Differential Localization of the Influence of Lysine Vasopressin and of ACTH 4–10 on Avoidance Behavior: A Study in Rats Bearing Lesions in the Parafascicular Nuclei

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Abstract
A single subcutaneous injection of either 1.8 or5.4 µg lysine vasopressin (LVP) into parafascicular (pf) lesioned rats induced a dose-dependent preservation of a pole-jump shock avoidance response. The effect of the higher dose of LVP lasted for a minimum of 5 days whereas the effect of the lower dose was present for only 2 days. These results can be contrasted with the effect of 1.8 µg LVP in sham-operated rats in which the avoidance response is maintained for many days after injection. Daily subcutaneous administration of either 1 or 9 µg of the ACTH analogue (ACTH 4–10) to pf rats did not preserve the pole-jump response. However, in sham-operated animals, 1 or 3 µg ACTH 4–10 was effective in preserving the avoidance response in a dose-dependent way. Because ACTH 4–10 does not preserve avoidance behavior in pf-lesioned animals, the results of these experiments support the conclusion that the parafascicular area is essential for the behavioral effects of this peptide. In contrast, the fact that LVP is effective in lesioned animals (even though higher doses are required than are normally used), together with the earlier finding that local application of LVP in the posterior thalamic region results in a preservation of the avoidance response, indicates that LVP may have its site of action in the parafascicular area as well as in other brain structures.

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