Antecedentes del problema

The resp on se of th e neurone Da to dopamine (Fleming, 1986; Pitm an & Baker, 1988) has been c h a r a c te ris e d in term s o f i t s pharm acology. The resp on se i s a d e p o la r is a tion , and th e re may be an involvem ent of sodium, potassium , o r c h lo rid e ion s in th e m ediation o f th e resp o n se, a lth o u g h t t hi s i s n o t c le a r . Calcium p la y s an im p o rtan t r o le , b u t w hether a s a ch arge c a r ri e r o r a s a tr i g g e r f o r o th e r membrane-based e v e n ts i s un c le a r.

The r e s u l t s p re s e n te d h e re show th a t dopamine d e p o la ris e s a MDtoneurone in th e in s e c t CNS, b u t a t th e same tim e i t does n o t appear to be a c tin g a s a prim ary e x c ita to r y tr an s mitte r . The voltage-dependency o f th e resp on se, cau sin g an in c re a s e in th e m agnitude of th e resp on se c u rre n t a t p o te n tia l s p o s itiv e to th e r e s tin g p o te n tia l o f th e c e l l , might allo w dopamine to e x e r t a p rim a rily m odulatory r o le in th e cockroach CNS.

The pharm acological p r o f il e , ta k en in c o njun c tion with th e d iffe ren c e

in c u rre n t v o lta g e cu rv es f o r dopamine, n o ra d re n a lin e , octopamine, and a c e ty lc h o lin e in dic a te s th a t dopamine i s a c tin g a t s p e cif ic re c e p to rs and n o t a t re c e p to r s f o r th e s e o th e r tr a n s m itte r s . The dopamine re c e p to r p re s e n t h ere does not however conform to th e c l a s si f i c a t i on scheme f o r v e r te b r a te c e n tr a l dopamine re c e p to rs of Kebabian & Caine (1979), T his may r e f l e c t e v o lu tion a ry changes in th e dopamine re c e p to r, sin c e hy p e rp o la ris in g and bip h a s ic re sp on se s

t a dopamine in some m ollu scs a ls o seem to be m ediated by re c e p to rs which do n o t conform to t hi s scheme (B okisch & W alker, 1988; A udesirk, 1989).

There i s s t i l l doubt, however, a s to w hether th e dopamine re sp o n se s re c o rd e d in neurone Ds a re m ediated by a s in g le c la s s o f re c e p to r o r th ro u g h a mixed re c e p to r p o p u la tion . U nitary c u ren t re c o rdin g s may d em on strate c o n c lu siv e ly w hether o r n o t a sin g le c l a s s of re c e p to r i s in v o lv ed .

F u rth e r re s e a rc h i s s t i l l n e c e ssa ry in o rd er to I d e n tif y c on c lu siv e ly th e ionic c u r r en ts u n d e rly in g th e response to dopamine, and to a s c e r tain w hether dopamine does indeed m odulate th e a c ti v i t y o f th e common in hib ito r y m otoneurone. Da,

APPENDIX 1

SALINE SOLUTIONS

S a lin e c o n s titu tion s were b ased upon th o se used by Yamasaki N arahashi (1959), and m o dified by Pitm an (1975).

Normal s a lin e s o lu tion had th e fo llo win g com position:

NaCl IM 5 3.5 ml

KOI IK 3. 1 ml

CaClsa IK 9. 0 ml

pH 7 ,2

T his s o lu tion was c o n tin u o u sly c ir c u la te d by b u b b lin g with oxygen, which allow ed f o r p ro lon g ed s u rviv a l of th e p re p a ra tion in th e b ath . S a lin e s o lu tion s f o r ion - s u b s tit u tion ex p erim en ts were made up a s fo llo w s:

Sodium-free s a lin e

by equim olar s u b s titu tion with TRIS-HCl TRIS-HCl IK 248,8 ml KOI IK 3. 1 ml CaClz IK 9. 0 ml

pH 7 ,2

The c on c e n tra tion o f TRIS-HCl was in c re a se d to 248.8 mH to com pensate fo r th e low er degree o f dis s o c ia tion of TRIS compared to NaCl.

31nil[ /£■■*■ s a l i n e by eq u im o la r s u b s t i t u t i o n o f Na+ w ith K" NaCl 4M 46.6 ml KCl IM 31. 0 ml CaCl-^ IM 9, 0 ml TES b u ffe r 2,292 g l- pH 7 .2

Calcium -free s a lin e

The p ro p o rtion o f NaCl was in c re a s e d to com pensate f o r th e lo s s of

ionic s tr en g th r e s u ltin g from th e removal of Ga®’*'

NaCl ,,4M 55 .5 ml KOI IM 3 ,1 ml TRIS-HCl IM 1.0 ml or TES b u ffe r IM 10,0 ml pH 7 .2 4?mN c h lo r id e s a lin e

NaCl was re p la c e d with N a -is e th ion a te , in an equim olar fa s h ion

NaCl 4M 6 .5 ml ICCl IM 3 .1 ml CaCle IM 9 .0 ml N a -is e th ion a te 27.8 g TES b u ffe r 2.292 g pH 7 .2 -1 7 3 -

36mH c a l c i u m s a l i n e

NaCl was re p la c e d by CaClz

NaCl 4M 49.7 ml KCl IM 3 ,1 ml CaCls IM 36.0 ml TES b u ffe r 2.292 g

pH 7 .2

C h lo rid e -fre e s a lin e

The c h lo rid e anion was re p la c e d by a c e ta te in a l l s a l t s

NaAc IM 214.0 ml KAc IM 3 .1 ..ml Ca(Ac)s IM 9 .0 ml TRIS-Ac IM 10.0 ml pH 7 .2 174-

APFBSDIX 2