DRL performance following anteromedial cortical ablations in rats

142

Brain Re~eat~h, 95 (1975) 142 146 © Elsevier Scientific Pubhshmg (ompany, Amsterdam - Printed ~n The Netherland~

DRL performance following anteromedial cortical ablations in rats

CARL E ROSENKILDE* AND IVAN DIVAC Institute of Neurophyswlogy, Umver~tty oJ Copenhagen, Copenhagen (Denmark) (Accepted May 12th, 1975)

It was hypothesized that the anteromedml cortex m rats mediates behavior m tasks revolving spahal cues s or spatial choices 4 These notions are supported by reports of deficient performance following anteromedlal ablahons m delayed response s, delayed alternation ~2, spatial reversal 3 and spontaneous alternation 4 Such les]ons, however, also impaired performance of go-no-go alternation 2,v and actwe avoidangel3,21 The present study assessed whether the syndrome following Injury of the anteromedial cortex included impaired performance in a D R L situation Neither stlmuh nor responses are spatially differentiated in this situation and, as m delayed responsetype tasks, no actual exteroceptwe stlmuh control execution of responses Four naive male Wlstar rats weaghed lmtlally 303-448 g They were fed 40 mm after testing and maintained at 90 % of their ad hb body weight A two-lever Campden rodent test chamber (CI-410) with a pellet dispenser (CI-442) was enclosed m a sound attenuating box A ventilator provided masking home The left lever was used while the right lever was present but locked Reinforcement contingencies were controlled by standard translstonzed equipment from a separate room Rewards were 45 mg pellets locally produced from standard Rostock rat mtxture Prior to the experiment the rats were handled daily for 6 days After magazine training and shaping of bar pressing, the ammals received 150 pellets m daffy sessions under C R F conditions until m 2 successwe sessions they obtained all pellets in less than 15 mm The rats were then shifted to a D R L 10 schedule without hmlted hold Sessions of 40 rain were gaven 6 days a week until the rats attained an efficiency ratio (number of reinforcements/number of responses) of at least 50 % in each of 5 successwe sessions After a rest period of l0 days the rats were tested for retention for 5 sessions, subjected to surgery, and allowed l0 days recovery Testing continued on D R L l0 until the preoperative criterion was reattalned or for a maximum of 25 sessions The rats were operated on under clean condmons whde anesthetized w~th * Present address Section on Neuropsychology, Laboratory of Psychology and Psychopathology, National Institute of Mental Health, Bethesda, Md 20014, U S A

143 TABLE I SESSIONS TO C R I T E R I O N

Subject

Preoperattve a~qutsttton

Po~toperattve lelearmng

MFI MF2 M F3 MF4 Medmns

11 47 24 13 18 5

3 12 18 25 15

* Faded to reach crltermn In 25 sessions

E q m t h e s m (3 3 ml/kg), the a n t e r o m e d l a l cortex was removed by subplal aspiration with the use of a dissecting microscope Following c o m p l e t i o n of behavioral testing the deeply anesthetized animals were perfused with saline a n d 10% f o r m a l i n m saline Blocks of the brains were e m b e d d e d in 20°o gelatin a n d cut frozen at 100/~m Every 5th section was m o u n t e d a n d covered unstained The n u m b e r of sessions to reach criterion for individual rats before and after the operation is shown m Table I The performance o n D R L l0 deteriorated in all a m m a l s following anteromedlal cortical lesions (Table II) The lnterresponse times were more evenly distributed a n d m two cases the mode was changed to shorter intervals (Fig l) The cortical ablations are illustrated in Fig 2 The corpus callosum was slightly d a m a g e d m one rat N o relation was f o u n d between size or location of the lesIons a n d the i m p a i r m e n t s A n t e r o m e d l a l cortical damage in rats impaired r e t e n t i o n of a D R L schedule Previous studies of the effects of frontal lesions o n D R L indicated that ablations sparing the medial wall produced no deficit 17, but large damage caused variable degrees of I m p a i r m e n t ~1 N o r m a l rats a n d rats with a n t e r o m e d i a l lesions were tested on a c q u l s m o n of a D R L 20 schedule for 15 or 20 days 8,12, the absence of differences between the groups may be a t t r i b u t a b l e to insufficiently extended observation periods TABLE 11 RETENTION ON

