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3 Acta Neurobiologiae Experimentalis

3 1993

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Behavioural changes after ablation of subdivisions of the rat prefrontal cortex

100%

Mogensen J. , Divac I.

Acta Neurobiologiae Experimentalis

1993

tom 53

nr 3

439-449

Sham operated controls and four groups of subjected to of various parts of their were compared in food and water intake and four behavioural tasks. The ablations were aimed at removing the ventral prefrontal cortex, the dorsal part of the medial prefrontal cortex, the total medial prefrontal cortex, and the anterior dorsolateral (non-prefrontal) cortex. Only two groups had a significantly impaired food and water intake: the ventral prefrontal and the non-prefrontal anterolateral. The Latter group was not adipsic. Two variants of spontaneous alternation were administered in a T-maze: a non-cued version in which both arms were grey and a sued version in which one arm was white and the other black. While all ablated groups behaved like the control group on the non-aued test, the number of perseverative responses of the total anteromedial group was significantly increased in the cued version of the test. Significant group differences could be seen neither in a test of conditioned taste aversion nor in extinction of operantly conditioned bar presses. Finally, in a vertical hole-board exploration test the only significant group difference was a prolongation of the mean visit duration of the ventrally lesioned animals in comparision with all other groups. The results of the present study further indicate functional differentiation within the prefrontal cortex of the rat.

Retention and relearning of spatial delayed alternation in rats after combined or sequential lesions of the prefrontal and parietal cortex

80%

Wortwein G. , Mogensen J. , Divac I.

Acta Neurobiologiae Experimentalis

1993

tom 53

nr 1

357-366

Lesions of the medial prefrontal cortex strongly impaired rats delayed alternation behaviour in a T-maze, both when the lesion was inflicted after the initial acquisition of the task and when the lesion was added after criterion performance had been reattained following an of the parietal cortex. Lesions of the parietal cortex did not impair this behaviour, either when the parietal lesion was inflicted after the initial acquisition of the task or when it was added to a prefrontal lesion after criterion performance had beed reattained. Combined, one stage, parietal and prefrontal lesions did not have a stronger effect on delayed alternation than did prefrontal lesions alone. These results indicate that in spite of the strong anatomical connectivity between the prefrontal and parietal "association" cortex the latter is not necessary for the recovery of delayed alternation after prefrontal lesions. In comparison with the parietal cortex, the prefrontal cortex seems to be uniquely involved in mediation of delayed alternation.

Cortical projections of the thalamic mediodorsal nucleus in the rat. Definition of the prefrontal cortex

70%

Divac I. , Mogensen J. , Petrovic-Minic B. , Zilles K. , Regidor J.

Acta Neurobiologiae Experimentalis

1993

tom 53

nr 1

425-429

Deposits of somatopetal tracers, that filled the entire dorsolateral cortex of one hemisphere, labelled only a few cell bodies in the thalamic mediodorsal nucleus (MD). Further experiments served to confirm the existence of strong projections from MD to the mesial and suprarhinal areas ofthe frontal cortex. Thus, only a very small proportion of the MD neurones in the rat projects outside the cortical areas described first by Leonard (1969). We conclude that at least in the rat, cortical projections of the MD are selective enough to be used as the basis for definition of the prefrontal cortex.