Ventrobasal Thalamus Necessary for Visually-Released Defensive Boxing of Rat
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Title/Summary Page

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Figure 1
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Tables 1-2
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Visually-released upright posture and boxing was totally abolished in seven of the eight rats with complete cross-sectional destruction of the ventrobasal thalamus on both sides. Data from these and other rats are shown in Table 2 and the histology from four rats are shown in Fig. 1. Seven of the rats with complete bilateral lesions of the ventrobasal thalamus (Rats 1, 2, 3, 6, 7 ,8, 9) showed no boxing at all after facial anesthesia although they had all boxed prior to anesthesia and all boxed again on the final postop tests without facial anesthesia. All aspects of the boxing were abolished, including the upright posture, tracking or following of the movements of the opponent, mouth-gaping, and paw movements, except for one case (Rat 6) in which limited paw movements were observed when the animal was held upright by means of a harness. The harness procedure was used in all tests in which the animal failed to show upright posture and with the exception of the paw movements of Rat 6, none of the other components of boxing were ever observed. The abolition of boxing was unrelated to the preoperative experience of the animal since both naive (Rats 1, 2, 3) and experienced (Rats 6, 7, 8, 9) showed similar results. In addition to complete cross-sectional destruction of the ventrobasal thalamus, there was damage in some cases to the parafascicular nucleus, lateral thalamus, medial lemniscus, and medial dorsal thalamus, although none of these other structures was destroyed in all of the rats with effective lesions. One rat with complete bilateral lesions of the ventrobasal thalamus (Rat 5) continued to show a low level of boxing after facial anesthesia.

Sham lesions, partial lesions of the ventrobasal thalamus, and destruction of other thalamic structures did not abolish visually-released boxing. The only exception was a bilateral destruction of the medial lemniscus, at a level posterior to its entry into the thalamus, which abolished visually-released boxing despite lack of damage to the ventrobasal thalamus (Rat 16). Among the animals which continued to show boxing were three sham-lesion controls (Rats 17, 18, 19), five animals with incomplete thalamic lesions (Rats 4, 10, 11, 13, 14) and one animal with a bilateral complete lesion of the parafascicular nucleus (Rat 20).

Although the parafascicular nucleus was often damaged in animals in which visually-released boxing was abolished, it was not critical for the effect. In two rats (11 and 20) the behavior was not abolished despite complete parafascicular nucleus destruction. And in three rats (8, 12, and 16) the behavior was abolished by ventrobasal lesions which did not destroy the parafascicular nucleus.

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