MODELAMIENTO DE TABLEROS

82S26 has no effect on the membrane potential or input resistance of the cell, Current pulses were applied through a second microelectrode, and the resting potential was -56 mV,

each.), a t a c on c e n tra tian of 100 mît in th e p r e s s u r e - eje c tlon micro- p ip e tte , and 5 - 10 mîl in th e b a th -a p p lic a tion s tu die s . Under c u rre n t-c la m p , th e resp o n se of neurone D3 i s s im ila r to t h a t e l i c i t e d by dopamine, in th a t i t i s a d e p o la ris a tion , a s s o cia te d w ith a modest f a l l in in p u t r e sis tan c e . The m agnitude of th e resp on se, however, i s

n o t a s g re a t a s th a t o f a dopamine resp o n se.

Under v o ltag e-clam p , th e resp o n se to p re s s u re -a p p lie d apom orphine i s seen a s an inw ard c u rre n t a t p o te n tia l s n ear to th e normal r e s tin g p o te n tia l of th e c e l l . At p o ten tia l s both p o s itiv e and n e g a tiv e to th e normal r e s tin g p o te n tia l o f th e c e l l , th e m agnitude o f th e c u rren t induced by apom orphine v a rie s in a very s im ila r manner to th a t of th e c u rre n t in duced by dopamine. In a ty p ic a l v o ltag e-clam p experim ent (Fig u re 4 9 ), th e v a lu e s of Induced c u rre n t were -45 nA a t a command p o te n tia l of -160 mV, -0 ,5 nA a t -60 mV, and +8 nA a t +30 mV.

Apomorphine was tested at concentrations as dilute as 1 x lO""^' M in the picQspritzer pipette, but the response obtained was extremely small, and a concentration of 1 x 1 0-^ j,i failed to elicit any response,

In th e p re s e n t stu dy , brom ocryptine a ls o proved to be a c lo se mimic of th e e f f e c t s o f dopam ine. Under both c u rre n t-c la m p and v o lta g e - clamp <7 e x p e rim en ts), th e resp o n se to 100 mil brom ocryptine was very s im ila r to th e resp on se to dopamine. Here a ls o , brom ocryptine was p re s s u re -a p p lie d a t c on c e n tra tion s down to 1 x 10"® H, and th e

Current (nA)

Oommand potential (mV)

Figure 49 Difference curve indicating the voltage-dependence of the voltage- clamp response to pressure-applied apomorphine, Holding potential -60 mV,

resp on se was s li g h t l y s m a lle r th an th a t to apom orphine a t th e same c o n c e n tra tion .

Under c u rre n t-c la m p c o n dition s , th e resp o n se was a d e p o la ris a tion , a s s o cia te d w ith a sm all f a l l in th e in p u t r e sis tan c e o f th e c e l l , A ty p ic a l v o ltag e-clam p re c o rd (F ig u re 50) shows th a t th e induced c u rre n t had a v ery s im ila r v o ltag e-d ep en d en cy to th a t o f th e resp on se to dopamine. At a oommand p o te n tia l of -160 mV, th e Induced c u r r e n t m agnitude was -43 nA, At -6 0 mV, i t was - 0 .5 nA, and a t +30 mV, +12,5 nA.

In th e se ex p erim en ts e rg o m e trin e proved to be a mimic o f th e e f f e c t s o f dopamine on th e p re p a ra tion . A pplied a t a c on c e n tra tion o f 100 mM (in th e eje c tion pip e t te ) , th e resp on se was e a sily re p e a ta b le , b u t a g ain , a t th e low er c o n c e n tra tion o f 1 x 10~® M, th e resp o n se was much reduced by com parison with apom orphine.

Under c u rre n t-c la m p (6 e x p e rim en ts), th e d e p o la ris in g resp o n se was a s s o cia te d w ith a modest f a l l in in p u t r e sis tan c e . The m agnitude of th e resp on se was s li g h t l y s m a lle r th an th a t e li c i t e d by dopamine. Under v o ltag e-clam p (6 e x p e rim en ts), th e resp o n se, seen a s an inw ard c u rre n t a t p o te n tia ls around th e normal r e s tin g p o te n tia l of th e c e l l , showed a v ery s im ila r v o ltag e-d ep en d en cy to th e resp on se to dopamine. In a r e p r e s e n ta tiv e experim ent (Fig u re 5 1 ), th e c u rren t m agnitude a t a command p o te n tia l of -140 mV was -75 nA, At -60 mV,

i t was - 0 .5 nA, and a t +30 mV, +12 nA.

Current (nA)