Neumw/ewce Letters, 36 (1983) 329-333 Elsevier Scientific Publishers Ire~nd Ltd.

329

RADIOACTIVE DEOXYGLUCOSE UPTAKE INTO THE PREFRONTAL CORTEX DURING A DELAYED RESPONSE TASK OF THE MONKEY

KEN'ICH! MATSUNAM! and KISOU KUBOTA

Department o f Neurophysiology, Primate Research Institute. Kyoto University. Dmyama City. 484 (Japan)

(Received January 6th. 1983: Revised version received and accepted February 15th, 1983)

Key words: prefrontal cortex - delayed response - 2-deoxyglucose - monkey

Radioactive 2-deoxy-D-glucose (2-DG) uptake into the prefrontal and the premotor cortex was in- vestilgated while a monkey was performing a two-choice delayed response task with visual cues. An in- creased 2-DG uptake was observed in the principal region, superior and inferior prefrontal convexities, arcuate area, orbital cortex, cingulate gyrus and premotor cortex, in most of these area~, the increased 2-DG uptake appeared in patch formations.

Ablation studies have revealed the importance of the prefrontal cortex in the cor- rect performance of delayed responses, and the principal region is claimed as being the crucial area (cf. ref. 10). However, prefrontal neurons outside the principal region, in the medial part of the dorsolateral prefrontal cortex, cingulate gyrus, in- ferior lateral cortex and orbital gyrus [2, I I, 15], change their activities in associa- tion with delayed responses. Broad extirpation of the dorsolateral prefrontal cortex produced more severe deficits in delayed response tasks than i,:sions restricted to the principal area [9]. These facts imply that the prefr:~atal cortex outside the principal region is also involved in the performance of delayed response.

On the other hand, recent anatomical studies revealed the presence of columnar arrangements of neural elements in the prefrontal cortex [3, 4, 7], which might pro- vide a basis for the prefrontal cell activation in columns duri.g a simple voluntary

forelimb movement of the monkey [8]. Therefore, it is expected that prefrontal neurons would be activated in columns during a delayed response. Using the 2-deoxy-D-glucose (2-DG) method [12], we studied whether or not 2-DG was incor- porated in regions outside the principal area during a delayed response, and attemp- ted to ascertain whether or not 2-DG uptake appeared in a patch formation as observed in a previous study [8].

Six young macaca monkeys (2.5-3.5 kg.) were used. Four were experimental and two were control monkeys. The experimental monkeys performed a two-choice direction delayed response task, identical to that employed in a previous report [6],

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but the delay period was changed to 5 sec. The monkey sat in a chair and faced a control panel with lamps (cf. Fig. I of t e l 6). When the monkey put a vertical handle in a central start zone, a green lamp at the center of the panel and a red lamp (left or right to the green one) was illuminated for I sec. A delay period for 5 sec

which the green lamp signalling a GO. The n

zone previously indicated by the red lamp. After 3 -4 months' training, all 4 monkeys reached the criterion level of 90°?0 correct responsfs.

Surgery, experimental procedures, the method of 2-13(3 injection and construc- tion of autoradiographs were similar to those in a previous report [8]. On the day of the isotope experiment, the monkey faced the panel, with its head tightly held by a holding apparatus (cf. ref. 8). 2-DG (New England Nuclear or Amersham, 100 #Ci/kg) was injected into the vein through the implanted cannula. The monkey per- formed the delayed response task for 45 rain and was then killed by injection of sodium pentobarbital (50 mg/kg) followed by saturated KCI solution. After death, the brain was quickly removed, cut into several blocks, and frozen in a cooling bath filled with isopentane at -40°C . The brain blocks were siored at -20°C . Blocks of the frontal cortex were mounted in a cryostat (CR-502, Yamato Koki Co.) to make frontal ~ctions at - 20°C. The thickness of a section was 30/Am, and one sec- tion every 260 ~m interval was mounted on a slide glass. Slides were dried with warm air on a heated plate at 70~C. Slide,, were pressed against an X-ray film (KX, Fuji) in light-proof cassettes for one ~c~k. The film was developed for 5 rain.

Control monkeys were anesthetized frith pentobarbitai (40 mg/kg, i.p.). The saphenous vein was dissected out and 2-DG was injected (100 ~Ci/kg). The contro! monkeys were left quietly on the floor for 45 min and then killed. The procedures to obtain autoradiographs were the same as for the experimental monkeys.