DRL 10

Subject

Preoperattve retention* Efjh~teno' t atto

MF1 MF2 MF3 MF4 Medians

77 8 46 2 54 9 72 9 63 9

* Medians for 5 sessions

Postoperattve retentton*

Number o[ reinforcement s

Numbo oJ responae7

154 115 129 148 138 5

198 250 226 224 225

Eric tent)

Number o f

Number o]

latto

reinforce-

te~ponse5

ment~

43 0 39 1 31 2 35 7 37 4

122 110 84 94 102

284 281 269 263 275

144

60I~ 4O

I T1I I I I I I

0

W

~PRE-OP RETENTION o.--.o POST-OP RETENTION

Z 040 W20

I l l l l

O0

ITII

h140 (J {X h120 n

0

I

I

i

i

t

I I r I 0 2 4 6 8 10 12 14 16-->18 INTERRESPONSE TIME (sec) Fig 1 Medianinterresponsetime distnbut~onsfor individualanimalsduring 5 days of pre- and postoperativeretention Leverpressesat intervalsshorterthan 10sec werenot reinforced o

~!1410 ~IISO

~ttFOO

~Oqlil

~

O

~ 7 0 Fig 2 Reconstructionon standard dmgramsof the largest (horizontal stripes) and the smallest (black)lesions

145 T h e s e findings, t h e r e f o r e , m a y n o t be mcons~stent w~th the p r e s e n t o n e s a n d it m a y be c o n c l u d e d t h a t t h e a n t e r o m e d t a l c o r t e x a l s o s u b s e r v e s b e h a w o r m a s i t u a t i o n w h i c h ts n o t c h a r a c t e r i z e d by s p a t i a l l y d~fferenttated s t l m u h o r r e s p o n s e s T h e a n t e r o m e d m l c o r t e x o f t h e rat r e c e w e s t h a l a m t c p r o j e c t i o n s f r o m b o t h the medlodorsal and anteromedml

nuclei 5,9 C o n s e q u e n t l y ,

th~s c o r t i c a l a r e a m a y be

c o n s i d e r e d ' p r e f r o n t a l ' as well as ' c t n g u l a t e '15A6 a n d it m a y p o s s i b l y m e d m t e different functions

U n i t a r y e x p l a n a t i o n s o f all s y m p t o m s f o l l o w i n g a b l a t i o n s o f the a n t e r o -

m e d i a l c o r t e x m a y t h e r e f o r e be m i s l e a d i n g A comparatwe

analysis a c r o s s species m a y reveal ff the D R L deficit m the

p r e s e n t e x p e r i m e n t ~s a ' p r e f r o n t a l ' o r a ' c m g u l a t e ' s y m p t o m

T h u s m the m o n k e y

the m e d l o d o r s a l a n d a n t e r o m e d m l nuclei seem to p r o j e c t to s e p a r a t e c o r t i c a l fields 1 ~4 20,',~ A f t e r lateral p r e f r o n t a l lesions m m o n k e y s , b e h a v i o r u n d e r D R L c o n t i n g e n c i e s was d~sturbed 6, u n a f f e c t e d 1° 18 o r f a c d t t a t e d t'~, w h d e d a m a g e o f the o r b i t a l TM o r c m g u l a t e c o r t e x ~s d~d n o t interfere w~th D R L p e r f o r m a n c e T h e a v a d a b l e d a t a are e~ther t o o c o n f l i c t i n g or i n a d e q u a t e to a l l o w d e f i m t e c o n c l u s i o n s o n w h e t h e r p r e f r o n t a l or c m g u l a t e c o r t i c e s m m o n k e y s c o n t r i b u t e to D R L b e h a v i o r

T h e p r e s e n t results

suggest, h o w e v e r , t h a t th~s q u e s t i o n d e s e r v e s f u r t h e r i n v e s t i g a t i o n

1 AKERT, K , Comparative anatomy ol the frontal cortex and thalamocortlcal connections

2 3 4 5 6 7 8

9 I0

[I 12

13 14 15

16

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