CStajSjS in the cockroach nervou-s system. We havc slcrwn thatexternally-applied octopamine prodluces marke-d changes in extranearenulpotcontiails and al.so onl the am-tplitude of the action potentiails in pi olerrti n:eXposed(-N to) SOCxiLI-d1Cfi cicnt 'Iln M adOn the rate of axonal cexl'~/Ioin conm.ectivcs in h igh--pootassii saie Ou,,r ~e ij~ycsra o' L~;

tha-t- oLU--Kr inc 'Tey affe,.ct HOl , thpr"t) l Ul'VjLvc tIm I2nlunra:-1 ''a Ja:1- n!kcJ c)La-:o-dsu ozac 11 .. ci.rynC i

12

B~aker, P.P. (1965). Phosphorus metabolisni of intact crab nerve and itsrelat ion to thc active tranjs1.)rt of ions1. J. Phsol., ond.180, 333-423.

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Carlson, .D. , Pichon, Y. & Trehernec, J.E. (198). Effects of osmoticstress on the electrical activities of the giant axon of a

marne sn~conon~r, ab~~a eniils.J . exrn. Biol 75,237-251.

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Lane, N.J. & Swales, L.S. (1978). Changes in the bicXxi-brain barrier ofthe central nervous ~.s cin in the bl4owfily cinrim ' developrvnt,with specia-l reference to the formajtion and (isagregation ofgap and tight jUnctionzc. 1. Larval cvelopwnej. Deveip. Bio~l62, 389-414.

13

Lane, N.J. & Trehlirne, J.E. (1972) . Studies on jx.rjneuiial junctionalcomplexes and the sites of uptake of micro-pcroxida-e andlanthanum by the cockroach central nervous system. T7;ssue &Coll 4, 427-436.

Pichon, Y., Moreton, R.B. & Treherne, J.E. (1971). A 'quantitative studyof the ionic basis of extraneuronal pxotential changes in thecentral nervous system of the cockroach (Periplaneta amnericana L.).J. exp. Biol. 54, 757-777.

Pichon, Y. & Treherne, J.E. (1970). Extraneuronal potentials and potassiumdepolarization in cockroach giant axons. J. exp. Biol. 53, 485-493.

Rand, R.P. (1964). Mechanical properties of the red cell membrane.I. Viscoelectric breakdown of the membrane. Biophy-s. J. 4,303-316.

Schofield, P.K. & 'Irehc-rne, J.E. (1978). K.in>tics of s-x'imri and it1LoMmovenywnts across the blood-brain barrier of an insect. 3. exo). Biol.74, 239-251.

Skaer, 11. le B. (1974a). The water balance of a serpulid polychaete,Mercicrel I a enicratica (1auvel). I. Osmotic concentr:ation andvolume regulation. J.exr. Biol. 60, 321-330.

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D. e 7 i:o. 6(, 331-338.

Skaer, H. le B., Trcherne, J.E., Benson, J. & Moreton, R.B. (1978).Axonal adaptations to osumotic and ionic stress in an extrCeeinvertebrate osrroconformer (Mercierella enigmatica, Fauvel).I. Ultrastructural and electrophysioolc ical ohaervations onaxonal accessibility. J. exp. Biol. 76, 191-204.

T-ehen', 3.1. (1962). The distribution an' -]chan'e of 2cX22 ions nd

Holecules in the central nervous sy;tcm of .asJcta JV<ricrn2.J. exp. Biol. 39, 193-217.

Treherne, J.. (1978). Neuronal adaptability. Trends in Neurosci. 1, 152-153.

Treherne, J.E., Lane, N.J., Moreton, R.B. & Pichon, Y. (1970). A quantitaivestudy of rxptassium movements in the central nervous system ofPeriplaneta americana. J. exp. Biol. 53, 109-136.

Treherne, J.E. & Pichon, Y. (1978). Adaptations of the Sabella giant axonto osmotic stress. J. exp. Biol.75, 253-263.

Tucker, L.E. & Pichon, Y. (1972). Sodium effu1." from the central nervousconnectives of the cockroach. J. exp. Biol. 56, 441-457.

Willfw~r, P.G. (1978).. Electrophysioloqical correlates of ionic and osmoticstress in an osmoconforming bivalve (Mytilus edulis). J. exp. Biol.77, 181-205.

14

tUBLICAPIONS DURING TENUflE OF GI"P

Carlson, A.D. & Treherne, J.E. (1977). Ionic basis of axonal excitabilityin an extreme euryhaline osnoconforner, the serpulid wormMercierella enigmatica (Fauvel). J. exp. Biol. 67, 205-215.

Treherne, J.E., Carlson, A.D. & Skaer, H. le B. (1977). Facultative blood-brain barrier and neuronal adaptation to osmotic stress in a marineosmoconformer. Nature 265, 550-553.

Carlson, A.D., Pichon, Y. & Treherne, J.E. (1977). Neuronal adaptation toosmotic stress in Sabella penicillus L. J. Physiol. 269, 76-77P.

Treherne, J.E., Benson, J.A. & Skaer, H. le B. (1977). Axonal accessibilityand adaptation to osmotic stress in an extreme osmoconformer.Nature 269, 430-431.

Lettau, J., Foster, W.A., Harker, J.E. & Treherne, J.E. (1977). Diel changesin potassiuim activity in the haemol3 ph of the cockroach Leucophaeamaderae. J. exp. Biol. 71, 171-186.

Schofield, P.K. & Treherne, J.E. (1978). Kinetics of sodium and lithiummovements across the blood-brain barrier of an insect. J. exp. Biol.74, 239-251.

Carlson, A.D., Pichon, Y. & Treherne, J.E. (1978). Effects of osmotic stresson the electrical activities of the giant axon of a marine osmoconformer,Sabella penicillus. J. exp. Biol. 75, 237-251.

Skaer, H. le B., Treherne,.J.E., Benson, J.A. & Moreton, R.B. (1978).Axonal adaptations to osmotic and ionic stress in an invertebrateosmoconformer (Mercierella eniqmatica Fauvel). I. Ultrastructuraland electrophysiological observations on axonal accessibility.J. exp. Biol. 76, 191-204.

Benson, J.A. & Treherne, J.E. (1978). Axonal adaptations to osmotic and ionicstress in an invertebrate osmoconformer (Mercierella enigmatica Fauvel).II. Effects of ionic dilution on the resting and action_-_n13tials.J. exp. Biol. 76, 205-219.

Treherne, J.E. & Pichon, Y. (1978). Long-term adaptations of Sabella giant axonsto hyposmotic stress. J. exp. Biol. 75, 253-263.

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15

Willmor, P.G., Skaer, 1i. Ic 13. & Treherne, J.E. (1979). Physio]og jca l1yinduce(dK changes in intramembranous particle frequency in theaxons of an osukoconforming bivalve. Tissue & Cell 11, 507-516.

Treherno, J.E. & Schofield, P.K. (1979). Ionic homeostasis of the brainmicroenviro-nment in insects. Trends in Neurosciences 2, 227-230.

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