As the results were qualitatively similar among the experimental monkeys, the descriptions are based on the one monkey illustrated in Fig. I. In this figure, autoradiographs of prefrontal (Fig. I A, B) and premotor (Fig. IC) cortices of con- trol (right) a~d task-performing (left) monkeys are illustrated. Fig. IA represents sections at the midpfincipal plane, Fig I B the postrior third of the principal sulcus, and Fig. IC the premotor area at the apex of the arcuate sulcus. As illustrated, 2-DG uptake into prefrontal and premotor cortex of the control monkey was small and unit\)rm. However, 2-DG uptake in the experimental monkeys was large and regional differences in the distribution of 2-DG were observed in patches. Patches were more distinct in the premotor cortex and became slightly less in the prefrontal cortex toward the rostral pole. These patch-like incorporations of 2-DG were observed in the following regions: the laterat and the medial banks and toe bottom of the principal sulcus, tile infolded cortex in the upper limb of the arcuate sulcus, superior and interior prefrontal convexities, the arcuate area, the orbital cortex and its infolded parts in the orbital and olfactory sulci, the cingulate cortex and its in- tolded part in the cingulate sulcus, m addition, as illustrated in Fig. IC, the

D R ¸ C O N T R O L

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B AS

AI ¢b" °

C

AP

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Fig. 1.2-DG uptake into prefrontal and premotor cortex during the delaycd response (left) and in a con- trol (right) monkey. A: the middle third of the principal region. B: posterior third of the principal region. C: premotor area. The arrow in B indicates an example of patch formation with more 2-DG uptake in upper layers of the cortex. The arrow in C indicates an example of patch formation, with more 2-13(3 in me lower layer.,, of the cortex. Abbreviations: AI, inferior limb of the arcuate suitors; AP, posterior spur of the arcua,~e sulcu.~; AS, superior limb o~" the arcuate sulcus; OfS, orbitofrontal stzlcus; O], olfac- tory sulcu~; O$, orbital sulcus; PS, wincipal sulcus.

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premotor cortex and the buried part in the posterior spur of the arcuate suicus also showed a patch or columnar formation in 2-DG uptake. In the upper mesi-,d cortex (Fig. IA, B) and its posterior part (Fig. IC), probably corresponr~.~ng to a ro:tral portion of the supplementary motor area, 2-DG uptake was observed. The sizes of patches varied, most commonly they were of I mm width. Occasionally two or

. . . . . . . . . T T - . . . . .

three patches seemed to fuse into a large patch, or rather a belt, which was common in the orbital cortex.

The 2-DG uptake in patches seems to develop in two ways: some patches were labeled more in the upper layers of the cortex (arrow in Fig. B) and others showed intense labeling in the middle to basal portions of the cortical laminae (arrow in Fig. IC). The former type was common in the prcmotor cortex or superior or inferior prefrontal convexities, while the latter type was found in infolded par~¢ ,~f several suici or in the orbital cortex.

Fig. IC also demonstrates the rostral part of the caudate and putamen, where 2-DG uptake was uniform, at least at this level of the frontal plane. No difeercnce in 2-DG uptake was observed between the left and the right hemispheres.

We could not find a distinct qualitative difference between 2-13(3 uptake during the simple voluntary movements of the previous study [8] and that during the delayed response in the present experiment. However, the number of trials in the delayed response task was 250-370 trials, while it was 6200-7500 for the simple alternation movement [8]. Therefore, the prefrontal cortex consumed more oxygen per trial during the delayed response than during the simple alternation movement.

The principal region is suppo~,-;d as the crucial area for delayed responses [2, 5, 10] but the increased 2-DG uptake in this region was not particularly higher than those in other prefrontal regions. Therefore, areas outside the principal region might be involved in delayed responses. Lesions of superior or inferior prefrontal convexities, arcuate area, orbital cortex or even the cingulate gyrus ca,,sed behavioral deficits in delayed response tasks (cf. ref. 10), though less severe than lesions in the principal region. Neuronal activit;.es associated with a delay period were also recorded outside the principal regio~l [2, 2a, I I, 15]. Therefore, the 2-DG uptake in areas outside the principal region could be attributed to spatial mnemonic tactors in the delayed response.

However, the amount of 2-DG uptake outside the principal region was almost comparable to that in the principal region itself. This may be explained by addi- tional factors involved in the delayed response. The arcuate area contains the 'fron- tal eye field', and reveives polymodal sensory signals, including vision [I, 13]. Therefore. the 2-DG uptake in this area was supposed to be concerned with the mechanisms of eye movements, or the signal processing of polymodal informations.

A kinesthetic function has been attributed to the superior prefrontal convexity, though only slight behavioral deficits followed after selective lesions of this area [9]. Therefore, the 2-DG uptake in this region may be attributable to kinesthetic factors necessary to perform forelimb movement in the delayed response task. The orbital

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cortex is ~:oncerned with gustatory inputs [14], and the increased 2-DG uptake in this region may be e~;plained in this context.

We thank Mrs. Takako Miwa for making illustrations. This research was sup- ported by Grant-in-Aids for Scientific Research, the Ministry of Education, Science and Cul,ure (no. 448010 for 1980--1981, no. 57570050/or 1982).

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